Biodiesels are the most popular fuels which can be used as an alternative fuel instead of diesel fuel in diesel engines. Low emission characteristics and high cetane numbers are the most significant advantages of biodiesels. However, JP-8 military aviation fuel which is a kerosene based fuel has a low viscosity, high lower heating value and very low freezing point. The usage of the fuel blends of biodiesel and JP-8 may be effective in improving the characteristics of biodiesel. In this study, JP-8 aviation fuel and sunflower methyl ester blends were tested at 7.5, 1125, 15 and 18.75 Nm engine loads and at maximum torque speed (2200 min(-1)) in a single cylinder, naturally aspirated, and direct injection diesel engine. In-cylinder pressure, ignition delay period, engine performance and exhaust emissions have been examined. As the engine load increases the specific fuel consumptions decrease for all test fuels. It was seen that NOx emissions increased with the increase of the amount of biodiesel in the test fuels. CO emissions decreased as the amount of biodiesel fuel increased in the test fuels. Consequently, it was observed that JP-8 and biodiesel fuel mixtures can easily and efficiently be used in diesel engine. (C) 2014 Elsevier B.V. All rights reserved.