Boosting the NOx production in microwave air plasma: A synergy of chemistry and vibrational kinetics

TL;DR

This paper investigates how vibrational and chemical kinetics influence NOx production in microwave air plasma, revealing that non-thermal processes significantly enhance NOx synthesis but diminish rapidly post-discharge, with turbulence affecting diffusion and cooling.

Contribution

It introduces a comprehensive quasi-1.5D multi-temperature model that combines chemistry, vibrational kinetics, and transport processes to analyze NOx production in microwave plasma reactors.

Findings

Non-thermal processes boost NOx production via vibrational energy transfer.

Turbulence enhances radial NO diffusion and cooling, affecting efficiency.

Simulation aligns well with experimental temperature and energy cost data.

Abstract

This study employs a quasi-1.5D multi-temperature model to investigate the mechanisms governing NOx production and energy costs in microwave plasma reactors operating at 80 mbar, focusing on the interplay of vibrational, chemical and electron kinetics, thermodynamics, and transport processes across the discharge and afterglow. In the plasma discharge zone, non-thermal processes enhance NOx production as electrons transfer energy effectively to the vibrational mode of N2. However, the non-thermal enhancement is found to diminish rapidly within the central-afterglow region. The simulation results show good agreement with experimental data for both the temperature profile and energy cost. Turbulent effects facilitate radial NO diffusion into cooler regions while simultaneously enhancing cooling of the axial region. These findings highlight the potential to improve NOx synthesis efficiency by optimizing turbulence and maintaining non-thermal conditions, offering new opportunities for the advancement of plasma-based chemical processes.