In the vein of the paper we presented at the last SAE Congress (SAE 970538), the evolution of the exothermic process of combustion (an event referred to popularly as ‘heat release’) in an engine is considered from the point of view of the utilization of fuel. Its consumption in the course of this process is expressed in a functional form, akin to that engendered for mathematical description of life. There are a number of such functions recorded in the literature and their salient features are revealed. Of particular relevance to fuel utilization in engines is a reverse form of the Vibe function (known in the English engine literature as the ‘Wiebe function’), which we call the fuel life function. Its parameters can be derived from numerical modeling of combustion in engines or from reduction of indicator diagram data. It can serve thus, on one hand, as a most concise means to confront the most vital results of numerical computations with experimental data, and, on the other, as the essential feedback for electronic control of the mechanism whereby the exothermic process of combustion is executed. Knowledge of this function plays then crucial role in extracting signal from noise that is inevitably embodied in the records of the sensing element, such as a pressure transducer, on which the operation of the control system is based.