Analysis of In-Cylinder Pressure Data in Two-Stroke Engines

Analysis of pressure traces from within the cylinder of IC engines is a long established technique, particularly in automotive applications. This approach allows burn rate data to be calculated from the shape of the pressure traces, providing direct combustion information to development engineers. With the proliferation of high-powered and low-cost computers, recording of pressure traces and analysis to give burn rates are now becoming standard measurements. However, this is still a complex technique, which is very open to error and prone to misinterpretation of results. This is particularly relevant for two-stroke engines where cyclic variations can be high and traces can be difficult to analyze.

This paper considers the standard techniques available for pressure trace analysis, highlighting the areas for problems and outlining good practice for reliable and accurate measurement. Results are presented for several different engines, ranging from high-performance competition engines to standard production applications. Cycle analysis is considered in detail with particular attention to accuracy of the burn rate data. The effects of various assumptions on burn events are closely scrutinized showing how easily these can assessed incorrectly. The importance of cyclic variations and different operating conditions on results is evaluated and recommendations presented. It is concluded that analysis of two-stroke data is much more problematic than analysis of similar data from conventional four-stroke engines.