Computer simulation of combustion processes in a stratified charge engine

Abstract

A numerical simulation model of a divided-chamber, stratified charge engine is described. The conservation equations of fluid mechanics, coupled to a simple, global chemical reaction model and an algebraic turbulence model have been solved by use of an arbitrary Lagrangian-Eulerian (ALE) numerical technique for a one-dimensional, variable area, combustion volume. Pollutant concentrations, e.g. NO x , are obtained by performing a calculation of the pollutant chemistry with a simple NO x chemical model. The simulation results in a prediction of the flame propagation dynamics which leads to temperatures, pressures and species concentration as functions of spatial location, time, and the various engine design parameters. The fluid mechanical aspects of the flow of the prechamber jet issuing into the main chamber is studied more realistically by use of a similar numerical procedure, extended to include two spatial dimensions and time as the independent variables. These calculations, performed for an axisymmetric combustion volume, illustrate the formation of a recirculation region, or vortex flow, due to the high-area expansion ratio downstream of the nozzle and the interaction of the jet with the piston. The technique, when improved by incorporation of more realistic models of turbulence and chemistry and experimentally validated, should be a very useful tool for investigating design and operating condition variations on engine performance.