Terminology used in IC engine

Cylinder bore (D): 

The nominal inner diameter of the working cylinder is know Cylinder Bore and it is measured in millimeter (mm)..

CrankCase :

Part of the engine block surrounding the crankshaft. In many engines the oil pan makes up part of the crankcase housing.

Connecting Rod :

Rod connection the piston with the rotating  crankshaft, usually made of steel or alloy forging in most engines but may be aluminum in some small engines.

Stroke (L): 

It is the distance traveled by the Piston from one of its dead center position to the other dead center position.

Inlet Valve :

The valve through which air and fuel mixture (in case of SI Engine) or air (in case of CI Engine) is introduced inside the leave the cylinder.

Exhaust Valve :

The valve through which the products of combustion leave the cylinder.

Cam Shafts :

Rotating shafts used to push open valves at the proper time in the engine cycle, either directly or through mechanical or hydraulic linkage (Push rods,rocker arms,tappets )

Crank Shaft: 

Rotating shaft through which engine work output is supplied to external systems.

*The crankshaft is connected to the engine block with the main bearings.
 * It is rotated by the reciprocating pistons through the connecting rods connected to the crankshaft,offset from the axis of rotation.This offset is sometimes called crank throw or crank radius.

Crank Throw :

This is the distance between the Center of Crankshaft and Center of Crank pin. Hence the distance will be equal to half the Stroke Length.

Push Rods :

The mechanical linkage between the camshaft and valves on overhead valve engines with the camshaft in the crankcase.

Dead centre: 

The position of the working piston and the moving parts which are mechanically connected to it at the moment when the direction of the piston motion is reversed (at either end point of the stroke).

(a) Bottom dead centre (BDC): The extreme position of the piston at the bottom of the cylinder of the 
vertical engine called bottom dead centre (BDC).In case of horizontal engines, it is known as outer dead center (ODC).

(b) Top dead centre (TDC):
The extreme position of the piston at the top of the cylinder of the vertical 
engine is called top dead centre (TDC),Incase of horizontal engines. It is known as inner dead centre (IDC).

Piston Rings :

Metal rings that fit into circumferential grooves around the piston and form a sliding surface against the cylinder walls.


This is the volume that the piston displaces during its movement from BDC to TDC .
Suppose D is the bore dia. and L is the stroke length. The piston displacement is given as
(π/4) D2L.
Example: For a four-cylinder engine with a 10 cm bore dia. and 8 cm stroke length, the piston
displacement (v) will be = (π/4) x 102 x 8 x 4= 2512cm

Displacement volume or swept volume (Vs):

The nominal volume generated by the working piston when travelling from the one dead centre to next one and given as,

Vs=A × L

Exhaust Manifold :

Piping system which carries exhaust gases away from the engine cylinders, usually made of cast iron .

Clearance volume (Vc): 

The nominal volume of the space on the combustion side of the piston at the top dead centre.

Cylinder volume (V): 

Total volume of the cylinder.

V= Vs + Vc

Compression ratio (r): VS/VC

Compression ratio is a ratio of the volume when the piston is at bottom dead centre to the volume when the piston is at top dead centre.


Compression ratio =   MinimumCylinderVolume/MaximumCylinderVolume

=SweptVolume + ClearenceVolume /ClearenceVolume

The compression ratio varies from 5 : 1 to 10 : I for petrol engines and from 12:1
to 22 : I for diesel engines.

Piston Speed :

It is the distance traveled by the Piston in one minute. The piston Speed=2LN meter/min. If the R.P.M. of Engine Shaft=N and length of Stroke=L meter.

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