A class of room-temperature ionic liquids (RTILs) that exhibit hypergolic activity toward fuming nitric acid is reported. Fast ignition of dicyanamide ionic liquids when mixed with nitric acid is contrasted with the reactivity of the ionic liquid azides, which show high reactivity with nitric acid, but do not ignite. The reactivity of other potential salt fuels is assessed here. Rapid-scan, Fourier transform infrared (FTIR) spectroscopy of the preignition phase indicates the evolution of N2O from both the dicyanamide and azide RTILs. Evidence for the evolution of CO2 and isocyanic acid (HNCO) with similar temporal behavior to N2O from reaction of the dicyanamide ionic liquids with nitric acid is presented. Evolution of HN3 is detected from the azides. No evolution of HCN from the dicyanamide reactions was detected. From the FTIR observations, biuret reaction tests, and initial ab initio calculations, a mechanism is proposed for the formation of N2O, CO2, and HNCO from the dicyanamide reactions during prei...

Fourier transform infrared studies in hypergolic ignition of ionic liquids.

Currently available or realizable applied e eld magnetoplasmadynamic (AF‐MPD) thrusters operating in the power range 5‐100 kW appear to be excellently suited for orbit change and stationkeeping (drag compensation) of large satellites because of their high specie c impulse, sufe cient thrust, and compact geometry They were developed to considerable maturity almost 20 years ago, but have not yet been used in space because of the lack of missions, appropriate power, and qualie cation There is evidence that these engines cannot be operated realistically in the laboratory, mainly because of the high vacuum needed to exclude unknown environmental interaction with the plume, even at very low vacua A space experiment is needed to provide proof of Isp and efe ciency The International Space Station now provides the opportunity to qualify the engine in space This paper describes the application potential, performance characteristics, and technological status of the AF‐MPD thruster, remaining application issues to be resolved, and a space experiment proposed to operate and investigate the engine under space-e ight conditions

Technology and Application Aspects of Applied Field Magnetoplasmadynamic Propulsion

A detailed kinetic model devoted to the gas phase hypergolic ignition of MMH/NTO mixtures below 298 K and their combustion above 1000 K is presented in this study. It consists of 403 equilibrated reactions among 82 species. This mechanism has been confronted with theoretical data available in the literature. The agreement between theory and predictions is found to be good. Important reactions for ignition at low initial temperature and pressure have been identified through sensitivity analyses. Two competing pathways can explain hypergolic ignition at low temperature. The formation of molecular preignition products is shown to promote the ignition. This conclusion was unexpected, as the formation of these products was generally considered to inhibit the ignition, by reactant consumption. Important reactions for combustion above 1000 K have been preliminarily identified. Some reactions are important both for low-temperature ignition and combustion, whereas some others are important either for ignition only or combustion only. The study is focused on the need for three reduced kinetic models.

Chemical kinetic model for monomethylhydrazine/nitrogen tetroxide gas-phase combustion and hypergolic ignition

N,N-Dimethylhydrazinium dicyanamide and nitrocyanamide ionic liquids (ILs) were prepared by quaterization of N,N-dimethylhydrazine with alkyl halides followed by metathesis reactions with silver dicyanamide or silver nitrocyanamide. The key physicochemical properties, such as melting point and decomposition temperatures, density, viscosity, heat of formation, detonation pressure and velocity, and specific impulse were measured/calculated. The impact of anions and alkyl-substituted cations on these properties is demonstrated. Droplet tests with white-fuming nitric acid (WFNA) as an oxidizer were utilized to show that the 14 new N,N-dimethylhydrazinium salts are hypergolic with ignition delay (ID) times ranging from 22 to 1642 ms, thereby suggesting that some may have potential as bipropellants.

Hypergolic N,N-dimethylhydrazinium ionic liquids.

MPD (MagnetoPlasmaDynamic) thrusters demonstrated between 2000 and 7000 seconds specific impulse at efficiencies approaching 40 percent, and were operated continuously at power levels over 500 kW. These demonstrated capabilities, combined with the simplicity and robustness of the thruster, make them attractive candidates for application to both unmanned and manned orbit raising, lunar, and planetary missions. To date, however, only a limited number of thruster configurations, propellants, and operating conditions were studied. The present status of MPD research is reviewed, including developments in the measured performance levels and electrode erosion rates. Theoretical studies of the thruster dynamics are also described. Significant progress was made in establishing empirical scaling laws, performance and lifetime limitations and in the development of numerical codes to simulate the flow field and electrode processes.

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MPD thruster technology

Current distribution and plasma acceleration mechanisms in MPD arcjets with applied magnetic fields are analyzed theoretically, based on induction and quasi-one-dimensional gasdynamic equations. The finite-element method is used to obtain current distribution and magnetic field patterns. The applied magnetic fields are of diverging type, and calculations are conducted in the cases of discharge currents of 1000 and 2000 A, and mass flow rate of 100 mg/s, for a conventional electrode geometry. Whether the magnetic Reynolds number R(m) is negligibly small or not, it is shown that current distribution on the cathode is not influenced by plasma flow, and the influence of it on current distribution is bounded in the downstream region. Information is presented concerning the relative importance of acceleration mechanisms in MPD arcjets with applied magnetic fields; it is also shown that although for most cases, an externally applied magnetic field is desirable, there exists the possibility that an efficiency-reducing current vortex will occur in the downstream region for the case of a strong magnetic field. 9 references.

Current distribution and plasma acceleration in MPD arcjets with applied magnetic fields

Current distribution on the electrodes of a conventional MPD arcjet without external magnetic field was calculated based on induction equation, with the assumption that the magnetic Reynolds number is small. The calculated result, which showed the influence of tensor conductivity, coincided fairly well with the corresponding experimental one. It was seen, however, that the current density near the cathode tip in experiment had a larger value than that in calculation. This discrepancy was explained tentatively as being the result of the occurrence of cathode spots. It is also suggested in this paper that the unfavorable current concentration at the cathode base can be suppressed by using a specially devised divided cathode.

Current distribution on the electrodes of MPD arcjets

Detailed falling droplet experiments (droplet: N2H4, pool: N2O4) were made, employing high-speed photography, pressure transducers and photodiodes to obtain information on the nature and the mechanisms of explosions. The probability and the strength of explosions increase with droplet size and impact velocity; and the strength has a tendency to saturate, when the impact velocity is increased beyond ≈4.0 m/sec. The magnitude of explosion overpressures observed and its dependency on droplet size could be explained based on the blast wave theory, using the source energy evaluated from high-speed motion picture records. The explosions of N2H4/N2O4 are always accompanied by simultaneous light emission. The time lag of the explosion fluctuates statistically for a fixed experimental condition. Introducing the concept of explosion probability in function of unit time, μ(t), it was shown that the time lag is composed of two parts: a first part of length to, where μ(t)=0, and a second part of length t1, where μ(t) is kept nearly constant (μ(t)=-μ). The length t0 was insensitive to droplet size and impact velocity (≈0.11 msec), although the value of -μ was influenced by them. High-speed motion picture records of ≈105 frames/second clearly showed a dispersed layer at the depressed N2O4 surface (the more volatile component), immediately before the beginning of the explosion. It is suggested, from considerations of the abrupt appearance of this layer and also the nature of the first period of explosion time lag, that the most likely explanation for the layer, which plays the role of a trigger for the explosion, is the sudden gasification of a thin surface layer of liquid N2O4, which was heated above the boiling point.

Masafumi Tanaka

Papers

Current distribution and plasma acceleration in MPD arcjets with applied magnetic fields

Current distribution on the electrodes of MPD arcjets

The mechanisms of explosions induced by contact of hypergolic liquid propellants, hydrazine and nitrogen tetroxide

Explosion phenomenon from contact of hypergolic liquids