Experimental Study on Mixture Formation and Ignition Processes of Spray Injected by Hole-Type Nozzle for DISI Engine

The purpose of this study is to investigate the spray characteristics and ignition stability of gasoline sprays injected from a hole-type nozzle. Using a single-hole VCO (Valve-Covered-Orifice) nozzle, the spray characteristics were studied with LAS (Laser Absorption Scattering) technique, and then flame propagation and ignition stability were investigated inside a high temperature high pressure constant volume vessel using a high speed video camera. The spatial ignition stability of the spray at different locations was tested by adjusting the position of the electrodes. By adjusting the ignition timings, the stable ignition windows for 3 determined locations where the ignition stability was high at a fixed ignition timing were studied. The flame propagation process was examined using high speed shadowgraph method. Experimental results show that when the ignition points are located on the spray axis, the ignition probability is low. When the distance between the ignition point and the spray axis increases, the ignition probability increases and then decreases. High ignition probability distribution did not coincide with vapor phase equivalence ratio distribution. Too dense liquid phase (droplets) will decrease ignition probability, while proper liquid phase density can improve the ignition stability. When the ignition point is located at downstream of the spray, the high ignition probability range becomes a little wider, while the ignition timing should be retarded. After ignition, the flame propagates mainly to the downstream and expands to the radial direction of the spray.