clean and efficient diesel engine: final report doe/ de .../67531/metadc839814/m2/1/high_res... ·...

Clean and Efficient Diesel Engine: Final Report Report Issue Date: April 2011

Clean and Efficient Diesel Engine: Final Report DOE/ DE-

FC26-08NT06560

This is the final report for the Clean and Efficient Diesel Engine project, DOE Award

DE-FC26-08NT06560. It summarizes the activities of the two phases of the project.

This material is based upon work supported by the Department of Energy National

Energy Technology Center under Award Number(s) DE-FG26-08NT06560.

This report was prepared as an account of work sponsored by an agency of the United

States Government. Neither the United States Government nor any agency thereof, nor

any of their employees, makes any warranty, express or implied, or assumes any legal

liability or responsibility for the accuracy, completeness, or usefulness of any

information, apparatus, product, or process disclosed, or represents that its use would not

infringe privately owned rights. Reference herein to any specific commercial product,

process, or service by trade name, trademark, manufacturer, or otherwise does not

necessarily constitute or imply its endorsement, recommendation, or favoring by the

United States Government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States Government

or any agency thereof.


Table of Contents Phase 1 ................................................................................................................................ 4

Task 1: Design Study for Fuel-Efficient System Configuration ......................................... 4

Task 2: Combustion System Studies ................................................................................ 12

GEVO Single Cylinder Experiments; Miller Cycle Tests for Improved Fuel Economy

....................................................................................................................................... 13

GEVO SCE Experiments with EGR; Effect of Injection Pressure and Multiple

Injections on an EGR-Equipped Engine ....................................................................... 15

GEVO SCE Experiments with EGR; Effect of Piston Bowl Geometry on an EGR-

Equipped Engine ........................................................................................................... 16

Summary ....................................................................................................................... 19

Task 3 ................................................................................................................................ 20

Phase 2 .............................................................................................................................. 53

Task 5 ................................................................................................................................ 53

Subtask 5A: Low Particulate Combustion Tests .......................................................... 53

Subtask 5B :Aggressive Valve Timing Studies. ........................................................... 53

Task 6: Advanced Air Handling. ...................................................................................... 53

Table of Figures Figure 1- Contour plot of normalized BSNOx with start of fuel injection and intake valve

closing for nominally sized turbine. Note that BSNOx values are normalized by

BSNOx at an IVC and SOI of 0. ................................................................................. 7

Figure 2- Contour plot of normalized BSFC with start of fuel injection and intake valve

closing for nominally sized turbine. The red squares superimposed on this plot are

of the normalized BSNOx equal to 1 from Figure 1. Note that BSFC values are

normalized by BSFC at an IVC and SOI of 0 from the nominal turbine case ............ 7

Figure 3- Contour plot of normalized BSNOx with start of fuel injection and intake valve

closing for the turbine with 20% reduced nozzle area. Note that BSNOx values are

normalized by BSNOx at an IVC and SOI of 0 from the nominal turbine case. ........ 8

Figure 4- Contour plot of normalized BSFC with start of fuel injection and intake valve

closing for the turbine with 20% reduced nozzle area. The red squares

superimposed on this plot are of the normalized BSNOx equal to 1 from Figure 3.

Note that BSFC values ................................................................................................ 8

Figure 5- Fuel injection timing trends of NOx and SFC for turbo-compounding engine

architecture ................................................................................................................ 10

Figure 6- Fuel injection timing trends of NOx and SFC for varying levels of EGR with

turbo-compounding. Results shown for EGR fractions of 10, 20, and 30% with an

intake valve closure 40° before the baseline. Baseline results are also shown for

comparison ................................................................................................................ 12

Figure 7: View of GE Global Research Single Cylinder Engine Lab .............................. 13

Figure 8- Comparison of engine performance for nominal and nominal-50 degree IVC

cams at (top) notch 8 and (bottom) notch 4. Triangles indicate NOx/SFC

improvement and asterisks indicate Smoke/SFC changes. ....................................... 15

Figure 9: Performance data for a notch 8 injection timing swing with 1800bar rail

pressure, notch 8 representative boost, and 25% EGR. ............................................ 17


Figure 10: Performance data for a notch 4 injection timing swing with 1800bar rail

pressure, notch 4 representative boost, and 25% EGR. ............................................ 19


Phase 1

Task 1: Design Study for Fuel-Efficient System Configuration

The objective of this task was to perform a system design study of locomotive engine

configurations leading to a 5% improvement in fuel efficiency. Modeling studies were

conducted in GT-Power to perform this task. GT-Power is an engine simulation tool that

facilitates modeling of engine components and their system level interactions. It provides

the capability to evaluate a variety of engine technologies such as exhaust gas circulation

(EGR), variable valve timing, and advanced turbo charging. The setup of GT-Power

includes a flexible format that allows the effects of variations in available technologies

(i.e., varying EGR fractions or fuel injection timing) to be systematically evaluated.

Therefore, development can be driven by the simultaneous evaluation of several

technology configurations.

A variety of engine technologies were investigated within GT-Power to determine their

potential to reduce locomotive fuel consumption and emissions. These included high-

pressure fuel injection, variable fuel injection and intake valve timings, advanced

turbocharger configurations, and variable EGR fractions.

A base model was previously developed in GT-Power to simulate locomotive size

engines. The model consists of a 12 cylinder, turbocharged compression ignition engine.

This engine model is designed with the capability to operate at high horsepower (ranging

up to 5000 HP) and medium speeds (in the range of 1000 rpm). The model is equipped

with a turbocharger (turbine and compressor) and intercooler, consistent with locomotive

applications. The turbocharger increases the air to the engine, resulting in an increase in

specific power output. An intercooler, downstream of the compressor, is then necessary

to reduce the manifold air temperature, which can lead to lower NOx emissions and fuel

consumption.

Combustion within the cylinders is modeled with a direct injection diesel model. This

tool divides the injected fuel mass into zones and predicts burn rates and NOx emissions.

The parameters of the implemented model have been tuned to agree with available

experimental data.

The model is set up to operate with user defined fuel injection profiles (including

injection pressure) and intake valve profiles. This flexibility allows for evaluation of

injection profiles from those of a unit pump system or those consistent with a common

rail system. The intake valve closure timing can also be varied from a baseline case (a

conventional intake valve closure that maximizes engine volumetric efficiency) to earlier

closure events, affecting the air handling (i.e., Miller Cycle). These variations will

indicate the potential entitlement of each of these in a locomotive application.


The model also allows for high-pressure EGR, with exhaust flow pumped from upstream

of the turbine to a location downstream of the compressor. An exhaust gas recirculation

pump and heat exchanger are in place to re-direct cooled exhaust gas back to the intake

manifold. EGR is a technology that can potentially reduce NOx emissions and overall

fuel consumption when incorporated with other engine technologies.

The current model is designed to be flexible and is equipped to rapidly investigate

different engine technology options. This format allows for evaluation of a relatively

large array of technology variations, providing significant data to guide single cylinder

experimental studies in subsequent tasks.

Intake valve timing profiles are an input to the model. Therefore, the user can define

intake valve profiles to vary the valve closure timing. Intake valve lift profiles have been

developed with intake valve closure events ranging from the baseline case to 120° earlier

than the baseline. These variations in valve closure will change the air handling of the

engine, potentially leading to a decrease in emissions and fuel consumption when

combined with other engine technologies such as fuel injection timing. The model

provides the flexibility to easily vary the start of fuel injection by changing the crank

angle to initiate the start of injection. Hence, a full parametric space of fuel injection

timing and valve lift closure timings can be evaluated.

The turbocharger is modeled as a simple turbine and simple compressor within GT-

Power. These tools simplify the turbine and compressor, as each element is not limited to

restrictions from their respective maps. The intention of these elements is for early

development purposes, so as not to restrict the turbocharger capabilities. Therefore,

various air handling techniques can be evaluated without being restricted to available

turbine and compressors.

The current model has been calibrated to experimental data providing confidence in the

model. The calibration was done with a fixed intake valve profile and a high-pressure

fuel injection profile consistent with a common rail system. GT-Power simulations of the

locomotive model were then conducted while varying intake valve lift profiles, fuel

injection timing, and turbine size. This parametric study consisted of the following range

of input parameters:

1. Variable intake valve lift profiles: Intake valve closure events from the baseline

to 70° earlier, in 10° increments.

2. Varying fuel injection timing: Fuel injection timing ranging from 2° after the

baseline to 8° before the baseline, in 2° increments.

3. Turbine size: Turbine size was varied by decreasing the nozzle area from its

nominal value by 10 and 20% (acting to effectively increase the turbine power

output).

Contour plots of brake specific NOx (BSNOx) and brake specific fuel consumption

(BSFC) over the entire operating space for the nominally sized turbine are shown in

Figure 1 and Figure 2, respectively. Note that each parameter is normalized by its

respective value at the nominal intake valve closing and nominal start of injection.

Figure 1 shows that, for a fixed start of injection, BSNOx can be reduced by earlier intake


valve closures. However, this decrease in BSNOx comes at the expense of increased fuel

consumption (see Figure 2). A second tradeoff between BSNOx and BSFC is seen with

injection timing. As the start of injection is advanced, BSFC is reduced while BSNOx

increases.

Figure 2 also has a constant BSNOx curve superimposed onto the contour plot. The red

line in Figure 2 correspond to the BSNOx = 1 contour from Figure 1. This superimposed

contour line shows that a 2% fuel benefit can be realized for the nominal turbine case by

injecting fuel 4° before the baseline and closing the intake valve approximately 50°

earlier than the nominal case.

GT-Power simulations were also performed with a turbine nozzle area reduced by 20%.

Contour plots of BSNOx and BSFC for the range of fuel injection timings and intake

valve closing for this turbine sizing are shown in Figure 3 and Figure 4, respectively.

Note that the BSNOx is normalized by the BSNOx value at nominal start of injection,

valve closing and turbine size. Similarly, BSFC is normalized by the BSFC at the

corresponding operating condition for the nominally sized turbine. Also, note that the red

line in Figure 4 correspond to the BSNOx = 1 contour from Figure 3.

The general trends of BSFC and BSNOx are similar for the smaller turbine as the nominal

turbine. However, it can be seen that the BSFC benefit of early injections is maintained

at the earliest intake valve closing (in contrast to the nominally sized turbine where BSFC

begins to drop off). Therefore, the emissions neutral point for the smaller turbine

corresponds to the earliest intake valve closing of –70° and a start of injection of -5°

(relative to nominal timing). At this operating point, there is an apparent 3.5% fuel

benefit from the baseline case with the nominal turbine (i.e., SOI = 0° and IVC = 0°) and

neutral emissions.


0.75 0.

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Figure 1- Contour plot of normalized BSNOx with start of fuel injection and intake valve closing for

nominally sized turbine. Note that BSNOx values are normalized by BSNOx at an IVC and SOI of 0.

0.96

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Figure 2- Contour plot of normalized BSFC with start of fuel injection and intake valve closing for

nominally sized turbine. The red squares superimposed on this plot are of the normalized BSNOx equal to

1 from Figure 1. Note that BSFC values are normalized by BSFC at an IVC and SOI of 0 from the nominal

turbine case


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Figure 3- Contour plot of normalized BSNOx with start of fuel injection and intake valve closing for the

turbine with 20% reduced nozzle area. Note that BSNOx values are normalized by BSNOx at an IVC and

SOI of 0 from the nominal turbine case.

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Figure 4- Contour plot of normalized BSFC with start of fuel injection and intake valve closing for the

turbine with 20% reduced nozzle area. The red squares superimposed on this plot are of the normalized

BSNOx equal to 1 from Figure 3. Note that BSFC values

Next, an evaluation on the fuel consumption benefits of turbo-compounding was

conducted. As with the Miller cycle studies, the analyses were conducted in order to


assess the fuel consumption benefits while holding the emissions to currently regulated

NOx levels. The GT-Power model that was exercised included an auxiliary power turbine

downstream of the turbocharger. This turbine was modeled as a simple orifice of varying

diameter and fixed efficiency. The impact of intake valve closure timing on turbo-

compounding was also investigated by including earlier intake valve closure timings.

Figure 5 displays NOx and SFC trends with varying fuel injection timing for six engine

architectures. The curves are shown with NOx and SFC values normalized with respect

to a baseline cam configuration and fuel injection timing. In each instance, the turbine

orifice diameters were sized to best minimize NOx and SFC. The six NOx/SFC curves

displayed in the figure include:

1. Baseline intake valve closure with the nominal turbocharger turbine diameter without

turbo-compounding.

2. Intake valve closure forty degrees before the baseline.

3. Intake valve closure one hundred degrees before the baseline.

4. Baseline intake valve closure timing with added power turbine (turbo-compounding).

5. Intake valve closure forty degrees before the baseline with added power turbine

(turbo-compounding).

6. Intake valve closure one hundred degrees before the baseline with added power

turbine (turbo-compounding).


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SFC Delta [%]

NOx Delta [%]

Baseline Valve Closure

Early Closure: 40° before Baseline

Early Closure: 100° before Baseline

Baseline Valve Closure: Turbocompounding

Early Closure (40° before Baseline): Turbocompounding

Early Closure (100° before Baseline): Turbocompounding

Figure 5- Fuel injection timing trends of NOx and SFC for turbo-compounding engine architecture

A full range of power turbine and turbocharger turbine sizes were investigated in this

study. Results are only presented for the cases yielding the lowest SFC for each

configuration. It was already shown that SFC, at a constant NOx level, could be reduced

with an early intake valve closure when combined with a timing advance. This trend is

displayed again in Figure 5. Relative to the baseline, the early intake valve closure

(without turbo-compounding) shows a 3.5% reduction in SFC.

A further reduction in SFC, at a constant NOx level, is seen when a power turbine is

added downstream of the turbocharger turbine (i.e., turbo-compounding). Figure 5

displays this trend for three intake valve closure timings (the baseline, 40°, and 100°

before the baseline). In these instances, SFC is reduced by approximately 8% from the

baseline NOx level. These fuel consumption benefits were shown to occur due to the

combination of work extracted from the power turbine combined with a lower BSNOx

level allowing fuel injection timing to be advanced. It needs to be noted that the lower

BSNOx is due both to the increased residual gas content (internal EGR) as well as the

greater power output produced. The baseline intake valve closure (with turbo-

compounding) shows a greater fuel benefit than the early intake valve closure (with

turbo-compounding). The results displayed in Figure 5 show the potential benefit for

turbo-compounding to provide a fuel consumption benefit. However, the relative benefit

Nominal

Point


of turbo-compounding appears to diminish with earlier intake valve closure timings. At

the earliest intake valve closure timing, turbocompounding does not appear to reduce

SFC (compare yellow triangle solid curve with yellow triangle dashed curve). This

diminishing turbo-compounding benefit is due to two reasons. First, with the more

aggressive valve timing, turbine back pressures are already at high levels in order to

deliver sufficient airflow to the engine. The additional backpressure due to the

turbocompounding unit creates an additional pumping loss. Secondly, the more

aggressive valve timing enables a greater effective expansion to take place in the

cylinder. As such, the turbocompounding unit sees less energy available in the exhaust

stream to recover.

The study was further broadened to include an engine architecture for which turbo-

compounding is utilized as a means of circulating EGR. This architecture provides a

means to reduce emissions levels while also decreasing fuel consumption. In this

architecture, the power turbine downstream of the turbocharger turbine served to

backpressure the engine in order to circulate the EGR flow as well as extract energy from

the exhaust stream.

Figure 6 displays NOx and SFC trends with varying fuel injection timing for a single

intake valve closure timing (forty degrees before the baseline) as EGR fraction is

increased. Turbo-compounding has been implemented as a means to backpressure the

engine and, hence, circulate the EGR flow. Three distinct EGR fractions are displayed in

the figure (10, 20, and 30%) to provide an indication of the trends of NOx and SFC with

EGR flow. In each instance, the sizing of the turbine diameters (turbocharger and power

turbine) has been optimized to best minimize SFC and NOx. The NOx and SFC values in

this figure are normalized with respect to the baseline configuration and fuel injection

timing. Note that the baseline configuration is with a baseline valve timing and does not

have EGR or turbo-compounding.

The results in Figure 6 indicate that turbo-compounding can be an efficient method to

circulate EGR flow for this intake valve closure timing. The results show the potential to

significantly reduce NOx emissions while maintaining or improving fuel consumption.

For instance, the results show a 60% reduction in NOx with an SFC benefit of 3 to 4%

could be achieved with EGR fractions of 10 to 20%. A further reduction in NOx, up to

70% from the baseline, can be achieved at SFC parity with EGR levels from 20 to 30%.

These results indicate that, depending on emissions regulations, a system can be

optimized to meet NOx regulations while maintaining or improving fuel consumption

levels by means of waste heat recovery.


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SFC Delta [%]

NOx Delta [%]

Baseline Valve Closure Timing

10% EGR: Valve closure 40° before baseline



Figure 6- Fuel injection timing trends of NOx and SFC for varying levels of EGR with turbo-compounding.

Results shown for EGR fractions of 10, 20, and 30% with an intake valve closure 40° before the baseline.

Baseline results are also shown for comparison

Task 2: Combustion System Studies

The EVO single-cylinder engine (SCE) has been used to explore engine configurations

more efficiently than a production multi-cylinder engine. The power assembly of the

SCE (i.e., combustion chamber, piston, connecting rod, cylinder liner strong back and

head) can be the same hardware as the current production engine, the GE Evolution, or

this hardware can be modified to investigate new technologies. For the data reported

here, a common rail fuel system was utilized, providing independent control of fuel

pressure, injection timing, and engine load. This technology is complimentary to the

miller-cycle testing, which requires some independent control of injection parameters to

control particulate matter (PM). Turbocharging is simulated through independent control

of intake and exhaust pressures. GT-power models and experimental data were used to

provide approximate air handling conditions for the SCE and post-processing calculations

were used to correct for minor pumping loop discrepancies.

The GRC Single cylinder facility is also equipped with a high-pressure cooled EGR

setup. The EGR is controlled via an electrically driven centrifugal pump. The EGR is

cooled with a standard shell and tube laboratory heat exchanger. The pump is a

necessary means of recirculating EGR as various points in the locomotive duty cycle

have the exhaust manifold pressure lower than the intake manifold pressure. While a

Nominal

Point


backpressure valve can raise the exhaust pressure to a level required to circulate EGR, it

also leads to an unfavorable gas exchange process and fuel economy penalty. As such, all

of the combustion experiments were conducted using a pump. All specific fuel

consumption numbers presented account for the power required to drive the pump.

GRC Single Cylinder Engine Lab

Figure 7: View of GE Global Research Single Cylinder Engine Lab

The SCE provided an avenue for evaluating a large amount of hardware including a high-

pressure common rail fuel system, miller cams with early intake valve closure, multiple

piston bowls and an EGR system. All of this hardware was tested with the goal of

reducing emissions while maintaining or improving fuel economy. Performance tests

focused on a high-load condition (notch 8) due to its substantial contribution to the

overall engine performance and also a moderate-load condition (notch 4) to provide a

more rounded survey of overall engine performance.

GEVO Single Cylinder Experiments; Miller Cycle Tests for Improved Fuel Economy

The first study performed under this contract was an investigation of miller cycle for

improved performance. In the so-called Miller cycle, the effective compression ratio is

reduced while expansion ratio is maintained. The benefit of this is that peak gas

temperatures are reduced, thereby lowering NOx emissions. If the NOx reduction is

significant, injection timing can be advanced and fuel economy can be gained as well.

Miller cycle was enabled in our experimental setup by using modified cams with early

intake valve closure.

Three cam configurations were compared in this study. The first configuration utilizes

the baseline cam with the nominal timing of valve closure and air-handling conditions

representative of a current production turbocharger. The second configuration utilizes a

miller cam where the intake valve closes 50 degrees earlier than nominal and air-handling

conditions representative of the current production turbocharger. The third configuration

utilizes a less aggressive miller cam with valve closure 40 degrees earlier than nominal

with air-handling conditions representative of a high-efficiency turbocharger. The data in

Figure 8 compares performance of the first two configurations.

Tests were performed at notches 4 and 8 for the baseline cam with nominal valve closing

and with a miller cam where the intake valve closed 50 degrees earlier than nominal. For

notch 8, the tests with the nominal cam were performed with low injection pressure and

tests with the -50deg cam were performed with both low and high injection pressure. The


data show that, for fixed rail pressure, fuel consumption improves by 5%, but smoke

increases by ~0.04 g/hp-hr. Increasing to high injection pressure was used to combat the

smoke penalty, resulting in no smoke increase and ~4.5% SFC improvement over the

nominal cam. Thus, for this high-load condition, the combination of increased injection

pressure and early intake valve closure has resulted in a significant fuel economy benefit

with no increase in emissions.

For notch 4, results are shown with low injection pressure for the nominal cam and

moderate and high with the –50 deg cam. These data show that the early valve closure

has a detrimental effect on the NOx/SFC performance at this moderate load condition.

The reason for this is that the air-fuel ratio at notch 4 is relatively low. These lower air-

fuel ratios result in poorer air utilization and slower combustion for the –50 cam.

Furthermore, even with an increase in rail pressure, the smoke is still ~0.02 to 0.04 g/hp-

hr higher for the –50deg cam. Thus, the performance benefit at notch 8 is somewhat

counterbalanced by some penalty at notch 4. Further investigations with rail pressure,

multiple injections, and turbocharger matching may help reduce the penalties at lower

loads while maintaining or improving the benefits at higher loads.

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Nominal-50deg, High Pressure

Figure 8- Comparison of engine performance for nominal and nominal-50 degree IVC cams at (top) notch

8 and (bottom) notch 4. Triangles indicate NOx/SFC improvement and asterisks indicate Smoke/SFC

changes.

For a locomotive engine targeting lower fuel consumption at NOx parity, miller cycle

using early intake valve closure is a potential pathway, but this may come at the expense

of particulate. Sample data were compared here and additional data are available in an

earlier report. It was shown that particulate can be reduced through higher rail pressure

and it is expected that further PM reductions are possible through the use of multiple

injections and careful specification of the fuel injector nozzle.

GEVO SCE Experiments with EGR; Effect of Injection Pressure and Multiple Injections

on an EGR-Equipped Engine

This section details a significant amount of combustion data that was collected using

exhaust gas recirculation (EGR) as a NOx reduction mechanism. The previous

combustion tests reported above sought to minimize specific fuel consumption at

constant NOx emissions levels. In other words, Miller cycle technology was being

evaluated to improve fuel economy without reducing NOx emissions. In contrast, EGR is

being assessed as a technology to drive down NOx emissions. While it is possible to

derive a fuel economy improvement from the use of EGR, this work aims at

understanding the benefits of using EGR as a fundamental mechanism to reduce NOx in a

large bore medium speed diesel engine. An unfortunate consequence of EGR is the

increase in particulate emissions. Therefore, tests conducted for this portion of the study

sought to understand the sensitivity of particulate emissions to injection pressure,

multiple injections and higher-pressure turbo-charging. The results of this study are

provided in a previous report, but some summary conclusions are listed below.


The study performed to investigate injection pressure and multiple injections shows that

in an EGR-equipped engine, particulate can be reduced using increased boost pressure,

increased fuel injection pressure and multiple injections. Furthermore, it was shown that

fuel economy can improve or degrade as injection pressure is increased, depending on

how high the injection pressure is. The data shown here suggest that increasing boost

pressure results in a fuel economy penalty, which is true for this case, but it is likely that

there are some engine operating conditions where increased boost will improve engine

performance. This is true for cases where the air-fuel ratio is very low to begin with.

Finally, it was shown that multiple injections can be beneficial for emissions while

having an insignificant effect on fuel economy.

GEVO SCE Experiments with EGR; Effect of Piston Bowl Geometry on an EGR-

Equipped Engine

In this portion of the study, combustion tests were performed with 4 different piston

crowns in the presence of EGR. Geometric information of the crowns is listed in Table 1.

Bowl Shape CR

A Mexican hat 17

B Double-Rim 17

C Double-Rim 15

D Double-Rim 17

Table 1- Piston crown configurations and corresponding compression ratios

Three of the bowls investigated the effects of contouring at the bowl rim by incorporating

double-rim bowl designs. One such bowl was also used to understand the performance

tradeoffs of using a lower compression ratio piston. It is well known that reducing the

compression ratio and keeping all other parameters fixed will reduce NOx but increase

SFC. There is less information about what the effect will be on PM and also whether the

overall NOx/SFC performance tradeoff will be better or worse with the lower

compression ratio (i.e., if compression ratio is reduced and injection timing is advanced

until the NOx is unchanged, will the fuel economy be better or worse). Performance of

the 4 bowls is compared using a common rail fuel system with rail pressure of 1800bar.


-60

-40

-20

0

20

40

60

80

-4 -2 0 2 4 6

SFC Change [%]

NOx Change [%]

Bow l A

Bow l B

Bow l C

Bow l D

-60

-40

-20

0

20

40

60

80

-50 0 50 100 150 200 250 300

Soot Change [%]

NOx Change [%]

Bow l A

Bow l B

Bow l C

Bow l D

Figure 9: Performance data for a notch 8 injection timing swing with 1800bar rail pressure, notch 8

representative boost, and 25% EGR.

Notch 8 performance data is shown in Figure 9. These data illustrate that Bowl C

exhibits a slightly inferior NOx/SFC tradeoff and that Bowl A shows the lowest overall

emissions. Furthermore, bowl B exhibits significantly higher soot emissions than the


other bowls. It is possible that the emissions from the other bowls may be improved

through further bowl/nozzle matching studies.

Figure 10 shows similar performance data for notch 4 operation. Bowl C clearly shows

worse NOx/SFC performance, resulting in almost 2% SFC penalty for NOx parity with

respect to bowl. However, in this case, the NOx/Soot characteristics of all 4 bowls are

about the same. It should again be noted that all bowls were tested with the same nozzle

and that further improvements may be recognized if the nozzles were optimized

individually for each bowl. However, these results suggest that the Mexican hat shape

with the higher compression ratio results in the best overall emissions and SFC

performance.

-40

-20

0

20

40

60

80

100

-4 -3 -2 -1 0 1 2 3

SFC Change [%]

NOx Change [%]

Bowl A

Bowl B

Bowl C

Bowl D


-40

-20

0

20

40

60

80

100

-80 -60 -40 -20 0 20 40 60

Soot Change [%]

NOx Change [%]

Bowl A

Bowl B

Bowl C

Bowl D

Figure 10: Performance data for a notch 4 injection timing swing with 1800bar rail pressure, notch 4

representative boost, and 25% EGR.

Summary

The work described in this section illustrates the impact of different hardware on engine

performance for locomotive applications. It was demonstrated that miller cycle can

reduce NOx at constant injection timing. This NOx reduction can be exploited either as a

direct emissions reduction strategy or as an enabler for injection timing advance for

improved fuel economy.

A high-pressure common rail system was shown to provide significant reductions in

particulate matter with modest fuel economy penalties for an EGR-equipped engine. The

prototype fuel system also enables multiple injections and it was shown that multiple

injections can further reduce the particulate with little or no penalty in NOx and fuel

consumption. Similar agile fuel injection systems will likely become a key tool for

meeting future particulate emission regulations.

Finally, engine performance was compared for 4 different piston crown geometries. It

was found that the simple Mexican hat design resulted in the best overall emissions and

fuel consumption. It was also found that the double-rim design resulted in worse engine

performance, however, it was noted that performance may be improved by matching the

injector nozzle to the crown.


Task 3

Subtask 3a: PM formation and characteristics Summary

The following is a summary of the key observations obtained under this task. A more

detailed description of the experiments that were performed is provided as an Appendix,

which includes the doctoral dissertation of Hee Je Seong, who performed much of the

work under this task.

Note that related to this task, three theses were completed in whole or in part with support

from this project:

Prabhakar, Bhaskar, “Effect of Common Rail Pressure on the Relationship Between

BSFC And BSPM at NOx Parity,” MS Thesis, Mechanical Engineering, Penn State

University, 2009.

Yehliu, Kuen, “Impacts of Fuel Formulation and Engine Operating Parameters on the

Nanostructure and Reactivity of Diesel Soot,” PhD Thesis, Energy & Mineral

Engineering, Penn State University, 2010. (three years of funding came from NSF Grant

#CTS-0553339).

Seong, Hee Je, “Impact of Oxygen Enrichment on Soot Properties and Soot Oxidative

Reactivity,” PhD Thesis, Energy and Geo-Environmental Engineering, Penn State

University, 2010.

Results

Fall 2007

The initial experiments performed with the SCE engine considered soot samples from

several operating conditions. Both oxidative reactivity and soot nanostructure were

analyzed for soot samples from the SCE and from the Cummins test engine at GE-GRC

for comparison. Figure 1 shows the variation in oxidative reactivity for the soot samples,

wherein the soot samples from the SCE and Cummins test engine are seen to be much

reactive than the light duty engine soot produced at PSU. All the soot samples from

different engines at GE fuel are very reactive and the SCE 20% EGR soot is more

reactive than SCE 30% EGR soot This raised questions about compatibility of the test

conditions, and experiments were begun at Penn State at higher intake oxygen

concentration to simulate the supercharged operation of the SCE.


0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40

We

igh

t lo

ss (

%)

Elapsed time (min)

DDC2.5L_1800rpm

Cummins_1050rpm

Cummins_1750rpm

SCE_20% EGR

SCE_30% EGR

Figure 1. Comparison of oxidative reactivity of soot samples from the SCE, the Cummins

test engine and the PSU 2.5L turbodiesel engine operating on a test fuel at GE GRC.

Thermophoretic samples were obtained from the SCE to compare the nanostructure of the

soot samples from 20% and 20% EGR conditions. Figure 2 shows HRTEM micrographs

comparison the nanostructure of the soots. Initial soot nanostructure is similar to that of

samples acquired from of DDC 2.5L turbodiesel engine at Penn State. Lamella length

(grapheme layers) in the 20% EGR soot appears longer than that in 30% EGR soot.

Raman spectrometry analyses of these soots show that the 30% EGR soot has greater

disorder, consistent with the HRTEM images: ID/IG(20%)=0.977, ID/IG(30%)=1.170.


(a) (b)

Figure 2. HRTEM images of SCE soot samples, 1050 rpm (a) 20% EGR soot and (b)

30% EGR.

Thus, these initial measurements of some of the characteristics of the SCE soot provided

a motivation for more extensive examination of the soots from the SCE and to better

understand the impacts of having higher levels of O2 in the cylinder on soot

characteristics.

August 2009

In these experiments, the SCE was operated over a range of conditions to provide data on

the range of PM morphologies emitted by the SCE and the impact of varying engine

operating conditions. Soot samples were collected from the GE SCE in 2009 to provide

further characterization of locomotive engine soot. As shown in Table 1, EGR rate,

injection timing and rail pressure were varied at the same engine speed and engine torque

to generate these soot samples.

Table 1. SCE Engine conditions under which diesel particulates were collected in 2009

1

post injection was applied

The analytical tools used in this study are the same as those used for characterization of

soot samples from the PSU 2.5L engine. Measurements of soot oxidative reactivity were

carried out in a thermogravimetric analyzer at 500oC, and x-ray photoelectron

spectroscopy (XPS) was used to get compositional information of soot. Figure 3 shows

that the SCE soot reactivity varies in the order of 20%, 0%, 25.7%, 24.8% and 10.5%

EGR. For the 0% EGR soot and the 10% EGR soot from the same injection timing and

rail pressure, the former is shown to be significantly more reactive than the latter with

increasing EGR rate. This trend is also observed for the 20% EGR soot and the 25.7%

EGR soot from the same injection timing and rail pressure. Although it is difficult to

evaluate the effect of injection timing and rail pressure on soot oxidative reactivity at

different EGR ratio, it appears that soot from the advanced injection timing with higher

rail pressure is more reactive than from the retarded injection timing with lower rail

pressure in this study.


Figure 3 TGA results at 500

oC for soot samples from GE SCE

Also, the 25.7% EGR soot is shown to be more reactive than the 24.8% EGR soot.

Although it is hard to determine the effect of 0.9% EGR difference, it seems that soot

from the post injection is less reactive. In order to better understand the TGA result,

surface oxygen content and other impurities of soot were investigated using XPS as

shown in Table 2. XPS result indicates that surface oxygen content increases with

increasing EGR ratio, and small amounts of Si are observed for the 0% EGR soot and

20% EGR soot. Consequently, the reason the 0% EGR soot and the 20% EGR soot being

more reactive than the other samples seems to be related to the catalytic effect by Si.

Although Si is the only inorganic component observed in these analyses, there is a

possibility that other inorganic components are also present in these soot samples because

XPS can detect elements down to only 15 nm depth in a material. The surface oxygen

content is also shown to be an important factor influencing soot oxidative reactivity when

no Si is present. Although XPS provides a general indication of factors affecting the

oxidative behaviors of different soot samples, further study is ongoing to get a better

understanding about the effect of soot crystalline structure on soot oxidative reactivity.

Table 2 Elemental analysis of soot samples from GE SCE using XPS

Sample Atomic concentration (%)

O Si

0% EGR soot

10.5% EGR soot

20.0% EGR soot

25.7% EGR soot

24.8% EGR soot

5.65

6.75

8.85

14.44

15.46

0.41

0

0.44

0

0


As indicated in a previous quarterly report, the elemental analysis by XPS showed that

soot samples from 0 and 20% EGR ratios contains Si as well as C and O in them, which

explains why they are more reactive in their soot oxidative reactivities than soot samples

from 10.5, 25.7 and 24.8% EGR ratios, where there are no metallic species present.

Although there might be a significant catalytic effect on these samples obtained from the

SCE by Si and other metals which may not be observed by XPS, it is also important to

investigate the effect of carbon crystalline structure on soot oxidative reactivity. Raman

spectroscopy and X-ray diffraction (XRD) have been popular instruments to examine this

property for various carbonaceous materials. In many studies, crystallite size represented

by crystallite height (Lc) and crystallite width (La) via XRD increases with increasing

degree in the crystalline order. In the case of Raman spectroscopy, many parameters from

first-order Raman spectrum have been investigated to study degree in the crystalline

order. From our extensive investigation, we found that this first-order Raman spectrum is

differently curve-fitted by different research groups and there has been no comparison

made for different curve-fitting methods. To better understand the relationship between

soot crystalline structure and soot oxidative reactivity, we compared many different

curve-fitting methods in order to find the best method to identify a good correlation.

Many carbonaceous materials show two characteristic peaks appearing at ~1360 cm-1

(D

peak) and ~1590 cm-1

(G peak) for first-order Raman spectra. The G peak is a stretching

mode at sp2 sites.

1 The D peak has been proven that it is from the existence of edge sites

and the relative position of the laser spot with respect to the edge.2 Some carbonaceous

materials like polycrystalline graphite show only sharp D and G peaks,3 but many

disordered and amorphous carbons also indicate additional peaks appearing at ~1180

(D4), ~1500 (D3) and ~1620 cm-1

(D2), which are related to sp3 or impurities,

3-5

amorphous carbon6 and disordered carbon,

3,7 respectively.

For this study, four different soot samples and a carbon black sample, which don’t

contain any metallic species, were used in this study in order to exclude their catalytic

effect. One diffusion flame soot (diffusion soot) was obtained from a laminar diffusion

burner with heptane fuel. DDC 30 and DDC 75 soots were collected at 30% and 75%

loads from the engine at Penn State, respectively. SCE soot was sampled from SCE at a

notch-8 condition with 10.5% EGR ratio. The carbon black investigated in this study is

obtained from Alfa Aesar. Among many curve-fitting methods, three, four and five

curve-fitting methods were employed for first-order Raman spectra, where 2 lorentzian

(L) (D1:1360cm-1

and G:1590cm-1

) and 1 gaussian (G) (D3:1500cm-1

), 3L (D1, D3 and

G), 3L (D1, D4:1180cm-1

and G) and 1G (D3), 4G (D1, D3, D4 and G), 4L (D1,

D2:1620cm-1

, D4 and G) and 1G (D3), and 5L (D1, D2, D3, D4 and G) were fitted as in

Figure 4.


1.0

0.8

0.6

0.4

0.2

0.0

Normalized intensity

200018001600140012001000

Raman shift (cm-1)

original spectrum

D1 band (L)

D3 band (G)

G band (L)

(a)1.0

0.8

0.6

0.4

0.2

0.0

200018001600140012001000

D1 band (L)

D3 band (L)

G band (L)

(b)

1.0

0.8

0.6

0.4

0.2

0.0

200018001600140012001000

D4 band (L)

D1 band (L)

G band (L)

D3 band (G)

(c)1.0

0.8

0.6

0.4

0.2

0.0

200018001600140012001000

D4 band (L)

D1 band (L)

G band (L)

D3 band (L)

(d)

1.0

0.8

0.6

0.4

0.2

0.0

200018001600140012001000

D4 band (L)

D1 band (L)

G band (L)

D3 band (G)

D2 band (L)

(e)1.0

0.8

0.6

0.4

0.2

0.0

200018001600140012001000

D4 band (L)

D1 band (L)

G band (L)

D3 band (L)

D2 band (L)

(f)

Figure 4 Curve-fitted shape of SCE soot : (a) 2L (lorentzian) and 1G (gaussian) (2L1G),

(b) 3L, (c) 3L1G, (d) 4L, (e) 4L1G, (f) 5L

The oxidative trends of the 5 samples were compared at 500,550 and 600 oC. Diffusion

flame soot is the most reactive among the samples, and carbon black is the least reactive.

The time to be completely oxidized for SCE soot and DDC 30 soot is almost the same,

but DDC 30 soot is shown to exhibit a greater reactive rate. The oxidative trend in this

study is well represented by the time that the soot is half oxidized as indicated by t50% in

Table 3. The bigger 1/t50% is, the more reactive the soot becomes. Since the difference is

not significant at 600 oC, 1/t50% at 550

oC was introduced in this study as a parameter

representing the soot oxidative rate.

Table 3 Time to reach 50% oxidation at different temperatures

Operating

temperature

(oC)

1/t50% ( /min )

Diffusion

flame soot SCE soot

DDC 30

soot

DDC 75

soot

Carbon

black

500

550

600

650

7.31e-3

3.72e-2

1.02e-1

-

5.11e-3

2.11e-2

6.61e-2

-

5.94e-3

2.30e-2

7.11e-2

-

4.49e-3

1.92e-2

5.94e-2

-

01

1.93e-3

8.10e-3

2.80e-2

1: 1/∞ because there was no reaction at this temperature

Our results show that D1 full width at half maximum (D1 FWHM) reflects a good

oxidative trend for the 4 and 5 curve-fitting methods, and ID1/IG shows an excellent trend

for the 4 curve-fitting method. Accordingly, 3L1G and 4L fittings from the four curve-

fitting method seem to provide good Raman parameters in this study. Although D1


FWHM for the five curve-fitting methods is a good parameter, the same good trend can

be obtained from that for the four curve-fitting methods. Since the trends in both

intensity and area of D2 band from 3L1G fitting are also shown to be consistent with that

in the reactivity, 3L1G is found to be the best fitting among the examined fitting

methods. However, it is difficult to conclude that all the factors like: the portion of

amorphous carbon which is related to D2 band, the density of edge sites and the

distribution of crystallite sizes (which are represented by ID1/IG or D1/G and D1 FWHM,

respectively,) should be on the same order of effectiveness for determining soot oxidative

reactivity as we observed for D1/G, ID1/IG, D1 FWHM, and intensity and area in D2 band

from 3L1G fitting (Figure 5). In spite of this difficulty in selecting between the different

methods of interpreting Raman parameters, we can conclude that the relation between

soot oxidative reactivity and crystalline structure is interpreted more reliably and

consistently when all these parameters are analyzed. In this comparison, 3L1G fitting

provides a reasonable explanation about the effect of crystalline structure on soot

oxidative reactivity. Soot oxidative reactivity is closely related to the abundance of edge

sites and amorphous carbon. Correspondingly, more reactive soot shows a wider

distribution of crystallite sizes with an increase in the disorder.

1.6

1.4

1.2

1.0

0.8

D1/G

40x10-3302010

1/t50% ( /min )

(a)

Diffusion soot SCE soot DDC 30 soot DDC 75 soot Carbon black

4.0

3.5

3.0

2.5

2.0

1.5

1.0

I D1/IG

40x10-3302010

1/t50% ( /min )

(b)


200

160

120

80

D1 FWHM (cm-1)

40x10-3302010

1/t50% ( /min )

(c)



Figure 5. Comparison of Raman parameters from 3L1G fitting:

(a) height ratio of D1 to G, (b) area ratio of D1 to G, (c) D1 FWHM

During the 2009 particle sampling effort with the SCE, particle were also acquired via

thermophoretic sampling for transmissions electron microscopy. Figure 6 shows low

resolution images of particulate morphology, with two images from the 20% EGR case.

There are no clear trends in particulate morphology. This is not unexpected give that the

scope of the engine setting changes was fairly modest. Speed and load were fixed, while

EGR level and injection pressure varied.

(a)

(b)

(c)

(d)

Figure 6. TEM micrographs of diesel soot from the SCE at conditions as listed in

Table 1. (a) 0% EGR, (b) 10.5% EGR, (c) 20% EGR – image #1, and (d)

20% EGR – image #2.


While there is no significant visible variation in morphology, and Figures 6c and 6d show

that there can be substantial variation in particle morphology at the same engine

operation condition, we have previously observed substantial variations in the oxidative

behavior of diesel soot and the mechanisms of oxidation when comparing 20% EGR and

0% EGR soots.1 Thus, it may be worthwhile to compare SCE or locomotive engine soots

from a broader range of operating conditions, such as from all 8 notch settings. From the

2009 SCE sampling, few high resolution TEM (HRTEM) images were produced. Figure

7 shows some of these images, from 0% and 10.5% EGR settings. Figure 7a shows signs

of long range order and the class shell-core nanostructure of mature diesel soot. Figure

7b lacks the fine resolution to draw any definitive comparisons with regard to

nanostructural characteristics, however, a qualitative (speculative) analysis of this image

shows a less ordered nanostructure than the 0% EGR case in Figure 7a. When

considering the differences in oxidative reactivity shown in Figure 3, it would be of great

interest to compare the nanostructures of the “as received” soots from 0% and 20% EGR,

since these showed the widest difference in reactivity. Also, it would be valuable to track

the changes in soot nanostructure at different extents of oxidation.

(a)

(b)

Figure 6. HRTEM micrographs of diesel soot from the SCE at conditions as listed in

Table 1. (a) 0% EGR, and (b) 10.5% EGR.

Conclusions

• Significant differences were observed in the oxidative reactivity for soots sampled

from the SCE at different test conditions. This significant variation in reactivity

warrants further study to assess what aspects of the soot structure or surface

chemistry are responsible for these variations in reactivity.

1 Al-Qurashi, K. and A.L. Boehman. Impact of Exhaust Gas Recirculation (EGR) on the Oxidative

Reactivity of Diesel Engine Soot. Combustion and Flame, 155, 675-695 (2008).


• Preliminary nanostructural analyses suggest differences in the degree of order in

the soot nanostructure is playing a role in variation in reactivity, but this needs

further measurements to confirm.

• There remain questions over whether oxidation behavior of the soot samples is

influenced by inorganic species present on the soot surface. Reactivity appears to

correlate with Si content for some of the soot samples. Again, this aspect of these

measurements warrants further study.

References

1. Ferrari. A. C.; Robertson, J. Interpretation of raman spectra of disordered and

amorphous carbon. Phys. Rev. B 2000, 61, 14095–14107

2. Casiraghi, C.; Hartschuh, A.; Qian, H.; Piscanec, S.; Georgi, C.; Fasoli, A.;

Novoselov, K. S.; Basko, D. M.; Ferrari, A. C. Raman spectroscopy of graphene

edges. Nano Letters 2009, 9, 1433–1441

3. Cuesta, A.; Dhamelincourt, P.; Laureyns, J.; Martínez-alonso, A. Tascón, J. M. D.

Raman microprobe studies on carbon materials. Carbon 1994, 32, 1523–1532

4. Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman

microspectroscopy of soot and related carbonaceous materials: spectral analysis

and structural information. Carbon 2005, 43, 1731–1742

5. Schwan, J.; Ulrich, S.: Batori, V.; Ehrhardt, H.; Silva, S. R. P. Raman

spectroscopy on amorphous carbon films, J. Appl. Phys. 1996, 80, 440–447

6. Nemanich, R. J.; Glass, J. T.; Lucovsky, G.; Shroder, R. E. Raman scattering

characterization of carbon bonding in diamond and diamondlike thin films. J.

Vac. Sci. Tech. A 1988, 1783–1787

7. Gruber, T.; Zerda, T. W.; Gerspacher, M. Raman studies of heat-treated carbon

blacks. Carbon 1994, 32, 1377–1382


Subtask 3b: Examine EGR cooler fouling process and mitigation strategies

Summary

To meet Tier 4 emissions requirements for locomotive engines, use of exhaust gas

recirculation may be necessary

Experimental Design

This task involves understanding the mechanisms of EGR cooler fouling, focusing first

on the design of an experimental facility for studying the deposit formation process.

To perform the investigation of diesel EGR cooler fouling, surrogate heat exchanger

tubes have been designed which can be easily removed from the assembly and replaced

depending on the type of experiment. The tubes are made of 316L stainless steel and are

¼’ in diameter and a total of 6 tubes are inserted into a shell and tube type heat

exchanger. A 3-d model of the entire setup is completed. Components have to be

purchased and the setup has to be completed.

Figure 7. Overview of EGR cooling setup with closed loop cooling system


a)

b) c)

Figure 8. Initial Design of EGR Cooler Test Rig

a: Arrangement of tubes within the shell in isometric view.

b: A detailed view of tubes inside the shell in a wire-frame view.

c: Solid view of the shell and tube heat exchanger.


Figure 9. Final design drawings of flanges for EGR cooler experiment

(a)


(b)

Figure 10. Final design drawings of the EGR Cooler, (a)View of EGR cooler without

shell and manifold and, (b) View of cooler with shell and manifold.

Once the EGR cooler design was finalized, components were ordered and given to the

machine shop for machining the model EGR cooler with surrogate tubes. A few final

modifications were made to the design during construction. The machined heat

exchanger with the components unassembled (Figure 11) and assembled (Figure 12) are

shown below.

Figure 11. Model EGR cooler: 2 flanges (with weld fittings and removable Swagelok

fittings), 2 headers, and 1 shell with 2 NPT fittings for coolant inlet and outlet. Tubes are

not shown.


Figure 12. Assembled view of EGR cooler; O-rings (4 in number) create the seal between

the coolant and the exhaust gas on either side

After the construction phase was completed, baseline testing was conducted on the

existing EGR coolers (2 in number) on the Ford 6.4 L engine to get information on

typical temperatures (coolant in, coolant out, exhaust gas in, exhaust gas out from cooler

1, exhaust gas out from cooler 2) and EGR ratios at various engine speeds and loads.

Results from these tests will helped to identify a few standard operating conditions for the

model EGR cooler for fouling studies.

Then the model EGR cooler was installed along with the differential pressure gauge and

thermocouples. To complete the installation of the EGR cooler on the test engine a

closed-loop coolant circulator and a wedge-flow meter (capable of operating at high

temperatures) to measure the flow rate of exhaust gas through the EGR cooler were

installed on the test engine.

A baseline test was performed on the 6.4L Ford Engine to map out exhaust temperatures

upstream and downstream of the stock, twin-EGR coolers. Additionally, fuel

consumption and EGR % at the particular conditions was calculated. Results from these

tests can be seen in Table 1.


Table 4. Effect of engine operating conditions on exhaust temperature, cooler-out

temperatures, fuel consumption, and EGR percentage

Speed Load Power Fuel Cooler 1 Cooler 2 Coolant CO2 EGR %

Cons Inlet T Outlet T Outlet T Temp in out

rpm ft-lb kW g/min deg C deg C deg C deg C % % %

The tests below are performed at varying speeds and loads

750 32 3.40 NA 133.6 91.8 38.6 88.6 1.15 3.89 29.56

1000 23.5 3.33 36 144.7 94 48.5 89.4 1.07 3.23 33.13

1300 30 5.53 48 160.2 98.2 50.4 90.5 1.07 3.4 31.47

1600 46.2 10.48 83 196.5 110.2 51.6 91 1.4 4.52 30.97

1900 65.1 17.54 116 232.1 121.8 51.8 91.6 1.42 4.9 28.98

2300 85 27.73 191.1 294.2 148.5 46.7 93.5 1.45 5.01 28.94

2600 100.3 36.98 266.2 328.9 166.3 48.5 95 1.5 5.29 28.36

The tests below are performed at constant speed = 1500 rpm

1500 92.2 19.61 102.3 252.8 108.4 37.3 90.8 1.43 5.1 28.04

1500 150.2 31.95 137.7 261.2 99.8 38.2 91.2 0.96 5.42 17.71

1500 200 42.55 172.2 281.3 96 36.8 91.4 0.8 5.83 13.72

1500 250 53.18 201.1 312.3 98.5 33.2 92 0.85 6.53 13.02

1500 300 63.82 238.8 340.1 100.4 31.2 92.7 0.95 7.13 13.32

1500 350 74.46 272.8 360.2 105.5 27.6 93.4 0.87 7.39 11.77

The tests were conducted in 2 phases. The first phase varied both speed and load, as

represented by the pink color in the table. In the second phase, the engine was operated at

medium speed (1500 rpm) while the load was increased in steps of 50 lb-ft – denoted in

light green. From both the tests, it was observed that the gas outlet temperature from the

2nd

EGR cooler was lower than the coolant temperature. This result needs to be

reinvestigated. Corrections, if any, will be provided in the upcoming reports. These

results are helpful to select operating point(s) to perform EGR cooler experiments. EGR

percentage was calculated as below.


0

50

100

150

200

250

300

28

29

30

31

32

33

34

0 5 10 15 20 25 30 35 40

Fuel Consumption, g/minEGR Ratio

Fuel Consumption, g/min

EGR, %

Power, kW

Figure 13: Variation of EGR ratio and fuel consumption with power at varying speeds

and loads

From Figure 13, it is apparent that EGR percentage reduces with an increase in engine

power output. However, higher power also means greater fuel consumption. For extended

EGR cooler runs, an optimum value has to be selected so that fuel consumption is not

excessive.

We need to pick an

operating condition in

this regime. Points here

represent medium EGR

and moderate fuel

consumption


0

5

10

15

20

25

30

100

150

200

250

300

50 100 150 200 250 300 350 400

CO2, intake, %

CO2, exhaust, %

EGR, %


Various %


Load, ft-lb

Speed = 1500 rpm

Figure 14. Variation of fuel consumption and EGR under conditions of fixed speed and

varying load

It can be observed from Figure 14 that when the speed was held constant, an increase in

load increased the CO2 content at the exhaust while the intake CO2 levels were reduced.

This indicates a decrease of EGR with load. These results have been obtained at the

baseline conditions – no modifications (such as rail pressure, injection timing, etc.) were

performed on the engine ECU.

Initial characterization of EGR cooler deposits

Soot deposits were collected from the EGR coolers of 2 engines - a 2.5L DDC VM

Motori engine and the 6.4L Ford power-stroke engine. These samples were subjected to a

non-isothermal test in TGA. The test involves pre-treating the soot sample under nitrogen

gas to drive away the volatiles and then subjecting it to oxidation in air, as the

temperature is ramped up to 800 °C. Results from these tests are shown in Figures 15 and

16.


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Temperature, deg C

Time, min

2.5L DDC Engine

Figure 15: Non-isothermal TGA analysis of EGR cooler deposit from the 2.5 L DDC-VM

Motori engine

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Figure 16: Non-isothermal TGA analysis of EGR cooler deposit from the 6.4L Ford

power-stroke engine

It can be observed that the EGR cooler soots contained significant amount of volatile

organic fraction (VOF). Typically, diesel engine exhaust soots have VOF in the range of


10-15%. However, EGR cooler soot deposits appeared to have VOF in the range of 35-

40% indicating a significant amount of condensed hydrocarbons. More investigation is

necessary to be confirm these initial results.

Preliminary investigation of the microstructure

EGR cooler soot deposits were investigated under a scanning electron microscope to

study the microstructure. Images from both the engines are shown in Figures 17 and 18.

Figure 17. Microstructure of carbon deposit from 2.5L engine EGR cooler

Figure 18. Microstructure of carbon deposit from 6.4L Ford engine EGR cooler

It can be inferred that the EGR cooler deposits from different engines have different

appearances, which could be either due to the conditions under which the engines were


operated, the time-temperature history of the EGR cooler temperature and the fuel used.

No direct conclusions can be drawn yet. Once we generate our own EGR cooler soot

samples under controlled and known conditions, analyses of the mechanism of EGR

cooler deposits will be possible.

Following the completion of the rig, several 5-6 hour tests were performed to check for

gas and coolant leaks - especially with the use of graphitic ferrules for gas-side sealing,

performance of the flow-meter and coolant circulator (coolant at 85°C), and the

sensitivity of the valve for flow adjustments, while the thermal effectiveness of the EGR

cooler was monitored.

Figure 19. EGR cooler test rig showing 1) EGR Cooler 2) High and low side pressure

taps 3) Coolant inlet and outlet

1

2

2

3

3


Figure 20. Test rig instrumented with 1) High temperature wedge-flow-meter with

pressure and temperature taps for corrections in gas density 2) Cooler downstream high

temperature valve.

Actual pressure of the exhaust gas entering the EGR cooler was monitored and was

observed to be in a range of 16-28 psia (ECU controlled), depending upon the engine

load. No data collection has been made so far, as the testing outline is still being

formulated. Additionally, the Ford 6.4L engine is currently being run on B40 biodiesel.

Experiments with ultra-low sulfur diesel (ULSD) will be performed once the current tests

conclude.

Current status research on EGR cooler fouling

Initial experiments were performed to monitor cooler effectiveness and pressure change

at two conditions of engine load, viz. 50 lb-ft and 100 lb-ft, while running the engine for

a total of 10 hours at 1500 rpm. The coolant temperature was maintained steady at 85° C

and the exhaust gas flow rate through the EGR cooler was held constant at 180 slpm. The

coolant flow rate was maintained sufficiently high to minimize coolant side temperature

gain.

After the completion of the initial tests, the tubes were removed from the EGR cooler and

evaluated for any deposits adhering to the inner surface. From a visual inspection, it

appeared as if the tubes were clean, but there was a significant amount of deposits glued

to the tube’s inner surface which appeared as a fine and undistinguishable layer. The

1

2


deposit layer was not affected by shaking the tube vigorously, which implied that they

were held by strong contact forces. A thin and long stainless steel tube was used to

remove the deposits by scraping them, ensuring that the underlying metal was not

scratched. Sufficient mass of sample (order of grams) was generated for particle

characterization purposes in just less than 10 hours of engine operation. Any remaining

particles were cleaned by running DCM through the tubes and thoroughly cleaning them

for the next experiment.

Condition 1: 1500 rpm, 50 lb-ft

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Effectiveness

Effectiveness

Time, min

Stop of Run#1

Stop of Run#2

Stop of Run#3

Stop of Run#4

Figure 21. Change in EGR cooler effectiveness with time at 1500 rpm, 50 lb-ft and

180lpm flow through the EGR cooler


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250

0 100 200 300 400 500 600 700

EGR inlet temp, deg C EGR outlet temp, deg C

EGR inlet temperature, deg C

EGR outlet te

mperature, deg C

Time, min

Steady EGR inlet temperature

Increasing EGR outlet temperature

Figure 22. EGR Inlet and outlet temperature as a function of time

From Figure 21, it can be observed that EGR effectiveness dropped from about 67%

when clean to about 46% in about 10-11 hours of operation. This is a significant loss

considering the model EGR cooler contains just 6 tubes to cool the exhaust gas. The

exhaust gas temperature at the inlet of the cooler remained a constant (~235°C), while the

gas temperature at the outlet increased from 130°C to 159°C, as observed in Figure 22.

Additionally, the pressure drop across the cooler increased as well as seen in Figure 4.

Interesting to note was that there was a slight improvement in the effectiveness after each

engine shutdown, which is termed as cooler recovery in the literature. Exact reasons for

this behavior are not understood yet. Researchers suspect that some condensation of

water during engine shutdown can have loosened the deposits, leading a blow-off of the

deposit layer during start-up.


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EGR del P, kPa

EGR del P, kPa

Time, min

Figure 23. EGR cooler delta P as a function of time.

Run 2: 1500 rpm, 100 lb-ft

In the second test, the engine load was increased to 100 lb-ft, while holding all other

conditions the same. The engine ECU commands a lower EGR% at higher loads, but the

reduction in flow rate through the EGR cooler was compensated by opening the valve to

allow a higher flow through the model cooler. A significant difference between the first

and the second test was that the effectiveness of the cooler when clean (start of the test)

was only 53% as against 67% in the first case. This is explainable in terms of higher gas

temperature at cooler inlet and a lower capacity of the cooler to cool the exhaust gas

down with just 6 tubes. The effectiveness at the end of the test dropped to as low as 39%.

The exhaust gas outlet temperature increased from 163°C to 189°C. Similar to the first

test, improvements in the effectiveness (cooler recovery) was seen during engine shut

down and start up conditions. All other trends were similar to condition 1.


0.38

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Effectiveness

Effectiveness

Time, min

End of run 1

End of run 2

End of run 3

Figure 24. Change in EGR cooler effectiveness with time at 1500 rpm, 100 lb-ft and

180lpm flow through the EGR cooler

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EGR Inlet Temp, deg C EGR Outlet Temp, deg C

EGR Inlet Temp, deg C

EGR Outlet Temp, deg C

Time, min

Increasing EGR outlet temp

Steady EGR Inlet temperature

Figure 25. EGR Inlet and outlet temperature as a function of time


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EGR del P, kPa

EGR del P, kPA

Time, min

Figure 26. EGR cooler delta P as a function of time.

Pyrolysis GC-MS analysis of samples

The chemical signature of the samples collected from the EGR cooler was analyzed using

a pyrolysis GC coupled to a mass spectrometer. Conventional GC cannot be used until

the samples are extracted using DCM, because of the presence of high molecular weight

compounds in diesel engine soot. Pyrolysis GC has proven to be a useful technique to

provide unique fingerprinting of soot produced from diesel engines. Figures 27 and 28

show the chromatographs of the samples collected after 10-11 hours from the two engine

conditions. As it can be seen, the two different engine conditions produced different soots

with different chemical signature. An attempt was made to identify some of the major

peaks from the chromatographs and the details can be seen in Table 5. The relative

proportions (area ratios) are not calculated yet, and needs more understanding.


0

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Figure 27. Chromatograph of the sample from 1500 rpm, 50 lb-ft engine condition

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Figure 28. Chromatograph of the sample from 1500 rpm, 100 lb-ft engine condition


Table 5. Probable compounds from Py-GC of the two EGR cooler samples

1500 rpm, 50 lb-ft 1500 rpm, 100 lb-ft

benzene benzene

methyl-benzene methyl-benzene

Ethyl-benzene styrene

styrene benzaldehyde

1,2 dimethyl benzene napthalene

benzaldehyde 2 methyl napthalene

methyl phenol tetradecane

napthalene 1,3 dimethyl napthalene

1-methyl napthalene heptadecane

1,3 dimethyl napthalene octadecane

heptadecane eicosane

octadecane

nonadecane

eicosane

Scanning electron microscopy

SEM technique was utilized to determine the microstructure of the sample surface, while

the EDS feature on the SEM was used to detect different elements other than hydrogen

on the surface of the sample. Results are available only for the condition at 50 lb-ft load.

Even though the microstructure images are presented in Figures 29 and 30, detailed

investigation is necessary as we believe that scraping the sample out of the EGR cooler

tubes and pressing the sample (to be held firmly on the sample holder for SEM) could

have changed the actual structure of the sample. In order to eliminate this for future

microscopy studies, the tubes need to be cut open carefully and mounted on the sample

holder, making sure the sample has not been disturbed.


Figure 29. SEM image of EGR cooler soot at 1500 rpm, 50 lb-ft

Figure 30. SEM image of EGR cooler soot at 1500 rpm, 50 lb-ft


Figure 31 shows a spectrum of different peaks from a spot on the sample surface. Some

of the major peaks observable are carbon, nickel, silicon, zinc, sulfur, calcium, and

nickel. The gold peak (Au) is shown due to gold sputtering on the sample to improve the

electrical conductivity. The copper peak is a result of using a copper tape to hold the soot

in place. Sulfur peak is observed even though ultra-low sulfur diesel is used for

experiments. Silicon, zinc, and calcium are typically constituents of a diesel lubricant.

Silicon is used as for foam control, while zinc is used for wear control and oxidation

protection, and calcium is used for protection against rust. Figure 32 shows that sample

also consists of iron, aluminum, and potassium. It is speculated that nickel and aluminum

originated from the engine manifold; however, the origin for potassium is still unclear.

Table 6 shows a distribution of normalized weight percentage of different elements

present in the sample.

Figure 31. Element scan at spot 1 from Figure 10

Figure 32. Elemental scan of the entire sample surface


Table 6. Weight percentage of different elements from sample 1

Another feature of the SEM was explored, where the elemental distribution was observed

over a given area of the sample, and is shown in Figure 33. This feature is helpful to get

an idea of the relative concentration of a given element in a given region. The denser the

distribution, more dots are observed. For example, diesel soot which is mostly carbon has

the greatest distribution, as seen in Figure 33. Zinc, on the other hand is dense only in a

small region, which is also seen in the SEM image (bottom right corner of Figure 33),

which has a bright spot. Sulfur and silicon are distributed evenly over the entire area, but

are less dense than carbon.

Figure 33. Area scan to determine elemental distribution


Conclusions

The current setup of the EGR cooler allows us to collect sufficient deposits within a short

period of time. Several characterization techniques have been applied to determine

physical and chemical properties of these deposits. A test matrix will be developed to

determine the changes to the deposit properties over time. Additional techniques will be

used as and when necessary.

This experimental apparatus represents a valuable tool for study the mechanisms of EGR

cooler fouling and can provide insights into mitigating such deposits in locomotive

applications.


Phase 2

Task 5 Subtask 5A: Low Particulate Combustion Tests

This task focused on the characterization of the impact of swirl on the formation of

particulate during combustion in large bore diesel engines. The cylinder head was

modified to realize higher levels of swirl than obtains in the current GEVO product. The

following observations were made in the course of these tests:

• For a given manifold air pressure, engine speed and load, a reduction in air-fuel

ratio was observed with the addition of swirl. This is attributed to higher port

losses and overall lower volumetric efficiency.

• Increasing the manifold air pressure increased the air fuel ratio back to baseline

levels. Correspondingly, the engine backpressure was increased to simulate actual

backpressure effects of a turbocharger.

• At notch 4, a small but measurable reduction in particulate matter was observed.

However, there was an adverse impact on BSFC.

• At notch 8, an increase in particulate matter was observed. In this case, there

appeared to be very little impact on BSFC.

Additional details of the results of the tests are available in the Phase 2 second quarter

report.

Subtask 5B :Aggressive Valve Timing Studies.

In this task, the effect of modified valve timing on engine performance was investigated.

Tests were performed at Notches 4 and 6 due to operating pressure limitations. The

following results were obtained:

• BSFC advantage was observed at both notches 4 and 6 at NOx parity.

• Particulate matter was the same for notch 6, but increased approximately 15% for

notch 4.

Additional details of the results of the tests are available in the Phase 2 second quarter

report.

Task 6: Advanced Air Handling. In this task, GT-Power modeling studies were performed to further our understanding of

advanced air-handling architectures. Two studies were performed; the first involved a

parametric analysis of fuel consumption tradeoffs with Miller cycle and cylinder

compression ratio variations. Results of this study showed that the efficiency improved

as the cylinder compression ratio was increased at the expense of increased cylinder

pressure and also delineated the efficiency response with Miller cycle.

The second study involved identifying turbocharger layouts that meet system

requirements over a broad operating range for selected intake valve closure timings. The

analysis entailed running the GT-Power model with turbocharger maps at selected


ambient conditions and engine loads. The model was exercised by scaling the

turbocharger maps to meet operational constraints (engine airflow levels and emissions

targets). Final scaling parameters were selected based on combinations that resulted in

minimum fuel consumption. Modeling results with these selected scaling parameters can

now be utilized to identify turbines and compressors to better match the engine

architecture.

Task 6 also included an experimental evaluation of Turbocompound technology. To this

end, a nominal 60 KWe subscale turbocompound system manufactured by Bowman

Power Group, Ltd, UK, was installed in the GRC turbocharger development cell and

evaluated over a range of operating conditions.

Testing was performed at generating speeds of 27,000, 33,000, and 35,000 rpm for inlet

temperatures of 650, 750, and 850F. In general, the Bowman TGS met performance

expectations over the operating ranges evaluated. Overall system efficiency exceeded

80% at design conditions, which is in line with estimates used for the modeling work

reported earlier. Application to the locomotive for power recovery would require

hardening of the components, both mechanical and electrical, to meet the harsh operating

environment found in rail service, as well as integration of the export power with the

locomotive electrical architecture. Cost and packaging are other important factors to be

addressed.

Further details of both the analysis and tests are available in the Phase 2 fourth and fifth

quarter reports.

APPENDIX


IMPACT OF OXYGEN ENRICHMENT ON SOOT PROPERTIES AND SOOT

OXIDATIVE REACTIVITY, Hee Je Seong, PhD Thesis, Energy & Geo-Environmental

Engineering, Penn State University,

2010

clean and efficient diesel engine: final report doe/ de .../67531/metadc839814/m2/1/high_res... ·...

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