 |
Which information you have already known and which was quite new for you?
|
|
|
|
Which information you have already known and which was quite new for you?
UNIT XII. CONSOLIDATION
1. Read the text and make up a plan of it
How Diesel Engines Differ from Gasoline Engines
Both types of engines run on liquid fuels. In certain special cases they even use exactly the same fuel. Gasoline engines were made to run kerosene, and so were diesels.
Both types of engines are internal combustion engines, that is, they burn the fuel inside their cylinders.
Most gasoline engines and many diesel engines work on the four-stroke cycle, that is, the piston makes a suction stroke (down), a compression stroke (up), a power stroke (down), and an exhaust stroke (up). What, then, are the main differences between diesel and gasoline engines?
First, a diesel engine has no ignition system because the fuel is ignited simply by contact with very hot air which has been highly compressed in the cylinder.
Second, a diesel engine draws into its cylinder air alone, it compresses this air on its compression stroke before the fuel enters the cylinder. On the other hand, a gasoline engine mixes air with fuel outside the cylinder before it enters the engine through the inlet valve.
Third, diesel engines use greater compression than gasolines ones. Gasoline engines compress at a ratio of 8: 1 to 12: 1, while diesel engines compress at a ratio of 14: 1 to as high as 25: 1. The higher compression ratio of diesel engines lead to better efficiency.
Fourth, diesel engines use less volatile (легко испаряющийся), heavier fuels than gasolines engines. These heavier fuels are generally cheaper than gasoline.
Fifth, diesel engines are heavier than gasoline engines of the same size because they work against greater pressures, and consequently their parts must be stronger. The greater strength is obtained by making the parts thicker and therefore heavier.
2. Read and translate the text. Use a dictionary if necessary
Advantages of Diesel Engines
Diesel engine offers the following advantages over gasoline engines:
Fuel economy. Diesel engines have higher compression ratios and therefore burn fuel more completely and efficiently.
Reliability. Diesel engines have no electrical ignition system which can fail. They are built with heavy-duty parts to withstand the higher compression ratios and to operate for long periods with minimum breakdown. In heavy-duty trucks, for instance, diesel engines have a long service life of many hundreds of thousands of miles.
Power. It depends on engine size, but diesel engines generally produce more torque and power output than gasoline engines.
Speaking
3. Look at the pictures. Compare and contrast the engines. Use the information from the texts “How Diesel Engines Differ From Gasoline Engines” and “Advantages of Diesel Engines”. You may also use the following plan
| Similarities | Differences |
| 1. Function | 1. Ignition system |
| 2. Application | 2. Some elements |
| 3. Main elements | 3. Efficiency |
| 4. Principle of operation | 4. Fuel |
| 
|
4. Translate the sentences with " there+be".
|
|
|
1. There are two-stroke and four-stroke cycle diesel engines.
2. There is no electrical ignition system in the diesel engine.
3. There are four piston strokes in one cycle of operation.
4. There are two types of cooling systems: liquid and air-cooling systems.
5. There is a film of oil between the working surfaces of metal parts.
6. There are internal and external combustion engines.
7. There is only one power stroke in a four-stroke cycle.
8. Engines can overheat when there is not enough water in the radiator.
9. There are four strokes in the action cycle of most car engines.
10. The operation principles of the four-stroke cycle diesel engine and four-stroke cycle gasoline engine are basically the same but still there is some difference between them.
5. Read the sentences and choose the alternative
1. Combustion requires the presence of oxygen, in order to / so fuel must be mixed with air.
2. The diesel uses less fuel than any other engines of the same power, therefore / owing to diesel-engined cars are cheaper to run than petrol-engined cars.
3. During the compression the volume is decreased because of / because the piston’s motion.
4. The combustion takes place in a totally enclosed cylinder because / therefore the intake and exhaust valves are closed.
5. During the power stroke the volume occupied by the gases is increased owing to / thus the piston’s motion.
6. As / consequently the exhaust valve is open, the exhaust gas is driven out of the cylinder by the ascending piston.
7. Because of / so as to high temperatures of operation, a diesel engine must be water-cooled.
6. Complete the text with verbs in Present Simple Active or Passive When a gas 1(compress), its temperature 2 (rise). A diesel engine 3 (use) this property to ignite the fuel. Air 4(draw) into the cylinder. The air temperature reaches 700-900°C, or 1300-1650°F. At the top of the piston stroke, diesel fuel 5 (inject) into the combustion chamber at high pressure, mixing with the hot, high-pressure air. The resulting mixture 6 (ignite) and 7 (burn) rapidly. This combustion 8 (cause) the gas in the chamber to heat up, which 9 (increase) its pressure, which in turn 10 (force) the piston downwards. The connecting rod 11 (transmit) this motion to the crankshaft.
|
|
|
