Used palm oil collected from different restaurants in Tirunelveli region of south India was converted into methyl esters (biodiesel) by transesterification. Biodiesel produced from used palm oil was blended with diesel by different volume proportions (25%, 50% and 75%). Biodiesel and its blends were tested in a DI diesel engine at constant speed by varying loads (between 20% and 100%) to analyze its performance, emission and combustion profile. The results obtained were compared with diesel fuel. 1325 and B50 showed performances similar to diesel fuel. Smoke density of B100 and 1375 were lower than diesel by 19% and 10% at full load. At full load measured CO emission for B100 and B75 were 52.9% and 35.2% lower than diesel HC emission for B100 and B75 were 38.09% and 19.05% lower than diesel. NOx emission was higher for all biodiesel blends. B75 showed lower amount of emissions throughout the test. Ignition delay for B100, B75, B50 and B25 were 2.1 degrees, 1.9 degrees, 1.7 degrees and 1 degrees lower than diesel. Combustion profile was smoother and no knocking was experienced while operating with biodiesel blends. B50 produced peak cylinder pressure. (C) 2012 Elsevier Ltd. All rights reserved.