The working cylinder's nominal inner diameter is called the cylinder bore.
It usually expressed in millimetre (mm).
Piston Area (A) :
Piston area is the area of a circle of diameter equal to the cylinder bore is called piston area.
It usually expressed in square centimetre (cm2).
Stroke :
The distance travelled by the piston from TDC to BDC is called a stroke.
In other words, the maximum distance travelled by the piston in the cylinder is also known as a stroke. It is equal to twice the radius of a crank.
Engine Nomenclature |
Dead Centre :
The engine has two dead centres:
1. Top Dead Centre (TDC)
2. Bottom Dead Centre (BDC)
Stroke :
The distance travelled by the piston from TDC to BDC is called a stroke.
In other words, the maximum distance travelled by the piston in the cylinder is also known as a stroke. It is equal to twice the radius of a crank.
Stroke to Bore Ratio :
Stroke to bore ratio is L/d is an important parameter in
classifying the size of the engine.
Stroke to bore ratio = Inner diameter of circle / Stroke length
- If d<L is called under-square engine
- If d=L is called square engine
- If d>L is called over-square engine
Displacement or Swept Volume (Vs) :
The nominal volume swept by the working piston when travelling
from one dead centre to another dead centre is called displacement volume.
It is expressed in terms of a cubic centimetre (cc).
Vs = A × L
Cubic Capacity or Engine Capacity :
It is known as the total volume of a cylinder.
The displacement volume of a cylinder multiplied by a number
of the cylinder in an engine will give the cubic capacity.
Cubic Capacity = Vs × K
Where k = Cylinders in an engine
Clearance Volume (Vc) :
The nominal volume of the combustion chamber above the
piston, when it is at the TDC, is the clearance volume.
It expressed in a cubic centimetre (cc).
Swept or displacement volume (Vswept) :
The difference between total volume and clearance volume is called swept volume.
Swept volume = Total volume - Clearance volume
Swept or displacement volume (Vswept) :
The difference between total volume and clearance volume is called swept volume.
Swept volume = Total volume - Clearance volume
Compression Ratio (r) :
The ratio of the total cylinder volume when the piston
is at the BDC to clearance volume is called compression ratio.
r = Vt/Vc = Vc+Vs/Vc
= 1+Vs/Vc
Compression ratio = Total volume / Clearance volume
Compression ratio = Total volume / Clearance volume
Mean effective pressure :
The mean effective pressure is known as the average pressure acting on the piston.
Mean effective pressure = Work done by engine / Total volume of a cylinder
Mean piston speed :
The distance per unit time travelled by the piston.
Mean piston speed = 2ln / 60
Where l = stroke length (mm)
N = rpm