Flames that don鈥檛 flicker could make stoves and engines more efficient. Creating such flames has previously required using artificially low gravity or pressure. Now, researchers have manged to do it in real-world conditions by pairing flames together.
Devices ranging from stoves and furnaces to aircraft and spacecraft engines use flames arranged close to each other. Flames consist of warm particles of air that can influence each other when close together, so putting one flame next to another can cause both to flicker. When flames flicker, devices using them can become less efficient or produce more pollutants, says at the University of California, Berkeley.
Ju and his colleagues set out to investigate whether flame flickering can be prevented by continuously changing the distance between the flames under standard conditions on Earth. In the past, producing non-flickering flames had required using aircraft where motion effectively lowers gravity or in special laboratory setups with precisely controlled pressure.
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The researchers used two identical methane gas burners. The left-most burner could not move, but they affixed the right-most one to a platform that oscillated between moving to the left and to the right. They recorded both flames with a high-speed camera.
From previous studies, the researchers knew that there was a critical distance between the flames where both would momentarily stop flickering. Their recordings showed that once one flame was put into motion flickering could be stopped for hundreds of milliseconds at a time.
When the two flames were closer than the critical distance they behaved almost as one, waving and flickering in unison. When they were further apart than the critical distance they wiggled in opposite directions. However, when the platform carrying the right-most flame was programmed to keep moving so that this flame was always just slightly off from the critical distance, the recordings showed both flames burning without moving or breaking up for up to 0.84 seconds at a time. Ju says that instead of influencing each other, or coupling, the flames would get 鈥渟tuck鈥� in a stable 鈥渢o be coupled but not yet coupled鈥� state.
at the City University of Hong Kong says that this experiment could be used as a starting point for investigating how gas-turbine engines in aircraft, where many flame burners are placed close to each, could be made even more stable and reliable, he says. 鈥淯nstable combustion not only makes an engine inefficient, but also may put it at risk of failure,鈥� he says.
Journal reference: Physical Review Applied, forthcoming
