During RP2, FLEX4H2 achieved a major step forward in the development and validation of a hydrogen-ready sequential combustion system capable of operating with natural gas/hydrogen blends up to 100% H2 under relevant gas turbine conditions
The reporting period focused on the design, optimisation, and validation of the Gen2 combustor prototypes, addressing the main Gen1 limitations—namely flashback margin and restricted firing temperature.
In WP1, Gen2 first- and second-stage burners were redesigned to enhance hydrogen flexibility. Key improvements included optimised fuel injectors for faster mixing at reduced pressure drop, high-speed low-swirl aerodynamics for improved flashback resistance, enhanced damping solutions for thermoacoustic robustness, and improved temperature profile homogeneity at the first stage outlet.
Additive manufacturing (SLM) enabled rapid prototyping of complex injection geometries, integrating instrumentation for detailed thermo-mechanical monitoring.
In WP2, high-fidelity LES simulations coupled with advanced turbulence-chemistry interaction models were further validated against new high-pressure experimental datasets using pure hydrogen at reheat conditions.
Numerical investigations improved understanding of autoignition-driven flame stabilisation, fuel–air mixing behaviour, and hydrogen-induced flashback mechanisms. These results directly informed Gen2 hardware optimisation and strengthened confidence in predictive modelling for hydrogen combustion.
In WP3, thermoacoustic characterisation advanced significantly. Mode shape-dependent flame transfer functions were developed and incorporated into interconnected system models, enabling prediction of transverse instability growth rates with strong agreement to experimental data.
New broadband acoustic dampers were experimentally validated, demonstrating improved absorption over relevant frequency ranges and enhanced system stability margins.
In WP4, two full-scale test campaigns (atmospheric and high-pressure) were successfully executed, leveraging the experience and the flame insights gained from the small-scale high-pressure tests. Gen2 prototypes demonstrated stable operation across the full natural gas–hydrogen blending range, including successful operation at 100% hydrogen under both half- and full-pressure conditions.
Flashback limits were systematically mapped, ignition procedures for 100% H2 were validated, and stable fuel switching was demonstrated. NOx emissions remained within project targets at adjusted firing temperatures.
While maximum firing temperature remains constrained at high hydrogen levels, broader flashback margins and extended operating windows were achieved compared to Gen1.
Overall, RP2 results confirm the technical feasibility of operating a sequential heavy-duty gas turbine combustor with up to 100% hydrogen at full engine pressure, representing a decisive step toward TRL6 demonstration.
