Effect of chamber pressure on the spray structure from a swirl pressure atomiser for direct injection gasoline engines

摘要

Images and droplet velocities/diameters of the spray generated by a swirl pressure atomiser have been measured inside a chamber with back pressures ranging from atmospheric to 12 bar and injection pressures up to 100 bar. The photographic investigation showed that the spray structure consists of a non-swirling pre-spray and the main spray whose structure was found to be very sensitive to chamber pressure. In general, the spray cone was contracted and had smaller tip velocity and, thus, reduced penetration at higher chamber pressures due to the enhanced drag; an increase in chamber pressure from 1 to 12 bar caused an overall reduction in the spray cone angle by 35% and in tip velocity by 50%. Measurements by phase-Doppler anemometry (PDA) confirmed the observed in the images effect of chamber pressure (up to 12 bar) and showed a similar reduction in droplet mean velocities to that obtained from flow visualisation, i.e. a suppression in droplet rms velocities by up to 40%, an increase in droplet Sauter mean diameter by up to 20%.