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The theoretical relationship between engine air consumption and exhaust back pressure is derived for an idealized, 4-stroke-cycle engine inlet process, and compared to results obtained by testing a typical automobile engine. The exhaust back pressure of a 1971 Ford 351-W, V8 engine was varied 0.5-1.5 atm, under a wide range of engine speeds and loads. The results show that engine air consumption responds to variation of the ratio of absolute exhaust back pressure to absolute inlet manifold pressure in a manner approximating that indicated by theory, with a strong dependence on engine speed. These data can be useful in the design of speed-density fuel injection systems for automobiles. Data are also presented concerning the effect of exhaust back pressure on performance and exhaust emissions. Increase in exhaust back pressure decreases nitric oxide, due to the increased exhaust gas remaining in the cylinder, as has also been demonstrated by others.

A correlation between the ignition delay, based on the start of pressure rise due to combustion, and the mean air charge temperature has been obtained for diesel, “CITE,” and gasoline fuels. The experimental work was done on a single cylinder open combustion chamber research engine. The intake air temperature was varied over a wide range from atmospheric to about 750 F. The experimental data indicated that the best correlation of the ignition delay and the reciprocal of the absolute temperature is of an exponential form. The apparent activation energy for the three fuels was found to have a straight line relationship with the cetane number of the fuel.

The ignition delay in diesel combustion has been studied in a turbulent chamber engine. The criteria used to define the end of this period are the pressure rise and illumination due to combustion. The pressure rise delay is generally shorter and more reproducible than the illumination delay. The effect of the following factors on the ignition delay were studied: cylinder pressure, fuel/air ratio, fuel injection pressure, cooling water temperature, and engine speed. Data concerning the effect of cylinder pressure on the pressure rise delay period, at constant air temperature, were correlated and compared with previous experimental results. The analysis indicated that the pressure rise delay is affected by physical and chemical factors as well as thermodynamic parameters that control the several forms of energy during the delay period.