PERFORMANCE ENHANCEMENT AND IGNITION DELAY SUPPRESSION OF TMEDA USING AMINE-BORANE ADDITIVES

Historically, most liquid rocket systems utilizing hypergolic propellants have used hydrazine-based fuels. Although these fuels offer good performance and short ignition delay times, they require special handling precautions that provide motivation to develop safer alternatives. Tetramethylethylenediamine (TMEDA) offers comparable levels of performance. However, its longer ignition delay time (compared to the hydrazine-based fuels) make it less attractive as a replacement fuel. This work investigates the use of amine boranes to reduce the ignition delay time and predicted performance of TMEDA-based hypergolic fuels. Saturated solutions of ammonia borane (AB), ethylenediamine bisborane (EDBB), and tetramethylethylenediamine bisborane (TMEDABB) in TMEDA reduced the average ignition delay times by 43-51%. Mixtures of triethylamine borane (TEB) with TMEDA resulted in the shortest ignition delay times observed in this study. Unfortunately, the formation of TMEDABB through a trans-borylation reaction between TMEDA and TEB suggests TEB is unsuitable for use with TMEDA. Gelling the fuel mixtures with higher loadings of these amine-boranes had mixed results, with higher weight fractions of AB or EDBB increasing the ignition delay time. The shortest ignition delay times measured for the gelled fuels were similar to those measured for the saturated solutions and could be considered if gelled propellants are desired. However, given their short ignition delay times, comparable theoretical performance, and simplicity compared to these gelled fuels, the saturated TMEDA liquid solutions appear to be the most promising, even though they are still much safer alternatives to the conventional hydrazine-based fuels.