Adaptability of gasoline, methanol, methane fuels to lean burn in an ATAC engine

Active thermo-atmosphere combustion (ATAC) is `bulk like' and/or `non-propagating' combustion caused by compression autoignition, and it is stable in a lean combustion region. We carried out an ATAC engine test to elucidate the effect of fuel properties on the engine performance in a lean combustion region. Several combustion characteristics, i.e, the ATAC operation region, brake-specific fuel consumption, exhaust emissions, the cyclic variation of maximum cylinder pressure, rate of heat release, autoignition timing, combustion duration, autoignition cylinder pressure and autoignition gas temperature were demonstrated for gasoline, methanol and methane. From the results of these tests, the influences of the equivalence ratio and the compression speed on the autoignition and combustion period were clarified, and we evaluated the adaptability of various fuels to lean burn in an ATAC engine. With use of methanol, the ATAC operation region could be widened in the lean region and the amount of brake-specific fuel consumption was decreased. With use of methane, ATAC operation was impossible. The autoignition temperature of methanol in an ATAC engine is lower than that of gasoline by about 140 K. We can say that methanol is most suitable for lean burn in an ATAC engine.