Experimental investigation of spray dynamics under jet engine augmentor-like conditions

This paper describes an experimental investigation of fuel spray jet breakup mechanisms when it is injected across the high temperature air flow in low and high pressure jet engine augmentor-like conditions. Phase Doppler particle analyzer data and short exposure pulsed shadow graph images were taken of fuel jet injected into an air cross flow with liquid to air momentum ratios ranging from 5 to 180. Measured droplet diameters taken at atmospheric pressure and a flow Mach number of similar to 0.15 show a progressive breakup of the droplets, gradually decreasing in size from 250 mu m to 150 mu m and finally to 25 mu m as the spray moves downstream. The progressive breakup of droplets follows the classical Rayleigh-Helmholtz breakup mechanism. At higher pressure and Mach number tests, the fuel jet undergoes a different breakup process; i.e., the fuel jet breaks up instantaneously into a monodispurse spray of smaller droplets near the injector. High speed images of this process suggest that an aerodynamic breakup mechanism dominates this atomization process near the injector. In summary, the results of this study show the fuel jet breakup mechanism in augmentors varies significantly over the flight envelope.