Study on the kinetics and energy transfer during ignition of methane excited by NRP-SDBD non-equilibrium plasma

Abstract

The energy deposition distribution is crucial factor during plasma assisted ignition (PAI) influenced by streamer morphology, electric field, electron density and gas temperature. This paper presents numerical studies on energy transfer induced by gas heating and kinetic enhancement effect during ignition of lean and stoichiometric CH₄/O₂/He mixture excited by NRP-SDBD plasma. The two-dimensional plasma solver PASSKEy is employed to analyze hydrodynamic perturbation in a very small time-spatial scale for CH₄/O₂/He mixture with different equivalence ratios. A faster early perturbation response after plasma excitation occurs for stoichiometric CH₄/O₂/He mixture owing to more concentrated energy release. The plasma-participant path flux analysis model is newly developed to reveal the kinetic effects of key plasma species, dominant global reaction paths for oxidation of CH₄. It is highlighted that the important role of CH₄(v13) and O(1D) enriched at higher PRF by plasma-oriented kinetic reactions on formation of active radical O atoms and key intermediate CH₃. High PRF is beneficial for release of H atoms along with the reduced consumption for O₂ on the global reaction path of conversion from CH₄ to CO₂. Ultimately, the energy efficiency of gas heating is discussed from the view of plasma kinetics. The enrichment of O(1D) and charged species owing to improved PRF facilitates increase in the proportion of total discharge energy spent on gas heating attributed to the quenching reactions of O(1D) and recombination reactions of charged particles.