IC Engine Terminology | Nomenclature | Basic Definitions used In IC Engine

The following terms/Nomenclature associated with an engine are explained for the better understanding of the working principle of the IC engines.

IC Engine Terminology
IC Engine Terminology

1. Bore (B) :

The nominal inside diameter of the engine cylinder is called bore.
2. Top dead center (T.D.C.)
In a reciprocating engine the piston moves to and fro motion in the cylinder. When the piston moves upper direction in the cylinder, a point at which the piston comes to rest or change its direction known as top dead center. It is situated at top end of cylinder.
3. Bottom dead center (B.D.C.)
When the piston moves in downward direction, a point at which the piston come to rest or change its direction known as bottom dead center. It is situated in bottom side of cylinder.
4. Stroke (L)
The distance travelled by the piston from TDC to BDC is called stroke. In other words, the maximum distance travelled by the piston in the cylinder in one direction is known as stroke.
It is equal to twice the radius of the crank.
5. Total volume of cylinder (Vtotal)
It is the volume of cylinder when the piston is at bottom dead center. Generally, it is measure in centimeter cube (c.c.).
6.  Clearance volume of cylinder (Vclearance)
It is the volume of cylinder when the piston is at top dead center.
Clearance volume: the space above the piston head at the TDC, and is denoted by Vc:
Volume of the cylinder: V = Vc + Vs
7. Swept or displace volume (Vswept)
It is the volume which swept by the piston. The difference between total volume and clearance volume is known as swept volume.
Swept volume = Total volume – Clearance volume
8. Compression ratio
The ratio of maximum volume to minimum volume of cylinder is known as the compression ratio. It is 8 to 12 for spark ignition engine and 12 to 24 for compression ignition engine.
Compression ratio = Total volume / Clearance volume
R= (Vc + Vs) /  Vc
9. Stroke bore ratio
Stroke bore ratio is the ratio of bore (diameter of cylinder) to length of stroke. It is generally equal to one for small engine and less than one for large engine.
Stroke bore ratio = inner diameter of cylinder / length of stroke
10. Mean effective pressure
The average pressure acting upon the piston is known as mean effective pressure. It is given by the ratio of the work done by the engine to the total volume of engine.
Mean effective pressure = Work done by engine / Total volume of cylinder 
11. Piston
Area (A) – The area of circle of diameter equal to the cylinder bore is called as piston area. It is
denoted by the letter ‘A’ and is expressed in cm2.
12. Mean piston speed: the distance traveled by the piston per unit of time:
Mean piston speed (m/s ) = 2lN/60
where, l= length of strokes  (mm)
N= Number of crankshaft revolution per minute (rpm).
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