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Research Papers: Internal Combustion Engines

Modeling the Performance of a Turbo-Charged Spark Ignition Natural Gas Engine With Cooled Exhaust Gas Recirculation

[+] Author and Article Information
Hailin Li

 National Research Council Canada, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canadahailin.li@nrc-cnrc.gc.ca

Ghazi A. Karim

Department of Mechanical and Manufacturing Engineering, The University of Calgary, Calgary, AB, T2N 1N4, Canadakarim@enme.ucalgary.ca

J. Eng. Gas Turbines Power 130(3), 032804 (Mar 28, 2008) (10 pages) doi:10.1115/1.2835058 History: Received February 02, 2007; Revised December 03, 2007; Published March 28, 2008

A variety of gaseous fuels and a wide range of cooled exhaust gas recirculation (EGR) can be used in turbo-charged spark ignition (S.I.) gas engines. This makes the experimental investigation of the knocking behavior both unwieldy and uneconomical. Accordingly, it would be attractive to develop suitable effective predictive models that can be used to improve the understanding of the roles of various design and operating parameters and achieve a more optimized turbo-charged engine operation, particularly when EGR is employed. This paper presents the simulated performance of a turbo-charged S.I. natural gas engine when employing partially cooled EGR. A two-zone predictive model developed mainly for naturally aspirated S.I. engine applications of natural gas, described and validated earlier, was extended to consider applications employing turbo-chargers, intake charge after-coolers, and cooled EGR. A suitably detailed kinetic scheme involving 155 reaction steps and 39 species for the oxidation of natural gas is employed to examine the pre-ignition reactions of the unburned mixtures that can lead to knock prior to being fully consumed by the propagating flame. The model predicts the onset of knock and its intensity once end gas auto-ignition occurs. The effects of turbo-charging and cooled EGR on the total energy to be released through auto-ignition and its effect on the intensity of the resulting knock are considered. The consequences of changes in the effectiveness of after and EGR-coolers, lean operation and reductions in the compression ratio on engine performance parameters, especially the incidence of knock are examined. The benefits, limitations, and possible penalties of the application of fuel lean operation combined with cooled EGR are also examined and discussed.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of the turbo-charged S.I. engines with cooled EGR being considered

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Figure 2

Experimentally observed variations in the combustion duration in degrees with the amount of CO2, H2O and N2 added to the stoichiometric mixture of CH4, fully open throttle un-turbo-charged engine

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Figure 3

Experimentally observed variations of combustion duration in degrees with changes in relative diluents ratio of CO2, H2O, and N2 for stoichiometric mixture of CH4 for fully open throttle un-turbo-charged engine

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Figure 4

Variations of the predicted knock criterion with changes in boost pressure ratio for different atmospheric temperature, fuel: CH4, CR=8.5, ER=1.0, ST=15°CA BTDC, no EGR, fully open throttle

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Figure 5

Variations of the predicted knock criterion with changes in boost pressure ratio for different after-cooler effectiveness, fuel: CH4, ER=1.0, To=311K, CR=8.5,ST=15°CA BTDC, no EGR, fully open throttle

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Figure 6

The maximum boost pressure ratio permissible for stoichiometric operation with changes in after-cooler effectiveness, fuel: CH4, To=311K, CR=8.5, ST=15°CA BTDC, ER=1.0, Kn=1.50, assigned max. peak cylinder pressure (MPCP)=70atm, no EGR, fully open throttle

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Figure 7

Variations of the predicted maximum boost pressure ratios with changes in after-cooler effectiveness for different atmospheric temperature, fuel: CH4, CR=8.5, ER=1.0, ST=15°CA BTDC, Kn=1.5, assigned MPCP=70atm, no EGR, fully open throttle

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Figure 8

Variations of the predicted maximum indicated power output with changes in after-cooler effectiveness for different atmospheric temperatures, fuel: CH4, CR=8.5, ER=1.0, ST=15°CA BTDC, Kn=1.5, assigned MPCP=70atm, fully open throttle

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Figure 9

Variations of the predicted maximum boost pressure ratio with changes in after-cooler effectiveness for different compression ratios, fuel: CH4, To=311K, ER=1.0, ST=15°CA BTDC, Kn=1.5, assigned MPCP=70atm, fully open throttle

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Figure 10

Variations of the predicted maximum indicated power with changes in after-cooler effectiveness for different compression ratios, fuel: CH4, To=311K, ER=1.0, ST=15°CA BTDC, Kn=1.5, assigned MPCP=70atm, fully open throttle

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Figure 11

Variations of the predicted knock criterion with changes in EGR ratios for different EGR-cooler effectiveness, fuel: CH4, boost pressure ratio=1.85CR=8.5, ST=15°CA BTDC, To=311K, ER=1.0, fully open throttle

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Figure 21

The comparison of the indicated power production efficiency when knock is suppressed through lean operation and the application of cooled EGR, CR=10, ST=15°CA BTDC, To=311K, after-cooler effectiveness=0.5, EGR-cooler effectiveness=0.9, fully open throttle

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Figure 20

The comparison of the indicated power production when knock is suppressed through lean operation and the application of cooled EGR, CR=10, ST=15°CA BTDC, To=311K, after-cooler effectiveness=0.5, EGR-cooler effectiveness=0.9, fully open throttle

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Figure 19

The suppression of the onset of knock through lean operation or cooled EGR only. There is no EGR for lean operation. Equivalence ratio is kept at 1.0 when cooled EGR is applied. CR=10, ST=15°CA BTDC, To=311K, after-cooler effectiveness=0.5, EGR-cooler effectiveness=0.9, fully open throttle.

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Figure 18

Variations of the predicted indicated power production efficiency with boost pressure ratio when the equivalence ratios shown in Fig. 1 are applied, fuel: CH4, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, no EGR, fully open throttle

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Figure 17

Variations of the predicted indicated power output with boost pressure ratios when the knock-limited equivalence ratios shown in Fig. 1 are applied, fuel: CH4, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, no EGR, fully open throttle

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Figure 16

Variation of the predicted knock-limited equivalence ratios with changes in boost pressure ratio for compression ratios of 8.5 and 10.0, Fuel: CH4, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, no EGR, fully open throttle

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Figure 15

Variations of the predicted indicated power production efficiency with changes in EGR-cooler effectiveness for different EGR ratios, fuel: CH4, ER=1.0, CR=8.5, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, assigned MPCP=70atm, fully open throttle.

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Figure 14

Variations of the predicted knock-limited maximum indicated power production with increasing EGR cooler effectiveness for different EGR-ratio, fuel: CH4, ER=1.0, CR=8.5, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, assigned MPCP=70atm, fully open throttle.

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Figure 13

Comparison in variations of the predicted knock-limited boost pressure ratio with changes in EGR-cooler effectiveness for different EGR ratios, fuel: CH4, ER=1.0, CR=8.5, To=311K, ST=15°CA BTDC, after-cooler effectiveness=0.5, Kn=1.5, assigned MPCP=70atm, fully open throttle.

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Figure 12

Variations of the predicted knock criterion with changes in boost pressure ratios for different EGR-cooler effectiveness, EGR rate=8.0%, To=311K, CR=8.5, ST=15°CA BTDC, after-cooler effectiveness=0.5, fuel: CH4, ER=1.0. The predicted knock criterion without EGR is also plotted for comparison, fully open throttle.

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