Transcript Document

Tomislav Skračić, MA
Undergraduate English
Course for
MARINE ENGINEERS
3nd Semester
Essential reading:
SPINČIĆ, A., PRITCHARD, B., An English Textbook For
Marine Engineers 2, Pomorski fakultet, Rijeka 2009.
LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog
jezika za pomorce, Pomorski fakultet, Rijeka 2003.
Lesson 4 – Cylinder Liners
KEY WORDS
close grained cast iron
- sitnozrnato lijevano željezo
flange (n.)
- prirubnica, "flanđa"
provide location
- smjestiti
joint ring
- spojni prsten
leak-off hole
- odušni kanal, kontrolni kanal, "špija",
inspekcijski provrt
promote (v.)
- pospješiti, pomagati, poboljšati
coolant (n.)
- rashladno sredstvo
bore cooled liner
- košuljica s provrtom za hlađenje
thermal insulation
- toplinska izolacija
Lesson 4 – Cylinder Liners
KEY WORDS
loop scavenging
- vrtložno ispiranje
uniflow scavenging - istosmjerno / uzdužno ispiranje
port belt
- pojas kanala na cilindru, zona otvora
sealing ring
- brtveni prsten
as the rings run in
- kako se prstenovi uhodavaju
running-in (n.)
- uhodavanje
wear-in (n)
- uhodavanje
resists wear
- otporna na izlizavanje
honing (n.)
- fino brušenje
harder wearing surface
- površina koja se teže troši
nitriding (n)
- nitriranje
Lesson 4 – Cylinder Liners
A cylinder liner is a removable component, cylindrical in shape,
inserted into the engine block. It provides the surface for the
piston to slide and carry out its compression task. It can be
replaced when worn out.
Cylinder liners are made from close grained cast iron.
In four-stroke engines they are simple cylindrical shapes flanged
at the top end to provide location and secure them in the
cylinder blocks or to the water jacket. Immediately below this
flange there is often a joint ring which may be of copper or in
some designs of a heat resistant rubber. The lower end is fitted
with rubber rings so as to form a seal for the bottom of the
water space. These rubber rings may be arranged also to
prevent oil from the crankcase entering the water jackets.
Lesson 4 – Cylinder Liners
In wet liners the water is in direct contact with outer surface of
the liner whereas in dry liners the water is in indirect contact
with outer surface of the liner, i.e. cylinder casting contains wet
jackets.
A leak-off hole is often provided between the upper and lower
rings to ensure that water passing the one or oil passing the
other runs to the outside of the engine. The upper part of the
liner bore, where the top piston ring reaches the top of its travel,
suffers the greatest wear. This is because at this point the ring
comes to rest and reverses its direction of motion and it is
difficult to maintain an adequate film of oil between the surface
of the ring and liner.
Lesson 4 – Cylinder Liners
Also, the gas pressure is highest when the ring is in this position,
forcing it hard against the liner. Besides, the top of the liner is
hot from the repeated combustion cycle which tends to dry any
oil there is. Liners are sometimes specially designed to
promote cooling without sacrificing strength.
Several designs of high output engines have cylinder liners with
deep flanges in which a large number of small passages is
drilled to carry coolant close to the cylinder bore. This is so
called bore cooled liner. There is a special tube inside the bore
for thermal insulation.
Cylinder Liners - Scavenging
In the diesel engines that are used as propulsion plants for
ships, the cylinder liner scavenge air ports are machined into
the liner. If exhaust ports are used these are machined above
the inlet ports. The position of the scavenge ports on the cylinder
liner, or the addition of an exhaust valve in the cylinder head
depends on the design of the scavenging air system used by
engine manufacturer.
Efficient scavenging is required to ensure an adequate supply
of combustion air to the engine. There are three basic types of
scavenging techniques in a two-stroke marine diesel engine
used to supply fresh air to the combustion chamber and extract
the resultant exhaust gasses: loop scavenging, cross-flow
scavenging and uniflow scavenging.
Cylinder Liners - Scavenging
Loop Scavenging
 In loop scavenging the inlet and exhaust ports are
machined in the same side of the cylinder liner; the exhaust
scavenge ports being above the inlet ports.
Cross-flow Scavenging
 In this technique, the inlet and exhaust scavenge ports are
machined into the opposite sides of the cylinder liner; the
exhaust ports being above the inlet ports.
Uniflow Scavenging
 This is quickly becoming the most common technique used
in scavenging. Here the inlet ports are machined around the
liner about 1/3rd of the way up from the bottom. Instead of the
usual exhaust ports, an exhaust valve can be used. This is
the current method of scavenging employed by the major
Scavenge Flow Systems
Cylinder Liners
The water jackets does not usually extend below the port
belt. The sealing rings are therefore situated just above the
ports and are designed to prevent scavenge air (and
exhaust, in case of loop scavenge engine ) entering the
water spaces as well as the water escaping from the jackets.
They are made of special rubber, highly resistant to heat
and oil. The bores of the cylinder liners, when new, have a
specially prepared surface designed to aid the running-in of
the piston rings and the liner. It is slightly rough in order to
retain the oil and to promote rapid wear-in. As the rings run
in, a glazed surface is produced which resists wear.
Cylinder Liners
When the piston rings are renewed the glaze on the liner
bore should be broken by honing to provide the surface
suitable for rapid running-in. In order to provide a harder
wearing surface, the bore of liners is subjected to the
process of nitriding.
Exercise 1 - Complete the following text:
A cylinder liner is a removable component, c_______ in
shape, inserted into the engine b_______ . It provides
the surface for the piston to s________ and carry out its
c________ task. It can be replaced when w________ out.
Cylinder liners are made from close g________ cast
iron.
In four stroke cycle engines they are simple cylindrical
shapes f________ at the top end to provide location and
s________ them in the cylinder b________ or to the
water j________ . Immediately below this flange there is
often a j________ ring which may be of copper or in
some designs of a heat r________ rubber. The lower end
is f________ with rubber rings so as to form a s________
for the bottom of the water space. These rubber rings
Exercise 2 – Complete the following text:
A __________ is often provided between the upper and lower
__________ to ensure that water passing the one or oil passing
the other __________ to the outside of the engine. The upper
part of the liner __________ , where the top piston ring reaches
the top of its travel, suffers the greatest __________ . This is
because at this point the ring comes to rest and __________ its
direction of motion and it is difficult to maintain an adequate
__________ between the surface of the ring and liner. Also, the
__________ pressure is highest when the ring is in this position,
forcing it hard __________ the liner. Besides, the top of the liner
is hot from the repeated __________ cycle which tends to dry
any oil there is. Liners are sometimes specially __________ to
promote cooling without sacrificing __________ .
Questions & Discussion
1.
2.
3.
4.
5.
6.
7.
What are cylinder liners made of?
What is the use of the flange at the top of the liner?
Why are the rubber rings fitted to the lower end of the liner?
What must be done if water runs outside through leak-off hole?
Why does the upper part of the liner bore suffer the greatest wear?
How are cylinder liners in high output engines cooled?
Describe the design features of the cylinder liner in loop scavenge
and uniflow scavenge engines.
8. Why is the inner surface of the cylinder liners in new engines rough?
What is the running-in period?
9. What is the meaning of the words “grinding” and “honing”?
10. What is inspected when the cylinder liners are removed during
periodical overhaul?