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A substance that can supply energy either alone or by reacting with another substance is known as fuel. Heat produced by fuel is measured in Calories.

An ideal fuel should
(i) have high calorific value
(ii) be cheap and easily available
(iii) be easily stored & transport
(iv) be regulated and controlled
(v) have low ignition temperature

» The quantity of fuel is expressed in the form of calorific value.
» Calorific value is the total quantity of heat liberated by complete combustion of a unit mass of fuel in air or oxygen.
» Calorific value of fuels are expressed in kcal /m3 or British Thermal unit (B.T.U) per cubic foot.
        1 kcal/m3 = 0.107 B.T.U/ft3
» Fuel may be sold (e.g wood, coal etc.)
» Liquid (e.g kerosene oil, petroleum, alcohol etc.) or gas (e.g water gas, producer gas, coal gas, oil gas, natural gas, gobar gas, LPG etc.) However, gaseous fuel are considered to be the best fuels.

Water gas (syn gas)

It is a mixture of carbon monoxide and hydrogen. It is obtained by the action of steam on a red hot coke at 1000° C.

        C + H2O → CO + H2 — 28 kcal
                          Water gas

» It has a high calorific value (2700 kcal / m3)

Producer gas

It is a mixture of CO and N2 It is prepared by burning coke in limited supply of air. It is the cheapest gaseous fuel, however its calorific value is not very high because it has a large proportion of nitrogen.

Coal gas

It is a mixture of H2, CH4, CO and other gases like N2, C2 H4, etc. It is obtained by destructive distillation of coal at about 1000°C

Oil gas

It is a mixture of H2, CH4, C, H4, CO and other gases like CO2. It is obtaineal by thermal cracking of kerosene oil. It is used in laboratories.

Gobar gas

It contains CH4, CO and H2 It is produced by fermentation of gobar in absence of air. It is used as a domestic fuel in villages.

Natural gas

It is a mixture of gaseous hydrocarbons viz methane 85% , ethane, propane butane etc. Liquefied petroleum mainly butane and isobutane.


On the basis of carbon % and calorific value there are four types of coal.

Nature % of carbon Calorific value
Peat: Low grade coal produces less heat & more smoke & ash. 50 - 60% 2500 - 3500
Lignite : High moisture content bums easily, low calorific value. 60 - 70% 3500 - 4500
Bituminous : Black, hard, smoky, flame, domestic fuel. 75 - 80% 7500 - 8000
Anthracite : Superior quality, hardest form, high calorific value. 90 - 95% 6700 - 7500

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