As hydrogen begins to move from demonstration projects into everyday energy systems, combustion stability remains one of the main engineering challenges. Although hydrogen can be burned without producing carbon dioxide, its high flame speed and reactivity make it difficult to control in equipment originally designed for natural gas. Addressing this issue, a research team led by Antonio L. Sánchez, professor of mechanical and aerospace engineering at the University of California, San Diego, has used large-scale supercomputer simulations to clarify how hydrogen flames can be kept stable in gas-turbine environments.
Li, B. W., Keeton, B. W., Nomura, K. K., Sánchez, A. L., & Williams, F. A. (2025). A numerical investigation of H <math altimg="si28.svg" display="inline" id="d1e1145"> <msub> <mrow/> <mrow> <mn>2</mn> </mrow> </msub> </math> -air lifted flames in swirling fuel injectors. Combustion and Flame, 282, 114461. https://doi.org/10.1016/j.combustflame.2025.114461
The work was carried out using the Expanse supercomputer at the San Diego Supercomputer Center and focused on operating conditions similar to those found in industrial gas turbines. In these systems, hydrogen fuel is typically injected as a swirling jet into hot, pressurized air. Swirl is introduced to help anchor the flame, but with hydrogen the balance is narrow. Small changes in flow or reaction conditions can cause the flame to either detach and blow out or move upstream toward the injector, increasing the risk of overheating and damage.
Antonio L. Sánchez, professor of mechanical and aerospace engineering at the University of California stated,
“Hydrogen will be an essential fuel if we’re serious about decarbonization. Our job is to make sure it can burn safely, reliably, and efficiently in the systems of the future.”
To better understand these effects, the researchers simulated nitrogen-diluted hydrogen jets under high-temperature and high-pressure conditions. A central part of the study was a comparison between two chemical descriptions of hydrogen combustion. One approach tracked the full sequence of reactions involved as hydrogen and oxygen form water, including the creation and destruction of short-lived radical species that drive the combustion process. This detailed model provided a precise picture of flame structure and behavior but required substantial computational resources.
The team then evaluated a reduced chemistry model that represents the entire combustion process as a single overall reaction. This simplified approach assumes that intermediate species remain at nearly constant levels, an assumption that is often valid at the elevated pressures typical of gas turbines. The simulations showed that, under these conditions, the reduced model reproduced the flame position and stability limits predicted by the detailed chemistry with close agreement. This finding suggests that engineers can use faster, less expensive simulations to explore hydrogen combustor designs without losing essential accuracy.
Beyond chemical modeling, the study highlighted the strong coupling between flow dynamics and reaction rates. Flame stability was found to depend on the relationship between how quickly the fuel burns and how long it remains in the combustion zone, as well as on the strength of the swirling motion imposed at the injector. When these factors are properly balanced, a lifted flame can form that remains stable while avoiding direct contact with the injector hardware.
The simulations also showed that an internal recirculation region created by swirl plays a critical role. This region continuously feeds hot combustion products back toward the incoming fuel, supporting sustained ignition. When the recirculation weakens, the flame becomes more sensitive to disturbances and is more likely to extinguish or shift into an unsafe configuration.
These results are particularly relevant as many power producers and engine manufacturers consider converting existing gas turbines to operate on hydrogen or hydrogen blends. The findings reinforce that hydrogen cannot simply replace natural gas without design changes. Injector geometry, swirl intensity, and operating conditions must all be adjusted to account for hydrogen’s faster chemistry.
High-performance computing made it possible to explore these interactions across a wide range of conditions. Although the simulations focused on simplified flow regimes to isolate key physical mechanisms, the researchers note that the underlying trends are expected to carry over to the more turbulent environments of real turbines. As hydrogen adoption accelerates, studies like this provide a physics-based foundation that can reduce development time and guide safer, more reliable combustion system designs.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
