Fuel is a substance that will undergo combustion and produce energy when the substance comes in contact with oxygen at a temperature that is equal to or higher than the ignition temperature of the Fuel. Any combustible substance can act as fuel.
The energy produced by fuel is expressed through calorific value.
Calorific value:
Calorific value can be defined as the amount of heat produced as a result of the combustion of a unit volume of the substance.
For a fuel to be categorized as good fuel, it should have a high calorific value, in other words, the greater the calorific value larger the amount of heat produced on burning that fuel.
Fuel efficiency:
Fuel efficiency may be defined as the amount of energy released per unit mass of the fuel.
A fuel that will be suitable for automobiles should have a high calorific value, be available in abundance, and should be easy to transport without emitting any pollutants.
Petrol, Diesel, and Compressed natural gas(CNG) are some fuels on which automobiles run.