.ABSTRACTThe 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. The results we obtained demonstrate the beneficial influence on its reduction attainable by lean combustion.