An experimental study was conducted on a Euro IV diesel engine to evaluate the performance, combustion and emission characteristics of pure biodiesel and its blend fuels. For each tested fuel, the performance and emissions were measured at four different engine speeds (800 rpm, 1200 rpm, 2400 rpm and 3600 rpm) under three different loads (25%, 50% and 100% load). The results showed that the use of biodiesel/blend fuels resulted in a higher brake specific fuel consumption, especially at low engine speed and partial load conditions. For example, at 25% engine load, the BSFC was found to be increased by 42% and 34.4% for biodiesel as compared to diesel at 800 rpm and 1200 rpm respectively. The brake thermal efficiency of biodiesel was found to be slightly higher compared to diesel at 50% and 100% load and the opposite tread was observed at 25% load. For combustion characteristics, a slightly shorter ignition delay and lower peak heat release rate were found for biodiesel compared to pure diesel. With respect to emissions, a slight reduction in the major emissions such as HC and NOx were observed with the use of biodiesel. But the opposite trend was seen at low engine speed, revealing that the low engine speed had a significant effect on the engine combustion and emission formation processes. (C) 2012 Elsevier Ltd. All rights reserved.