Catalytic Combustion of Hydrogen and Oxygen for an Electrolysis Micro Rocket Thruster

This investigation plans to address the growing need for a chemical propulsion system which can cater for the strict power, size and weight requirements of small satellites. The use of water electrolysis to produce hydrogen and oxygen in orbit allows highly efficient propellants to be stored and utilized in a non-hazardous manner. The use of electrolysis avoids the power restrictions associated with comparable electric propulsion systems and would significantly extend the conceivable mission paradigms of small satellites. Of particular interest in the near future is the application to space debris removal, satellite inspection and CubeSat constellations.
For this purpose, the primary research aim of this project is to identify and tackle the major technological bottlenecks associated with developing a microthruster system utilizing electrolysis propellant capture and catalytic ignition. In the pursuit of this, initial studies into H2/O2 catalytic ignition must be extended with a focus on stoichiometric mixtures. This will be accompanied by research into effective means of maintaining temperature limits while regulating thermal and viscous losses. The culmination of this work will be an initial outline of the best practice methodology of micro-scale stoichiometric H2/O2 rocket design. This methodology can then be applied to concept design and fabrication followed by the quantification of system performance. To this end, the primary research objectives have been identified under three key areas of the work:

Microchannel Flow & Catalytic Combustion
- Develop a numerical model which is capable of capturing the multifaceted microthruster flow regime from injection to nozzle exit, combining a suitable compressible flow scheme with a combustion model.
- From experimental data, determine a justified measure of the key empirical relations of the convective heat transfer coefficient and the friction factor.
- Determine the lower limit of necessary catalyst heating required to initiate combustion in stoichiometric H2/O2 mixtures, expanding current microchannel catalytic ignition investigations which have focused only on fuel rich mixtures.
- Quantify the transient and steady state characteristics of the ignited mixture as well as the point at which the heat of combustion is able to maintain sustained ignition.

Thermal Control
- Expand the numerical model to capture the coupled dynamics of the combustion process and the heat transfer within the combustion chamber and nozzle walls through thermal modelling.
- Validate the 2D numerical model through experimentation, consisting of stand alone resistive heating testing as well as investigations done in conjunction with catalytic combustion experiments by temperature measurements of the outer wall.
- Explore and utilize a suitable thermal design strategy; using the validated model to determine the most appropriate cooling strategy.

System Level Design and Optimization
- Develop an optimization process in conjunction with a computational modelling procedure aimed at addressing the clear geometric dependence of both the inside of the combustor as a catalytic surface and the outer combustor as an emmissive surface.
- Suitably design and fabricate a microthruster which is able to achieve a desirable chemical decomposition while balancing thermal and viscous losses. This laboratory prototype will serve as a proof of concept and will therefore aim to provide a realization of the propulsion system demonstrating its feasibility and providing an experimental demonstration of performance characteristics.
- Quantify the system level propulsive capabilities and performance metrics of the microthruster and identify further means of improving the overall system efficiency.