• Written By Ankita Sahay
  • Last Modified 10-11-2022

Fuel: Definition, Classification, Properties, Examples

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Fuel is a combustible substance that mostly consists of carbon. On proper burning in the presence of air, Fuel releases a considerable amount of energy in the form of heat and light. There are different classifications of fuels, like natural and artificial fuels. Fuels produce an immense amount of energy, which is economically used for various domestic and industrial purposes.

The flame, for example, produces light when we burn a paper with a matchstick. If we look closely, light energy is not created there; rather, it is produced as a result of the matchstick’s heat energy being transformed into light energy. As a result, humans always require certain materials to convert one form of energy into another in order to complete numerous tasks. Fuels are what we term such materials. In this article, let us learn everything about Fuel and its properties in detail.

Types of Fuel

Based on occurrence, fuel can be classified into two types: Natural or Primary fuel (Ex. coal, wood, crude oil, natural gas, etc.), and Artificial or Secondary fuel (Ex. kerosene, charcoal, petrol, water gas. etc.) 

Another basis of fuel classification is on the state in which they exist, i.e., solid, liquid, and gas. Fuels have some unique properties, such as ignition temperature and calorific value. Based on these properties, we can decide the use of fuels in various aspects of our life. 

Fuel has become a significant part of our life. We need fuel for running vehicles, generating electricity, running factories, and other necessary activities. With the increased demand for fuel, we are overusing them, but some fuels are present in limited quantities in nature, such as coal, petroleum, natural gas, etc. They are also known as non-renewable sources of energy. If we use them recklessly, we may end up with them. Thus, we should switch to renewable energy sources such as wind energy, solar energy, etc.

Renewable Vs Non-Renewable Sources of Energy

The difference between renewable and non-renewable sources of energy are explained below:

Renewable Sources of EnergyNon-Renewable Sources of Energy
The sources of energy, which, when once consumed, can be replenished quickly by various biogeochemical cycles occurring in nature, are known as renewable sources of energy.The sources of energy that, once consumed, cannot be replenished quickly are known as non-renewable sources of energy.
They are inexhaustible.2. They are exhaustible.
They are Eco-friendly.3. They cause pollution.
Resources of renewable sources of energy are abundant.4. Resources of non-renewable sources of energy are scarce and limited.
Examples: Solar energy, wind energy, hydropower, etc.5. Examples: Fossil fuels like coal and petroleum.

Learn Everything About Natural Gas Here

What is Fuels Classified on the Basis of?

Fuels are classified on various bases. Let us learn about them in detail.

Fuel Classification on the basis of Occurrence

The classification of fuel on the basis of occurrence is explained below:

1. Natural or Primary Fuels

Primary or natural fuels are obtained naturally and can be extracted, filtered, cleaned, or graded without any energy expenditure. Such fuels are processed and collected before converting into heat or mechanical work. These primary fuels are likely to be non-renewable, and some of the well-known primary fuels are fossil fuels—examples: coal, wood, crude oil, natural gas, peat, etc.

2. Artificial or Secondary Fuels

Secondary fuels or Artificial fuels are derived from primary fuels by purifying or removing some impurities by various chemical or physical processes. Secondary fuels are not found directly as a natural resource. But they are processed forms of primary fuels—examples: kerosene, charcoal, petrol, diesel, water gas, biogas, etc.

Based on the State of Aggregation

All matter in the universe is divided into solid, liquid, and gas states. Thus, fuels are classified based on the state in which it is available. This classification does not consider primary and secondary fuels.

1. Solid Fuel – All the fuels that exist in a solid-state are known as solid fuels. Example: Coal, Bituminous, Anthracite, Peat, Wood, Coke, Charcoal, etc.

Solid Fuel

2. Liquid Fuel – All the fuels that exist in the liquid state are known as liquid fuels. Example: Diesel, Petrol, Kerosene, Crude oil.

Liquid Fuel

3. Gaseous Fuel – All the fuels that exist in the gaseous state are known as gaseous fuels. Example: Natural gas, Biogas, Water gas, etc.

Gaseous fuels are derived from different sources. They are:

  1. Natural gas: Natural gas occurs near coal and petroleum deposits. They mainly contain methane gas along with other components. They have high calorific value. Natural gas is liquified to form compressed Natural Gas (CNG).
  2. Gaseous fuels are obtained from other processes: Biomass and waste produce biogas from fermentation, LPG (Liquified Petroleum Gas) is obtained from various petroleum refining processes and many more.

What are Fossil Fuels?

Fossil Fuels

Fossil fuels are fuels made from the decomposition of dead remains of plants and animals. These fuels mainly contain carbon and hydrogen and are found in the Earth’s crust. Some examples of fossil fuels are coal, petroleum, crude oil. We can take up the entire process of a coal formation to understand how these fossil fuels are formed.

Formation of Coal

Millions of years ago, dead plants and animals were deposited deep inside the Earth. Initially, these dead organic materials decomposed into peat. As time passed on, under high pressure and temperature, oxygen, hydrogen, and nitrogen was removed from them, and only carbon content was left that decomposed into coal. Coal is a natural fossil fuel that is extracted by mining. It is a huge source of energy. This process of coal formation from the decomposition of buried plants is known as ‘Metamorphism’.

Formation of Coal

Why are Fossil Fuels Exhaustible Natural Resources?

The formation of fossil fuels is a time-consuming process; it takes millions of years. Hence, it will again take another million years to replenish them once they get completely consumed.It means the rate at which fossil fuels are consumed due to human activities is very fast compared to the rate of their formation. The amount of these exhaustible resources of energy is available in a limited quantity. Thus, fossil fuels are exhaustible natural resources.

Burning Fossil Fuels

Burning Fossil Fuels

The burning of fossil fuels refers to burning coal, crude oil, and natural gas to generate energy. This energy is used to generate electricity and other industrial activities. Petrol, diesel, and CNG are widely used as fuels for running vehicles that help transportation. Coal was firstly used around the \({\rm{1700s}}\) as a fuel in fired steam engines. With time, the burning of fossil fuels has steadily increased. Each year, all across the world, fossil fuels are burned to produce around \(35\) million tonnes of carbon dioxide, which is a significant reason for global warming. Along with carbon dioxide, other gases such as nitrogen oxides, sulphur, and many other harmful gases are released into the atmosphere that adversely affects our environment. This combustion of fossil fuels can be explained by the chemical equation given below:

\({\rm{C}}{{\rm{H}}_4} + 2{{\rm{O}}_2} \to {\rm{C}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + {\rm{Energy}}\)

Alternatives to Fossil Fuels

Alternatives to Fossil Fuels

Thus, to avoid environmental pollution, we should opt for renewable energy sources such as wind energy, solar energy, etc., as an alternative to these fossil fuels as they are available in abundant quantities because these sources of energy are continuously available in the environment.

  1. Wind Energy is widely used to produce electricity by using wing mills.
  2. Solar energy is one of the major renewable energy sources available on our planet. Various solar cells and solar panels are used to generate electricity.
  3. Hydroelectricity – Water is used as a source of energy in hydropower plants.
  4. Biofuel – Biodiesel is a liquid fuel produced from renewable sources, such as vegetable oils and animal fats and is a suitable replacement for diesel fuel. Biodiesel is non-toxic and biodegradable.
  5. Nuclear Fuel – Nuclear fuel is the fuel that is used to produce a tremendous amount of energy in a nuclear reactor to carry on a nuclear chain reaction. These fuels are fissionable; Uranium\(-235\) and Plutonium\(-239\) are the most common nuclear fuels. They also produce less air pollution.
  6. Hydrogen fuel – Nowadays, Hydrogen fuel has proved to be one of the best alternatives to fossil fuels due to its high calorific value and efficiency.
    a. Hydrogen is readily available in the environment in \({{\rm{H}}_2}{\rm{O}},\) hydrocarbons, and other organic matter.
    b. It is highly efficient as compared to other energy sources. 
    c. Hydrogen fuel is environmentally friendly as it will produce only water vapour on burning.
Alternatives to Fossil Fuels

Properties of an Ideal Fuel

Some Properties of an Ideal Fuel are as follows:

  1. Calorific Value: It is the quantity of heat produced by the combustion of a fuel. The primary purpose of the fuel is to convert the maximum of its chemical energy into heat energy and other forms of energy on combustion. The higher the calorific value of a fuel, the more ideal a fuel is considered.
  2. Ignition Temperature: The minimum temperature at which a substance catches fire is known as its ignition temperature. An ideal fuel must have an easily achievable ignition temperature. 
  3. Rate of Combustion: Combustion of an ideal fuel should take place at a constant or ordinary rate. If a fuel undergoes rapid and explosive combustion, it cannot be considered an ideal fuel.
  4. Environmental Friendly: The major concern while using fuel is its impact on our environment. An ideal fuel must leave less residue on burning by complete combustion, so as not to add particulate matter in the atmosphere—for example, CNG, LPG, etc.
  5. Readily available: Availability is also a significant factor for an ideal fuel. It should be readily available whenever needed and at a low cost.
  6. Handling: Easy storage and transportation of fuel gives better accessibility, prevents the loss of fuel, and protects the environment.

Summary

In a nutshell, fuel is defined as a material that produces heat and energy on combustion. Fuels are used in petrol and diesel in vehicles; coal is used in power plants to generate electricity; natural gas is another type of fuel used to generate energy. Based on occurrence, fuel can be classified into natural or Primary fuel and Artificial or Secondary fuel.

 Another basis of fuel classification is the state in which they exist, i.e., solid, liquid, and gas. Most natural fuels are fossil fuels, such as coal, bituminous, anthracite, peat, wood, coke, charcoal, diesel, petrol, kerosene, crude oil, natural gas, biogas water gas, etc. 

A good fuel must have moderate ignition temperature and high calorific value. Though these fossil fuels are very useful in energy generation, they are non-renewable and pollute the environment significantly. 

Hence, we should switch to renewable energy sources such as solar energy, wind energy, hydro-energy, etc. These sources of energy can help to protect our natural resources to a great extent.

Study Types of Combustion Here

FAQs based on fossil fuel

Below here we have provided all of the most asked questions related to Fossile fuels:

Q.1. How are fossil fuels formed?
Ans: Millions of years ago, dead plants and animals were deposited deep inside the Earth. As time passed, under high pressure and temperature inside the Earth’s crust, oxygen, hydrogen, and nitrogen were removed from the organic matter. Only carbon content was left that decomposed into fossil fuels like coal and petroleum.

Q.2. Among coal, petroleum, and hydrogen fuel, which of the following is not a fossil fuel?
Ans: Hydrogen fuel is not a fossil fuel, while coal and petroleum are fossil fuels because decomposing buried plants and animals formed them under the Earth’s crust for millions of years. Hydrogen fuel is a green fuel as hydrogen is readily available in the environment in ({{\rm{H}}_2}{\rm{O}},) hydrocarbons, and other organic matter. It is highly efficient as compared to other energy sources. Hydrogen fuel is environmentally friendly as it will produce only water vapour on burning.

Q.3. What is the calorific value of fuel?
Ans: Calorific value is the quantity of heat produced by the combustion of a fuel. The higher the calorific value of a fuel, the more ideal a fuel is considered.

Q.4. What are fossil fuels?
Ans: Fossil fuels are defined as fuels made from the decomposition of dead remains of plants and animals for millions of years. These fuels mainly contain carbon and hydrogen and are found in the Earth’s crust. Some examples of fossil fuels are coal, petroleum, and crude oil.

Q.5. What are the disadvantages of fossil fuels?
Ans: Fossil fuels are an exhaustible and non-renewable source of energy. The formation of fossil fuels is a time-consuming process; it takes millions of years. Hence, it will take another million years to replenish them once they are consumed entirely. Another disadvantage is that they increase the pollution as on combustion, they produce toxic gases; also they are the cause of global warming.

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