Energy is the prerequisite for modern civilization. Fossil fuel is still the main source of energy. But the endless consumption of fossil fuel has brought its reserve about to an end. As a result, spiraling demand and diminishing supply. Therefore, researchers are seeking for alternative and cost effective fuels to meet the human demands. Experiments have been performed on a four strokes, two cylinder, direct injection, and naturally aspirated Diesel engine when operating on 10%, 20%, 30% and 40% blends with Diesel fuel. The purpose of this research is to test the effects of pongamia oil biodiesel inclusion in Diesel engine on power, specific fuel consumption (SFC), thermal efficiency, emission composition changes and exhausts temperature. At a higher speed of 1800 rpm, the (SFC) of the fully loaded engine for the B20 blend is the same as that for Diesel fuel, whereas B30 suggest the (SFC) is higher by 11.65%. The (SFC) of blend B10 appeared to be the same as that of blend B20, both of them have lower (SFC) by 2.9 % compared to Diesel fuel. The fuel energy conversion efficiency depends actually on both the biodiesel inclusion percent in the Diesel fuel and the engine performance conditions. The results indicate that higher than 10 vol% of biodiesel in Diesel fuel reduces the fuel energy conversion efficiency for the biodiesel.