Comparison of lean combustion behavior of conventional gasoline and alternative fuels for S.I. engine

An SI engine test was carried out to elucidate the effect of fuel properties on the engine performance in a lean combustion region. Several combustion characteristics, i.e., the indicated mean effective pressure (IMEP), the cycle variation of IMEP, the combustion duration, the fuel consumption and the indicated thermal efficiency, were demonstrated for four kinds of alternative fuels and regular gasoline with equivalence ratio ranging from 0.56 to 1.0. From the results of this test, we have confirmed that the fuel composition significantly affected engine combustion under lean-burn conditions. This study has also revealed the effect of fuel properties on exhaust emissions, such as the carbon monoxide (CO), the total hydrocarbon (THC) and the nitrogen oxide (NOx) amount. The CO emissions did not depend on the fuel types, but the THC emissions and the NOx emissions were affected by differences between several fuel types in the lean region. In an extremely lean region, however, the NOx emissions became similar for all fuels.