A Wall-Modified Flamelet Model for Diesel Combustion

In this paper, a wall-modified interactive flamelet model is developed for improving the modeling of Diesel combustion. The objective is to include the effects of wall heat loss on the transient flame structure. The essential idea is to compute several flamelets with several representative enthalpy defects which account for wall heat loss. Then, the averaged flamelet profile can be obtained through a linear fit between the flamelets according to the enthalpy defect of the local gas which results from the wall heat loss. The enthalpy defect is estimated as the difference between the enthalpy in a flamelet without wall heat loss, which would correspond to the enthalpy in the gas without wall heat loss, and the gas with wall heat loss. The improved model is applied to model combustion in a Diesel engine. In the application, two flamelets, one without wall heat loss and one with wall heat loss, are considered. Results are shown from computations for the cases without heat loss and with wall heat loss in the flamelet. Effects of spray angle on engine emissions are investigated. The computed emissions from the engine for different spray angles are compared to measurements. It is shown that the wall-modified interactive flamelet model is able to reproduce the trends more accurately.