Interaction between in-cylinder airflow and spray and its influence on flame development in a loop-scavenged two-stroke GDI engine

For loop-scavenged two-stroke gasoline engines, the direct injection (DI) mode offers the advantage of eliminating fuel short-circuit losses. However, the short mixing time and complex interaction between spray and flow often lead to poor mixing. Clarifying the flow-spray interaction is crucial for improving mixture quality. Therefore, the mutual influences between flow and spray are investigated, along with their effects on mixture formation, flame development, and combustion characteristics. Moreover, the air-fuel spatial distribution is evaluated by modifying the cylindrical partition method, in which Cartesian coordinate quadrants are introduced into the original framework. The relationship between the mixture distribution and the combustion is also analyzed. Results show that a strong tumble flow is formed under the loop-scavenged mode, with the maximum tumble ratio reaching 4.45, and gradually develops into a dual-vortex structure, where the spark plug is located at the junction of the two vortices. The flow-spray interaction consumes tumble energy to guide the spray, which is crucial for adequate mixing. Fuel entering flow-dead zones cannot be directly guided by the tumble flow, which worsens the mixing quality. After the spark plug ignites the mixture, the dual-vortex flow governs the flame propagation direction, causing the flame front to develop in an enveloping manner. A higher fuel concentration in the upstream region of the vortices accelerates the initial heat release rate (HRR), while a greater concentration downstream leads to more severe post-combustion. The modified cylindrical partition method provides a more comprehensive assessment of the fuel spatial distribution, enabling the qualitative prediction of HRR.