Abstract
KEYWORDS – Conditional Moment Closure, Diesel engine, Split injection, Flame group, OpenFOAM
ABSTRACT
The Lagrangian CMC model with multiple flame groups is employed to simulate a diesel engine with split injections in this simulation. The model is implemented in OpenFOAM, which is a free open-source CFD program package to deal with various processes in internal combustion engine simulation, e.g. turbulence, combustion, spray break-up and dynamic meshes with piston movement. The total injected fuel is divided into N independent flame groups according to the evaporation sequence in the cylinder. Each flame group is assumed to have the same conditional flame structure, while the Favre mean quantities are obtained through PDF integration of the conditional flame structures. Calculated pressure traces are compared with measurements for a commercial diesel engine in diverse operating conditions and injected fuel mass ratios, etc. The single injection case at the full load and a high rpm shows good agreement with the measured pressure traces by incompletely stirred reactor (ISR) hypothesis. However, the ISR assumption tends to overpredict the combustion rate for split injection cases, because it assumes that the conditional flame structure is uniform in the whole cylinder domain. The Lagrangian CMC model with the multiple flame group approach shows better results than the ISR for these split injection cases. Further research may be required to consider flame group interaction through premixed combustion at any given mixture fraction.