Modelling The Interaction of Plasma “Hot Pockets” with Gas Containing Nitric Oxide

Abstract

The paper concerns modelling of the effects produced when nitrogen plasma is injected into atmospheres containing nitric oxide with characteristics similar to flue gas. The basis of the model is that the nitrogen atoms generated by low voltage DC discharge emerge into a process gas while located initially within relatively small “pockets” of very hot gas. Experimental evidence for these pockets has been published elsewhere by Weinberg and co-workers. Following the concepts of N.N. Llepojevic the processes of diffusion of chemical species into and out of such pockets are computed, as are also the rates of competitive reactions in which N atoms react respectively with NO (removal) and with O₂ (generation) of NO. By these calculations profiles are predicted in concentrations of N, NO, and O₂ as functions of the temperature field around these pockets. The main findings of the investigations can be summarized as follows: the time during which the chemical reactions are accomplished for temperatures examined in this work was found to be roughly 10^-4s; higher plasma temperatures lead to shorter reaction times; diffusion processes take place at a much slower pace. A greater presence of oxygen enhances the effect of the build-up of nitric oxide inside the plasma pocket, since the N-radicals and O₂ combine to NO. The concentration of NO in the outside gas mixture has, with the present model, only very little influence on the production of nitric oxide inside the plasma pocket. Smaller plasma pockets lead to less formation of NO inside the pocket, and furthermore they tend to affect the outside gas to a larger extent than bigger pockets. The results are discussed in relation to experiments in which net removal/production of NO have been measured. Finally, suggestions are made on future adaptations of the model employed in the programme.