A team from the National University of Singapore (NUS) reports on the effects of piston bowl geometry on the combustion and emission characteristics of a diesel engine fueled with biodiesel under medium load condition in a paper in the journal Fuel.

The team investigated three different bowl geometries in its numerical study: Hemispherical Combustion Chamber (HCC), Shallow depth Combustion Chamber (SCC), and the baseline Omega Combustion Chamber (OCC). All used the same compression ratio of 18.5.

Computational fluid dynamics (CFD) modeling based on KIVA-4 code simulated combustion. was performed.

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.

They found that the narrow entrance of the combustion chamber could generate a strong squish, especially at high engine speed, hence enhancing the mixing of air and fuel.

The simulation results indicate that in terms of performance, the Shallow depth Combustion Chamber is favorable at low engine speed, while at high engine speed, OCC is preferred.

As a consequence, they suggested, 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.