How a flame burns in space
When a flame burns on earth, heated gases rise from the fire, drawing oxygen in and pushing combustion molecules out. As the flame burns, it heats the air around it and causes it to expand and rise upward. Denser air sinks downward to fill the void. The process continues in a sort of loop. This upward rising of air is what causes the classic teardrop shape we see in a candle flame.
In microgravity however, hot gases do not rise. Air pretty much remains unmoved in all areas around the flame. So an entirely different process, called molecular diffusion, drives flame behavior and gives it an unusual round appearance. Since no flow of air replaces the oxygen that is burnt, only random oxygen molecules make it to the flame. This causes flames in space to burn blue and much cooler.
A scientist at NASA explained:
“In space, molecular diffusion draws oxygen to the flame and combustion products away from the flame at a rate 100 times slower than the buoyant flow on Earth.”
Scientists at NASA are studying the phenomena to learn more about fires in space. What they discover will be used to create fire prevention processes applicable to the unique environment in space. If the process can be replicated on earth, we may be able to create things such as car engines that burn cooler.
Wait a minute, is there oxygen in space?
The photo of the blue flame above was taken during a fire experiment in controlled space in the International Space Station. But yes, there are indeed pockets of oxygen in space, especially around stars.