The sole purpose of combustion in a piston engine is to generate pressure in order to push the piston and produce work.
Pressure diagnostics provides means to deduce data on the execution of the exothermic process of combustion in an engine cylinder from a measured pressure profile. Its task is that of an inverse problem: evaluation of the mechanism of a system from its measured output. The dynamic properties of the closed system in a piston engine are expressed in terms of a
dynamic stage - the transition between the processes of compression and expansion. All the phenomena taking place in its course were analyzed in the predecessor of this paper, SAE
2002-01-0998. Here, on one hand, its concept is restricted to the purely dynamic effects, while on the other, the transformation of system components, taking place in the course of the exothermic chemical reaction to raise pressure, are taken into account by the
exothermic stage. Moreover, the scope of the analysis is extended to cover the whole operation of a closed system, from the moment when the inlet valve is closed to that when the exhaust valve is opened. Both stages occur, of course, concurrently, starting at the same instant, whereas the exothermic stage may terminate somewhat later than the dynamic stage. Their duration is relatively short, taking typically somewhere around one tenth of a revolution. Provided thus is a model of a closed system in a piston engine to serve as basis for design of micro-electronic control system for its operation.