Influence of reentrant piston bowl geometry on combustion in CI engine

Abstract

The geometry of the piston bowl can affect flow, turbulence, mixing and combustion in an engine. In addition, the optimum geometry can be fuel specific. In this work, the effect of the piston bowl geometry variation on combustion of Dimethyl Ether (DME) in a compression ignition engine is investigated computationally by using AVL FIRE software. A reentrant piston bowl configuration is taken and the bowl diameter is varied while keeping the clearance at TDC, compression ratio (17.8) and operating conditions same. The objective is to exploit the non-sooting characteristics of DME and get an understanding of the re-entrant geometry for NO minimization without compromising the efficiency. Results show that there is negligible effect of the geometry on pressure traces and efficiency. However, geometry does have an influence on flow near TDC and thereby affects fuel/air mixing. It is noted that the geometry with the largest bowl diameter led to relatively rapid combustion and higher NO emissions. In contrast, the geometry with the smallest bowl diameter showed more prominent tail in the heat release rate and lowest NO emissions. Based on this work, the re-entrant configuration with smaller bowl diameter is preferred.