A Method for Screening and Identification of Green Hypergolic Bipropellants

Abstract

As of now, the most widely used hypergolic fuels are hydrazine derivates with nitrogen tetroxide as the oxidizer. The toxicity and carcinogenic character of these substances make their handling challenging even if gelled. Therefore, there is great interest throughout the propulsion community in finding alternatives for these substances. However, despite a thorough literature review, clear selection criteria for 'green' hypergols could not be found. To tackle this issue, we developed a set of key requirements and criteria for propellant selection. The major drivers were hypergolic ignitability, propellant performance, reduced toxicity, and economic factors. Then we used these criteria to carry out a screening aimed at identifying potential oxidizers, fuels, and additives. Hypergolicity was assessed by capturing ignition events of a simple drop test experiment with a high-speed camera. This setup allowed us to find a set of promising novel hypergolic propellants and to verify our screening method. Not only do liquid and gelled diamine fuels with hydrogen peroxide as the oxidizer provide 96% of the specific impulse of the monomethylhydrazine/nitrogen tetroxide propellant system, but they also feature ignition delay times on the order of 15 ms.