In the process of burning, a flame is formed, the structure of which is caused by the reacting substances. Its structure is divided into regions depending on temperature indicators.
Definition
Flame is called hot gases, inwhich contains plasma components or substances in solid dispersed form. They carry out transformations of the physical and chemical type, accompanied by luminescence, the release of thermal 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
Обычно так называют процессы, связанные с burning. Compared to air, gas density is less, but high temperature indicators cause gas to rise. This is how flames form, 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 describedphenomena enough to ignite the gas burner. Appearing non-luminous flame can not be called homogeneous. Visually, we can distinguish three of its main areas. By the way, studying the structure of the flame shows that various substances burn with the formation of a different type of torch.
When burning a mixture of gas and air at the beginninga short torch is formed, the color of which has blue and purple hues. In it the kernel - green-blue, reminding a cone is looked through. Consider this flame. Its structure is divided into three zones:
- Allocate a preparatory area in which the mixture is heated from gas and air as it leaves the burner port.
- It is followed by the zone in which the combustion takes place. It occupies the top of the cone.
- When there is a lack of air flow, gasdoes not burn completely. Carbon monoxide and hydrogen residues are emitted. Their burnout takes place in the third area, where there is oxygen access.
Now separately consider the various processes of combustion.
Candle burning
Burning a candle is like burning a match orlighters. And the structure of the flame of a candle resembles a hot gas stream, which is drawn upwards due to the pushing forces. The process begins with heating the wick, followed by evaporation of paraffin.
The lowest zone inside andadjacent to the thread, called the first area. It has a slight blue glow due to the large amount of fuel, but a small amount of oxygen mixture. Here is the process of incomplete combustion of substances with the release of carbon monoxide, which is further oxidized.
Первую зону окружает светящаяся вторая оболочка, characterizing the structure of the flame of a candle. It receives a larger oxygen volume, which causes the continuation of the oxidative reaction with the participation of fuel molecules. Temperature indicators here will be higher than in the dark zone, but insufficient for the final decomposition. It is in the first two areas that the glowing effect appears when the unburned fuel droplets and coal particles are strongly heated.
The second zone is surrounded by a subtle shell withhigh temperature values. It enters a lot of oxygen molecules, which contributes to the complete combustion of the fuel particles. After oxidation of substances in the third zone, the glowing effect is not observed.
Schematic illustration
For clarity, we present to your attention the image of a burning candle. The flame scheme includes:
- First or dark area.
- The second luminous zone.
- The third transparent shell.
The thread of the candle is not exposed to burning, but only the charring of the curved end occurs.
Burning a spirit stove
For chemical experiments often usesmall tanks with alcohol. They are called spirit lamps. The burner wick is impregnated with liquid fuel poured through the hole. This is facilitated by capillary pressure. When reaching the free tip of the wick, the alcohol begins to evaporate. In the vapor state, it is ignited and burns at a temperature not exceeding 900 ° C.
The flame of a spirit-lamp has the usual form, it is almost colorless, with a slight shade of blue. Its zones are not as clearly visible as those of a candle.
У спиртовой горелки, названной в честь ученого Barthel, the beginning of the fire is located above the burner grid burner. Such a deepening of the flame leads to a decrease in the internal dark cone, and the middle section, which is considered to be the hottest, comes out of the hole.
Color characteristic
Radiation of various colors of the flame causedelectronic transitions. They are also called thermal. Thus, as a result of the combustion of the hydrocarbon component in the air, a blue flame is caused by the release of compound H – C. And when emitting particles C-C, the torch is painted in orange-red color.
It is difficult to consider the structure of the flame, chemistrywhich includes compounds of water, carbon dioxide and carbon monoxide, OH bond. Its languages are almost colorless, as the above-mentioned particles emit ultraviolet and infrared radiation when burning.
Flame color is interconnected with temperatureindicators, with the presence of ionic particles in it, which relate to a specific emission or optical spectrum. Thus, the burning of some elements leads to a change in the color of the fire in the burner. Differences in the coloring of the torch are associated with the location of elements in different groups of the periodic system.
Fire for the presence of radiation related tovisible spectrum, study with a spectroscope. It was found that simple substances from the general subgroup have a similar staining of the flame. For clarity, use of sodium burning as a test for this metal. When it is brought into the flame, the tongues turn bright yellow. Based on the color characteristics, the sodium line in the emission spectrum is distinguished.
For alkali metals characteristic propertyrapid excitation of light emission from atomic particles. When volatile compounds of such elements are introduced into the Bunsen burner fire, it is stained.
Spectroscopic examination showscharacteristic lines in the area visible to the human eye. The speed of excitation of light radiation and the simple spectral structure are closely interrelated with the high electropositive characteristic of these metals.
Characteristic
The classification of the flame is based on the following characteristics:
- state of aggregate burning connections. They are gaseous, aerodisperse, solid and liquid forms;
- the type of radiation that may be colorless, luminous and colored;
- distribution speed. There is a fast and slow spread;
- flame height. The structure can be short and long;
- the nature of the movement of the reacting mixtures. There is a pulsating, laminar, turbulent movement;
- visual perception. Substances burn with a smoldering, colored or transparent flame;
- temperature index. The flame can be low temperature, cold and high temperature.
- The state of the fuel phase is an oxidizing agent.
Combustion occurs as a result of diffusion or with preliminary mixing of the active components.
Oxidative and reducing region
The oxidation process takes place in the low-visibility zone.It is the hottest and is located at the top. In it, the fuel particles undergo complete combustion. And the presence of excess oxygen and fuel deficiency leads to an intensive oxidation process. This feature should be used when heating objects above the burner. That is why the substance is immersed in the upper part of the flame. Such burning proceeds much faster.
Reduction reactions take place in the central and lower parts of the flame. It contains a large supply of flammable substances and a small amount of O2 molecules that carry out combustion. When oxygen-containing compounds are introduced into these regions, the O element is cleaved.
As an example of a reducing flame, the process of cleavage of iron bivalent sulfate is used. When hit by FeSO4 in the central part of the torch torch, occursfirst, it is heated, and then decomposed into ferric oxide, anhydride, and sulfur dioxide. In this reaction, the recovery of S with a charge of +6 to +4 is observed.
Welding flame
This type of fire is formed by the combustion of a mixture of gas or vapor liquid with oxygen of pure air.
An example is the formation of an oxyacetylene flame. In it there are:
- core area;
- medium recovery area;
- flare marginal zone.
So many gas-oxygen mixtures burn.Differences in the ratio of acetylene and oxidant lead to a different type of flame. It can be normal, carburizing (acetylene) and oxidative structure.
Theoretically, the process of incomplete combustion of acetylene in pure oxygen can be characterized by the following equation: HCCH + O2 → H2 + CO + CO (one mol O is required for the reaction2).
The resulting molecular hydrogen and carbon monoxide react with air oxygen. The end products are water and tetravalent carbon oxide. The equation looks like this: CO + CO + H2 + 1½O2 → CO2 + CO2 + X2O. This reaction requires 1.5 moles of oxygen. When summing O2 it turns out that 2.5 mol spent on 1 mol of HCCH. And since in practice it is difficult to find perfectly pure oxygen (often it has little contamination by impurities), the O ratio is2 to HCCH will be 1.10 to 1.20.
When the value of the proportion of oxygen to acetyleneless than 1.10, a carburizing flame occurs. Its structure has an enlarged core, its outlines become blurred. From such a fire, soot is emitted due to the lack of oxygen molecules.
Если же соотношение газов больше 1,20, то an oxidizing flame is obtained with an oxygen excess. Its extra molecules destroy the atoms of iron and other components of the steel burner. In such a flame, the nuclear part becomes short and has cusps.
Temperature readings
Each zone of fire candles or burners has its own values, due to the oxygen molecules. The temperature of an open flame in its different parts ranges from 300 ° C to 1600 ° C.
An example is a diffusion and laminar flame,which is formed by three shells. Its cone consists of a dark area with temperatures up to 360 ° C and a lack of an oxidizing agent. Above it is a zone of illumination. Its temperature index ranges from 550 to 850 ° C, which contributes to the decomposition of the thermal combustible 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 speed of receipt of the oxidizing agent. Here the burning is the most energetic.
Substances are ignited at different temperatures.conditions. So, metallic magnesium burns only at 2210 ° С. For many solids, the flame temperature is about 350 ° C. Ignition of matches and kerosene is possible at 800 ° С, while wood - from 850 ° С to 950 ° С.
A cigarette burns with a flame whose temperaturevaries from 690 to 790 ° С, and in the propane-butane mixture - from 790 ° С to 1960 ° С. Gasoline is ignited at 1350 ° C. The flame of burning alcohol has a temperature of not more than 900 ° C.
