Investigation of ignition delay and combustion efficiency of tmeda and various concentrations of nitric acid

The focus of this experimental research was to characterize the ignition delay and combustion performance of non-toxic reactants as a viable replacement for highly toxic propellants, such as hydrazine. The liquid reactants consisted of blends of N,N,N',N'-tetramethylethylenediamine (TMEDA) fuel and white fuming nitric acid (WFNA) oxidizer. Hypergolic ignition characteristics of the reactants were initially evaluated using TMEDA with either >90% or >99.5% WFNA through a series of droplet ignition experiments. Results showed that the >90% WFNA was found to have three times longer average ignition delay than >99.5% WFNA with both mixtures producing delays less than 50 ms. Based upon the demonstrated hypergolic droplet test results, the same mixtures were examined in a bipropellant rocket engine. Both injector design and characteristic length were varied under similar operating conditions to determine combustion efficiency. Results to date have demonstrated similar engine performance between both oxidizers and improvements of over 30% in combustion efficiency with increased characteristic length, with TMEDA/>90%WFNA achieving 88%.