This paper describes the requirement of the Numerical simulation of compression ignition diesel injection by the use of computer language and it also compares the performance parameter for the biodiesel such as jatropha and karanja. The Engine test was carried out in 512 Army base workshops for the experimental validations. It was carried out on SAJ dynamometer which was installed in Engine test house for testing of Engines. Performance parameters such as Brake power, Brake Torque, Mechanical efficiency, Thermal Efficiency, Pressure vs Crank angle and Heat release Rate vs Crank Angle was taken from the Engine test house. The Program code for the Performance parameter of Engine was developed in C++ language.Then the simulation was carried out. The simulation results were compared and analyzed with the experimental results. The final results was effective for compression ignition diesel injection. As we know that today's world is approaching towards computer simulated results, so the numerically simulated results will save time and money for engine testing house. Likewise we can approach towards numerical simulation for various types of Engines.