Kinetic study of plasma assisted oxidation of H2 for an undiluted lean mixture

Abstract

For the past couple of decades, electrical discharges (or plasmas) have been widely investigated in pursuit of the advancement in combustion and fuel reforming. Particularly, nonthermal plasma has attracted researchers’ attention to improve ignition characteristics, promote flame stability, and reform hydrocarbons. Nevertheless, due to the nonthermal plasma's complex physicochemical nature, most of the experimental findings have not been fully explained yet. Recently, plasma-chemical kinetic studies have been initiated to address the important roles of plasma chemistry in hydrocarbon chemistry including combustion phenomena. However, we still have a long way to go to fully understand the underlying mechanisms and predict experimental outcomes. Here, we present a kinetic study of plasma-assisted low-temperature oxidation of H2 for an undiluted H2/O2 mixture. The aim of this study is to establish a foundation for low-temperature plasma assisted combustion as well as high-temperature plasma assisted reforming processes. We employed a plasma-chemical reaction mechanism and plasma-chemical kinetic modeling platform (KAUSTKin) and a temperature controlled dielectric barrier discharge reactor to study the plasma assisted oxidation of H2. As a result of systematically varying the gas temperature and discharge power, we found a non-linear oxidation behavior highlighting a Negative Temperature Coefficient (NTC)-like trend in a temperature range of 600–750 K. We investigated the effects of both the reduced electric field and the temperature on the plasma assisted oxidation chemistry. We found that (i) the oxidation is initiated by the electron impact dissociation of O2, which is governed by the reduced electric field and controls the oxidation degree, (ii) HO2 is the key intermediate for the full oxidation to H2O, and (iii) O3 and H2O2 production negatively affect the oxidation for temperatures below 400 K and over 600 K, respectively. We believe that these findings will further contribute to a better description and deeper understanding of the plasma chemistry with hydrocarbons as well as other H2 mixtures.