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It is an engine in which the combustion of fuel takes place inside the engine. When the fuel burns inside the engine cylinder, it generates a high temperature and pressure. This high-pressure force is exerted on the piston (A device that frees to moves inside the cylinder and transmits the pressure force to crank by use of connecting rod), which used to rotate the wheels of the vehicle. In these engines, we can use only gases and high volatile fuel like petrol, diesel. These engines are generally used in automobile industries, generation of electric power, etc.

Advantages of I.C. engine

  • It has overall high efficiency over the E.C. engine.
  • These engines are compact and required less space.
  • The initial cost of the I.C. engine is lower than the E.C. engine.
  • This engine easily starts in cold because it uses high volatile fuel.


1. Cylinder block

A cylinder is the main body of the IC engine. The cylinder is a part in which the intake of fuel, compression of fuel and burning of fuel take place. The main function of the cylinder is to guide the piston. It is in direct contact with the combustion products, so it has to be cooled. When cooling a cylinder, on the outer side of the cylinder there is a water jacket (when liquid cooling used in most cars) or fin (for air cooling used in most bikes). The cylinder head and crankcase at the bottom end of the cylinder are fixed at the top end of the cylinder. The upper side of the cylinder is consisting of a combustion chamber where fuel burns. To handle all this pressure and temperature generated by the combustion of fuel, cylinder material should have high compressive strength. So it is made by high grade cast iron. It is made by casting and usually cast in one piece.

2. Cylinder head

The top end of the engine cylinder is closed by means of the removable cylinder head. There are two holes or ports at the cylinder head, one for the intake of fuel and another for exhaust. Both the intake and exhaust ports are closed by the two valves known as inlet and exhaust valve. The inlet valve, exhaust valve, spark plug, injector, etc. are bolted on the cylinder head. The main function of the cylinder head is to seal the cylinder block and not to permit entry and exit of gases on the cover head valve engine. Cylinder head is usually made by cast iron or aluminum. It is made by casting or forging and usually in one piece.

3. Piston

A piston is fitted to each cylinder as a face to receive gas pressure and transmit the thrust to the connecting rod. It is a prime mover in the engine. The main function of the piston is to give a tight seal to the cylinder through the bore and slide freely inside the cylinder. The piston should be light and sufficiently strong to handle gas pressure generated by the combustion of fuel. So the piston is made by aluminum alloy and sometimes it is made by cast iron because light alloy piston expands more than cast iron so they need more clearances to the bore.

4. Piston rings

A piston in the cylinder must be a fairly loose fit
So, that it can move freely within the cylinder. If the piston is too small to suit, it will expand as it gets hot and may stay
Tightly in the cylinder, and if it loses too much,
The vapor pressure will leak. Pistons are fitted with piston rings to provide good sealing
Fit and less friction resistance between the piston and the nozzle.
These rings are fitted with grooves cut into the piston. They are split at one end to allow them to expand or slip over the piston’s edge. There are two piston rings in a small two-
Stroke engine to provide effective sealing,
But a four-stroke engine has an additional ring known as the oil ring.
Piston rings are made of fine-grain cast iron and
High elastic material not affected by working heat.

5. Connecting rod

The connecting rod connects the piston to the crankshaft and transmits the motion and thrust of the piston to the crankshaft. It converts the reciprocating motion of the piston into rotary motion of the crankshaft. There are two ends of the connecting rod; one is known as a big end and the other as a small end. The big end is connected to the crankshaft and the small end is connected to the piston by use of piston pin. The connecting rods are made of nickel, chrome, and chrome vanadium steels. For small engines, the material may be aluminum.

6. Crankshaft

The crankshaft of an internal combustion engine receives the efforts or thrust supplied by the piston to the connecting rod and converts the reciprocating motion of the piston into rotary motion of the crankshaft. The crankshaft mounts in bearing so it can rotate freely. The shape and size of crankshaft depend on the number and arrangement of cylinders. It is usually made by steel forging, but some makers use special types of cast-iron such as spheroidal graphitic or nickel alloy castings which are cheaper to produce and have a good service life.

7. Engine bearing

Everywhere there is rotary action in the engine, bearings are needed. Bearings are used to support the moving parts. The crankshaft is supported by bearing. The connecting rod big end is attached to the crankpin on the crank of the crankshaft by a bearing. A piston pin at the small end is used to attach the rod to the piston is also rides in bearings. The main function of bearings is to reduce friction between these moving parts. In an IC engine sliding and rolling types of bearing used. The sliding-type bearing which is sometimes called bush is used to attach the connecting rod to the piston and crankshaft. They are split in order to permit their assembly into the engine. The rolling and ball bearing is used to support crankshaft so it can rotate freely. The typical bearing half is made of steel or bronze back to which a lining of relatively soft bearing material is applied.

8. Crankcase

The main body of the engine at which the cylinder is attached and which contains the crankshaft and crankshaft bearing is called the crankcase. It serves as the lubricating system too and sometimes it is called oil sump. All the oil for lubrication is placed in it.

9. Valves

To control the inlet and exhaust of the internal combustion engine, valves are used. The number of valves in an engine depends on the number of cylinders. Two valves are used for each cylinder one for inlet of air-fuel mixture inside the cylinder and other for exhaust of combustion gases. The valves are fitted in the port at the cylinder head by use of strong spring. This spring keep them closed. Both valves usually open inwards.

10. Spark plug

It is used in a spark-ignition engine. The main function of a spark plug is to conduct a high potential from the ignition system into the combustion chamber to ignite the compressed air-fuel mixture. It is fitted on the cylinder head. The spark plug consists of a metal shell having two electrodes which are insulated from each other with an air gap. When high potential current supply to spark plug it jumping from the supply electrode and produces the necessary spark.

11. Injector

An injector is usually used in the compression ignition engine. It sprays the fuel into the combustion chamber at the end of the compression stroke. It is fitted on the cylinder head.

12. Manifold

The main function of the manifold is to supply the air-fuel mixture and collects the exhaust gases equally from all cylinder. In an internal combustion engine two manifold are used, one for intake and other for exhaust. They are usually made of aluminum alloy.

13. Camshaft

Camshaft is used in the IC engine to control the opening and closing of valves at proper timing. For proper engine output inlet valve should open at the end of the exhaust stroke and closed at the end of the intake stroke. A cam, which is oval in shape, is used to control its timing and exerts pressure on the valve to open and release to close. It is operated by the crankshaft’s timing belt. It is mounted at the cylinder’s top or bottom.

14. Gudgeon pin or piston pin

These are hardened steel parallel spindles fitted through the piston bosses and the small end bushes or eyes to allow the connecting rods to swivel. It connects the piston to the connecting rod. It is made hollow for lightness.

15. Pushrod

The pushrod is used when the camshaft is situated at the bottom end of the cylinder. It carries the camshaft motion to the valves which are situated at the cylinder head.

16. Flywheel

A flywheel is secured on the crankshaft. The main function of the flywheel is to rotate the shaft during a preparatory stroke. It also makes crankshaft rotation more uniform.


I.C. engine is widely used in automobile industries so it is also known as an automobile engine. An automobile engine may be classified in many manners.

According to a number of strokes:

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