Tip-Wetting Film Analysis Using Laser-Induced Fluorescence for Multihole Gasoline Direct Injectors under Flash Boiling Conditions

It is desirable to reduce the amount of liquid fuel adhesion to combustor walls since the liquid film can usually cause pool fire and thus deteriorate combustion performance, that is, increase soot formation and particulate emissions. The recent advances of spark ignition engines have required that the amount of fuel film that remained on the injector tip should be minimized to comply with emission regulations. Gasoline atomization will be under flash boiling conditions during normal engine operations, but tip-wetting mechanisms for flash boiling atomization are still unclear and under investigation, especially for multihole fuel injectors. This investigation performed a laser-induced fluorescence study of the tip film using microscopic measurements. Two six-hole fuel injectors were studied, including a center-mounted one and a side-mounted one, respectively. The experiments were carried out under different thermodynamic boundary conditions, for instance, fuel temperature, ambient pressure, injection duration, and so forth. The film area and film intensity distribution at different injection timings were recorded and compared. The results showed that the ambient pressure has a strong influence on tip film formation. Furthermore, injector design is a parameter optimized for improved tip-wetting performance.