Experimental study on cavitation pattern and near-field spray characteristics of methanol in the scaled-up fuel injection nozzle

Methanol, as a clean fuel, particularly when synthesized from green electricity and recycled CO₂, has zero-carbon potential and is gaining increasing attention. However, due to methanol’s corrosivity and unique physical properties, designing high-pressure injectors for methanol engines presents numerous challenges. This study presents the first comprehensive analysis of methanol’s flow characteristics and near-field spray behavior using a scaled-up optical nozzle. Rounded and sharp nozzles were used to investigate vortex-induced string cavitation and geometry-induced sheet cavitation. By adjusting the needle lift and injection pressure, the onset and development of various cavitation patterns in methanol were studied. Additionally, comparative experiments between methanol and diesel were conducted to analyze the differences in flow and spray characteristics under different cavitation regimes, providing insights for the use of methanol as a replacement for diesel in engines. Experimental results show that methanol’s lower viscosity promotes the exsolution of dissolved gases, forming free gas bubbles that accumulate in the vortex core, thereby enhancing string cavitation. Under identical operating conditions, methanol exhibits a stronger tendency for string cavitation and greater cavitation intensity compared to diesel. In contrast, the difference in geometric-induced cavitation intensity between methanol and diesel is relatively small, attributed to methanol’s less sensitive response to variations in fuel properties.