In the present work, the effect of using neat orange oil, optimum orange oil-diesel blend and the optimum flow rate of DEE with orange oil are evaluated for the performance, emissions and combustion characteristics of a single cylinder, diesel engine. The experimental results show that carbon monoxide (CO), hydrocarbon (HC) and smoke emissions decrease while oxides of nitrogen (NO(x)) emissions increase for orange oil and its blends compared to diesel fuel and DEE with orange oil. The brake thermal efficiency in the case of DEE with orange oil is higher than that of orange oil, orange oil-diesel fuel blend and diesel fuel. The peak cylinder pressure and heat release rate for DEE with orange oil are higher than those of diesel fuel operation. (C) 2009 Elsevier Ltd. All rights reserved.