State-of-the-art combustion systems, such as Rich-Quench-Lean (RQL) concepts or diffusion flame-based concepts, offer potential options for transitioning to 100% H2 fuel. However, these systems have significant drawbacks in terms of nitrogen oxide (NOx) formation. Therefore, lean premixed combustion, which allows for accurate control of flame temperature and therefore deduction of NOx formation should be favoured. However, these processes have not yet reached the technological maturity required for the direct use of 100% H2 as a fuel in real engines. This is mainly due to the distinctly different flame characteristics of hydrogen compared to conventional fuels, including ignition behaviour, flame flashback, and adiabatic flame temperature.
Ignition behaviour of hydrogen involves shorter ignition delay times, making preheated H2-air mixtures more prone to autoignition in the premixing section. Additionally, the significantly higher flame propagation velocity of H2 compared to conventional fuels increases the risk of flame flashback, particularly near walls. Furthermore, stoichiometric and rich H2-air mixtures have higher flame temperatures than conventional fuels. Insufficient mixing of H2 and air can result in locally elevated temperatures, leading to significantly increased thermal NOx formation and high thermal loads on the combustion chamber.
Methodology
To develop functional models, a close collaboration between experimentation and simulation in the context of the UTC is essential. The partner institutes of STFS and RSM work in close cooperation. RSM provides detailed measurements of micro- and macrostructure of the hydrogen flames. This data will then be used at STFS to analyse, evaluate, and improve numerical models.
Flame Microstructure and Macrostructure Analysis: The microstructure and macrostructure of inner reaction zones, flame stabilization, and burning rate are investigated using experimental techniques. This includes quantifying local thermochemical states using Raman/Rayleigh spectroscopy and analysing turbulent flame structures using Particle Image Velocimetry (PIV) and planar laser-induced fluorescence (PLIF).
Model Development and Validation: Models for Large Eddy Simulation (LES) are developed based on the experimental data. The Tabulated Chemistry approach is used to describe the microstructure, and the Artificially Thickened Flame (ATF) model is employed to simulate the turbulent flame macrostructure. These models are further extended and adapted specifically for hydrogen combustion. The developed models are integrated into the Rolls-Royce in-house CFD solver PRECISE-UNS. The models are validated using reference data and compared with experimental measurements to assess their predictive capability.
Key Scientific Takeaways
- Enhanced understanding and modelling of H2 combustion, contributing to the design and optimization of combustion chambers
- Quantitative analysis of the specific effects of hydrogen transport and combustion properties on turbulent H2 combustion
Funding and cooperation
WotAn (Wasserstoffverbrennungstechnologie für Antriebssysteme der neuen Generation) is a joint research program in the frame of LuFo VI, Call 2. It is financially supported by the Federal Ministry for Economic Affairs and Climate Action (BMWK) under grant number 20M2104D, and Rolls-Royce Deutschland. Calculations for this research were partly conducted on the Lichtenberg high performance computer of the TU Darmstadt.
Publications
- Vance, Faizan; Alanyalioglu, Cetin; Hasse, Christian: Analysis of Lewis number effects on dynamic response of laminar premixed flames. In: Combustion and Flame 2023, 248, ISSN: 1556-2921, doi:10.1016/j.combustflame.2022.112508, [Article]
- Nicolai, Hendrik; Dressler, Louis; Janicka, Johannes; Hasse, Christian: Assessing the importance of differential diffusion in stratified hydrogen-methane flames using extended flamelet tabulation approaches. In: Physics of Fluids 2022, 34(8), ISSN: 1089-7666, doi:10.1063/5.0102675, [Article]
