UNSTEADY SPRAYS BY A PINTLE INJECTOR

Measurements of size-velocity correlations and mean diameters have been obtained with a phase-Doppler velocimeter in the space and time domains of an unsteady spray injected by a pintle petrol injector into an inert atmospheric pressure environment of a test chamber. The injector was operated at a constant injection pressure of 3 bar, and with a frequency of 10 Hz, while the injection duration was varied from 2.5 to 7 ms. The environment was saturated with petrol vapour, so that petrol evaporation was negligible during the experiment. A hollow cone spray with 10° half-angle was observed with the larger droplets outside the centreline and transporting most of the fuel flowrate. Two low velocity transitional periods, corresponding to the opening and the closing of the pintle, were observed with a higher nearly constant velocity period between the two, during which the spray was in a steady state. All droplet sizes moved with similar velocities close to the nozzle, but further downstream in the time and space domains larger droplets moved faster due to their different relaxation times.