Tu Vienna 2009

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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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Frankfurt,09.11.2009

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







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







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







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







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


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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


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


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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Frankfurt,09.11.2009Content

1. Introduction



4. Simulation Results

4.1. Full Load Results for both Fuels and Comparison with Test Results




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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1. Introduction








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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1. Introduction

2. Specifics of Ethanol compared to conventional fuel







6. Summary

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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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1. Introduction

2. Specifics of Ethanol compared to conventional fuel







6. Summary

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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!

Tu Vienna 2009

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