Before the exam

• Do you know the types of Diesel engines?

• Certainly, I do. They are four-stroke and two-stroke engines.

• As to the principle of operation, what are they?

• Single-acting and double-acting.

• And what about their construction?

• I know it too. They are crosshead, trunk-piston and opposed-piston types.

• Oh, I see, you’re preparing for the exam.

• Yes, I am.

• During the compression stroke, all the valves should be closed, shouldn’t they?

• What valves do you mean?

• Air inlet valve, fuel valve and exhaust.

• Yes, naturally. Otherwise there will be no compression.

• What is the pressure and temperature of compression?

• It’s about 500 pounds and about 1,000 deg. F, i.e. about 100 kg/cm² and 500º C.

• Fuel is injected under pressure, isn’t it?

• Yes, it’s quite high. 3,500 pounds per square inch.

• Does the burning raise the temperature of the gas?

• Up to 3,000ºF, i.e. about 1,500º.

• At the end of the expansion stroke the pressure of gases drops to about 40 pounds and they start to flow out, don’t they?

• Yes, they do. So we see now the whole cycle of operation. It’s quite simple.

• I think I’ll be able to explain everything in English. Besides I’ll use the scheme.

• We go on with our talk. Now we have to revise the principles of a two-cycle engine operation.

• Is there any difference in construction between the four- and two-cycle engine?

• Yes, a principal one. In a four-stroke cycle there are valves in the cylinder head, and in the two-cycle Diesel there are ports. There are exhaust ports and scavenging ports.

• What is their location?

• It’s very important. As far as I know the scavenging ports are always lower than exhaust ones.

• Why so?

• To provide scavenging of the cylinder. The working processes are absolutely the same as in the four-stroke cycle, but they occur during the two cycles.

• Right. I see that you know this material.

Exercise 8.

Describe the four-cycle and two-cycle internal combustion engines and all the processes occurring in them.

While speaking, use the following plan.

1. Types of engines as to their construction and principle of operation.

2. The four-stroke cycle (every stroke separately).

3. The two-stroke cycle. Principal changes in construction with the same processes.

4. Number of revolutions of the crankshaft in both types.

Lubricating oil system

A lubricating oil system for a large main engine includes pressure pumps, strainers and fine filters which are in duplicate, one set being used while the other acts as standby. Fine filters should be capable of being cleaned without interruption of the oil flow. Mesh size will depend on the bearing materials and clearances: in most large engines it is 50 microns. Capacity of the system must be adequate for the type of installation. If the engine has oil-cooled pistons the capacity and throughput will be increased accordingly.

Lubricating oil pressure pumps draw oil from the engine drain tank through suction strainers, the tank suction being clear of the lowest point to avoid picking up any water or sludge which may have settled.

The pumps discharge at pressure through the oil cooler, ensuring that sea water at its lower pressure can not leak into the oil system in the event of a fault in the cooler. The oil then passes through the fine filters to the engine. It will be distributed to all bearings, piston cooling, sprayers, exhaust valve actuators, control systems etc.

Various sections of the lubricating system may require different pressures and to accommodate this engine driven booster pumps may raise the supply pressure while pressure reducing valves and restricted orifices may reduce or flow to other parts.

Used oil drains to the bottom of the crankcase and passes through strainers by gravity to the drain tank. Drain returns are kept remote from the pump suction and must be submerged to reduce aeration and to make a safe seat. With oil-cooled pistons each piston oil return has its temperature monitored and it then passes through a sight glass before returning to the crankcase.

The oil drain tank is usually built into the ship’s double bottom but it must be surrounded by a cofferdam to prevent any contamination from leakages. It is fitted with an air vent, level measuring gauge and sounding pipe. Central positioning of the level gauge will reduce fluctuation in readings due to pitching and rolling at sea. The tank must be of sufficient size to accommodate the full charge of oil. Its interior surfaces may be coated to prevent rusting due to condensation on its non-flooded surfaces. The system should also have low pressure, high temperature and low tank level alarms fitted.

A bypass centrifuge system is fitted to purify oil from the drain tank to remove water, sludge and insolubles. This should be operated continuously at with a slow throughput, the oil being preheated to 70-90ºC to assist separation.

When the engine is not in use batch purification of the whole charge may be carried out. It is most important that water content in the oil is eliminated or kept to a minimum.

Exercise 1.

Find equivalents of these words in the text and learn them:

Масляные насосы высокого давления; междудонное пространство; фильтры грубой отчистки; сливная цистерна; картер; поток масла; система управления; зазор; масляные клапаны; форсунки; редукционные клапана; маслоохладители; подшипник; фильтры тонкой отчистки; поддон картера; масляное охлаждение поршней; тип установки.

Exercise 2.

Answer the following questions:

1. What filters does a lubricating oil system include?

2. Why are they in duplicate?

3. How do lubricating oil pressure pumps draw oil from the engine drain tank?

4. Where can water and sludge settle?

5. Where is the oil distributed to all bearings, piston cooling, control systems etc?

6. What pumps increase the supply pressure?

7. What pumps reduce pressure?

8. Where does used oil go?

9. What filters does it go through?

10. Where is the oil drain tank usually located?

11. Why is it surrounded by a cofferdam?

12. What is every tank fitted with?

13. What is important to do when the engine is not in use for a long time?

Exercise 3.

Find these sentences in the text:

1. Масляные насосы, фильтры грубой и тонкой очистки обязательно должны дублироваться.

2. Когда один насос в работе, то другой должен быть в состоянии немедленной готовности.

3. Производительность и общий объем системы смазки должны быть соответственно увеличены, если двигатель имеет масляное охлаждение поршней.

4. Фильтры грубой отчистки должны быть расположены достаточно удаленно от наинизших точек.

5. Масло через фильтры тонкой отчистки поступает к двигателю.

6. Масло распределяется для смазки всех подшипников, охлаждения поршней, форсунок, привода выпускных клапанов, систем управления и др.

7. Различные секции системы смазки могут использовать масло при различных давлениях.

8. Для предотвращения загрязнений вследствие течи танк окружают коффердамом.

9. Система должна быть оборудована аварийной сигнализацией понижения давления, высокой температуры и низкого уровня масла в танке.

10. Центрифуги постоянно работают во время рейса, обеспечивая качественную сепарацию части потока масла.

Exercise 4.

Agree with the statements, completing the main idea with the words given in brackets.

Model 1:

A: Pressure pumps, strainers are in duplicate (fine filters).

B: Fine filters are in duplicate as well.

1. The oil will be distributed to all bearings, piston cooling, sprayers, exhaust valve actuators (control system).

2. The oil drain tank is fitted with an air vent, level measuring gauge (sounding pipe).

3. Central positioning of the level gauge will reduce fluctuation in readings due to pitching at sea (rolling).

4. The system should also have low pressure, high temperature alarms fitted (low tank level alarm).

5. A bypass centrifuge system is fitted to purify oil from the drain tank to remove water, sludge (insolubles).

Exercise 5.

Speak about the lubricating oil system.