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Research Papers: Internal Combustion Engines

# The Lean Mixture Operational Limits of a Spark Ignition Engine When Operated on Fuel Mixtures

[+] Author and Article Information
Hailin Li, A. Sohrabi

Department of Mechanical and Manufacturing Engineering, The University of Calgary, Calgary, AB, T2N 1N4, Canada

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 131(1), 012801 (Nov 20, 2008) (7 pages) doi:10.1115/1.2978998 History: Received February 06, 2007; Revised October 22, 2007; Published November 20, 2008

## Abstract

The operation of spark ignition (SI) engines on lean mixtures is attractive, in principle, since it can provide improved fuel economy, reduced tendency to knock, and extremely low $NOx$ emissions. However, the associated flame propagation rates become degraded significantly and drop sharply as the operating mixture is made increasingly leaner. Consequently, there exist distinct operational lean mixture limits beyond which satisfactory engine performance cannot be maintained due to the resulting prolonged and unstable combustion processes. This paper presents experimental data obtained in a single cylinder, variable compression ratio, SI engine when operated in turn on methane, hydrogen, carbon monoxide, gasoline, iso-octane, and some of their binary mixtures. A quantitative approach for determining the operational limits of SI engines is proposed. The lean limits thus derived are compared and validated against the corresponding experimental results obtained using more traditional approaches. On this basis, the dependence of the values of the lean mixture operational limits on the composition of the fuel mixtures is investigated and discussed. The operational limit for throttled operation with methane as the fuel is also established.

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## Figures

Figure 1

Schematic diagram of the experimental engine setup

Figure 2

Comparison of the variation in the trends of COV in imep, CO emissions, and relative emissions of CH4 with leaning operation, fuel: CH4, CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle

Figure 3

Variation of the indicated work with changes in equivalence ratio for 20 consecutive cycles; fuel: CH4. The vertical chained line shows the lean operational limit derived in this research. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 4

Variation of the misfire frequency with leaning operation; fuel: CH4. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 5

Comparison of the variation trends of the COV in imep, relative emissions of CH4, and development of misfire frequency with leaning operation; fuel: CH4. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 6

Variation in the exhaust temperature with changes in equivalence ratio for CH4 and 70%CH4+30%H2 operations. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 7

Comparison of the variation in the indicated power production efficiency with changes in equivalence ratio for CH4 and 70%CH4+30%H2 operations. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 8

Variation in the COV in imep with changes in equivalence ratio for CH4 and 70%CH4+30%H2 operations. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 9

Variation in the lean operation limited equivalence ratio with the changes in composition of the binary mixture of H2 with CH4 and CO with CH4. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 10

Comparison of the variation in the lean limits with changes in compositions of the corresponding binary fuel mixtures of CO with CH4 and CO with H2. CR=8.5, Tin=22°C, ST=15° CA BTDC, and fully open throttle.

Figure 11

Variations in the knock limited equivalence ratio with changes in the composition of the binary fuel mixtures of CO with CH4 and CO with H2. CR=12, ST=12° CA BTDC, Tin=38°C, N=900 rpm, and fully open throttle.

Figure 12

Variations in the lean operation limited equivalence ratio with changes in composition of the binary mixture of CH4 with gasoline and CH4 with iso-octane. CR=10, ST=19° CA BTDC, Tin=38°C, N=900 rpm, and fully open throttle.

Figure 13

Variations in the lean operation limits with changes in compression ratio for gasoline and iso-octane operations. Spark timing varies with compression ratio, as shown in literature (Li (26)), Tin=38°C, N=900 rpm, and fully open throttle.

Figure 14

Comparison of variations in the misfire frequency with leaning operations for fully and partially open throttles. Fuel: CH4, CR=8.5, ST=15° CA BTDC, Tin=22°C, and N=900 rpm.

Figure 15

Variation in the lean operational limits with throttling noted as volumetric efficiency. Fuel: CH4, CR=8.5, ST=15° CA BTDC, Tin=22°C, and N=900 rpm.

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