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Incomplete combustion

Incomplete combustion - course, disadvantages and reaction equations

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Incomplete combustion - requirements, course and reaction equations

Incomplete combustion is one possible form of combustion process. Burns are a chemical reaction; fuels oxidize, which means that they form a chemical bond with oxygen. In addition to the incomplete there is the complete combustion. Energy is generated through combustion, for example in boilers, thermal power plants and internal combustion engines.1

Conditions and course of a burn

In order for combustion to take place, there must be sufficient quantities of combustible material and an oxidizing agent, usually oxygen. The combustion process can be accelerated with a catalytic converter. A catalytic converter may also be required to start the combustion, but heat can also trigger the combustion process. Fuels can be solid, liquid, liquid or gaseous. Solid fuels include wood and coal, while liquid fuels include gasoline, diesel, ethanol and heating oil. Wax is a fuel that becomes liquid, while natural gas and biogas are gaseous fuels. When burned, these substances react with oxygen, and in rare cases with another gas.

In combustion processes, energy is often released in the form of light. Combustion processes are always accompanied by a strong increase in temperature; this thermal energy can be used for heating or for doing work. In heat generation systems, mostly hydrocarbons react with the oxygen in the air. This creates atmospheric nitrogen, exhaust gases such as carbon dioxide and water. The reaction products differ depending on whether there is complete or incomplete combustion.2

Complete and incomplete combustion

Complete combustion is characterized by the fact that the hydrocarbons react completely with oxygen. Complete combustion results in products with the highest oxidation level, namely water and carbon dioxide. This applies to all hydrocarbons. If there is insufficient oxygen in a combustion process for a complete reaction with the hydrocarbons or if the substances are not mixed, it is an incomplete combustion. In this case, in addition to water and carbon dioxide, residues of the starting materials or not completely oxidized products can be found among the reaction products. In the case of incomplete combustion, the oxygen is insufficient for the most oxidized products possible, so that carbon monoxide is formed. Other reaction products such as soot, which consists of pure carbon, can also be the result of incomplete combustion.

In addition to the proportions of oxygen and hydrocarbons, pressure and temperature play a role in incomplete combustion. This means that the reaction processes differ; for example, if long-chain alkanes are not completely burned, short-chain alkanes can be formed. Since various reactions can occur in the event of incomplete combustion, the course of the reaction and the conditions of the combustion process must be known in detail in order to be able to set up a reaction equation.3

Disadvantages of incomplete combustion

Carbon monoxide, which is produced by incomplete combustion, is a poisonous, colorless, tasteless and odorless gas. Carbon monoxide poisoning can be fatal. In the body, carbon monoxide binds to hemoglobin, the pigment in red blood cells. This blocks the uptake of oxygen. As a result, there is a lack of oxygen in the blood, organs, tissues and brain. Symptoms of carbon monoxide poisoning include headache, racing heart, nausea, and drowsiness.

Another disadvantage of incomplete combustion is that the heat yield is lower than with complete combustion. The energy available in the fuels cannot be used optimally, so that heating costs rise. Incomplete combustion can be counteracted by setting an excess of air, for example on the burner of a heating system. In this way, more oxygen is supplied than is necessary for the combustion process. However, the additional air must also be heated, for which combustion heat is consumed. In addition, the additional air supply increases exhaust gas losses and heating costs.4

Incomplete combustion of methane

Methane is one of the alkanes, its molecular formula is CH4. When methane is burned with oxygen, a faintly glowing flame appears. Methane mixtures with oxygen are highly flammable and explosive. If methane is not completely burned, carbon black is produced. This is a very fine carbon black that is used in the printing industry and in rubber production, among other things. The reaction equation for the complete combustion of methane is:5

CH4+ O2→ C + H2O

Reaction equations of alkanes

Alkanes are saturated hydrocarbons with only single compounds between the atoms. They are made up of carbon and hydrogen. In addition to methane, the alkanes also include ethane, propane and butane. The following equations apply to these substances for complete combustion:6

Ethane: 2 C2H6+7 O2→ 4 CO2+6 H.2O

Propane: C3H8+5 O2→ 3 CO2+4 H.2O

Butane: 2 C4H10+13 O2→ 8 CO2+10 H.2O

If too little oxygen is supplied, the alkanes will not burn completely. For example, under certain circumstances this can happen with a butane-filled lighter. If this is the case, the following reaction formula applies, for example:7

2 C4H10+9 O2→ 2 CO2+4 CO + 2 C + 10 H2O

Formation of ethine through combustion

Ethyne belongs to the so-called alkynes - these are unsaturated hydrocarbon compounds with a C-C triple bond in their carbon chain. The molecular formula of ethine is C.2H2, its structural formula is the following:

H − C≡C − H

Ethyne is the simplest compound among the alkynes. It does not occur naturally on Earth, but has been detected in the atmosphere of Jupiter, the largest planet in our solar system. Ethyne is used in industry, for example as a starting compound in the manufacture of basic chemicals or as a dissous gas in oxy-fuel welding and cutting. There are various ways of obtaining ethyne, for example by pyrolysis, the reaction of calcium carbide with water or by the dehydrogenation of ethene. In addition, ethane can also be formed from incomplete combustion of methane, but this method is not economical.8