AN EXPERIMENTAL STUDY ON MICROSCOPIC CHARACTERISTICS OF FLASH BOILING SPRAY WITH EXTENDED GLARE POINT VELOCIMETRY AND SIZING

摘要

Flash boiling spray can produce superior atomization and promote the fuel/air mixture formation for gasoline direct injection engines, which are further capable of reducing fuel consumption and harmful emissions. Most recent studies on flash boiling spray focus on the macroscopic characteristics. The microscopic characteristics (i.e., diameter and velocity of droplets) of flash boiling spray, which determine the combustion and exhaust emissions in internal combustion engines, are not well explored yet. In flash boiling spray, the high number density of droplets causes serious multiple scattering, low signal to noise ratio, and high deviation of droplet diameter, making most of the well-known techniques for measurements of microscopic characteristics of droplets unsuitable for flash boiling spray. Thus, the extended glare point velocimetry and sizing technique is improved and utilized for the measurement in this paper. The droplet size and velocity of flash boiling spray were obtained under various conditions of fuel temperature and ambient pressure for the first time. It was found that flash boiling has the effects of promoting the atomization process, reducing the local Sauter mean diameter (SMD), and narrowing the diameter distribution of the droplets. Additionally, the overall results demonstrate that flash boiling spray is an effective approach for producing fine droplets with uniform size.