Analyzing the Cycle-to-Cycle Variations of Vapor and Liquid Phases of Evaporating SIDI Sprays via Proper Orthogonal Decomposition Technique

In this study, the spray characteristics of three multi-hole injectors, namely a 2-hole injector, a 4-hole injector, and a 6-hole injector were investigated under various superheated conditions. Fuel pressure was kept constant at 10MPa. Fuel temperature varied from 20°C to 85°C, and back pressure ranged from 20kPa to 100kPa. Both liquid phase and vapor phase of the spray were investigated via laser induced exciplex fluorescence technique. Proper orthogonal decomposition technique was applied to analyze the cycle-to-cycle variations of the liquid phase and vapor phase of the fuel spray separately. Effects of fuel temperature, back pressure, superheated degree and nozzle number on spray variation were revealed. It shows that higher fuel temperature led to a more stable spray due to enhanced evaporation which eliminated the fluctuating structures along the spray periphery. Higher back pressure led to higher spray variation due to increased interaction between spray and ambient air. In addition, flash boiling sprays were more stable than non-flash boiling sprays. The spray variation of the 6-hole injector was the smallest under all test conditions. It was because a symmetrical hole distribution contributed to a more stable spray structure. Asymmetrically distributed holes would lead to larger spray variation under transition conditions due to more pronounced ambient air effects.