Liquid Fuels: A Detailed Guide All you Need

Hello, Mate !!

Welcome to Engineers Rail, your final destination for articles about engineering. In this article, I am going to discuss Liquid Fuels today.

If you want to learn about the types, definitions, Properties, Specifications, Advantages and limitations of Liquid Fuels, Then you’ve come to the correct place. If you stick with me and scroll slowly, this could be your last stop.

Therefore, I won’t take much of your time and will focus on the subject of today’s session.

Let’s Begin…

liquid fuels

Liquid Fuels-

Liquid fuels are the products of petroleum which is found in nature as mineral oil underneath the earth. It is believed that petroleum was formed under the sea bed in millions of vegetation and fossils reacting under high temperatures and pressure in the absence of air.

It is found in the depth of the sea below rocks. To bring it to the surface of the earth, first of all, deep holes are drilled and wells are formed by digging and large size pipes are installed.

Due to gas pressure, it comes out itself. It is then transferred to refineries by pipelines or other means where it is refined.

In the refineries, it passes through several chemical processes like fractional distillation and is converted into useful liquid fuels like petrol, diesel etc along with other products.

The process of extracting mineral oil from beneath the earth is shown in the figure.

Extraction of Mineral Oil-

liquid fuel extraction

Properties of Petroleum:

Petroleum is thick mineral oil which is found in different colours from light A Rock Gas Oil yellow to black. Its specific gravity varies from 0.76 to 1.0 and its calorific value varies from 27 MJ/kg to 49.3 MJ/kg.

Basically, petroleum is a mixture of hydrocarbons and contains molecules of hydrogen and carbon only. It also contains a very low percentage of oxygen, nitrogen and sulphur etc.

The percentage composition of Petroleum by weight is:

Elements Percentage
Carbon71 to 87%
Hydrogen7.5 to 17%
Oxygen & Nitrogen0 to 6%
Sulpher0 to 17%

Fractional Distillation of Petroleum:

The process of fractional distillation of petroleum involves slow and gradual heating to high temperatures. At about 200°C petrol and gasolene vaporize.

In between, 200°C to 300°C kerosene oil and ligroin are separated. In between 300°C to 380°C solar oils vaporize and at the end, residual materials in the form of fuel oil are obtained.

It is used in making lubricants and other things of use. All types of oils have different physical and chemical properties depending upon the place of their extraction, refinement process, types of sources etc.

Liquid fuels are generally used in boilers, industrial furnaces, internal combustion engines (LC. Engines) etc. For Domestic use kerosene oil is the most useful liquid fuel. These can be supplied by pumping to distant places. Their use and control are easy.

Many types of equipment are used for the combustion of liquid fuels, depending upon their properties. The classification of liquid fuels is according to their viscosity, fire point and freezing point etc.

Types of liquid fuels-

Some important liquid fuels are listed and described below-

  1. Petrol or Gasoline
  2. Diesel Oil
  3. Kerosene Oil
  4. Alcohol
  5. Gas Oil
  6. Shale Oil
  7. Vegetable Oil
  8. Heavy Fuel Oil
  9. Coal Tar
  10. Tar
  11. Benzol
  12. Colloidal Fuel
  13. Acetone

Let’s deal with these types one by one-

1. Petrol or Gasoline-

It is the lightest and most highly volatile liquid fuel which is obtained by fractional distillation of petroleum Petrol thus obtained is in crude form.

It is refined further and some additives are mixed in it to improve its properties. Now it becomes suitable to be used in I.C. Engines like cars. scooter, motorcycle, aeroplane etc.

Petrol is a light yellow, highly inflammable liquid fuel. Its distillation varies from 65°C to 220°C. It contains 85% Carbon and 15% Hydrogen. Its specific gravity is 0.73. The calorific value of petrol is 42 to 44 MJ/kg.

2. Diesel Oil-

It is comparatively cheaper oil than petrol which is obtained during fractional distillation of petroleum after kerosene oil and before lubricating oil. It is obtained between temperatures of 175°C to 350°C. Its specific gravity is 0.82 to 0.95.

Its composition by weight is 85% to 88% Carbon, 10% to 15% Hydrogen, 2% Nitrogen and up to 2% Sulphur and Oxygen.

Diesel oil is classified according to the percentage quantity of sulphur in it as given below:

  • Light diesel oil Contains sulphur of up to 0.05%
  • Medium diesel oil Contains sulphur of up to 0.2%
  • Heavy diesel oil Contains sulphur up to 0.4%.

Light diesel oil is comparatively more volatile, having less calorific value and low viscosity. Therefore it is used for high-speed engines as fuel.

High-speed engine diesel should contain ash, moisture, and residue not more than 0.15% and asphalt not more than 0.1%. Its cetane value should be at least 50 or more.

Properties of Diesel Oil:

Some important properties of diesel oils mentioned above are given in the table below:

PropertiesLight Diesel Oil


Medium Diesel Oil


Heavy Diesel Oil


Initial Fire Point174°C190°C200°C
Final Fire Point280°C327°C380°C
Flash Point56°C72°C85°C

Uses of Diesel Oil:

Diesel oil is used as liquid fuel in I.C. Engines like-Trucks, buses, cars, tractors, Rail-engine etc. It is also used for domestic and commercial uses in Motor-generator sets. Electric power is obtained by using diesel oil in diesel power plants.

3. Kerosene Oil-

It is a very important liquid fuel which is obtained during the fractional distillation of petroleum next to petrol. It is less volatile as compared to petrol.

It is obtained at about 140°C to 280°C after the distillation of petrol.

Kerosene Oil is of two types:

  • Ordinary Kerosene: It is mostly used as domestic fuel.
  • Power Kerosene: It is used in jet engines as fuel. It is more volatile in comparison to ordinary kerosene.

Its specific density is 0.77 to 0.82 and its weight per gallon is 2.88 kg to 2.9 kg. Its composition by weight is 85 to 89% carton, 12 to 15% hydrogen. Sulphur up to 0.5% and traces of nitrogen and oxygen.

The calorific value of kerosene oil is 43 MJ/kg to 47 MJ/kg. Its minimum flash point is 25°C but an ordinary kerosene oil has a flash point of 46 C.

Its dynamic viscosity at 38°C is 1.4 to 2. 4.

Uses of Kerosene Oil:

Kerosene oil is a multi-purpose liquid fuel used in stoves, heaters, furnaces, lamps, electric generator sets etc.

4. Alcohol-

It is also known as ethyl alcohol (CH, OH). It is commercially known as ethanol. It is used as fuel in IC Engines by mixing it with petrol.

In India alcohol is produced by the fermentation of molasses. Its calorific value is about 29 MJ/kg and its specific gravity is 0.8. To reduce moisture from alcohol, distillation should be done with benzene.

Two other types of alcohol:

  • Methanol (CH, OH)
  • Propanol

These two types of alcohol ie. Methanol (CH, OH) and Propenol are also used as fuel. Their calorific values are less than ethanol

5. Gas Oil-

During fractional distillation of petroleum, it is obtained in between kerosene oil and light lubricating oil. From the commercial point of view, it is not useful.

6. Shale Oil-

This oil is purified by fractional distillation. It is similar to petroleum. It contains ash up to 34%, and From the commercial point of view, it is also not an important fuel to consider.

7. Vegetable Oil-

Vegetable oil like palm oil or cotton seed oil can be used in IC Engines, and also used in homes nowadays. Their calorific value is about 39 MI/kg and their thermal efficiency is 21 to 25%. 

8. Heavy Fuel Oil-

Liquid fuels which are distilled from petrol and kerosene oil are called heavy fuel oils. They have higher atomic weight. Their distillation is carried out between 345°C to 370°C.

Their calorific value is about 42 MJ/kg. They are used in diesel engines and oil-fired boilers. They can be mixed with other oils also to be used as liquid fuels.

9. Coal Tar-

 It is a dark-coloured thick liquid. It is obtained as a by-product during the process of conversion of coal to coke. The coal tar obtained from coal is about 4.5 to 5% by weight.

Its specific density is 0.95 to 1.25. Its composition by weight is- Carbon 84 to 91%, Hydrogen 5 to 9%, Nitrogen 1%, Oxygen 4%, Sulphur 0.5% and remaining ash.

Its calorific value is 37 to 50 MJ/kg. Before use, it has to be heated to the melting stage. It is used in the furnace suitable for it.

10. Tar-

It is obtained from a coke oven. It contains some precipitated matters like pitch and Creosote,  Anthracene etc. Its specific density is 1.15. It is comparatively thicker than coal tar.

Its calorific value is about 37 MJ/kg. Its composition by weight is 91% Carbon, 7% Hydrogen, 2% Oxygen and remaining nitrogen. Sulphur and Ash.

Before use, it has to be heated to a thin state. It is used in open hearth furnaces along with gaseous fuels.

11. Benzol-

 It is obtained by the distillation of coal tar. Its composition by weight is 70% Benzene, 20% Toluene, 9% Xylene and traces of sulphur.

Its calorific value is 42 MJ/kg and the Octane number is 90. It is used in the form of a mixture of 60% petrol and 40% benzol in I.C. Engines.

It has a tendency to freeze because its freezing point is 6°C.

12. Colloidal Fuel-

It is the emulsion of two elements i.e. powder of solid fuel and oil fuel. Powder of solid fuel normally contains Bituminous, Anthracite, Coke, Peat, Lignite, Charcoal and dust from wood.

To prepare a homogenous mixture of fuel, powders of various solid fuels are mixed with oils to form colloidal fuel. It contains 2/3 parts of dry solid fuel and 1/3 part of oil.

The best mixture is formed by nixing 45% oil, 20% tar and 35% coal powder. By the use of colloidal fuel about 50% liquid fuel can be saved.

Colloidal fuel of 35% coal-powder has a calorific value of 40 MJ/kg. This fuel is burnt by means of oil burners using oil-equipments.

13. Acetone-

Acetone (C, H, OH) can be used in place of petrol. It is more volatile than methanol. It has better anti-knocking properties than butanol. So it is mixed with butanol to form a good mixture of fuel.

Desirable Properties of Liquid Fuels-

The Main desirable properties of liquid fuels are:

  • The calorific value should be high.
  • It should be free from impurities like water, dust, soil etc.
  • Its viscosity should not be high.
  • It should not be volatile.
  • It should vaporise on heating only at a fixed temperature.
  • Its octane or cetane number should be high.

General Specifications Liquid Fuels-

General specifications are required to be mentioned with purchase, uses etc, are:

  • The calorific value of the fuel.
  • Octane or Cetane number of fuel.
  • The percentage value of elements of fuel i.e. carbon, hydrogen, moisture, ash, volatile matter.
  • General properties of fuel like-Volatility, Specific gravity, Flash point, Fire point, Viscosity etc.

Liquid Fuels Examples-

Here are some of the example of liquid fuels

  • Diesel
  • Petrol
  • Bio-Diesel
  • Liquid Hydrogen
  • Liquified Petroleum gas(LPG)
  • Compressed natural gas(CNG)

Now, Let’s move to another session of this topic, Which is liquid fuels advantages and disadvantages

Advantages of Liquid Fuels-

Due to several advantages, liquid fuels are preferred in comparison to other types of fuels. Its main advantages are:

  • The supply of fuel can be regulated during the combustion process.
  • The combustion rate can be maintained uniform.
  • Transportation and storage are easy.
  • It can be transported from one place to another within the plant premises.
  • Less air or oxygen is required for combustion.
  • The calorific value is comparatively higher than other fuels.
  • Liquid fuels are economical. Consumption of liquid fuel in comparison to coal of the same calorific value is 30% less by weight and 50% less by volume.
  • Combustion takes place quickly.
  • During the combustion process, there is no residual matter like ash etc. So their use is very neat and clean.

Disadvantages of Liquid Fuels-

  • Its quantity is very rare on Indian soil.
  • Some volatile liquid fuels like petrol cannot be kept in the open because they can catch fire or explode 
  • Some liquid fuels have to be pre-heated before their use.
  • It is costly.
  • Costly tankers are required for transportation.

Applications of Liquid Fuels-

Here are some well-known applications of liquid fuels:

  • To run vehicles
  • Generating Electricity
  • Diesel power plants
  • Cooking Food
  • Provides heat to houses
  • To run Rail Engines


Wrapping Up-

The session on Liquid fuels is now completed. I hope you’ve gained the knowledge you were hoping to. If so, kindly share this crucial information with your friends, coworkers, and anyone else who might need it.

If you want to read more articles like this one, you can bookmark Engineers Rail to make it simpler for you to return.

You might like to read the following articles further:

Classification of Engine: How do They work?

Classification of Turbines


Leave a comment