Combustion and Flame

Introduction to Fuel and Fuel Efficiency

Fuel meaning: Meaning of fuel is a substance that is burned to provide nuclear energy, heat or power. Materials like coal, wood, oil, or gas can provide heat when burned. Methanol, Gasoline, Diesel, Propane, Natural gas, Hydrogen are types of fuel. Nuclear energy is produced by burning plutonium. From fuel efficiency or fuel economy, we can measure how long any vehicle could travel, which is the opposite of fuel consumption. Fuel consumption is the amount of fuel vehicle uses to travel a particular distance. Fuel efficiency is measured in kilometers per liter. The efficiency with which the fuel does a conversion of energy is known as fuel efficiency. Let us understand the definition of Fuel, Fuel Efficiency, and Types of Fuel in greater detail.

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What is Fuel?

Definition of fuel is any substance that can provide heat and produce energy when it is burned. This energy that releases is generally in the form of chemical energy or heat energy. The recent invention of nuclear technology means now even nuclear energy may be released due to nuclear fission or fusion.

This heat energy that fuels release is used for various purposes such as cooking, in heaters, for many industrial and manufacturing purposes. At other times we use an engine to convert this heat energy into mechanical energy. Like when we use petrol to run our cars. The oil which is used to as fuel in the engine is known as Fuel oil.

And then there is the fuel our bodies use. Every cell requires energy to perform its functions. They get this energy from organic molecules such as carbohydrates, fats etc. This process of using fuels is known as cellular respiration. And these organic molecules are obtained via nutrition, which is why we call food as the fuel of our bodies.

Learn more about Fuel cell here. A fuel cell is a device which can generate electricity by force of chemical reaction.

Examples of Fuel

  • Methanol.
  • Gasoline.
  • Diesel.
  • Natural gas.
  • Hydrogen.
  • Biodiesel.

Types of Fuel

  • Solid Fuel
  • Liquid Fuel
  • Fuel Gas
  • Biofuel
  • Fossil Fuel

Let us discuss them one by one:

Solid Fuel

These are solid materials that combust to produce energy. Some examples of Solid fuel are coal, charcoal, soot, wood etc. These were most likely the first fuels utilized by mankind. They were the fuels responsible for the invention of fire. Even today they have very widespread household and industrial uses. Charcoal is still a very important fuel source for all manufacturing products and power industry, And wood is still widely used in houses to cook food and provide warmth.

Learn about Fuel injection here.

Liquid Fuel

These are the fuels we burn to produce mechanical energy and kinetic energy. Most liquid fuels such as crude oil form due to exposure to intense heat and pressure to fossilized remains of plants and animals. Then there are biofuels in liquid form such as ethanol and hydrogen fuel. These fuels are easy to transport and relatively easy to use,

Fuel Gas

Fuel Gas as the name suggests are fuels that are in a gaseous state under normal conditions. Some examples are methane, carbon monoxide, propane etc. They have an advantage that they can be easily transported to the place of consumption. However, they also tend to leak from pipes and every precaution must be taken to avoid this. The best example would be the CNG gas that comes to your kitchen via pipes that you utilize for cooking. This is also known as Domestic fuel.


Biofuel can be solid, liquid or a gas. The only condition is that it must be derived from Biomass. So essentially it is fuel derived from living matter that can be replenished. One such example is ethanol made from sugarcane wastes

Fossil Fuel

These are conventional fuels. They are also non-replenishable. They have formed over thousands of years in the earth’s core where fossilized remains of animals and plants have been exposed to high pressure and temperatures. These are fast depleting and our dependence on them is a major concern for all of humanity.

Fuel meaning


Fuel Efficiency

Now you know that energy cannot be created or destroyed, All energy can only be transferred. Fuel also do not create energy. They only convert the chemical energy of the fuel to the kinetic energy with the help of the thermal energy supplied to them. The efficiency with which the fuel does this conversion of energy is known as fuel efficiency.

Now let us take a look at how we measure this fuel efficiency. Fuel efficiency is measured as the amount of heat that 1 kg of fuel (any fuel) produces on combustion. This is known as the calorific value of the fuel. The unit of measurement of fuel efficiency is kilojoules per kg, i.e. kJ/kg.

Solved Questions for You

Q: What is a calorific value?

  1. The Amount of heat energy produced on complete combustion of 1 Kg of fuel
  2. Amount of heat energy produced on complete combustion of 100 Kg of fuel
  3. The Amount of heat energy produced on complete combustion of 1 g of fuel
  4. Amount of heat energy lost on complete combustion of 1 Kg of fuel

Solution: The correct option is “A”. Calorific value is the quantity of heat produced by the complete combustion of a given mass of a fuel, usually expressed in joules per kilogram. It can be defined as the amount of heat energy produced on complete combustion of 1 Kg of fuel.

Q: What are the characteristics of an ideal fuel?

Ans: The characteristics of good fuel are as follows

  • High calorific value.
  • Proper ignition temperature (neither be too low nor too high)
  • Cause no pollution to the atmosphere on combustion.
  • A controllable rate of combustion.
  • Easily available in plenty and cheap in cost.
  • Easy to handle and transport.
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