Flame: structure, description, scheme, temperature

In the process of combustion, a flame is formed, the structure of which is due to the reacting substances. Its structure is divided into regions depending on the temperature indexes.

Definition

Flames are gases in an incandescent form, in which components of a plasma or substances in a solid dispersed form are present. In them, physical and chemical transformations are carried out, accompanied by glow, release of heat energy and heating.

The presence of ionic and radical particles in the gaseous medium characterizes its electrical conductivity and special behavior in the electromagnetic field.

What are the flames

Usually the so-called combustion processes are called so. Compared to air, the gas density is less, but high temperature indices cause a rise in gas. Thus, flames are formed, which are long and short. Often there is a smooth transition of one form to another.

Flame: structure and structure

To determine the appearance of the described phenomenon, it is enough to light a gas burner. The non-luminous flame that appears can not be called homogeneous. Visually, three main areas can be distinguished. By the way, the study of the structure of the flame shows that various substances burn with the formation of a different type of torch.

When the mixture is burned from gas and air, a short flame is formed, the color of which is blue and violet. It looks through the core - green-blue, like a cone. Consider this flame. Its structure is divided into three zones:

1. A preparatory region is selected in which the mixture is heated from the gas and air as it leaves the burner opening.
2. It is followed by a zone in which combustion occurs. It occupies the tip of the cone.
3. When there is a lack of air flow, the gas does not burn completely. The carbon is released from the divalent oxide and hydrogen residues. Their afterburning takes place in the third area where there is oxygen access.

Now let us consider separately the different combustion processes.

Burning candles

Burning a candle is like burning a match or a lighter. And the structure of the flame of a candle resembles a glowing gas stream, which is pulled up by an ejecting force. The process begins with heating the wick, followed by evaporation of paraffin.

The lowest zone, located inside and adjacent to the filament, is called the first region. It has a small glow of blue color due to the large amount of fuel, but the small volume of the oxygen mixture. Here the process of incomplete combustion of substances is carried out with the release of carbon monoxide, which is subsequently oxidized.

The first zone is surrounded by a luminous second shell, which characterizes the structure of the candle flame. It receives a larger oxygen volume, which causes the continuation of the oxidative reaction involving fuel molecules. The temperature indices here will be higher than in the dark zone, but insufficient for the final decomposition. It is in the first two regions, when the droplets of unburnt fuel and charcoal particles are strongly heated, a luminous effect appears.

The second zone is surrounded by a weakly noticeable shell with high temperature values. It involves a lot of oxygen molecules, which contributes to the complete burn-out of fuel particles. After the oxidation of substances, in the third zone the luminous effect is not observed.

Schematic representation

For clarity, we present to your attention the burning image of a candle. The flame diagram includes:

1. The first or dark area.
2. Second glowing zone.
3. The third transparent shell.

The thread of the candle does not burn, but only the charring of the bent end occurs.

Burning of the spirit lamp

For chemical experiments, small reservoirs with alcohol are often used. They are called spirits. The burner wick is impregnated with liquid fuel filled through the hole. This is facilitated by capillary pressure. When the free tip of the wick is reached, the alcohol begins to evaporate. In the vapor state, it is ignited and burned at a temperature of no more than 900 ° C.

The flame of the spirit lamp has the usual form, it is almost colorless, with a slight shade of blue. Its zones are not as clearly visible as a candle.

In an alcohol burner named after the scientist Barthel, the beginning of the fire is located above the mantle grid of the burner. Such a penetration of the flame results in a decrease in the inner dark cone, and the middle section, which is considered to be the hottest, emerges from the hole.

Color characteristic

Radiation of different colors of the flame, is caused by electronic transitions. They are also called thermal. Thus, as a result of combustion of the hydrocarbon component in the air, a blue flame is due to the release of the HC compound. And when the particles of CC are emitted, the torch is painted in an orange-red color.

It is difficult to consider the structure of a flame, the chemistry of which includes compounds of water, carbon dioxide and carbon monoxide, OH bond. Its languages are almost colorless, since the above particles emit ultraviolet and infrared radiation during combustion.

The color of the flame is interrelated with temperature indices, with the presence of ionic particles in it, which belong to a certain emission or optical spectrum. So, the burning of some elements leads to a change in the color of the fire in the burner. Differences in the coloration of the torch are associated with the arrangement of elements in different groups of the periodic system.

The fire for the presence of radiation, related to the visible spectrum, is studied by the spectroscope. It was found that simple substances from the general subgroup also exert similar staining of the flame. For clarity, use of sodium combustion as a test for this metal is used. When you add it to the flame, the tongues become bright yellow. Based on the color characteristics, the sodium line is released in the emission spectrum.

For alkali metals , the property of rapid excitation of light radiation from atomic particles is characteristic. When introducing such non-volatile compounds of such elements into the fire of a Bunsen burner, it stains.

Spectroscopic examination shows characteristic lines in the region visible to the human eye. The speed of excitation of light radiation and the simple spectral structure are closely interrelated with the high electropositive characteristics of these metals.

Characteristic

The classification of the flame is based on the following characteristics:

• State of aggregate combustion compounds. They are gaseous, aerodisperse, solid and liquid form;
• Type of radiation, which can be colorless, luminous and colored;
• Distribution speed. There is a rapid and slow spread;
• Height of flame. The structure can be short and long;
• The nature of the movement of the reactive mixtures. They distinguish pulsating, laminar, turbulent movement;
• Visual perception. The substances burn with the release of a smoky, colored or transparent flame;
• Temperature index. The flame can be low-temperature, cold and high-temperature.
• Phase state of the fuel - oxidizing reagent.

The combustion occurs as a result of diffusion or with preliminary stirring of the active components.

Oxidation and reduction area

The oxidation process takes place in a weakly visible zone. It is the hottest and is located at the top. In it, the fuel particles undergo complete combustion. And the presence of an oxygen excess and a fuel defect leads to an intensive oxidation process. This feature should be used when the objects are heated above the burner. That is why the substance is immersed in the upper part of the flame. This combustion proceeds much faster.

Rehabilitation reactions take place in the central and lower parts of the flame. It contains a large supply of combustible substances and a small amount of O ₂ molecules that carry out combustion. When oxygen-containing compounds are introduced into these regions, the element O is split off.

As an example of a reducing flame, the process of splitting iron of divalent sulfate is used. When the FeSO ₄ enters the central part of the torch, it first heats, then decomposes into trivalent iron oxide, anhydride and sulfur dioxide. In this reaction, a reduction of S with a charge of +6 to +4 is observed.

Welding flame

This type of fire is formed as a result of combustion of a mixture from a gas or a vapor of a liquid with oxygen of pure air.

An example is the formation of an oxygen-acetylene flame. It distinguishes:

• The core zone;
• Average recovery area;
• Flare edge zone.

So many oxygen-oxygen mixtures burn. Differences in the ratio of acetylene and oxidizer lead to different types of flame. It can be normal, carburizing (acetylenic) and oxidative structure.

Theoretically, the process of incomplete combustion of acetylene in pure oxygen can be characterized by the following equation: HCCH + O ₂ → H ₂ + CO + CO (one mole of O ₂ is required for the reaction ₎ .

The obtained molecular hydrogen and carbon monoxide react with air oxygen. The final products are water and tetravalent carbon oxide. The equation looks like this: CO + CO + H ₂ + 1½O ₂ → CO ₂ + CO ₂ + H ₂ O. This reaction requires 1.5 moles of oxygen. When O ₂ is added, 2.5 moles is consumed per 1 mole of HCCH. And since in practice it is difficult to find ideally pure oxygen (often it has a small contamination with impurities), the ratio of O ₂ to HCCH will be 1.10 to 1.20.

When the ratio of oxygen to acetylene is less than 1.10, a carburizing flame occurs. Its structure has an enlarged core, its outlines become vague. From such a fire, soot is released, due to the lack of oxygen molecules.

If the gas ratio is greater than 1.20, an oxidizing flame with an oxygen excess is obtained. Its excess molecules destroy the iron atoms and other components of the steel burner. In such a flame, the nuclear part becomes short and has sharp points.

Temperature readings

Each zone of a candle flame or a burner has its own values due to the arrival of oxygen molecules. The temperature of the open flame varies in different parts from 300 ° C to 1600 ° C.

An example is the diffusion and laminar flame, which is formed by three shells. Its cone consists of a dark section with a temperature of up to 360 ° C and a lack of an oxidizing substance. Above it is a glow zone. Its temperature range ranges from 550 to 850 ° C, which contributes to the decomposition of the thermal fuel mixture and its combustion.

The outer area is barely noticeable. In it, the temperature of the flame reaches 1560 ° C, which is due to the natural characteristics of the fuel molecules and the rate at which the oxidizing agent enters. Here burning is the most energetic.

Substances are ignited under different temperature conditions. Thus, metallic magnesium burns only at 2210 ° C. For many solid substances, the flame temperature is about 350 ° C. The fire of matches and kerosene is possible at 800 ° C, whereas wood - from 850 ° C to 950 ° C.

The cigarette burns with a flame, the temperature of which varies from 690 to 790 ° C, and in the propane-butane mixture - from 790 ° C to 1960 ° C. Gasoline ignites at 1350 ° С. The flame of combustion of alcohol has a temperature of not more than 900 ° C.