Methodology for Geometric Optimization and Sizing for Subnewton Monopropellant Catalyst Beds

Abstract

Experimental testing of a number of novel additively manufactured monopropellant microthrusters was conducted under atmospheric conditions using 87.5% concentration hydrogen peroxide. The aim of this work was to select a specific catalyst bed geometry for the thruster system and to investigate more general methodologies for monopropellant packed catalyst bed optimization. Characteristic velocity efficiencies approaching 0.98 were demonstrated, and performance improved for smaller beds with low aspect ratios; although, these beds flooded at lower propellant flow rates. The onset of bed flooding was used to identify physical limits of propellant flow rate supported by the catalyst. The particular propellant–catalyst pairing limit was defined by a Damköhler number of 56, independent of the bed geometry, with thermal performance peaking for the high flow rates just before flooding occurred. It is suggested that this method is extensible to other monopropellant systems, although with further work required to confirm it is a more general effect beyond thrusters using hydrogen peroxide.