The solution to this burning question requires launching fires in space.
Ongoing experiments on the International Space Station could help resolve a scientific debate about why some fires burn without producing soot. Made of carbon particles that are produced when fuel does not burn completely, soot is a pollutant. The particles are associated with health problems such as cancer ( SN: 8/4/07, p. 69 ) and contribute to global warming ( SN Online: 3/8/11 ).
One technique for removing soot is to play around with the composition of the fuel and the surrounding air. Oxygen in the air is necessary for combustion, but air also contains nitrogen that is inert. By removing nitrogen from the air and mixing that nitrogen with the fuel, scientists can produce soot-free flames.
However, there are two contradictory views about why soot does not form. One theory is that the clean flame is due to a changed gas flow in the fire. The other is that the temperature and composition of the fire vary so much over the flame that no soot builds up.
To test which idea is right, scientists need to control the flow of gases in a flame. However, this is difficult for the earth, as hot gases inevitably flow upwards and, for example, give candle flames their familiar elongated shape. In the weightlessness of the space station, however, this upward flow is prevented. The gases do not rise and create a fireball that can be adjusted to accommodate the flow.
"A beautiful spherical flame is simply not possible on Earth," says engineer Richard Axelbaum of Washington University, St. Louis. Axelbaum is one of the researchers working on the experiments that are remotely controlled from the ground. "With the space station we can study the problem carefully and understand better." The results of the experiments should be published in a few months.