Abstract
The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by the direct diesel fuel injection. The internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the mixture temperature. The effect of internal EGR is varied by the back pressure level. It is confirmed that the lean methanol-air mixture of air-fuel ratio between 130 and 18 could be ignited and burned when the back pressure of 106.6 [kPa] is applied. The ignition delay reduces and the maximum combustion pressure increases as the back pressure increases. Fluctuation of maximum combustion pressure is gradually decreased as back pressure increases. However, the brake mean effective pressure decreases as the back pressure increases, because the pumping loss and the reduction of the rate of specific heat cause the output power reduction. Therefore, the ignition and combustion characteristics can be improved by applying the internal EGR, however, the engine performance is deteriorated. When the back pressure of 106.6 [kPa] is applied, a lot of CO is emitted, and HC and NOx concentrations decrease as back pressure increases. The stabilization of ignition and combustion caused by internal EGR make HC concentration reduce.