Abstract: A fuel injection system comprises a cam, an injection pump, a delivery valve, an injection pipe, a nozzle holder, and a nozzle. The fuel oil passage in the nozzle holder is reduced in diameter as compared with the inside diameter of the injection pipe, with the ratio F3/F1, or the ratio of the effective flow-passage cross sectional area F3 of the fuel oil passage to that F1 of the injection pipe, ranging from about 0.5 to 0.15, over the length l of the fuel oil passage which is 90 to 30 times the inside diameter of the injection pipe, so that the fluctuation of fuel pressure in the injection pipe is converted to kinetic energy thereby to control abnormalities of fuel injection.

Abstract: A combustion chamber of a direct fuel injection type diesel engine has a cavity at the crown of a piston, within which a swirl occurs and onto which fuel is injected from a multi-orifice fuel injection nozzle toward a inner side wall of the cavity. The cavity is regular polygonal in horizontal cross-section. The inner side wall is so inclined inwardly of the cavity as to provide a restriction at the opening of the cavity. The inner side wall and the injection nozzle are so arranged that the fuel jet is distributed to the downstream side of the swirl after being impinged the inner side wall, whereby the distribution of the injected fuel is improved to provide ideal mixture in the cavity, resulting in reduced amount of pollutant emissions.