Cracking the secrets of the super-efficient "blue whirl" flame

A couple of years ago, some scientists were experimenting ways to clean up oil spills in the ocean by using flame. They accidentally created something they'd never seen before — a "blue whirl" flame, which consumes all its fuel and burns soot-free.

Since then, scientists have been trying to figure out what sort of physics and chemistry are going on inside this thing. It'd be cool if we could harness it intentionally; a soot-free flame is super efficient, and thus useful. But they'd be hard to use safely, because they begin in a highly volatile and dangerous "fire whirl" state, before settling down into the "blue whirl" formation.

Some tantalizing hints are emerging, though. Recently, some scientists created a computer simulation that closely tracked the actual blue whirl's behavior. What they found is that a blue whirl is actually three flames combined together: An invisible outer flame, where there's more oxygen than fuel, and two internal flames where there's more fuel than oxygen, which are visible.

Not enough info yet to deduce how to route around the unstable "fire whirl' state, but a cool first step.

As they note in their paper writing up the experiment:

The blue whirl is at least a curious phenomenon that has many intriguing aspects. The most curious aspect is that it evolves spontaneously and presents itself as a stable state persisting until all of the fuel is burned. The second curiosity was that it is laminar and burning soot free, whereas the initial state was sooty, turbulent, and noisy. A third curiosity was that, in the experiments, it was not burning a gas, but a liquid hydrocarbon sitting on a water surface. Further experimentation revealed more features, such as its averaged temperature profile and its sensitivity to the boundary layer. Added to all of this was that it was very beautiful, both in its stable state, as a spinning blue top-like flame, and when it went slightly unstable, perhaps revealing some of its inner structure. The route to its formation and its transient unstable states implied its relation to the fluid phenomenon of vortex breakdown and the various states that evolve from this instability.

A recurring question, however, was whether the blue whirl could be useful in any way for efficient combustion with no soot formation. This involves questions such as: Can it be formed under controlled conditions more directly and without going through the fire whirl state? Can the size be controlled? Can it be made larger or smaller? Is there a scaling that can be used? Other, perhaps more far out questions, were: Can it be made without the confining walls? Can multiple blue whirls be made and work together? Could it be part of a combustor or a propulsion device? The lure of being able to burn any liquid hydrocarbon efficiently and cleanly is extremely attractive.