The influence of ambient pressure on the spray structure of methanol injected from outward-opening injector

The spray characteristics of methanol are critical in the formation of the air-fuel mixture and the combustion process in internal combustion engines. This study employs high-speed camera on an optical measurement platform within a constant-volume chamber (CVC) to investigate the effects of ambient pressure on the spray behavior of methanol from an outward-opening injector. The spray was captured from both side and bottom views to analyze in penetration length, spray velocity, spray area, and fluctuations in spray contour. For the side view, the spray front fluctuation, penetration length, spray velocity, and spray area all decrease as ambient pressure increases. The spray angle exhibits notable sensitivity to ambient pressure. In the bottom view, both the spray area and spray profile fluctuations decrease with increasing ambient pressure. However, in the mid-to-late stages of spray development, changes in the external contour of the spray are observed. To quantify these effects, a relationship between the dimensionless number and ambient pressure is established, and under this dimensionless scaling, both the diffusion distance and diffusion velocity of the spray decrease as ambient pressure increases. This study provides useful perspectives for the optimization of methanol engine mixture formation, spark plug placement, and combustion chamber design.