The present work investigates the effect of varying the combustion chamber geometry on the performance of a diesel engine using biodiesel in terms of brake specific fuel consumption, brake thermal efficiency as well as exhaust emissions and combustion characteristics. Engine tests have been carried out using a blend of 20% Pongamia Oil Methyl Ester (POME) with standard diesel as fuel and with three types of combustion chambers namely Hemispherical combustion chamber, Toroidal combustion chamber and Shallow depth combustion chamber without altering the compression ratio of the engine. The test results showed that brake thermal efficiency for toroidal combustion chamber is higher than for the other two types of combustion chambers. Significant improvement in reduction of particulates, carbon monoxide and unburnt hydrocarbons is observed for toroidal combustion chamber compared to the other two. However oxides of nitrogen were slightly higher for toroidal combustion chamber. The combustion analysis shows improved characteristics for toroidal combustion chamber compared to baseline engine at all loads of operation. (C) 2012 Elsevier Ltd. All rights reserved.