**Cylinder Bore (d) :**

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 (cm

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.

^{2}).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 (V**_{swept}) :**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