In this experimental study, the influences of re-entrant combustion chamber geometry on a diesel engine emission, performance and on the combustion were investigated using Pongamia Oil Methyl Ester (POME). For this purpose, the pistons with Toroidal Re-entrant Combustion Chamber (TRCC) and Shallow Depth Re-entrant Combustion Chamber having the same volume as that of the baseline Hemispherical open Combustion Chamber were tested in a four stroke, single cylinder, DI diesel engine. Two fuels namely, 20 percent POME blend (20% POME) with petroleum based diesel fuel (PBDF) and PBDF were used for this study. The test results for re-entrant type combustion chambers fuelled with 20% POME and PBDF were compared with baseline engine having hemispherical open type combustion chamber operated with PBDF and 20% POME blend. The test results showed that substantially higher brake thermal efficiency and lower specific fuel consumption for TRCC compared to baseline engine fuelled with 20% POME. Sharp reduction of particulates, CO and UBHC were observed for TRCC compared to the other two. However oxides of nitrogen (NOx) were higher for TRCC. The combustion analysis shows that, the ignition delay is lower for TRCC compared to baseline engine and the peak pressure is also higher at full load. (c) 2012 Elsevier Ltd. All rights reserved.