Physical insights into plasma-assisted methane reforming: microdischarge dynamics and diluent effects

Dielectric barrier discharge (DBD) in fuel reforming processes has been widely investigated for its well-defined physical properties relevant to chemical kinetics and discharge physics, supporting the transition toward carbon-neutral society. However, a spatially and temporally resolved investigation of the physical and chemical aspects of plasma-assisted fuel reforming is essential to enhance our understanding and refine plasma kinetic mechanisms. In this study, we investigated the microscopic discharge characteristics in gas mixtures for partial oxidation (POx) and dry reforming of methane (DRM), focusing on the effects of N2 and Ar dilution on successive microdischarges. Using a pin-to-line electrode configuration, we found that organized, recurring microdischarge patterns were achievable only with N2 or Ar dilution, highlighting the crucial role of their excited metastable states in facilitating Penning ionization. For both POx and DRM mixtures, discharge power maintained consistently across N2 dilution ratios but decreased significantly as the Ar dilution ratio decreased. BOLSIG+ simulations attributed these trends to differences in electron energy loss to ionization and electronic excitation. Recognizing the importance of consistent temporal and spatial microdischarges for laser diagnostics, we mapped successive microdischarges characteristics as a function of applied voltage and frequency. These findings provide a foundational reference for future studies, enabling spatially and temporally resolved measurements of key parameters such as electric field intensity, electron density, temperature, and radical species. We plan to investigate CH3 and CH radicals using the same experimental setup to further advance our understanding of plasma-assisted reforming processes in the near future.