Numerical Study of Microscale Monopropellant Fuel Injection Using Two-Phase Slug Formation

Abstract

Gas and liquid converging at a microchannel cross junction results in the formation of periodic, dispersed microslugs. This microslug-formation phenomenon has been proposed as the basis for a fuel-injection system in a novel, discrete monopropellant microthruster design for use in next-generation miniaturized satellites. Experimental work by McCabe et al. (“A Micro-Scale Monopropellant Fuel Injection Scheme Using Two-Phase Slug Formation,” Journal of Propulsion and Power, Vol. 27, No. 6, 2012, pp. 1295–1302) demonstrated the ability to generate fuel slugs with characteristics commensurate with the intended application. In this work, numerical modeling and simulation is used to further study this problem and identify the sensitivity of the slug characteristics to key material properties including surface tension, contact angle, and fuel viscosity. These concerns are of practical concern for this application due to the potential for thermal variations and/or fluid contamination during typical operation. For each of these properties, highly stable regions exist where the slug characteristics are essentially insensitive to property variations. Next, a series of three-dimensional simulations were performed to study the effects of channel depth on the slug-formation process. These simulations show that the relative slug volume and the detachment location increase with channel depth. Over the range of depths studied, the relative slug volume increased by up to 20% and the detachment location increased by 10 channel widths. The results demonstrate the impact of three-dimensional effects on the ability of the system to throttle the fuel flow rate to a level necessary for low thrust applications, which will have ramifications on the design and manufacture of the microthruster system.