Astronauts played with fire in space

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We deal with it every day, or almost: it fire has been used by humans for over 400,000 years. But in space, everything is different, and so is its behavior. This is what researchers from Nasa who created the project Advanced combustion via microgravity experiments, Where Acme, spread over four and a half years. Thus, since 2017 astronauts on board International Space Station (ISS) experiment around this theme.

“An environment of micro-gravity allows scientists to explore the behavior of the flames without affecting gravityso they can study physical underlying structure and behavior of flamessaid Dennis Stocker, Acme project researcher at Nasa. This knowledge can help designers and engineers here on Earth develop furnaces, power plants, boilers and more combustion more efficient, less polluting and safer. »

In the micro-gravity force, the flames are spherical!

On the program are six experiments that cover different themes, but with one thing in common: they generate spread flamesor not premixed, i.e. when combustible and oxidizing agentnecessary in addition to a source of heat in order for the fire to form, separate before ignition. This is the case, for example, for candles, where the fuel is wax, the oxidizing agentoxygen surrounding, and the activation energy the flame from a lighter or a Matches. “More than 1,500 flames were lit, more than three times as many as originally plannedsaid Dennis Stocker. More “first” have also been manufactured, perhaps especially in areas with cold and spherical flames. »

Already created in 2012 with combustible material liquids, this time the flames were made only with gaseous fuels. But the main result is the same: the flame assumes a spherical shape, very different from the one we usually know. In the question, the absence of gravity: on the ground, hot air rises by convection because it is less dense and the cold air falls down by gravity and nourishes the bottom of the flame. But these phenomena do not come into play on board the ISS. The combustion products no longer fall by gravity and then remain around the flame: oxygen is supplied from all sides, provided movements enough air for CO2 let him pass. In this case, the flame is maintained.

Six experiments to understand the dynamics of fire in microgravity

All in all, these six experiments, which are impossible to perform in a terrestrial laboratory, have improved the computer models that simulate growth andExtinction flames in a microgravity environment. A fire created in the room will be more stable and therefore harder to put out. It is for this purpose that NASA performed these tests: prevent fires, and better understand the dynamics of fire in microgravity. Especially in spacecraft, where everything is trapped, and where an uncontrolled fire quickly becomes catastrophic.

Among these tests, cold flames were performed, an experiment that had already been performed in 2012 aboard the ISS. But also it burning Missing Simulator (BRE) consisted of igniting different materials in one atmosphere at rest, then to observe the ignition and to perform various extinguishing tests. Several fuels have been used, in different atmospheres, in conditions similar to those envisaged for future space exploration ”.

During the s-Flame experiment, the fuel and the surrounding atmosphere were diluted with helium, which replaced the nitrogen. As it is a better heat conductor than nitrogen, the size of the flame has increased markedly, but also its structure and its dynamics. Analyzes are underway to model it, thus predicting effective extinguishing methods. © Nasa

The case of the sooty flames

Other experiences such as Coflow Laminar Diffusion Flame (CLD Flame), made it possible to study sooty flamesi.e. which generates sweetthis polluting blackish-looking substance resulting from incomplete combustion of materials carbonated. They found that ” Microgravity soot flames are wider and higher than their normal gravitational counterparts, and the concentration of soot can be as much as a factor of ten greater.

But that’s not all! NASA explains that if the fuel is diluted by one gas inert, likenitrogenthen the soot and flame disappear “may detach from the surface of burner and appears as a small cone blue”. In case of extreme dilution, the flame even assumes the shape of a disc and then goes out. Finally, researchers have shown that one electric field makes it possible to reduce the emissions of diffusion flames: this thanks to ions created as a result of combustion reactions that are sensitive to it. Depending on the field used, the shape of the flame can be changed until the formation of soot is eliminated.

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