Abstract
In the power cycle or thermodynamic cycle of a spark ignited engine the processes in the combustion chamber (compression, combustion, expansion) are simulated from the inlet valve closing till exhaust valve opening.
In the literature different models of the combustion are presented. The used model, based on the work by Tabaczynski, is explained. Special attention is necessary for the laminar flame speed. Formulas are given for different gaseous fuels (methane, propane, hydrogen).
For validation of the simulation models a comparison with experiments is necessary. The pressure-time history in the combustion chamber is one of the main important elements. A first evaluation of a simulation model is a comparison of the calculated and measured pressure diagram. Of course the measured pressure signal has to be correct. The absolute pressure level, the location of the top dead centre, a correct compression ratio can influence the pressure values. Log p by log V diagrams give indication of the accuracy of the measurements. But the mayor effect limiting the accuracy of in-cylinder pressure measurements is the sensitivity to the thermal loading effects of the intermittent combustion process (transducer response to thermal shock). Different methods are presented for evaluating the effect of this thermal shock on the measured pressure signal.
A comparison is made of the measured and calculated pressure diagrams for different fuels (methane, propane) in a one cylinder S.I. engine.