Abnormal Combustion in a Two-Stroke Spark Ignited Methanol Engine

Methanol (90% methanol + 10% gasoline) when used as a fuel in a 2-stroke spark ignition (SI) engine gave rise to abnormal combustion even at a low compression ratio. The regime of engine operation in which abnormal combustion occurs was identified and the effects of engine parameters such as mixture strength, compression ratio, ignition timing, combustion chamber geometry etc. were studied. Analysis of pressure-time histories of engine cycles when abnormal combustion occurred revealed that abnormal combustion at higher loads is similar to knocking in four-stroke engines. At light loads the nature of abnormal combustion was different.

The CFR octane rating of methanol does not correlate with actual anti-knock quality in two-stroke engine combustion. Comparison with primary reference fuels indicated that the two-stroke engine has a very high severity. The hot residual gases seem to have a major role on onset of abnormal combustion.