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This paper presents a fundamental study on the mixture formation process in a direct injection stratified charge (DISC) engine. Helium is injected intermittently and impinged on a wall to clarify the unsteady wall impinging jet. Instantaneous concentration and pressure distributions are obtained by using fast-response concentration and pressure probes, respectively. The jet tip rolls up after the impingement on the wall, consequently the volume of an unsteady wall impinging jet becomes larger than that of a steady wall impinging jet. Wall impingement increases air entrainment, which could promote faster combustion in DISC engines.

The mixture formation process plays an important role on combustion in the direct injection stratified charge engine. A new mixture formation technology named OSKA has been developed for direct injection stratified charge SI engines. The OSKA process has the potential to yield better fuel economy and cleaner emissions. However, the mixture formation process has not been clarified completely, and detailed studies of the mixture formation process with the OSKA technology are needed. As a fundamental study on the OSKA mixture formation, time and space resolved distribution is obtained on concentration and on pressure in the unsteady gas jet, which discharges with constant injection pressure into a quiescent atmosphere and impinges on a projection placed on a wall.

The mixing process of fuel with the surroundings are necessary to verify combustion process and then to make a combustion model. In this study, a single shot of diesel spray is injected through either a constant pressure injection system or bypass type injection system which has the same characteristics as the one of an actual engine. Measurement are made on the gas velocity distribution around the spray and its time history using a hot wire anemometer. The gas flow direction is determined by the smoke tracer method. In this investigation the axial and radial distributions of entrainment air are determined, and also their time histories are observed. Radial distribution of the entrainment velocity can be shown ū(t) = CrA and the entrainment coefficient αe is estimated to be a volume between 0.2 ∼ 0.3.

This paper presents the experimental study on the characteristics of a transient gas jet. Helium was injected instantaneously into a quiescent atmosphere with constant pressure. The distributions of instantaneous static pressure, radial and axial velocities and concentration at measuring points in the jet, which is obtained by the statistical data processing, are discussed to explain a transient mixture formation in the jet. The analogy between this jet and a diesel spray as for this mixture formation are also discussed by using these results.