• Adharit

What is fuel and their types

Fuel is a substance which, when burnt, i.e. on coming in contact and reacting with

oxygen or air, produces heat. Thus, the substances classified as fuel must necessarily

contain one or several of the combustible elements : carbon, hydrogen, sulphur, etc. In

the process of combustion, the chemical energy of fuel is converted into heat energy.

To utilize the energy of fuel in most usable form, it is required to transform the fuel from

its one state to another, i.e. from solid to liquid or gaseous state, liquid to gaseous state,

or from its chemical energy to some other form of energy via single or many stages. In

this way, the energy of fuels can be utilized more effectively and efficiently for various



Fuels may broadly be classified in two ways, i.e.

  1. According to the physical state in which they exist in nature – solid, liquid and gaseous

2. According to the mode of their procurement – natural and manufactured


Solid fuels are mainly classified into two categories, i.e. natural fuels, such as wood,

coal, etc. and manufactured fuels, such as charcoal, coke, briquettes, etc


(a) They are easy to transport.

(b) They are convenient to store without any risk of spontaneous explosion.

(c) Their cost of production is low.

(d) They posses moderate ignition temperature.


(a) Their ash content is high.

(b) Their large proportion of heat is wasted.

(c) They burn with clinker formation.

(d) Their combustion operation cannot be controlled easily.

(e) Their cost of handling is high.


The liquid fuels can be classified as follows :

(a) Natural or crude oil

(b) Artificial or manufactured oils.


(a) They posses higher calorific value per unit mass than solid fuels.

(b) They burn without dust, ash, clinkers, etc.

(c) Their firing is easier and also fire can be extinguished easily by stopping

liquid fuel supply.

(d) They are easy to transport through pipes.

(e) They can be stored indefinitely without any loss.

(f) They are clean in use and economic to handle.

(g) Loss of heat in chimney is very low due to greater cleanliness.

(h) They require less excess air for complete combustion.

(i) They require less furnace space for combustion.


(a) The cost of liquid fuel is relatively much higher as compared to solid fuel.

(b) Costly special storage tanks are required for storing liquid fuels.

(c) There is a greater risk of five hazards, particularly, in case of highly

inflammable and volatile liquid fuels.

(d) They give bad odour.

(e) For efficient burning of liquid fuels, specially constructed burners and

spraying apparatus are required.


Gaseous fuels occur in nature, besides being manufactured from solid and liquid fuels.


(a) They can be conveyed easily through pipelines to the actual place of

need, thereby eliminating manual labour in transportation. They can be lighted at ease.

(c) They have high heat contents and hence help us in having higher


(d) They can be pre-heated by the heat of hot waste gases, thereby

affecting economy in heat.

(e) Their combustion can readily by controlled for change in demand like

oxidizing or reducing atmosphere, length flame, temperature, etc.

(f) They are clean in use.

(g) They do not require any special burner.

(h) They burn without any shoot, or smoke and ashes.

(i) They are free from impurities found in solid and liquid fuels.


(a)Very large storage tanks are needed.

(b)They are highly inflammable, so chances of fire hazards in their use is high.

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