Plasma conversion of carbon dioxide in DC glow discharge in a channel-type chamber

The experiments were carried out in a discharge tube with an internal diameter of 7.5 mm and a length 140 mm. The electrodes were hollow. We obtained a family of dependencies of conversion factor and energy efficiency of conversion on discharge power, CO₂ gas flows, specific energy input over a wide range of gas pressures, including Martian atmosphere (5 Torr). The spatial evolution of the conversion process was studied using spectral-spatial analysis. Current-voltage characteristics (CVC) are measured, which are stabilitronic in the case of a narrow gap between the electrodes due to the normal discharge mode, and in the case of a long tube, CVCs have a negative slope, which is determined by processes in a long positive column. It has been found that at low flow rates, the directional gas flow rate along the tube is low, so that diffusion gas mixing is possible. In this case, the composition of the gas mixture over the entire length is approximately the same, and therefore the entire length of energy input occurs in both CO₂ and reaction products, which reduces energy efficiency.

It is shown that the conversion rate reaches 85%, but energy efficiency does not exceed 10% due to the loss of power for accelerating positive ions, heating of the cathode and tube, excitation of gas molecules and products of conversion through electron impact. It is found that the highest conversion efficiency is observed in the range 5–10 Torr, whereas energy efficiency decreases monotonically with increasing pressure.