Effects of piston bowl geometry on combustion and emission characteristics of biodiesel fueled diesel engines

This paper presents the numerical study of the effects of piston bowl geometry on combustion and emission characteristics of a diesel engine fueled with biodiesel under medium load condition. Three different bowl geometries namely: Hemispherical Combustion Chamber (HCC), Shallow depth Combustion Chamber (SCC), and the baseline Omega Combustion Chamber (OCC) were created with the same compression ratio of 18.5. To simulate the combustion process, computational fluid dynamics (CFD) modeling based on KIVA-4 code was performed. Moreover, CHEMKIN II code was integrated into the KIVA-4 code as the chemistry solver to incorporate detailed chemical kinetics mechanisms consisting of 69 species and 204 reactions for the biodiesel combustion, thereby improving the accuracy of the simulation. It is found that the narrow entrance of combustion chamber could generate a strong squish, especially at high engine speed, hence enhancing the mixing of air and fuel. Also, the simulation results indicate that in terms of performance SCC is favorable at low engine speed; whereas at high engine speed, OCC is preferred. As a consequence, SCC will generate relatively higher NO compared to other two piston bowl designs at low engine speed condition. Similarly, the high performance of OCC bowl geometry could result in a high NO emission at high engine speed condition.