Fire in zero gravity burns completely differently than on earth - scientists have encountered a strange phenomenon. Fire in zero gravity burns completely differently than on earth - scientists have encountered a strange phenomenon. Will a candle burn in a state of weightlessness?

The FLEX experiment, carried out on board the International Space Station, gave unexpected results - the open flame behaved completely differently than scientists expected.

As some scientists like to say, fire is the oldest and most successful chemical experiment humanity. Indeed, fire has always been with humanity: from the first fires on which meat was fried, to the flame of the rocket engine that brought man to the moon. By and large, fire is a symbol and instrument of progress of our civilization.

The difference in flame on Earth (left) and in zero gravity (right) is obvious. One way or another, humanity will again have to master fire - this time in space.

Dr. Forman A. Williams, a professor of physics at the University of California, San Diego, has long worked on the study of flame. Usually fire is a very complex process thousands of interconnected chemical reactions. For example, in a candle flame, hydrocarbon molecules evaporate from the wick, are broken down by heat, and combine with oxygen to produce light, heat, CO2, and water. Some of the hydrocarbon fragments, in the form of ring-shaped molecules called polycyclic aromatic hydrocarbons, form soot, which can also burn or turn into smoke. The familiar teardrop shape of a candle flame is given by gravity and convection: hot air rises up and draws fresh into the flame cold air, due to which the flame stretches upward.

But it turns out that in zero gravity everything happens differently. In an experiment called FLEX, scientists studied fire on board the ISS to develop technologies for extinguishing fires in zero gravity. The researchers ignited small bubbles of heptane inside a special chamber and watched how the flame behaved.

Scientists have encountered strange phenomenon. In microgravity conditions, the flame burns differently; it forms small balls. This phenomenon was expected because, unlike flames on Earth, in weightlessness oxygen and fuel are found in thin layer on the surface of the sphere, This simple circuit, which is different from earthly fire. However, a strange thing was discovered: scientists observed the continued burning of fireballs even after, according to all calculations, the burning should have stopped. At the same time, the fire went into the so-called cold phase– it burned very weakly, so much so that the flame could not be seen. However, it was a combustion, and the flame could instantly burst into flames with great force upon contact with fuel and oxygen.

Typically visible fire burns at a high temperature between 1227 and 1727 degrees Celsius. Heptane bubbles on the ISS also burned brightly at this temperature, but as the fuel ran out and cooled, a completely different combustion began - cold. It takes place at a relatively low temperature of 227-527 degrees Celsius and produces not soot, CO2 and water, but the more toxic carbon monoxide and formaldehyde.

Similar types of cold flame have been reproduced in laboratories on Earth, but under gravitational conditions such fire itself is unstable and always quickly dies out. On the ISS, however, a cold flame can burn steadily for several minutes. This is not a very pleasant discovery, since cold fire poses an increased danger: it ignites more easily, including spontaneously, it is more difficult to detect and, moreover, it releases more toxic substances. On the other hand, the opening may find practical use, for example, in HCCI technology, which involves igniting fuel in gasoline engines not from spark plugs, but from a cold flame.

Many physical processes proceed differently than on Earth, and combustion is no exception. A flame behaves completely differently in zero gravity, taking on a spherical shape. The photo shows the combustion of an ethylene droplet in air under microgravity conditions. This photo was taken during an experiment to study the physics of combustion in a special 30-meter tower (2.2-Second Drop Tower) at the Glenn Research Center, created to reproduce the conditions of microgravity during free fall. Many experiments that were later carried out on spacecraft underwent preliminary testing in this tower, which is why it is called “a gateway to space”.

The spherical shape of the flame is explained by the fact that in conditions of weightlessness there is no upward movement of air and convection of its warm and cold layers does not occur, which on Earth “pulls” the flame into the shape of a drop. The combustion flame does not have enough fresh air containing oxygen, and it turns out smaller and not as hot. The yellow-orange color of the flame, which is familiar to us on Earth, is caused by the glow of soot particles that rise upward with a hot stream of air. In zero gravity, the flame acquires a blue color, because little soot is formed (this requires a temperature of more than 1000 ° C), and the soot that exists will glow only in the infrared range due to the lower temperature. In the top photo there is still a yellow-orange color in the flame, since the early stage of ignition was captured, when there is still enough oxygen.

Combustion studies under microgravity conditions are especially important for ensuring the safety of spacecraft. Fire suppression experiments (FLEX) have been carried out for several years in a special compartment on board the ISS. The researchers ignite small droplets of fuel (such as heptane and methanol) in a controlled atmosphere. A small ball of fuel burns for approximately 20 seconds, surrounded by a sphere of fire with a diameter of 2.5–4 mm, after which the droplet decreases until either the flame goes out or the fuel runs out. The most unexpected result was that a drop of heptane, after visible combustion, entered the so-called “cold phase” - the flame became so weak that it could not be seen. And yet it was combustion: fire could instantly flare up when interacting with oxygen or fuel.

As the researchers explain, when normal combustion the flame temperature fluctuates between 1227°C and 1727°C - at this temperature in the experiment there was visible fire. As the fuel burned, “cold combustion” began: the flame cooled to 227–527 ° C and did not produce soot, carbon dioxide and water, and the more toxic materials are formaldehyde and carbon monoxide. During the FLEX experiment, they also selected the least flammable atmosphere based on carbon dioxide and helium, which will help reduce the risk of fire in spacecraft in the future.

For combustion and flame on Earth and in zero gravity, see also:
Konstantin Bogdanov “Where is the dog buried?” - "5. What is fire? .

Janash Bannikov

Approaching New Year, and the astronauts at the orbital station are preparing to meet him. They ask the next transport ship to send them candles. But engineers on Earth believe that there is no need to send candles, since they will not burn in zero gravity.
What do you think, will an ordinary candle burn in zero gravity?

Answer
In order for a candle to burn, a constant flow of oxygen to its flame is necessary. Under terrestrial conditions, this influx occurs due to convection. The hot gases resulting from the combustion of stearin are lighter than air and therefore rise upward, and new portions of air enter in their place. As a result, the flow of oxygen to the flame and the removal of carbon monoxide (CO) and carbon dioxide (CO2) gases from the combustion zone is ensured. It is clear that in conditions of weightlessness there will be no convection. There will be only a weak air flow due to air flow inside the spacecraft, as well as influx due to the expansion of combustion products and due to diffusion. The listed processes are weak and whether they will be sufficient to burn a candle could only be determined experimentally.

By the way Such experiments were carried out on space station"Mir" in 1996. It turned out that a candle can burn in zero gravity. In one experiment, a candle burned for 45 minutes. However, in zero gravity a candle burns differently than on Earth. Since there are no convection currents, the candle flame does not have an elongated shape, as in terrestrial conditions, but a spherical shape. In the absence of convection, the flame cools less, so its temperature is higher than on Earth; The stearin in the candle becomes very hot and releases hydrogen, which burns with a blue flame.

Think

In experiments with a candle in zero gravity, a combustion mode sometimes occurred with periodic micro-explosions, which led to sharp fluctuations in the flame.
Why did micro-explosions occur?

Answer
Due to the lack of convection, the candle flame cooled less, which means its temperature was high. The stearin in the candle overheated greatly and began to evaporate. The concentration of stearin vapor in the air near the flame increased until an explosive mixture was formed. This was followed by a small explosion, while the combustion products were carried away by the blast wave, and in their place came Fresh air. If the explosion was not too strong, then the candle continued to burn, a new portion of stearin evaporated from its surface, and the next explosion followed.

Candle flame: a) in gravity conditions; b) in conditions of weightlessnesshttp://n-t.ru/tp/nr/pn.htm

Think

How can we ensure more intense combustion candles or regular matches? Suggest different ways.

Answer
You can blow on a match. You can begin to rotate the match in a circle, thereby ensuring the movement of the match relative to the air. You can throw a match. In one of documentaries about weightlessness, the following plot was shown: a thrown match moved smoothly inside the spaceship and burned quite intensely due to the supply of new portions of air to its flame.http://mgnwww.larc.nasa.gov/db/combustion/combustion.htmlhttp://science.msfc.nasa.gov/newhome/headlines/msad08jul97_1.htm

EXPLOSION IN A BAKERY

In ancient times, the baker used one sure remedy to cope with annoying flies. Taking a handful of flour, he threw it into the air and set it on fire. A cloud of flour flared up. Flame, clap - and the annoying insects were gone. This method always helped, although sometimes the glass from the windows flew out from the cotton. However, on December 14, 1785, a disaster occurred in Turin (Italy). Deciding to use a proven method to get rid of flies, the unlucky baker blew up his entire household. He and his assistants died under the rubble of the bakery. In 1979, flour dust exploded at one of the flour mills in Bremen. As a result, 14 dead, 17 injured, damage - 100 million marks.
Could flour dust really cause terrible explosions? After all, it’s not dynamite scattered in the air, but just particles of flour?Volkov A. Adventures of dust.

Answer
Flour contains substances of organic origin, which means it can burn. Of course, under normal conditions it is not easy to set fire to flour. But if flour is sprayed in the air, then every speck of dust comes into contact with oxygen. In addition, the total surface area of ​​dust grains is many times greater than the surface area of ​​a single piece of matter of the same mass. This means that when a substance is sprayed, its surface area increases a huge number of times. Combustion occurs on the surface, since it is the surface of the substance that comes into contact with atmospheric oxygen. In this case, the smallest specks of dust burn so quickly that an explosion occurs.

Reference An explosion is a combustion, and incredibly fast - an insignificant fraction of a second. In this case, the explosive turns into gas. The resulting gas has high temperature and enormous pressure - tens of billions of pascals. The sudden expansion of the gas causes a deafening roar and severe destruction.Sometimes seemingly completely harmless substances explode. These include any dust of organic origin: flour, sugar, coal, bread, paper, pepper, pea and even chocolate.Only those types of dust that contain substances that react with oxygen explode. An explosion occurs only when the amount of dust in the air reaches a certain level, and even a microscopic spark can cause it.

By the way The rapid combustion of a substance in an atomized state is widely used in technology. For example, coal is supplied to the furnaces of boiler houses of thermal power plants in the form of fine dust. And the quiet rumbling of the car is an echo of the explosions of a mixture of gasoline vapors and air inside its engine.

Shablovsky V. Entertaining physics. St. Petersburg: Trigon, 1997. P. 101.

By the way The first very strong explosive was synthesized by Ascanio Sobrero in 1846 in Turin (Italy). It was nitroglycerin - oily clear liquid sweetish taste. In those days, chemists tasted all substances. Even a few drops of nitroglycerin made my heart pound and my head hurt. Forty years later, nitroglycerin was recognized as a drug.

Think

The energy contained in the explosive is not that great. For example, the combustion of 1 kg of TNT releases 8 times less energy than the combustion of 1 kg of coal. But then why is TNT so destructive?

Answer
When TNT explodes, energy is released tens of millions of times faster than during normal coal combustion.Shablovsky V. Entertaining physics. St. Petersburg: Trigon, 1997. P. 100.

Think

The tendency of nitroglycerin to explode is truly amazing. They say that once in England one peasant drank a bottle of nitroglycerin in winter in the hope of keeping warm. He was found dead on the road. The frozen body was brought into the house and placed to thaw near the stove. As a result, the peasant's body exploded and the house was destroyed.Question: Can this story be trusted?Krasnogorov V. Imitating lightning. M.: Znanie, 1977. P. 72.

An unusual experiment was carried out in space. Japanese astronaut Takao Doi,

located on board the American module of the ISS, launched an ordinary boomerang.

Experts wanted to see how this object would behave if thrown in zero gravity.

To the surprise of many, including world champion boomerang thrower Yasuhiro Togai, the boomerang is back!

Another experiment in zero gravity

Albert Einstein, long before space flights, thought about a curious question: will a candle burn in the cabin of a spaceship? Einstein believed that “no,” since due to weightlessness, hot gases will not escape from the flame zone. Thus, the access of oxygen to the wick will be blocked, and the flame will go out.

Modern experimenters decided to test Einstein's statement experimentally. The following experiment was carried out in one of the laboratories. A burning candle placed in a closed glass jar, dropped from a height of about 70 m. The falling object was in a state of weightlessness, if air resistance is not taken into account. However, the candle did not go out, only the shape of the flame changed, it became more spherical, and the light it emitted became less bright.

The experimenters explained the ongoing combustion in weightlessness by diffusion, due to which oxygen from the surrounding space still entered the flame zone. After all, the diffusion process does not depend on the action of gravitational forces.

However, combustion conditions in zero gravity are different than on Earth. This circumstance had to be taken into account by Soviet designers who created a special welding machine for welding in zero gravity conditions.

This device was tested in 1969 at the Soviet spaceship Soyuz-8 worked successfully.

Did you know?

First buttons

How did people fasten clothes a long time ago?
For this they used cufflinks, and more often laces and ribbons.

Then buttons appeared, and often they were sewn on much more than loops were made. The fact is that buttons were initially intended only for rich people, not only for fastening, but more often for decorating clothes. Buttons were made from precious stones and expensive metals.

The more noble and rich a person was, the more buttons there were on his clothes. Many people at that time opposed the new fasteners, considering them an unaffordable luxury. Often this was actually the case. For example, the King of France, Francis the First, ordered to decorate his black velvet camisole with 13,600 gold buttons.

How does fire burn in zero gravity? What is combustion? This chemical reaction oxidation with release large quantity heat and the formation of hot combustion products. The combustion process can only occur in the presence of a combustible substance, oxygen, and provided that oxidation products are removed from the combustion zone. Let's see how the candle works and what exactly burns in it. A candle is a wick twisted from cotton threads, filled with wax, paraffin or stearin. Many people think that the wick itself burns, but this is not so. It is the substance around the wick, or rather its vapor, that burns. The wick is needed so that the wax (paraffin, stearin) melted from the heat of the flame rises through its capillaries into the combustion zone. To test this, you can conduct a small experiment. Blow out the candle and immediately bring the burning match to a point two or three centimeters above the wick, where the wax vapor rises. The match will ignite them, after which the fire will fall onto the wick and the candle will light again. So, there is a flammable substance. There is also quite enough oxygen in the air. What about the removal of combustion products? There are no problems with this on earth. The air, heated by the heat of a candle flame, becomes less dense than the cold air surrounding it and rises upward along with the combustion products (they form a tongue of flame). If the combustion products, which are carbon dioxide CO2 and water vapor, remain in the reaction zone, the combustion will quickly stop. It is easy to verify this: place a burning candle in a tall glass - it will go out. Now let’s think about what will happen to a candle on a space station, where all objects are in a state of weightlessness. The difference in density of hot and cold air will no longer cause natural convection, and through for a short time there will be no oxygen left in the combustion zone. But an excess of carbon monoxide (carbon monoxide) CO is formed. However, for a few more minutes the candle will burn, and the flame will take the shape of a ball surrounding the wick. It is equally interesting to know what color the candle flame will be on the space station. On the ground, it is dominated by a yellow tint, caused by the glow of hot soot particles. Typically the fire burns at a temperature of 1227-1721oC. In weightlessness, it was noticed that as the combustible substance is exhausted, “cold” combustion begins at a temperature of 227-527 ° C. Under these conditions, the mixture of saturated hydrocarbons in the wax releases hydrogen H2, which gives the flame a bluish tint. Has anyone lit real candles in space? It turns out that they lit it - in orbit. This was first done in 1992 in the experimental module of the Space Shuttle, then in NASA's Columbia spacecraft, and in 1996 the experiment was repeated on the Mir station. Of course, this work was not done out of simple curiosity, but in order to understand what consequences a fire on board the station could lead to and how to deal with it. From October 2008 to May 2012, similar experiments were carried out under a NASA project on the International Space Station. This time the astronauts examined flammable substances in an isolated chamber at different pressures and different oxygen content. Then “cold” combustion was established at low temperatures. Let us recall that combustion products on earth are, as a rule, carbon dioxide and water vapor. In weightlessness, under combustion conditions at low temperatures, highly toxic substances are released, mainly carbon monoxide and formaldehyde. Researchers continue to study combustion in zero gravity. Perhaps the results of these experiments will form the basis for the development of new technologies, because almost everything that is done for space, after some time, finds application on earth.