SafE and reliabLE COmbustion Technologies powered by Hydrogen

Project Information

SELECT-H

Grant agreement ID: 101097984

DOI

10.3030/101097984

EC signature date 26 June 2023

Start date 1 October 2023

End date 30 September 2028

Funded under

• European Research Council (ERC)

Total cost

€ 2 499 489,84

EU contribution

€ 2 499 489,84

Coordinated by

UNIVERSITE DE TOULOUSE
France

Periodic Reporting for period 1 - SELECT-H (SafE and reliabLE COmbustion Technologies powered by Hydrogen)

Reporting period: 2023-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

Hydrogen has the potential to become a unique energy vector, contributing simultaneously to energy security and net-zero greenhouse-gas emission goals, provided that (1) it can be produced from low-carbon resources and (2) hydrogen-powered systems can be operated safely and reliably. SELECT-H addresses the second challenge.

SELECT-H is an ERC Advanced Grant led by the Institut de Mécanique des Fluides de Toulouse (IMFT, Université Toulouse and CNRS), in partnership with CERFACS. These institutes have a long-standing collaboration and internationally recognized expertise in hydrogen combustion. The project started in 2023, runs for five years, and aims to develop and validate predictive tools to guide the design of safe and reliable combustion technologies operating with pure hydrogen.

Because of the very high reactivity of hydrogen with oxygen, replacing conventional hydrocarbon fuels with hydrogen can trigger undesired and potentially violent transient combustion phenomena which are only rarely observed with other fuels. Such events may compromise system integrity, reliability, and safety, and therefore require a fundamental rethinking of combustor design, fuel-injection strategies, and ignition concepts.

The main objectives of SELECT-H are to:
1. Develop new experimental approaches to characterize transient, often violent hydrogen combustion dynamics, obtain detailed flow characterization to improve fundamental understanding of these transient phenomena, and provide high-quality data for the validation of numerical models.
2. Systematically develop digital twin numerical configurations tailored for high-fidelity simulations, using CERFACS CFD tools, in order to accurately reproduce and predict the hydrogen combustion dynamics observed in the experiments across relevant operating conditions.

The results of SELECT-H will support the transition from hydrocarbon-based technologies to safe and reliable hydrogen-powered systems in two main areas:
1. Power and propulsion systems for heat or thrust production, where hydrogen must burn efficiently and safely with smooth dynamics.
2. Safety-critical scenarios involving undesired hydrogen combustion, such as accidental hydrogen leaks, to understand ignition mechanisms and the resulting flame interactions with surrounding structures and walls.

Overall, the advances achieved through the combined experimental and numerical approaches of SELECT-H will enable the development of next-generation predictive tools capable of anticipating violent transient hydrogen combustion phenomena, thereby providing robust guidance for the design of safe and reliable hydrogen-based energy systems.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first two years, the project focused on building and using advanced experimental facilities to better understand the rapid and sometimes violent behavior of hydrogen flames. These facilities made it possible to identify the key physical mechanisms underlying these unsteady phenomena, determine the conditions under which they occur, and initiate detailed flow characterizations and companion numerical flow simulations under steady flow configurations before addressing fully unsteady situations.

For low-power laminar premixed hydrogen flames, the research concentrated on flashback, a hazardous phenomenon in which a flame propagates backward into the opening above which its is stabilized. It was demonstrated that flashback can arise from different mechanisms depending on the size of the burner opening. In large openings, flashback is mainly governed by the flow dynamics along the burner boundary layer, as for conventional fuels, although hydrogen preferential diffusion significantly increases the risk. As openings become smaller, new physics should be considered. when the aperture width is comparable to the flame thickness, flashback is controlled by the balance between the heat released by chemical reactions and heat losses to the solid walls. When the opening is smaller than the flame thickness, it was shown that flashback remains possible and is in this case controlled by near-wall hydrogen rapid chemistry kinetics.

For high-power hydrogen systems, advanced optical laser diagnostics were coupled with acoustic measurements to investigate high-frequency self-sustained combustion oscillations, which can cause severe damage and are difficult to predict. These diagnostics provided new insights into the triggering of these undesired phenomena, showing that acoustics mainly act indirectly by synchronizing vortical structures in the flow, which in turn modify the flame in a resonant manner.

In parallel, dedicated experimental setups were developed to study hydrogen leaks through small openings. These studies focused on characterizing the mixing process of hydrogen flowing from the leaking orifice with air, which is key to understanding flame ignition and subsequent possible flame stabilization. A technique was also developed to measure the heat flux from a flame impinging on a wall, providing critical data for safety assessments and guidelines for engineers to design wall resistant to hydrogen fires. Companion numerical simulations of these configurations have been initiated to support and interpret the experimental observations.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The facility dedicated to studying flashback enabled the development of a new technique for measuring quenching distances, i.e. the minimum aperture size below which a premixed flame cannot propagate through. This distance depends on the hydrogen–air molar ratio, thermodynamic conditions, orifice shape and material. Unlike previous methods, which were limited to specific geometries, the technique developed within the SELECT-H framework can be applied to arbitrary aperture shapes. It was also demonstrated that the hydraulic diameter can be used to generalize quenching distances across different geometries. While this method has so far been tested for lean hydrogen–air flames under ambient conditions, future work in SELECT-H will extend it to other mixtures and operating conditions.

Detailed investigations of the interaction of a hydrogen air swirling flame with acoustic and hydrodynamic fields during high-frequency, self-sustained combustion oscillations revealed the key physical mechanisms driving these synchronized heat-release rate fluctuations. These observations could be reproduced by a new mathematical framework derived from first principles, whose predictions show excellent agreement with experimental results. This framework provides the foundation for predictive tools for thermo-acoustic phenomena, which are currently being tested within SELECT-H.

The extensive experimental database obtained under steady-flow conditions now serves as a reference for the scientific community, supporting the validation of numerical flow models for hydrogen-air combustion. More than 30 research groups around the world are currently testing their codes and models against these benchmarks. The next step is to extend these benchmarks to the unsteady-flow configurations explored in SELECT-H, including flashback, high-frequency combustion instabilities, and hydrogen leaks through small orifices.