Abstract: The increasingly stringent emission regulations and fuel consumption requirements have elevated the demands of internal combustion engines with higher fuel efficiency and lower emissions. It has been widely demonstrated that flash boiling spray can generate shorter and wider spray with improved atomization and evaporation to promote a better air-fuel mixing process. In this study, macroscopic (far-field) spray morphologies and primary breakup (near-field) characteristics of a two-hole gasoline direct injection injector are investigated under non-flash boiling and flash boiling conditions. High speed macroscopic and microscopic imaging was used to capture the overall spray structure and near-field characteristics, respectively. N-Hexane is used as the test fuel with the injection pressure ranging from 10 MPa up to 40 MPa. For sub-cooled liquid fuel sprays, increasing fuel pressure contributes to enhanced fuel atomization and evaporation. Evident collapses occurred under flare flash boiling conditions, and higher injection pressure weakened this phenomenon since the spray cone angle decreased due to a higher injection velocity.

Key words: flash boiling atomization, high-pressure injection, internal combustion engines, optical diagnostics

摘要： 日趋严格的排放法规和燃油消耗要求对内燃机燃油效率和更低排放提出了更高的需求。大量研究表明，闪急沸腾雾化可以产生更短、更宽的喷雾，具有改善雾化和蒸发的特性，促进更好的空燃混合过程。本研究在非闪沸和闪沸条件下，对两孔汽油直喷喷油器的宏观（远场）喷雾形态和初级破碎（近场）特性进行了研究。研究采用高速宏观和显微成像技术分别捕捉整体喷雾结构和近场特性，采用正己烷作为测试燃料，喷射压力范围从10 MPa到40 MPa。对于冷态液体燃料喷雾，增加燃油压力有助于提高燃油雾化和蒸发；而在闪沸条件下明显发生坍塌，而较高的喷射压力因喷射速度增加，导致喷雾锥角减小，抑制了这一现象发生。

关键词: 闪急沸腾雾化，高压喷射，内燃机，光学诊断