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The dynamic stage of combustion - the intrinsic process for pushing the compression polytrope away from the expansion polytrope to generate the indicator work output of a piston engine - was studied to reveal the influence of the air/fuel ratio on the effectiveness with which the fuel was utilized. The results of tests carried out for this purpose, using a 12 liter diesel engine, were reported last year [SAE 1999-01-0517]. Presented here is an analytic interpretation of the data obtained for part-load operation at 1200 and 1800 rpm. A solution is thus provided for an inverse problem: deduction of information on the dynamic features of the exothermic process of combustion from measured pressure record. Provided thereby, in particular, is information on the effectiveness with which fuel was utilized in the course of this process - a parameter reflecting the effect of energy lost by heat transfer to the walls.

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.

The refinement of heat release analysis stems from the recognition that a combustion system is intrinsically non-linear. Thus, as appropriate for such an entity, its properties are expressed in terms of a thermochemical phase (or state) space, of which the thermodynamic aspects are exposed on a so-called Le Chatelier diagram, providing the fundamental background for the development of micro-electronic control to attain the most effective utilization of fuel. Implementation of this method of approach is illustrated by the analysis of the exothermic process taking place in two typical internal combustion engines, spark-ignition and diesel.

The concept of the paper stems from the premise that the process of “heat release” in engines involves in essence the evolution and deposition of exothermic energy generated by combustion-events that can be governed promptly by a feedback, adaptive micro-electronic control system. The key to its realization is the principle of DISC (Direct Injection Stratified Charge) engine, implemented by a multi-jet system. The background and the salient features of such a system, referred to as a CCE (Controlled Combustion Engine), have been described in a companion paper (SAE 951961). Presented here are fundamental aspects of the model of the exothermic process and the intrinsic properties of its control system.

In order to advance the technology of combustion in engines, the execution of heat release, or, more precisely, the evolution of exothermic energy, should be treated as a manufacturing process: at the input are the reactants, the cylinder charge comprised of compressed air mixed with fuel and recirculated exhaust or, better, residual gas, and at the output are products, among which the most noteworthy are useful work and harmful pollutants. The conversion of reactants into products is carried out by the exothermic process of the oxidation of a hydrocarbon fuel. It is then the execution of this process that warrants particular attention, so that in the engine of the future it would be modulated by an electronic control system. Described in the paper is a rational method for engineering implementation of this concept, associated with the exploitation of the best that modern computer and control technologies have to offer.