Experimental characterization of liquid-gas slip in high-pressure, swirl-stabilized, liquid-fueled combustors

This paper implements a recently developed technique to conditionally analyze the liquid vs gaseous phase velocity vectors in a high-pressure, liquid-fueled, swirl-stabilized combustor. The technique consists of joint analysis of high repetition rate stereoscopic particle image velocimetry (s-PIV) and fuel planar laser-induced fluorescence (fuel PLIF). The s-PIV measurement is conducted simultaneously on the gas and liquid phases by seeding the gas with titanium dioxide flow tracers. The liquid fuel spray serves as its own flow tracer. A fuel PLIF measurement is used to distinguish the vectors that represent liquid fuel velocities from the vectors that represent gas-phase velocities. This technique provides two useful capabilities to the combustion diagnostics community. First, it enables the removal of bias error that the larger, high Stokes number fuel droplets can introduce to the gas-phase velocity measurements due to gas-liquid slip. Second, it enables the simultaneous study of gas- and liquid-phase velocity fields where there may be liquid-gas slip. In the present study, the results show that the liquid fuel spray is a reasonable flow tracer for the time-averaged flow. However, this study does identify regions in the time-averaged flow that contain sufficiently high accelerations and sufficiently large droplets to introduce liquid-gas slip.