Studies of NOx, CO, soot formation and oxidation from a direct injection stratified-charge engine using the k-ɛ turbulence model

Abstract

In this investigation, a model has been developed to predict the performance and emissions—NOx, CO and soot—in a direct injection stratified-charge engine with a Texaco controlled combustion system. This model uses the k-ε turbulence model to determine characteristic velocities for heat transfer calculations and has only an empirical constant, by comparison with the Woschni equation in which separate constants are used for each process in the four-stroke cycle to determine the velocity for use in the Reynolds number. The modified Keck and Blizard model is used for combustion calculation by considering the rapid compression effects on the turbulence intensity. An extended Zel'dovich mechanism has been used to predict NOx emissions. To predict CO emissions, the Zeleknik and McBride models have been used. The model of Hiroyasu and Kodota has been used to predict the mass of soot formed and oxidized. Comparison of the model predictions with available experimental data shows a good agreement. Moreover, the program has a high flexibility for parametric studies to calculate the effect of engine parameters such as fuel-air ratio, engine speed, injection timing period and percentage of exhaust gas recirculation on the performance and emissions characteristics of the engine.