May 28, 2019
Ryan Whitwam

Scientists Use Spherical Flames on ISS to Understand Soot-Free Fires

Fires aboard the International Space Station (ISS) are a very bad thing unless it’s part of an experiment that helps unravel the most fundamental mysteries in the natural world. Scientists haven’t been sure why some fires produce soot and others don’t. The unique nature of microgravity on the ISS allowed the crew to create spherical flames to shed light on the problem.

It’s well understood that you can create soot-free flames by altering the composition of your fuel. Oxygen is, of course, necessary for combustion to take place. Air on Earth also contains nitrogen. Nitrogen is inert, but by removing nitrogen from the air and adding it to the fuel, you can create a soot-free flame. But why?

There are two opposing views about the mechanism at work here. On one side, scientists believe it’s the altered flow of gasses in the fire that captures the carbon that would form soot. Others say that moving nitrogen from the air to the fuel changes the temperature of the fire, and the variation in temperature and shape across the flame prevents soot from forming.

To break the stalemate, scientists need to precisely control the flow of gasses in the flame. On Earth, the gasses always flow upward, giving flames that characteristic elongated shape. On the ISS, flames don’t stretch upward, and you can control the flow of gasses.

So, on the International Space Station, researchers have been starting small fires that are naturally completely spherical. These flames don’t have a yellow component, which is a sign of impurities like soot.

International_Space_Station

Using flames on the International Space Station, scientists can figure out which proposal is right. If the gas flow theory is right, then spherical flames in space will produce soot. If it’s a function of temperature and structural variation, then there won’t be any soot. Astronauts will be able to measure the strength and longevity of the flames. They expect flames on the ISS to be stronger than those on Earth with a mixture of nitrogen and oxygen in the air.

This research, which is still ongoing, could help clarify some fundamental areas of combustion science. Even though humans have been lighting fires since the earliest era of human civilization, we might have to go to space to understand how fires work.

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