Mechanical Basics MECHANICAL THEORY Thermal Engineering

Classification of IC Engines PDF-Types of Heat Engines, Components, Nomenclature, Cooling Systems, Types, Performance Parameters, Lubrication of IC Engines

Classification of IC Engines PDF-Types of Heat Engines, Basic Engine Components & IC Engine Nomenclature: In the previous sessions, we had discussed about SI Engine, CI Engine, Otto Cycle, Diesel Cycle, Carnot cycle etc.

Whereas In this article, I can explain about Classification of IC Engines-Types of Heat Engines, Basic Engine Components & IC Engine Nomenclature in a detailed way as of 1st part and in the Second part I can explain about Cooling Systems, Types of Cooling systems, Air cooling, Fluid cooling systems, Performance Parameters of IC Engines and Lubrication of IC Engines.

Note: Download Classification of IC Engines PDF  at the end of the article.

Table of Contents:

1.Heat Engine

2.Classification of Heat Engines

3.Advantages of IC Engines over EC Engines

4.Components of IC Engines

5.IC Engines Nomenclature

6.Classification of IC Engines

7.Cooling Systems in IC Engine

8.Performance Parameters of IC Engines

9.Lubrication of IC Engines

10.Properties of Lubricant

11.Types of Lubrication Systems

#1.Definition of Heat Engine:

Any type of engine or machine which derives heat energy from the combustion of fuel or any other sources and converts that energy into mechanical work is termed as a heat engine.

#2.Classification of Heat Engines:

Heat engines may be classified into two types.

1.External Combustion Engine and 

2.Internal Combustion Engine

The detailed explanation of the above engines is as follows.

1.External Combustion Engine:

In this case, combustion of fuel takes place outside of the cylinder as in the case of steam engines, where the heat of combustion is employed to generate steam which is used to move a piston in a cylinder.

Example: The steam turbine and closed-cycle gas turbine.

These engines are generally used for driving locomotives, ships, generation of electric power etc.

2.Internal Combustion Engine:

In this case, combustion of the fuel occurs within the cylinder of the engine. The IC Engines group includes engines employing mixture of combustible gases and air known as gas engines.

Those using lighter liquid fuel are known as Petrol Engines and those using heavier liquid fuels are known as oil compression ignition or diesel engines.

Combustion: Burning of the fuel (Air Fuel Mixture) is known as Combustion.

#3.Advantages of IC Engines over EC Engines:

  • Requires less space
  • Simple in Design
  • Low initial cost
  • High Thermal Efficiency
  • Easy to start even in cold conditions

#4.Components of IC Engines:

Classification of IC Engines-components of IC Engines
components of IC Engines

Image Source

The components of IC Engines are as follows.


It is a cylindrical vessel or space in which the piston makes a reciprocating motion.

The varying volume created in the cylinder during the operation of the engine is filled with working fluid and is subjected to different thermodynamic processes.

2.Piston: It is a cylindrical component fitted into the cylinder for converting one form of energy into another form. It fits perfectly into the cylinder providing a gas-tight space with the Piston rings and the lubricant.

3.Cylinder head:

The main function of the cylinder head is to close the cylinder to make a confined space. The valves(Inlet and Exhaust Valve), Spark plug, cam and camshaft are present in the head section only.

4.Connecting rod:

It interconnects Piston and the crankshaft and transmits the gas forces from the Piston to the crankshaft.


It is enclosed in a crankcase. It converts the reciprocating motion of the piston into useful rotary motion of the output shaft.

6.Piston rings:

They are fitted into the slots around the piston, providing a tight seal between the piston and the cylindrical wall thus preventing the leakage of combustion gases.

7.Gudgeon Pin:

 It forms the link between the small end of the connecting rod and the Piston. 


 It is used to connect the connecting rod and piston.

8.Inlet and Exhaust valves:

 They are provided on the cylinder head or on the side of the cylinder for regulating the charge coming into the cylinder(inlet valve) and for discharging the products of combustion(exhaust valve) from the cylinder.

9.Spark Plug:

 It is a component to initiate the combustion process in SI engines and is usually located on the cylinder head.


 It is a stationary body of the engine which serves as an enclosure for moving parts.


It is used to control the opening and closing of the two valves.

It also provides the drive to the ignition systems and the camshaft is driven by the crankshaft.


 They are made as integral parts of the camshaft and are designed in such a way to open the valves at the correct timing and to keep them open for the necessary duration.

#5.IC Engines Nomenclature:

1.Cylinder Bore (d):

The nominal inside diameter of the engine cylinder is called a Cylinder bore. It is designated by the letter “d” and is expressed in “mm”.

2.Piston Area:

Area of a circle of diameter equal to the cylinder bore is called the Piston Area. It is designated by “A” and expressed in cm2.


The distance travelled by the piston from one Dead Centre to the other Dead Centre is called Piston Stroke.

During one stroke, the crankshaft rotates half a turn.

It is denoted by letter “L” and expressed it in “millimetre”

4.Dead Centre:

 There are two dead centres in the engine.

1.Top Dead Centre(TDC) and 

2.Bottom Dead Centre(BDC)

The piston reciprocates in the cylinder between two fixed positions. The uppermost position i.e. position nearest to the cylinder cover is termed as Top Dead Centre(TDC) while the lowermost position(nearer to the crankshaft) is Bottom Dead Centre(BDC).

For a horizontal engine, these terms are referred as Inner Dead Centre(IDC) and Outer Dead Centre(ODC).

5.Swept Volume:

The volume displaced by the piston, when travelling from one dead Centre to the other Dead center is called as swept volume.

It is expressed in terms of cubic-centimetre(cm3) and is given by

Vs = (π/4)d2L

6.Clearance Volume:

 The space between the cylinder head and the Piston face at the Top Dead Centre(TDC) is known as the clearance volume. It is designated as Vc and is expressed in cubic-centimetre  (cm3)

7.Compression ratio:

It is the ratio of the total cylinder volume when the piston is at the bottom dead centre(VT) to the clearance volume. It is designated by the letter “r”.

Compression ratio,r = (VT/VC)

                                    = (Vc + Vs)/Vc

                                    = 1+(Vs/Vc)

#6.11 Classification of IC Engines-Every Mechanical Engineer must know:

IC Engines stands for Internal Combustion Engines which can have Higher Overall Efficiency, Low Weight to Power Ratio, Requires less space and has Greater Mechanical Simplicity.IC Engines are classified in various ways depending on their functional characteristics.

11 Classification of IC Engines:

The classification of IC Engines are as follows.

  1. Basic Engine Design
  2. A cycle of Operation(Working Cycle)
  3. Number of Strokes
  4. Type of Ignition
  5. Method of Cooling
  6. Method of Charging
  7. No. of Cylinders
  8. Cylinder Arrangement or Type of cylinder
  9. Fuel used
  10. Method of Fuel Supply
  11. Engine Speed
  12. Applications

Detailed classification of IC Engines:

The Detailed classification of IC Engines was presented below.

1.Basic Engine Design:

  1. Reciprocating Engines
  2. Rotary Engines (Wankel Engine)

2.Cycle of Operation(Working Cycle):

  1. Engines working on OTTO Cycle (SI Engines)
  2. Engines working on DIESEL Cycle (CI Engines)

3.Number of Strokes:

  1. Four Stroke Engines
  2. Two Stroke Engines

4.Based On Type of Ignition

  1. Spark Ignition Engines

             Spark Is Generated through an External Source

  b.Compression Ignition Engines

              Air Is Heated to a Sufficiently High Temperature Because of High Compression Ratio

5.Method of Cooling

  • Cooling Is Essential for the Satisfactory and Healthy Working Of the Engine (Otherwise Results In Engine Seizing)

Two Types of Engine Cooling In Practice

  1. Air-cooled Engine
  2. Water Cooled Engine

6.Classification Based On Method of Charging

a.Naturally Aspirated Engines

Admission of Fuel-air Mixture at Near Atmospheric Pressure

b.Super-charged Engines

Admission of Fuel- Air Mixture Under Pressure (Above Atmospheric)

7.No. of Cylinders:

  • Single Cylinder
  • Multi Cylinder

8.Type Of Cylinder Arrangements

  • V- Engine
  • Opposed Cylinder Engine
  • Opposed Piston Engine
  • Radial Engine
  • X-type Engine
  • H-type Engine

9.Fuel used :

  1. Gasoline or Petrol Engines
  2. Compressed Natural Gas (CNG) Engines
  3. Diesel Engines

10.Fuel Supply:

  1. Carbureted type- Fuel supplied through Carburetor
  2. Injection type- Fuel supplied through injector

    Fuel injected into the cylinder just before Ignition.

11.Classification Based On Engine Speed

  • Low Speed – up to 500 rpm
  • Medium Speed – 500 to 1000 rpm
  • High Speed – above 1000 rpm

12.Classification Based On Applications:

  • Motor cycle engine
  • Automobiles
  • Earth Movers
  • Locomotive engine
  • Marine engine
  • Aero engine
  • Prime movers for Electric Generators

This is the complete Classification of IC Engines in detailed.If you have any doubt feel free to ask from the comments section.

Let’s discuss…

IC Engines-Cooling Systems, Types, Performance Parameters, Lubrication of IC Engines

Here, in this article, I want to discuss Cooling Systems, Types of Cooling systems, Air cooling, Fluid cooling systems, Performance Parameters of IC Engines and Lubrication of IC Engines.

IC Engines

#7. Cooling Systems in IC Engine:

If the engine is allowed to run without external cooling, then the cylinder walls, cylinder, and Piston will tend to assume the average temperature of the gases to which they are exposed, which may be of the order of 1000 to 1500 degree centigrade.

At that temperature, the metal will lose their characteristics and Piston will expand and seize the liner.

Thus the cooling system is provided in an engine for the following reasons.

  • The even expansion of piston in the cylinder may result in seizure of piston.
  • High temperatures reduce the strength of piston and cylinder liner.
  • The overheated cylinder may lead to pre-ignition of the charge in case of SI engine.
  • Physical and chemical changes may occur in lubricating oil which may cause stocking of piston rings and excessive wear of cylinder.

There are mainly two methods of cooling in IC engines.

1.Air Cooling or Direct Cooling

2.Liquid Cooling or Indirect Cooling


1.Air Cooling System:

  • In this method, heat is carried away by air flowing over and around the engine cylinder.
  • It is used in scooters, motorcycles, etc.
  • Here, fins are cast on the cylinder head which provides an additional conductive and radiating surface.
  • The fins are arranged in such a way that they are at right angles to the cylinder axis.

Advantages of Air Cooling:

  • Absence of cooling pipes, radiator etc.makes the cooling system simpler.
  • No danger of coolant leakage etc.
  • The engine is not subjected to freezing troubles etc.that are usually encountered in case of water cooling.
  • Installation of air-cooled engines is easier.
  • It requires no external components. Example: tank, radiator, etc.

Disadvantages of Air Cooling:

  • Their movement is noisy.
  • Non-uniform cooling.
  • The output of an air-cooled engine is less than that of a liquid-cooled engine.
  • Maintenance is not easy.

2.Liquid Cooling System:

  • In this method of cooling engines, the cylinder walls and heads are provided with jackets through which the cooling liquid can circulate.
  • The heat is transferred from cylinder walls to the liquid by conduction and convection.
  • The liquid is heated in its passage through the jackets and is itself cooled by means of air cooling radiator system. The heat from a liquid, in turn, is transferred to the air.

Advantages of Liquid Cooling:

In the case of a water-cooled engine, installation is not necessary at the front of mobile vehicles, aircraft, etc. As the cooling system can be conveniently located wherever required. This is not possible in case of air-cooled engines.

Dis-Advantages of Liquid Cooling:

  • This is a dependent system in which the supply of water for circulation in the jacket must be required.
  • In the event of failure of the cooling system, serious damage may be caused to the engine.
  • Cost of the system is considerably high.
  • The system requires considerable attention to the maintenance of various parts of the system.

#8. Performance Parameters of IC Engines:

Indicated Power

Brake Power

Frictional Power

Indicated Thermal Efficiency

Brake Thermal Efficiency

Mechanical Efficiency

Volumetric Efficiency

Relative Efficiency/ Efficiency Ratio

The calorific value of the Fuel

Mean Effective Pressure

Specific Power Output

Fuel-Air or Air-Fuel Ratio










pm OR mep


F/A or A/F


The explanation of Performance parameters of IC engines is as follows.

1.Indicated power (I.P):

The total Power developed by the combustion of the fuel in the combustion chamber is called as Indicated power.

2.Break power (B.P):

The Power developed by an engine at the output shaft is called break power.

B.P=[2πNT/60]*1000 KW

3.Frictional power (F.P):

The difference between Indicated Power(I.P) and Brake Power(B.P) is called frictional power (F.P).


4.Indicated Thermal Efficiency (ηith):

It is defined as the ratio of energy in the indicated power, to the input fuel energy in appropriate units.

ηithI.P/(mass of fuel*Calorific value of fuel)

       = I.P/(mf*CV)

5.Brake Thermal Efficiency (ηbth):

It is defined as the ratio of energy in the brake power, to the input fuel energy in appropriate units. 

ηbth = B.P/(mass of fuel*Calorific value of fuel)

       = B.P/(mf*CV)

6.Mechanical Efficiency (ηm):

It is defined as the ratio of Brake Power (delivered power) to the Indicated Power (power provided to the piston).

ηm = B.P/I.P


 It is also defined as the ratio of the brake thermal efficiency to the indicated thermal efficiency.

ηm = ηbth/ηith

7.Volumetric Efficiency (ηv):

It is defined as the ratio of the volume of air actually inducted at ambient conditions to the swept volume of the engine.

ηv = Vol.of air actually inducted/Swept Volume

8.Relative Efficiency or Efficiency ratio(ηrel):

It is defined as the ratio between actual thermal efficiency to the ideal efficiency (air standard efficiency) of the cycle employed.

ηrel = Actual thermal efficiency/ideal efficiency (air standard efficiency)

9.Calorific Value:

It is the thermal energy released per unit quantity of the fuel when the fuel is burned completely and the products of combustion are cooled back to the initial temperature at the combustion mixture.

10.Mean Effective Pressure:

It is defined as the average pressure inside the cylinders of an I.C engine based on the calculated or measured power output.

11.Specific Power Output:

It is defined as the broken output per unit of piston displacement.

Specific Power Output=B.P/(A*L)

12.Fuel-air Ratio:

It is defined as the ratio of the mass of the fuel to the mass of the air in the air-fuel mixture.

 This is the detailed explanation of Performance Parameters of IC Engines.

#9. Lubrication of IC Engines:

Lubrication is the admittance of oil having relative motion between two surfaces.

The purpose of lubrication maybe one or more of the following.

  • Reduce wear and friction between the parts having relative motion.
  • Cool the surfaces by carrying away heat due to friction.
  • Seal a space adjoining the surfaces such as Piston rings and cylinder liner.
  • Absorb shock between bearings and other parts and consequently reduce noise.
  • Cleaning the surfaces by carrying away the carbon and metal particles caused by wear.

#10. Properties of Lubricant:

  • Fire point

It is the lowest temp at which oil burns continuously.

  • Cloud point

When the oil is subjected to low temperature, the change in the state takes places from liquid to plastic or solid-state such that it appears to a cloud called Cloud Point.

  • Pour Point

It is the lowest temperature at which the lubricating oil will pour. It is an indication of its ability to move at low temperature.

  • Oiliness

Property which enables oil to spread over is called Oiliness.

  • Corrosion

Should not corrode the working parts

  • Physical and chemical stability

Physically and chemically stable between operating temperatures

  • Adhesiveness

Oil particles stick to the metal surface is called Adhesiveness.

  • Specific gravity

It is the measure of the density of oil.

#11. Types of Lubrication Systems:

  1. Dry sump lubrication
  2. Mist lubrication
  3. Wet sump lubrication
  • Splash
  • Semi pressure system or Pressure Fed or Force Feed.
  • Full pressure system or Combination Pressure Fed and Splash.


Note: PDF Download

You can download Classification of IC Engines PDF by the below links

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Lessons for You:

Thermal Engineering

Theory of Machines

Non-Traditional Machining


Material Science Engineering

Production-Casting, Welding, Forming Processes


Sheet Metal Operations

Elements of Mechanical Engineering

Workshop Manufacturing Practices 

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