In order to clarify the mixture formation process of the direct injection gas engine, helium gas was injected into a quiescent atmosphere. The time- and space-resolved velocity, pressure and concentration distributions were measured in the free unsteady gas jet and in the wall impinging unsteady gas jet. They were also obtained for the unsteady gas jet impinging onto a projection on a wall to enhance mixture formation.
Empirical equations for the unsteady free jet were obtained, and the mixture formation mechanism of the wall impinging unsteady gas jet were clarified. The unsteady gas jet impinging onto the projection on a wall entrains much more air than the unsteady wall impinging jet.