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The increasing requirements imposed on diesel engine manufacturers have required the study of fuel injection system faults and the development of means to eliminate them. Until now, improved injection system characteristics have been obtained by experimental trial-and-error procedures. These procedures, however, have proved to be inconvenient, tedious, and have had limited success in eliminating system faults such as after-injection. This is mainly because the transient nature of the injection process requires a more thorough study of the system time-varying parameters. In this paper the residual transients which cause after-injection are analytically investigated. The control of these transients required specification of some system parameter. The rapidly varying nature of the system pressures and flows prevented the use of these variables as control parameters.

Possible mechanisms for smoke formation in the diesel engine are discussed. Emphasis is placed on the effects of some engine and fuel factors on carbon formation during the course of combustion, including cetane number, fuel volatility, air charge temperature, and after-injection. The tests were made with a single-cylinder, open chamber research engine, with three fuels, covering a wide range of inlet air temperatures and pressures. There is evidence that smoke intensity increased with increase in the cetaine number of the fuels with inlet air temperatures near atmospheric. Increase in the air charge temperature caused an increase in smoke intensity for volatile fuels and had an opposite effect on less volatile fuels for the open chamber engine used. The smoke intensity was found to increase dramatically with after-injection, with all other parameters kept constant. The concept that flame cooling is the main cause for smoke formation is examined.

Cycle-to-cycle variation of pressure is a common problem in all spark-ignition engines. To examine the suspected influence of mixture-motion on this variation, a study was performed in a constant volume cylindrical bomb in which a jet of propane-air mixture was directed at the initial flame kernel. The rate of pressure rise of the jet-influenced combustion was compared to the rate for combustion in a quiescent mixture. The flame area, obtained using a spark schlieren photographic technique, and the calculated combustion rate were correlated with the pressure rate. The major results were: the rate of pressure rise increased approximately linearly with mixture jet velocity; and the width of the mixture-jet had an effect on the rate of pressure rise. A jet profile width slightly greather than the spark-gap produced the highest rate of pressure rise.

The object of this research was to learn more about the effects of mixture motion upon ignition in spark ignited piston engines, and to determine how variations in mixture velocity alter the combustion process. To provide effective means for producing and measuring the mixture velocity, all tests were made in a constant volume bomb, using mixtures of propane and air. The effects of mixture motion on the lean spark ignition limit, rate of pressure rise, and burning time were determined for mixture ratios ranging from stoichiometric to the lean limit. The mixture pressures corresponded to those in Otto cycle engines at the time of spark occurrence. The results reveal that a mixture velocity of 50 fps, relative to the spark plug, requires an enrichment of 17% with respect to the stagnant lean limit. Increases in mixture velocity were found to greatly increase the rate of pressure rise during combustion. This effect was more pronounced for lean mixtures than for stoichiometric mixtures.