The paper presents experimental investigations carried out on a stationary diesel engine at a constant speed and full load with preheated pongamia biodiesel. The preheating of pongamia biodiesel attempted with the help of gravity assisted heat pipe (Thermosyphon) heat exchanger. The heat exchanger designed to utilize the engine exhausted waste heat to preheat the biodiesel. The experiments were conducted to investigate the influence of different geometric and physical parameters of heat pipe heat exchangers (HPHX) on heat transfer characteristics. The effect of preheating on engine performance and emissions were also studied and compared with diesel. The 80% acetone charged HPHXs exhibit better results in respect to the performance of HPHX and the engine. The maximum effectiveness of 0.757 achieved for 80% acetone HPHX with section ratio 1:3(SR1), Aspect ratio (AR) 10 and tube diameter D3. The tubes with larger diameter and evaporator length show lower thermal resistance, higher BTE much near to diesel fuel. The preheating tends to reduce CO, HC and smoke emissions, while increasing emission of CO2, NOx and EGT leaving the engine.
