Thermodynamical nonequilibrium nitrogen plasmas in a direct-current arcjet engine nozzle

Spectroscopic measurements were carried out to understand the arc structure and the flowfield in a 10-kW-class water-cooled direct-current nitrogen arcjet engine with a supersonic expansion nozzle for material processing. In the expansion nozzle, the pressure and electron density drastically decreased downstream, and therefore the plasma was in thermodynamical nonequilibrium, although the plasma in the constrictor was expected to be nearly in a temperature-equilibrium condition. The radial profiles of the physical properties for N₂ and N₂ ^{showed that there existed a core flow with high vibrational and rotational temperatures and large electron number densities on the center axis, even at the nozzle exit. Both of these temperatures on the arcjet axis at the nozzle exit and the electron temperature in the constrictor increased linearly with the input power, regardless of mass flow rate. The vibrational temperature ranged from 6000 to 10000 K in input power levels of 5-11 kW and the rotational temperature from 500 to 2000 K}