In this experimental study cumulative heat release of a variable compression ratio (VCR) Diesel engine operating with diesel and Pongamia pinnata oil blends were studied under different crank angle (-360˚ to +359˚), five different percentage loading conditions (0%, 25%, 50%, 75% & 100%), two compression ratio (17:01 & 18:01) and three different Pongamia pinnata oil blends (B10, B15 & B20) which are blended with diesel by volumetric basis (100 ml Pongamia pinnata oil: 900 ml pure Diesel, 150 ml Pongamia pinnata oil: 850 ml pure Diesel, 200 ml Pongamia pinnata oil: 800 ml pure Diesel) respectively. For comparative purpose initially the engine was run by pure Diesel. This study shows that the cumulative heat release is maximum (1.01 kJ//s) when the engine operates with Pongamia pinnata oil (B10 blend) which was blended with pure Diesel on full load conditions (100% load) at a crank angle of 42˚ and compression ratio 17:01. This study shows that the cumulative heat release is minimum (0.58 kJ/s) when the engine operates with pure Diesel on no load conditions (0% load) at a crank angle of 48˚ and compression ratio 17:01.