A visualization study on flow behavior of ethanol-assisted hydrocarbon fuel endothermic reactions under supercritical pressure

The utilization of ethanol-assisted hydrocarbon fuel for the cooling of combustor walls in scramjet engines has recently garnered significant attention from researchers. However, under high-temperature and high-pressure conditions, blended fuel undergoes multiple complex processes, including phase transitions, chemical reactions, and supercritical state transformations, which significantly influence the heat absorption capacity. In this study, the catalytic cracking process of ethanol-assisted hydrocarbon fuel was investigated through visualization experiments, and the flow behaviors of blended fuel under different stages were captured by high-speed camera. The results show that the cooling process are categorized into three stages according to different physical states transition of blended fuel. Ethanol phase transition occurs in first stage. Differences in viscosity and surface tension at different pressures result in variations of multiphase flow patterns. The bubbly flow I, bubbly/slug flow I, churn flow I, and annular flow I are defined to describe the flow patterns of blended fuel at standard atmospheric pressure. Similarly, bubbly flow II, bubbly/slug flow II, and annular flow II are defined to describe flow patterns at 2.5 MPa. The second stage is characterized by the chemical reactions of ethanol. Once liquid ethanol has completely vaporized into ethanol vapor, the appearance of refractive points with varying brightness indicates the generation of small molecular gases resulting from the ethanol cracking. The phase interface between n-decane in the supercritical state and gaseous ethanol is fused in the third stage. This study is of significance in revealing the multiphase flow pattern distribution of ethanol -assisted hydrocarbon fuel.