The Pennsylvania State University
The Graduate School
College of Engineering
PERFORMANCE OPTIMIZATION OF A DIESEL ENGINE
FOR DUAL-FUEL COMBUSTION
A Thesis in
Industrial Engineering
by
Srinivas Jayaraman
© 2012 Srinivas Jayaraman
Submitted in Partial Fulfillment
of the Requirements
for the Degree of
Master of Science
August 2012
ii
The thesis of Srinivas Jayaraman was reviewed and approved* by the following:
André L. Boehman
Professor of Fuel Science, Material Science and Engineering and Mechanical
Engineering
Thesis Co-advisor
Jose Ventura
Professor of Industrial and Manufacturing Engineering
Thesis Co-advisor
Paul M. Griffin
Professor of Industrial and Manufacturing Engineering
Peter and Angela Dal Pezzo Department Head Chair
*Signatures are on file in the Graduate School
iii
ABSTRACT
With recent emphasis on clean fuel and environmental sustainability, it has
become increasingly important to look into methods of reducing fuel consumption and
emissions while simultaneously maintaining the level of engine performance. Through
this study an attempt has been made to observe the effects of using fumigated fuels and
an injection of diesel on the performance of an engine and subsequent emissions. The
performance of the engine will be judged primarily on brake specific fuel consumption
(BSFC), brake specific energy consumption (BSEC), brake thermal efficiency (BTE),
peak cylinder pressure and the apparent heat release rate, while total hydrocarbon content
(THC), nitrogen oxides (NOx), carbon dioxide (CO2) and carbon monoxide (CO) were
considered to analyze the emissions. The data collected was statistically analyzed to
determine which factors are most significant in determining the engine‘s performance.
Exhaust gas recirculation was also used to observe its effects on the above outcomes.
The engine used to conduct the tests is a DDC/VM-Motori 2.5L, 4 cylinder,
turbocharged, direct injection, light duty diesel engine. The fuels to be fumigated in the
cylinder are dimethyl ether (DME) and propane, and the injection is of ultra-low sulphur
diesel (ULSD). Previous studies have shown that DME, which has a low boiling point
and high cetane number, tends to advance the ignition point by increasing the low
temperature heat release. Methane has also been used in the past along with DME to
delay the heat release, provide for a more controlled reaction as well as reduce NOx
emissions. This study attempts to achieve the same effects using propane instead of
iv
methane along with DME. The concentrations of DME and propane in the fumigated fuel
were varied over a span of 0 to 60% energy equivalent of the total fuel requirement.
The experiments were conducted in two sets, the first set of experiments utilized
just DME as the fumigated fuel in the cylinder along with an injection of ULSD. In the
second set of experiments, propane was added to the DME to be fumigated in the
cylinder. Previous studies have shown favorable trends in the values of BSFC and BSEC
due to the addition of a fumigated fuel (usually natural gas) along with an injection of
diesel. Similar results were observed for the addition of DME and propane as the
fumigated fuels along with diesel along with an increase in BTE. It was observed that the
heat release was advanced with increasing energy substitution. There was also an
increase in the peak cylinder pressure with increasing fumigation as compared to baseline
diesel. Reduction in NOx emissions was observed which further reduced with EGR
introduction. THC emissions on the other hand increased with increasing substitution.
On completion of the experiments, a statistical analysis was performed to
determine the factors which had the most influence on the performance of the engine.
The tests were treated as a General Full Factorial Experimental Design and an analysis of
variance (ANOVA) was performed to determine the significant factors. Once, the
significant factors were determined, regression analysis was used to determine the effect
each factor has on the performance of the engine with interactions between the variables
also considered. Based on these conclusions, operating conditions were obtained for the
next set of tests. The engine was run at these conditions and the results were noted. It was
noticed that BTE increased with increasing substitution with DME and Propane along
with a corresponding decrease in BSEC and BSFC values. THC in the emissions
v
decreased with increasing DME but increased with propane. Total NOx, on the other hand
reduced with increasing DME and propane energy substitution.
vi
TABLE OF CONTENTS
LIST OF FIGURES ............................................................................................................ viii
LIST OF TABLES .............................................................................................................. xii
GLOSSARY ....................................................................................................................... xiii
ACKNOWLEDGEMENTS ................................................................................................ xv
Chapter 1 INTRODUCTION .............................................................................................. 1
1.1 Oil Depletion and Global Warming ...................................................................... 1 1.2 The Diesel Engine ................................................................................................ 3 1.3 The Diesel Engine Combustion Process ............................................................... 6 1.4 Differences between SI engines and CI Engines ................................................... 8 1.5 Thesis Overview .................................................................................................. 8
Chapter 2 Literature Review ............................................................................................... 10
2.1 Homogeneous Charge Compression Ignition (HCCI) Combustion........................ 10 2.1.1 Mixed Mode Combustion ........................................................................... 11 2.1.2 Premixed Charge Compression Ignition (PCCI) combustion ....................... 12
2.2 Reactivity Controlled Compression Ignition (RCCI) combustion .......................... 13 2.3 Fumigated Fuels .................................................................................................. 16
2.3.1 Dimethyl Ether (DME) ............................................................................... 16 2.3.2 Propane ...................................................................................................... 18 2.3.3 Advantages of Propane over Methane ......................................................... 21
Chapter 3 Experimental Setup ............................................................................................. 23
3.1 Engine Specifications ........................................................................................... 23 3.2 Load Generation and Dynamometer ..................................................................... 24 3.3 Engine Control ..................................................................................................... 25 3.4 Data Acquisition .................................................................................................. 25 3.5 Pressure Trace and Needle Lift Sensor ................................................................. 26 3.6 Mass of Air Flow (MAF) and Diesel Flow Rate ................................................... 26 3.7 Flowmeter Setup .................................................................................................. 27 3.8 Engine Emissions Measurement ........................................................................... 29
Chapter 4 Experiments and Analysis – Part 1 ...................................................................... 31
4.1 Experimental Runs ............................................................................................... 31 4.1.1 Multilevel Factorial Design ........................................................................ 32 4.1.2 Analysis of Variance (ANOVA) ................................................................. 34
4.2 Regression Analysis ............................................................................................. 35 4.2.1 Brake Thermal Efficiency (BTE) ................................................................ 37 4.2.2 Brake Specific Energy Consumption (BSEC) ............................................. 39
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4.2.3 Brake Specific Fuel Consumption (BSFC) .................................................. 40 4.2.4 Brake Specific Diesel Consumption ............................................................ 42 4.2.5 Heat Release Rate (HRR) ........................................................................... 43 4.2.6 Pressure Rise Rate (PRR) ........................................................................... 45 4.2.7 Obtaining a trade-off point.......................................................................... 47
Chapter 5 Experiments and Analysis – Part 2 ...................................................................... 50
5.1 Experimental Runs ............................................................................................... 50 5.2 DME and Propane fumigation without Exhaust Gas Recirculation ........................ 53
5.2.1 Brake Specific Energy Consumption (BSEC).............................................. 53 5.2.2 Brake Thermal Efficiency (BTE) ................................................................ 54 5.2.3 Brake Specific Fuel Consumption (BSFC) .................................................. 55 5.2.4 Heat Release Rate ....................................................................................... 55 5.2.4 Pressure Rise Rate (PRR) ........................................................................... 61 5.2.5 Total Hydrocarbon Emissions (THC) .......................................................... 66 5.2.6 Nitrogen Oxide emissions (NOx)................................................................. 67 5.2.7 Carbon Dioxide Emissions (CO2)................................................................ 69 5.2.8 Carbon Monoxide (CO) .............................................................................. 70
5.3 DME and Propane fumigation with Exhaust Gas Recirculation (EGR) ................. 71 5.3.1 Engine Performance parameters: ................................................................. 72 5.3.2 Engine Emissions ....................................................................................... 79
5.4 DME and Propane fumigation with exhaust gas recirculation (EGR) and split
injection ............................................................................................................... 84 5.4.1 Engine Performance Parameters .................................................................. 85
5.4.2 Engine Emissions ........................................................................................ 88
Chapter 6 Summary and Conclusions .................................................................................. 92
6.1 Summary ............................................................................................................. 92 6.2 Observations and Conclusions .............................................................................. 93 6.3 Suggestions for Future Work ................................................................................ 95
Bibliography ....................................................................................................................... 97
Appendix A Matheson Gas Flowmeter Calibration ..................................................... 102 A.1 Flowmeter 605 Calibration Chart: ........................................................................ 102 A.2 Flowmeter 603 Calibration Chart: ........................................................................ 103 A.3 Flowmeter 604 calibration chart: .......................................................................... 104 A.4 Flowmeter 605 Calibration Chart: ........................................................................ 105
Appendix B Interaction Plots ............................................................................................. 106
Appendix C Regression Analysis – Minitab Output ............................................................ 120
viii
LIST OF FIGURES
Figure 1.1: United States Oil Consumption [4] .................................................................... 2
Figure 1.2: The Diesel Cycle ............................................................................................... 4
Figure 1.3: Heat Release Profile of a Diesel Engine [9] ....................................................... 6
Figure 2.1: Rate of heat release for propane and DME at various equivalence ratios [46] ..... 19
Figure 3.1: Photograph of 2.5 L DDC/VM Motori Engine ................................................... 24
Figure 3.2: Matheson Gas 7410 series flow meter................................................................ 27
Figure 3.3: Block Diagram of DME, Propane flow and mixing into the engine .................... 28
Figure 3.4: AVL CEB II emissions bench............................................................................ 29
Figure 4.1: Brake Thermal Efficiency at varying DME and propane substitution levels ....... 38
Figure 4.2: Brake Specific Energy Consumption at varying DME and propane
substitution levels ........................................................................................................ 39
Figure 4.3: Brake Specific Fuel Consumption at varying DME and propane substitution levels ........................................................................................................................... 41
Figure 4.4: Brake Specific Diesel Consumption at varying DME and propane substitution
levels ........................................................................................................................... 42
Figure 4.5: Apparent Heat Release Rate at varying DME and propane substitution levels .... 44
Figure 4.6: Average Pressure Rise Rate at varying DME and propane substitution levels ..... 45
Figure 4.7: Visual representation of optimal points for the individual response variables ..... 46
Figure 4.8: Visual representation of the optimal point for obtaining a trade-off between BTE and PRR .............................................................................................................. 49
Figure 5.1: Brake Specific Energy Consumption at varying DME and propane
substitution levels without EGR ................................................................................... 53
Figure 5.2: Brake Thermal Efficiency at varying DME and propane substitution levels
without EGR ............................................................................................................... 54
Figure 5.3: Brake Specific Fuel Consumption at varying DME and Propane levels
without EGR ............................................................................................................... 55
ix
Figure 5.4: Heat Release Rate at varying DME and Propane levels without EGR ................. 56
Figure 5.5: Heat release rate v/s crank angle for 0% DME substitution and 0 – 40%
propane substitution without EGR ............................................................................... 57
Figure 5.6: Heat release rate v/s crank angle for 10% DME substitution and 0 – 30% propane substitution without EGR ............................................................................... 58
Figure 5.7: Heat release rate v/s crank angle for 20% DME substitution and 0 – 30%
propane substitution without EGR ............................................................................... 58
Figure 5.8: Heat release rate v/s crank angle for 30% DME substitution and 0 – 30%
propane substitution and 40% DME substitution and 0% propane without EGR ........... 59
Figure 5.9: Heat release rate v/s crank angle for 10 - 40% DME substitution and 0% propane substitution without EGR ............................................................................... 60
Figure 5.10: Pressure rise rate in the cylinder at varying DME and propane levels ............... 61
Figure 5.11: Pressure rise rate v/s crank angle for 0% DME substitution and 0 – 40%
propane substitution without EGR ............................................................................... 62
Figure 5.12: Pressure rise rate v/s crank angle for 10% DME substitution and 0 – 40%
propane substitution without EGR ............................................................................... 63
Figure 5.13: Pressure rise rate v/s crank angle for 20% DME substitution and 0 – 30% propane substitution without EGR ............................................................................... 63
Figure 5.14: Pressure rise rate v/s Crank Angle for 30% DME substitution and 0 – 30%
propane substitution and 40% DME substitution and 0% propane without EGR ........... 64
Figure 5.15: Pressure rise rate v/s crank angle for 0% propane substitution and 10 – 40%
DME substitution ........................................................................................................ 65
Figure 5.16: Total hydrocarbon emissions at varying DME and propane levels without
EGR ............................................................................................................................ 66
Figure 5.17: Nitrogen oxide (NOx) emissions at varying DME and propane levels
without EGR ............................................................................................................... 67
Figure 5.18: Nitric oxide (NO) emissions at varying DME and propane levels without EGR ............................................................................................................................ 68
Figure 5.19: Nitrogen Dioxide (NO2) emissions at varying DME and Propane levels
without EGR ............................................................................................................... 69
Figure 5.20: Carbon Dioxide emissions at varying DME and propane levels without EGR .. 70
Figure 5.21: Carbon Monoxide emissions at varying DME and propane levels without
EGR ............................................................................................................................ 71
x
Figure 5.22: Brake thermal efficiency (BTE) at varying DME and propane levels with
and without EGR ......................................................................................................... 72
Figure 5.23: Brake Specific Energy Consumption (BSEC) at varying DME and propane
levels with and without EGR ....................................................................................... 73
Figure 5.24: Average Heat Release Rate (HRR) at varying DME and Propane levels with
and without EGR ......................................................................................................... 74
Figure 5.25: Heat release rate v/s crank angle for 10% DME substitution and 0, 20 and 40% propane substitution with EGR ............................................................................ 74
Figure 5.26: Heat release rate v/s crank angle for 20 and 30% DME substitution and 0
and 20% propane substitution with EGR ...................................................................... 75
Figure 5.27: Heat release rate v/s crank angle for cases with and without EGR .................... 76
Figure 5.28: Average pressure rise rate (PRR) at varying DME and propane levels with
and without EGR ......................................................................................................... 77
Figure 5.29: Pressure rise rate v/s crank angle for 10% DME substitution and 0, 20 and 40% propane substitution with EGR ............................................................................ 77
Figure 5.30: Pressure rise rate v/s crank angle for 20 and 30% DME substitution and 0
and 20% propane substitution with EGR ...................................................................... 78
Figure 5.31: Pressure Rise v/s Crank Angle for cases with and without EGR ....................... 79
Figure 5.32: Total hydrocarbon emissions (THC) at varying DME and propane levels
with and without EGR ................................................................................................. 80
Figure 5.33: Nitrogen oxide emissions (NOx) at varying DME and propane levels with
and without EGR ......................................................................................................... 81
Figure 5.34: Nitric oxide emissions (NO) at varying DME and propane levels with and
without EGR ............................................................................................................... 82
Figure 5.35: Nitrogen dioxide emissions (NO2) at varying DME and propane levels with
and without EGR ......................................................................................................... 82
Figure 5.36: Carbon dioxide emissions (CO2) at varying DME and propane levels with and without EGR ......................................................................................................... 83
Figure 5.37: Carbon monoxide emissions (CO) at varying DME and propane levels with
and without EGR ......................................................................................................... 84
Figure 5.38: Brake Thermal Efficiency (BTE) at 20% DME, 20% propane, 16 deg BTDC pilot injection and varying main injection timing ......................................................... 85
xi
Figure 5.39: Brake Specific Energy Consumption (BSEC) at 20% DME, 20% Propane,
16 deg BTDC pilot injection and varying main injection timing with EGR ................... 86
Figure 5.40: Heat release rate (HRR) at 20% DME, 20% propane, 16 deg BTDC pilot
injection and varying main injection timing with EGR ................................................. 87
Figure 5.41: Pressure rise rate (PRR) at 20% DME, 20% propane, 16 deg BTDC pilot
injection and varying main injection timing with EGR ................................................. 88
Figure 5.42: Total Hydrocarbon emissions (THC) at 20% DME, 20% propane, 16 deg BTDC pilot injection and varying main injection timing with EGR .............................. 89
Figure 5.43: Total Nitrogen Oxide emissions (NOx) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR .............................. 89
Figure 5.44: Total Carbon dioxide emissions (CO2) at 20% DME, 20% Propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR .............................. 90
Figure 5.45: Total Carbon dioxide emissions (CO) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR .............................. 91
Figure 6.1: Scatter plot of data points at which optimal values of response variables occur .. 95
Figure A.1: Calibration for Flowmeter tube 605 at 0 psig for Propane ................................. 102
Figure A.2: Calibration for Flowmeter tube 603 at 0 psig for Propane ................................. 103
Figure A.3: Calibration for Flowmeter tube 604 at 0 psig for DME ..................................... 104
Figure A.4: Calibration for Flowmeter tube 605 at 0 psig for DME ..................................... 105
Figure B.1: DME-Propane interaction plot for BTE ............................................................. 106
Figure B.2: DME-Propane interaction plot for BTE ............................................................. 106
Figure B.3: DME-Propane interaction plot for BSFC........................................................... 107
Figure B.4: DME-Propane interaction plot for BSDC .......................................................... 107
Figure B.5: DME-Propane interaction plot for PRR ............................................................. 108
Figure B.6: DME-Propane interaction plot for PRR ............................................................. 108
xii
LIST OF TABLES
Table 1.1: Differences between SI and CI Engines .............................................................. 8
Table 2.1: Physical Properties of Diesel, DME, Propane and Methane [35,36] ..................... 17
Table 3.1: 2.5 L DDC/VM-Motori Engine Specifications .................................................... 23
Table 4.1: Data collected from the preliminary experimental runs........................................ 33
Table 4.2: ANOVA significance table ................................................................................. 34
Table 4.3: Maximum and minimum values of Brake Thermal Efficiency and Pressure Rise Rate ..................................................................................................................... 48
Table 4.4: Trade-off point for optimizing BTE and PRR ..................................................... 48
Table 5.1: Test Matrix for DME and Propane fumigation with no EGR ............................... 51
Table 5.2: Test Matrix for DME and Propane fumigation with EGR .................................... 51
Table 5.3: Test Matrix for DME and Propane fumigation with EGR and split injection........ 51
Table C.1: Residuals and Fits table for Brake Thermal Efficiency ....................................... 110
Table C.2: Residuals and Fits table for Brake Specific Energy Consumption ....................... 112
Table C.3: Residuals and Fits table for Brake Specific Fuel Consumption ........................... 114
Table C.4: Residuals and Fits table for Brake Specific Diesel Consumption ........................ 116
Table C.5: Residuals and Fits table for Average Heat Release Rate ..................................... 118
Table C.6: Residuals and Fits table for Average Pressure Rise Rate ..................................... 120
xiii
GLOSSARY
Acronym Definition
(A)HRR (Apparent) Heat Release Rate
ANOVA Analysis of Variance
ATDC After Top Dead Centre
BDC Bottom Dead Centre
BSDC Brake Specific Diesel Consumption
BSEC Brake Specific Energy Consumption
BSFC Brake Specific Fuel Consumption
BTDC Before Top Dead Centre
BTE Brake Thermal Efficiency
CI Compression Ignition
CO Carbon Monoxide
CO2 Carbon dioxide
DDC Detroit Diesel Corporation
DME Dimethyl Ether
DOE Design of Experiments
ECU Engine Control Unit
EGR Exhaust Gas Recirculation
HCCI Homogeneous Charge Compression Ignition
IC Internal Combustion
NO Nitric Oxide
xiv
NO2 Nitrogen Dioxide
NOx Nitrogen Oxide
PCCI Premixed Charge Compression Ignition
PPM Parts per million
PRR Pressure Rise Rate
P-value Probability Value
RCCI Reactivity Controlled Compression Ignition
SI Spark Ignited
SLPM Standard liters per minute
TDC Top Dead Centre
THC Total Hydrocarbon Content
ULSD Ultra low sulphur diesel
xv
ACKNOWLEDGEMENTS
This thesis has given me the opportunity to study both the theoretical and the
experimental portion of improving the performance of a diesel engine, which is
something that has always fascinated me. I was able to observe and apply the concepts of
statistical analysis which are a very important component of my degree in Industrial
Engineering. I would firstly like to thank my advisor Dr. André Boehman for giving me
this opportunity and the guidance to work on my masters‘ thesis. It was through his
vision and motivation that I was able to complete the experiments achieving the desired
results in the process. I would also like to thank Dr. Jose Ventura and Dr. Paul Griffin for
their advice and time in reviewing my thesis.
This work was supported in part under US Department of Energy
through Contract: DE-EE0004232, as a subcontract from Volvo Group Truck
Technology. Thanks go to the Jerry Gibbs, Roland Gravel, Gurpreet Singh and
Ken Howden of the US DOE and Ralph Nine of the National Energy Technology
Laboratory. Thanks also go to Pascal Amar and Sam McLaughlin of Volvo Group for
their support and guidance.
I am extremely grateful to Bhaskar Prabhakar for helping me throughout the
experiments and the data analysis. It would have been impossible for me to conduct the
experiments without his knowledge and help on the setup and running of the engine. I
would also like to thank Vickey, Claire and Dongil for their time in helping me
understand the operation of the engine and the emissions bench.
xvi
Finally, a very special thanks to my parents K.S. Jayaraman and Padma
Jayaraman for their support through every stage of my life. My friends also deserve a
special mention in motivating me to complete my thesis so that we could all take the
graduation walk at the same time.
Chapter 1
INTRODUCTION
1.1 Oil Depletion and Global Warming
The conservation of the environment has been a topic of growing concern among
countries especially those with low-lying areas which are under the threat of being
submerged due to rising global temperatures. The Kyoto Protocol was one of the widely
agreed protocols whereby all the ratifying countries agreed to legally binding
commitments to cut down on emissions of global warming gases [1]. The lack of success
for this protocol was attributed to the fact that the United States rejected the treaty on the
basis that it placed too much pressure on the developed nations while exempting
developing countries like India and China [2]. The United States is among the highest
emitters of greenhouse gases and also has the highest per capita emissions [3]. Having
rejected the Kyoto Protocol, it is now essential for the United States to put in place steps
to independently reduce emissions. Exploring alternate blends of fuels capable of
reducing carbon dioxide, carbon monoxide and nitrogen oxide emissions is thus of
paramount importance.
Another growing environmental concern is the rapid depletion of oil reserves
worldwide. The United States of America has one of the largest automotive vehicle bases
in the world (254 million registered highway vehicles in 2009) Consequently, they are
2
among the largest consumers of fuel (19.1 million barrels per day in 2010)[4]. The United
States Energy Information Administration predicted in 2006 that world consumption of
oil will increase to 98.3 million barrels per day (15,630,000 m3/d) (mbd) in 2015 and 118
mbd in 2030 [5]. At this rate it is estimated that the world petroleum reserves will be
depleted by 2060. As shown in Figure 1.1 below, even though the United States is the
third largest producer of crude oil in the world [4], the majority of its oil consumption
comes from imports. The recent instability in the Middle East including the sanctions on
Iran could result in interruptions to the oil supply routes jeopardizing US industries. The
recent development of shale oil reserves in North Dakota should not be used as an excuse
to shy away from looking at alternate fuels to reduce diesel/gasoline consumption.
Figure 1.1: United States Oil Consumption [4]
Against the backdrop of such international uncertainty regarding oil reserves,
research focused on reducing fuel consumption and looking at alternate fuels is now all
3
the more important. This study is part of the Volvo Group‘s ‗Super truck‘ project which
aims at achieving 55% BTE by gaseous fuel fumigation and other changes to the engine.
1.2 The Diesel Engine
As stated, the objective of this thesis is to look at ways to reduce fuel
consumption and emissions while at the same time maintaining if not improving the
performance of the diesel engine. In order to facilitate further understanding it would be
appropriate to begin with a brief introduction of the diesel engine and its operation.
The diesel engine was invented by Rudolf Diesel in 1893, while he was
experimenting with methods of ‗converting heat to work‘ by compressing air in the
engine, thereby raising its temperature above the fuel‘s ignition temperature and then
injecting the fuel to expand in the cylinder [6]. This is the principle of the modern diesel
engine. Figure 1.2 shows the idealized diesel cycle.
4
Figure 1.2: The Diesel Cycle (Source: http:// hyperphysics.phy-astr.gsu.edu)
The diesel cycle differs from the Otto cycle for the petrol/gasoline engine in that
the fuel injection and the subsequent ignition takes place at constant pressure as opposed
to constant volume in the case of the Otto cycle [7]. Also, there is no spark to ignite the
fuel in the diesel engine unlike the gasoline or spark ignition (SI) engine. Ignition takes
place due to the compression of the intake air and consequently the injected fuel, thereby
the name ‗Compression-Ignition‘ (CI) engines. Figure 1.2 gives the diagram of an
idealized 4-stroke diesel engine.
1. Intake Stroke (e-a):
Atmospheric air after passing through the air filter gets inducted into the
engine through the intake valve while the exhaust valve remains closed. This
happens during the downward motion of the piston.
5
2. Compression Stroke (a-b):
Inducted air gets compressed adiabatically (without heat loss- under ideal
cycle) into the clearance volume as the piston moves upwards completing the
second stroke. This is also accompanied by a rise in temperature in the cylinder.
While this happens, both intake and exhaust valves remain closed.
3. Expansion Stroke (c-d):
Fuel is injected into the cylinder at this point (b). Injection occurs at
constant pressure and continues till point c. Injection stops at point c and at this
point, the temperature in the cylinder is greater than the fuel‘s auto-ignition
temperature. This causes the air-fuel mixture to expand (c-d) to the bottom dead
centre (BDC) adiabatically performing work. This is the stroke in which the
engine generates energy to perform work.
4. Exhaust Stroke (a-e):
The piston moves back to the TDC, pushing the exhaust gases created
during combustion out of the cylinder. Once, the exhaust stroke is complete, the
engine again goes through the four cycles.
6
1.3 The Diesel Engine Combustion Process
The combustion in a CI engine is generally considered as taking place in 4 stages
[6] as can be seen in Figure 1.3. The four stages are the ignition delay period, the period
of rapid combustion, the period of controlled combustion and the burnout or late-
combustion phase [8]
Figure 1.3: Heat Release Profile of a Diesel Engine [9]
1. Ignition Delay:
This is the preparatory phase between the injection of the fuel into the
cylinder and the actual ignition of the fuel. There is a period of inactivity between
when the first drop of fuel enters the cylinder to when the fuel undergoes actual
burning. The ignition delay period is extremely important in determining the
7
combustion rate and the knocking of the engine. For CI engines, the ignition delay
should be small to avoid knocking in the engine.
2. Period of Rapid Combustion:
At this stage, most of the fuel injected into the cylinder has evaporated
forming a combustible mixture with the air. This period is characterized by a
sharp rise in pressure, which continues until the peak cylinder pressure is reached
(for light to medium loads). In some cases, peak pressure is not reached in this
stage but in the next one. The heat-release rate is also usually at its maximum
during this period.
3. Period of Controlled Combustion:
Entering this stage, the temperature and pressure in the cylinder are
already quite high. Hence, any fuel injected into the cylinder burns quickly with a
reduced ignition delay. Further rises in the pressure and temperature are
dependent on the injection rate. As can be seen from the Figure 1.3, the heat
release during this period is over a larger crank-angle range.
4. After-burning period:
This is the final phase of combustion; where unburnt and partially burnt
fuel or fuel rich combustion products burn on coming in contact with oxygen. The
heat release is low during this stage and continues into the expansion stroke after
TDC.
8
1.4 Differences between SI engines and CI Engines
Table1.1: Differences between SI and CI Engines
Description SI engine CI engine
Ignition Spark induced due to high self-
ignition temperature of gasoline
Self-ignition induced by
compression of air and fuel
injection
Compression
Ratio
Lower compression ratios (6-10) Higher compression ratios
(16-20)
Thermal
Efficiency
Lower thermal efficiency due to lower
compression ratios
Higher thermal efficiency due
to greater compression ratios
Air-Fuel Ratio Usually close to stoichiometric ratio
over full range of load conditions
Varies based on engine load.
Low at full load to high at no
load
Power to
Weight ratio
Higher ratio due to lower weight Lower ratio due to increased
weight to withstand greater
peak pressures
Alternate fuels Ethanol can be used as an additive to
gasoline and also directly depending
on modifications to the engine.
Can be used directly instead
of diesel (e.g.: biodiesel)
depending on the engine and
fuel type
1.5 Thesis Overview
The objective of this thesis is to observe the effects of mixed-mode combustion
using a combination of fumigated fuels and diesel fuel on the performance of a CI engine.
This is also referred to as dual-fuel combustion. The fumigated fuels are dimethyl ether
(DME) and propane, while the injected fuel is ultra low sulphur diesel (ULSD). Previous
studies have been done along similar lines (Chapter 2) using DME and Methane. This
9
study attempts to achieve the same using propane which has a lower octane rating as
compared to methane.
An initial set of runs was made on the engine using DME and propane (Chapter
4). For these runs, the engine‘s emissions values were not noted. A regression analysis of
the data obtained was performed and the regression equation for each response variable
was used as the objective function for an optimization problem. The significance of each
factor in changing the response variables was also determined. The solution to the
optimization problem for each variable would be the energy substitution percentages at
which that variable would be at its optimum value. These solutions would comprise some
of the operating points to be run in the next set of experiments (Chapter 5). In the next
set of experiments, in addition to the engine performance parameters of BTE, BSEC,
BSFC, BSDC, HRR and PRR, engine emissions data was also measured which included
total hydrocarbon content (THC), carbon dioxide (CO2), carbon monoxide (CO) and
nitrogen oxides (NOx). The results obtained from Chapter 4 and Chapter 5 were tallied
and a set of conclusions were drawn (Chapter 6).
Chapter 2
Literature Review
2.1 Homogeneous Charge Compression Ignition (HCCI) Combustion
Recent research into reducing emissions and increasing thermal efficiency in
diesel engines has shown that homogeneous charge compression ignition (HCCI) is an
effective way of achieving these objectives. HCCI is a form of internal combustion in
which well-mixed fuel and air are compressed to the point of auto-ignition. In many
ways, HCCI incorporates the best features of both spark ignition (SI) combustion engines
and compression ignition (CI) combustion engines. As in an SI engine, the charge is
premixed while entering the cylinder and like the CI engine, the charge in the cylinder is
compression ignited [10]. HCCI combustion has gained popularity due to the fact that it
can operate at diesel engine-like compression ratios thus achieving greater efficiencies
than gasoline engines [11]. The homogeneous mixing of the fuel also results in cleaner
combustion and lower NOx emissions which are especially important considering the
current environmental scenario [12]. HCCI also has a large variety in terms of the fuels
that can be used [13].
While, the advantages of HCCI combustion have been well documented,
researchers have also found hindrances to successful application in engines [14-17].
11
Firstly, HCCI usage is limited by a sharp rise in peak cylinder pressure [14]. This can
cause significant damage to the engine if the engine is not designed capable of
withstanding these pressures. Secondly, previous studies have documented the difficulty
in controlling the auto-ignition point and thereby the heat release [15, 16]. This is due to
the fact that unlike SI or CI engines, the ignition is not controlled by the spark timing or
the fuel injection timing respectively. Though HCCI combustion engines have shown to
reduce NOx emissions levels, the levels of hydrocarbons (HC) and carbon monoxide
(CO) in the emissions have increased [17]. The operation of the engine in HCCI mode is
also limited in its range of operability over different speeds and loads as well as the
cylinder pressure levels [18].
Recent research has focused on overcoming the hindrances of HCCI using
different types of fuel mixing and preparation [19, 20]. This has resulted in the
development of mixed mode combustion and dual fuel combustion.
2.1.1 Mixed Mode Combustion
In mixed mode combustion, a gaseous fuel is fumigated into the intake air and a
conventional diesel injection is used with the intention of igniting the pre-mixed the
gaseous-fuel charge. This is similar in some respects to ‗dual fuel‘ combustion, where the
fuel is usually natural gas or bio-gas [14]. Karim states that there can be two categories of
‗dual fuel‘ operation [21]. The first is one where a small amount of diesel is injected
primarily to provide ignition to the gaseous fuel-air charge [21]. The second category is
one where the gaseous fuel is added to the air of a fully operational diesel engine [21].
12
As stated in the previous section, one of the hindrances to the usage of HCCI
combustion engines is the lack of control over point of ignition [15, 16]. HCCI
combustion takes place over two stages, first a low-temperature stage which is followed
by high temperature reactions for the main heat release [18]. Controlling the autoignition
in an HCCI combustion process is thus a function of controlling the low temperature heat
release reactions [15]. It is for this reason that ‗mixed mode combustion‘ is being
explored.
Musardo et al. have experimented with using traditional diesel injection along
with HCCI combustion to enable the engine to operate over a range of loads while
keeping in mind the objective of reducing NOx emissions [22].Their experiments also
attempt to bring greater control over the heat release rate for the HCCI combustion
process [22]. Some authors have also explored the combination of HCCI combustion
with spark ignition engines (SI) to achieve greater loads, [23-25]. These findings though
would not be applicable in this study as here the focus is mainly on diesel engines.
2.1.2 Premixed Charge Compression Ignition (PCCI) combustion
With a view to obtaining greater control over HCCI combustion another form of
combustion was envisaged which was a form of HCCI approximated by early fuel
injection and exhaust gas recirculation (EGR) [9]. PCCI is essentially injecting the fuel
into the intake port at variable timing during the intake cycle or the middle stage of the
compression stroke and allowing it sufficient time to mix with the injected air before
13
auto-ignition and subsequent premixed combustion [26]. EGR offers a method of
controlling the auto-ignition point for this type of combustion.
The main difference between HCCI and PCCI is in the homogeneity of the charge
injected into the cylinder. In HCCI, as the name indicates, the charge is homogeneous
when entering the cylinder after which it is compressed to the point of auto-ignition. In
PCCI on the other hand the fuel is injected early and then allowed time to mix with the
air and auto-ignite. The overall reduced temperatures in the cylinder result in reductions
in the NOx emission levels [26]. As the mixing in PCCI occurs in the cylinder, there is a
high possibility of incomplete combustion due to fuel sticking to the cylinder walls [9].
This consequently leads to greater HC and CO emissions.
Another limitation of PCCI as pointed out by Nakakita is the need for an injector
with a weak spray-tip and high diffusiveness for adequate diffusion and preventing fuel
adhesion to the cylinder walls [26]. This is contrary to the type of injector required for
normal combustion. Thus an engine intended to be operated in normal as well as PCCI
modes may need to have an injector with variable spray characteristics. In spite of the
difficulties in the practical use of PCCI, research into PCCI is ongoing as it offers a
practical route to approximate HCCI through injection timing and EGR control [9].
2.2 Reactivity Controlled Compression Ignition (RCCI) combustion
The present work deals with changing the concentrations of the gaseous pre-
mixed charge and observing its effects on the combustion process and consequently the
performance and emissions of the engine. Essentially, the changing fuel concentrations
14
are considered as a means of controlling the ignition point. This is very similar to the
concept of Reactivity Controlled Compression Ignition (RCCI) which is explained in this
section.
RCCI is a dual fuel engine combustion technology that was developed at the
University of Wisconsin-Madison Engine Research Center laboratories. RCCI is a variant
of Homogeneous Charge Compression Ignition (HCCI) that provides more control over
the combustion process and has the potential to dramatically lower fuel use and emissions
[27]. This is the combustion mode that closely resembles the conditions that are
attempted to be achieved during the experiments conducted in this study.
RCCI uses in-cylinder fuel blending with at least two fuels of different reactivity
and multiple injections to control in-cylinder fuel reactivity to optimize combustion
phasing, duration and magnitude. The process involves introduction of a low reactivity
fuel into the cylinder to create a well-mixed charge of low reactivity fuel, air and
recirculated exhaust gases. The high reactivity fuel is injected before ignition of the
premixed fuel occurs, using single or multiple injections directly into the combustion
chamber. Examples of fuel pairings for RCCI are gasoline and diesel mixtures, ethanol
and diesel, and gasoline and gasoline with small additions of a cetane-number booster
(di-tert-butyl peroxide (DTBP) [28].
RCCI allows optimization of HCCI and Premixed Controlled Compression
Ignition (PCCI) type combustion in diesel engines, reducing emissions and the need for
after-treatment methods [29]. By appropriately choosing the reactivities of the fuel
15
charges, their relative amounts, timing and combustion can be tailored to achieve optimal
power output (fuel efficiency), at controlled temperatures (controlling NOx) with
controlled equivalence ratios (controlling soot). Key benefits of the RCCI strategy
include:
Lowered NOx and PM emissions
Reduced heat transfer losses
Increased fuel efficiency
Eliminates need for costly after-treatment systems
Reitz et al. have demonstrated a net thermal efficiency of almost 56% using the
RCCI mode of combustion [27]. Hence, this is one of the combustion modes which are
being investigated in detail. Reitz et al. have run the engine at a maximum of 9 bar IMEP
which is lower than the 16 bar IMEP achieved by Bessonette et al. with HCCI
combustion [28, 30].
The various modes of combustion have been discussed in the previous sections
along with advantages and disadvantages of each mode. The following sections will
discuss the fuels considered for fumigation in the engine.
16
2.3 Fumigated Fuels
As stated in Chapter 1, this thesis will study the effect of mixed mode combustion
using dimethyl ether (DME) and propane as fumigated fuels along with a main injection
of diesel. The advantages and the reasons behind the selection of these fuels for
fumigation in the cylinder will be explained in this section.
2.3.1 Dimethyl Ether (DME)
The use of DME as a fuel in compression ignition engines has been considered
since the l990s. Fleisch et al. have shown in 1995 that DME can be used in a diesel
engine to obtain reductions in NOx emissions [31]. The main reason for the popularity of
DME is the fact that it has a high cetane number (higher than diesel) [32] and it can be
easily prepared from a variety of feedstock including bio-mass, coal and natural gas [33,
34]. Table 2.1 compares some of the properties of diesel and DME along with methane
and propane.
17
Table 2.1: Physical Properties of Diesel, DME, Propane and Methane [35,36]
Property Diesel DME Propane Methane
Chemical Formula C10.8H18.7 C2H6O C3H8 CH4
Mole Weight (g/mol) 148.6 46.07 44.11 16.04
Boiling point (°C) 71-193 -24.9 -42.1 -162
Autoignition temperature (°C) 250 235 470 650
Stoichiometric Air/Fuel Ratio 14.6 9 15.6 16.9
Liquid Viscosity (cP) 2-4 0.15 0.10 -
Lower Heating Value (MJ/kg) 42.5 28.8 46.4 49.9
Cetane Number 40-55 55-60 - -
Octane Number - - 97 120
As can be seen from Table 2.1, DME has a greater cetane number and a lower
autoignition temperature as compared to diesel. This means that DME when injected into
the cylinder can burn quicker than diesel with a smaller ignition delay. One of the reasons
attributed to the greater reactivity of DME in the combustion chamber is the lack of a
carbon-carbon bond [37]. Research on the oxidation of DME has demonstrated the
presence of OH, H and CH3 radicals during the propagation phase of the combustion
process [37]. The OH radical is then responsible for improving the ignition quality of the
fuel and shortening the ignition delay thus resulting in increased oxidation rates [38].
One of the primary disadvantages of DME is its low lubricity, which inhibits flow
in the flow tubes. However, Oguma and co-workers have recently found a method to
improve the lubricity of DME using fatty acid based lubricity improvers [56]. But, this
has also been stated as one of the biggest concerns of DME usage by researchers who
have presented evidence that DME leaks from the fuel injectors [39, 40]. The lower
boiling point of DME is another advantage for use as a fuel in cold weather conditions.
18
The flipside to this however is that for use under normal atmospheric conditions, DME
must be kept slightly pressurized as in the case of Liquefied Petroleum Gas (LPG). The
lower heating value of DME as compared to diesel also means that greater amount of fuel
has to be injected to provide the same combustion output. The main advantage of DME,
however, is in its ability to reduce particulate matter (PM) and NOx emissions [31].
The numerous advantages of DME as listed above had led to many researchers
experimenting with DME and DME blends in both SI and CI engines [14, 31, 33, 35, 38,
41]. The fuel blend of DME and methane is one of the commonly used by researchers
while experimenting with HCCI and mixed mode combustion [35, 38, 42]. Methane has
been popular for usage along with DME due to the fact that increasing the methane
concentration delays ignition and thereby the low temperature heat release event [35].
There is also a noticeable increase in the thermal efficiency and reduction in NOx
emissions due to the usage of mixtures with high methane and low DME proportions
[35]. Work has been done considering blends of DME with other fuels like propane and
butane [43, 44] as well a mixed mode combustion process using DME, methane and a
pilot injection of diesel. This study attempts to replicate the mixed mode combustion
process using DME and propane and a main injection of diesel.
2.3.2 Propane
Propane is produced as a by-product of two other processes, natural gas
processing and petroleum refining [45]. It accounts for about 2% of the energy used in
the United States. Uses include home and water heating, cooking and refrigerating food,
19
clothes drying, powering farm and industrial equipment and drying corn [45]. In addition
to these, the usage of propane as a gaseous fuel in automotive vehicles is gaining
popularity.
Like methane, propane has also been used as the gaseous fuel for the pre-mixed
charge in HCCI combustion to varying results [46, 47]. Takatsuto et al. observed that the
combustion of propane has just a single heat release peak at higher temperatures unlike
the two peaks observed for DME combustion [46]. The reason for this could possibly be
attributed to the higher autoignition temperature of propane as compared to DME (Table
2.1). An increase in the fuel equivalence ratio also appeared to advance the high
temperature heat release as can be observed in Figure 2.1 below.
Figure 2.1: Rate of heat release for propane and DME at various equivalence ratios [46]
20
Aceves et al. have shown that in order that propane be used as an HCCI fuel in
diesel engines, high compression ratios (>18) and inlet heating (~140°C) are required
[48]. As propane alone when used as a fuel is intended to be a substitute for gasoline,
such conditions are not feasible in a HCCI engine. In order to overcome this barrier, Yap
et al. experimented with internal trapping of the exhaust gases to raise in-cylinder
temperatures [47]. They were able to run the engine at a compression ratio (CR) of 15
without any intake air heating system while observing reduced NOx emissions.
Propane is one of a series of n-alkanes used by researchers experimenting with
gaseous fuels for HCCI combustion [16, 49, 50]. As stated in Section 2.1, controlling the
auto ignition is one of the main difficulties in HCCI combustion. Propane when used as
the solitary gaseous fuel in an HCCI combustion process also faces the same problem due
to its high auto ignition temperature. For n-alkane HCCI combustion, researchers have
experimented with various controlling techniques like EGR recirculation [16], ozone
addition [49] or the use of additives to modify the cetane number of the fuel [50].
Mehresh et al. have attempted to achieve control over the auto ignition point by the use of
an ion sensor to determine the crank angle at 50% of the heat release [51].
But, propane when used in conjunction with another gaseous fuel along with an
injection of diesel can be used to control the ignition and heat release as has been
demonstrated in this study. The following section will identify the advantages for
selecting propane over methane as a fumigated fuel in addition to DME in the mixed
mode combustion process.
21
2.3.3 Advantages of Propane over Methane
As has been previously stated, the fuel blend of DME and methane has been used
by researchers experimenting with HCCI combustion [35, 38, 42]. In this study, we
attempt to replicate those experiments replacing methane with propane.
Chen et al. have shown through their experiments that methane when used alone
for HCCI combustion does not auto ignite due to its high auto ignition temperature
(650°C) [35]. On the other hand, propane when used alone does auto ignite albeit with
high compression ratios and possibly inlet air heating [48]. Propane having a lower auto
ignition temperature than methane (470°C) presents the possibility of observing an
increased amount of heat release at lower temperatures than would have been possible
with methane. This gives an increased amount control over the ignition in terms of the
range of crank angles over which ignition can occur. Similar to methane, a mixture have
a high proportion of propane and low in DME would result in delayed ignition which
could be controlled to occur at TDC. Chen et al. have shown that for a high methane and
low DME mixture, the high temperature heat release can occur as late as 12° after TDC
[35]
A comparison of the octane numbers of propane and methane shows that methane
has a higher octane number (120) as compared to propane (97) (Table 2.1). This implies
that propane has a higher cetane number than methane and thereby is more suitable for
compression ignition than methane. Both gases have similar lower heating values by
mass and stoichiometric air-fuel ratios.
22
In this chapter, previous research on HCCI, PCCI and RCCI combustion and
DME and DME blend fumigation has been reviewed. The following chapters will deal
with the setup for the experiments conducted and the results and conclusions derived
thereby.
23
Chapter 3
Experimental Setup
3.1 Engine Specifications
The engine used for the experiments is 2.5 L Detroit Diesel Corporation/VM-
Motori engine. The engine specifications are listed in Table 3.1 and the engine is shown
in Figure 3.1.
Table 3.1: 2.5 L DDC/VM-Motori Engine Specifications
Engine DDC 2.5 L Turbo-charged, Direct Injection(DI)
Number of valves 4 valves/cylinder
Displacement 2.5 L
Bore 92 mm
Stroke 94 mm
Compression ratio 17.5
Length of the connecting rod 159 mm
Rated power 103 kW@ 4000 rpm
Peak torque 340 Nm@1800 rpm
Injection system Bosch common rail injection
24
Figure 3.1: Photograph of 2.5 L DDC/VM Motori Engine
3.2 Load Generation and Dynamometer
The engine load was generated by a 250 Hp Eaton Eddy current dynamometer
coupled to the engine. The dynamometer was water cooled and in order to prevent
scaling from water flow in the dynamometer, the water was mixed with L5139 (Lycorine
Hydrochloride- a selective inhibitor) and TK 2354 chemicals. The engine and the
dynamometer were controlled by adjusting the settings on a Digalog Testmate 25 dyno
25
and throttle controller. Throughout the test, cooling water temperatures were monitored
to prevent overheating of the dynamometer.
3.3 Engine Control
The running conditions of the engine namely throttle opening, speed and load
were controlled by using an unlocked Electronic Control Unit (ECU). The ECU was
connected to an ETAS MAC 2 unit via an ETK connection. This was in turn connected to
a computer running INCA software, version 4.0. INCA is a measurement, calibration and
diagnostic software published by ETAS. All programming modifications to the engine
were performed using this interface. During the experiments, INCA was used to vary the
injection timing.
3.4 Data Acquisition
The engine data was collected real-time by means of a series of custom written
programs on National Instruments LabView, Version 7. This enables gathering of a
number of signals such as cylinder pressures and temperatures, air flow mass, fuel flow
rate etc. through a series of FieldPoint modules. This data can then be saved and viewed
in Microsoft Excel or Minitab and easily be processed and analyzed. Once all the
parameters reached steady state, a sampling interval of 2 seconds was used for a total
sampling time of 3-4 minutes.
26
3.5 Pressure Trace and Needle Lift Sensor
Cylinder pressure signals were measured using AVL GU12P pressure transducers.
The voltages from these transducers were amplified by a set of Kistler type 5010 dual
mode amplifiers. The signals were read by an AVL Indimodul 621 data acquisition
system. Needle lift data were obtained from a Wolff Controls Inc. Hall effect needle lift
sensor, which was placed on the injector of cylinder 1. This signal was read by the AVL
Indimodul, which was triggered by a crank angle signal from an AVL 365 C angle
encoder placed on the crank shaft. The Indicom interface recorded these signals over a
0.1 degree crank angle resolution and averaged them over 200 cycles.
3.6 Mass of Air Flow (MAF) and Diesel Flow Rate
The mass of air entering the engine at any given condition was calculated based
on the voltage reading on the MAF sensor. This sensor was calibrated using a laminar
flow element at room temperature, which was assumed to be 300 K.
The diesel fuel consumption was measured using a Sartorius electronic
microbalance. LabView was programmed to calculate the actual flow rate based on 100
measurements of the fuel tank mass, while it tracked small changes in mass over 60
seconds.
27
3.7 Flowmeter Setup
As the experiments required two gases (DME and Propane) to be mixed with the
air intake in specific proportions, it was important to setup the mixing process in a
manner that would be easy to control while at the same time ensuring a homogeneous
mixture. To this end, the flowmeter used was a Matheson Gas FM7410 series flowmeter
capable of flowing 4 gases. A picture of the flowmeter is given in Figure 3.2.
Figure 3.2: Matheson Gas 7410 series flow meter
The flowmeter consists of the following flow tubes numbered 605, 603, 604, 605
of which the tubes 605, 603 were used for propane while 604 and 605 were used for
DME. Each of the tubes was calibrated for the specific gases flowing through them at 0
28
psig. The calibration tables and equations can be found in Appendix A. The conversion
equation obtained was then corrected to the DME and propane cylinder pressure of 50 psi
in the LabView program. The flow obtained using the Matheson Gas flowmeter was
verified using a Hastings bubble flowmeter as well as an Omega FMA 1700/1800 digital
flowmeter. It was found that the Matheson Gas flowmeter was under-estimating the flow
by 25%. A factor of 1.25 was hence multiplied to the DME and propane flow rates
obtained using the Data Acquisition software to accurately reflect actual flow. A
schematic diagram of the liquefied gas flow into the engine is given in Figure 3.3.
Figure 3.3: Block Diagram of DME, Propane flow and mixing into the engine
29
3.8 Engine Emissions Measurement
Figure 3.4: AVL CEB II emissions bench (Source: www.avl.com)
Engine gaseous emissions were measured using an AVL CEB II combustion
emissions bench. A photograph of the bench is shown in Figure 3.4. The hot exhaust
from the engine was sampled through a series of head-line filters into an insulated heated
line which was maintained at 1900C. The gases were then filtered through smaller filters
to ensure particulate free exhaust entered the bench. Before data collection, the bench
was switched on at least 1-2 hrs in advance to let the analyzers warm up. Each day prior
30
to beginning experiments, the bench was recalibrated by flowing the span gas and zero
air for sufficient duration.
NOx and NO were measured in parts per million (ppm) using an Ecophysics
chemiluminescence analyzer. NO2 concentration was calculated as the difference
between the NOx and NO concentrations measured. Carbon monoxide (CO, ppm) and
carbon dioxide (CO2, %) were measured using two separate Rosemount infrared
analyzers and oxygen (O2, %) was measured using a Rosemount paramagnetic analyzer.
The emission bench also has the capability to measure total hydrocarbons (THC) and
methane in the exhaust. THC values were recorded, but methane values were not
measured as part of this study.
Chapter 4
Experiments and Analysis – Part 1
Two sets of experiments were performed, the first set by Bhaskar Prabhakar in
August 2011. This was intended as a preliminary study on the effects of DME and
propane fumigation in a diesel engine. For these experiments, only the engine
performance parameters were noted while the effects on the engine‘s emissions were not
considered. Also, exhaust gas recirculation was not used while running the engine for
these experiments. The data from these experiments was analyzed to determine DME and
propane substitution proportions where the engine‘s performance could be optimized.
For these experiments, the engine speed and torque were held constant at 1800
rpm and 65 ft-lb (25% load) respectively. The diesel injection timing was held constant at
7 deg BTDC with no pilot injection introduced.
4.1 Experimental Runs
The experiment was setup as a full factorial experimental design on Minitab 16.
The two factors are DME and propane, while the responses are BSEC, BTE, BSFC,
BSDC, HRR and PRR.
32
4.1.1 Multilevel Factorial Design
Factors: 2 (DME and Propane)
Replicates: 1
Base runs: 21
Total runs: 21
Base blocks: 1
Total blocks: 1
Number of levels: 3 for DME (10, 20, 30)
7 for Propane (0, 5, 10, 15, 20, 25, 30)
Note:
The number of levels for DME could have been considered as 4 including the
value for 0%. But, as there is only one experimental run available for DME = 0 (baseline
diesel), this would have resulted in an unbalanced design and hence is not considered
[52].
It is ideally required that the experimental runs be randomized in order to avoid
any bias or error. But, in this case, the experiments have not been carried out in a
randomized manner due to limitations with the experimental setup. The results of the
experiments are given in the Table 4.1. The Heat Release Rate and Pressure Rise Rate
given in the table are the averages of the values from 40o BTDC to 40
o ATDC.
33
Table 4.1: Data collected from the preliminary experimental runs
DME
(%)
Propane
(%)
BSEC
(MJ/kWh)
BSDC
(kg/kWh)
BSFC
(kg/kWh)
BTE
(%)
HRR
(J/deg)
PRR
(bar/deg)
0.00 0.00 10.02 233.59 233.59 35.93 10.1019 0.4969
10.00 0.00 9.66 200.82 237.52 37.31 9.4948 0.4624
10.00 5.00 10.16 202.19 247.86 35.44 9.8197 0.4793
10.00 10.00 10.32 191.37 251.13 34.96 10.0765 0.4924
10.00 15.00 10.51 180.27 255.92 34.41 10.2347 0.5008
10.00 20.00 10.26 166.57 249.42 35.11 10.4954 0.5146
10.00 25.00 10.40 154.60 251.70 34.62 10.0073 0.4941
10.00 30.00 10.84 147.06 260.57 33.22 9.7149 0.4820
20.00 0.00 11.02 203.44 284.02 32.68 9.6369 0.4668
20.00 5.00 10.18 175.16 261.87 35.38 9.8863 0.4793
20.00 10.00 10.34 165.12 264.61 34.84 10.3167 0.4996
20.00 15.00 10.05 148.33 256.68 35.84 10.5778 0.5121
20.00 20.00 10.52 144.91 267.16 34.24 10.7996 0.5217
20.00 25.00 10.60 132.69 268.14 33.98 10.6960 0.5186
20.00 30.00 10.70 122.89 269.10 33.66 10.9406 0.5330
30.00 0.00 9.22 148.69 248.55 39.10 10.1919 0.4924
30.00 5.00 9.29 142.77 247.59 38.76 10.2429 0.4936
30.00 10.00 9.03 123.49 241.66 39.87 10.7662 0.5160
30.00 15.00 9.04 113.68 240.61 39.85 11.1494 0.5346
30.00 20.00 9.27 102.82 246.19 38.87 11.7175 0.5586
30.00 25.00 8.58 87.70 227.38 41.95 11.9030 0.5658
30.00 30.00 8.51 73.76 226.63 42.31 12.1254 0.5738
34
4.1.2 Analysis of Variance (ANOVA)
The ANOVA results from Minitab for each of the 6 responses were obtained to
determine the effect changes in DME and propane have on them. Table 4.2 summarizes
the results and also states based on the P-value whether the factors are significant in
affecting the responses.
Table 4.2: ANOVA significance table
DME Propane R2-adj
Response Factor P-Value Significance P-value Significance (%)
BTE 0.000 Yes 0.997 No 72.28
BSEC 0.000 Yes 0.996 No 71.36
BSFC 0.001 Yes 0.977 No 51.60
BSDC 0.000 Yes 0.000 Yes 97.13
HRR 0.000 Yes 0.008 Yes 75.02
PRR 0.000 Yes 0.002 Yes 78.23
A P-value < 0.05 is considered as a criterion for the rejection of the null
hypothesis (that the factor is insignificant). As can be seen from the above table, DME is
significant in affecting all the responses unlike propane which significantly affects only
BSDC, HRR and PRR.
The R2-adj values give an indication of the percentage of variation in the response
that can be explained by the factors currently considered in the model. The values show
that there is still room for improvement which can be achieved by possibly adding more
factors. One such term could be the interaction term between DME and propane. The
significance of the interaction terms can be determined by the non-parallel nature (if
present) of the interaction plots (Appendix B).
35
It is observed that with exception to BSDC, all the interaction plots have non-
parallel lines. This indicates the presence of a significant interaction between the factors
in determining the responses BTE, BSEC, BSFC, PRR and HRR. The interaction term
however cannot be included in the ANOVA due to insufficient degrees of freedom
available leading to the ‗Error‘ term in the analysis having zero degrees of freedom. This
stresses the need for replications in future runs of the experiment.
4.2 Regression Analysis
The previous section dealt with the significance of the factors, DME and Propane
in determining the responses, BTE, BSEC, BSFC, BSDC, HRR and PRR. It was also
noted that the DME-Propane interaction could potentially be significant in affecting the
values of the responses. This section will attempt to fit a regression model to describe the
relationship between each of the responses and the factors mathematically. This will be
followed by an optimality analysis to determine the operating point where the parameter
is at its optimal value. The relationship between the factors and the response need not
always be linear. To increase the accuracy of the model, it may be necessary to include
higher powers.
In the case of the regression analyses carried out in this study, it was noticed that
the data for some of the responses was following a decreasing trend initially and then an
increasing trend. This suggests the inclusion of a quadratic term in the variables DME
and Propane. On inclusion of further powers, it was observed that the correlation between
the variables was too high resulting in a reduction in the R2-adj value (whose significance
36
is explained below). It is for this reason that no powers beyond the squared term of the
variables were used.
The accuracy of the regression model will be based on the value of R2-adj – the
adjusted co-efficient of determination which is a measure of the percentage of variation
in the response explained by the regression model. A model with a R2-adj value of greater
than 80% is considered reasonably accurate [53]. In addition to the R2-adj values, the
residuals will also be considered while determining the feasibility of the model. Once an
appropriate model has been fitted, it will be checked to determine the validity of the
regression assumptions listed below,
1. The residuals are normally distributed
2. They have a variance which is constant.
Any of these assumptions not being met would lead to the need for
transformations in the model so that a regression model can be fitted.
The point (DME, Propane) = (0, 0), i.e., the readings for baseline diesel, has been
excluded from the dataset considered for regression. This is because the initial Minitab
iterations noted that the point (0, 0) had a lot of leverage over the regression line and was
resulting in reduced values of R2-adj. Also, the initial testing dataset given in Section 4.1
is incomplete in that the responses for when DME = 0% and propane is varied have not
been measured. While analyzing the regression results all terms with a P-value less than
0.05 will be considered significant. The Minitab output of the regression results are given
in Appendix C.
Once appropriate regression models have been fitted for the responses, it is
needed to obtain operating conditions to optimize the values of the responses. The
37
regression models obtained in the previous section will be used as objective functions for
each of the responses. Microsoft Excel solver was used as the optimization tool to solve
the problem.
The constraints for the optimization problem are given below.
10 ≤ DME ≤ 30
0 ≤ Propane ≤ 30
DME, Propane, BTE, BSEC, BSFC, BSDC, HRR, PRR ≥ 0
The following sections give the optimal desired values of the response variables
subject to the above constraints. The DME and propane substitution quantities to obtain
the optimal values are also given.
4.2.1 Brake Thermal Efficiency (BTE)
Regression Equation:
BTE = 45.1 - 1.17*DME + 0.204*Propane + 0.0318*DME2 + 0.0103*DME*Propane
R2-adj = 89.4%
Terms DME Propane DME*Propane DME^2
P-value 0 0.002 0.001 0
Significance Yes Yes Yes Yes
The table above gives the P-values and the significance for each of the terms included in
the regression equation.
38
Figure 4.1: Brake Thermal Efficiency at varying DME and propane substitution levels
In the X-axis of the graph (10, 0) = 10%DME and 0% propane
The bar graph of the actual data in Figure 4.1 shows an increasing trend in the
brake thermal efficiency with increasing energy substitution. This is corroborated by the
optimality analysis using Excel Solver.
Maximize BTE = 45.1 - 1.17*DME + 0.204*Propane + 0.0318*DME2 +
0.0103*DME*Propane
DME Propane BTE BSEC BSDC BSFC HRR PRR
30 30 41.77 8.668 78 228.71 12.052 0.5716
The point of maximum efficiency is found to be at 30% DME substitution and
30% propane substitution.
25.00
27.00
29.00
31.00
33.00
35.00
37.00
39.00
41.00
43.00
45.00
Bas
elin
e
10,0
10,5
10,1
0
10,1
5
10,2
0
10,2
5
10,3
0
20,0
20,5
20,1
0
20,1
5
20,2
0
20,2
5
20,3
0
30,0
30,5
30,1
0
30,1
5
30,2
0
30,2
5
30,3
0
BTE
(%
)
DME, Propane (% energy substitution)
39
4.2.2 Brake Specific Energy Consumption (BSEC)
Regression Equation:
BSEC = 7.69 + 0.308*DME + 0.0537*Propane - 0.0026*DME*Propane -
0.00837*DME2
R2-adj = 88.0%
Terms DME Propane DME*Propane DME^2
P-value 0 0.003 0.002 0
Significance Yes Yes Yes Yes
The P-values and the significance for each of the terms included in the regression
equation are given in the table above. As can be seen all the terms included are
significant.
Figure 4.2: Brake Specific Energy Consumption at varying DME and propane
substitution levels
6.00
7.00
8.00
9.00
10.00
11.00
12.00
Bas
elin
e
10,
0
10,
5
10,
10
10,
15
10,
20
10,
25
10,
30
20,
0
20,
5
20,
10
20,
15
20,
20
20,
25
20,
30
30,
0
30,
5
30,
10
30,
15
30,
20
30,
25
30,
30
BSE
C (
MJ/
kWh
)
DME, Propane (% energy substitution)
40
BSEC is observed to decrease in Figure 4.2 as the energy substitution is
increased. There is however, a slight increase when the DME substitution is 10% and the
amount of propane is increased from 0 to 30%. The optimality analysis supports this
trend with the point DME = 30% and propane = 30% estimated to have the lowest brake
specific energy consumption.
Minimize: BSEC = 7.69 + 0.308*DME + 0.0537*Propane - 0.0026*DME*Propane -
0.00837*DME2
DME Propane BTE BSEC BSDC BSFC HRR PRR
30 30 41.77 8.668 78 228.71 12.052 0.5716
4.2.3 Brake Specific Fuel Consumption (BSFC)
Regression Equation:
BSFC = 173 + 9.28*DME + 1.13*Propane - 0.0631*DME*Propane - 0.222*DME2
R2-adj = 79.2%
Terms DME Propane DME*Propane DME^2
P-value 0 0.008 0.002 0
Significance Yes Yes Yes Yes
It can be seen from the P-values in the above table that all the terms included are
significant.
41
Figure 4.3: Brake Specific Fuel Consumption at varying DME and propane substitution
levels
As seen in Figure 4.3, BSFC is also found to exhibit a similar trend as BSEC with
an initial increase around the 20% DME substitution mark followed by a later decrease.
The Excel Solver analysis puts the point of minimum brake specific fuel consumption at
30% DME and 30% propane which is an indication of reduced fuel consumption with
increasing energy substitution.
Minimize: BSFC = 173 + 9.28*DME + 1.13*Propane - 0.0631*DME*Propane -
0.222*DME2
DME Propane BTE BSEC BSFC BSDC HRR PRR
30 30 41.77 8.668 78 228.71 12.052 0.5716
150.00
170.00
190.00
210.00
230.00
250.00
270.00
290.00
310.00
Bas
elin
e
10,0
10,5
10,1
0
10,1
5
10,2
0
10,2
5
10,3
0
20,0
20,5
20,1
0
20,1
5
20,2
0
20,2
5
20,3
0
30,0
30,5
30,1
0
30,1
5
30,2
0
30,2
5
30,3
0
BSF
C (
kg/k
Wh
)
DME, Propane (% energy substitution)
42
4.2.4 Brake Specific Diesel Consumption
Regression Equation:
BSDC = 213 + 1.05*DME - 2.34*Propane - 0.107*DME2
R2-adj = 97.9%
The regression equation for BSDC does not include an interaction term as
interactions were deemed insignificant in determining BSDC. From the table below, it is
seen that DME is included inspite of being insignificant. This is due to the presence and
significance of the DME^2 term.
Terms DME Propane DME^2
P-value 0.305 0 0
Significance No Yes Yes
Figure 4.4: Brake Specific Diesel Consumption at varying DME and propane
substitution levels
50.00
70.00
90.00
110.00
130.00
150.00
170.00
190.00
210.00
230.00
250.00
Bas
elin
e
10,
0
10,
5
10,1
0
10,1
5
10,2
0
10,2
5
10,3
0
20,
0
20,5
20,1
0
20,1
5
20,2
0
20,2
5
20,3
0
30,
0
30,
5
30,1
0
30,1
5
30,2
0
30,2
5
BSD
C (
kg/k
Wh
)
DME, Propane (% energy substitution)
43
The bar plot in Figure 4.4 shows a steady decreasing trend in BSDC with
increasing energy substitution with the least diesel consumption occurring at the extreme
point of 30% DME and 30% propane substitution.
Minimize BSDC = 213 + 1.05*DME - 2.34*Propane - 0.107*DME2
DME Propane BTE BSEC BSDC BSFC HRR PRR
30 30 41.77 8.668 78 228.71 12.052 0.5716
4.2.5 Heat Release Rate (HRR)
Regression Equation:
HRR = 9.97 - 0.0510*DME + 0.0271*Propane + 0.00308*DME*Propane +
0.00159*DME2 - 0.00156*Propane
2
R2-adj = 94.40%
Terms DME Propane DME*Propane DME^2 Propane^2
P-value 0.145 0.102 0 0.066 0.003
Significance No No Yes No Yes
From the above table, it is seen that the 3 of the 5 terms included are shown to be
insignificant. The DME and propane terms have to be included as the interaction term,
DME*Propane is significant. Exclusion of the DME2 terms results in a reduction in the
R2-adj value.
44
Figure 4.5: Apparent Heat Release Rate at varying DME and propane substitution levels
There is a steady increasing pattern visible with increasing energy substitution
reaching a peak at 30% each DME and propane substitution as observed in Figure 4.5.
The average values of the heat release rather than the peak heat release values were used
as the average values indicated a clear gradation between different runs which was not
observed with the peak values. The optimality analysis suggests that the minimum heat
release rate would be at 0% DME and 30% propane substitution.
Minimize HRR = 9.97 - 0.0510*DME + 0.0271*Propane + 0.00308*DME*Propane +
0.00159*DME2 - 0.00156*Propane
2
DME Propane BTE BSEC BSDC BSFC HRR PRR
0 30 38.98 9.301 142.8 206.9 9.379 0.4753
6.0000
7.0000
8.0000
9.0000
10.0000
11.0000
12.0000
13.0000
Bas
elin
e
10,0
10,5
10,1
0
10,1
5
10,2
0
10,2
5
10,3
0
20,0
20,5
20,1
0
20,1
5
20,2
0
20,2
5
20,3
0
30,0
30,5
30,1
0
30,1
5
30,2
0
30,2
5
30,3
0
Ave
rage
HR
R (
J/d
eg)
DME, Propane (% energy substitution)
45
4.2.6 Pressure Rise Rate (PRR)
Regression Equation:
PRR = 0.484 - 0.00231*DME + 0.00184*Propane - 0.000071*Propane2 +
0.000114*DME*Propane + 0.000070*DME2
R2-adj = 93.30%
Terms DME Propane DME*Propane DME^2 Propane^2
P-value 0.152 0.029 0 0.078 0.003
Significance No Yes Yes No Yes
This is again similar to the previous case with HRR as some of the terms have to included
due to the presence of the interaction term and for increasing the R2-adj value.
Figure 4.6: Average Pressure Rise Rate at varying DME and propane substitution levels
As with the heat release rate, the average pressure rise rate also exhibits an
increasing trend with increasing energy substitution in Figure 4.6. The point with no
0.3000
0.3500
0.4000
0.4500
0.5000
0.5500
0.6000
Bas
elin
e
10,0
10,5
10,
10
10,
15
10,
20
10,
25
10,3
0
20,0
20,5
20,
10
20,
15
20,
20
20,
25
20,
30
30,0
30,5
30,
10
30,
15
30,
20
30,
25
30,
30
Ave
rage
PR
R (
bar
/deg
)
DME, Propane (% energy substitution)
46
propane and 16.5% DME substitution is calculated to have the minimum pressure rise
rate. As with HRR, average values have been used rather than peak values for the same
reasons stated in Section 4.2.5.
Minimize PRR = 0.484 - 0.00231*DME + 0.00184*Propane - 0.000071*Propane2 +
0.000114*DME*Propane + 0.000070*DME^2
DME Propane BTE BSEC BSDC BSFC HRR PRR
16.5 0 34.45255 10.49327 201.1943 265.6805 9.561377 0.464943
All the response variables were individually optimized using the GRG Nonlinear
type solving method in Excel Solver. The DME and propane values for each of these are
plotted in the graph below.
Figure 4.7: Visual representation of optimal points for the individual response variables
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
Pro
pan
e (%
en
ergy
su
bst
itu
tio
n)
DME (% energy substitution)
Max BTE Min BSEC
(30,30)
Min HRR
(0,30)
Min PRR
(16.5,0)
47
The above plot (Figure 4.7) leads us to the following inferences.
1. Maximum brake thermal efficiency and minimum fuel and energy consumption
are obtained when there is maximum substitution of diesel with DME and
propane. The pressure rise rate and the heat release rate at these points are also at
their maximum values.
2. The pressure rise rate in the cylinder is minimum with low DME substitution and
zero propane substitution. The thermal efficiency is noticeably low at this point.
3. The heat release rate in the cylinder is minimum for low DME and high propane
substitution.
Thus, there is a trade-off between optimizing BTE, BSFC, BSDC and BSEC on
one hand against HRR and PRR on the other hand. An ideal condition would be one
where both BTE and PRR are reasonably close to their optimum values. The next section
attempts to obtain such a condition.
4.2.7 Obtaining a trade-off point
In order to maximize BTE and minimize PRR at the same time, it is essential to
bring both the response variables into a single objective function. One such function
could be ‗BTE – PRR‘, but this would not work as BTE is of the order of the first power
of 10 while PRR is less than 1. Thus, it is necessary to scale both variables so that they
can be included in the same objective function.
48
Scaled BTE = (BTE - BTEmin)
(BTEmax- BTEmin)
Scaled PRR = (PRR - PRRmin)
(PRRmax- PRRmin)
The new objective function is now ‗Scaled BTE – Scaled PRR‘ which needs to be
maximized to maximize BTE and minimize PRR. The maximum and minimum values of
BTE and PRR obtained from the previous section are given below in Table 4.3.
Table 4.3: Maximum and minimum values of Brake Thermal Efficiency and Pressure
Rise Rate
Max Min
Brake Thermal Efficiency (BTE) 41.77 32.42
Pressure Rise Rate (PRR) (bar/deg) 0.6417 0.4649
The constraints for the optimization problem are the same as were used in the
previous section to optimize the response variables individually. The results are given in
the table below.
Table 4.4: Trade-off point for optimizing BTE and PRR
DME Propane BTE BSEC BSDC BSFC HRR PRR
Sc. BTE -
Sc.PRR
22.76 29.66 35.85 10.20 112.06 260.13 11.14 0.537 0.473384
49
Figure 4.8: Visual representation of the optimal point for obtaining a trade-off between
BTE and PRR
Figure 4.8 shows the condition obtained with respect to the points plotted from
the previous section. The BTE value obtained at 22.76% (~23%) DME substitution and
29.66% (~30%) propane (35.86%) is 14% lower than the maximum possible value of
41.77%. The PRR value of 0.537 bar/deg obtained at the same condition is 15% higher
than the minimum possible value of 0.4648 bar/deg. Thus, the point with 20% DME
substitution and 30% propane is the trade-off point for optimizing both BTE and PRR.
The results of the preliminary set of experiments along with the optimization
analysis were dealt with in this chapter without delving into the possible reasons behind
the trends observed. The following chapter deals with the next set of experiments wherein
it will be attempted to practically verify the analytically obtained results in this chapter in
addition to explaining the reasons behind the trends observed.
0
5
10
15
20
25
30
35
0 10 20 30 40
Pro
pan
e
DME
Max BTE
Min PRR
(22,30)
Chapter 5
Experiments and Analysis – Part 2
The previous chapter described the preliminary experiments conducted as part of
the study of DME and propane fumigation in a diesel engine. Based on the analysis of the
results of those experiments, the next set of experiments was formulated in order to verify
the results of the optimality analysis done in Chapter 4. In addition to the engine
performance parameters considered for the previous set of experiments, emission data
was also measured in this set of experiments.
5.1 Experimental Runs
The experiments were conducted for the following cases
1. DME and propane fumigation without exhaust gas recirculation (EGR)
2. DME and propane fumigation with EGR
3. DME and propane fumigation with EGR and split injection
The test matrices for each of these cases are given in Tables 5.1 – 5.3 respectively
based on the results of the regression analysis carried out in Section 4.2. The engine
speed and torque were held constant at 1800 rpm and 65 ft-lb (25% load) respectively as
in the previous set of experiments. The diesel injection timing was held constant for the
first two cases at 7 deg BTDC with no pilot injection introduced.
51
Table 5.1: Test Matrix for DME and Propane fumigation with no EGR
DME (%) Propane (%)
0 0 10 20 30 40
10 0 10 20 30 40
20 0 10 20 30
30 0 10 20 30
40 0
Table 5.2: Test Matrix for DME and Propane fumigation with EGR
DME (%) Propane (%)
0 0
10 0 20 40
20 0 20 40
30 0 20
Table 5.3: Test Matrix for DME and Propane fumigation with EGR and split injection
DME (%) Propane (%) Pilot Injection (deg) Main Injection (deg)
0 0 16 BTDC 3 ATDC
20 20 16 BTDC 3 ATDC
20 20 16 BTDC 2 ATDC
20 20 16 BTDC 5 ATDC
The measured values or responses are listed below
1. Brake Thermal Efficiency (BTE)
2. Brake Specific Energy Consumption (BSEC)
3. Brake Specific Fuel Consumption (BSFC)
4. Heat Release Rate (HRR)
5. Pressure Rise Rate (PRR)
6. Total Hydrocarbon Emissions (THC)
52
7. Nitrogen Oxide emissions (NOx)
8. Carbon dioxide emissions (CO2)
9. Carbon monoxide emissions (CO)
The Heat Release Rate and Pressure Rise Rate given in the table are the averages
of the values from 30o BTDC to 30
o ATDC as in the previous experiment.
53
5.2 DME and Propane fumigation without Exhaust Gas Recirculation
It was desired to initially observe the effects of DME and propane fumigation
alone on the engine‘s performance and emissions.
5.2.1 Brake Specific Energy Consumption (BSEC)
It can be seen from Figure 5.1 that the BSEC values appear to decrease towards
the right end of the graph with increasing DME substitution values. Overall, 20% less
energy is required when the engine is run with 60% of the diesel is substituted with 30%
DME and 30% propane as compared to baseline diesel. As obtained in the optimality
analysis (Section 4.2.2), it is seen that the lower BSFC values occur as the amount of
energy substitution with DME and propane increases.
Figure 5.1: Brake Specific Energy Consumption at varying DME and propane
substitution levels without EGR
4
5
6
7
8
9
10
11
0,0
0,1
0
0,2
0
0,3
0
0,4
0
10
,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30
,0
30,1
0
30,2
0
30,3
0
40
,0
BSE
C (
MJ/
kWh
)
DME, propane (% energy substitution)
54
5.2.2 Brake Thermal Efficiency (BTE)
The general trend observed in Figure 5.2 indicates an increase in the BTE values
with increasing DME substitution. Chen et al. have documented this in their work on
DME and methane saying that mixtures with low DME and high methane content tend to
have higher brake thermal efficiencies [35]. It can be observed that the increases are
greater with increasing propane than with increasing DME. The maximum BTE was
observed at the case where DME substitution was 20% and propane substitution 30%.
The efficiency at this point was found to be 49.91% which is almost 25% greater than the
BTE for baseline diesel with no substitution. It was observed that the heat release peaks
were closer to the top dead centre (TDC) towards the right end of the graph which meant
less negative work to be done against the piston motion.
Figure 5.2: Brake Thermal Efficiency at varying DME and propane substitution levels
without EGR
20
25
30
35
40
45
50
55
60
0,0
0,1
0
0,2
0
0,3
0
0,4
0
10,
0
10,
10
10,
20
10,
30
10,
40
20,
0
20,
10
20,2
0
20,
30
30,
0
30,
10
30,
20
30,3
0
40,
0
BTE
(%
)
DME. propane (% energy substitution)
55
5.2.3 Brake Specific Fuel Consumption (BSFC)
As can be seen from Figure 5.3, the values of BSFC decrease with increasing
propane at constant DME. The values remain more or less the same for increasing DME
substitution at constant propane values. The BSFC value at 20% DME and 30% Propane
substitution represents a decrease of 18% from the BSFC value for baseline diesel.
Figure 5.3: Brake Specific Fuel Consumption at varying DME and Propane levels
without EGR
5.2.4 Heat Release Rate
Figure 5.4 shows that the average heat release rate appears to increase with
increasing substitution of diesel. A closer look shows that the increase is mainly observed
with increasing DME. As discussed in Chapter 2, DME has a higher cetane number than
100
120
140
160
180
200
220
240
260
280
300
0,0
0,10
0,20
0,30
0,40
10,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
BSF
C (
g/kW
h)
DME, propane (% energy substitution)
56
diesel and is therefore even better suited for compression ignition than diesel. DME also
has a lower auto ignition temperature than diesel. The trends are erratic with constant
DME and increasing propane. In some cases it is observed that increasing propane
decreases the heat release rate. This could be attributed to the higher autoignition
temperature for propane as compared to DME and diesel. As determined in the
optimization analysis, the lowest heat release occurs at a condition with low DME (0%)
and high propane (40%). The error bars for the heat release rate have not been plotted
owing to the high variability in the heat release per crank angle degree value.
Figure 5.4: Heat Release Rate at varying DME and Propane levels without EGR
Figures 5.5 - 5.8 depict the effect of increasing propane substitution on the heat
release rate. In each graph it can be seen that an increase in propane in the fuel appears to
retard the start of ignition as compared to the previous running condition with lesser
propane. Consider Figure 5.7 for instance, for the condition with 20% DME and no
propane there are two peaks observed, a low temperature heat release peak at around 25o
8
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
9.8
0,0
0,10
0,20
0,30
0,40
10,0
10,
10
10,
20
10,
30
10,4
0
20,0
20,
10
20,
20
20,
30
30,0
30,
10
30,
20
30,
30
40,0
Ave
rage
HR
R (
J/d
eg)
DME, propane (% energy substitution)
57
before TDC and a high temperature peak at 12o before TDC. But as propane substitution
is introduced in steps of 10%, it can be observed the low temperature peak is delayed and
decreased in amplitude until at 30% each DME and propane substitution there is a single
heat release peak at 5° after TDC. The same can be noticed in Figures 5.5, 5.6 and 5.8.
This is very similar to the effect noticed by Chen et al. [35] when experimenting with
DME and methane. Propane, also being part of the alkane family, it is hardly surprising
that it exhibits similar trends.
Figure 5.5: Heat release rate v/s crank angle for 0% DME substitution and 0 – 40%
propane substitution without EGR
In the legend of the graph, 0D10P = 0% DME and 10% Propane substitution
-10
10
30
50
70
90
-60 -40 -20 0 20 40 60
Hea
t R
elea
se (
J/d
eg)
Crank Angle (deg)
Baseline
0D10P
0D20P
0D30P
0D40P
58
Figure 5.6: Heat release rate v/s crank angle for 10% DME substitution and 0 – 30%
propane substitution without EGR
Figure 5.7: Heat release rate v/s crank angle for 20% DME substitution and 0 – 30%
propane substitution without EGR
-10
10
30
50
70
90
-60 -40 -20 0 20 40 60
He
at R
ele
ase
(J/
de
g)
Crank Angle (deg)
Baseline
10D0P
10D10P
10D20P
10D30P
10D40P
-10
10
30
50
70
90
-60 -40 -20 0 20 40 60
Hea
t R
elea
se (
J/d
eg)
Crank Angle (deg)
Baseline
20D0P
20D10P
20D20P
20D30P
59
Figure 5.8: Heat release rate v/s crank angle for 30% DME substitution and 0 – 30%
propane substitution and 40% DME substitution and 0% propane without EGR
Figure 5.9 shows the effect on combustion and the heat release rate exclusively
due to increases in DME substitution. As compared to the curve for baseline diesel, it can
be seen that all the other graphs appear to have two heat release peaks which become
more prominent with increasing DME substitution. This is then followed by a phase of
diffusion combustion.
-20
-10
0
10
20
30
40
50
60
70
80
-60 -40 -20 0 20 40 60
He
at R
ele
ase
(J/
de
g)
Crank Angle (deg)
30D0P
30D10P
30D20P
30D30P
40D0P
60
Figure 5.9: Heat release rate v/s crank angle for 10 - 40% DME substitution and 0%
propane substitution without EGR
-20
0
20
40
60
80
-60 -40 -20 0 20 40 60
He
at R
ele
ase
(J/
de
g)
Crank Angle (deg)
Baseline
10D0P
20D0P
30D0P
40D0P
61
5.2.4 Pressure Rise Rate (PRR)
Figure 5.10 shows the trend in the average pressure rise rate with diesel
substitution. Overall there is no particular trend visible in the plot, but it can be seen that
with increasing DME and constant propane there is an increase in the pressure rise rate.
This, as in the case of the heat release, can be attributed to the high suitability of DME
towards compression ignition. With increasing propane and constant DME, the pressure
rise rates appear to decrease initially and then increase with increasing propane. As in the
case with the average heat release rate, the error bars have not been plotted due to high
variability in the values used.
Figure 5.10: Pressure rise rate in the cylinder at varying DME and propane levels
0.245
0.25
0.255
0.26
0.265
0.27
0.275
0.28
0.285
0.29
0.295
0,0
0,1
0
0,2
0
0,3
0
0,4
0
10
,0
10,1
0
10,2
0
10,3
0
10,4
0
20
,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
Ave
rage
PR
R (
bar
/deg
)
DME, Propane (% energy substitution)
62
Figures 5.11 – 5.14 show the graphs for the cylinder pressure at different DME
and propane substitution values. In each case, it can be seen that the peak pressure
appears to decrease with increasing propane. Increasing propane also appears to introduce
a second peak in the pressure graph which is absent when only DME is present in the
cylinder as can be seen clearly in Figures 5.13 and 5.14.
Figure 5.11: Pressure rise rate v/s crank angle for 0% DME substitution and 0 – 40%
propane substitution without EGR
0
10
20
30
40
50
60
-60 -40 -20 0 20 40 60
Pre
ssu
re R
ise
(bar
/deg
)
Crank Angle (deg)
Baseline
0D10P
0D20P
0D30P
0D40P
63
Figure 5.12: Pressure rise rate v/s crank angle for 10% DME substitution and 0 – 40%
propane substitution without EGR
Figure 5.13: Pressure rise rate v/s crank angle for 20% DME substitution and 0 – 30%
propane substitution without EGR
0
10
20
30
40
50
60
70
-60 -40 -20 0 20 40 60
Pre
ssu
re R
ise
(b
ar/d
eg)
Crank Angle (deg)
Baseline
10D0P
10D10P
10D20P
10D30P
10D40P
0
10
20
30
40
50
60
70
-60 -40 -20 0 20 40 60
Pre
ssu
re R
ise
(bar
/deg
)
Crank Angle (deg)
Baseline
20D0P
20D10P
20D20P
20D30P
64
Figure 5.14: Pressure rise rate v/s Crank Angle for 30% DME substitution and 0 – 30%
propane substitution and 40% DME substitution and 0% propane without EGR
Figure 5.15 shows the changes in the peak cylinder pressure due to changes in the
DME substitution values. A steady rise in both the pressure rise rate and the peak
cylinder pressure can be seen which can again be attributed to the greater suitability of
DME towards compression ignition.
0
10
20
30
40
50
60
70
80
-60 -40 -20 0 20 40 60
Pre
ssu
re R
ise
(b
ar/d
eg)
Crank Angle (deg)
Baseline
30D0P
30D10P
30D20P
30D30P
40D0P
65
Figure 5.15: Pressure rise rate v/s crank angle for 0% propane substitution and 10 – 40%
DME substitution
0
10
20
30
40
50
60
70
80
-60 -40 -20 0 20 40 60
Pre
ssu
re R
ise
(b
ar/d
eg)
Crank Angle (deg)
Baseline
10D10P
20D0P
30D0P
40D0P
66
5.2.5 Total Hydrocarbon Emissions (THC)
A very clear trend can be observed from Figure 5.16 where with increasing
propane at constant DME, the hydrocarbon content in the emissions increases. This
would be due to the lower reactivity and higher autoignition temperature of propane. In
comparison, the increase is very marginal for constant propane and increasing DME and
is almost comparable to that of baseline diesel in the case of 10% and 20% DME with no
propane. Aceves et al have also documented similar effects with DME and methane [41]
Figure 5.16: Total hydrocarbon emissions at varying DME and propane levels without
EGR
-
500.00
1,000.00
1,500.00
2,000.00
2,500.00
3,000.00
3,500.00
0,0
0,1
0
0,2
0
0,3
0
0,4
0
10
,0
10,1
0
10,2
0
10,3
0
10,4
0
20
,0
20,1
0
20,2
0
20,3
0
30
,0
30,1
0
30,2
0
30,3
0
40
,0
Tota
l Hyd
roca
rbo
ns
(pp
m)
DME, Propane (% energy substitution)
67
5.2.6 Nitrogen Oxide emissions (NOx)
Figure 5.17 shows that the NOx emissions appear to decrease with increasing
energy substitution with DME and Propane. The lowest NOx ppm value occurs at 30%
each DME and Propane substitution which represents a 41% decrease over the value for
baseline diesel. The general trend seen is that NOx decreases with both increasing DME
and propane. This could possibly be due to the reduced heat release from the mixing
controlled phase of combustion.
Figure 5.17: Nitrogen oxide (NOx) emissions at varying DME and propane levels
without EGR
Figures 5.18 and 5.19 give the nitric oxide (NO) and nitrogen dioxide (NO2)
emissions respectively. It can be seen from Figure 5.18 that NO seems to reduce with
increase propane. This is consistent with previous research carried out by Hori and his
-
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
450.00
500.00
0,0
0,1
0
0,2
0
0,3
0
0,4
0
10,0
10,
10
10,
20
10,
30
10,
40
20,0
20,
10
20,2
0
20,
30
30,0
30,
10
30,
20
30,
30
40,0
Toto
al N
Ox
(pp
m)
DME, Propane (% energy substitution)
68
co-workers who showed that increasing propane increases the NO to NO2 conversion rate
[54]. This effect is seen in Figure 5.19 where an increase in NO2 emissions is observed
for the corresponding decrease in NO emissions. This effect was also observed (though to
a lesser extent) by Chapman and Boehman using DME and methane [14].
Figure 5.18: Nitric oxide (NO) emissions at varying DME and propane levels without
EGR
-
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
0,0
0,10
0,20
0,30
0,40
10,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
NO
(p
pm
)
DME, Propane (% energy substitution)
69
Figure 5.19: Nitrogen Dioxide (NO2) emissions at varying DME and Propane levels
without EGR
5.2.7 Carbon Dioxide Emissions (CO2)
It can be seen from Figure 5.20 the carbon dioxide emissions appear to decrease
mainly with increasing propane while they remain more or less constant with increasing
DME. The increased reactivity of DME leads to its oxidation into CO2 and water whereas
propane remains unburnt to an extent and thus contributes in decreasing CO2 levels but
increasing hydrocarbon levels as was seen in Section 5.2.7.
-
50.00
100.00
150.00
200.00
250.00
0,0
0,10
0,20
0,30
0,40
10,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
NO
2 (p
pm
)
DME, Propane (% energy substitution)
70
Figure 5.20: Carbon Dioxide emissions at varying DME and propane levels without
EGR
5.2.8 Carbon Monoxide (CO)
Figure 5.21 shows that the carbon monoxide levels in the emissions tend to
increase with increasing propane and DME uptil 30% DME. This could be the result of
propane burning in a reduced supply of oxygen which produces CO instead of CO2.
When propane is increased with DME at 30% substitution, the CO levels remain around
the same and actually decrease at one point.
4.20
4.40
4.60
4.80
5.00
5.20
5.40
5.60
0,0
0,10
0,20
0,30
0,40
10,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
Car
bo
n D
ioxi
de
(%
)
DME, Propane (% energy substitution)
71
Figure 5.21: Carbon Monoxide emissions at varying DME and propane levels without
EGR
5.3 DME and Propane Fumigation with Exhaust Gas Recirculation (EGR)
The next objective was to observe the effects of exhaust gas recirculation (EGR)
on the performance of the engine and its emissions. EGR is primarily a method to reduce
NOx emissions in the exhaust by diluting the intake air with the exhaust gas. It lowers the
flame temperature and oxygen concentration in the cylinder thereby reducing NOx [55].
Unlike the previous case without EGR, the analysis here will be divided into engine
performance parameters including BTE, BSEC, BSFC, BSDC, HRR and PRR and engine
emissions including THC, NOx, CO2 and CO.
-
500.00
1,000.00
1,500.00
2,000.00
2,500.00
3,000.00
3,500.00
4,000.00
0,0
0,10
0,20
0,30
0,40
10,0
10,1
0
10,2
0
10,3
0
10,4
0
20,0
20,1
0
20,2
0
20,3
0
30,0
30,1
0
30,2
0
30,3
0
40,0
Car
bo
n M
on
oxi
de
(pp
m)
DME, Propane (%)
72
5.3.1 Engine Performance parameters:
As can be seen from Figure 5.22, BTE with EGR displays a similar trend as
without EGR. The individual values for the engine with EGR are however lower with the
gap widening with increasing energy substitution.
Figure 5.22: Brake thermal efficiency (BTE) at varying DME and propane levels with
and without EGR
For BSEC as with BTE, the introduction of EGR in the engine has no effect on
the trends displayed with increasing energy substitution (Figure 5.23). However, more
energy is required to produce the same brake power. This would be due to the reduction
in cylinder flame temperature and dilution of the oxygen in the intake air.
20
25
30
35
40
45
50
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
BTE
(%
)
DME, Propane (%)
BTE EGR
BTE
73
Figure 5.23: Brake Specific Energy Consumption (BSEC) at varying DME and propane
levels with and without EGR
Figure 5.24 shows that the heat release rates for the engine with and without EGR
show slightly different trends. HRR for the engine with EGR increases with increasing
propane and DME substitution. This is not seen in the engine without EGR for 30% DME
substitution and increasing propane. Also, in most cases the average heat release rate is
lesser for the EGR introduced engine. The heat release patterns in Figures 5.25 and 5.26
appear similar to the patterns observed in Figures 5.6 – 5.9.
4
5
6
7
8
9
10
11
12
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
BSE
C
DME, Propane (% energy substitution)
BSEC EGR [MJ/kW.h]
BSEC [MJ/kW.h]
74
Figure 5.24: Average Heat Release Rate (HRR) at varying DME and Propane levels with
and without EGR
Figure 5.25: Heat release rate v/s crank angle for 10% DME substitution and 0, 20 and
40% propane substitution with EGR
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Ave
rage
HR
R (
J/d
eg)
DME, Propane (% energy substitution)
Heat Release Rate
Heat Release Rate (EGR)
-20
0
20
40
60
80
100
120
-60 -40 -20 0 20 40 60
Hea
t R
ele
ase
(J/
deg
)
Crank Angle (deg)
Baseline
10D0P
10D20P
10D40P
75
Figure 5.26: Heat release rate v/s crank angle for 20 and 30% DME substitution and 0
and 20% propane substitution with EGR
Figure 5.27 shows the heat release curve for two cases 30% DME and 20%
Propane and 10% DME and 0% Propane with and without the use of EGR. As can be
seen, for both sets of energy substitutions, the start of combustion and subsequent heat
release is delayed with the use of EGR.
-20
0
20
40
60
80
100
120
-60 -40 -20 0 20 40 60
He
at R
ele
ase
(J/
de
g)
Crank Angle (deg)
Baseline
20D0P
20D20P
30D0P
30D20P
76
Figure 5.27: Heat release rate v/s crank angle for cases with and without EGR
The average pressure rise rate in Figure 5.28 for EGR introduction increases with
DME and propane substitution as with the previous case but the values are considerably
lower. This could be attributed to the slower combustion owing to reduced cylinder
temperatures and slow pressure rises. The pressure rise graphs from Figures 5.29 and
5.30 are also similar to their counterparts from Section 5.2.6 except that the peak
pressures here are much lower.
-20
-10
0
10
20
30
40
50
60
70
80
-60 -40 -20 0 20 40 60
He
at R
ele
ase
(J/
de
g)
Crank Angle (deg)
30D20P
30D20P EGR
10D0P
10D0P EGR
77
Figure 5.28: Average pressure rise rate (PRR) at varying DME and propane levels with
and without EGR
Figure 5.29: Pressure rise rate v/s crank angle for 10% DME substitution and 0, 20 and
40% propane substitution with EGR
0.25
0.255
0.26
0.265
0.27
0.275
0.28
0.285
0.29
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Ave
rage
PR
R (
bar
/de
g)
DME, Propane (% energy substitution)
Pressure Rise Rate
Pressure Rise Rate (EGR)
0
10
20
30
40
50
60
-60 -40 -20 0 20 40 60
Pre
ssu
re (b
ar)
Crank Angle (deg)
Baseline
10D0P
10D20P
10D40P
78
Figure 5.30: Pressure rise rate v/s crank angle for 20 and 30% DME substitution and 0
and 20% propane substitution with EGR
Figure 5.31 shows the cylinder pressure trace for two conditions, 10% DME and
0% Propane and 30% DME and 20% Propane with and without EGR. Similar to the heat
release curve in Figure 5.27, the pressure rise is lower for the cases with EGR
introduction as compared to the corresponding ones without.
0
10
20
30
40
50
60
70
-60 -40 -20 0 20 40 60
Pre
ssu
re (b
ar)
Crank Angle (deg)
Baseline
20D0P
20D20P
30D0P
30D20P
79
Figure 5.31: Pressure Rise v/s Crank Angle for cases with and without EGR
5.3.2 Engine Emissions
From Figure 5.32, THC emissions with EGR introduction increase with
increasing DME and propane substitution similar to the previous case without EGR. At
high substitution proportions, however, THC emissions for EGR exceed those cases
where EGR is not used. This would be due to the lower combustion rates in this case
resulting in a greater amount of propane being unburnt and released as exhaust.
-10
0
10
20
30
40
50
60
70
80
-60 -40 -20 0 20 40 60
Pre
ssu
re (b
ar)
Crank Angle (deg)
10D0P
10D0P EGR
30D20P
30D20P EGR
80
Figure 5.32: Total hydrocarbon emissions (THC) at varying DME and propane levels
with and without EGR
As previously stated, the main intention of introducing exhaust gases into the
intake air is to reduce NOx emissions by bringing down flame temperature and oxygen
concentration in the air. The results can be seen in Figure 5.33 where NOx emissions are
lower in almost every case and further decrease with increasing substitution with DME
and propane. As compared to regular HCCI or RCCI combustion where increased heat
release facilitates better combination of nitrogen and oxygen to form oxides, with EGR
less heat is released during the combustion process as was seen in Section 5.3.1 which
leads to reduced oxidation of nitrogen.
0
500
1000
1500
2000
2500
3000
3500
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Tota
l Hyd
roca
rbo
ns
(pp
m)
DME, Propane (% energy substitution)
Total Hydrocarbons EGR (ppm)
Total Hydrocarbons (ppm)
81
Figure 5.33: Nitrogen oxide emissions (NOx) at varying DME and propane levels with
and without EGR
Figures 5.34 and 5.35 show the trend in NO and NO2 concentrations in the
exhaust. As seen in the case without EGR, the NO emissions reduce with increasing
propane and lower than the corresponding case without EGR. NO2, on the other hand
increases with increasing propane while there is also an increase observed with increasing
EGR.
0
50
100
150
200
250
300
350
400
450
500
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Tota
l NO
x (p
pm
)
DME, Propane (% energy substitution)
Total Nox EGR (ppm)
Total NOx (ppm)
82
Figure 5.34: Nitric oxide emissions (NO) at varying DME and propane levels with and
without EGR
Figure 5.35: Nitrogen dioxide emissions (NO2) at varying DME and propane levels with
and without EGR
0
50
100
150
200
250
300
350
400
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
NO
em
issi
on
s (p
pm
)
DME, Propane (% energy substitution)
Nitric Oxide EGR (ppm)
Nitric Oxide (ppm)
-
50.00
100.00
150.00
200.00
250.00
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Tota
l NO
2 (p
pm
)
DME, Propane (% energy substitution)
Nitrogen Dioxide EGR (ppm)
Nitrogen Dioxide (ppm)
83
Figure 5.36 shows that the carbon dioxide emissions levels for the engine when
EGR is used are considerably higher than when EGR is not used. Carbon monoxide
emissions levels on the other hand are much lower (Figure 5.37). This because of the
CO2 being recirculated from the exhaust which increases the concentration of CO2 in the
cylinder. CO levels are reduced because of reduced combustion and heat release when
EGR is introduced.
Figure 5.36: Carbon dioxide emissions (CO2) at varying DME and propane levels with
and without EGR
2
3
4
5
6
7
8
9
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
Tota
l CO
2
DME, Propane (% energy substitution)
Carbon Dioxide EGR (%)
Carbon Dioxide (%)
84
Figure 5.37: Carbon monoxide emissions (CO) at varying DME and propane levels with
and without EGR
5.4 DME and Propane Fumigation with Exhaust Gas Recirculation (EGR) and
split injection
This section describes the last set of experiments run with split diesel injection. In
this case, the diesel injection is split into a pilot injection and a main injection. The role
of the pilot injection is to serve as an aid in the ignition of the gaseous mixture already in
the cylinder, while the main injection facilitates the major heat release when the gaseous
mixture is already burning.
0
500
1000
1500
2000
2500
3000
3500
4000
0,0 10,0 10,20 10,40 20,0 20,20 30,0 30,20
CO
em
issi
on
s
DME, Propane (% energy substitution)
Carbon Monoxide EGR (ppm)
Carbon Monoxide (ppm)
85
5.4.1 Engine Performance Parameters
The trends observed for brake thermal efficiency (BTE) and brake specific energy
consumption (BSEC) can be seen in Figures 5.38 and 5.39 respectively. There is not too
much of a change observed in the BTE values due to changing the main injection timing.
There is, however, a drop from the BTE value observed at the same substitution without
EGR and split injection.
Figure 5.38: Brake Thermal Efficiency (BTE) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing
(20 DME 20 Prop, 16, -2 represents the value at 20%DME and 20% propane substitution
with pilot injection at 16 deg BTDC and main injection at 2 deg ATDC. 20 DME, 20
Prop, 7 represents the case with a single injection at 7 deg BTDC)
0
5
10
15
20
25
30
35
40
45
50
Baseline, 16, -3 20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
BTE
(%
)
DME, Propane (% energy substitution)
86
Figure 5.39 gives the values of BSEC for varying main injection timing. As can
be seen, the BSEC values for the split injection cases remain more or less the same, but at
a slightly higher value than that for the same energy substitution without EGR or split
injection.
Figure 5.39: Brake Specific Energy Consumption (BSEC) at 20% DME, 20% Propane,
16 deg BTDC pilot injection and varying main injection timing with EGR
The apparent heat release curve in Figure 5.40 shows the presence of two peaks
for the two injection times. As expected with delaying the main injection, the second
peak is delayed. It is also seen that there is a considerable amount of diffusion burn.
0
2
4
6
8
10
12
14
Baseline, 16, -3
20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
BSE
C (
MJ/
kWh
)
DME, Propane (% energy substitution)
87
Figure 5.40: Heat release rate (HRR) at 20% DME, 20% propane, 16 deg BTDC pilot
injection and varying main injection timing with EGR
The default case is the one with pilot injection at 16 deg BTDC and main injection 3 deg ATDC
From Figure 5.41, it is observed that the pressure rise is delayed for the cases
with energy substitution. Split injection appears to reduce the peak cylinder pressure as
compared to the case with single injection. The two peaks corresponding to the heat
releases are not observed as distinctly with the pressure rise to the peak looking smooth
and uniform.
-10
0
10
20
30
40
50
-60 -40 -20 0 20 40 60
AH
RR
, J/d
eg
Crank Angle, deg BTDC
Baseline
20D20P 16Pilot -2Main
20D20P 16Pilot -5Main
20D20P Default
88
Figure 5.41: Pressure rise rate (PRR) at 20% DME, 20% propane, 16 deg BTDC pilot
injection and varying main injection timing with EGR
5.4.2 Engine Emissions
This section will look at the effects of varying injection timing on the engine‘s
emissions mainly total hydrocarbons (THC), total nitrogen oxides (NOx) and carbon
dioxide (CO2). From both Figures 5.42 and 5.43, it can be seen the trends for varying
main injection are a bit erratic. The overall value of THC emissions is however greater
than for the case without split injection. This would be due to the introduction of EGR
which is absent for the last case. The same goes for NOx emissions which are lower than
the case without EGR and split injection.
0
10
20
30
40
50
60
70
-60 -40 -20 0 20 40 60
Pre
ssu
re, b
ar
Crank Angle
Baseline
20D20P 16Pilot -2Main
20D20P 16Pilot -5Main
20D20P Default
89
Figure 5.42: Total Hydrocarbon emissions (THC) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR
Figure 5.43: Total Nitrogen Oxide emissions (NOx) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR
0
200
400
600
800
1000
1200
1400
1600
1800
Baseline, 16, -3
20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
Tota
l Hyd
roca
rbo
ns
(pp
m)
DME, Propane (% energy substitution)
0
50
100
150
200
250
300
Baseline, 16, -3
20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
Tota
l NO
x (p
pm
)
DME, Propane (% energy substitution)
90
Figure 5.44 shows a slight decrease in CO2 emissions with delaying main
injection. The reverse trend is observed in Figure 5.45 where CO increases with delaying
main injection. This indicates that there is a decrease in the proportion of the gases in the
cylinder getting combusted completely leading to a decrease in CO2 and increase in CO
emissions.
Figure 5.44: Total Carbon dioxide emissions (CO2) at 20% DME, 20% Propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR
0
1
2
3
4
5
6
7
8
9
Baseline, 16, -3 20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
Tota
l CO
2 (%
)
DME, Propane (% energy substitution)
91
Figure 5.45: Total Carbon dioxide emissions (CO) at 20% DME, 20% propane, 16 deg
BTDC pilot injection and varying main injection timing with EGR
Through chapters 4 and 5, the experiments carried out for DME and propane
fumigation in the engine have described and the results discussed. It is now appropriate to
summarize the findings of the preliminary experiments, the subsequent optimality
analysis and then the second set of experiments carried out. This will be done in Chapter
6.
0
500
1000
1500
2000
2500
3000
3500
4000
Baseline, 16, -3
20 DME, 20 Prop, 16, -2
20 DME, 20 Prop, 16, -3
20 DME, 20 Prop, 16, -5
20 DME, 20 Prop, 7
Tota
l CO
(p
pm
)
DME, Propane (% energy substitution)
Chapter 6
Summary and Conclusions
6.1 Summary
Before stating the conclusions derived from the experimental data, the motivation
and objectives of this study will be restated. The motivation for this research was to study
strategies that could be used to improve the brake thermal efficiency while reducing
emissions from compression ignition engines. This work is intended to support the
development of 55% thermal efficiency engines. Additional objectives were to minimize
the heat release rate and the pressure rise rate to prevent damage to the cylinders. The
following strategies were employed to this end:
1. Fumigating dimethyl ether and propane along with the intake air to modify the
cetane number of the fuel and gain better control over the combustion process.
2. Introduce exhaust gas recirculation along with DME and propane fumigation to
reduce flame temperature and oxygen concentration and thereby reduce NOx
emissions.
3. Use split pilot and main diesel injections to observe effects on heat release,
efficiency and emissions.
93
6.2 Observations and Conclusions
Preliminary experiments carried out were described in Chapter 4 and a regression
analysis was carried to determine patterns in the data and obtain optimal points for the
response factors. It was then attempted to verify these findings in the next set of
experiments in Chapter 5. The findings for each response factor are listed below.
1. Brake Thermal Efficiency (BTE) is at its maximum value for high DME and
propane energy substitution. This was observed during both the preliminary and
main set of experiments. Maximum efficiency of 49.91% was observed during the
second set of experiments at 20% DME and 30% Propane substitution.
Introduction of EGR tends to reduce BTE as it results in lower heat release rates.
2. Brake Specific Energy Consumption (BSEC), Brake Specific Fuel
Consumption (BSFC) and Brake Specific Diesel Consumption (BSDC) are at
their minimum values for high DME and propane substitutions. All the above
listed response factors were close to their observed minimum values at 30% each
DME and propane substitution.
3. The Apparent Heat Release Rate (HRR) was found to be minimum at low
DME and high propane substitution values. This is due to the high autoignition
temperature of propane which delays ignition and the subsequent heat release.
The preliminary experiments and the optimization analysis found HRR to be
minimum at 10% DME and 40% propane substitution, while the second set had
the minimum value at 0% DME and 40% propane substitution. Just as with the
other factors listed, EGR tends to decrease the average HRR value.
94
4. The Average Pressure Rise Rate (PRR) was found to be minimum at 30%
DME and 20% propane during the second set of experiments. This was contrary
to the preliminary set where PRR was minimum at 20% DME and 0% propane.
But, on the whole it was observed that both the pressure rise rate and the peak
cylinder pressure were maximum at high DME and propane substitution values
EGR introduction tended to decrease the pressure rise as well as the peak cylinder
pressure.
5. Total Hydrocarbon Emissions (THC) tended to increase with increased DME
and propane substitution. The increase was more substantial with propane than
with DME owing to propane‘s 3 carbon alkane structure and higher autoignition
temperature. THC emissions are low at low DME and propane substitution
values. At these values, THC emissions are further lowered with EGR
introduction. This is not the case however with high substitution values. The
minimum ppm value for THC emissions was observed at 10% DME and 0%
propane substitution.
6. Nitrogen Oxide Emissions (NOx) were observed to decrease with increasing
DME and propane. The ppm values were further reduced with EGR introduction.
The minimum NOx emissions value was obtained at 10% DME and 40% propane
substitution. This incidentally is the point in the preliminary set of experiments
where the heat release rate was minimum and which had low heat releases in the
main set as well. As stated in previous studies, the conversion from NO to NO2
increases with increased propane substitution.
95
Figure 6.1 gives a visual representation of the distribution of the optimal data
points across the energy substitution range considered for DME and propane.
Figure 6.1: Scatter plot of data points at which optimal values of response variables
occur
6.3 Suggestions for Future Work
1. One of the main hindrances with running higher substitution proportions in the
engine was due to concerns over the capability of the engine to withstand the high
pressures at those conditions. If for experimental purposes, an engine could
reinforced to handle peak cylinder pressures of around 90 bar, it would be
extremely interesting to see the effects on brake thermal efficiency and emissions
at higher substitution percentages.
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30 35
Pro
pan
e (%
)
DME (%)
Min HRR (0,40)
Max BTE (20,30)
Min NOx (10,40)
Min THC (10,0)
Min BSEC (30,30)
Min PRR (30,20)
96
2. The injection time during the course of these experiments was maintained at a
constant main injection of 7 deg BTDC for the first two sets while the last set with
split injection was not extensive. The effects of varying injection timing on the
performance of the engine could be observed by perhaps making a sweep across a
crank angle of around 10 deg.
3. The percentage of the exhaust gas recirculated into the engine was maintained at
around 25% for the experiments conducted. Varying the %EGR and observing its
effects on BTE and NOx emissions would make an interesting study.
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102
Appendix A
Matheson Gas Flowmeter Calibration
A.1 Flowmeter 605 Calibration Chart:
Figure A.1 gives the flowmeter calibration chart for the 605 flowmeter tube for
propane at 0 psig. The readings are calibrated for reading the glass ball in the tube. It
could also have been calibrated for the steel ball in which case the equation would have
been different. The value obtained from the equation then has to be corrected for a flow
of 50 psig.
Figure A.1: Calibration for Flowmeter tube 605 at 0 psig for Propane
y = 0.000x2 + 0.081x + 0.041R² = 0.999
0.0000
5.0000
10.0000
15.0000
20.0000
25.0000
0.0 50.0 100.0 150.0 200.0
Flo
w R
ate
(sl
pm
)
Scale Reading
103
A.2 Flowmeter 603 Calibration Chart:
Figure A.2 gives the flowmeter calibration chart for the 603 flowmeter tube for
propane at 0 psig for the glass ball in the tube.
Figure A.2: Calibration for Flowmeter tube 603 at 0 psig for Propane
y = -4E-05x2 + 0.020x - 0.039R² = 0.999
0
0.5
1
1.5
2
2.5
0 50 100 150 200
Flo
w R
ate
(slp
m)
Scale Reading
104
A.3 Flowmeter 604 calibration chart:
Figure A.3 gives the flowmeter calibration chart for the 604 flowmeter tube for
DME at 0 psig for the glass ball in the tube.
Figure A.3: Calibration for Flowmeter tube 604 at 0 psig for DME
y = 1E-05x2 + 0.050x + 0.034R² = 1
0.00
2.00
4.00
6.00
8.00
10.00
0.00 50.00 100.00 150.00 200.00
Flo
w R
ate
Scale Reading
105
A.4 Flowmeter 605 Calibration Chart:
Figure A.4 gives the flowmeter calibration chart for the 605 flowmeter tube for
DME at 0 psig for the glass ball in the tube.
Figure A.4: Calibration for Flowmeter tube 605 at 0 psig for DME
y = 0.000x2 + 0.095x - 0.011R² = 0.999
0
5
10
15
20
25
0 50 100 150 200
Flo
w R
ate
(slp
m)
Scale Reading
106
Appendix B
Interaction Plots
The significance of the interaction between two factors can be determined by the
parallelism of the plot lines or lack of it. The Minitab interaction plots for each of the 6
responses are given below in Figures B.1 – B.6.
7654321
42
40
38
36
34
32
B
Me
an
1
2
3
A
Interaction Plot for BTEData Means
Figure B.1: DME-Propane interaction plot for BTE
7654321
11.0
10.5
10.0
9.5
9.0
8.5
B
Me
an
1
2
3
A
Interaction Plot for BSECData Means
Figure B.2: DME-Propane interaction plot for BTE
107
7654321
290
280
270
260
250
240
230
220
B
Me
an
1
2
3
A
Interaction Plot for BSFCData Means
Figure B.3: DME-Propane interaction plot for BSFC
7654321
220
200
180
160
140
120
100
80
60
B
Me
an
1
2
3
A
Interaction Plot for BS Diesel CData Means
Figure B.4: DME-Propane interaction plot for BSDC
108
7654321
0.575
0.550
0.525
0.500
0.475
0.450
B
Me
an
1
2
3
A
Interaction Plot for PRRData Means
Figure B.5: DME-Propane interaction plot for PRR
7654321
12.5
12.0
11.5
11.0
10.5
10.0
9.5
B
Me
an
1
2
3
A
Interaction Plot for HRRData Means
Figure B.6: DME-Propane interaction plot for PRR
Thus, as seen from the interaction plots, all the graphs except for the one with
Brake Specific Diesel Consumption display non-parallel behavior. This points to the
presence of an interaction term in the regression analysis which has been included.
109
Appendix C
Regression Analysis – Minitab Output
1. Brake Thermal Efficiency:
The regression equation is
BTE = 45.1 - 1.17 DME - 0.204 Propane + 0.0103
DME*Propane + 0.0318 DME^2
Predictor Coef SE Coef T P
Constant 45.060 1.747 25.80 0.000
DME -1.1718 0.1796 -6.53 0.000
Propane -0.20354 0.05419 -3.76 0.002
DME*Propane 0.010272 0.002508 4.10 0.001
DME^2 0.031805 0.004345 7.32 0.000
S = 0.938519 R-Sq = 91.5% R-Sq(adj) = 89.4%
Analysis of Variance
Source DF SS MS F P
Regression 4 152.655 38.164 43.33 0.000
Residual Error 16 14.093 0.881
Total 20 166.748
Source DF Seq SS
DME 1 90.667
Propane 1 0.008
DME*Propane 1 14.773
DME^2 1 47.207
Unusual Observations
Obs DME BTE Fit SE Fit Residual St Resid
8 20.0 32.685 34.346 0.469 -1.662 -2.04R
19 30.0 38.867 40.623 0.390 -1.757 -2.06R
R denotes an observation with a large standardized
residual.
110
Table C.1: Residuals and Fits table for Brake Thermal Efficiency
DME Propane BTE
(Actual)
Residuals Fits
0 0 35.93 -9.17 45.1
10 0 37.31 0.73 36.58
10 5 35.44 -0.64 36.075
10 10 34.96 -0.61 35.57
10 15 34.41 -0.65 35.065
10 20 35.11 0.55 34.56
10 25 34.62 0.56 34.055
10 30 33.22 -0.33 33.55
20 0 32.68 -1.74 34.42
20 5 35.38 0.95 34.43
20 10 34.84 0.40 34.44
20 15 35.84 1.39 34.45
20 20 34.24 -0.22 34.46
20 25 33.98 -0.49 34.47
20 30 33.66 -0.82 34.48
30 0 39.10 0.48 38.62
30 5 38.76 -0.38 39.145
30 10 39.87 0.20 39.67
30 15 39.85 -0.35 40.195
30 20 38.87 -1.85 40.72
30 25 41.95 0.71 41.245
30 30 42.31 0.54 41.77
Table C.1 gives the actual and fitted values along with the residuals from the
regression analysis for BTE.
111
2. Brake Specific Energy Consumption:
The regression equation is
BSEC = 7.65 + 0.308 DME + 0.0537 Propane - 0.00260
DME*Propane - 0.00837 DME^2
Predictor Coef SE Coef T P
Constant 7.6518 0.4856 15.76 0.000
DME 0.30776 0.04992 6.16 0.000
Propane 0.05367 0.01506 3.56 0.003
DME*Propane -0.0025972 0.0006974 -3.72 0.002
DME^2 -0.008366 0.001208 -6.93 0.000
S = 0.260925 R-Sq = 90.4% R-Sq(adj) = 88.0%
Analysis of Variance
Source DF SS MS F P
Regression 4 10.2827 2.5707 37.76 0.000
Residual Error 16 1.0893 0.0681
Total 20 11.3720
Source DF Seq SS
DME 1 6.0660
Propane 1 0.0063
DME*Propane 1 0.9444
DME^2 1 3.2660
Unusual Observations
Obs DME BSEC Fit SE Fit Residual St
Resid
8 20.0 11.0185 10.4608 0.1305 0.5577 2.47R
R denotes an observation with a large standardized
residual.
112
Table C.2: Residuals and Fits table for Brake Specific Energy Consumption
DME Propane BSEC (Actual) Residuals Fits
0 0 10.0200 2.33 7.69
10 0 9.6600 -0.27 9.933
10 5 10.1636 0.09 10.0715
10 10 10.3173 0.11 10.21
10 15 10.5103 0.16 10.3485
10 20 10.2644 -0.22 10.487
10 25 10.4032 -0.22 10.6255
10 30 10.8400 0.08 10.764
20 0 11.0185 0.52 10.502
20 5 10.1776 -0.33 10.5105
20 10 10.3375 -0.18 10.519
20 15 10.0549 -0.47 10.5275
20 20 10.5211 -0.01 10.536
20 25 10.5991 0.05 10.5445
20 30 10.6984 0.15 10.553
30 0 9.2177 -0.18 9.397
30 5 9.2906 0.02 9.2755
30 10 9.0345 -0.12 9.154
30 15 9.0420 0.01 9.0325
30 20 9.2655 0.35 8.911
30 25 8.5818 -0.21 8.7895
30 30 8.5113 -0.16 8.668
Table C.2 gives the actual and fitted values along with the residuals from the
regression analysis for BSEC.
113
3. Brake Specific Fuel Consumption:
The regression equation is
BSFC = 173 + 9.28 DME + 1.13 Propane - 0.0631 DME*Propane
- 0.222 DME^2
Predictor CoefSECoef T P
Constant 172.52 11.92 14.47 0.000
DME 9.278 1.226 7.57 0.000
Propane 1.1287 0.3699 3.05 0.008
DME*Propane -0.06312 0.01712 -3.69 0.002
DME^2 -0.22176 0.02965 -7.48 0.000
S = 6.40610 R-Sq = 83.4% R-Sq(adj) = 79.2%
Analysis of Variance
Source DF SS MS F P
Regression 4 3297.62 824.41 20.09 0.000
Residual Error 16 656.61 41.04
Total 20 3954.23
Source DF Seq SS
DME 1 407.21
Propane 1 37.58
DME*Propane 1 557.85
DME^2 1 2294.98
Unusual Observations
Obs DME BSFC Fit SE Fit Residual St Resid
8 20.0 284.02 269.38 3.20 14.64 2.64R
R denotes an observation with a large standardized
residual.
114
Table C.3: Residuals and Fits table for Brake Specific Fuel Consumption
DME Propane BSFC (Actual) Residuals Fits
0 0 233.590 60.59 173
10 0 237.520 -6.08 243.6
10 5 247.861 1.77 246.095
10 10 251.130 2.54 248.59
10 15 255.919 4.83 251.085
10 20 249.415 -4.16 253.58
10 25 251.698 -4.38 256.075
10 30 260.572 2.00 258.57
20 0 284.022 14.22 269.8
20 5 261.873 -7.27 269.14
20 10 264.611 -3.87 268.48
20 15 256.682 -11.14 267.82
20 20 267.164 0.00 267.16
20 25 268.144 1.64 266.5
20 30 269.099 3.26 265.84
30 0 248.546 -3.05 251.6
30 5 247.594 -0.19 247.785
30 10 241.658 -2.31 243.97
30 15 240.606 0.45 240.155
30 20 246.194 9.85 236.34
30 25 227.381 -5.14 232.525
30 30 226.633 -2.08 228.71
Table C.3 gives the actual and fitted values along with the residuals from the
regression analysis for BSFC.
115
4. Brake Specific Diesel Consumption:
The regression equation is
BS Diesel C = 213 + 1.05 DME - 2.34 Propane - 0.107
DME^2
Predictor CoefSECoef T P
Constant 212.834 8.934 23.82 0.000
DME 1.0514 0.9950 1.06 0.305
Propane -2.3421 0.1161 -20.18 0.000
DME^2 -0.10664 0.02462 -4.33 0.000
S = 5.31859 R-Sq = 98.2% R-Sq(adj) = 97.9%
Analysis of Variance
Source DF SS MS F P
Regression 3 26511.9 8837.3 312.41 0.000
Residual Error 17 480.9 28.3
Total 20 26992.8
Source DF Seq SS
DME 1 14462.0
Propane 1 11519.2
DME^2 1 530.7
Unusual Observations
BS
ObsDME Diesel C Fit SE Fit Residual St Resid
1 10.0 200.82 212.68 2.66 -11.86 -2.58R
8 20.0 203.44 191.21 2.66 12.23 2.65R
R denotes an observation with a large standardized
residual.
116
Table C.4: Residuals and Fits table for Brake Specific Diesel Consumption
DME Propane BSDC (Actual) Residuals Fits
0 0 233.590 20.59 213
10 0 200.820 -11.98 212.8
10 5 202.191 1.09 201.1
10 10 191.366 1.97 189.4
10 15 180.273 2.57 177.7
10 20 166.565 0.57 166
10 25 154.596 0.30 154.3
10 30 147.064 4.46 142.6
20 0 203.437 12.24 191.2
20 5 175.163 -4.34 179.5
20 10 165.121 -2.68 167.8
20 15 148.325 -7.77 156.1
20 20 144.913 0.51 144.4
20 25 132.688 -0.01 132.7
20 30 122.892 1.89 121
30 0 148.691 0.49 148.2
30 5 142.774 6.27 136.5
30 10 123.490 -1.31 124.8
30 15 113.678 0.58 113.1
30 20 102.823 1.42 101.4
30 25 87.697 -2.00 89.7
30 30 73.757 -4.24 78
Table C.4 gives the actual and fitted values along with the residuals from the
regression analysis for BSDC.
117
5. Heat Release Rate:
The regression equation is
HRR = 9.97 - 0.0510 DME + 0.0271 Propane + 0.00308
DME*Propane + 0.00159 DME^2
- 0.00156 Propane^2
Predictor Coef SE Coef T P
Constant 9.9681 0.3274 30.45 0.000
DME -0.05099 0.03318 -1.54 0.145
Propane 0.02707 0.01650 1.64 0.122
DME*Propane 0.0030778 0.0004635 6.64 0.000
DME^2 0.0015943 0.0008029 1.99 0.066
Propane^2 -0.0015620 0.0004370 -3.57 0.003
S = 0.173440 R-Sq = 95.8% R-Sq(adj) = 94.4%
Analysis of Variance
Source DF SS MS F P
Regression 5 10.3565 2.0713 68.86 0.000
Residual Error 15 0.4512 0.0301
Total 20 10.8077
Source DF Seq SS
DME 1 4.8651
Propane 1 3.6624
DME*Propane 1 1.3262
DME^2 1 0.1186
Propane^2 1 0.3843
Unusual Observations
Obs DME HRR Fit SE Fit Residual St Resid
5 10.0 10.4954 10.1497 0.0792 0.3457 2.24R
15 30.0 10.1919 9.8733 0.1239 0.3186 2.62R
R denotes an observation with a large standardized
residual.
118
Table C.5: Residuals and Fits table for Average Heat Release Rate
DME Propane HRR (Actual) Residuals Fits
0 0 10.1019 0.13 9.97
10 0 9.4948 -0.12 9.619
10 5 9.8197 -0.05 9.8695
10 10 10.0765 0.03 10.042
10 15 10.2347 0.10 10.1365
10 20 10.4954 0.34 10.153
10 25 10.0073 -0.08 10.0915
10 30 9.7149 -0.24 9.952
20 0 9.6369 0.05 9.586
20 5 9.8863 -0.10 9.9905
20 10 10.3167 0.00 10.317
20 15 10.5778 0.01 10.5655
20 20 10.7996 0.06 10.736
20 25 10.6960 -0.13 10.8285
20 30 10.9406 0.10 10.843
30 0 10.1919 0.32 9.871
30 5 10.2429 -0.19 10.4295
30 10 10.7662 -0.14 10.91
30 15 11.1494 -0.16 11.3125
30 20 11.7175 0.08 11.637
30 25 11.9030 0.02 11.8835
30 30 12.1254 0.07 12.052
Table C.5 gives the actual and fitted values along with the residuals from the
regression analysis for HRR.
119
6. Pressure Rise Rate:
The regression equation is
PRR = 0.484 - 0.00231 DME + 0.00184 Propane + 0.000114
DME*Propane + 0.000070 DME^2 - 0.000071 Propane^2
Predictor Coef SE Coef T P
Constant 0.48377 0.01513 31.97 0.000
DME -0.002314 0.001533 -1.51 0.152
Propane 0.0018394 0.0007624 2.41 0.029
DME*Propane 0.00011449 0.00002142 5.34 0.000
DME^2 0.00007013 0.00003710 1.89 0.078
Propane^2 -0.00007087 0.00002020 -3.51 0.003
S = 0.00801481 R-Sq = 94.9% R-Sq(adj) = 93.3%
Analysis of Variance
Source DF SS MS F P
Regression 5 0.0181081 0.0036216 56.38 0.000
Residual Error 15 0.0009636 0.0000642
Total 20 0.0190717
Source DF Seq SS
DME 1 0.0068272
Propane 1 0.0084254
DME*Propane 1 0.0018350
DME^2 1 0.0002295
Propane^2 1 0.0007910
Unusual Observations
Obs DME PRR Fit SE Fit Residual St Resid
5 10.0 0.51458 0.49898 0.00366 0.01560 2.19R
7 10.0 0.48201 0.49339 0.00572 -0.01138 -2.03R
15 30.0 0.49241 0.47746 0.00572 0.01495 2.66R
R denotes an observation with a large standardized
residual.
120
Table C.6: Residuals and Fits table for Average Pressure Rise Rate
DME Propane PRR (Actual) Residuals Fits
0 0 0.4969 0.01 0.484
10 0 0.462387 -0.01 0.4679
10 5 0.479316 0.00 0.481025
10 10 0.492402 0.00 0.4906
10 15 0.500828 0.00 0.496625
10 20 0.514576 0.02 0.4991
10 25 0.494100 0.00 0.498025
10 30 0.482013 -0.01 0.4934
20 0 0.466785 0.00 0.4658
20 5 0.479300 -0.01 0.484625
20 10 0.499589 0.00 0.4999
20 15 0.512064 0.00 0.511625
20 20 0.521742 0.00 0.5198
20 25 0.518617 -0.01 0.524425
20 30 0.533013 0.01 0.5255
30 0 0.492409 0.01 0.4777
30 5 0.493625 -0.01 0.502225
30 10 0.515961 -0.01 0.5232
30 15 0.534582 -0.01 0.540625
30 20 0.558589 0.00 0.5545
30 25 0.565824 0.00 0.564825
30 30 0.573793 0.00 0.5716
Table C.6 gives the actual and fitted values along with the residuals from the
regression analysis for PRR.