Combined thermal imaging and radiative modelling for temperature reconstruction of a CO2 plasma jet

Journal article, 2026

To mitigate greenhouse gas emissions, high-temperature industries must transition toward electrified and more sustainable heating technologies. For some processes, replacing fossil-fired burners with plasma-based heat sources is promising but requires careful small-scale evaluation. In this work, radiative characteristics of a 50 kWel non-transferred CO2 plasma torch operating in open air are investigated using thermal infrared imaging and radiative intensity measurements. The two measurements are combined with detailed spectral modelling of the gas radiation to reconstruct the temperature distribution within the plasma jet. The model accounts for emission and absorption by CO2 and CO within the broadband range of the radiative intensity measurement (0.1–100 µm) as well thermal camera’s detection range (6.8–17 µm) and accounts for the spectral properties of the optics and detector sensitivity. The modelled photon flux incident on the camera sensor is converted into equivalent units of digital counts and compared to measurements. A supporting CFD analysis indicates significant CO₂ dissociation near the plasma torch exit and air entrainment downstream, both of which reduce optical thickness and help interpret discrepancies between measured and modelled IR signals. Sensitivity analysis shows that background reference levels and gas composition exert stronger influence on IR counts than on broadband intensity. Results demonstrate that thermal imaging, combined with radiative intensity measurements and modelling, constrains the plasma temperature field, with IR imaging defining the spatial structure and radiative intensity matching setting the absolute temperature scale. Overall, the combined diagnostic–modelling framework demonstrates a feasible pathway for non-intrusive, spatially resolved temperature reconstruction in CO₂ plasmas relevant to electrified high-temperature industrial applications, where spectrally resolved diagnostics are often difficult to implement. Novelty and significance statement This work demonstrates a new approach for temperature reconstruction in CO₂-based thermal plasma jets by combining calibrated infrared imaging with total radiative intensity measurements and detailed spectral radiative transfer modelling. The method links camera counts, photon flux, and gas temperature through radiative transfer modelling, enabling non-intrusive, spatially resolved diagnostics of plasma-assisted heating. By combining the different measurement techniques, the possible temperature distributions within the plasma jet can be more narrowly constrained, improving agreement between modelled and measured radiation. The study provides new insight into radiative heat transfer mechanisms relevant to electrified, high-temperature industrial processes.