FUELS AND COMBUSTION
Fuels are any material that store potencial energy in any forms that can be particularly used as heat energy.
- The concept of fuel was originally applied solely to those materials that are storing energy in the form of chemical energy that could be released through combustion.
- The heat energy released by many fuels is convert into mechanical energy through an engine
- .Fuels are contrasted with other methods of storing potential energy, such as those that directly release electrical energy (such as batteries and capacitors) or mechanical energy (such as flywheels, springs, compressed air, or water in a reservoir.
- Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant that is carried out by production of heat and conversion of chemical species.
- The release of heat can produce light in the form of either glowing or a flame.
there are basically two types of combustion:-
- complete combustion
- incomplete combustion.
- rapid combustion
- turbelent combustion
- micro combustion
- stochiometric combustion
1. complete combustion:-
In a complete combustion reaction, a compound reacts with an oxidizing element, such as oxygen or fluorine, and the products are compounds of each element in the fuel with the oxidizing element. For example:
CH4 + 2 O2 → CO2 + 2 H2O + energy
A simple example can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines:
2 H2 + O2 → 2 H2O(g) + heat
The result is water vapor.
In a incomplete combustion it will only occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water. It also happens when the combustion is quenched by a heat sink such as a solid surface or flame trap.
Container of ethanol vapour mixed with air, undergoing rapid combustion.Rapid combustion is a form of combustion, otherwise known as a fire, in which large amounts of heat and light energy are released, which often results in a flame. This is used mainly in a form of machinery such as internal combustion engines and in thermobaric weapons.
Turbulent Combustion is that type of combustion that resulting in a turbulent flame is the most used for industrial application (e.g. gas turbines, gasoline engines, etc.) because the turbulence helps the mixing process between the fuel and oxidizer.
It is a processes which happen in very small volumes are considered micro-combustion. The high surface-to-volume ratio increases specific heat loss. Quenching distance plays a vital role in stabilizing the flame in such combustion chambers.
Stoichiometric combustion of a hydrocarbon in oxygen is Generally, the chemical equation for stoichiometric combustion of a hydrocarbon in oxygen is:For example, the stoichiometric burning of propane in oxygen is:Stoichiometric combustion of a hydrocarbon in air is the stoichiometric combustion takes place using air as the oxygen source, the nitrogen present in the air can be added to the equation (although it does not react) to show the composition of the resultant flue gas:
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. and reserves are being depleted much faster than new ones are being made. The production and use of fossil fuels raise environmental concerns. A global movement toward the generation of renewable energy is therefore under way to help meet increased energy needs.
origin of fossil fuel:-
Petroleum and natural gas are formed by the anaerobic decomposition of remains of organisms including phytoplankton and zooplankton that settled to the sea (or lake) bottom in large quantities under anoxic conditions, millions of years ago.. Many of the coal fields date to the Carboniferous period of Earth’s history.
Fossil fuels are of great importance because they can be burned (oxidized to carbon dioxide and water), producing significant amounts of energy per unit weight. The use of coal as a fuel predates recorded history. Coal was used to run furnaces for the melting of metal ore. Semi-solid hydrocarbons from seeps
There are three major forms of fossil fuels:-
Coal is a hard, black colored rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur.
There are three main types of coal –
Anthracite coal :-is the hardest and has more carbon, which gives it a higher energy content.
Lignite coal:- is the softest and is low in carbon but high in hydrogen and oxygen content.
The coal is then shipped by train and boats and even in pipelines. In pipelines, the coal is ground up and mixed with water to make what’s called a slurry. This is then pumped many miles through pipelines. At the other end, the coal is used to fuel power plants and other factories.
Oil is another fossil fuel. It was also formed more than 300 million years ago. Some scientists say that tiny diatoms are the source of oil. Diatoms are sea creatures the size of a pin head. They do one thing just like plants; they can convert sunlight directly into stored energy.
Natural gas is lighter than air. Natural gas is mostly made up of a gas called methane. Methane is a simple chemical compound that is made up of carbon and hydrogen atoms. It’s chemical formula is CH4 – one atom of carbon along with four atoms hydrogen. This gas is highly flammable.
saving fossil fuels:-
Fossil fuels take millions of years to make. Once they are gone they are gone.So, it’s best to not waste fossil fuels. They are not renewable; they can’t really be made again. We can save fossil fuels by conserving energy.
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