Soot and flow field in turbulent swirl-stabilized spray flames of Jet A-1 in a model combustor

Abstract

Soot production processes and their interaction with the swirling flow field were studied experimentally in turbulent spray flames in a model gas turbine combustor. Two Jet A-1/air spray flames with two different air flow rates both with constant fuel flow corresponding to a thermal power of 10 kW were stabilized in the combustor with a swirl number of 0.55. Soot measurements were collected using auto-compensating laser-induced incandescence and velocity measurements were obtained using stereoscopic particle image velocimetry techniques. The particle image velocimetry displayed a distinct change in spray pattern from a V-shaped hollow cone to a V-shaped solid cone when the air flow rate was increased. The first soot event was not detected until 30 mm above the combustor inlet was reached, which was expected as it was necessary for liquid fuel to disperse and evaporate. The flow field featured strong inner and outer recirculation zones as well as the inner and outer shear layers. Soot concentration distributions were found to be confined to the outside of the inner recirculation zone; this is in contrast to the gaseous fuel swirl-stabilized flames in which soot particles are mainly detected within the inner recirculation zone. Time-averaged maximum soot volume fraction level decreased by about 60% with a 20% increase in air mass flow rate instigated by enhanced oxidation rate and turbulent mixing. The primary soot particle size was found to fall in the range of 30 and 60 nm for both cases. The results obtained emphasize the role played by the intermittent structures and air flow rate on soot processes in swirling spray combustion. Observed soot distributions in liquid spray flames in this work differ drastically from those reported previously for gaseous fuel combustion in swirl-stabilized flames.