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Calorific Value of Fuels With Examples and Characteristics of Fuels

Contents

The concept of equilibrium in Chemistry Topics refers to the state of balance in a chemical system where the forward and reverse reactions occur at equal rates.

What is Fuel and What are the Characteristics of Good Fuel ?

A material which is burnt to produce heat is called a fuel. Some of the common fuels are : Wood, Coal, LPG (Cooking gas), Kerosene, Petrol, Diesel, Natural gas and Biogas. A fuel is a very good source of heat energy. The heat energy produced by burning a fuel can be used directly to cook food and for running motor vehicles and factory machines or it can be converted into electrical energy at thermal power stations.

And this electrical energy (or electricity) is then used for various purposes. The fuels which we use for various purposes can be in the form of a solid, a liquid or a gas. Thus, there are three types of fuels : Solid fuels, Liquid fuels and Gaseous fuels.
Characteristics of Fuels 1

  1. Some of the examples of solid fuels are : Wood, Charcoal, Coal, Coke, Agricultural wastes and Cow- dung cakes (LIple).
  2. The examples of liquid fuels are : Kerosene, Petrol, Diesel, and Alcohol (Ethanol).
  3. The examples of gaseous fuels are : Natural gas, Petroleum gas, Biogas and Coal gas.

We use different types of fuels for various purposes at home, in industry and in transport for running automobiles. Some of the fuels used in homes are wood, charcoal, coal, LPG and kerosene. Some of the fuels used in industry are coal and natural gas. The fuels used in running automobiles (or vehicles) are petrol, diesel and CNG.

Fuel Efficiency: Calorific Value of Fuels

All the fuels produce heat on burning. All the fuels, however, do not produce the same amount of heat. Different fuels produce different amounts of heat on burning. Some fuels produce more heat whereas other fuels produce less heat. The efficiency of a fuel is expressed in terms of its calorific value.

The amount of heat produced by the complete burning (or complete combustion) of 1 kilogram of a fuel is called its calorific value. The calorific value of a fuel is expressed in the unit of ‘kilojoules per kilogram’ (which is written in short form as kJ/kg). We know that kerosene is a fuel.

Now, when 1 kilogram of kerosene is burned completely, then 45000 kilojoules of heat energy is produced. So, the calorific value of kerosene is 45000 kilojoules per kilogram (or 45000 kJ/kg). The ‘calorific value’ of a fuel is also known as ‘heat value’ of the fuel. The calorific values of some of the common fuels are given below.

Calorific Values of Some Common Fuels

Fuel Calorific value
1. Cow-dung cakes (Uple) 6000 to 8000 kJ/kg
2. Wood 17000 to 22000 kJ/kg
3. Coal 25000 to 33000 kJ/kg
4. Biogas 35000 to 40000 kJ/kg
5. Petrol 45000 kJ/kg
6. Kerosene 45000 kJ/kg
7. Diesel 45000 kJ/kg
8. Methane 50000 kJ/kg
9. CNG (Compressed Natural Gas) 50000 kJ/kg
10. LPG (Liquefied Petroleum Gas) 55000 kJ/kg
11. Hydrogen gas 150000 kJ/kg

From the above table we can see that the calorific value of LPG is 55000 kJ/kg. By saying that the calorific value of LPG is 55000 kJ/kg, we mean that if 1 kilogram of LPG is burnt completely, then it will produce 55000 kilojoules of heat energy.

The calorific value of LPG is much higher than the calorific value of cow- dung cakes and coal. This means that the burning of a given amount of LPG will produce much more heat than burning the same amount of cow-dung cakes or coal.

So, if we are asked to heat some water to boil it, then we should prefer to use LPG as fuel rather than cow-dung cakes or coal (because LPG produces much more heat on burning than an equal amount of cow-dung cakes or coal). We will now solve some problems based on calorific value.

Example Problem 1.
In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer:
Calorific value of a fuel is the heat produced by burning 1 kg of fuel. Now,
Heat produced by burning 4.5 kg fuel = 180000 kJ
So, Heat produced by burining 1 kg fuel = \(\frac{180000 \times 1}{4.5}\)
= 40000 kJ
Thus, the calorific value of the given fuel is 40000 kJ/kg.

Example Problem 2.
Arrange the following fuels in the increasing order of their calorific values (keeping the fuel with the lowest calorific value first) :
Kerosene, Hydrogen gas, LPG, Coal, Wood
Answer:
(Lowest) Wood, Coal, Kerosene, LPG, Hydrogen gas (Highest)

Characteristics of an ideal Fuel (or Good Fuel)

An ideal fuel (or a good fuel) has the following characteristics :

  1. It has a high calorific value. That is, it produces a large amount of heat (per unit mass).
  2. It burns easily in air at a moderate rate. That is, it burns neither too fast nor too slow.
  3. It has a proper ignition temperature (which is neither very low nor very high).
  4. It does not produce any harmful gases or leaves any residue after burning (which may pollute the environment).
  5. It is cheap, readily available, and easy to transport.

Please note that there is perhaps no fuel which can be considered to be an ideal fuel. We should choose a fuel which fulfils most of the requirements for a particular use.