Imaging of Lean Premixed Flames in Spark-Ignition Engines

Two optical single-cylinder spark-ignition engines equipped with two- and four-valve cylinder heads were used to examine the flow and flame interaction under lean mixture conditions. Images of the developing flame under quiescent, swirl, low tumble and high tumble flow conditions corresponding to a wide range of mean velocity and turbulence levels around the time of ignition were obtained with an image-intensified CCD camera using the light radiated by the flame and the flow in the vicinity of the spark plug was quantified by laser Doppler velocimetry. In the case of the tumbling flow, the flame images were software-processed to allow estimation of the total flame area, the displacement of its centre as a function of crank angle and their correlation with the cylinder pressure.