Cycles of diesel engines

Any internal combustion engine, regardless of principle it operates in, is said to have a four-stroke cycle or a two-stroke cycle. The engines of either type may be single or double acting, trunk-piston type, crosshead type, opposed-piston type.

The four-stroke cycle consists of the suction stroke, compression stroke, combustion and expansion stroke and exhaust stroke. The piston starts a downward, suction stroke. The air inlet valve is open and air is being drawn into the cylinder through the air inlet pipe. The exhaust valve, fuel valve are all closed. As the piston reaches the end of the suction stroke the air inlet valve closes and as the piston rises on the second, or compression, stroke the air in the cylinder is compressed. At the end of this stroke the air has been compressed to about 480 pounds and its temperature has risen to about 1,000 degrees F. the fuel injection valve now opens and the fuel oil is sprayed into the cylinder under a pressure of 3,550 p.s.i. the high temperature of the compressed air in the cylinder ignites the fuel, and it continues to burn as long as injection is maintained. This burning raises the temperature of the gas to approximately 3,000 degrees F. in the meantime, the piston has started down on the third, or expansion, stroke with the gas expanding behind it. The injection valve closes shortly after the piston has started down on this stroke. At the end of this stroke the exhaust valve opens and the burned gases in the cylinder, now reduced to about 40 pounds pressure, and correspondingly reduced in temperature, start to flow out through the exhaust pipe. Retuning on the fourth, of exhaust, stroke the piston pushes the remaining gas out of the cylinder. At the end of this stroke the exhaust valve closes, the air inlet valve opens and the cycle of operation starts again.

It is thus seen that one complete cycle requires four strokes of the piston; the four strokes comprise two complete revolutions of the crankshaft.

The majority of medium and high speed diesel engines for main and auxiliary drive operate on the four-stroke cycle.

In the 2-cycle, single acting Diesel engine instead of an exhaust valve there is a ring of exhaust ports around the bottom of the cylinder, communicating with the exhaust pipe. The spray valve and starting valve are the same as in the 4-cycle. In place of air inlet valves there are scavenging ports, in place of exhaust valves there are exhaust ports, in uniflow scavenging engines there are exhaust valves. The scavenging ports are in communication with a passage leading to a low pressure scavenging air compressor, operated from the engine.

When the piston on its downward stroke uncovers the exhaust ports and the cylinder pressure drops to atmospheric, the scavenging ports open and the air, under the pressure, flows into the cylinder and pushes the exhaust gases out through these ports. As the piston on its up stroke covers the scavenging ports, the exhaust ports close leaving the cylinder full of fresh air. The piston moving upward on its compression fuel injection occurs, just as previously described for the 4-cycle. It is thus seen that the complete series of operations, including fuel injection and combustion, expansion, exhaust, filling cylinder with fresh air and compression, occurs in two strokes of the piston, or one revolution of the crankshaft.

Practically all large slow-speed, direct drive marine diesel engines operate in the two-stroke cycle.

Exercise 1.

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

Впускной патрубок; выхлопной ход; топливо впрыскивающий клапан; продувочное окно; выхлопное окно; выхлопные газы; простого или двойного действия; ход сжатия; поршень; ход всасывания; впрыскивающий клапан; давление; коленчатый вал; пусковой клапан; оборот коленчатого вала; впускной клапан; выхлопной клапан; ход горения и расширения.

Exercise 2.

Ask question as if you want to know the time of the action.

Look at the model and do the same.

Model 1.

The inlet valve closes at the end of the suction stroke.

When does the inlet valve close?

1. The fuel injection valve opens after the compression stroke.

2. The oil gets into the cylinder at the end of the compression stroke.

3. The gas expands during the combustion and expansion strokes.

4. The gas exhausts during the exhaust stroke.

5. The exhaust valve opens during the exhaust stroke.

6. The gas reduces in pressure and temperature during the expansion stroke.

Exercise 3.

Ask questions as if you want to find out the place of Diesel engine parts.

Model 1.

The exhaust valve is placed in the cylinder head.

Where is the exhaust valve placed?

1. There is an exhaust pipe connected to the cylinder.

2. The fuel is ignited in the cylinder.

3. The inlet valve is placed in the cylinder head.

Exercise 4.

Complete the sentences:

1. The four-stroke cycle includes … .

2. When air is being drawn into the cylinder through the …, the … and … are all closed.

3. At the end of the … the air has been compressed to about four hundred eighty pounds.

4. … of the compressed air in the cylinder … the fuel.

5. When the piston returns on the exhaust stroke, it pushes … out of the cylinder.

6. There is a ring of exhaust ports around the bottom of the cylinder in place of … .

7. There are scavenging ports instead of … .

8. There are exhaust ports instead of … .

9. A low pressure scavenging air compressor is operated from the … .

10. The complete series of operations occurs in one revolution of the … .

Exercise 5.

Translate extending the sentences gradually.

a)

1. Впрыскивается топливо.

2. Топливо впрыскивается в цилиндр.

3. Топливо впрыскивается в цилиндр двигателя.

4. Топливо впрыскивается в цилиндр двигателя под давлением.

5. Топливо впрыскивается в цилиндр двигателя под давлением 3500 фунтов на 10В. дюйм.

b)

1. Поршень движется вверх.

2. Поршень движется вверх на выхлопной ход, на ход «выпуск».

3. Поршень движется вверх на выхлопной ход, выталкивая газы.

4. Поршень движется вверх на выхлопной ход, выталкивая газы через окна.

5. Поршень движется вверх на выхлопной ход, выталкивая газы через открытые выхлопные окна.

Exercise 6.

Questions on the text and problems.

Test your comprehension.

1. Enumerate all types of Diesel engines you know.

2. Name the strokes of a four-stroke cycle. What valves are there on the cylinder head? When is the air inlet valve open? What valves should be closed during the comprehension. Under what pressure is the fuel injected into the cylinder? When does the gas expand? What is its action? When do the gases flow out of the cylinder? How many revolutions of the crank dot he four piston strokes require? Where are the four-stroke cycle engines used?

3. Name the strokes of a two-stroke cycle.

4. Show the principal difference in construction.

5. Speak about location of exhaust and scavenging ports. On what stroke does the piston uncover the exhaust ports? When do scavenging ports open during operation? When is the cylinder full of fresh air? When does fuel injection occur? How many revolutions of the crankshaft are required in a 2-cycle engine? Where are these engines used?

Exercise 7.

Read and translate the dialogues and learn them by heart.