Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2, Pomorski fakultet, Rijeka LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka Tomislav Skračić, MA Undergraduate English Course for MARINE ENGINEERS 3nd Semester

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

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. Lesson 4 – Cylinder Liners

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 1/3 rd 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 manufacturers of large two-stroke marine diesel engines. Cylinder Liners - Scavenging

Scavenge Flow Systems

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. Cylinder Liners

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 may be arranged also to prevent oil from the crankcase e ________ the w ________ jackets. Exercise 1 - 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 __________. Exercise 2 – Complete the following text:

1. 1. 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 Why is the inner surface of the cylinder liners in new engines rough? What is the running-in period? What is the meaning of the words “grinding” and “honing”? What is inspected when the cylinder liners are removed during periodical overhaul? Questions & Discussion