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The concept of JPIC (Jet Plume Injection and Combustion) is introduced as a radical refinement of DISC (Direct Injection Stratified Charge). The system for its implementation consists of a fuel injector and a PJC (Pulsed Jet Combustion) generator (described in our previous papers) connected in series via a check valve. In operation, rich air-fuel mixture is admitted thereby first to a lean charge in the cylinder, forming a turbulent jet plume, and, thereupon, the process of combustion is executed using a pulsed jet of combustion products created upon ignition, by means of a conventional spark discharge, of the mixture remaining in the cavity of the PJC generator. Charge stratification thus obtained affects not only chemical composition, but also the scale and intensity of turbulence. The latter is, under such circumstances, associated with a significant amount of entrainment due to the large scale vortex structure of the turbulent plume.

In the course of our studies on pulsed jet combustion (PJC) a series of tests were carried out to determine the performance of multi-stream systems. This included multi-jet efflux, as well as dual-generator aggregates. The essential performance indicator of a PJC system is the pressure transducer record, yielding, in particular, data on the rise time and amplitude of the pressure pulse, as well as the rate of pressure rise. Concomitantly with pressure measurements, a sequence of schlieren records were obtained to reveal the salient features of the fluid mechanical phenomena of the PJC process. Elucidated thereby are the effects of entrainment induced by large scale vortex structures of turbulent jet plumes, and their decisive role in governing the process of combustion, as influenced by their particular configuration.

The methodology put forth in this paper stems from the premise that the primary reason for the generation of major pollutants by diesel engines, particulates and nitric oxides, is associated with over-reliance upon diffusion flames to carry out the process of combustion. Specific means are, therefore, proposed to inhibit their formation. This consists of refinements involving the use of either hollow cone spray injectors or air blast atomizers. Concomitantly, the process of combustion is staged by either regulating the rate of injection or employing a number of consecutively activated injectors per cylinder under a microprocessor command, while regions of high temperature peaks are distributed throughout the charge and kept at a relatively low level by exploiting the large scale vortex structure of turbulent pulsed jets combined with residual gas recirculation.

Pulsed Jet Combustion (PJC) is introduced here as a key element for engines where the progress of combustion is interactively controlled by a microprocessor system. Practical realization of PJC presented here involves the use of an 18 mm plug containing a cavity, where a rich mixture is ignited by a conventional spark discharge, closed by a tip with a suitable orifice to form the effluent stream. Its performance is determined by tests carried out in a constant volume vessel, simulating the enclosure of a CFR engine at 60 CAD with compression ratio of 7:1, using propane/air mixtures at equivalence ratios of an order of 0.6, in comparison to that of a flame traversing the charge, a so-called FTC mode, upon ignition by standard spark discharge under identical geometrical and initial thermochemical conditions. The results demonstrate the superiority of PJC for executing the exothermic process of combustion in a lean burn engine.

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.

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.

The paper reports a preliminary study of jets of active radicals used as igniters for lean mixtures. The jets were generated either by combustion or by electric discharge. Experiments were performed in a cylindrical steel vessel, 9 cm in diameter and 9 cm long, filled initially with either air or an ultra-lean (equivalence ratio: 0.5) methane-air mixture at atmospheric pressure and room temperature. Observations were made by schlieren photography, using a sub-microsecond spark discharge in air as a point light source. The gasdynamic properties of the jets were shown to be primarily governed by their initial velocity, while the particular process by which they were formed played, in this respect, a secondary role. The jets of radicals invariably appeared as turbulent plumes which were embedded in blast waves headed by hemispherical shock fronts.