Hydrocarbon (HC) emissions from direct injection (DI) diesel engines are mainly due to fuel injected and mixed beyond the lean combustion limit during ignition delay and fuel effusing from the nozzle sac at low pressure. In the present paper, the concept has been developed to provide an elegant model to predict the HC emissions considering slow burning. Eight medium speed engines differing widely in bores, strokes, rated speeds, and power were studied for applying the model. The engines were naturally aspirated, turbocharged, or turbocharged with intercooling. The model has been validated by collecting data on HC emission, and pressures in the cylinder and in the fuel injection system from the experimental engines. New coefficients for the correlation of HC with operating parameters were obtained and these are different from the values published earlier, based on single-engine experiments.

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