Abstract
Optical measurements have been performed to visualize the fuel distribution from an air-assisted GDI injector in a constant volume spray chamber. In the air-assisted injector, fuel droplet breakup occurs as the droplets are accelerated by the expanded air flow passing out through the injector nozzle. The injector design allows for two distinct modes of operation: stratified (low load) and homogenous (full load). Therefore, measurements were taken at back-pressure and temperature settings corresponding to both low and full loads, to investigate the influence of these variables on fuel distribution, droplet sizes and velocities in the two modes. Results from PDA measurements show that most of the droplet break-up occurs inside the nozzle. Downstream of the nozzle, rates of break-up and evaporation are low. The cause of the low breakup and evaporation rates downstream of the nozzle is believed to be the low relative velocity between the liquid fuel and the surrounding cold air jet. The fuel distribution has been visualized qualitatively by simultaneous MIE and LIF measurements with two intensified digital cameras in combination with a 266 nm YAG-laser.
