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3. Read the words in the box and guess their meaning
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3. Read the words in the box and guess their meaning
| lightweight, emission, power-to-weight ratio (удельная мощность), portable, space, special, to specialize |
4. Learn the words and translate their derivatives
accomplish (v) выполнять – accomplishing, accomplished, accomplishment;
capacity (n) – емкость, мощность
complete (v) завершать – completely, incomplete, incompletely, completion;
lubricate (v) смазывать – lubrication, lubricant;
pollute (v) загрязнять – polluted, pollutant, pollution, polluter;
revolve (v) вращаться – revolution, revolving
5. For questions 1-4 read the text and decide which answer A, B, C best fits each space. Which of the linking words in bold helped you to understand that the author a) added some information, b) contrasted the information, c) explains the cause, d) shows the effect?
The two-stroke engine is simpler than the four-stroke engine. The two-stroke engine 1_______________ one power stroke every two strokes (one 2______________ of the crankshaft), thus it develops more power or can be lighter and yet deliver the same power. For this reason, it is used in lawnmowers, chain saws, small automobiles and motorcycles. However, there are several disadvantages that restrict its use. Since there are twice as many power strokes during the operation, the engine tends to heat up more, and thus is likely to have a shorter life. Also, in the two-stroke engine 3_______________ oil is mixed with fuel. This causes a very high level of 4_______________ in its exhaust.
1. a) accomplish b) accomplishes c) accomplished
2. a) revolve b) revolving c) revolution
3. a) lubricating b) lubrication c) lubricate
4. a) pollutants b) polluted c) pollute
6. In this text some lines contain a word that should not be there. Decide which lines contain them and correct
1. The cylinder of the two-stroke an engine
2. has no valves as so in the four-stroke
3. engine. Intake and exhaust are
4. is accomplished by means of ports,
5. which are a special holes cut into
6. the cylinder wall which has allows
7. fuel-air mixture to enter from the
8. crankcase, and exhaust to exit the engine.
7. Read the text beneath and the plan to it. Rearrange the items of the plan according to the text content
A. Application of two-stroke engines
B. Principle of operation
C. Inventors
D. Advantages and disadvantages
Two-Stroke Cycle
The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having the same four processes (intake, compression, power, exhaust) in only two strokes of the piston rather than four. This is accomplished by using the space below the piston for air intake and compression, thus allowing the chamber above the piston to be used for just the power and exhaust strokes. Thus, there is a power stroke per piston for every revolution of the crankshaft, instead of every second revolution as in a four-stroke engine. For this reason, two-stroke engines provide high specific (удельная) power.
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The two-stroke spark-ignition engine’s invention is generally credited to Joseph Day (and Frederick Cock for transfer-port), whereas the two-stroke valved compression-ignition engine was invented by Dugald Clark.
The smallest gasoline engines are usually two-stroke ones. They are popular due to their simple design (and therefore, low cost) and very high power-to-weight ratios. The biggest disadvantage is that the engine lubricant is almost always mixed in with the fuel, thus increasing the emission of pollutants. For this reason, two-stroke engines are being replaced with four-stroke engines in as many applications as possible.
Two-stroke engines are still commonly used in high-power applications where light weight is essential, such as string trimmers (обрезной станок) and chainsaws (бензопила). These engines may be used for certain small, portable, or specialized machine applications. These include high-performance, small-capacity motocycles, mopeds, scooters, snowmobiles, karts, model airplanes (and other model vehicles) and lawnmowers. In the past, two-stroke cycles were experimented with for use in diesel engines, most notably with opposed piston design, low-speed units such as large marine engines, and V8 engines for trucks and heavy machinery.
Speaking
8. Look at the picture, then read the text and try to explain to you partner how a two-stroke engine operates
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| A mixture of fuel and air is sucked from fuel-air inlet port into crankcase. Then the mixture gets to the combustion chamber through transfer port. When the mixture is in the combustion chamber, it is compressed by the movement of the piston. When it is compressed enough, spark plug fires and mixture ignites. The resulting explosion drives the piston downward. As the piston moves downward, the exhaust pipe is uncovered. |
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