4079564-Engine-Performance.pdf

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Engine Performance
Engine Performance
Military Institute of Science & Technology, ME Dept.
© Rubaiyat
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Geometric Properties
V C
TC
Piston displacement: y = l + a - s
y
B
s
=
a
cos
q
+
(
l
2 sin
-
a
2
2
q
)
/
2
L
BC
When the piston is at TC ( s= l+a ) the
cylinder volume equals the clearance
volume V c
The cylinder volume at any crank
angle is:
s
l
p
B
2
Connecting
rod
V c
V
+
A
y
=
V
+
(
l
+
a
-
s
)
c
c
4
q
Maximum displacement, or swept,
volume:
2
p
B
a
V d 4
=
L
Compression ratio:
For most engines B ~ L
r +
BC
c V
=
V
=
V
c
V
d
V
(“square engine”)
TC
c
Military Institute of Science & Technology, ME Dept.
© Rubaiyat
1
=
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Geometric Properties
V C
TC
Average piston velocity: LN
U p 2
B
Where N is the rotational speed of the crank shaft
in units revolutions per second
L
Average piston speed for standard auto engine is
about 15 m/s. Ultimately limited by material
strength. Therefore engines with large strokes run
at lower speeds
BC
s
l
“Over square engines” (B > L) with light pistons
have higher rev limits (Formula 1 cars)
q
a
Military Institute of Science & Technology, ME Dept.
© Rubaiyat
=
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