CFD parametric analysis of the combustion chamber shape in a small HSDI Diesel engine

The paper aims at providing information about the influence of the combustion chamber shape on the combustion process evolution in a high speed direct injection (HSDI) small unit displacement engine for off-highway applications. Small HSDI Diesel engines require a deep optimisation process in order to maximize specific power output, while limiting pollutant emissions without additional expensive pollutant aftertreatment equipments. Making reference to a current production engine, the purpose of this paper is to investigate the influence of combustion chamber design on both engine performances and combustion efficiency. The actual piston omega-shape is progressively distorted in order to assess the influence of some of the main bowl-features on both mean-flow evolution, mixture formation and pollutants.

Using previously validated intake stroke CFD results as initial conditions, compression, injection and combustion simulations are performed in an attempt to trend the influence of bowl depth, bowl entrance angle, omega curvature radius and relative spray-bowl orientation on the engine performances and pollutants. Spray mixing effectiveness, combustion efficiency and NOx and Soot formation are used to compare the different geometries, operating the engine at high-speed full load.