Supersonic expansion of CO2 plasmas*

Finding solutions for global warming, caused by greenhouse gas emissions, is one of the key challenges facing modern society. Plasma-assisted green technologies have significant potential in creating a sustainable planet. Microwave-induced plasma expansion is considered an energy-efficient approach for CO2 dissociation. This method utilizes surplus green energy to power microwave sources, treating CO2 and converting it into high-energy-density, value-added fuels. One of the main issues in plasma-assisted CO2 valorization is the downstream destruction of dissociated CO2. Incorporating shock-free supersonic nozzles downstream of the plasma source not only prevents nullification of dissociation but also enhances further dissociation. Understanding and optimizing the complex physico-chemical mechanisms of microwave plasmas, including plasma kinetics, plasma chemistry, heat transfer, and fluid mechanics, pose challenges for comprehensive comprehension. The main objective of this work is to develop numerical models that comprehensively capture the inherent complexities of plasma gas flow dynamics and determine optimal plasma conditions for CO2 dissociation. This study focuses on CO2 dissociation in a shock-free supersonic expansion. The results indicate that recombination is completely obstructed by the supersonic expansion, while high degrees of dissociation can be achieved along the nozzle axis. The dissociation degree shown in this study represents additional dissociation beyond the active plasma zone, as the dissociation associated with the active plasma zone is not considered. The results presented here are obtained using 1D models, and future work will involve integrating the active plasma zone upstream of the supersonic nozzle for further investigation.