FLAME IMAGING STUDIES OF COMBUSTION COMPLETION IN A SI 4-STROKE ENGINE

Direct flame imaging through a transparent cylinder liner has been use d to study the final phase of lean combustion in a spark-ignition four -stroke optical engine. Two image-intensified video cameras record ins tantaneous lean flame radiation at two preset times to examine the str ucture and development of the flame as it approaches the wall to compl ete the flame travel. There is one peripheral spark plug on the side o f the cylinder opposite the cameras, so that combustion completion ima ges capture only one flame thickness and provide a unique map of flame intensity. These flames have highly structured intensity patterns on all of the scales associated with in-cylinder turbulence. Although the large-scale pattern of burning results from the flame shape early in the cycle, intensity variations of the flame images indicate that the burning rate varies significantly over the flame area on both large an d small scales, indicating that the flame front is not a uniformly pro pagating sheet.