Application of conditional sampling to the study of cyclic variability in a spark ignition engine

Conditional sampling of cylinder pressure data is used to investigate cyclic variability in a premixed charge, spark ignited engine operating under fuel lean conditions. Unlike straight ensemble averaging of pressure data, conditional sampling applies a set of constraints to the pressure data such that like combustion events can be identified and grouped together. Ensemble averaging of pressure data from an engine that exhibits significant cycle to cycle variation is shown to produce a mean pressure history that is not representative of the combustion process. Conditional sampling provides a means of identifying and analyzing the different groups of pressure histories and therefore the different types of combustion processes that occur in an engine that exhibits cyclic variability (a).