Any substance that can produce heat and energy on burning is called fuel. We use this heat for various purposes such as cooking, heating and many industrial and manufacturing purposes. Some of the fuels that we use in our daily life are wood, coal, petrol, diesel and natural gas.
1. Types of fuel
Fuels are classified into different types according to their physical state. They are classified into solid, liquid and gaseous fuels.
Fuels like wood and coal are in solid state and they are called solid fuels. This type of fuel was the first one to be used by man. These fuels are easy to store and transport. The production cost is also very low.
Most of the liquid fuels are derived from the fossil remains of dead plants and animals. Petroleum oil, coal tar and alcohol are some of the liquid fuels. These fuels give more energy on burning and burn without ash.
Coal gas, oil gas, producer gas and hydrogen are some of the gaseous fuels. These fuels can be easily transported through pipes and they do not produce pollution.
2. Characteristics of fuel
An ideal fuel should have the following characteristics.
* It should be readily available
* It should be easily transportable
* It should be less expensive
* It should have high calorific value
* It should produce large amount of heat
* It should not leave behind any undesirable substances
3. Efficiency of Fuel
Any fuel contains carbon as its main constituent. During the combustion of fuel carbon combines with oxygen and liberates large amount of heat. It is expected that a fuel liberates maximum amount of heat in the short time. The efficiency of a fuel can be understood from the following terms.
Specific energy is the amount of energy produced by unit mass of a fuel. It is defined as the energy per unit mass. It is used to measure the stored energy in certain substances. Its unit is Jkg-1.
It is the quantity of heat produced by the complete combustion of fuel at constant pressure and normal conditions. It is measured in terms of KJ kg-1.
Octane number denotes the amount of octane present in petrol. The fuel having high octane number is called as an ideal fuel.
Cetane number measures the ignition delay of the fuel in diesel engine. When cetane number is higher the ignition delay is shorter. The fuel with high cetane number is called as the ideal fuel.