Spray Characterization at Jet Engine Thrust Augmentor Flow Conditions

Abstract

This paper describes experimental characterization of the spray formed by fuel jet injection in cross-flow under simulated modern augmentor operating conditions. Such data is needed to obtain a better understanding of the fundamental processes that control the performance of aircraft engine augmentors and to support the development of CFD based design tools. The study employed a single flame holder augmentor (SFA) model of a modern jet engine thrust augmentor with a cross-section of 76.2×152.4 mm (3×6 inches) located in a test setup with full optical access to the spray and flame zones provided by a 914.4 mm (36 inches) long transparent quartz section. Tests were performed under conditions simulating those encountered with modern jet engines: Mach number varying between 0.25 and 0.40, temperature ranging from 760°C to 900°C (1860 R to 2111 R), and vitiated air with oxygen content ranging from 12% to 15% by volume. The flame was maintained by a bluff-body flame holder with fuel injector orifice diameter d = 0.711 mm (0.028 inch). Flow rate of the Jet-A fuel varied in the range of 23 ± 0.4 g/s, resulting in a fuel to air momentum flux ratio of Q = 10.5 and an aerodynamic Weber number We = 970. The nature of the fuel spray atomization, both with and without afterburning, was determined using a two dimensional Phase Doppler Particle Analyzer (PDPA) system. The PDPA system simultaneously measured droplet diameters and velocities. The results were used to generate profiles of the droplet diameter distributions and velocities in the center plane and cross-section planes at two locations downstream of the injection point. Measurements with combustion were limited to outside the recirculation zone behind the flame holder due to the evaporation of the droplets there from the heat of combustion. The results showed that the presence of combustion reduces the level of incoming air flow inclination approximately by a factor of 2 and increased the turbulence intensity level by 60% to 70%. The presence of combustion increases the Sauter mean droplet diameters from the range 44 to 68 microns without flame to the range 47 to 79 microns and reduces mean droplet velocities by approximately 10% in the core of the spray and up to 25% near the peripheries of the spray.