Wall-Impingement Characteristics and Near-Wall Flow Dynamics of Diesel/Methanol Dual-Fuel Sprays under High Pressure

The adoption of diesel/methanol dual direct injection has emerged as an effective strategy for reducing greenhouse gas and pollutant emissions in marine engines. However, dual-fuel sprays in the cylinder exhibit complex interaction, mixing, and wall-impingement behaviors. The high in-cylinder ambient pressure further intensifies liquid-wall and inter-spray dynamics. To clarify these effects, this study examines the wall-impingement characteristics of diesel/methanol dual-fuel sprays in a high-pressure constant-volume chamber. Shadowgraph imaging and quantitative analysis were used to resolve the evolution of spreading radius and uplift height under varying impingement distances and angles. Larger impingement distances enhance pre-impingement vapor formation and post-impact atomization, while reducing early-stage spreading and uplift. Increasing the impingement angle enhances the wall-guided deflection of the spray and shifts the gas-phase region from the methanol side toward the frontal vortex. Variations in impingement distance modify the balance between spray-wall and inter-spray interaction. In contrast, the impingement angle exerts a notably stronger influence on dual-fuel spray dynamics than methanol alone.