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

Abstract

Non-thermal plasma discharges are considered as an assisted method for supporting conventional thermal processes, because the discharge-generated radicals can be used to benefit them. In this regard, plasma assisted combustion has been investigated extensively, and plasma assisted fuel reforming has expanded its horizons to include plasma assisted chemical synthesis, in accord with a global megatrend—electrification. To scientifically advance this area, plasma-chemical kinetic studies must be conducted, and their mechanisms should consider both electron and gas temperatures to describe electron-induced and thermally-induced chemistry, respectively. Here we present a temperature-dependent plasma-chemical kinetic study for the plasma assisted oxidation of an undiluted rich H2/O2 mixture; it represents our continued effort to establish a foundational plasma assisted reaction mechanism for H2/O2 systems. A plasma-chemical kinetic model (KAUSTKin) and a modified plasma-chemical reaction mechanism were used for the zero-dimensional simulation; a temperature-controlled dielectric barrier discharge reactor was employed for the experiment. Non-linear oxidation behavior was observed in a range of 300–850 K for various discharge powers. To unravel the underlying mechanisms, analysis was broken down to a physical effect, described by the reduced electric field (E/N), and a chemical effect originating from the temperature dependence of the plasma assisted oxidation chemistry. We concluded that (i) the oxidation was initiated by the electron impact dissociation of H2, (ii) E/N governed the degree of H2 dissociation (and thus the degree of oxidation), (iii) the key intermediate was HO2, and (iv) a significant increase in the chain termination reaction, H + HO2 → H2 + O2, suppressed the oxidation (especially in the Negative Temperature Coefficient (NTC)-like regime of 600–725 K). The need to improve existing thermal reaction mechanisms for temperatures below 1000 K was emphasized, and a method for temperature-dependent plasma-chemical kinetic studies to provide a novel and complementary tool for this task was demonstrated.