In this study, regulated and unregulated exhaust emissions with petroleum diesel fuel and Jatropha-based biodiesel blends at proportions of 5%, 10%, 20%, 50% and 100% (v/v) have been investigated. This study examines four regulated emissions: nitrogen oxide, carbon monoxide, unburned hydrocarbon and smoke, and four typical unregulated emissions: formaldehyde, acetaldehyde, acetone and toluene. The biodiesel shows no obvious NOx emission difference from the pure diesel fuel at low and medium engine loads. Biodiesel blend ratios have little effect on the NO/NOx ratio at medium and high engine loads. The CO emission of biodiesel increases at low engine loads. The HC emissions show a continuous reduction with increasing biodiesel blend ratios. There is a good correlation between smoke reduction and the ratio of the biodiesel blends. The addition of biodiesel fuel increases formaldehyde emission. Compared to the pure diesel fuel, the acetaldehyde emission of B5 fuel is higher. The acetaldehyde emission of the B100 fuel is lower than the pure diesel fuel at low and middle engine loads. The acetone emission of biodiesel, from B5 to B100, is higher than the pure diesel fuel. The higher biodiesel blend ratio the fuel has, the lower toluene emission the engine has. (c) 2012 Elsevier Ltd. All rights reserved.