Visualization of Flow/Flame Interaction in a Constant-Volume Combustion Chamber

A visualization study using shadowgraphy was performed in an optically-accessible, cylindrical constant-volume combustion chamber to identify the mechanism of flow/flame interaction in spark-ignited, lean propane-air mixtures. The effect of the flow on flame initiation and propagation was examined by varying the pre-ignition mean flow and turbulence within a range typical of modern four-valve spark-ignition (SI) engines, as well as the spark plug orientation relative to the mean flow. The initial flame development was quantified in terms of 2-D images which provided information about the projected flame area and the displacement of the flame center as a function of flow conditions, time from the spark initiation and spark plug orientation.

The results showed that high mean flow velocities and turbulence levels can shorten combustion duration in lean mixtures and that the positioning of the ground electrode can have an important effect on the initial kernel formation. Under these flow conditions which are typical of advanced our-valve engines, the optimum position of the ground electrode was found to be downstream of the mean flow but its effect on flame development was reduced at lower velocities typical of conventional two-valve engines.