Decomposition and hybrid combustion of hydrazine, MMH and UDMH as droplets in a combustion gas environment

Abstract

The combustion characteristics of monopropellant hydrazine, MMH and UDMH as droplets have been investigated at atmospheric pressure. In order to simulate combustion chamber conditions, droplet burning was observed in the combustion products of a flat flame burner. Gas temperatures in the range 1660–2530°K and oxygen concentrations of 0–42%, by mass, were employed at the droplet position. This allowed the observation of both decomposition and hybrid (monopropellant droplet combustion in an oxidizing medium) combustion. Both the supported droplet and porous sphere experimental techniques were employed to provide droplet diameters in the range 0.11–1.91 cm. The experimental mass burning rates increased with increasing droplet diameter, ambient temperature, and ambient oxygen concentration. As the droplet diameter increased, the influence of ambient conditions decreased, particularly for hydrazine. A simplified hybrid combustion model, postulating an infinitely thin decomposition flame surrounded by an infinitely thin oxidation flame, was developed to aid in correlating the data. This theory was found to correlate the present data, as well as that of other investigators, over a wide rantge of burning rates and experimental conditions.