Discover Internal Combustion Engine 20 Types, Cycles, & Effects [PDF]

In this article, we shall have a detailed overview of the internal combustion engine. We have also provided a PDF for the same.

The engine in which the combustion of fuel takes place inside the engine cylinder. It is more compact occupies less space, is more efficient, and is portable. Two principal types of reciprocating internal combustion engines that are in general use are the Otto Cycle engine & the Diesel engine. The inventor of the Otto cycle engine was the German technician Nikolaus August Otto and the Diesel engine was French-born German engineer Rudolf Christian Karl Diesel. Both Otto-cycle and Diesel-cycle engines are manufactured in two-stroke and four-stroke cycle models.

Internal Combustion Engine
Photo By CarBlogIndia

Classification of Internal Combustion Engines

Internal Combustion engines are classified as follows

Video By Donut Media

According to the type of fuel used

  • Gas engine
  • Petrol engine
  • Light oil engine (kerosene)
  • Heavy oil engine (diesel)
ICE Gas Engine

According to the Type of working cycle

  • Otto cycle engine
  • Diesel cycle engine
  • Dual combustion engine

According to the speed of the engine

  • Low-speed engine-N < 300 RPM
  • Medium speed engine- 500<N< 1000 RPM
  • High-speed engine – 3600<N< 6000 RPM

According to the method of ignition

  • Spark ignition engine
  • Compression ignition engine
ICE Spark Ignition Engine

According to the type of arrangement of the cylinder

  • Horizontal engine
  • Inline engine
  • V – engine
  • Opposed Piston engine
  • Radial engine

According to the method of cooling

  • Air-cooled engine
  • Water-cooled engine

Components of Internal Combustion Engines


The cylinders of internal combustion engines are generally made of cast iron and Nickel cast iron. In the case of a large engine, all the cylinders are cast in one block. For smaller engines the cylinder with a water jacket is cast in one block; for a large engine, however, cylinder liners are used with the main cylinder. In the case of water, it is sufficient to replace the liner.

A cylinder head containing the spark plug. And atomizer is fitted with the cylinder on the head and side of the Piston through studs and nuts. The cylinder body contains the passage for the inlet and outlet of the gases.


Pistons commonly used in Internal combustion engines moving to the end inside the cylinder are known as trunk pistons. Several piston rings are fitted in groups towards the top of the Piston to prevent the leakage of charge passing the piston. Piston rings are known as compression rings.

Pistons Internal Combustion Engine

Connecting rod

It is the link between the piston and the crank. The small end of the connecting rod is connected with the Piston through a wrist pin or Piston Pin. The big end of the connecting rod is connected with the Crank through a pin known as a crank pin. Through the connecting rod, the pressure of the working gases is transmitted to the Crank. The connecting rod is made of steel or Nickel steel or duralumin for Enlarge engines.

Connecting rod Internal Combustion Engine

Crank and crankshaft

The crankshaft which is the rotating member of the internal combustion engine is built with one or more concentric portions called the cranks, the big end of the connecting rod is connected with the crank pin. The crank is rectangular in cross-section. The crank and crankshaft are made of steel forging. The main body of the engine which contains the crankshaft and bearing is known as the crankcase.

Crankshaft Internal Combustion Engine


To control the fluctuation of speed due to the fluctuation of energy during a cycle of operation, a heavy mass in the form of a wheel is mounted on the crankshaft of the engine. The wheel is known as flywheel. In the case of a multi-cylinder engine, the size of the flywheel is smaller. It is made of cast iron.

Flywheel Internal Combustion Engine


To control the fluctuation of the speed of the engine due to fluctuation in external load, the mechanism used is known as the governor. It also connects with the engine crankshaft

Governors Internal Combustion Engine
Photo By Shutterstock

Valve Gear

The mechanism for controlling the admission and exhaust of the gases to and from the cylinder is known as the valve gear. It consists of valves and their driving mechanism. Generally, Poppet valves are used in internal combustion engines but in some cases, light valves are also used for the purpose. In the two-stroke cycle engine, the Piston itself serves the purpose of a slide valve in controlling the admission and exhaust of the gases to and from the cylinder.

The motion to the valve is imparted from the camshaft through the cam, push Road, and the rocker arm, the profile of the cam depends on the type of motion to be imparted to the valve.

Intake manifold

The intake manifold means the pipe through which the admission charge is admitted into the engine cylinder. The best cross-section of an intake manifold is circular because it produces list resistance to the flow of charge. The amount of charge admitted to each cylinder must be the same. This requires that equal resistance should exist between the carburetor and the intake port to each cylinder.

Intake and Exhaust manifold of Internal Combustion Engine
Photo By Rochling Group

Since the distance to different intake ports is different, the resistance in the intake manifold is made equal by charging the cross-section of the manifold.

Exhaust manifold

The exhaust manifold means the pipe through which the exhaust gas goes out of the engine cylinders. The heat exhaust system has a separate connection from each cylinder into one or several exhaust pipes.

Piston rings

Piston rings are accommodated in the grooves of the internal combustion engine’s pistons provided around the outer surface of the piston. The Piston rings provide gas-tight fitted between the Piston and the cylinder so that leakage of high-pressure gas is prevented. The Piston rings are made of special quality cast iron which can retain its elastic property even at high temperatures. The Piston rings near the head are called “compression rings” and those away from the compression ring are called “oil rings”.


It is a part of the valve gear mechanism. The function of the camshaft is to operate the intake and exhaust valve through the cam, push road, and rocker’s arm. The camshaft is driven by the crankshaft at a speed that is the half speed of the crankshaft.

Camshaft of Internal Combustion Engine

Push Rod and Rocker arm

The motion of the cam is transmitted to the valve through the push rod and rocker’s arm which swings in a vertical plane about a fulcrum due to the rotation of the cam.

Push Rod and Rocker Arm Internal Combustion Engine
Photo By Mech Explanation


Crankcase is a casing that accommodates the cylinder, the connecting rod, and the crankshaft. It is also used as a sump for storing lubricating oil.

Crankcase Internal Combustion Engine
Photo By PNG Wing

Exhaust valve

The function of this exhaust valve is to control the exhaust of the burnt gases from the engine cylinder into the atmosphere.

Valve spring

Valve springs help to close the valve.

Valve Springs Internal Combustion Engine
Photo By NHRA

Inner dead center

The IDC is the extreme position of the Piston at the head end of the cylinder is called the inner dead center. In the case of a horizontal engine or top dead center in the case of a vertical engine.

Outer dead center

The extreme position of the Piston at the Crank end side of the cylinder is called the outer dead center, in case of a horizontal engine or bottom dead center in case of a vertical engine at O.D.C OR B.D.C

Stroke or stroke length

It is the distance through which Piston moves in the cylinder during one stroke. In other words, the stroke length is the distance between two dead centers. Numerically, it is equal to twice the crank length or crank radius.

Cylinder bore

Cylinder Bore is the internal diameter of the cylinder.

Stroke volume

Stroke volume is the volume through which the Piston moves in one stroke within the cylinder.

Clearance volume

Clearance Volume is the volume left between the cylinder head and the piston when the piston is at I.D.C or T.D.C.

Cycles of Internal Combustion Engine

Otto Cycle

Otto Cycle of internal combustion engine consists of two reversible adiabatic, two constant volume processes. Heat is supplied during processes 2-3 at constant volume and heat is rejected during the process 4-1 at constant volume. During adiabatic processes 1- 2 and 3- 4, no heat is supplied and rejected. All gas and petrol engines run on this Otto cycle.

Otto Cycle PV diagram
Photo By Wikipedia
Otto cycle Processes
Photo By Shubham Kola

Diesel cycle

Diesel cycle of internal combustion engine consists of constant pressure and a constant volume, and two adiabatic processes. Heat is supplied during constant pressure processes 2-3 and is rejected during constant volume processes 4-1. During adiabatic processes 1-2 and 3-4, no heat is supplied or rejected.

Diesel Cycle PV Diagram
Photo By Wikipedia
Diesel Cycle Processes
Photo By Shubham Kola

Dual Combustion Cycle

Dual Combustion cycle of internal combustion engine consists of two constant volume processes, two adiabatic processes, and one constant pressure process. Heat is supplied partly at constant volume processes 2-3 and partly at constant pressure processes 3-4. Heat is rejected at constant volume process 5-1. No heat is added during the adiabatic processes 1-2 & 4-5.

Dual Cycle Processes
Photo By Shubham Kola

What is a 4-Stroke Engine?

If the four events of operation i.e. suction, compression, expansion, and exhaust are completed in 4 strokes of the piston i.e. by two revolutions of the crankshaft, this internal combustion engine is called four-stroke engine.

Video By saVRee

The working principle of 4-Stroke Petrol engine

It is based on the Otto cycle of internal combustion engine. The inlet valve, exhaust valve, and spark plugs are mounted over the cylinder head. It runs in the following sequence of operation

4 Stroke Petrol Engine
Photo By GrabCAD

Suction Stroke

In this stroke, the Piston moves outward. The pressure within the cylinder falls and the mixture of oil and fuel enters the cylinder through the inlet valve till the end of the stroke. In this stroke, the exhaust valve will remain closed and no Spark will give by the spark plug.

Compression Stroke

In the stroke, the Piston moves inward and the inlet and exhaust valves are in closed condition. So the charge within the cylinder is compressed adiabatically. At the end of the stroke, the spark plug supplies the spark, and the burning of the charge starts.

Expansion Stroke

As the charge burns, the high pressure is built up above the piston and for which Piston moves outward and the expansion of burnt gas takes place adiabatically. So power is produced in this stroke. At the end of the stroke, the exhaust valve opens and some of the burnt gases escape into the atmosphere, and pressure Falls.

Exhaust Stroke

In this stroke, the inlet valve is in closed condition and the exhaust valve is in open condition and Piston moves inward. So, burn gases are driven out from the cylinder. At the end of the stroke and exhaust valve will close and the inlet valve will open to start the next cycle.


Working principle of 4-stroke diesel engine

This type of internal combustion engine consists of three valves, an inlet and an exhaust, and a fuel injection valve in the following sequence of operation.

Video By Automotive System

Suction Stroke

During the stroke, the Piston moves outward within the cylinder and only air is drawn through the inlet valve. The exhaust and fuel injection valves remain closed and this process continues till the end of the stroke.

Compression Stroke

In the stroke, the Piston moves inward with all valves closed condition. So, the air inside the cylinder is compressed adiabatically and high pressure with a high temperature of the air is attended. At the end of the stroke, the fuel injection pump supplies the fuel due to the high temperature of compressed air, fuel gets ignited automatically.

4 stroke diesel engine
Photo By GrabCAD

Expansion Stroke

In this stroke, the Piston moves outward due to the burnt gases exerting a force on the piston, and then the burnt gas expands adiabatically. At the end of the stroke, the exhaust valve open

Exhaust Stroke

In the stroke, the Piston moves inward, and the remaining burnt gases are driven out from the cylinder. The exhaust valve will be closed and the inlet valve will open at the end of the stroke to start the next cycle.

What is a 2-Stroke Engine?

If the basic four events of operation of an internal combustion engine i.e. suction, compression, expansion, and exhaust stroke are completed in two-stroke of pistons i.e. one revolution of the crankshaft, this internal combustion engine is called a two-stroke engine.

2 Stroke Petrol Engine
Photo By GrabCAD

The working principle of 2-Stroke Petrol engine

This internal combustion engine consists of three parts namely inlet, exhaust, and transport instead of the valve that works in the following ways

Video By saVRee


The Piston moves upward and first cover the inlet port. So the charge enters into the casing through the inlet port, for the movement of the piston, It covers the transfer port and then the exhaust port. So the charge above the piston compressed adiabatically. Thus in this stroke suction and compression are completed in single Piston movement. After compression ignition of the charge starts through the spark plug.


The Piston moves downward due to a force exerted by the burnt gases. So, the expansion of burnt gases takes place. After expansion, it fast uncovers the exhaust port and then the transfer port. So, scavenging of burnt gases takes place. For further movement of the piston, it covers the inlet port. Thus, the cycle is repeated.

Difference between 2-stroke and 4- stroke engine

Video By Concerning Reality
2 Stroke Engine4 Stroke Engine
For same power, it is lighter and occupies less floor areaFor same power, it is heavier and occupies more floor area
For the same speed, 2 times more power is developed than 4 stroke engineFor the same speed, half power is developed than the two-stroke engine
Lighter flywheel foundationHeavier flywheel foundation
The mechanism is simple due to the absence of valvesThe mechanism is complex due to the presence of valves
High lubricating oil consumptionLow lubricating oil consumption

Difference between Otto cycle and diesel cycle engine

Otto Cycle (S.I. Engine)Diesel Cycle (C.I. Engine)
A mixture of air fuel is admitted during a suction strokeOnly air is admitted during a suction stroke
Low Compression RatioHigh Compression Ratio
Charge is ignited by spark plugsIgnited by high temperature of compressed air
Expansion takes place at constant volume processExpansion takes place at constant pressure process
Quantity Method of governing is usedQuality Method of governing is used
Lighter in weightHeavier in weight
Low Thermal EfficiencyHigh Thermal Efficiency

What is Scavenging in IC Engine?

The process of removing or cleaning out burnt gases by blowing the fresh air or charge in the internal combustion engine cylinder is known as scavenging. In this process, a mixture of air and fuel or pure air is admitted into the engine cylinder during exhaust at a pressure slightly above at pressure to remove the burnt gases from the cylinder for two-stroke engines.

For four-stroke engines at the end of the exhaust stroke by opening the inlet valve before closing the exhaust valve. The Fresh charge is admitted at a pressure slightly above the atmospheric pressure.

What is Supercharging?

The process of admitting air or a mixture of air and fuel in a large quantity than the cylinder volume of internal combustion engine during normal suction is known as supercharging or boosting. the device used for supercharging is called a supercharger


The objectives of Super Charging are as follows

  • Increase the output power of the engine.
  • To overcome the effect of high altitude.
  • To reduce the weight of the engine Per KW power developed.
  • To reduce the volume of the engine.
  • To enable the engine to take overloads.

What is Turbocharger?

By this device, a large amount of energy within the exhaust gas is used for other purposes. The outgoing exhaust gas is allowed to expand in a nozzle and a huge quantity of K.E. is obtained which is used to drive the exhaust gas turbine. The exhaust gas turbine is used to drive the supercharger. A combination of a supercharger and an exhaust gas turbine is called a turbocharger.


the Combustion Process in SI engine

When the electric Spark is produced in the spark plug at first there is no risk of pressure or temperature which is called delay time or lag of ignition. But a change of chemical reaction takes place Which produced a flame that moves radially from the spark plug. This flame progresses across the combustion chamber, the temperature of the burnt fuel within the flame front increases rapidly and the flame moves at high velocity. The pressure rises during combustion because of the increases in temperature within the flame front.

The combustion process in CI engine

When the fuel is sprayed into the highly heated atmosphere, a delay occurs during which the fuel particles are being evaporated. The vapor of fuel then comes in contact with the oxygen at high temperatures. Thus, fuel combustion takes place and high pressure is developed.

What is Detonation?

Very rapid combustion of the last portion of the Unburnt charge will generate high-pressure waves and unusual sounds in the cylinder.

Causes of Detonation

If the ignition temperature is reached and the delay period is shorter than the time taken by the flame front to reach the last portion of the Unburnt charge, detonation will take place.

Effects of Detonation

  • Reverberating shock wave in the combustion chamber.
  • Break of parts due to high-pressure waves.
  • Loss of power.
  • Overheating of the spark plug causes a charge of Pre-ignition.
  • Increase heat loss and reduced thermal efficiency.

Methods of Preventing Detonation

  • The air-fuel mixture is to be reduced during admission.
  • The temperature of charge is to be reduced.
  • The rich air-fuel mixture should be used.
  • And then of the mixture may be added with the fuel

What is Pre-ignition in Spark Ignition engine?

The automatic ignition of charge before normal ignition given by spark plug. It occurs in Spark ignition engine

Causes of Pre-Ignition

  • The overheated carbon deposit on the combustion chamber, exhaust valve, and spark plug supply spark to ignite the fresh charge before the spark plug.

Effects of Pre-Ignition

  • It causes detonation
  • Reduce output power
  • Rough engine operation
  • Damage of part due to high temperature.

Working Principle of Simple Carburetor

It consists of two main parts which are as follows

Carburetor of ICE

Float chamber containing a float and needle valve. Mixing chamber containing the main nozzle, throttle, and chock valve.

Float chamber

It is a small tank where the level of the fuel is maintained within it. And the flow of fuel from it is regulated by the needle valve. If the metering jet and the metering rod are installed, it measures the amount of fuel going out from the float chamber to the main nozzle.

Mixing Chamber

It is a long barrel attached to a float chamber and contained venturi. It contains a throttle valve which is regulated by the flow of air-fuel mixture going out from it. A chock valve controls the flow of air into the mixing chamber.

Working Principle

During the suction stroke of the engine, the atmosphere air rushes into the carburetor through the air filter and passes through the fuel nozzle, and made the air-fuel mixture. The amount of air-fuel mixture entering to the engine cylinders is controlled by the throttle valve which is operated by acceleration. So, more fuel and a small amount of air are mixed to get a rich mixture.

What is Firing Oder in I.C. Engine?

The sequence in which the firing takes place in the different cylinders in a multi-cylinder engine. Proper firing order reduce the engine vibration, ensure the balancing of the engine and provide an even flow of power from different cylinder to the common crankshaft

The Firing Order Of Multi-Cyclinder Engine

  • 3-cylinder engine: 1-3-2
  • 4-cylinder engine:1-3-4-2 or 1-2-4-3
  • 6-cylinder engine:1-5-3-6-2-4 or 1-2-4-6-5-3
  • 8-cylinder engine:1-6-2-5-8-3-7-4 or 1-4-7-3-8-5-2-6

Lubrication of Internal Combustion Engine

The function of Lubrication

  • To minimize wear and friction.
  • To prevent metal-to-metal contact of moving parts.
  • To remove the heat of the engine parts by acting as a cooling agent.
  • To absorb shock between the bearing and other engine parts thus reducing noise and improving life.
  • To form an effective seal between the piston ring and cylinder walls.
  • To keep the engine parts, clean by carrying way parts.
  • To prevent oxidation of engine parts.
Lubrication System For Internal Combustion Engine
Photo By FAI Auto Parts

Parts to be lubricated

The following parts of Internal combustion Engine need to be lubricated

  • Main bearing of the crankshaft.
  • Big end bearing of the connecting rod.
  • Cylinder wall.
  • Small end bearing.
  • Valves guides.
  • Camshaft bearing.
  • Camshaft driving gears.

Properties of Lubricating oil

  • Viscosity
  • Physical stability.
  • Chemical stability.
  • Corrosion resistance.
  • Pour point.
  • Flashpoint.
Lubrication System For Internal Combustion Engine
Photo By Automotive Papers

Method Of Lubrication

Splash Method

In this system, a dipper on the lower part of the connecting rod bearing cap enters into the oil by containing lubrication oil with each revolution of the crankshaft. The dipper flashes the oil to the upper part of the engine as a fine oil spray that lubricates the cylinder wall, piston ring, big end bearing, and small end bearing of the connecting rod.

Forced Feed System Method

In this system, the oil is pumped to all lubricating points. The lubricating oil is supplied under pressure using a pump operated by the camshaft of the engine.

The cooling system of the Internal Combustion engine

The necessity of cooling

Cooling of Internal combustion Engine is necessary due to the following reasons

  • To prevent damage to engine parts due to high temperature.
  • To prevent the breakdown of the lubricating system.
  • To prevent overheating valves, its guide/ seats prevent wear of valves.
  • To prevent loss of strength of piston and other parts.

The purpose of the cooling system is to keep the engine at its efficient temperature (700– 900) at all engine speeds and operating conditions.

Cooling System for Internal Combustion Engine

Method of cooling

Air Cooling

In this system, the engine cylinder is cast with a no. of extended surface known as fines provided around the surface of the cylinder. Atmospheric air flows through this fine and carried away the heat generated from the cylinder into the atmosphere. This type of cooling is used in scooters/motorcycles etc.

Liquid Cooling

Water is used for cooling media. In this system cylinder and cylinder head are surrounded by water jackets and cold water is circulated. It is subdivided as follows

Thermosyphon/ natural or gravity circulated

Siphon is simplest but not suitable for large engines. The cooling tank is placed slightly above the engine level. The hot water comes from the engine jackets fitted into the tank through the hot water outlet pipe where it is cooled by radiation. The cooled water from the bottom of the tank flows back to the engine through a pipe. The H2O level in the tank should be above the level of the hot water inlet to the tank.

Forced or Pump Circulation

In this system, a pump is used near the cylinder head and is driven by the engine through belts and pulleys. The pump forced the water flow through the system high rate. The hot water comes from the cylinder jackets enters the top of the radiation and cools. The cold water again circulated through this pump.

Cooling fan for Internal Combustion Engine


In conclusion, The internal combustion engine has been vital to transportation for over 100 years, converting fuel into mechanical energy. Despite advancements in alternative power sources, it remains critical to many industries. Improving efficiency and reducing environmental impact will be a priority as we move towards a more sustainable future.

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1 thought on “Discover Internal Combustion Engine 20 Types, Cycles, & Effects [PDF]”

  1. The information is very helpful to me as a student from PNG University of Natural Resources and Environment. I used it as my reference to complete my assignment especially Applied Physics and I am happy for that.


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