Simulation of Diesel Engine Combustion with Split Injections by Lagrangian Conditional Moment Closure Model

Abstract

The Lagrangian conditional moment closure (CMC) model is applied to combustion simulation of a small diesel engine of a passenger vehicle at different load conditions. Calculation is performed by OpenFOAM which is a free opensource CFD program package with the features of turbulence, combustion, spray break-up and dynamic meshes for piston movement. The total fuel injected is divided into a given number of fuel groups according to the evaporation sequence. evolving independently or with possible same group interaction. Each fuel group is assumed to have the same residence time, consequently the same conditional same structure in Lagrangian CMC. Favre mean quantities are obtained by integration of the conditional same structure weighted by an assumed beta PDF in terms of local mean and variance of mixture fraction. Calculated pressure traces are compared with measurements in five operating conditions involving a single or multiple injections with different fuel mass ratios. There was no improvement in the results by same group interaction, which is considered not relevant in the given diesel engine conditions. The Lagrangian CMC model showed acceptable agreement with measured pressure traces at full, medium and low load with a single or multiple injections.