PREDICTION OF EFFECT OF PREMIXED COMBUSTION ON DIESEL EMISSIONS

Abstract

There are efforts ongoing to improve emission characteristics of direct injection diesel engine which is considered to be a fuel efficient system. The combusition process in any diesel system is mainly diffusion-controlled. However, some premixed burning is found to occur in the diesel spray region during the ignition delay period. The onset of premixed combustion soon after the ignition period significantly affect the production of various emittants in engines mainly NO and soot. The function of premixed burning is increased by longer, ignitiondelay-high air swirl and the rates of fuel injection and large surface area of the multi-hole fuel sprays. In the present work the influence of the premixed burning and the parameters affecting it on diesel emissions are predicted using a multizone phenomenological model developed based on discription of various important diesel engine processes. The trends of predicted results showing effects of the parameters such as speed, injection timing, compression ratio, injector orifice hole geometry1injection pressure and duration of injection are discussed. The ignition delay, the injection and the combustion durations are identified as important periods which seem to show correlation with engine emission characteristics.