COMBUSTION OF HAN-BASED LIQUID PROPELLANT SPRAYS AT 28 TO 38 MPA

Experiments were conducted to elucidate the jet breakup, atomization,a nd combustion of liquid gun propellant (LGP) sprays through the use of imaging techniques. Hydroxylammonium nitrate (HAN)-based monopropella nts were injected at velocities ranging from 100 to 240m/s through cir cular orifices into 33 MPa, 500 degrees C nitrogen. Spray dynamics wer e recorded via high speed cinematography. Breakthroughs in the imaging of combusting sprays were achieved by side illumination of the sprays with pulsed laser light sheets and by seeding the propellants with va rious nitrate salts to enhance flame luminosity. The sprays were obser ved to ignite in the far field, and flame advanced upstream, sustained by extensive turbulent gas recirculation in the closed chamber. The e xperiments revealed the significance of intense, random burning in vor tices. The formation and combustion of large liquid droplets in the vo rtices were also observed. In addition to the LGP sprays, experiments were conducted with liquids whose thermodynamic critic;al point could be exceeded. These results suggest that the LGP spray combustion was s ubcritical at the ambient conditions achieved in this study. The appli cability of single phase incompressible turbulent jet theory and aerod ynamic theory for characterizing the dynamics of these sprays is discu ssed.