Taming the rings of fire in hydrogen combustors

Transitioning toward clean energy has led to the rise of fuel blends containing natural gas and clean fuel, like hydrogen. The addition of hydrogen, however, also has negative effects: It can cause the gas to ignite, emit additional pollutants, or heat up and cause engine failure. Understanding the origins of these instabilities can help inform new combustor designs. Toward this goal, Thirumalaikumaran et al. studied how hydrogen influences the flame and low dynamics of methane-hydrogen fuels in combustion engines.

“Its flames can lock into a feedback loop with sound waves inside the combustor, producing intense pressure oscillations that shake the engine and can damage or destroy it,” said author Saptarshi Basu. “This combustion instability resembles the screech of a loudspeaker when a microphone drifts too close.”

Using a model combustor, the researchers imaged the flow and flame in the combustion chamber for both methane-only fuel and a methane-hydrogen blend. They found the addition of hydrogen leads to a much stronger response to thermal oscillations and large, violent heat release rate fluctuations within a much smaller flame. These fluctuations couple with vortices that originate at the engine’s swirler exit, a set of vanes that rotate to guide airflow.

“The cause lay in the flow. Gas leaving the swirler rolls up into vortex rings, much like smoke rings,” Basu said. “With hydrogen in the mix, these rings fall into step with the flame’s heat release, so each feeds the other and the oscillation grows.”

How these vortices affect hydrogen instabilities is important to modern combustors, especially those that use mixed fuels.

“If we can tweak these vortex structures at their source, we could break the feedback loop,” said author SK Thirumalaikumaran. “That points the way to safer hydrogen engines.”

Source: “Insight into the dynamics of intrinsic thermoacoustic instability-driven swirl flames,” by S. K. Thirumalaikumaran, Balasundaram Mohan, and Saptarshi Basu, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0357784 .