Studies Toward Optimal Charge Stratification in a Rotary Engine

Abstract

With charge stratification, efficiency and emission improvements are possible with relatively minor modifications of standard power plants. However, for most stratified charge engines, more research and development is necessary to obtain uniformly clean and efficient combustion over broad speed-load operating ranges. A theoretical model for the early stages of the fuel-air mixing process was developed and applied to a direct injection stratified charge rotary engine. The goal is the selection of injection parameters so as to achieve an optimal spatial distribution of the vapor fuel in the combustion chamber at the time of ignition. The constraint is imposed that this optimal distribution is to be maintained over the entire speed-load operating range. The model makes use of semi-empirical relationships for the initial conditions for the spray and enables one to compute the penetration, vaporization and mixing processes as they unfold in space and time. The trends predicted by the model are shown to be in agreement with the experimental ones in that cases of misfire and knock have been satisfactorily interpreted. Results are presented concerning the selection of specific injection design parameters for the optimal use of shower-head nozzles over as broad a speed-load operating range as possible. However, extensive computations have revealed certain inherent limitations of showerhead nozzles which make it advisable to explore more flexible fuel injection nozzle designs.