Three simplified thermodynamic methods for calculating combustive heat release are presented. The first method requires two pressure transducers for the data collection and is generally used for a divided chamber engine. The second method is a simple thermodynamic method for single chamber engines, and the third method calculates the pressure change due to combustion, and from this pressure calculates the combustive rate of heat release. The latter two methods require data from one pressure transducer. In this study all three methods have been applied to divided chamber and single chamber diesel engines.All three methods give information about the length and type of combustion. The dual transducer method gives a slightly longer period of combustion than the other two methods but the third method, the combustion pressure method, gives the same information about the beginning of combustion as the dual transducer method. All three methods give information about the influence of engine load, engine speed and fuel properties on combustive heat release.