TYPES OF FUELS

Combustion and Flame of Class 8

FUELS

Fuels are substances that produce heat and light energy on burning. For e.g. Wood, Coal, Cow dung cakes, Kerosene, LPG etc. are used as fuel for cooking and heating. Petrol, diesel, etc. are used in automobile.

Some fuels are also used to generate electricity.

TYPES OF FUELS:

Fuels may be classified as follows -

(i) Solid fuels : Fuels that exist in solid state at room temperature are called soild fuels. Firewood, charcoal,cow dung cakes, agricultural waste and coal are some examples of solid fuels. 

coal516_Firewood

(ii) Liquid fuels : Fuels that exist in liquid state at room temperature are called liquid fuels. Kerosene, petrol, diesel and fuel oil are some examples of liquid fuels.

25Petrol_400x300

(iii) Gaseous fuels : Fuels that exist in gaseous state at room temperature are called gaseous fuels. Petroleum gas, natural gas and biogas are some commonly used gaseous fuels.

Lpg_Cylinders

CHARACTERISTICS OF FUELS :

Important characteristics of a fuel are as follows :

(i) Calorific value : The amount of heat produced by complete burning of per unit mass of a fuel is known as calorific value of that fuel.

 

The higher the calorific value of n fuel, the more heat it produces when burned. The higher the calorific value of n fuel, the better fuel It is.

Calorific value of some fuels:

Fuel

Calorific value (kJ/g)

Cow-dung cakes

7

Wood

17

Coal

25-33

Coke

33

Charcoal

35

Biogas

35-40

Petrol

47

Kerosene

48

LPG

50

Methane

55

Hydrogen

150

  (ii) Efficiency: When a fuel is burnt, some of the energy produced is given off as waste heat, which cannot be used for cooking or other purposes. So, the efficiency of fuel is decreased. So, lower the losses in waste heat higher is the efficiency.The energy of fuels can be converted into usable forms of energy such as heat energy, mechanical energy etc. This conversion is done by energy conversion devices.

 

 

Till date, no fuel-burning device is known to exhibit 100% efficiency.

The following table gives the approximate values of efficiencies of some energy conversion devices.

 

Energy conversion device

Efficiency

Petrol engine

25%

Wood stove

66%

Diesel engine

38%

Fossil fuel powered electricity generating plant

40%

Solar cell

10%

CHARACTERISTICS OF AN IDEAL FUEL (OR GOOD FUEL):

While choosing the most appropriate fuel for our domestic use or for use in industry, we should keep in mind the following characteristics of an ideal fuel or a good fuel .

  • It should have a high calorific value : In other words, an ideal fuel (or good fuel) is that which gives us more heat per unit weight.
  • It should burn without giving out any harmful gases : An ideal fuel (or good fuel) is that which does not pollute air on burning by giving out poisonous gases.
  • It should have a proper ignition temperature, so that it can be burned easily : The ignition temperature of an ideal fuel (or good fuel) should be neither too low nor too high. Because if the ignition temperature of the fuel is very low, then the fuel will catch fire too easily and hence it will be very unsafe to use it. On the other hand, if the ignition temperature is too high, then it will be very difficult to burn the fuel.
  • It should not be more valuable for some other purpose than a fuel : An ideal fuel (or good fuel) should not have a more important use than being burnt to obtain heat. For example , though coke is a good fuel but it is more valuable as a reducing agent in the extraction of metals. So, coke should not be used as a fuel. It should better be used as a reducing agent in metallurgy.
  • It should be cheap and easily available : An ideal fuel (or good fuel ) is that which is not expensive and which is available in plenty everywhere.
  • It should be easy to handle, safe to transport, and convenient to store : An ideal fuel (or good fuel) is that which does not create any safety risks during handling, during its transportation from one place to another or during its storage.
  •  It should not leave much residue behind after burning : An ideal fuel (or good fuel) should have low percentage of non-volatile materials which do not burn, so that it may burn completely without leaving much ash.
  • It should burn smoothly : An ideal fuel (or good fuel) should have a moderate rate of combustion and should burn at a steady rate. In other words, the fuel should not burn either too fast or too slow.

BURNING OF FUELS LEAD TO HARMFUL PRODUCTS:

The increasing fuel consumption has harmful effects on the environment.

  • Carbon fuels like wood, coal, petroleum release unburnt carbon particles. These fine particles are dangerous pollutants causing respiratory diseases, such as asthma.
  • Incomplete combustion of these fuels give carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that room.
  • Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause global warming.
  • Burning of coal and diesel releases sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Moreover, petrol engines give off gaseous oxides of nitrogen. Oxides of sulphur and nitrogen dissolve in rain water and form acids. Such rain is called acid rain. It is very harmful for crops, buildings and soil. The use of diesel and petrol as fuels in automobiles is being replaced by CNG, (Compressed Natural Gas), because CNG produces the harfmul products in very small amounts. CNG is a cleaner fuel. NCERT solutions for class 8 Science prepared by Physics wallah will help you to solve your NCERT text book exercise. 

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