Preheating applied on a 915 MHz CO₂ microwave plasma: Unlocking the potential for heat recycling in plasma systems

We investigated the effects of inlet gas preheating on plasma performance in a vortex-stabilized 915 MHz CO₂ microwave plasma reactor. Spatially resolved spectroscopic measurements of the plasma were employed to understand how preheating affects the temperature profile. Thermographic measurements of the reaction chamber analyzed losses through the wall, offering deeper insights into the thermal changes within the system. The overall conversion performance was evaluated using gas chromatography. We demonstrate that recycling less than 10 % of the input power to preheat CO₂ (T_inlet = 700 K) can increase the energy efficiency of CO₂ conversion by up to 1.7 times at conditions near atmospheric pressure (700 mbar), at moderate microwave power (1132 W). The results indicate that preheating affects plasma fluid dynamics, resulting in shifts in plasma contraction and increased spatial temperature profile, or reactive volume, with higher inlet temperatures. This study provides new insights into the potential of integrating heat recycling in plasma reactors for future industrial applications.