Simulation of combustion in direct injection diesel engines using a eulerian particle flamelet model

Abstract

An overview of flamelet modeling for turbulent non-premixed combustion is given. A short review of previous contributions to simulations of direct injection (DI) diesel engine combustion using the representative interactive flamelet concept is presented. A surrogate fuel consisting of 70% (liquid volume) n-decane and 30% α-methylnaphthalene is experimentally compared to real diesel fuel. The similarity of their physical and chemical properties is shown to result in a very similar combustion process for both fuels. The mathematical derivation for the Eulerian particle flamelet model is outlined. A strategy based on physical arguments is described for subdividing the computational domain and assigning these domains to different flamelet histories associated with Eulerian marker particles. For each of these marker particles, a transport equation has to be solved. Experiments conducted with an Audi DI diesel engine equipped with a piezo injector and running with diesel fuel are compared to simulations using the surrogate fuel. The use of multiple flamelets, each having a different history, significantly improves the description of the ignition phase, leading to a better prediction of pressure, heat release, and exhaust emissions such as soot and NOx. The effect of the number of flamelet particles on the predictions is discussed.