High Weber number fuel drop breakup during impact with heated walls

Abstract

Understanding high Weber number fuel drop breakup during impact with walls is critical to the prediction and optimization of fuel-air mixture distribution in internal combustion engines. In combustors, drops impact walls over a range of wall temperatures and drop velocities, resulting in complex outcomes. In this paper, diesel and methanol drops were tested under wall temperatures ranging from 27 to 400 °C with Weber numbers extending up to 2000. The drop impact events were recorded using high-speed imaging, allowing the identification of impact outcomes and analysis of secondary droplets. Initially, the basic dynamic behaviors of drops impacting on the wall at high Weber numbers were discussed, including the edge splashing that occurred at the initial moment and the subsequent phase-change characteristics. The results show that the effect of wall temperature on the critical Weber number for splashing differs between the two types of fuel. As the wall temperature rises, four heat transfer phenomena are observed: film evaporation, nucleate boiling, transition boiling, and film boiling. Subsequently, the disintegration behavior of drops impacting walls above the fuel’s dynamic Leidenfrost temperature was investigated, with statistical analyses of both impact residence time and the normalized Sauter mean diameter of secondary droplets. The mechanism of liquid film levitation and its disintegration into secondary droplets depend on the vaporization of the wetted area of the spreading liquid film. This article enhances the understanding of drop impact dynamics on heated surfaces, which can provide a theoretical basis and data support for the development of methanol/diesel dual-fuel direct injection engines.