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A study of the influence of dilution, attained by air excess, upon the dynamic stage of combustion - the nucleus of a work producing cycle - in a diesel engine, is reported as a sequel of SAE 2000-01-0203. While the latter has been restricted to variation in dilution obtained by bleeding air compressed by the supercharger, here the scope of engine tests was expanded by incorporating an additional stage of compression. Besides revealing the mechanism of the dynamic stage, the paper demonstrates that its effectiveness is a linear function of the air excess coefficient, irrespectively how it is attained.

Presented here is a reportage on the OPEN DEBATE ON THE FUTURE OF COMBUSTION IN PISTON ENGINES, held at the '97 SAE Congress and Exposition, with commentaries and amendments.

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.