Understanding the two different stable states of lean hydrogen-air flames.

What is it about?

Hydrogen-air flames that are very lean (have a low fuel-to-air ratio) can behave in two distinct ways when they move through narrow spaces. These flames can take on either circular or double-cell shapes and move at different speeds, with the double-cell shapes being larger and faster. The way hydrogen spreads, how heat moves around, and how heat is lost all contribute to these differences in shape and speed. In previous experiments, researchers found these different flame shapes under specific conditions. Now, in new tests using horizontal channels, they noticed that these two flame shapes can appear at the same time under the same conditions. This is the first time anyone has seen that multiple stable flame shapes can exist together in real devices. To gain a better understanding of this phenomenon, they conducted computer simulations suggesting that slight asymmetries during the flame's ignition can lead to the formation of these two distinct stable shapes.

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Photo by Peter Fly on Unsplash

Photo by Peter Fly on Unsplash

Why is it important?

There are many examples of physical systems that can have multiple solutions, with the outcome depending on the initial conditions. What makes this study significant is the simultaneous observation of two stable and stationary solutions emerging under identical initial and boundary conditions. This bi-stability has been observed for first time in this work in both experiments and simulations, underscoring the critical role of modeling in fully understanding laboratory measurements.

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