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An experimental study of the induction period for ignition of fuel sprays with particular consideration of its dependence upon temperature and pressure is reported. Emphasis in the study was placed upon conditions of thermodynamically supercritical state for the fuel. The tests were performed in a stainless steel cylindrical chamber located in an oven, both provided with quartz windows for optical insight in axial direction of the radially injected spray. Spray formation and ignition were observed by high-speed schlieren cinematography concomitantly with measurements of chamber pressure and the displacement of the injector needle. The induction period was evaluated as the time interval between the rise in the displacement transducer signal and the instant when pressure attained three percent of its peak value.

Formation of pulsed plasma jets, or puffs, was examined using several visualization techniques. Self-light streak photography was first employed to record salient global features of the development and structure of the jet. This provided information on the motion of the luminous gas particles in its core, revealing that plasma jets can have two distinct modes, being either totally subsonic or embodying a supersonic efflux manifested by the recorded streaks of Mach discs. At a fixed power pulse of electrical energy discharge in the plenum chamber, the outcome depends on the constriction imposed by an orifice at its outlet. Whereas the difference between the two types of jets was quite small, penetration in the subsonic case was found to be definitely larger than in supersonic.

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.