Composition optimization of a hypergolic green propellant based on monoethanolamine, n-butanol and 90% hydrogen peroxide

The design of satellite attitude-control thrusters depends on a trade-off between minimum impulse bit and specific impulse, where the width of pulse maneuvers relies on the combination of delays in the hydraulic system (feed tubes and valves) and the ignition delay time of the propellant used. The most well-established propellants in this context are hydrazine derivatives and nitrogen tetroxide. However, their high toxicity makes satellite integration costly and environmentally hazardous. To replace these propellants, research is focused on developing new hypergolic green propellants, most of which use high-concentration hydrogen peroxide as an oxidizer. In this study, the hypergolic reaction between a blend of n-butanol and monoethanolamine and hydrogen peroxide was catalyzed using copper nitrate trihydrate. The central composite design method was applied to optimize fuel composition using 90% hydrogen peroxide as the oxidizer. The optimization yielded two key outcomes: for ignition delay time (31.5% n-butanol, 60% monoethanolamine, and 8.5% copper nitrate, resulting in an ignition delay time of 21.5 ms with a standard deviation of +/- 1.30 ms and a systematic error of +/- 0.4), and for theoretical specific impulse (36% n-butanol, 60% monoethanolamine, and 4% copper nitrate, with an ignition delay time of 26 +/- 0.4 ms). For the ignition delay time optimization, an oxidizer-fuel ratio of 4 was selected using CEA NASA software to achieve a maximum theoretical specific impulse of 170.64 s, while for specific impulse optimization, a ratio of 4.4 was chosen, resulting in a specific impulse of 171.58 s. Although the maximum theoretical specific impulse of the proposed green propellant pair does not present an advantage if compared to traditional hypergolic propellants, it offers a competitive advantage in terms of density-specific impulse, with the highest value achieved in the ignition delay time optimization, where the density-specific impulse of the system reached 267.5 gs/cm3. Furthermore, the addition of n-butanol effectively reduced fuel viscosity, enhanced density-specific impulse, increased specific impulse, and improved ignition delay time response with 90% hydrogen peroxide compared to pure monoethanolamine formulations for a specific chamber and nozzle configuration. These findings highlight the potential of this green propellant system to enhance performance and efficiency in aerospace applications.