Hydrogen is a potential enabler of a low-carbon economy and can be a key instrument for the European Green Deal and the recent REPowerEU Plan objectives. However, hydrogen storage and distribution issues represent a challenge for its implementation: for example, ammonia (NH₃) is currently considered a promising solution as hydrogen carrier to overcome such barriers, but other unconventional hydrogen blends can be identified (including NH₃/H₂/N₂ blends obtained through partial decomposition of NH₃) whose reactive features should be well established before their exploitation in combustion applications.

While knowledge on hydrogen enriched natural gas combustion is well established, new blends (like NH₃/H₂/N₂ blends) were not investigated enough and require some fundamental research, also exploring conditions due to specific approaches that can be adopted to reduce NO_x emissions like Exhaust Gas Recirculation (EGR). Gaining insights in these unconventional hydrogen blends combustion will contribute to enhance gas turbine fuel-flexibility and to strengthen the backbone of the future hydrogen infrastructure, finally supporting EU’s energy system decarbonisation pathway and effectively ensuring the grid stability and security of supply, thus promoting the sustainability of an increasing share of variable renewable energy sources. Besides, progressing technology using hydrogen and its blends as fuel will promote the commercial viability of hydrogen generation, an important step for the realisation of a circular economy system and sustainable development. Finally, the topic fundamental low TRL activities on gas turbines would be beneficial for all combustion applications, including industrial boilers and burners, and marine and aerospace transportation.

Project results are expected to provide fundamental knowledge about several aspects related to the utilisation of hydrogen blends with ammonia or other not well-known hydrogen blends with methane (natural gas) in Dry Low Emission (DLE) gas turbines (which use premixed lean-combustion principles to achieve a reduction in NO_x emissions).

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

• Identify accurate chemical kinetics mechanisms of oxidation and pollutants formation;
• Enhance knowledge in combustion dynamics and define reliable and suitable indexes for the real-time identification of instability precursors;
• Identify fuel-flexible low-NOx combustion technologies, upon exploration of currently promising sequential combustion, EGR and micro-mixing approaches, and evaluate their technological feasibility for applications in distributed systems all the way to large scale power generation plants;
• Overcome the remaining barriers to the performance of combustion units using such blends;
• Ensure a cost effective and safe utilisation of unconventional hydrogen blends, including hydrogen mixtures with ammonia, as gas turbine fuel.

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

• Preparing gas turbines to run on 100% hydrogen, while ensuring the required fuel-flexibility in the energy transition and keeping conversion efficiencies and NO_x emission to acceptable levels.
• Increase hydrogen percentage in the fuel (at least 70% by volume in 2024);
• Maintain low NO_x emissions (<25 ppmv @ 15%O₂/dry @ 70% and 100% vol H₂, or more specifically, 29 NO_x mg/MJ fuel @ 70% vol H₂ in 2024 and 24 NO_x mg/MJ fuel @ 100% vol H₂ in 2030);
• Enhance gas turbine ability to handle hydrogen content fluctuations (at least ±15% points H₂ volume / minute in 2024, with a view to reach ±30% points in 2030).

Use of natural gas mixtures with high hydrogen content still exhibits high NO_x pollutant emissions, thus requiring the implementation of appropriate combustion technologies in new or existing gas turbines, such as DLE, sequential combustion, EGR and micro-mixing approaches. Besides, although recent research has shown that partial decomposition of ammonia (after transportation) to a blend of ammonia/hydrogen/nitrogen can be an interesting solution, many fundamental aspects of ammonia/hydrogen flames are not yet known, and NO_x emissions are a concern too. Other potential not well-known hydrogen blends could show similar issues.

Proposals should address the following areas of R&I:

• Development/validation of chemical kinetics mechanisms for combustion of unconventional hydrogen blends also in different technological contexts, e.g. with and without exhaust gas recirculation, from atmospheric to industrially relevant pressures, giving special emphasis on NO_x and N₂O formation pathways especially for ammonia/hydrogen blends. Achieving an optimal balance between accuracy and complexity (i.e. computational cost in its use) should be considered as an important achievement;
• Numerical modelling and laboratory-scale experimental investigation of the conditions that ensure static (flashback and blow-out control) and dynamic (control of thermo-acoustic instabilities) stabilisation of premixed and non-premixed flames of unconventional, not well-known hydrogen blends while conserving low-emission performance, from atmospheric to industrially relevant pressures. The specific strategy that will be adopted to pursue the main goal should be clearly described in the proposal (e.g. fuel/air staging, fuel injection, blending etc.);
• Identification of real-time monitoring strategies of combustion, that can be reasonably implemented in gas turbines. The selected strategy should also come up with the definition of reliable and suitable indexes for the real-time identification of instability precursors.

In developing its concept, proposals are expected to address the following related aspects:

• To lower the environmental impact of the proposed solution (in particular, the level of pollution it will create and in general, the overall contribution to harden the climate emergency);
• To lower the barriers to the deployment of such technologies, including issues related to social acceptance and safety.

Proposals should address the validation of unconventional, not well-known hydrogen blends (like NH₃/H₂/N₂ blends ) combustion to TRL 4, presenting a robust research methodology and activities, establishing its technological feasibility. The methodology should include proper assessment of the technological feasibility, safety, and risk of using new blends in DLE gas turbines for power generation and transport applications, including environmental, social, and economic risk/benefit balance (e.g. evaluation of cost reduction and efficiency improvements vs consequences in case of accident). These aspects may provide ideas, experiences, technology contributions, knowledge, new approaches and skills.

Successful projects should provide supporting data, guidelines, and design tools for equipment manufacturers in combustion applications (mainly gas turbine).

Consortia are expected to include research and academic centres as well as gas turbine manufactures that can provide guidance and suggestions on the combustion technologies.

Proposals are expected to collaborate and explore synergies with projects 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”.

Activities are expected to start at TRL 2 and achieve TRL 4 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 3.00 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 2023 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2023–2024 which apply mutatis mutandis.