Page 116 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

2
100 Automobile mechanical and electrical systems

V c Clearance
volume
TDC

BDC

Figure 2.32 Clearance and swept volumes

2.1.2.3 Engine terminology and methods
The following are some of the technical terms that are used to describe features
of the engine:
Engine capacity –the total, combined, displaced volume of all engine cylinders
●
as a single value stated in units of cubic capacity. This is generally given in
3
cubic centimetres (cm ) or litres. In America, engine capacity is normally stated
3
in cubic inches (in ).
Swept volume –the volume of a cylinder bore between the TDC and BDC
●
piston positions, excluding the volume above the piston at TDC ( Fig. 2.32 ).
Clearance volume –the volume above the piston at TDC. Note that it is the
●
volume of the combustion chamber itself ( Fig. 2.32 ).
Bore –the diameter of the engine cylinder.
●
Stroke –the total linear distance travelled by the piston in the bore between
●
TDC and BDC positions. Note that it is twice the crankshaft throw.

Compression ratio –the total volume of the cylinder at BDC (swept
●
clearance volume), expressed as a ratio of the volume of the cylinder at TDC
(clearance volume).
The information on cylinder dimension can generally be found in workshop or
manufacturer manuals. In addition, these values can be measured directly or
derived via calculations.
Swept volume can be calculated via the formula:

(ldπ 2 )/4

where d is cylinder bore and l is stroke. Note that units of bore and stroke
must be consistent. Engine volume is mostly stated in litres by manufacturers,
but remember that 1000 cc (cubic centimetres) equals 1 litre. The total engine
displacement is the sum of all cylinders’ individual displacements.
The formula used to calculate the compression ratio is:

CR (V V / ) V
s c c
where CR is compression ratio, V is swept volume, and V is clearance volume.
c
s
Note the correct order of preference when carrying out this calculation
(remember or google BODMAS).