Fuel
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Fuel is any material that is burned to obtain energy that can be used to heat or move another object. Fuels release heat and light energy through a chemical reaction known as combustion.

A good fuel must:

       •  Be readily available.
       •  Be cheap.
       •  Burn easily at a moderate rate.
       •  Produce a large amount of heat.
       •  Not leave behind any undesirable substances.

Unfortunately, there is no fuel that has all these qualities, and hence no fuel can be considered as an ideal fuel.

There are different types of fuels – solid, liquid and gaseous. This classification is based simply on the state of the fuel. 

Solid fuel:
Fuels which exists in solid state under normal conditions are called solid fuels.
Example: Wood, cow dung, charcoal...etc
Wood was the first fuel that was used 2 million years ago by homo erectus, the predecessor of human beings.

Liquid fuel: 
Fuels which exists in liquid state under normal conditions are called liquid fuels.
Example:
Petrol, diesel, kerosene...etc

Gaseous fuel:
Fuels which exists in gaseous state under normal conditions are called gaseous fuels.
Example: CNG, LPG...etc


Calorific value:
Calorific value is defined as the amount of heat energy produced on complete combustion of 1 kilogram of a fuel. It is expressed in a unit called kilojoule per kg. The higher the calorific value of a fuel, the more is its efficiency.

Table below shows calorific value of different fuels:

     Fuel   Calorific value
Hydrogen     150000
LPG      55000
CNG      50000
Methane      50000
Petrol      45000
Kerosene      45000
Diesel      45000
Biogas      40000
Coal      33000
Wood      22000
Cow dung      8000

Each kilogram of LPG produces much more heat than one kilogram of wood or coal. The calorific value of LPG is the highest among wood, charcoal and LPG. In rural areas, cow dung and wood are still used as fuel because these are very cheap and easily available.

Harmful effects of fuels:
Burning wood produces a lot of smoke, which is very harmful to humans, since it causes respiratory problems. 
Cutting down trees for fuel also leads to deforestation, which harms the environment and also deprives us of all the other benefits of trees.

Unburned carbon particles released when carbon fuels like wood, coal and petroleum burn, cause pollution and respiratory diseases such as asthma.
Incomplete combustion of carbon fuels causes the release of carbon monoxide – a very harmful gas. 
Combustion of fuels causes the release of carbon dioxide, which leads to global warming. It causes rise in temperatures, melting of polar glaciers,  rise in sea levels and the flooding of low-lying areas of the world. 
Oxides of sulphur and nitrogen dissolve in rain water to form acid rain, which ruins soil, crops and buildings.

By choosing the right fuel, it is possible to reduce the negative impact on the environment.
Example: Cars, buses and auto rickshaws that run on Compressed Natural Gas or CNG, instead of petrol as CNG is a much cleaner and cheaper fuel.

Summary

Fuel is any material that is burned to obtain energy that can be used to heat or move another object. Fuels release heat and light energy through a chemical reaction known as combustion.

A good fuel must:

       •  Be readily available.
       •  Be cheap.
       •  Burn easily at a moderate rate.
       •  Produce a large amount of heat.
       •  Not leave behind any undesirable substances.

Unfortunately, there is no fuel that has all these qualities, and hence no fuel can be considered as an ideal fuel.

There are different types of fuels – solid, liquid and gaseous. This classification is based simply on the state of the fuel. 

Solid fuel:
Fuels which exists in solid state under normal conditions are called solid fuels.
Example: Wood, cow dung, charcoal...etc
Wood was the first fuel that was used 2 million years ago by homo erectus, the predecessor of human beings.

Liquid fuel: 
Fuels which exists in liquid state under normal conditions are called liquid fuels.
Example:
Petrol, diesel, kerosene...etc

Gaseous fuel:
Fuels which exists in gaseous state under normal conditions are called gaseous fuels.
Example: CNG, LPG...etc


Calorific value:
Calorific value is defined as the amount of heat energy produced on complete combustion of 1 kilogram of a fuel. It is expressed in a unit called kilojoule per kg. The higher the calorific value of a fuel, the more is its efficiency.

Table below shows calorific value of different fuels:

     Fuel   Calorific value
Hydrogen     150000
LPG      55000
CNG      50000
Methane      50000
Petrol      45000
Kerosene      45000
Diesel      45000
Biogas      40000
Coal      33000
Wood      22000
Cow dung      8000

Each kilogram of LPG produces much more heat than one kilogram of wood or coal. The calorific value of LPG is the highest among wood, charcoal and LPG. In rural areas, cow dung and wood are still used as fuel because these are very cheap and easily available.

Harmful effects of fuels:
Burning wood produces a lot of smoke, which is very harmful to humans, since it causes respiratory problems. 
Cutting down trees for fuel also leads to deforestation, which harms the environment and also deprives us of all the other benefits of trees.

Unburned carbon particles released when carbon fuels like wood, coal and petroleum burn, cause pollution and respiratory diseases such as asthma.
Incomplete combustion of carbon fuels causes the release of carbon monoxide – a very harmful gas. 
Combustion of fuels causes the release of carbon dioxide, which leads to global warming. It causes rise in temperatures, melting of polar glaciers,  rise in sea levels and the flooding of low-lying areas of the world. 
Oxides of sulphur and nitrogen dissolve in rain water to form acid rain, which ruins soil, crops and buildings.

By choosing the right fuel, it is possible to reduce the negative impact on the environment.
Example: Cars, buses and auto rickshaws that run on Compressed Natural Gas or CNG, instead of petrol as CNG is a much cleaner and cheaper fuel.

Videos

Activities

Activity1:
Glencoe.com has developed an activity based on the calorific value of fuels wood, coal, oil and methane. From this activity student can learn capacity of these fuels in generating electricity.
Go to Activity

Activity2:

Cset.sp.utoledo.edu has developed an interactive simulation about fuels. The simulation includes definition, formation and followed by self test.For better unstanding of the concept it again takes you to that page where mistake is done in self test.
Go to Activity

Activity3:

Mrhardy.wikispaces.com has developed an interactive simulation regarding fuels. The simulation explained interestingly about the formation of fuels and how fuels are useful in our daily life. Impact of over usage of fuels and alternatives for the fuels.
Go to Activity

References

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