7/5/2012
AENG 61
Agricultural Power and
Energy Engineering
ENGINE OPERATING
CHARACTERISTICS
REVIEW:
REVIEW:
Engine Nomenclature
Bore (d)
-diameter of the engine cylinder
Stroke (L)
-the distance that the piston travels from
bottom-dead center (BDC) to top-dead
center (TDC), or from TDC to BDC
- movement of the piston from TDC to BDC
or vice versa.
Engine Nomenclature
Engine Nomenclature
Bore- Stroke Ratio
-ranges from 0.8 -1.2 for common engines
For a given displacement volume, longer
stroke allows smaller bore:
-less surface area for heat loss, hence higher
thermal efficiency
-higher piston speed and higher friction
losses, hence reduce output power
Engine Nomenclature
In other literature,
TDC (top dead center)
= HDC (head dead center)
BDC (bottom dead center)
= CDC (crank dead center)
TDC (top dead center) – highest position
attained by the piston when it goes up.
BDC (bottom dead center) – lowest position
attained by the piston when it goes down.
REVIEW:
Engine Nomenclature
Crank throw (r)
– the distance from the center of the
crankshaft to the center of the crankpin
r = L/2
Clearance volume (Vc)
– the volume within the cylinder above
the piston when the piston is at the top
of its stroke
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7/5/2012
REVIEW:
REVIEW:
Engine Nomenclature
Engine Nomenclature
Piston Displacement/Swept Volume(Vd)
– the volume displaced by the piston
during one stroke
Engine displacement /Total piston
displacement (Ve)
– sum of the Vd of individual cylinders
n = number of cylinders
REVIEW:
REVIEW:
Engine Nomenclature
Engine Nomenclature
Total cylinder volume (VT)
– the sum of piston displacement
and clearance volume
REVIEW:
Compression ratio (CR) – ratio of total
cylinder volume to clearance volume
EXAMPLE 1:
Engine Nomenclature
Average Piston Speed (S)
-distance the piston travels in the
cylinder per unit time
N = engine rpm
The crankshaft of a certain 4-cylinder 100-mm
square engine rotates at 2200 rpm. Each cylinder
has a clearance volume of 45 cc. Determine/
answer the following:
a. Stroke-Bore Ratio
b. Piston Displacement
c. Engine Displacement
d. Compression Ratio
e. Average Piston Speed
f. Is the engine a diesel or a gasoline engine?
For common engines, S = 5 to 15 m/s
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