Is named combustion to all types of exothermic chemical reaction (that generates heat), relatively fast and that develops in gaseous or heterogeneous phases (liquid-gas or solid-gas), both in a controlled way (as in internal combustion engines) and uncontrolled ( in explosions). For example: a campfire, fireworks, a gas stove.
However, traditional approaches (the classical theory) understand combustion as a process of rapid oxidation of fuels, consisting mainly of hydrogen, carbon, and sometimes sulfur, which takes place in the presence of oxygen and releases large amounts of thermal energy.
In these reactions products such as carbon dioxide (COtwo) and water vapor, among other solid waste from the process, depending on the nature of the fuel (the substance that is consumed) and the oxidizer (the substance that promotes the reaction) involved.
The fireFor example, it is a product that emits heat and light from the violent oxidation of combustible matter.
Combustion phases
Everything combustion process it is actually a set of rapid and simultaneous reactions, which are usually taken as one. This process comprises the following stages or phases:
- A first stage or pre-reaction. The hydrocarbons in the fuel decompose and react with the oxygen present in the air, thus forming radicals, that is, compounds that are very molecularly unstable. This starts a chain reaction of the appearance and disappearance of compounds, which tends to create more than it destroys.
- Second stage or oxidation. Here most of the heat energy is generated, when oxygen reacts with radicals and initiates a process of displacement of electrons. The previous accumulation of radicals leads to a massive and violent reaction known as an explosion.
- Third stage. The oxidation of the radicals is completed and the molecules of the gases that will be released in the combustion are formed.
Types of combustion
Three different types of combustion are commonly distinguished:
- Complete or perfect combustion. It is a reaction in which combustible materials are completely oxidized, producing oxygenated compounds such as carbon dioxide, sulfur dioxide or water vapor.
- Stoichiometric or neutral. It is an ideal complete combustion that uses just the right amounts of air for its reaction and therefore generally occurs in a controlled laboratory environment.
- Combustion incomplete. Half-oxidized (unburned) compounds appear in the combustion gases, such as carbon monoxide (CO), hydrogen, carbon particles, etc.
Examples of combustion
- A bonfire. A typical example is the campfire, which has accompanied man throughout the centuries. It is a lot of organic matter (usually firewood, dry leaves, paper, etc.) piled up to concentrate the heat and keep the reaction going, in contact with oxygen and in the initial presence of heat (a spark produced with a phosphorus, for example).
- A match. The most emblematic case of combustion is that of the safety phosphor (matches, match, etc.), which consists of a wooden stick or wax paper, with a head of potassium chlorate and sulfur that when scraped against a rough surface composed of Red phosphorus and other compounds, heats up by friction and starts a combustion that generates a flame.
- A gas stove. Domestic kitchens operate on the combustion of a flammable gas, usually a mixture of propane (C3H8) and butane (C4H10), extracted from a pipe or a cylinder and put in contact with the air and with an initial charge of heat energy (such as the pilot flame).
- Strong bases and organic matter. Strong bases (such as caustic soda, caustic potash, and other extremely basic pH corrosives) can cause a drastic oxidation reaction on contact with organic matter, which can burn on contact and even start fires as it reaction is very exothermic.
- The wisps. Known by this name since ancient times and associated with spirits and other supernatural manifestations, these spontaneous flames that take place in swamps and bogs of abundant decomposing organic matter (and therefore many hydrocarbon gases) are an example of combustion in nature.
- Fireworks. They are displays of color, sound and light that consist of small detonations and combustion of gunpowder and other elements contained in a cylindrical cartridge. As the wick is lit, the fire eventually introduces the heat load necessary to initiate combustion and this to detonate the gunpowder in a chain reaction.
- The shot from a revolver. Firearms operate based on the introduction of a heat spark, the product of the blow of a small hammer on the rear metal of the bullet, which initiates combustion and the subsequent explosion of the powder contained in the ammunition. This reaction is so violent that it generates the force necessary to throw the lead forward with great force.
- An internal combustion engine. The engines of cars, boats and other vehicles that run on fossil fuels (diesel, gasoline, kerosene) are a daily example of controlled combustion. These combustions consume the hydrocarbons in the fuel and generate controlled explosions that are transformed into movement, as well as gases that are released into the atmosphere.
- The forest fires. Like campfires or wood stoves, wildfires are uncontrolled combustions that spread across acres of trees, leaves, and flammable organic matter, unless something is done to stop them. In many cases they are the result of the injection of heat product of the action of the sun intensified by the glass of an abandoned bottle, which literally starts the spark of the fire.