Large eddy simulation of partially premixed combustion in an internal combustion engine

This paper reports on numerical investigations of the mixing, ignition and combustion processes in a laboratory engine operating under partially premixed combustion (PPC) conditions. The engine is a modified version of a 13-liter Scania D13 engine. The fuel is injected at two different timings with different fuel mass portions at the two injections, with and without swirl. For comparison one single injection simulation with swirl is also performed. In literature it has been found that by optimizing the injection timing and amount of injected fuel at different injection timing, the heat release and combustion process can be optimized and thus high engine efficiency and low emission levels can be achieved. The goal of this study is to improve the understanding of the important phenomena involved. Large Eddy Simulation for the gas phase is coupled with Lagrangian Particle Tracking (LPT) for the liquid phase. Dynamic mesh motions and parallelized computations are taken into account using OpenFoam. It was shown that the approach used in this study could capture the important characteristics of the phenomena occurring in the engine. With sufficient time between the pilot injection and the main injection, fuel distribution becomes more homogeneous in the presence of swirl compared with that of non-swirling case. It was found that with 25 % less fuel the pressure rise rate for the two split injection case with swirl is almost identical to that of non-swirling case; indicating a higher efficiency with swirl. Also, the combustion fronts were found to be more uniformly spreading in the cylinder when swirl was present, while in the non-swirling case the combustion front is limited to the neighborhood of the spray fuel jet.