Maxim Kurilov

This paper discusses the development of a model monopropellant that is aimed at exploring the applicability of nitromethane‐based propellants as an alternative to hydrazine. This approach addresses the challenges faced by HAN‐, ADN‐based propulsion by being more cost‐effective while providing similar performance figures. Additionally, storability issues, as is the case for hydrogen peroxide, are avoided. The development began with determining the solubility of ferrocene in nitromethane. This substance was identified as a promising low‐pressure combustion catalyst in a previous study. A BAM Fallhammer screening was then conducted to determine the required phlegmatizer amount to reach a minimal impact sensitivity of 10 J, resulting in two formulations. Testing in a liquid strand burner showed that the formulation with 2 wt.% ferrocene and 13 wt.% dimethyl sulfoxide achieved a low‐pressure combustion limit of 1.25 MPa, which is significantly lower than pure nitromethane (2.7 MPa). This property enables the effective use of nitromethane‐based propellants in state‐of‐the‐art blowdown propulsion architectures as used with hydrazine. Therefore, this formulation was designated NMP‐001 and selected for further research.

This paper presents the results of a hot-fire test campaign aimed at characterizing a newly developed ignition system for nitromethane-based green monopropellants. Nitromethane-based propellants are a cost-effective replacement for hydrazine and energetic ionic liquid hydrazine alternatives such as LMP-103S and ASCENT. The developed system uses a glow plug as the ignition source. Additionally, gaseous oxygen is injected simultaneously into the combustion chamber at the beginning of a firing. After closing the oxygen valve, a pure monopropellant operation follows. Three test series were carried out using NMP-001, a previously characterized nitromethane-based monopropellant. During the first test series, the required ROF for ignition was identified to be above 0.3. In the second test series, the low-pressure combustion limit was shown to be 13.9 bar, which is significantly lower than the 30 bar limit of heritage nitromethane-based monopropellants. In the third test series, the oxygen injection timing was optimized to minimize the required amount of oxygen for successful ignition to 1.5 g per ignition in this test setup. This approach to ignition is more cost effective than the catalytic initiation used for other monopropellants because neither costly precious-metal catalytic materials nor lengthy preheating procedures are required.