FUELS AND COMBUSTION
Fuel:
A Fuel is a combustible substance, containing carbon as the main constituent, which on burning gives large amount of heat. During the process of combustion of a fuel, the atoms of carbon, hydrogen, etc. Combine with oxygen with simultaneous liberation of heal.
C+O2 → CO2 + 94 kcals
2H2 + O2 → 2H2O+68.5 k cals
The main source of fuel is coal and crude petroleum oil. These are stored fuels available in earth’s crust and are generally called fossil fuels, because they were formed from fossilised remains of plants and animals.
Classification of fuels:
- Primary fuels – occur in nature such as coal, petroleum & natural gas.
- Secondary fuels – derived from primary fuels, such as gasoline, coal gas
Primary & Secondary fuels are further classified
- i) Solid fuels – Wood, coal
- ii) Liquid fuels – Petroleum oil
iii) Gaseous fuels – Natural gas
Solid Fuels:
- Easily available
- Cheap
- Handling & Transportation are easy
- Can be stored conveniently without any risk
- Have a moderate ignition temperature
- Form large amount of ash during burning, so disposal is a big problem.
- Large space is required for storage.
- Combustion is a slow process & cannot be easily controlled.
Liquid Fuel:
- Have higher calorific value than solid fuels.
- Occupy less storage space than solid fuels.
- Combustion is uniform & easily controllable.
- Do not yield any ash after burning.
- More costly than solid fuels.
- Give unpleasant odour during incomplete combustion.
- Special type of burners are required for effective combustion.
Gaseous fuels:
- Gaseous fuels have high calorific value than solid fuels.
- During burning they do not produce any ash or smoke.
- Compared lo solid & liquid fuels, they have high thermal efficiency.
- Con be easily transported through the pipes.
- Are highly inflammable & hence the chances for fire hazards are nigh
- Since gases occupy a large volume, they require large storage tanks.