Effects of Cylinder Head Geometry on Mixture Stratification, Combustion and Emissions in a GDI Engine - A CFD Analysis

Preparation of air-fuel mixture and its stratification, plays the key role to determine the combustion and emission characteristics in a gasoline direct injection (GDI) engine working in stratified conditions. The mixture stratification is mainly influenced by the in-cylinder flow structure, which mainly relies upon engine geometry i.e. cylinder head, intake port configuration, piston profile etc. Hence in the present analysis, authors have attempted to comprehend the effect of cylinder head geometry on the mixture stratification, combustion and emission characteristics of a GDI engine. The computational fluid dynamics (CFD) analysis is carried out on a single-cylinder, naturally-aspirated four-stroke GDI engine having a pentroof shaped cylinder head. The analysis is carried out at four pentroof angles (PA) viz., 80 (base case), 140, 200 and 250 with the axis of the cylinder. The entire CFD simulations are performed at the engine speed of 2000 rev/min., and the overall equivalence ratio (ER) of 0.75. Finally, it is observed that the PA of 140 produced a rise of about 10.5% in indicated thermal efficiency (ITE) and 3% rise in peak heat release rate (HRR) with a compromise of 10.7% higher NOx emissions than that of the base case.