LAUSR

Abstract Flash boiling spray has been considered as a promising atomization scheme in improving fuel-air mixture and reduce spray impingement in internal combustion engine applications. Because of its distinctive breakup mechanism, the thermal process of flash boiling spray has not been fully illustrated, in which the fluctuation of flash boiling sprays is not sufficiently studied. This work utilized a high-speed imaging system to implement Schlieren and backlit measurement, with a micro-lens to capture the near-field characteristics and a regular lens for macroscopic studies. A practical two-hole gasoline direction injection fuel injector was used, and the fuel temperature and ambient pressure were varied to generate different superheat indices. Image processing methods were used to find the variation of the center of mass in the spray image to quantify the fluctuation of the spray. Near-field and far-field spray fluctuations were studied systematically for the first time. The results show that near-field fluctuation is enhanced by flash boiling sprays, while far-field fluctuation of flash boiling sprays is suppressed, thus yielding a more stable overall spray cycle-to-cycle variation. The detailed breakup process of flash boiling sprays in the near-field is analyzed. The near-field cone angle and its uncertainty under various boundary conditions are investigated as well. Furthermore, the results have the potential to optimize the problems related to engine stability.