Thermodynamic modeling and validation of in-cylinder flow in diesel engines

The formation of a suitable air and fuel mixture in diesel engines is one of the most important factors in quality of combustion and engine exhaust emissions. The mixture formation depends on mass transfer phenomenon inside the combustion chamber. This study presents a new thermodynamic model to simulate the mass transfer phenomenon in diesel engines. Diesel engine is simulated utilizing a thermodynamic multi zone model coupled to a semi-detailed chemical kinetics mechanism. Heat and mass transfer submodels are linked to the multi zone model. Bulk flow and diffusion mass transfer between zones are considered in the mass transfer submodel. Bulk mass transfer simulates fluid motion between different zones caused by piston speed and difference in zonal temperature and pressure. Diffusion mass transfer occurs due only to difference in composition of different zones. The results indicate diesel engine performance and exhaust emissions can be predicted accurately applying mass transfer submodels. Bulk mass transfer mechanism has more significant effects on engine performance and emission compared to diffusion mechanism. Neglecting mass transfer submodels, calculated in-cylinder peak pressure is under predicted and both of exhaust NOx and soot are over predicted. The rates of soot oxidation reactions decrease and rates of NOx important reactions increase when mass transfer submodels are ignored.