

Jul 28, 2014
This is a picture of the FLEX experiment set up on the International Space Station. Credit: NASA

A team of international researchers has discovered a new type of cool burning flames that could lead to cleaner, more efficient engines for cars. The discovery was made during a series of experiments on the International Space Station by a team led by Forman Williams, a professor of mechanical and aerospace engineering at the University of California, San Diego. Researchers detailed their findings recently in the journal Microgravity Science and Technology.

"We observed something that we didn't think could exist," Williams said.

A better understanding of the cool flames' chemistry could help improve in cars, for example by developing homogenous-charge compression ignition. This technology is not currently available in cars. But it could potentially lead to engines that burn fuel at cooler temperatures, emitting fewer pollutants such as soot and nitric oxide and nitrogen dioxide, also known as NOx, while still being efficient.

During the experiments, researchers ignited large droplets of heptane fuel. At first, it looked like the flames had extinguished themselves, just as they would have on earth. But sensors showed that the heptane was still burning, although the resulting cool flames were invisible to the naked eye.

These are screen shots taken during one of the FLEX experiments. Credit: NASA

The cool flames occurred in a wide range of environments, including air similar to the earth's atmosphere and atmospheres diluted with nitrogen, carbon dioxide and helium. The resulting combustion reaction creates toxic products, such as carbon monoxide and formaldehyde, which in turn burn off.

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The difference between earth and the is buoyancy. When droplets of fuel burn on earth, buoyancy limits the amount of time gases can hang around in the high temperature zone around the droplets. So there isn't enough time for the droplets' chemistry to support the cool flames. But in micro-gravity, there is no buoyancy, so there is enough time for the gases to stay around the droplets and for that chemistry to develop.

The challenge for future applications is to get the right mix of fuels to generate this cool flame combustion here on earth. To investigate this question, NASA is planning a new series of experiments tentatively called COOL FLAME INVESTIGATION, starting next winter and continuing for about a year.

Researchers emphasized that the research is only possible on the ISS, where scientists have access to a microgravity environment that provides a sufficient amount of test time for cool flames to occur. All the experiments take place in the Multiuser Droplet Combustion Apparatus that can generate and ignite droplets from different fuels in different atmospheric conditions. The chamber is crammed with sensors and equipped with video cameras that record experiments. The chamber is inside an experimental facility called the Combustion Integrated Rack, which is roughly the size of a 5.5-foot bookcase and weighs close to 560 lbs and which records the data and transmits it to ground. The Combustion Integrated Rack is located in the Destiny module of the ISS.

"Things can happen out there that can't happen here," Williams said.

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User comments : 6

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3.6 / 5 (8) Jul 28, 2014
Interesting science. It's hard to imagine making a slow burn like this happen inside of an internal combustion engine. Maybe the combustion would be external with the hot gasses flowing back to a cylinder or turbine? Better still the controlled burn could feed energy to a device that converts heat to electricity directly.
4.7 / 5 (3) Jul 28, 2014
Ok. I'm impressed. That is not how land dwellers expects to see a flame. I'm glad the author of the article included the video because it's hard to even guess what combustion is like in micro gravity. Very cool no pun intended.
3.5 / 5 (4) Jul 29, 2014
But a temperature difference is required to do work. The the larger the difference the larger the amount of work.
2 / 5 (2) Jul 29, 2014

i like thermal dynamics too. and you are right. but we are talking about the cold vacuum of space, where a few degrees translates into something more significant than it does here on Terra firma. i was going to throw in how this relates to thrust... but i quickly realized that i don't understand it well enough to explain it. :(
also, this is an old experiment.

1 / 5 (2) Jul 29, 2014
OK so cool 'burn' is good for waste products but not much energy output.
This burn is what the car CAT converter does, releases just enough energy to run the CAT.
Lex Talonis
1 / 5 (3) Jul 29, 2014
Hmmm I call bullshit on this.

The reason why the fuel drops burn cool is they are combusting slowly from the outside (vapour) in (to the liquid); and not from the bottom up - when gravity is involved.


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