Flow and Combustion in a Four-Valve, Spark-Ignition Optical Engine

The in-cylinder flow during induction and compression in the pentroof chamber of a four-valve, single-cylinder, spark-ignition optical engine was quantified by LDV and correlated with combustion development especially under lean mixture conditions. The tumble-generating capacity of the cylinder head was first characterised by a tumble adaptor under steady flow conditions and, subsequently, enhanced by two sleeves introduced into the intake ports which generated a stronger tumbling motion. LDV measurements of the in-cylinder flow confirmed the correlation between the stronger tumble during induction and the higher convective velocity and turbulence levels near the spark gap at the time of ignition, which resulted in faster combustion rates and more stable combustion under lean mixture conditions, Combustion development was monitored by a pressure transducer and the flame propagation was visualized by a UV intensified CCD camera which allowed comparisons to be made of the initial flame images generated by the sleeved and non-sleeved port configurations.