An experimental investigation has been carried out to analyze the performance and emission characteristics of a compression ignition engine fuelled with Karanja oil and its blends (10%, 20%, 50% and 75%) visa-vis mineral diesel. The effect of temperature on the viscosity of Karanja oil has also been investigated. Fuel preheating in the experiments - for reducing viscosity of Karanja oil and blends has been done by a specially designed heat exchanger, which utilizes waste heat from exhaust gases. A series of engine tests, with and without preheating/pre-conditioning have been conducted using each of the above fuel blends for comparative performance evaluation. The performance parameters evaluated include thermal efficiency, brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC), and exhaust gas temperature whereas exhaust emissions include mass emissions of CO, HC, NO and smoke opacity. These parameters were evaluated in a single cylinder compression ignition engine typically used in agriculture sector of developing countries. The results of the experiment in each case were compared with baseline data of mineral diesel. Significant improvements have been observed in the performance parameters of the engine as well as exhaust emissions, when lower blends of Karanja oil were used with preheating and also without preheating, The gaseous emission of oxide of nitrogen from all blends with and with out preheating are lower than mineral diesel at all engine loads. Karanja oil blends with diesel (LIP to 50% v/v) without preheating as well as with preheating can replace diesel for operating the Cl engines giving lower emissions and improved engine performance. Crown copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.