Modeling of a premixed hydrogen-air combustion in a gas condensing boilerJaeger, Marc (Avtor) Samec, Niko (Mentor) Hriberšek, Matjaž (Komentor) CFDhydrogen combustionflashbackflame stabilityperforated flame holdergas condensing boilerexperimental flashback measurementsThis work addresses the urgent need for decarbonization of heating sector, focusing on the potential of hydrogen-air combustion in gas condensing boilers. In the field of gas condensing boilers, groups of holes or slits can be used in perforated burner surfaces, providing a possible solution to the challenge of hydrogen air combustion. Real burners are always adjacent to an area with non-existent combustion, which can lead to a disturbed flame pattern. For this reason, a comparison between single-slit and multi-slit perforated flame holders with a significantly reduced structure temperature with a hydrogen-air premix is carried out as part of this study. Using Ansys Fluent, a 2D simulation approach is employed to analyze laminar flame stability behind a perforated flame holder. Inlet conditions consider fully premixed and homogenous distributed mixtures as well as non-homogeneous premixed mixtures, with variations in pressure, velocity, and mixing degree. The model examines various slit-burner configurations and flashback behaviors based on an actual geometric shape used in a gas heating device. It has been found that with finite multi-slit burners, the bulk flow rates at the critical flashback point are 30-50% higher compared to infinitely symmetrical burners. A further deterioration of 32% is to be expected due to real mixture quality fluctuations and inhomogeneous inflow conditions. The numerical model was validated using a prototype heat exchanger and a production-ready mixture preparation system in combination with various burner geometries. From a practical standpoint, the results provide clear guidance for burner design. Long and narrow holes with moderate spacing -ideally at least one diameter apart- promote flame stability while maintaining a compact configuration. In clustered geometries, optimizing the number of flow passages can prevent local overheating and enhance operational robustness. For complex or thermally sensitive geometries, the use of 3D CFD simulations with conjugate heat transfer (CHT) coupling is strongly advised to ensure accurate and safe designs. Additionally, at higher air excess ratios, the current numerical model becomes less accurate due to intensified preferential diffusion and Soret effects, highlighting the need for a 3D CFD approach using the Konnov reaction mechanism. Finally, the findings demonstrate the model's potential for designing efficient surface stabilized burners and lay the groundwork for future 3D simulations in the pursuit of sustainable heating solutions.[M. Jäger]20252025-06-06 10:20:05Doktorsko delo/naloga93113UDK: [662.61:662.769.2]:697.245(043.3)COBISS_ID: 266347523sl