Abstract: Compression Ignition (CI) engine operates in lean air fuel mixture in most of the running conditions. In our work castor oil based biodiesel extracted from the plants of Ricinuscommunis testing in a four stroke constant speed running CI engine. The extracted non-edible oil was then transformed to into biodiesel for testing in the engine and the same was mixed with 100ppm of Cerium Oxide (CeO2) nano particles. Then the prepared castor oil biodiesel (CBD) was diversified with the diesel in numerous ratio (5:95, 10:90 & 15:85).These three biodiesel blends were then tried in a constant speed CI engine to associate its enactment and discharge characteristics with that of diesel. The engine was tested in a different Brake power (1.15, 1.71, 2.29 & 2.75 kW) for all the three mixtures and the diesel fuel. The numerous emissions of the engine like Carbon monoxide (CO) and Hydro Carbon (HC) and Oxides of Nitrogen and smoke emissions released at this engine load for all the test fuels were measured and discussed here.