Experimental investigation on effect of gas/spray interactions on transient diesel spray behaviors

Abstract

The ever-increasing rail pressure in diesel engines may cause the injection induced shock waves. In the present study, different gases (N₂ and CO₂) were used as the ambient mediums in order to understand the effect of shock waves induced by the high-speed jets on the near-field spray penetration. The tests were carried out in an optically-accessible constant volume vessel and a single-hole diesel injector was used. The injection pressure (P_inj) ranged from 80 to 150 MPa and the ambient density (ρ_ambient) are 11.25, 22.52, and 33.81 kg/m³, respectively. Schlieren imaging was used to capture the shock waves ahead of the sprays with a frame speed of 100,000 fps and high-speed imaging was used to capture the spray penetration evolution with a frame speed of 300,000 fps in order to provide sufficient high temporal and spatial resolutions of the spray development. Shock waves can be observed under CO₂ atmosphere over all the tested conditions and almost invisible under N₂ atmosphere. The timings of occurrence and detachment of the shock waves are advanced with the increase in ρ_ambient, but less sensitivity to P_inj. The difference in penetration lengths for N₂ and CO₂ atmosphere are not consistent as P_inj and ρ_ambient varied, indicating the complicated role of shock waves in influencing the spray behaviors. Several mechanisms for the generation of shock waves were discussed, as well the physical meaning of the timing to the peak velocity of the spray tip with breakup time.