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Square piston engine simulator experiments reveal flame kernel development and flame propagation for single event combustion. High speed color and black and white schlieren cinematography provide time and space resolved records for the combustion of intake manifold injected iso-pentane with air at a compression ratio of 6.6 to 1, engine speed of 900 rpm, spark and plasma ignition, and flat and squish pistons. Digitized schlieren records provide visual and quantitative data on the evolution of the volumetric burning rate. The numerical analysis is based on the zero Mach number model, a simplification based on the concept that the local speed of sound, as a consequence of the relatively high temperature, is practically infinite in comparison with the flow velocity. The results provide information on the propagation of the flame front and the velocity vector field that is first generated by the flame and later causes its deformation.

A square-piston engine simulator used at Berkeley to study both spark-ignited and diesel engine processes is described. The square piston configuration provides optical access to fluid mechanical and combustion processes through two fiat quartz windows used as cylinder walls. Results from three previous research projects are reviewed to illustrate the engine's capabilities. Since these studies, we developed and used a color schlieren cinematography system to record in-cylinder processes. Color schlieren movies of both spark-ignition and diesel combustion reveal the essential fluid mechanical and combustion features within the engine. For these movies, we redesigned the diesel fuel system and installed a new liquid fuel injection system for spark-ignited operation. By preventing fuel and soot condensation on the windows, these new fuel systems improved the quality of our Schlieren images.