Researchers were astonished to accidentally discover a new kind of eerie blue flame when it erupted into existence mid-experiment in a laboratory, but now scientists understand the "blue whirl" flame's structure, according to a new study recently published in the journal Science Advances.
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Ghostly 'blue whirl' flame structure revealed
In reality, three distinct kinds of flames comprise the blue whirl, according to the study. "It's amazingly complex," said engineer Elaine Oran of Texas A&M University in College Station, reports Science News.
Initially reported in 2016, the blue whirl came to light when a group of scientists ignited fuel floating on water in a container made to force in-flowing air into a vortex. A tornado of fire erupted before it settled into a spinning blue flame just a few centimeters tall.
The blue hue means the flame burns without soot, implying such flames might prove to be an efficient way of cleaning oil spills or even eco-friendly power generation.
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Flames typically fall under two categories: premixed and diffusion. For the latter, the fuel and its oxidizer (usually oxygen) start separate, putting a bound on the speed at which the fire burns. Premixed flames, by contrast, begin with the two swirling together, and come in several varieties. They can have either a dearth or an excess of fuel relative to an oxidizing agent — and are called lean or rich flames, respectively.
Stoichiometric flames are the sweet-spot of flames, when there's just enough fuel for total combustion.
Oran and colleagues compared their experimental observations with computer simulations to uncover the blue whirl's structure. Within the flame's conical base is a rich premixed flame, with a layer of diffusion on top. On its sides is a lean premixed flame — the part resembling a faint wisp. And where they all come together, we see a stoichiometric flame: the bright blue ring.
This is significant because it could help researchers understand how to scale-up the blue whirl to larger sizes, or make it without the dangerous firenado phase. Either way, it's rare to be so fascinated by something as ostensibly simple and commonsense as a little blue flame.