Chemical kinetics of NO removal by pulsed corona discharges

Abstract

Nitric oxides (NO and NO2) and SO2 emissions are amajor environmental problem because of their negative influence on humanhealth and vegetation. The federal regulations on limiting the pollutionemitted by the engines of motor vehicles have triggered intense research onnew techniques for the removal of these pollutants. New methods for exhaustgas cleaning are needed and among the several approaches to reduce thepollutant emissions, the non-thermal plasma technique shows promise(Luo J, Suib S L, Marques M, Hayashi Y and Matsumoto H 1998 J. Phys. Chem. A 102 7954).In this work, a volume-averaged model is presented that can describe theremoval of NOx by the multi-pulse treatment of the exhaust gases atlow temperatures and at atmospheric pressure in corona reactors. The modeltakes into account the production of active radicals after every discharge andthe removal of NO by these radicals. Furthermore, the effect of ethene, one ofthe most important unburnt hydrocarbons in the exhaust gas, on the removal ofNO is also investigated in this study. The effect of ethene has beeninvestigated experimentally by several authors (Mizuno A, Chakrabati A and Okazaki K 1993Non-Thermal Plasma Techniques for Pollution Controled B M Penetrante and S E Schultheis (Berlin: Springer) p 165,Prather M J and Logan J A 1994 Proc. Combustion Institute 25 1513), but there are almost nostudies which try to explain, in detail, the chemical processes in such asystem. The detailed reaction mechanism used in this study consists of 443elementary reactions and 50 chemical species. The results of our numericalsimulations show good agreement with the experimental results published in theliterature. Reaction flow analysis and sensitivity analysis are performed inorder to identify the specific reaction paths and the rate-limiting reactionsfor typical operating conditions of pulsed corona reactors.