Improved thermal efficiency, reduction in fuel consumption and pollutant emissions from biodiesel fueled diesel engines are important issues in engine research. To achieve these, rapid and perfect air-fuel mixing are the most important requirements. The mixing quality of biodiesel spray with air can be improved by selecting the best injection parameters and better design of the combustion chamber. Experiments were performed using a DI (direct injection) diesel engine equipped with a conventional jerk type injection system and pistons having HCC (hemispherical combustion chamber) and TRCC (toroidal re-entrant combustion chamber) geometries. The combined effect of varying, injection pressure and combustion chamber geometries, on the combustion, performance and exhaust emissions, using a blend of 20% POME (pongamia oil methyl ester) by volume in diesel were evaluated. The test results showed that improvement in terms of brake thermal efficiency and specific fuel consumption for TRCC operated at higher injection pressure. Substantial improvements in reduction of emissions levels were also observed for TRCC operated at higher injection pressure. However improved combustion, due to better air motion inside the cylinder and high pressure injection, increased the oxides of nitrogen (NOx). Increasing injection pressure decreased ignition delay, and increased peak in-cylinder pressure and maximum heat release rate. (C) 2013 Elsevier Ltd. All rights reserved.