Investigation of glycerol atomization in the near-field of a flow-blurring injector using time-resolved piv and high-speed visualization

Abstract

Glycerol has very high kinematic viscosity and high vaporization and auto-ignition temperatures, but it has been effectively atomized at room temperature by using a novel flow blurring (FB) injector and then cleanly combusted without any combustor hardware modification. The present study qualitatively and quantitatively reveals the details of glycerol atomization in the near field of the FB injector. Time-resolved Particle Image Velocimetry (PIV) with exposure time of 150 ns and image pair acquisition rate of 15 kHz is utilized to probe the glycerol spray at spatial resolution of 16.83 μm per pixel. PIV results describe the droplet dynamics in terms of instantaneous, mean, and root-mean-square (RMS) profiles of the axial velocity. In addition, high-speed imaging (75 kHz) coupled with backside lighting is applied to reveal the glycerol breakup process at spatial resolution of 7.16 μm per pixel and exposure time of 1 μs. Results indicate that the primary breakup by FB atomization or bubble explosions occurs inside the injector and it results in ligaments and droplets at the injector exit. Then, the secondary breakup by Rayleigh-Taylor instability occurs in the near-field of the injector exit where the high-velocity atomizing air stretches the ligaments into thin ligaments that disintegrate into smaller ligaments, and subsequently, into droplets. Thus, within a short distance downstream of the injector exit (<30 mm), most of the glycerol is atomized into fine droplets demonstrating excellent atomization performance of the FB injector.