Exploring the Catalytic Combustion Mechanism of Hydroxylammonium Nitrate Using Rmg-Cat

Hydroxylammonium Nitrate (HAN) can be used as an oxidizer in liquid propulsion systems, and is an attractive alternative to hydrazine for use in rocket thrusters. Unfortunately, the full catalytic decomposition and combustion mechanism are currently unknown, although several studies have proposed either a partial or a reduced mechanism from both empirical and a priori analysis. Further, for a given thruster/catalyst system, the specifics of the heat transfer mechanism from the catalyst surface to the reacting gas are mostly unexplored.

The Reaction Mechanism Generator (RMG) software can be utilized to generate a mechanistic model for a HAN-based combustion system. RMG is an open source, a priori mechanism generation suite for creating detailed microkinetic models for gas phase, solution phase, and heterogeneous catalytic systems [1]. The mechanism for HAN decomposition and combustion in the presence of methanol is generated using established thermodynamic and kinetic libraries for known species. The parameters for unknown species and reactions are determined using a combination of automated quantum chemistry calculations [2], Benson Group Additivity, and a hierarchical estimation of kinetic parameters based on known reaction families. Sensitivity analyses are performed to find the rate determining steps for a given catalyst surface, and to guide future research.

The mechanism generated by RMG-Cat is analyzed in Cantera, an open-source suite of tools for problems involving chemical kinetics, thermodynamics, and transport processes. A plug flow reactor is simulated with varied reactant stoichiometry, residence time, surface area to volume ratio, and reactor geometry, to explore the effects of these variables.

References:

[1] C. F. Goldsmith and R. H. West, J. Phys. Chem. C, vol. 121, no. 18, pp. 9970–9981, 2017. https://doi.org/10.1021/acs.jpcc.7b02133

[2] P. L. Bhoorasingh, B. L. Slakman, F. Seyedzadeh Khanshan, J. Y. Cain, and R. H. West, J. Phys. Chem. A, vol. 121, no. 37, pp. 6896–6904, 2017. https://doi.org/10.1021/acs.jpca.7b07361