Vaporizer Performance

Abstract

Measured values of fuel droplet velocity, size and flux are presented for a vaporizer based on a T-shaped duct with upstream atomization by a single axial jet and by six radial jets. They were obtained for a practical range of kerosene and air flowrates and inlet air temperatures with the vaporizer in free air and in a sector of an annular combustor with combustion. Phase Doppler velocimetry was used to measure droplet velocity and size distributions and was complemented by photographic visualization of the flames within the combustor.

The results obtained outside the combustor, and without combustion, showed that the Sauter mean diameter of the droplets ranged from 20 to 60 μm and the liquid-fuel flux from 0.2 to 30 per cent of the total fuel as the inlet air temperature was increased from that of ground-idle to that of full power. The droplet size and liquid-fuel flux also diminished with an increase in air flowrate, and an arrangement of six radial jets resulted in better atomization than an axial arrangement. The corresponding fluxes with combustion were in the range between 0.1 and 8 per cent as a consequence of heat transfer from combusting gases to the vaporizer tubes.

Experience with the vaporizer operating within the combustor at fuel flowrates and inlet air temperatures representative of take-off showed that the vaporizer performance could deteriorate rapidly due to the formation of carbon deposits, particularly in the region where the flow impinged on the cross tube. The deposits led to reduced heat transfer and vaporization with a consequently larger proportion of larger droplets and a tendency for the region of intense combustion to move downstream.