Авіаційно-космічна техніка та технологія (Aug 2024)
Modelling of the processes inside the nozzle of resistojet and arcjet with molecular propellant
Abstract
The first sample of the resistojet, which together with the arcjet belongs to the class of electrothermal thrusters, was developed in 1929-33 by the Ukrainian designer Valentyn Hlushko. Electrothermal thrusters combine the gas-thermodynamic principle of acceleration in a profiled nozzle with the use of electrical energy to heat the propellant. In resistojets, energy is supplied to the gas by an ohmic heater. In arcjets, the source of energy is the arc discharge. The advantage of this type of thruster is the greater value of the specific impulse compared to chemical rocket engines with solid or liquid propellants. In view of the inverse proportionality of the specific impulse to the square root of the molecular weight, hydrogen was initially chosen as the propellant. However, the operation of electric propulsion thrusters involves long-term propellant storage and excludes the use of hydrogen in liquid form. When stored in a gaseous state, due to the significant rarefaction of hydrogen, the mass of the balloon significantly exceeds the mass of hydrogen itself, negating the gain in propellant mass reduction compared to chemical engines. Interest in the development of electrothermal thrusters was revived by the proposal to use molecular propellants: ammonia and hydrazine. A mathematical model and a method for calculating thermochemical processes in the primary dissociation and secondary synthesis reactions of molecular nitrogen and hydrogen in the nozzle of an electrothermal thruster were developed in this work. The calculation method involves the use of continuity, momentum, and energy equations, considering the change in the molecular composition as the gas expands in the nozzle. The problem of lack of equilibrium constants was solved by generalizing the Saha ionization formula to the case of the interaction between nitrogen and hydrogen atoms. The calculation results demonstrate the possibility of obtaining a specific impulse at the level achieved when working on hydrogen. The necessity of using the non-stationary form of the equations during the creation of the process model in the heater or thruster arc is also indicated.
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