Effect of Jet Momentum Ratio and Equivalence Ratio on the Ignition Process of TMEDA and White Fuming Nitric Acid (WFNA)

Abstract

The focus of this research work was to characterize ignition and combustion of TMEDA / DMAZ fuels and white fuming nitric acid oxidizer, using a single-element injector to provide characteristics on hypergolic propellant reactants in terms of ignition delays under atmospheric pressure and ambient temperature conditions. This study assists in determining whether TMEDA and DMAZ are viable replacements for highly toxic fuels such as hydrazine. A series of experiments was conducted to determine the ignition delay as a function of: volumetric flow rate, momentum ratio, L/D ratio, and equivalence ratio. Highspeed images of the ignition transient were ascertained. As the total reactant volumetric flow rate increases, the ignition delay was reduced for  = 1 and MTMEDA/MWFNA = 1. The ignition time delay decreased from nearly 17 ms down to approximately 5 ms when the total propellant flow rate was increased by a factor of six. The jet velocity of the fuel stream, VTMEDA, ranged from 8 to 66 m/s (ReD from ~ 0.3x10 4 to 3x10 4 ), while the jet velocity in the oxidizer stream, VWFNA, ranged from 2 to 60 m/s (ReD from ~ 0.4x10 4 to 4x10 4 ) in order to change the momentum ratio. The effect of equivalence ratio on ignition delay shows that at very fuel rich conditions ( = 5.8) the ignition delay was approximately 3 times longer. However, for cases at  = 3.2 and below, it was evident that the ignition delay is not significantly affected by stoichiometry. This can be interpreted, that for ignition, stoichiometry is not as nearly as important as for combustion. Blends of TMEDA and DMAZ fuels were examined. It was found for 70%TMEDA/30%DMAZ (by wt%), the ignition delay decreased nearly 38%. To simulate the reactants being introduced into a rocket engine, a curved glass surface was applied tangent to the injector exit to study the effect of wall impingement. Data show that when the curved glass surface is present, up to an 8 ms increase in ignition delay is observed.