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A premixed charge compression ignition methanol engine targeting a drastic decrease in NOx emissions and a brake specific energy consumption equivalent to that of a DI diesel engine has been developed (1). The problems of this combustion system are that the brake thermal efficiency decreases, and CO and THC emissions increase due to a deterioration of high load combustion. The purpose of this study is to improve the high load combustion of a premixed charge compression ignition methanol engine using a flash boiling fuel injection technique. The results of this study have shown that the premixed charge compression ignition methanol combustion system using a flash boiling fuel injection technique increases the brake thermal efficiency, decreases CO and THC emissions, while maintaining low NOx emissions in the high load region.

A new combustion system targeting a drastic decrease in NOx emission and a brake specific energy consumption equivalent to that of a DI diesel engine has been developed. In this new combustion system, a lean burn system using early injection was employed to reduce NOx emission and an auto-ignition DI engine system was employed to achieve the low energy consumption. Methanol was used as the fuel for reducing NOx emission. The objective of this study is to clarify the possibility of the system for the auto-ignition of a premixed lean mixture of methanol fuel. This study shows that the gas temperature at ignition, Tig, is the predominant factor affecting auto-ignition. Auto-ignition occurs when Tig exceeds approximately 1000K. The methanol lean burn system in an auto-ignition DI engine drastically decreased NOx emission with almost the same brake specific energy consumption as a diesel engine in the middle load region.

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.

A diesel engine with a dual-fuel (methanol-diesel) injection system has been developed, and the practicality of a prototype bus equipped with the developed engine has been confirmed. This study showed that methanol could be substituted for diesel fuel at the rates of 86 vol. percent in transient mode operation and 94 vol. percent in steady-state operation. Driving performance was equivalent to that of a conventional bus. Fuel economy of the dual-fuel injection engine was the same as that of a conventional diesel engine in steady-state operation, and decreased by about 9 percent in transient mode operation. The dual-fuel injection engine met the Japanese regulations on exhaust emissions stipulated in 1979. Exhaust smoke and particulate emissions were extremely reduced to the level of smoke-free operation.

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.