3D PIC-MCC simulations of positive air-methane streamers for plasma-assisted combustion

We investigate the properties of positive streamers in a stochiometric air-methane mixture, motivated by plasma-assisted combustion. For this purpose we have performed large-scale simulations using a 3D particle-in-cell model. Methane requires additional electron impact cross sections that we have discussed in a recent paper Bouwman et al. (2021) [https://arxiv.org/pdf/2106.01935.pdf], and the photoionization of air (needed for positive streamer propagation) is reduced due to photon absorption by methane. We find that methane influences the dynamic poperties in several ways, mainly due to the short photoionization length: (1) the front becomes more unstable and branches often. (2) the velocity decreases while the maximum electric field increases (3) the tail of the EEDF is enhanced, with energies of 200 eV observed in a  background field of 24 kV cm^-1. Moreover, from our simulations we extract quantities relevant for plasma-assisted combustion at different applied voltages. For instance, we calculate the density of deposited energy which shows a very high peak exceeding 10 kJ m^-3 which has the potential to evolve into an ignition kernel. Moreover we calculate the density of relevant chemical species and radicals produced by a streamer.