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The process of releasing energy is called combustion. This can occur directly by the exchange of gases with oxygen, or with a mixture of substances that contains oxygen: when combustion occurs with air, one is in the presence of one of these. The products of a combustion reaction are commonly called fumes, and they can contain different substances beyond those that react.
From the industrial revolution, fuel is an essential element in people's lives, as it is present as a complementary good in a large number of mass consumer products, as well as in many industrial processes.
The price of fuel, then, is usually a more than important factor in decision-making regarding which means to use to obtain energy, from which many alternatives and classifications emerge.
Although there are many classifications that can be made regarding fuels, one of the most frequent is the one that divides them according to their state of aggregation. The classification includes three groups:
The solid fuels They are the ones that burn producing ashes. Its combustion depends on factors such as its moisture content, speed of propagation, shape, nature of the heat source. When it comes to plastics, it is possible that in the composition of the fumes there are toxic gases, which can be harmful to people. Applying heat without contact with the air can obtain this type of fuel.
Examples of Solid Fuels
| Wood | Aluminum |
| Paper | Coal |
| Fabrics | Tars |
| Peat | Lignite |
| Plastics | Petroleum |
| Magnesium | Natural gas |
| Anthracite | Liquid gas |
| Sodium | Textile fibers |
| Lithium | Splinters |
| Potassium | Firewood |
The liquid fuels are those that at ambient temperature and pressure are in liquid state. They have a property which is the flashpoint, that point from which they produce a sufficient amount of vapor so that before an ignition source it ignites and ignites: in this way, what burns is not the liquid itself but its vapors.
It has, like all liquids, a melting temperature and an evaporation temperature. Liquids can be dangerous when their flash point is relatively low, so they must be maintained with extreme care regarding the conditions to which they are exposed.
Examples of Liquid Fuels
| Hexane | Resins |
| Chlorine propane | Methylcyclopentane |
| Isopropenyl acetate | Acetaldehyde |
| Pesticides | Isobutylaldehyde |
| Methyl acetate | Sulfuric ether |
| Butyl nitrite | Petroleum ether |
| Rosin oil | Ethyl acetate |
| Liquid gas | Liquid tar |
| Dichlorethylene | Fats |
| Butene | Rubbers |
The gaseous fuels they are called natural hydrocarbons, as well as those manufactured exclusively for use as fuel or waste from other industrial products that can be used as fuels.
The mixture with the substance that makes the combustion is simple, and the process is fast, but not instantaneous: a mixing time is needed to facilitate the reaction. Gases also have a ignition temperature and certain limits for its flammability. Unlike the previous cases, there are not many gaseous fuels used today.
Examples of Gaseous Fuels
- Natural gas, extracted from underground gas fields.
- Coal gas, gasification of coal destined to produce ‘pipeline type’ gas.
- Blast furnace gas, produced by the interaction of limestone, iron ore and carbon in blast furnaces.
- Petroleum liquid gas, a mixture of liquefied gases such as propane or butane.
