Coupled Kinetic and Electrical Simulations of Methane Plasmalysis by Nanosecond Discharges

We model the conversion of methane (CH4) towards hydrogen (H2) and acetylene (C2H2) at atmospheric pressure via Nanosecond Repetitively Pulsed (NRP) discharges. The chemical kinetic mechanism includes hydrocarbon species, CxHy, up to ethane (C2H6), along with their corresponding ions. The reaction rate constants available in the literature are reviewed and compared to build a kinetic model valid in the temperature range of interest for plasmalysis of methane. A zero-dimensional kinetic model is then used in a closed two-temperature system to solve the temporal evolution of species concentrations, the gas (heavy particle) energy, and the electron energy. This model also includes the interactions between the pulser, the transmission line (coaxial cable), and the load (plasma). Furthermore, pressure relaxation effects are considered. The simulated electron number density reproduces the trends observed in experimental data within one order of magnitude. The simulation provides the plasma resistance, which can then be used to design optimal pulsing strategies to increase the energy efficiency.