In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed a...In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed and validated to study the effect of unsymmetrical electric arc discharge on thruster performance.The unsymmetrical arc discharge is realized by introducing a radial shift of the cathode so that the cathode tip offset is 80μm(25%of the constrictor radius).Simulations are conducted for both axially centered cathode(coaxial)and off-centered cathode(non-coaxial)configurations with identical propellant flow rates and input current.Simulations show asymmetrical arc discharge in the non-coaxial cathode configuration,resulting in azimuthally asymmetric Joule heating,species concentrations,and velocity field.This asymmetry continues as the plasma expands in the divergent section of the nozzle.Temperature,species concentrations,and axial velocity exhibit asymmetric radial distribution at the nozzle exit.The computed Joule heating was found to reduce with cathode shift,and consequently,the thrust and specific impulse of the thruster was decreased by about 6.6%.In the case of the non-coaxial cathode,geometric asymmetry also induces a small side thrust.展开更多
A 1 kW-class arcjet thruster was fired in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 ： N2 = 2.8 ： 1.5 in volume at a total flow rate of 4.3 slm was used as the propellant with an input power fixed ...A 1 kW-class arcjet thruster was fired in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 ： N2 = 2.8 ： 1.5 in volume at a total flow rate of 4.3 slm was used as the propellant with an input power fixed at 860 W. The time-dependent thrust, nozzle temperature and inlet pressure of the propellant were measured simultaneously. Results showed that with the increase in nozzle temperature the thrust decreased and various losses increased. The physical mechanisms involved in these effects are discussed.展开更多
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 proces...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, coolflow 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.展开更多
A diamond-shaped shock wave was created in a helium arcjet plasma. Visi- ble/ultraviolet emission spectroscopy was used to investigate the condition for the formation of stable shocks and to determine characteristics ...A diamond-shaped shock wave was created in a helium arcjet plasma. Visi- ble/ultraviolet emission spectroscopy was used to investigate the condition for the formation of stable shocks and to determine characteristics of the plasma. Dependence of the position of the shock front on the gas pressure in the expansion region was investigated. It was found that the shock wave arises from the collision of plasma particles and residual neutral atoms in that region. Continuum and line spectra of neutral helium were measured, from which the electron temper- atures were derived. The electron density was deduced from the Inglis-Teller limit of the He I 2p3p-3d3D series. The temperature and density were found to have almost constant values of 0.2 eV and 8.5x 1013 cm-3, respectively, across the shock front.展开更多
Arcjet thruster has been a widely used electrical propulsion technology on GEO satellites since 1993.In its long history of technical development and commercial application,lifetime verification of an arcjet thruster ...Arcjet thruster has been a widely used electrical propulsion technology on GEO satellites since 1993.In its long history of technical development and commercial application,lifetime verification of an arcjet thruster is always one of the most important and expensive tasks.Considering that the main life limitation of an arcjet thruster is electrode ablation and a significant share of the total ablation happens in its starting-up process,the starting-up process is studied with arc voltage signals.Through interpretation of arc voltage signals,the transfer process of the arc root on the anode surface is identified,and?T(the duration of the arc root transfer process)is suggested to be a characteristic parameter for fast evaluation of lifetime assessment and design optimization for an arcjet thruster.With this criterion,the influences of typical parameters on the starting-up process are established through comparison with a benchmark parameter.According to experimental results,an increase of the gas flow will obviously reduce?T,while a smaller swirl aperture and a longer throat channel do not have a remarkable correlation with?T.Moreover,with a sample of a smaller throat diameter to increase the flow velocity,a reduction of?T is achieved.Meanwhile,the modifications also affect the stability of arcjet thruster operation,which is also discussed.展开更多
In the present work,a complete 2D chemical and thermal non-equilibrium numerical model coupled with a relatively simple sheath model is developed for hydrogen arcjet thruster.Conduction heat transfer in the anode wall...In the present work,a complete 2D chemical and thermal non-equilibrium numerical model coupled with a relatively simple sheath model is developed for hydrogen arcjet thruster.Conduction heat transfer in the anode wall is also included in the model.The operating voltages predicted by the model are compared with those in the literature and are found to be in close agreement.Power distributions for the various operating conditions are obtained,anode radiation loss primarily determines the thruster efficiency.Higher thruster efficiency was found to be associated with longer arc length.At cathode ion diffusion contribution dominates except at low input current where thermo-field electron current is dominant.展开更多
基金the Indian Space Research Organization(VSSC-ISRO)for funding this research through ISRO-IITM Cell。
文摘In an arcjet thruster,the cathode and constrictor degrade with time,and the electrical arc discharge may become unsymmetrical.In this work,a three-dimensional numerical model of a hydrogen plasma arcjet is developed and validated to study the effect of unsymmetrical electric arc discharge on thruster performance.The unsymmetrical arc discharge is realized by introducing a radial shift of the cathode so that the cathode tip offset is 80μm(25%of the constrictor radius).Simulations are conducted for both axially centered cathode(coaxial)and off-centered cathode(non-coaxial)configurations with identical propellant flow rates and input current.Simulations show asymmetrical arc discharge in the non-coaxial cathode configuration,resulting in azimuthally asymmetric Joule heating,species concentrations,and velocity field.This asymmetry continues as the plasma expands in the divergent section of the nozzle.Temperature,species concentrations,and axial velocity exhibit asymmetric radial distribution at the nozzle exit.The computed Joule heating was found to reduce with cathode shift,and consequently,the thrust and specific impulse of the thruster was decreased by about 6.6%.In the case of the non-coaxial cathode,geometric asymmetry also induces a small side thrust.
基金supported by National Natural Science Foundation of China (Nos.50836007, 10775164 and 10921062)
文摘A 1 kW-class arcjet thruster was fired in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 ： N2 = 2.8 ： 1.5 in volume at a total flow rate of 4.3 slm was used as the propellant with an input power fixed at 860 W. The time-dependent thrust, nozzle temperature and inlet pressure of the propellant were measured simultaneously. Results showed that with the increase in nozzle temperature the thrust decreased and various losses increased. The physical mechanisms involved in these effects are discussed.
基金Supported by National Natural Science Foundation of China(Grant Nos.11575019,11275021)
文摘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, coolflow 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.
文摘A diamond-shaped shock wave was created in a helium arcjet plasma. Visi- ble/ultraviolet emission spectroscopy was used to investigate the condition for the formation of stable shocks and to determine characteristics of the plasma. Dependence of the position of the shock front on the gas pressure in the expansion region was investigated. It was found that the shock wave arises from the collision of plasma particles and residual neutral atoms in that region. Continuum and line spectra of neutral helium were measured, from which the electron temper- atures were derived. The electron density was deduced from the Inglis-Teller limit of the He I 2p3p-3d3D series. The temperature and density were found to have almost constant values of 0.2 eV and 8.5x 1013 cm-3, respectively, across the shock front.
基金co-supported by the Defense Industrial Technology Development Program,China(No.JCKY2018203B029)the National Natural Science Foundation of China(No.11702021)。
文摘Arcjet thruster has been a widely used electrical propulsion technology on GEO satellites since 1993.In its long history of technical development and commercial application,lifetime verification of an arcjet thruster is always one of the most important and expensive tasks.Considering that the main life limitation of an arcjet thruster is electrode ablation and a significant share of the total ablation happens in its starting-up process,the starting-up process is studied with arc voltage signals.Through interpretation of arc voltage signals,the transfer process of the arc root on the anode surface is identified,and?T(the duration of the arc root transfer process)is suggested to be a characteristic parameter for fast evaluation of lifetime assessment and design optimization for an arcjet thruster.With this criterion,the influences of typical parameters on the starting-up process are established through comparison with a benchmark parameter.According to experimental results,an increase of the gas flow will obviously reduce?T,while a smaller swirl aperture and a longer throat channel do not have a remarkable correlation with?T.Moreover,with a sample of a smaller throat diameter to increase the flow velocity,a reduction of?T is achieved.Meanwhile,the modifications also affect the stability of arcjet thruster operation,which is also discussed.
基金supported by the Indian Space Research Organization(VSSC under grants ASE1415160ISROAMIK and ASE1718174ISROAMIK)。
文摘In the present work,a complete 2D chemical and thermal non-equilibrium numerical model coupled with a relatively simple sheath model is developed for hydrogen arcjet thruster.Conduction heat transfer in the anode wall is also included in the model.The operating voltages predicted by the model are compared with those in the literature and are found to be in close agreement.Power distributions for the various operating conditions are obtained,anode radiation loss primarily determines the thruster efficiency.Higher thruster efficiency was found to be associated with longer arc length.At cathode ion diffusion contribution dominates except at low input current where thermo-field electron current is dominant.
