Abstract
A phenomenological combustion model for the direct-injection, quiescent chamber, diesel engine based on axial division of the fuel spray was modified to enable accurate for prediction of exhaust NOx and particulate emissions. The fuel spray axial divisions are further sub-divided into radial divisions. This allows the fuel-air concentration to vary from fuel rich at the spray core to fuel lean around the spray periphery
Modification of the air entrainment model was needed for the multi -zone fuel-air distribution since there were air compositional variations in the cylinder. The air could be normal or rich in oxygen or deficient in oxygen (EGR) practically achieved by a delayed port admission inlet valve. In the model the air entrainment in the free spray is now estimated from momentum conservation. However, the volumetric estimation of wall jet is based on Porehs wall jet velocity distribution for estimating the rate of air entrainment at the wall jet. It is shown that the predicted cylinder pressure diagrams are in good agreement with experimental results. The extended Zeldovich mechanism is used for calculating NO formation using the rate constant as recommended by Hanson and Salimian. The modified Hiroyasus soot production model is used for estimating soot production.
Hiroyasus soot oxidation coefficient was replaced by using the Nagle and Strickland-Constables oxidation model. The predicted results of emissions are acceptable.