Hydrogen-fired gas turbines can potentially produce electric power (or mechanical work) at unmatched scale with zero carbon emissions. Furthermore, they will yield this potential at high cycle efficiency and with virtually zero emissions of atmospheric pollutants once advanced Dry Low Emission (DLE) combustion systems, able to robustly and reliably stabilise premixed hydrogen flames at high pressures, are successfully developed.

However, the development of such advanced DLE combustion systems is presently hampered by the existence of knowledge gaps about premixed hydrogen combustion at high pressure. More specifically, a crucial lack of knowledge concerns the pressure dependence of the turbulent burning rate in premixed hydrogen flames. This is due to the fundamental combustion characteristics of premixed hydrogen flames, largely deviating from those of natural gas and other more conventional hydrocarbons and affects our ability to accurately predict the stability limits of these flames.

These knowledge gaps need to be closed through fundamental research in order to facilitate, in the short and medium term, the adaptation of existing DLE combustion systems to operate with various hydrogen-enriched fuel blends that will constitute the principal energy carrier in the upcoming transition period. In the longer term, once large quantities of hydrogen become widely available, the knowledge acquired will play a crucial role in enabling the development of advanced combustion systems based on novel fuel injection and staging strategies that are able to burn pure hydrogen without incurring in the penalties related to steam/water injection or nitrogen dilution of the fuel.

Project results are expected to contribute to all the following expected outcomes:

• Development of breakthrough technologies for DLE combustion systems able to burn 100% hydrogen at the most demanding operating conditions for the gas turbine (full-load);
• Maintaining European leadership in the field of combustion dynamics control and facilitating the implementation of mitigation measures for thermo-acoustic instabilities in DLE combustion systems burning 100% hydrogen across the gas turbine load range (idling to full-load);
• Development of game-changing technologies for truly fuel-flexible operation of gas turbines, contributing to establish a crucial competitive edge to European gas turbine manufacturers and end-users in a future market for low-carbon chemical energy carriers dominated by uncertainty.

Attainment of the three project outcomes listed above will have positive impact to the gas turbine industry in maximising of the gas turbine cycle efficiency and positively impact mitigation measures targeting NO_x emissions, in compliance with strictly regulated emissions limits.

Project results are expected to contribute to the following objectives and KPIs of the Clean Hydrogen JU SRIA for gas turbines:

• Increase hydrogen percentage in the fuel (100% by 2030);
• Minimise cycle efficiency reduction during hydrogen operation (max 2%);
• Maintain low NOx emissions (<24 NOx mg/MJ fuel @100% vol H2 by 2030).

The research scope involves acquisition of fundamental knowledge, development of modelling and analytical tools, optimisation of advanced fuel injection concepts and/or combustion staging strategies to increase the robustness of operation and the fuel flexibility of gas turbines, while conserving their cycle efficiency and emissions performance. More specifically, proposals should:

• Establish accurate experimental data and reliable model estimates about the burning rate and the boundaries of static flame stabilisation (flashback and blow-out avoidance) in turbulent premixed combustion of hydrogen-enriched fuel blends (up to 100% H2) from atmospheric to high-pressure conditions (up to 10 bar, at least).
• Accurately predict the thermo-acoustic response and the boundaries of dynamic flame stabilisation (combustion dynamics control) in turbulent premixed combustion of hydrogen-enriched fuel blends (up to 100% H2) from atmospheric to high-pressure conditions (up to 10 bar, at least).

The above-mentioned two points can be achieved by exploiting a combination of first-principle numerical simulations, to minimize the modelling assumption, and advanced optical measurements, to obtain an accurate characterization of the flames across the pressure range investigated. Furthermore, it is of crucial importance to seek the widest generality and applicability of the results. This objective can be conveniently pursued by the adoption of canonical turbulent premixed flames configurations (e.g. Bunsen, bluff-body, transverse jets or swirl-stabilised) for the proposed work.

• Establish the optimal combustion process and combustion system layout, fuel injection and fuel staging strategies that simultaneously achieve the most robust flame stabilisation and the best low-NOx performance for different hydrogen-enriched fuel blends (e.g. with ammonia or natural gas) at high-pressure conditions. This can be achieved by developing numerical modelling and experimental testing of advanced, less generic and more specialized, combustion systems at laboratory scale (TRL 3-5), featuring novel fuel injection concepts and combustion staging strategies, with downscaled prototypes simulated and tested in laboratory facilities spanning atmospheric to high-pressure conditions (up to 10 bar, at least). Flame stability and emissions performance should be compared between alternative designs based on different fuel injection and staging strategies.

Although not strictly required to develop fuel-flexible combustion system layouts and innovative solutions, the involvement of a Gas Turbine Original Equipment Manufacturer (GT OEM) in the relevant research activities should be considered of crucial importance to significantly strengthen the industrial relevance of the research and its applicability and transferability to gas turbine applications.

The numerical and experimental methodologies should be selected to achieve a clear analytical differentiation between concurrently occurring and tightly interconnected processes, i.e. the increase in bulk Reynolds number and thermo-diffusive instabilities with pressure with the variation in chemical reactivity. In order to ensure that the principal rate-controlling processes and their trends are correctly and accurately captured at relevant conditions, laboratory experiments and numerical modelling efforts should target a pressure range covering a significant portion of the range relevant in gas turbine operation. Therefore, as a minimum requirement, the pressure range comprised between 1 and 10 bar should be investigated using state-of-the-art numerical modelling and experimental measuring techniques, i.e. featuring detailed optical diagnostics of the flame geometrical characteristics, of its stabilisation, structure and response to acoustic forcing.

Proposals are expected to collaborate and explore synergies with the following:

• projects FLEX4H2 and HELIOS supported under the topic “HORIZON-JTI-CLEANH2-2022-04-04: Dry Low NOx combustion of hydrogen-enriched fuels at high-pressure conditions for gas turbine applications”;
• project supported under the topics “HORIZON-JTI-CLEANH2-2023-04-02: Research on fundamental combustion physics, flame velocity and structure, pathways of emissions formation for hydrogen and variable blends of hydrogen, including ammonia” and “HORIZON-JTI-CLEANH2-2023-04-03: Retrofitting of existing industrial sector natural gas turbomachinery cogeneration systems for hydrogen combustion”.
• projects HYDEA and CAVENDISH supported by the Clean Aviation JU (CA-JU)

Proposals are expected to contribute towards the activities of Mission Innovation 2.0 - Clean Hydrogen Mission. Cooperation with entities from Clean Hydrogen Mission member countries, which are neither EU Member States nor Horizon Europe Associated countries, is encouraged (see section 2.2.6.7 International Cooperation).

For additional elements applicable to all topics please refer to section 2.2.3.2.

Activities are expected to start at TRL 3 and achieve TRL 5 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 4.00 million would allow these outcomes to be addressed appropriately.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2024 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2023–2024 which apply mutatis mutandis.