A new computer code has been developed to predict the performance and emissions parameters of a compression ignition direct injection (CIDI) diesel engine. This code comprises both thermodynamics and dynamical modeling of processes occurring during closed cycle, the time span in which both intake and exhaust valves are closed. The thermodynamics modeling includes a two zone combustion model dividing the cylinder charge into a non-burning zone of air surrounding the fuel spray jets issuing from injector nozzle holes and another homogenous zone in which fuel is supplied continuously from injector and burned with entrained air from the air zone. For spray calculations the main related parameters such as break-up point, spray tip penetration, spray cone angle and air entrainment into the spray are carefully modeled. Furthermore, compression stroke, heat transfer, ignition delay, rate of combustion, pollutants formation and expansion stroke are considered in the thermodynamic modeling section. The amount of nitric oxide (NO) in exhaust gases is calculated by a chemical kinetics model and the soot formation is modeled by considering both the formation and oxidation processes in net soot formation. Finally, a dynamical analysis has been done on the total system of engine and load including special sub-models to model conservation of energy in the crankshaft and inertia forces. There are good correlation between simulation and experimental results.