The effect of fuel inlet temperature on performance, emission and combustion characteristics of a diesel engine is evaluated. A single cylinder direct injection diesel engine developing a power output of 2.8 kW at 1500 rev/min is tested using preheated animal fat as fuel. Experiments are conducted at the fuel inlet temperatures of 30, 40, 50, 60 and 70 degrees C. Animal fat at low temperature results in higher ignition delay and combustion duration than diesel. Preheated animal fat shows reduced ignition delay and combustion duration. Peak pressure and rate of pressure rise are found as high with animal fat at high fuel inlet temperatures. Heat release pattern shows reduced premixed combustion phase with animal fat as compared to neat diesel at normal temperature. Preheating improves the premixed combustion rate. At low temperature, animal fat results in lower smoke emissions than diesel. The maximum smoke density is K = 6.5 m(-1) with diesel and K 3.6 m(-1) with animal fat at 30 degrees C. Preheated animal fat further reduces smoke levels at all temperatures. The smoke level is reduced up to K = 1.7 m(-1) with preheated animal fat at the temperature of 70 degrees C. Hydrocarbon and carbon monoxide emissions are higher with animal fat at low temperature as compared to diesel. Fuel Preheating reduces these emissions. NO emission is found as low with animal fat at low temperature. Fuel preheating results in increased NO emission. However, the level is still lower than diesel even at high temperature (i.e. 70 degrees C). On the whole it is concluded that preheated animal fat can be used in diesel engines with reduced smoke, hydrocarbon and carbon monoxide emissions with no major detoriation in engine performance. (c) 2004 Elsevier Ltd. All rights reserved.