Application of Fuel Spray Theory to Exhaust Emission Control in a D.I. Diesel Engine

Recently diesel engines are required to get not only high performance but also low pollution gas quality (oxides of nitrogen, carbon monoxide, unburned hydrocarbons and smoke). Our approach to this requirement is based on the fuel spray theory that good fuel-air mixing in the fuel spray developed into the quiescent air depends upon high kinetic energy of the spray motion. From the theoretical analysis of fuel spray motion in the quiescent air and the photographic study of the fuel spray combustion, it was found that higher rate of air entrainment into the fuel spray by its own kinetic energy gives a very important effect on the increasing of combustion efficiency in the diesel engine and the reduction of soot formation. So, we designed the high volumetric efficiency but low swirl generating intake port in order to charge sufficient air into the cylinder, and an improved fuel injection system to attain high injection rate and high injection pressure so as to obtain high cycle efficiency and good fuel-air mixing in the quiescent air. As a result of many tests on this system using a single cylinder engine, a D.I. multi-cylinder diesel engine with high cycle efficiency and low smoke density was developed. The fuel injection timing of this engine is retarded to reduce the oxides of nitrogen in the exhaust gas. The fuel injector and fuel injection timing at light loads are improved to reduce the hydrocarbons in the exhaust gas.