Experimental Investigation of the Effects of Ambient Pressure and Temperature on Spray Characteristics of Methanol Air-Assisted Injection

To address the energy crisis and environmental pollution, the development of low-carbon or zero-carbon fuels has become an important research direction in the field of internal combustion engines. Methanol, as a low-carbon fuel with broad application prospects, shows good potential when used in air-assisted injection systems (AAIS). To achieve efficient and clean combustion, it is necessary to conduct in-depth studies on its spray characteristics. Accordingly, this study employs a constant-volume chamber (CVC) optical testing platform to investigate the effects of ambient pressure and temperature on the macroscopic characteristics of methanol air-assisted spray. High-speed backlit imaging technology was utilized to capture the spray morphology, penetration distance, width, and cone angle. The results show that, under high injection pressure, the sharp drop in temperature and pressure in the far-field spray region causes the spray to collapse and the width to reduce, creating a second peak in width near the spray tip. As ambient pressure increases, the methanol spray morphology transforms from a spindle shape to an anchor shape. With increasing ambient pressure, the spray cone angles of methanol and aviation kerosene exhibit opposite trends. Under the same ambient pressure, the cone angle of aviation kerosene is larger than that of methanol. Under identical conditions, methanol atomizes more easily and effectively than aviation kerosene. This suggests that methanol can mix and combust more effectively with air in the engine than aviation kerosene. This study investigates the spray characteristics of methanol under air-assisted injection, with the aim of enhancing its atomization quality and mixture uniformity. By systematically analyzing the mechanisms through which ambient temperature and pressure affect its spray characteristics, this study deepens the understanding of air-assisted atomization mechanisms and provides both theoretical and experimental support for optimizing the atomization of alternative fuels.