Spectroscopic diagnostics in a highly constricted oxygen arc

Abstract

Plasma properties in a highly constricted arc were measured using spectroscopic techniques. The arc configuration studied is typical of those produced by plasma cutting equipment. Temperatures and electron densities in the arc were measured using several different emission lines and several different methods for property calculation. Factors such as fluctuations in the arc intensity, arc asymmetry and the validity of the assumptions used for property calculation were shown to affect the accuracy of the measurements. Selection of the temperature measurement method can influence the measurement results. For this arc configuration, methods which use oxygen ion emission lines provide the most accurate results. The measurement methods developed in this study were used to investigate differences in arc properties related to arc current and nozzle diameter. Large changes in the temperature and electron density due to shocks were measured in the under-expanded region near the nozzle exit.

On the influence of the nozzle length on the arc properties in a cutting torch

“…Although the effects of non-LTE have been studied in cutting torches [5,7] a theory based on LTE can in general give satisfactory temperature predictions when compared with experiments [1].…”

“…On the other hand, such long and narrow nozzle reduces the gas mass flow, with the consequent de-stabilization and asymmetry of the arc. Differences in cutting arc properties related to changes in the nozzle radius were measured using spectroscopic techniques in [5]. In this work, an experimental study on the influence of the nozzle length on the physical properties of a cutting arc is reported.…”

Numerical Modelling of a Cutting Arc Torch

“…That experimental validation consists in obtaining a good matching with the experimental temperature values within the experimental uncertainty, which typically amounts to 10 % of the measured value (Peters et al, 2007). However, since in a cutting torch the plasma pressure is close to the atmospheric pressure, the plasma temperature is mainly determined by the energy equation (with the dominant energy loses being due to inelastic electron collisions that produce a sort of "anchorage" in the temperature), and so it is almost decoupled from the hydrodynamic flow.…”

Relating Spectroscopic Measurements in a Plasma Cutting Torch to Cutting Performance

“…These include the absolute line intensity method, Boltzmann plot method or atom to ion line ratios. Each of these methods has been investigated in detail for this specific plasma system [4]. Temperature measurements presented in this work were obtained using the absolute intensity method from ion emission lines.…”

“…Multiple studies of the influence of the plasma cutting parameters on the plasma properties have been reported [2][3][4][5][6]. These investigations span a wide region of the available operating conditions.…”