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13. For questions 1-5 read the text and decide which answer A, B, C best fits each space
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13. For questions 1-5 read the text and decide which answer A, B, C best fits each space
In a diesel engine first air is drawn into the cylinder and compressed by the 1_____________ piston to a high pressure of about 500 lb. per sq. in. When the charge of air is compressed, its temperature 2____________, reaching 700-900°C or 133-1650°F. At the top of the compression stroke, diesel fuel is 3_________________ into the combustion chamber at high pressure through a 4_________________. It mixes with the hot, high-pressure air. The resulting mixture ignites and burns very rapidly. This explosion 5_____________ the gas in the chamber to expand and force the piston downwards. The connecting rod transmits this motion to the crankshaft.
1. a) rising b) raising c) risen
2. a) raise b) rise s c) risen
3. a) inject b) injected c) injects
4. a) valve b) nozzle c) spark
5. a) cause b) caused c) causes
14. Read the explanations on the box
Watch out
| That (of) и those (of) используются для замены существительных Например: The efficiency of the diesel engine is higher than that of other engines. The thermal efficiency of diesel engines is much higher than that of steam engines. Compression ratios of diesel engines are higher than those of gasoline engines. |
15. Read and translate the sentences
1. The most significant heat-engine invention was that of the steam engine.
2. Newcomen’s steam engine was an atmospheric one, and was thus dependent for its operation on obtaining a pressure within the cylinder below that of atmospheric pressure.
3. The life of a diesel engine is generally about twice as long as that of a petrol engine.
4. As the speed of the diesel engine has been increased, it has been used in more farm tractors, particularly in those of the crawler type.
5. The pressure on the outside is much greater than that of on the inside.
6. In order to give reasonable smoothness, the minimum number of cylinders is two, which provides one power stroke for each crankshaft revolution. This greatly improves the balance, in comparison with that of a single-cylinder engine.
7. Newcomen’s steam engine was an atmospheric engine and depended for its operation on obtaining a pressure within the cylinder below that of atmospheric pressure.
8. Several designs and patents for gas engines were obtained by inventors in the mid 19-th century, but most of them were never constructed; those that were had limited success.
9. Horizontally opposed cylinders are used in only a few engine designs, frequently those with engines at the rear, where space is limited.
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10. Spark-ignition systems are basically the same on all modern cars; those which use electronic ignition may differ in detail.
Reading
16. Read paragraph 1 and sentences a, b, c. Which of them expresses the main idea?
a) Diesel engines operate differently from the Otto-cycle engines.
b) In diesel engines fuel burns instantly because of the high temperature of the air in the chamber.
c) Some diesels have auxiliary electrical ignition systems.
Read paragraph 2 and sentences a, b, c. Which of them expresses the main idea?
a) In general diesels are slow-speed engines.
b) Diesels use compression ratios of 14 or more to 1.
c) The efficiency of diesel engines is greater than that of Otto cycle engines.
Read the text and choose the title of it from a-c
a) Operation of diesel engines
b) Differences between Otto-cycle and diesel engines
c) Advantages of diesel engines
1___________________________________
The diesel cycle differs from the Otto cycle in that combustion takes place at constant volume rather that at constant pressure. Most diesels are also four-stroke engines but they operate differently than the four-stroke Otto-cycle engines. The first, or suction, stroke draws air, but no fuel, into the combustion chamber through an intake valve. On the second, or compression, stroke the air is compressed to a much smaller volume and is heated to about 440°C (820°F) by this compression. At the end of the compression stroke, pulverized fuel is injected into the combustion chamber and burns instantly because of the high temperature of the air in the chamber. Some diesels have auxiliary (вспомогательный) electrical ignition system to ignite the fuel when the engine starts and until it warms up. This combustion drives the piston back on the third, or power, stroke of the cycle. The fourth stroke, as in the Otto-cycle engine, is an exhaust stroke.
2__________________________________
The efficiency of the diesel engine, which is in general governed by the same factors that control the efficiency of Otto-cycle engines, is greater than that of any Otto-cycle engine and in actual engines today is slightly more than 40 %. Diesels are, in general, slow-speed engines with crankshaft speeds of 100 to 750 rpm as compared to 2500 to 500 rpm for typical Otto-cycle engines. Some types of diesel engines, however, have speeds up to 2000 rpm. Because diesels use compression ratios of 14 or more to 1, they are generally more heavily built than Otto-cycle engines, but this disadvantage is counterbalanced by their greater efficiency and the fact that they can be operated on less expensive fuel oils.
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