Biofuel is a prominent alternative fuel because of its environmental benefits and similar physiochemical properties to diesel fuel. This study investigated the impact of high quality refined, bleached and deodorized (RBD) coconut oil blends and fuel throttle setting on performance and exhaust emissions of diesel engine. The criteria regulated emissions and particulate-phase polycyclic aromatic hydrocarbons (PAHs) were studied. The engine was operated with pure diesel and blended fuels contain of 10%, 30% and 50% of coconut oil by volume. Experiments were conducted under 75% and 50% throttle opening conditions at 2000 rpm. The use of coconut oil blends resulted in a reduction of all of the regulated emissions, except for slight fluctuations in CO2 emissions. There was no significant difference in total PAH emissions with the different throttle settings. All the coconut oil blends showed lower PAH emissions except for fluoranthene (FL) and benzo[a]pyrene (BaP) compounds. Notably, coconut oil blends resulted in a maximum reduction of 40% in total PAH concentration. It was observed that coconut oil blends increased the total benzo[a]pyrene equivalent (BaPeq). However, the reduction in benzo[a]anthracene (BaA) indicated the positive effects on toxicity reduction of coconut oil as a potential substitute for fossil diesel. (C) 2012 Elsevier Ltd. All rights reserved.