Flames burn differently aboard the International Space Station than on Earth. Down here, hot air from a fire rises, bringing in cool air full of oxygen at the fire's base to replace it. Not only does this feed the reaction, but it results in the flickering, tapered candle flame familiar to people the world over.
Unfortunately, this turbulence also makes the process difficult to study. However, combustion proceeds more slowly and uniformly when it is freed from the effects of gravity. Without the distinction between up and down, there’s less convection of oxygenated air replacing the flame’s heated exhaust. The result is a steady, spherical flame.
To learn more about how combustion works, astronauts are studying it in microgravity — on board the International Space Station. The most recent research of this type is a set of six major studies called the Advanced Combustion via Microgravity Experiments (ACME), which began in November 2017.
About 85 percent of the energy humans use comes from combustion, according to ACME project scientist David Stocker. "If we can learn more about the process, we might be able to find newer and less polluting ways to burn fuel," the video explains.