The internal combustion engines are generally a major source of air pollution.However the spark ignition engines are recognized by their carbon monoxide andunburned hydrocarbon emission. One of the methods used to reduce the emission ofthese pollutants is the blending of hydrogen with the gasoline fuel, either on a massbasis or on energy replacement basis. The present research study is devoted to concernwith developing a numerical model to predict the effect of hydrogen blending (based on energy replacement) on the emitted concentrate of carbon and nitrogen oxides and the temporal and local variation of cylinder temperature. It is found that hydrogen blending improves combustion process by increasingthe flame propagation speed and hence increasing maximum cylinder temperature. Thetiming of maximum cylinder temperature is also advanced due to hydrogen blending. It is also found that the hydrogen blending reduces CO and CO concentrationsand increases NO concentrations. It is found that when the hydrogen blending ratioexceeds 20% the engine performance is deteriorated. x2