1. 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 a top dead center. It is situated at the top end of the cylinder.

2. Bottom dead center (B.D.C.)
When the piston moves in the downward direction, a point at which the piston comes to rest or change its direction known as the bottom dead center. It is situated on the bottom side of the cylinder.

3. Stroke (L)
The maximum distance travel by the piston in a single direction is known as the stroke. It is the distance between the top dead center and bottom dead center.

4. Bore (b)
The inner diameter of the cylinder known as the bore of the cylinder.

5. The maximum or total volume of a cylinder (Vtotal)
It is the volume of a cylinder when the piston is at bottom dead center. Generally, it is measured in centimeter cube (c.c.).

6. Minimum or clearance volume of a cylinder (V clearance)
It is the volume of the cylinder when the piston is at top dead center.

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 the minimum volume of the 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
9. Ignition delay
It is the time interval between the ignition start (spark plug start in S.I. engine and inject fuel in C.I. engine) and the actual combustion starts.

10. Stroke bore ratio
Stroke bore ratio is the ratio of the bore (diameter of a cylinder) to the length of stroke. It is generally equal to one for small engine and less than one for the large engine.

Stroke bore ratio = inner diameter of cylinder/length of stroke
11. 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 the engine.

Mean effective pressure = Work done by engine / Total volume of the cylinder

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