Though a considerable amount of work has been carried out in the field of diesel engine combustion, it still poses a great challenge to researchers. While the purist's concern is to understand the true mechanism of the complex combustion process, the design engineer requires mathematical models which produce quick solutions. In this respect, the models proposed by previous researchers for determining the rate of heat release have been widely used for low rating diesel engines but their applications to highly pressure charged engines at low compression ratios are limited. A correlation for the rate of heat release for high power output diesels has been developed and tested experimentally for a range of operating conditions. The details of the model, the parameters on which it is based and the empirically deduced expressions are given in the paper.