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Fuel Types

Last updated date: 28th May 2024
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Fuel Types - Characteristics of Ideal Fuel

Any substance that when undergoing chemical or nuclear change to produce energy and which can be converted into useful work is known as fuel.

The calorific value of a fuel is defined as the amount of energy released when the unit mass of the substance(fuel) undergoes complete combustion. 

The SI Unit to Measure Calorific Value is J/kg.


Calorific Value (J/kg)

Cow dung cakes

6000 - 8000


17000 - 22000


25000 - 33000











Fuels can be Generally Classified Into

Renewable Sources of Energy

The sources of energy that when once consumed can be obtained back by various biogeochemical cycles occurring in nature are known as renewable sources of energy. Energy from running water is an example of a renewable source of energy because once consumed we can get it back through rain. Another example is solar energy. For sustainable development, we should try to make maximum use of renewable energy resources. 

Non-Renewable Sources of Energy

The sources of energy that once consumed cannot be obtained back by any biogeochemical cycle is known as a non-renewable energy resource. For example, fossil fuels take millions of years to come into existence, once finished cannot be generated back for our use, hence termed non-renewable energy resources. Non-renewable resources must be used judiciously, before their use all other alternative sources of energy must be taken into consideration.


Some Properties of Ideal Fuel are

  1. Ignition Temperature: The temperature at which a substance catches fire is known as its ignition temperature. An ideal fuel must have an easily attainable ignition temperature. For example, the chemical present on the head of the matchstick catches fire easily using the heat produced by friction generated by rubbing it with the side of the matchbox. 

  2. Calorific Value: The purpose of the fuel is to convert its chemical energy into heat and other forms of energy on burning. An ideal fuel must have a high calorific value to serve the purpose better.

  3. Impact on Environment: An ideal fuel must leave less residue (harmful) on burning. It should undergo complete combustion so as not to add particulate matter to the atmosphere. For example, Compressed natural gas leaves almost no residue on burning. 

  4. Rate of Combustion: An ideal fuel must burn at a constant/moderate rate. Rapid and explosive combustion is not the characteristic feature of an ideal fuel. 

  5. Availability: An ideal fuel should be easily and ever available. It should be available at a low cost. 

  6. Handling: Easy storage and transportation prevent the loss of fuel and also protects the environment. It improves the accessibility of the fuel.

Types of Fuels 

  1. On Basis of Their State

    1. Solid Fuels: The fuels which exist in a solid state only in their primary stage are termed solid fuels.

    2. Liquid Fuels: The fuels which exist in a liquid state only in their primary stage are termed liquid fuels.

    3. Fuel Gases: The fuels which exist in a gaseous state only in their primary stage are termed fuel gases.

  1. On Basis of their Occurrence

    1. Natural Fuels: The fuels which are present naturally are known as natural fuels.

    2. BioFuels: The fuels obtained from the living matter on earth are termed biofuels.

    3. Fossil Fuels: Dead and decaying plants and animals buried deep under the earth, under high pressure and temperature gets converted into extremely high-quality fuel termed fossil fuels. Coal and petroleum are two important types of fossil fuels. Coal is mainly obtained from dead and decaying plants, whereas petroleum (crude oil) is obtained from dead and decaying animals (especially aquatic animals). Since fossil fuels are generated from organic matter, they are a rich source of energy but are non-renewable as it takes millions of years for the conversion of organic matter into fossil fuels.

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  1. Artificial Fuels: The fuels which are obtained through different chemical processes are termed artificial fuels. For example, water gas and producer gas are fuels obtained in a laboratory under required conditions.


Examples of Fuels

Solid Fuels:





Cow dung cake


Paraffin wax

Nuclear fuel


Liquid Fuels:


Gasoline, Diesel, Kerosene


Coal tar


Biodiesel obtained from Jatropha tree 

Gaseous Fuels




Water Gas

Carbon monoxide + Hydrogen

Reaction of red-hot coke with steam

Producer Gas

Carbon monoxide + Nitrogen

Reaction of red-hot coke with insufficient air

Coal Gas

Hydrogen + Methane + ethylene + Acetylene + CO + N2

Destructive distillation of coal 

Natural gas

Methane (83%) + Ethane

Petroleum deposits

Liquified petroleum gas (LPG)

Butane (C4H10) 95%

Fractional distillation of Petroleum

Compressed natural gas (CNG)

Methane (CH4) 95%

Petroleum deposits

Biogas or Gobar Gas

Methane (CH4) + Carbon dioxide (CO2) + Hydrogen (H2) + Nitrogen (N2)

Organic wastes

Types of Gaseous Fuels

Terms to Describe Natural Gas 

(Depending on the Composition) 


Dry or lean

High methane content


C5-C10 carbon content dominates


Higher concentration of H2S


Lower concentration of H2S

Residue gas

Residue after condensation

Casing head gas

Extracted from oil wells

  1. Naturally Occurring Gaseous Fuels: Natural gas is found over petroleum deposits and around coal deposits (Firedamp). The composition of natural gas obtained from different sources vary with the main component being methane gas. Other than methane some higher hydrocarbons are also found in natural gas. Traces of H2S gas are also present in Natural gas.


  1. High calorific value

  2. Proper ignition temperature

  3. Extraction of natural gas from Petroleum deposits is comparatively easier than extracting from coal deposits.

  4. Natural gas can be easily liquified for distribution by tanker. It is termed liquified natural gas (LNG)

  1. Gaseous Fuels Derived From Solid Fuels: Methane gas found around coal deposits, Gaseous fuels obtained from waste and biomass, Fuels obtained from industrial processes such as gases produced in blast furnaces. 

  2. Gaseous Fuels Obtained From Petroleum: Liquified petroleum gas, Gases obtained from various refining processes, Gaseous fuel obtained from oil gasification. 

  3. Gaseous Fuels Obtained From Fermentation Processes: For example, ethyl alcohol is obtained from the fermentation of sugarcane. 

Nuclear Fuels

The energy obtained during nuclear reactions (Nuclear fusion or nuclear fission reactions) is known as nuclear energy and the reactants are termed nuclear fuels. Uranium-235 is a widely used nuclear fuel because - energy released from a single pellet of uranium = energy released from one ton of coal = energy released from 149 gallons of oil = energy released from 17000 cu ft of Natural gas

Apart from Uranium-235, plutonium-239 is also used extensively in nuclear reactions.

Advantages of Nuclear Energy 

  1. Sustainable Development: The world population living without electricity is more than one billion. Nuclear energy is the low-cost and ever-available source of energy for developing nations. It is an affordable source of energy. 

  2. Climate: Almost all sources of energy emit some or other kind of harmful gases, but nuclear fuel is emissions-free. Nuclear energy prevents more than 52b million metric tons of CO2 from entering our atmosphere. 

  3. National Security: Nuclear fuel empowers nations by building weapons for their own security purposes.

Disadvantages of Nuclear Energy

  1. High Upfront Costs: Nuclear thermal plants that are needed to harness the nuclear energy of a substance are though cheaper to run, but require an enormous amount of money to establish. 

  2. Radioactive Waste: The use of nuclear energy produces Radioactive Waste, which can be dangerous to the environment. And it is also very troublesome to get rid of this waste.

FAQs on Fuel Types

1. What are the main advantages and disadvantages of solid fuels?

The fuels that remain in the solid state at room temperature are said to be solid fuels and they are the first type of fuel that humans encounter. Till today they are one of the most used types of fuel. Coal, wood and cow dung cakes are the most widely used examples of solid fuels. 

Advantages of using solid fuels:

  1. Solid fuels such as coal are very easy to transport and store, thus also readily available around the markets.

  2. They also got lower production costs.

Disadvantages of consuming solid fuels:

  1. Solid fuels are not efficient enough, the major part of the energy is wasted.

  2. Produces a lot of ash content and a clinker is formed with the burning process. 

  3. They might be very easy to store, but are difficult to control.

2. What are fossil fuels? 

Fossil fuels are conventional fuels that humans have been using for a long time, major fuel resources like coal and petroleum that are used by humans are a type of fossil fuel. Fossil fuels are named so as they are formed from the fossils, the fossilised remains of the animals and plants, decomposed with the presence of oxygen and under very high pressure and temperature, those remains eventually get converted into the fuels that we use today. It takes over thousands of years for the formation of fossil fuels, thus they are non-replenishable resources and on top of that, they are depleting way faster than the expectation and their dependence on human civilization is becoming a burning issue. 

3. What is the meaning of calorific value?

Calorific value is the parameter used to define the energetic content of any material (food or duel). It is the measurement of heat or the energy produced in the process of combustion of a unit mass of a particular substance. The amount of heat produced by the complete combustion of a substance is the calorific value of that substance and it is usually measured in the joules per  kilogram (J kg-1).

The efficiency of any food or fuel is highly dependent on the calorific value it has, the higher the calorific value, the higher the efficiency. The calorific value of the major food substance is - for proteins and carbohydrates the calorific value is 4 Kcal/gram, while for the fat it goes to 9 Kcal/gm.

4. What are the characteristics of Ideal fuel?

There are many types of fuels in existence and many new types of fluids are being created but not every fuel can provide a sustainable future. One must identify the ideal fuel that can lead to a sustainable future. 

Let us discuss some of the characteristics of an ideal fuel, 

  • Handling: The fuel should be easy to store and transport without any complications. 

  • Calorific Value: Calorific value determines the efficiency of the fuel, the higher it is, the better will be the efficiency. Thus, the ideal fuel should have a high calorific value

  • Rate of Combustion: The fuel should be able to maintain a constant/moderate rate of burning.

  • The Impact on the Environment: The combustion of the fuel should not produce any residue which may bring harm to the environment.

5. What is meant by the terms of “Fuel Efficiency”?

Fuel does not create energy in itself, the energy in this world can not be created nor destroyed by any means. In the case of fuels, the energy trapped in the chemical combination of the substance (known as chemical energy) is first converted into kinetic energy which gives rise to thermal energy or heat energy. The Efficiency of this conversion of chemical energy into heat energy is called the efficiency of that fuel. One major way to find fuel efficiency is the calorific value of a particular substance.