Abstract
Exhaust gas recirculation (EGR) is widely used for reduction of NO_x emission from diesel engines. However, particulate matter emission and thermal efficiency tend to be worse at the high EGR ratios. EGR induces the heterogeneous distributions of oxygen and temperature in a combustion chamber and these heterogeneities affect the emissions and combustion characteristics of diesel engine. If the heterogeneities of oxygen and temperature distributions can be controlled, it is expected that the simultaneous reduction of NO_x and PM from diesel engine will be achieved by active control of internal and external EGR devices. In this study, the NO_x and PM emissions and combustion characteristics of diesel combustion achieved in various distributions of oxygen concentration and temperature are investigated in order to clarify the effect of these heterogeneities of surroundings on the diesel combustion. The experiment was conducted with the rapid compression expansion machine (RCEM) and the combustion chamber in which various distributions of intake gas can be formed. The enthalpy and the amount of oxygen entrained into the spray upstream the ignition region are selected as the parameters in order to clarify the effect of heterogeneities of surrounding conditions on the diesel spray combustion. The results indicated that the NO_x and soot emissions from diesel combustion are governed mainly by the amount of enthalpy entrained into the spray upstream the ignition region, when the temperature distribution in a chamber is changed with keeping the oxygen fraction at constant.
