 |
17. Look at the underlined words in the text beneath and guess their meaning.
|
|
|
|
17. Look at the underlined words in the text beneath and guess their meaning.
Read the text. In what part of it do you think the author expresses the main idea? Rewrite in your own words
The diesel engine has certain very definite advantages over other types of internal combustion prime movers. In the first place, because of their greater thermal efficiency, diesels run on low-grade (низкосортное) fuel. This is true because diesels convert a higher amount of fuel into mechanical energy. The efficiency of the diesels at fractional (неполный) loads decrease much less than those of other types of engines. Also fuel consumption per horsepower per hour of small engines are almost as good as those of much larger size. Long useful life of diesel engines is one of their greatest advantages. Other advantages include their simplicity of operation, less smoke and ashes, small space occupied and little water supply. In general, diesel engines have advantages over other types of prime movers.
Which information you have already known and which was quite new for you?
Grammar. Cause and effect
18. Read the explanations on the box
| Союзы, которыми вводятся придаточные причины as, since, due to, owing to, because. Например: Piston engines are used in cars owing to their requirement for high level of torque. Two-stroke engines require more fuel than four-stroke engines due to less efficient combustion. Diesels occupy little space compared with steam engines since no boiler is needed. Союзы, с помощью которых показывается результат: as a result, because of this, so, that’s why, therefore, thus, consequently. Например: All four processes form a closed working cycle of the engine, thus the complete working cycle can be divided into the preparatory part and the working part. The process of combustion causes expansion, as a result the burning gases force the piston downward. Compression ratio of diesel engines is higher than that of gasoline engines, therefore they are more efficient. |
19. Read and translate the sentences
1. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density
2. Vapour pressure increases with temperature, so the volatility of a fuel can be increased by raising the temperature.
3. Petrol engines run at higher speeds than Diesels partially due to their lighter pistons.
4. The diesel engine has the highest thermal efficiency of any regular internal or external combustion engine due to its very high compression ratio.
5. The oil in an engine does more than simply cut down friction and wear due to lubrication of the pistons, bearings and other moving parts.
6. Because of the higher pressure in the diesel engine it has heavier parts than the gasoline engines.
|
|
|
7. The imperfections of the steam engine led to the design of a new type. It was called the internal combustion engine, because its fuel ignites and burns inside the engine itself and not in a furnace. It is smaller and lighter than a steam engine because it does not have a boiler.
8. The oil injected in the air has been compressed and thus heated to a high temperature.
9. Since only the third stroke produces work, the piston needs help over
the other strokes.
10. The fuel, normally a mixture of petrol and air, is burnt in cylinders inside the engine – that is why the term ‘internal combustion’ is used.
11. Petrol engine is also more powerful, as it uses better-quality fuel: petrol or kerosene.
12. The heat produced on the power stroke of the diesel engine may be as high as 1600° F that is why the engine must have a good cooling system.
13. The steam engine uses a fire in a boiler rather than inside the engine; for this reason, steam engines are sometimes called external combustion engines.
14. Since the burning or combustion takes place within the engine itself, it is called an internal-combustion engine.
15. The spark ignition system, the type, is the one which is more complicated, and therefore it is the frequent cause of poor engine performance.
16. The fuel, normally a mixture of petrol and air, is burnt in cylinders inside the engine – that is why the term ‘internal combustion’ is used.
17. The hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler.
18. The oil injected in the air has been compressed and thus heated to a high temperature.
20. Read the text and choose the most suitable conjunction in brackets
There is an injector or nozzle for every cylinder. Their purpose is to prevent the air within the combustion chamber from leaking out but at the same time inject a spray of fuel into the hot compressed gases at the correct time and interval. It is, (since / therefore ), apparent that the air and fuel must mix within the combustion space.
Spark ignition engine power is varied by manifold throttling (дросселирование). This means that the amount of the fuel mixture is varied. In the diesel, only the fuel amount is varied; the air volume remains relatively constant. (Thus / owing to ) a diesel can operate on such a small quantity of fuel that the air-to-fuel ratio may became 100: 1, which is a very economical ratio. This explains why the diesel will operate economically at light loads. The large amount of surplus (излишний) air also causes the diesel to operate at lower temperatures. (As / Thus ), (because / because of ) combustion characteristics, the diesel runs more economically, and cooler at the slower speeds. And, ( owing to / that’s why ) the possible higher compression ratio, the diesel is able to convert more of the heat energy of the fuel into work energy at any speed.
|
|
|
