Correlation of Flame Propagation and In-Cylinder Pressure in a Spark Ignited Engine

Flame propagation results from individual combustion cycles obtained with either the multi-optical fiber technique or with high-speed schlieren cinematography (both combined with the ion current technique) are presented and discussed for different engine operating conditions. The flame propagation results are correlated with results from in-cylinder pressure measurements, which are performed simultaneously with the flame propagation measurements. It is shown that combustion cycles which have similar in-cylinder pressure traces often show different flame propagation behavior. Therefore, conditional sampling methods which use only in-cylinder pressure traces as a criterion to select individual combustion cycles are not very accurate. Additionally, flame propagation behavior must be considered when analyzing combustion cycles.