Transcript Cylinder Design

Cylinder Design
 Cylinder
Liner (Barrel) Design
The liner functions both as
– a structural member
– a bearing surface for the piston and rings
Material
– Cast Iron for wet liners
– Steel for dry liners
 Dry
liners are inserted into wet liners
 Only Wet Liners are normally used in large Diesel
Engines
Cylinder Design
 In
passenger car engines and small
industrial engines
– Liner is cast integrally with the jacket structure
» Worn-out bore surfaces may be refinished to
a larger diameter, and over-sized pistons are
inserted.
 For
long-life industrial and commercial use
– Separate removable cylinder liners are used
» Repair and replacement is possible
» Appropriate materials can be used
cast iron is preferred
steel is occasionally used
Cylinder Liner Loading
 The
liner thickness may be calculated from
Pmax . D and
tl 
2s c
t l  2 x 10 3 m
tl = Liner thickness (m)
sc= Permissible cicumferential stress (kN/m2)
Pmax= Maximum combustion Pressure (kPa)
D = Inner liner Diameter (m)
sc = (1.0 - 1.5 ) x 105 kN/m2 for steel
sc = (0.2 - 0.3 ) x 105 kN/m2 for cast iron
tl = tl1 + tl2 for composite dry liners
tsteel > 2 mm
Effect of Thermal Stresses
sc
reduced
where
sc

 . E. Q . t l
1
2. k . s c
  1. 1 x 10 5
K 1
E  0 . 8 x 10 5
kN
Q  30 kW
m2
m2
k  4 . 4 x 10 2
kW
mK
Typical Wet Liner Configuration
Typical Dry Liner Configuration
Advantages of Wet Type Liners
It
can be removed and replaced with
great ease and without the need for
any special tools or equipment.
It is possible to provide for a highvelocity water circulation around the
liner and therefore reduce the piston
temperature.
Since the liner is held only by a flange
at the top end, it is free to expand
without any restraint.
Advantages of Dry Liners
 Suitable
when cylinder block and crankcase
are formed in one piece with detachable
cylinder heads
 Cooling water can come nearer to the top end
of the liner
 No gas or water joints are required
 Stiffness of the cylinder block is increased
Main Disadvantage
A
dry liner must be pressed or shrunk into the
cylinder barrel.
– It is difficult to remove or replace without
special equipment
Lcen/D = 1.20 - 1.28 for SI engines
Lcen/D = 1.25 - 1.30 for CI engines
Liner Flange Design Calculation
 Taking
Mb
moments around A ;
 Fg . L g
D i2
Fg  1. 25
Pmax
4
 Section Modulus of the
 cross-section between B&C ;

S m  D o . h s2
6
Maximum bending stress :
Mb
sb 
 ( s b ) allowable
Sm
Design Notes
on Water Cooled Cylinder Blocks
 Walls
are tensioned by the gas forces
transmitted to the studs via the cylinder head
 Tensile forces are only applied to the walls of
the water jacket and the partitions between
the cylinders
 In-Line and V-Engines with water cooling
usually have cylinders cast integral with the
upper half of the crankcase
 Main casting forming the cylinder block and
crankcase may be made from alimimium
alloy.
Design Notes
on Cylinder Blocks
 The
crankcase width is determined from the
trajectory of the extreme point of the
connecting rod bolt head.
 Minimum distance between bolt head and
internal surface of crankcase is 10-15 mm
Wall Thicknesses
 Cast-Iron crankcase walls and partitions are
5 - 8 mm
 Cast-Iron water jacket thickness : 4 - 7 mm
 Aluminium casting thicknesses are 1 - 2 mm
more.
 Die-cast Aluminium thickness is less than
cast-iron