Structure and mixing properties of combusting monopropellant sprays

The spray combustion properties of a hydroxylammonium nitrate (HAN)-based monopropellant (LGP 1845) were studied both theoretically and experimentally. Drop size, liquid mass flow rate, and liquid mass flux distributions were measured for pressure-atomized sprays in the atomization breakup regime, burning within a combustion gas environment at pressures of 4.5-5.0 MPa. Two separated-flow models were evaluated using the new measurements: a deterministic separated-flow model where drop-turbulence interactions were ignored, and a stochastic separated-flow model where drop-turbulence interactions were considered using random-walk computations for drop motion. When based on burning rates found from earlier single-drop experiments, both models were in reasonably good agreement with the measurements. Separated-flow effects are quite important for these sprays, with the length of the liquid-containing region being relatively independent of injector diameter and extending roughly 300 mm from the injector exit for injector exit velocities of roughly 70 m/s and injector diameters of 0.3 and 0.6 mm.