european gt-suite conference 2009 · 9th november 2009 european gt-suite conference 2009 mechanisms...

Frankfurt,9th November 2009

European GT-SUITE Conference 2009

Mechanisms 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 Technology

2GM – Powertrain Germany GmbH

Sheet 2

Frankfurt,09.11.2009

Content

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

Sheet 3


Content

1. Introduction








6. Summary

Sheet 4


• 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

Sheet 5


Content

1. Introduction








6. Summary

Sheet 6


Fuel Characteristics of RON95 and Ethanol E100 (I)

Sheet 7


Fuel Characteristics of RON95 and Ethanol E100 (II)

Sheet 8


Correction of the Lower Heating Value

• In a bomb calorimeter the lower heating value at constant volume (ΔU)V,T‘ ismeasured. GT-Power expects the lower heating value at constant pressure(ΔH)p,T‘ . There is a difference between both values if the number of moleschanges during the reaction:

(ΔH)p,T‘ – (ΔU)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(ΔH)p,T‘ + HOV

28.8641.983(ΔH)p,T‘

28.9642.063(ΔU)V,T‘

E85RON 95Chemical Energy [MJ/kg]

Sheet 9


Content

1. Introduction








6. Summary

Sheet 10


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 cm³Displacement

1.4 L Gasoline EngineEcotec Family 0, Generation 2,Multi Point Fuel Injection

Engine Type

Sheet 11


Numerical Model and Test Equipment

High-pressure sensors in the combustion chambers

Low-pressure senors in the inlet- and exhaust-manifold

Test EquipmentNumerical Model

Sheet 12


Content

1. Introduction








6. Summary

Sheet 13


Gasdynamics @ Full Load –Comparison with Measurements

n = 2,800 rpm

n = 4,400 rpm

n = 6,000 rpm

Measurement location

pInlet

Sheet 14


Full Load Performance w/ RON95 –Comparison with Measurements

Sheet 15


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 vapourdisplaces more air during intake. Therefore the volumetric efficiencyshould 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. Thereforethe density of the mixture and the volumetric efficiency should beINCREASED.

Sheet 16


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 6000Speed [rpm]

Volu

met

ricA

ir-Ef

ficie

ncy

[-]Measurement RON95

Measurement E85

Simulation RON95

Simulation E85

Sheet 17


Full Load Performance E85 –Comparison with Measurements

8

9

10

11

12

13

1000 2000 3000 4000 5000 6000Speed [rpm]

Bra

ke M

ean

Effe

ctiv

ePr

essu

reB

MEP

[bar

]

Measurement RON95

Measurement E85

Simulation RON95

Simulation E85

Sheet 18


0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2Volume / Vmax [-]

Cyl

inde

rPre

ssur

e[b

ar]

Measurement

Simulation E85 (30% Vaporized Fuel Fraction)

Simulation E85(100% Vaporized Fuel Fraction)

Influence of the Fraction of EvaporatedFuel on the Compression Curve

nMOT = 2,000 rpm

Sheet 19


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 1200Temperature [K]

Spec

ific

Hea

tCap

acity

c p[k

J/kg

K]

Heptane1 Benzene1

Iso-Octane2 Indolene (GT-Power)Ethanol1 Ethanol2

Liquids

Vapours

1 VDI-Wärmeatlas2 NASA Thermobuild

Sheet 20


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 540Crank Angle [°CAaTDC]

Spec

ific

Hea

tRat

io κ

= c

p/ c

v[-]

RON95 (100% Vapour)RON95 (30% Vapour)

E85 (100% Vapour)

E85 (30% Vapour)

Compression

Sheet 21


0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1000 2000 3000 4000 5000 6000Speed [rpm]

Volu

met

ricA

ir-Ef

ficie

ncy

[-]Measurement E85

Sim. 30% Vapour (default)

Sim. 50% Vapour

Sim. 100% Vapour

Volumetric Efficiencies for Different Fractions of Evaporated E85

Further increase of the volumetricefficiency and therefore higherdiscrepancy to the measurements

Sheet 22


Content

1. Introduction








6. Summary

Sheet 23


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 fuel

results 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 fulfills 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 vaporization

is therefore taken rather from the structure than from the air.

Sheet 24


Conclusions and Model Adaptations

Sensing massflow and fuel vapour fraction

Actuate externalheat source

HOVFraction of fuel thatevaporates in the puddle

1. Approach (Heat Fluxes): Sensing and actuation of the heat of vaporizationthat is „lost“ to the structure (see picture above)

2. Approach (Reduced HOV): Reduction of the fuel‘s heat of vaporization in accordance to the mass fraction that evaporates in the puddles

Additional parameter to tune the model to the measurements

Sheet 25


Full Load Results for E85-Operation –85% Vaporized Fuel Fraction, 80% Heat

of Vaporization from Structure

Constant values for:Vaporized fuel fraction: 85%Vaporized in Puddle: 80%

Sheet 26


Cyl. Pressure Curve for E85-Operation –85% Vaporized Fuel Fraction, 80% Heat of

Vaporization from Structure

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2Volume / V max [-]

Cyl

inde

rPre

ssur

e[b

ar]

Measurement

30% Vapour

Reduced HOV

nMOT = 2,000 rpm

Sheet 27


Content

1. Introduction








6. Summary

Sheet 28


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.

Sheet 30


NO-Emissions for both Fuels –Comparison with Test Results

A constant NOx calibration multiplier of 1.1 was used for both fuels

Difference ExhaustTemperature RON95-E85 NO-Emissions

Sheet 31


Content

1. Introduction

2. Specifics of Ethanol compared to conventional fuel







6. Summary

Sheet 32


Outlook 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 engineoperated with RON95 and E85 could be shown.

• However, it 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 inletports that is provided by GT-Power and thermal models of the portwalls are carried out right at the moment.

Sheet 33


Content

1. Introduction

2. Specifics of Ethanol compared to conventional fuel







6. Summary

Sheet 34


Summary

• 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 portfuel injection regarding full load performance. It could be shown that the fuel‘s 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 evaporationimproved the correlation with the measurements in terms of volumetricefficiency 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 thermodynamicbehaviour of the wall film and the inlet port walls are carried out right at the moment.

Sheet 35


Thank You Very Much

For Your Attention!

european gt-suite conference 2009 · 9th november 2009 european gt-suite conference 2009 mechanisms...

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