Evaluation of N,N,N′,N′-Tetramethylethylenediamine (TMEDA) as an Alternative Fuel for a Hypergolic Bipropellant Rocket Engine

Experimental research was conducted to characterize the ignition delay time and combustion performance of non-toxic reactants as a possible replacement for highly toxic fuels, such as hydrazine. The liquid fuel and oxidizer were N,N,N′,N′-tetramethylethylenediamine (TMEDA) and white fuming nitric acid (WFNA), respectively. The hypergolic ignition delay of the reactants was determined using 100% TMEDA with either >90% or >99.5% WFNA that was distilled, titrated, and droplet-tested in a laboratory setting while controlling the parameters that affect the quality of the yielded product. It was observed that >90% WFNA had three times longer average ignition delay than >99.5% WFNA with both mixtures producing ignition delay times less than 20 ms. Based upon the demonstrated hypergolic droplet test results, a fluid delivery feed system and hypergolic heavyweight bipropellant rocket engine were designed and fabricated to characterize the combustion efficiency of these non-toxic reactants. The rocket injector and characteristic length differed while operating under similar flow conditions to evaluate combustion efficiency. Results demonstrated similar engine performance between both cases of WFNA with improvements of over 30% in combustion efficiency with increased characteristic length. Tests using 100% TMEDA/>90% WFNA achieved a combustion efficiency of 88%.