Study on catalytic ignition of HNF based non-toxic monopropellants

Hydrazinium nitroformate (HNF) is the salt of hydrazine (N2H4) and nitroform (HC(NO2)3). Nowadays there is interest in HNF dissolved in a solvent/fuel combination. This is a promising propellant to replace hydrazine that is currently commonly used for thrusters for attitude control of satellites. TNO PML, APP and Delft University of Technology cooperate on the development of HNF based monopropellants in the Netherlands. One important aspect is the ignition of the HNF based monopropellant. The state-of-the-art hydrazine thrusters use catalytic ignition, which is a reliable, simple ignition method. Within this study the application of catalytic ignition for HNF- based monopropellants has been investigated. This paper presents the results of some scanning experiments with HNF/water and a catalyst. Experiments with ten different catalysts are performed in a batch reactor. In this reactor the monopropellant is injected on a catalyst bed at a certain temperature. Experiments are performed at catalyst preheat temperatures of 100 °C and 140 °C. The pressure and temperature changes are measured. The results of the tested catalysts were compared with one another. The absolute pressure increase was used to discriminate between the different catalysts and select the most promising ones for further research. This research showed that catalytic ignition seems a very promising method for an HNF based monopropellant. Catalytic activity of iridium and rhodium on alumina has been demonstrated at pre-heat temperatures of around 100 °C to 140 °C in comparison to 200 °C pre-heat temperatures applied in hydrazine thrusters. Catalytic activity of Shell 405 has been qualitatively demonstrated at room temperature. These results have shown that current state-of-the-art catalytic ignition technology used for hydrazine thrusters could very well be applicable for the ignition of future non-toxic HNF monopropellants with minor modifications. © 2003 by Delft University of Technology, the Netherlands.