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Frankfurt,
9th November 2009
European GT-SUITE Conference 2009Mechanisms of the Mixture Preparation and
Combustion for an Engine Operation with
the Ethanol Blend E85
Thomas Lauer1 , Markus Klein2
1Institute for Internal Combustion Engines and Automotive
Engineering, Vienna University of Technology2GM Powertrain Germany GmbH
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Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Efforts will have to be made in the future to reduce the greenhouse gas CO2.
A fleet emission limit of 120 g/km will be introduced by the European Union
by 2012.
In addition a steadily growing number of vehicles faces limited oil resources.
Therefore low carbon fuels and fuels from biomass with an improved CO2-
balance like ethanol are considered as an important alternative to
conventional fuels for SI engines.
Because of different physical and chemical properties compared to
conventional fuels a detailed analysis of the engine process is necessary.
Introduction
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Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Fuel Characteristics of
RON95 and Ethanol E100 (I)
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Fuel Characteristics of
RON95 and Ethanol E100 (II)
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Correction of the
Lower Heating Value
In a bomb calorimeter the lower heating value at constant volume (U)V,T is
measured. GT-Power expects the lower heating value at constant pressure
(H)p,T. There is a difference between both values if the number of moles
changes during the reaction:
(H)p,T (U)V,T= Rm (nP nR) T
For liquid fuels the lower heating value is reduced by the heat of
vaporization.
2.490.63Deviation [%]29.7042.33(H)p,T+ HOV
28.8641.983(H)p,T
28.9642.063(U)V,T
E85RON 95Chemical Energy [MJ/kg]
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Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Engine Specification GM Z14XEP
125 Nm @ 4,200 rpmMax. Torque
RON95, E85 (85 Vol.-%Ethanol, 15 Vol.-% RON95)
Fuels
66 kW @ 5,600 rpmMax. Power
80.6 mmStroke
73.4 mmBore
1364 cmDisplacement
1.4 L Gasoline Engine
Ecotec Family 0, Generation 2,
Multi Point Fuel Injection
Engine Type
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Numerical Model and Test
Equipment
High-pressure sensors in
the combustion chambers
Low-pressure senors in the
inlet- and exhaust-manifold
Test EquipmentNumerical Model
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Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Gasdynamics @ Full Load
Comparison with Measurements
n = 2,800 rpm
n = 4,400 rpm
n = 6,000 rpm
Measurement location
pInlet
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Full Load Performance w/ RON95
Comparison with Measurements
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Expected Impact of E85-Fuel on
the Engine Operation
Two effects must be considered when operating the engine with E85:
Because of the lower stoichiometric air/fuel-ratio of E85 its vapour
displaces more air during intake. Therefore the volumetric efficiency
should be DECREASED.
The higher heat of vaporization of E85 combined with the lower air/fuel-
ratio causes an intense cooling of the mixture during intake. Therefore
the density of the mixture and the volumetric efficiency should be
INCREASED.
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Full Load Performance w/ E85
Comparison with Measurements
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1000 2000 3000 4000 5000 6000
Speed [rpm]
VolumetricAir-E
fficiency[-]
Measurement RON95
MeasurementE85
Simulation RON95
Simulation E85
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Full Load Performance E85
Comparison with Measurements
8
9
10
11
12
13
1000 2000 3000 4000 5000 6000
Speed [rpm]
BrakeMean
EffectivePr
essureBMEP[bar]
Measurement RON95
Measurement E85
Simulation RON95
Simulation E85
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0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1 1.2
Volume / Vmax [-]
C
ylinderPressure[bar]
Measurement
Simulation E85(30% Vaporized Fuel Fraction)
Simulation E85(100% Vaporized Fuel Fraction)
Influence of the Fraction of Evaporated
Fuel on the Compression Curve
nMOT = 2,000 rpm
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Specific Heat Capacity for Liquid
and Evaporated Fuels
0.0
1.0
2.0
3.0
4.0
5.0
6.0
200 400 600 800 1000 1200
Temperature [K]
Specific
HeatCapacitycp
[kJ/kgK
]
Heptane1 Benzene1
Iso-Octane2 Indolene (GT-Power)
Ethanol1 Ethanol2
Liquids
Vapours
1 VDI-Wrmeatlas
2 NASA Thermobuild
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Specific Heat Ratios for Different
Fractions of Evaporated Fuel
1.1
1.15
1.2
1.25
1.3
1.35
1.4
-180 -90 0 90 180 270 360 450 540
Crank Angle [CAaTDC]
SpecificH
eatRatio
=
cp
/cv
[-]
RON95 (100% Vapour)
RON95 (30% Vapour)
E85 (100% Vapour)
E85 (30% Vapour)
Compression
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0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1000 2000 3000 4000 5000 6000
Speed [rpm]
Vol
umetricAir-Efficiency[-]
Measurement E85
Sim. 30% Vapour (default)
Sim. 50% Vapour
Sim. 100% Vapour
Volumetric Efficiencies for Different
Fractions of Evaporated E85
Further increase of the volumetric
efficiency and therefore higher
discrepancy to the measurements
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Sheet 22
Frankfurt,09.11.2009Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results
4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Conclusions and
Model Adaptations
A comparison with the measured compression curves indicates that most
of the fuel is obviously evaporated at inlet valve closing i.e. the fraction of
evaporated fuel should be close to 1.
A simulation with an increased fraction of instantaneously evaporated fuelresults in a further overestimation of the volumetric efficiency and full load
performance for E85 due to its high heat of vaporization. There is obviously
no solution that fulfi lls both demands.
From video observations in the inlet ports it became obvious that a
considerable part of the fuel puddles on the walls. The heat of vaporizationis therefore taken rather from the structure than from the air.
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Conclusions and
Model Adaptations
Sensing massflow and
fuel vapour fraction
Actuate external
heat source
HOV
Fraction of fuel that
evaporates in the puddle
1. Approach (Heat Fluxes): Sensing and actuation of the heat of vaporization
that is lost to the structure (see picture above)
2. Approach (Reduced HOV): Reduction of the fuels heat of vaporization in
accordance to the mass fraction that evaporates in the puddles
Addi tional parameter to tune
the model to the measurements
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Full Load Results for E85-Operation
85% Vaporized Fuel Fraction, 80% Heatof Vaporization from Structure
Constant values for:
Vaporized fuel fraction: 85%
Vaporized in Puddle: 80%
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Cyl. Pressure Curve for E85-Operation
85% Vaporized Fuel Fraction, 80% Heat ofVaporization from Structure
0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1 1.2
Volume / V max [-]
CylinderPressure[bar]
Measurement
30% Vapour
Reduced HOV
nMOT = 2,000 rpm
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Sheet 27
Frankfurt,09.11.2009Content
1. Introduction
2. Specifics of Ethanol Compared to Conventional Fuel
3. Model Setup and Calibration
4. Simulation Results
4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Full Load Results for E85-Operation
Comparison with Test Results
The model predicts a moderately increased mean effective pressure in
spite of a lower volumetric efficiency and is in good agreement with the
measurements. The results can be explained with a moderately higherheating value of the mixture and a higher efficiency of the process.
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NO-Emissions for both Fuels
Comparison with Test Results
A constant NOx calibration multiplier of 1.1 was used for both fuels
Difference Exhaust
Temperature RON95-E85 NO-Emissions
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Sheet 31
Frankfurt,09.11.2009Content
1. Introduction
2. Specifics of Ethanol compared to conventional fuel
3. Model Setup and Calibration
4. Simulation Results
4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Sheet 32
Frankfurt,09.11.2009Outlook and Conclusion
When simulating engines operated with alcohol blends like E85 a
higher impact of the fluid properties on the volumetric efficiency and
compression curve was observed.
With the integration of the heat fluxes in the inlet port a good
correlation with the engine performance could be achieved. The
differences in combustion temperature and efficiency for an engine
operated with RON95 and E85 could be shown.
However, i t must be considered that this approach is not predictive butmust be tuned to measurements.
Investigations with a more predictive model of the wall film in the inlet
ports that is provided by GT-Power and thermal models of the portwalls are carried out right at the moment.
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Sheet 33
Frankfurt,09.11.2009Content
1. Introduction
2. Specifics of Ethanol compared to conventional fuel
3. Model Setup and Calibration
4. Simulation Results
4.1. Full Load Results for both Fuels and Comparison with Test Results
4.2. Conclusions and Model Adaptations
4.3. Impact of E85 Fuel on Combustion and Efficiency
5. Outlook and Conclusion
6. Summary
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Sheet 34
Frankfurt,09.11.2009Summary
Because of the higher market share of alternative fuels like ethanol in the
future an analysis of their impact on the engine process is necessary.
Investigations were carried out with a 4-cylinder gasoline engine with port
fuel injection regarding full load performance. It could be shown that the
fuels fluid properties and wall film effects have a higher impact on the
quality of the simulation results than for conventional fuels.
Modifications of the engine model concerning puddling and fuel evaporation
improved the correlation with the measurements in terms of volumetric
efficiency and torque. The differences in engine operation between the twofuels RON95 and E85 could be understood with the adapted model.
Investigations with a more detailed model regarding the thermodynamic
behaviour of the wall film and the inlet port walls are carried out right at themoment.
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Thank You Very Much
For Your Attention!