Compression

This article deals with the design, operation and maintenance of air-cooled, four-stroke engines. These engines are available for operation on petrol or vaporizing oil and are being used for driving stationary and mobile farm machinery. We examine these engines under five headings: 1) compression, 2) lubrication, 3) fuel, 4) ignition, 5) cooling.

Compression. Compression is the basis if engine power, and the components used to obtain it are crankcase and crankshaft; connecting-rod, piston and rings; cylinder, cylinder head and gaskets; valves and tappets. The crankshaft in carried by (1) two main bearings mounted in the crankcase. The piston carries two or three compression rings and one oil scraper ring; worn rings should be renewed if the gap measures (2) 0.030 in. or more.

The compression ratio is relationship between the volume of the fuel and air mixture (combustible mixture) in the cylinder when the piston is at the bottom and the volume of the same combustible mixture when the piston is at the top of the stroke. If the volume of combustible mixture in a cylinder when the piston is at the bottom of the stroke is 72 cubic inches, and the mixture is compressed to a volume of 12 cubic inches when the piston is at the top of the stroke, the compression ratio is 6 to 1. The significance of the compression ratio of an engine can be fully understood if one remembers that the amount of. pressure on the piston determines the power of the engine. Other things being equal (3), the greater the pressure at the beginning of the power stroke, the greater will be the power developed.

Compression ratio is directly related to the kind of fuel that can be used without knocking. As the com-pression ratio goes up, the tendency to knock increases.

NOTES:

(1) is carried by – опирается на

(2) if the gap measures – если зазор оставляет

(3) otherthingsbeingequal– при прочих равных условиях

Learn some new words:

Maintenance – уход

To be available – быть в наличии

Stationary – неподвижный

Tappets – кулачки

To mount – устанавливать

Oil scraper ring – малосъемное кольцо

Worn rings – изношенные кольца

Compression ration – степень сжатия

Significance – значение

Relationship – отношение

Practice 1. Reread the text and answer the questions:

1. What components are used to obtain compression?

2. What types of engines do you know?

3. What is crankshaft carried by?

4. How many rings does the piston have?

5. How often should worn rings be renewed?

6. What is the significance of the compression ration?

7. What is the compression ration?

8. What determines the power of the engine?

Practice 2. Give the English equivalents to the following words and word combinations:

72 кубических дюйма

отношение

сжатая смесь

маслосъемное кольцо

шатун

коленчатый вал

прокладки

неподвижные машины

смазка

зажигание

охлаждающая система

достигать сжатия

горючая смесь

нижняя мертвая точка

тот же самый объем

значение сжатия

Practice 3. Match up the words on the left with the definitions on the right:

compression
compression ratio
inch
crankshaft
gap
power
machinery

Practice 4. Complete the sentences using the words from the box:

Steam; to renew; compression; crankshaft; the volume; power; to obtain

1. … is connected to the kind of fuel.

2. The more compression ratio the more … is produced.

3. Many details are used … compression.

4. I have … worn rings.

5. … of the cylinder is 72 cubic inches.

6. The main bearing carries … .

7. … engine is the external combustion engine.

Practice 5. Complete the table:

noun	verb	adjective
compression
	wear
	operate
		new
freedom