Studies on the Penetration of Fuel Spray of Diesel Engine

Abstract

Regarding the penetrating distance of fuel spray of Diesel engine, the old theory dealing with the motion of a fuel droplet in still air is recognized not to coincide with the actual phenomenon because of extremely small size of atomized fuel droplets and very high density of gas in cylinder. In this paper, the characteristics of spray penetration are discussed from the viewpoint of momentum theory based on the idea that air induced into fuel jet stream makes a kind of mixed gas together with fuel droplets. As the results of a series of experiments, the following conclusions have been reached : (1) Theory of momentum for the spray penetration holds good, and effects of elements which control the penetrating distance can be expressed by relatively simple relations consisting of non-dimensional numbers. (2) The distance of spray penetration is proportional to square roots of each of nozzle orifice diameter, injection velocity and time after injection begins, and also is influenced by density of gas in cylinder, but the effect of viscosity of gas on the penetrating distance which remained uncertain is very little. (3) Excess air coefficient of spray mixture increases in proportion to penetrating distance, and the ratio between cylinder bore and such a penetrating distance that excess air coefficient becomes one (1) gives a base of similarity of fuel spray distribution in cylinder. In the design, accordingly, nozzle orifice diameter may be determined only in proportion to cylinder bore.