Study of spray collapse phenomenon at flash boiling conditions using simultaneous front and side view imaging

Abstract

Flash boiling has become a topic of interest to researchers due to its potential of achieving good fuel atomization and negative influence on GDI engine emissions when spray collapses and spray-wall impingement exists. Under flash boiling conditions, the accompanying spray collapse phenomenon and plume interaction are not clearly elucidated. Simultaneous side view diffused back illumination (DBI) and front view Mie-scattering were implemented in this work to capture transient plume to plume interaction of iso-octane fuel spray from a 10 hole gasoline direct injection (GDI) injector at flash boiling conditions. Fuel temperature and ambient gas pressure were varied in a wide range to cover collapse, transitional and non-flashing regimes. Two new criteria named 'spray collapse percentage', defined based on the front view Mie-scattering technique and 'optical thickness' based on the side view DBI

Investigation of fuel volatility on the heat transfer dynamics on piston surface due to the pulsed spray impingement

“…Over the years, researches on the spray-wall interaction in GDI engine have been widely studied, but most focus on the atomization and its impinging morphology [12][13][14]. Only a few scholars have studied the dynamic heat transfer on piston surface from the fuel spray impinging the wall.…”

Study of spray structure under flash boiling conditions using 2phase-SLIPI

“…(Zhang et al, 2011) and (Xu et al, 2013) studied flash boiling spray cross-section along the injector axis by employing laser-induced fluorescence and Miescattering. However, due to the high spray optical thickness (Du et al, 2019) under flash boiling conditions, the strong multiple-scattering effect can not be neglected. As shown in Figure 2, interference from out-ofplane droplets cannot be distinguished due to multiple scattering effects.…”

“…In the front-view cross-section experiments, fuel temperature (90 • C) and injection pressure (100 bar) were fixed, and the ambient gas pressure was changed from 4 kP a to 19 kP a. The ratio (R p ) of ambient gas pressure to saturation vapor pressure ranged from 0.05 to 0.25, covering the collapsing regime and the transitional regime as identified in our previous work (Du et al, 2019) by side-view diffused back illumination (DBI) and front-view Mie scattering. The laser sheet swept from 2 mm to 40 mm downstream of the injector tip in steps of 1 mm.…”

Investigation of Split Flash Boiling Injection Schemes in a constant volume chamber and an optical GDI engine under lean combustion condition

“…Despite the positive performance observed, there are also concerns with regards to the implementation of flash boiling spray, for instance, spray targeting change (spray collapse). The mechanisms for spray collapses are still not completely clear, and many explanations have been provided to illustrate the said physical process [6][7][8][9]. There are also investigations indicating that spray collapse may increase the amount of fuel impingement on the plate [10].…”