Radiative Heat Transfer Analysis in a Hybrid Plasma Combustion System for Fuel-Flexibility

Other conference contribution, 2025

Greenhouse gas (GHG) emissions, especially CO₂, are a significant global concern in many industries, where fossil fuels drive the energy-intensive, high-temperature processes required for production. This reliance on conventional fuels impacts climate change and highlights the industry’s need for more sustainable and flexible energy solutions. Here, thermal plasma technology offers a promising path forward. With its ability to reach extremely high temperatures and support the combustion process of alternative fuels, plasma-based systems can directly reduce GHG emissions and lessen dependency on traditional fuels. This study aims to characterize the heat transfer in an experimental hybrid plasma combustion system for fuel-flexible glass manufacturing, focusing on methane (CH₄) and hydrogen (H₂) combustion with and without plasma assistance as well as presenting temperature estimations of the same.

The study is based on experiments conducted using a 50 kWel plasma generator and 100 kWth combustion burner to study the combustion of CH₄ and H₂ with and without plasma assistance. The experimental setup included detailed measurements of radiative intensity, flame structure, and temperature distribution, using Narrow Angle Radiometers (NAR) and a FLIR infrared (IR) camera. Four NAR probes, each equipped with a thermopile detector sensitive to wavelengths between 1-100 µm, were positioned along the flame axis, measuring radiative intensity, and the IR camera, with a spectral range of 7.5-14 µm, were placed opposite to these probes to capture detailed flame radiance profiles and structural dynamics across the axial length (Figure 1).

The NAR measurements show a distinct radiative intensity profile, peaking at the second downstream NAR probe placed at 17 cm from the burner, indicating a somewhat local hot zone along the flame axis for both pure combustion and plasma-assisted combustion cases.  The hydrogen cases consistently showed on higher radiative intensity values than the methane cases for both combustion modes. In both plasma-assisted and non-plasma-assisted cases, the radiative intensity increased with increasing plasma power, highlighting plasma's role in enhancing combustion.

In contrast to the NAR measurements, the IR camera radiance profiles showed on a concentrated radiance near the plasma source, decreasing gradually along the flame’s axial length for the plasma-assisted cases. Still, both methane and hydrogen cases displayed similar radiance patterns, with the highest radiance recorded at the probe position close to the plasma generator suggesting the majority of radiative energy being emitted close to the plasma source. However, combustion cases show lower values near the burner end and increase along the flame’s axis. This difference between the two measurement techniques in terms of radiance profile can probably be attributed to different spectral ranges of the equipment and is partly examined within this work. 

This work further aims to present estimations of reasonable temperature ranges for the various cases. Based on basic combustion and heat balances, gas composition at the NAR probe positions are estimated and a discrete transfer method using the Malkmus statistical narrow-band model for gases is applied to fit modelled and measured radiative intensities as a function of temperature.

 This initial experimental campaign provides foundational insights into heat transfer in a hybrid plasma combustion system. The findings on radiative intensity offer a basis for optimizing fuel flexibility and combustion efficiency. Future work will build on these results to refine plasma-assisted combustion models and support pilot-scale applications.