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An autoignition DI methanol engine has been developed to improve the thermal efficiency under low load conditions. The engine was compared with glow-assisted and spark-assisted DI methanol engines, and with conventional DI diesel engines. The results show that the autoignition occurs when the gas temperature in the cylinder exceeds approximately 900K. In the autoignition DI methanol engine, combustion proceeds rapidly, which results in high peak of heat release and short combustion duration. The thermal efficiency of the autoignition DI methanol engine, therefore, is higher than that of other type methanol engines and almost the same as that of diesel engines under low load conditions. NOx of the autoignition DI methanol engine is the lowest since it has the highest EGR.

For the purpose of developing direct injection heavy-duty methanol engines which surpass diesel engines in purformace, this paper first clarifies the methanol concentration around the spark plug for achieving a high ignition stability by sampling the gas near the spark plug using a sampling valve. The combustion process of methanol is then observed by the method of high-speed Schlieren photography to clarify the mode of methanol combustion. A new methanol DISC combustion system having a protrusion in the combustion chamber is devised based on such results. This study clarifies that the methanol concentration at the point of ignition for high ignition stability is in the range of 6 to 22 vol%. The methanol mixture burns by flame propagation so far as the compression ratio is on the order of 16.5.

Ignition and combustion of methanol in a spark-assisted methanol diesel engine were studied for the purpose of developing such an engine that is practical for actual vehicles. It became clear through investigations on combustion of methanol in a spark-assisted methanol diesel engine that methanol combustion proceeds mainly by flame propagation. Based on this finding, effects of such parameters as the injection direction, ignition position, ignition energy, compression ratio, injection timing and ignition timing were studied to obtain optimal conditions for methanol combustion. It was found through such studies that it is effective to form the mixture upstream of the spark, plug relative to the swirling direction and increase the inductive component of the ignition energy to achieve a high ignition stability.