Spray characterization of a piezo pintle-type injector for gasoline direct injection engines

Abstract

The sprays from a pintle-type nozzle injected into a constant volume chamber have been visualised by a high resolution CCD camera and quantified in terms of droplet velocity and diameter with a 2-D phase Doppler anemometry (PDA) system at an injection pressure of 200 bar and back-pressures varying from atmospheric to 12 bar. Spray visualization illustrated that the spray was string-structured, that the location of the strings remained constant from one injection to the next and that the spray structure was unaffected by back pressure. The overall spray cone angle was also stable and independent of back pressure whose effect was to reduce the spray tip penetration so that the averaged vertical spray tip velocity was reduced by 37% when the back-pressure increased from 1 to 12 bar. Detailed PDA measurements were carried out under atmospheric conditions at 2.5 and 10 mm from the injector exit with the results providing both the temporal and the spatial velocity and size distributions of the spray droplets. The maximum axial mean droplet velocity was 155 m/s at 2.5 mm from the injector which was reduced to 140 m/s at z = 10 mm. The string spacing determined from PDA measurements was around 0.375 mm and 0.6 mm at z=2.5 and 10 mm, respectively. The maximum mean droplet diameter was found to be in the core of the strings with values up to 40 μm at z=2.5 mm reducing to 20 μm at z=10 mm.