Characteristics of in-cylinder flow and mixture formation in a high-pressure spray-guided gasoline direct-injection optically accessible engine using PIV measurements and CFD

In this study, a spray-guided gasoline direct-injection 2-cylinder optically accessible engine was used to analyze the characteristics of the in-cylinder flow and mixture formation using PIV measurements and computational fluid dynamics (CFD; CONVERGE v2.4). The mean velocity, tumble ratio, turbulent kinetic energy, and tumble center were calculated to quantify the characteristics of the in-cylinder flow. Moreover, flow rotation intensity was defined to evaluate the in-cylinder flow depending on the crank angle. In the early stage of the intake stroke, the intake air flowed into the cylinder with high momentum and velocity. Subsequently, tumble flow was generated in the middle stage of the intake stroke, and weak in-cylinder flow occurred during the compression stroke owing to the dissipation of momentum. The fuel injection caused intensification of the in-cylinder flow, increasing the in-cylinder flow velocity, tumble ratio, and turbulent kinetic energy. Furthermore, mixture formation was affected by the end of the injection timing and its characteristics were classified into homogeneous, stratified, and mal-distribution mixtures, depending on the region to which the end of injection timing belonged.