Arcjet Nozzle Research Articles

Computational Predictions of the Hypersonic Material Environmental Test System Arcjet Facility

The Hypersonic Materials Environmental Test System arcjet facility located at the NASA Langley Research Center in Hampton, Virginia, is primarily used for the research, development, and evaluation of high-temperature thermal protection systems for hypersonic vehicles and reentry systems. To improve testing capabilities and knowledge of the test article environment, a detailed three-dimensional model of the arcjet nozzle and the freejet portion of the flowfield is developed. The computational fluid dynamics model takes into account nonuniform inflow state profiles at the nozzle inlet as well as catalytic recombination efficiency effects at the probe surface. The results of the numerical simulations are compared to the calibrated pitot pressure and the stagnation-point heat flux for three test conditions at low, medium, and high enthalpies. Comparing the results and the test data indicates a partially catalytic copper surface on the heat flux probe of about 10% recombination efficiency and a 2–3 kPa pressure drop from the total pressure measured at the plenum section in front of the nozzle. With these assumptions, the predictions are within the uncertainty of the stagnation pressure and heat flux measurements. The predicted velocity conditions at the nozzle exit are also compared and show good agreement with the radial and axial velocimetry data.

Nonequilibrium modeling study on plasma flow features in a low-power nitrogen/hydrogen arcjet thruster

Gasdynamic flow features in an electrothermal arcjet thruster with a mixture of 1:2 nitrogen/hydrogen as the working gas have been studied by a two-temperature numerical simulation. Seven species and 17 kinetic processes are included in the chemical kinetic model used to represent dissociation, ionization, and the corresponding recombination reactions in this nitrogen/hydrogen mixture system. Based on the gas flow characteristics inside the arcjet nozzle, a new method is introduced to define the edge of the cold boundary layer, which is more convenient to analyze the evolution and development of plasma flow in an arcjet thruster. The results show that the arcjet thruster performance is determined largely by the exchange of energy and momentum between the low-density, high-temperature arc region and the high-density, cool-flow region near the nozzle wall. A significant thermal nonequilibrium is found in the cold boundary layer in the expansion portion of the nozzle. The important chemical kinetic processes determining the distribution of hydrogen and nitrogen species in different flow regions are presented. It has been shown that the reaction rate of hydrogen species ionization impacted by electrons is much higher than that of nitrogen species ionization in the center of the constrictor of the arcjet thruster. This indicates that hydrogen species is very important in the conversion of applied electric energy into thermal energy in the constrictor region of the arcjet thruster.

A new design of foam spray nozzle used for precise dust control in underground coal mines

In order to improve the utilization rate of foam, an arc jet nozzle was designed for precise dust control. Through theoretical analysis, the different demands of foam were compared amongst arc jets, flat jets and full cone jets when the dust source was covered identically by foam. It is proved that foam consumption was least when an arc jet was used. Foam production capability of an arc jet nozzle under different conditions was investigated through experiments. The results show that with the gas liquid ratio (GLR) increasing, the spray state of an arc jet nozzle presents successively water jet, foam jet and mist. Under a reasonable working condition range of foam production and a fixed GLR, foam production quantity increases at first, and then decreases with the increase of liquid supply quantity. When the inner diameter of the nozzle is 14mm, the best GLR is 30 and the optimum liquid supply quantity is 0.375m3/h. The results of field experiments show that the total dust and respirable dust suppression efficiency of arc jet nozzles is 85.8% and 82.6% respectively, which are 1.39 and 1.37 times higher than the full cone nozzles and 1.20 and 1.19 times higher than the flat nozzles.

Temporal Evolution of Excited Level Populations in a High-Velocity Argon Plasma Flow

A simplified collisional-radiative model is applied to a high velocity plasma flow through the arcjet nozzle to investigate the temporal evolution of excited level population densities in the selected spatial positions inside arcjet thruster. Computations are carried out for various sets of input parameters such as electron temperature, electron number density, atom temperature, and pressure. The numerical results illustrate that the extent of the ionization-recombination non-equilibrium is strongly dependent on the electron temperature and pressure, and is significantly affected by resonance radiation.

Numerical and Experimental Study of a 1-kW Hydrazine Engineering Design Model Arcjet Thruster

AbstractNumerical and experimental study of a 1-kW hydrazine engineering design model arcjet thruster with simulated hydrazine reaction products as propellant was performed. A two-dimensional numerical model incorporating the effects of viscous dissipation, Lorentz force, ohmic heating, heat conduction, radiation loss, and pressure work was developed to model the plasma processes inside the arcjet nozzle. The flow field and heat-transfer characteristics inside the arcjet nozzle obtained from the numerical study are discussed. The effects of the electrical conductivity and the anode wall temperature on arcjet performance prediction are also discussed. Experimental tests of the engineering design model arcjet thruster with simulated hydrazine reaction products as propellant were carried out with a mass flow rate range of 20–32 mg/s and an arc current range of 8–10 A. Over the mass flow rate and arc current ranges tested in the experiment, the specific impulse of the arcjet was in the range 479–528 s, and th...

Mass Deposition Measurements from 26-Kilowatt Electric Propulsion Space Experiment Flight

The Electric Propulsion Space Experiment (ESEX) was launched and operated in early 1999 to demonstrate the compatibility and readiness of a 30-kW class ammonia arcjet for satellite propulsion applications. As part of the onboard sensor array, thermoelectric quartz crystal microbalances were used to measure material deposition at selected locations on the spacecraft surface. The sensors were held at a temperature that would allow them to condense metallic materials eroded from the electrodes, but that are insensitive to possible deposition of the propellant gas. The ESEX arcjet was fired eight times, constituting 33 min and 26 s of operating time. No material deposition was observed that could be attributed to nominal the arcjet firings, although during the first firing, significant deposition was observed near the arcjet nozzle. This deposition is attributed to contaminants within the arcjet body, collected during handling and storage, which were ejected during the first firing. For future programs, although engineering measures may be needed to protect spacecraft equipment in the immediate vicinity of the thruster body, the arcjet environment causes negligible deposition of electrode material.

Improved DC arc-jet diamond deposition with a secondary downstream discharge

Abstract The efficiency of a polycrystalline diamond coating in a DC arc-jet setup with a power of 5–10 kW was enhanced by extension of a high temperature jet core. Two approaches were investigated. First, an expansion of the plasma jet anode channel was employed. It allowed us to increase the process efficiency from 5.5 to 10 mg/h/kW by optimizing values of pressure and CH4 content in a reactionary Ar/H2/CH4 mixture. In the second approach, the extension of the hot jet core was achieved by an additional downstream discharge with a power of 2.5 kW. The secondary discharge was initiated between a positively biased auxiliary electrode and the arc-jet nozzle. This method allowed us to obtain a growth rate of 40 μm/h on an area of 12 cm2, which corresponds to an efficiency of 16 mg/h/ kW.

Arcjet nozzle flow-field characterization by laser-induced fluorescence

Laser-induced fluorescence of the Balmer-alpha (H(alpha)) transition of atomic hydrogen was performed within the nozzle of a 1-kW class radiatively cooled arcjet thruster operating on hydrogen and synthesized-hydrazine propellants. Axial velocities were determined from the Doppler shift of the H(alpha) line center relative to a stationary reference, whereas translational temperatures and electron number densities were determined from a line-shape analysis of the H(alpha) transition. The results are compared with a numerical model and indicate excellent agreement with the velocities, as well as temperatures near the nozzle exit. There are discrepancies, however, in the temperatures far upstream of the exit and in the electron densities, suggesting needed improvements in the modeling of the recombination chemistry.

Optical diagnostics for temperature measurement in a DC arcjet reactor used for diamond deposition

a-state in this plume. LIF measurements of CH are complicated by the presence of C3 and we discuss strategies to deal with this interference. The gas temperature describing the rotational distributions obtained for NO, C2 and CH agree within experimental error. Optical emission measurements indicate that the rotational and vibrational distributions of the excited A-state of CH and a-state of C2 are characterized by vibrational and rotational populations which are at least 1000 K above the ground state distributions. The excited states are collisionally quenched before their population distributions equilibrate with the gas temperature. We also determine relative populations of the ground and excited states along the axis of the plume between the arcjet nozzle and the substrate and relative populations for a cross section of the jet, midway between the nozzle orifice and the substrate. The measured relative ground and excited state populations for both CH and C2 show different trends along the plume axis, indicating that the ground and excited states of these molecules are products of different chemical mechanisms; such mechanisms are discussed.

Plasmadynamics model for nonequilibrium processes in N2/H2 arcjets

A two-temperature chemical nonequilibrium model is developed for nitrogen/hydrogen (N 2/H2) arcjet thrusters. All viscous flow properties are considered assuming steady, laminar, continuum, and axisymmetric flow. A seven-species N2/H2 plasma composition of molecules, atoms, ions, and electrons is assumed, and a finite rate chemistry model is employed to model collisional processes among the species. Separate energy equations are formulated for the electrons and heavy species. The anode temperature distribution is included, and propellant electrical conductivity is coupled to the plasma properties, allowing for a selfconsistent current distribution. The numerical solution employs the compressible form of the pressureimplicit with splitting of operators algorithm to solve the continuity and momentum equations. Numerical results are presented for a low-power simulated hydrazine thruster. The centerline constrictor region of the arcjet flowfield is predicted to be near thermal equilibrium, whereas a high degree of thermal nonequilibrium is predicted in the near-anode region of the arcjet nozzle. Strong electric fields near the anode produce elevated electron temperatures that enhance ionization levels and electrical conduction through the arcjet boundary layer. Radial diffusion of electrons from the arc core also enhances the near-anode ionization levels. Thus, the nonequilibrium approach is required to accurately model the plasma current distribution.

Fluorescence velocity measurements in the interior of a hydrogen arcjet nozzle

The first use of laser-induced fluorescence for spatially resolved plasma velocity measurements within an arcjet nozzle are described.The arcjet was operated on a propellant of pure hydrogen.The Balmer-α transition of atomic hydrogen was scanned by the excitation laser source while simultaneously detecting the spectrally integrated resonance fluorescence.Velocity was determined from the Doppler shift in the peak of the laser excitation spectrum relative to a stationary reference.The arcjet operating conditions were chosen to facilitate a comparison between these measurements and arcjet modeling results of Butler et al.

Techniques for spectroscopic measurements in an arcjet nozzle

A successful attempt has been made to gain optical access to the inside of an arcjet nozzle without changing internal thruster design or affecting performance characteristics. Both fiber optics and small open holes have been used for emission spectroscopy of a small, confined, high-temperature plasma source. The plasma was found to be in a highly nonequilibrium state, with electron excitation temperatures more than double the rotational or vibrational temperatures.