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

ABSTRACT

The Lagrangian conditional moment closure (CMC) model is applied to combustion simulation of a diesel engine at different load conditions. Calculation is performed by the free open-source computational fluid dynamics (CFD) package, OpenFOAM (Jasak, 1996). In Lagrangian CMC total injected fuel is divided into a given number of fuel groups with each group assumed to have the same residence time, consequently the same conditional flame structure. The Favre mean quantities are obtained by local conditional flame structures weighted by an assumed probability density function (PDF) through the improved beta-PDF integration method. Calculated pressure traces are compared with measurements in five operating conditions involving a single or multiple injections with different fuel mass ratios, rpms, swirl ratios, and exhaust gas recirculation (EGR) rates. The Lagrangian CMC model showed acceptable agreement with measured pressure traces and apparent heat release rates for all test cases. There was no improvement in the results by flame group interaction, which is considered not relevant in the given engine conditions.

KEYWORDS:

• Conditional moment closure
• Diesel engine
• Multiple flame groups
• OpenFOAM
• Split injection