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21. a) Read the text. Pay attention to the linking words in bold. Where do you think the author: a) explains the cause? b) shows the effect?
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21. a) Read the text. Pay attention to the linking words in bold. Where do you think the author: a) explains the cause? b) shows the effect?
b) Read the statements beneath the text and cross out the statements that do not correspond to the text content
c) After reading the text explain the title of it
Diesels versus Petrol Engines
Diesel engines are called compression ignition engines because they use compression to cause the fuel to ignite. They do not need a spark plug due to the fact that they ignite the fuel by compressing it. Compression causes the air to heat up, so when fuel is sprayed into the hot, compressed air, the fuel explodes.
The pressure created by compression requires diesel engines to be more strongly constructed, and thus, heavier than gasoline engines. They are more powerful and require a less expensive fuel, therefore diesel engines are generally found in large vehicles, such as trucks, and in stationary machines. Gasoline engines are lighter than diesel engines, because of this they require more highly refined (улучшенный, качественный) fuel and are mostly used in cars.
1. Diesel engines are called compression ignition engines.
2. They do not need an element which we find in gasoline engines.
3. Most diesels use four strokes to complete the cycle.
4. Fuel sprayed into the cylinder explores because the air is highly heated.
5. Diesels are more heavily built.
6. Diesels use less expensive fuel than petrol engines.
7. Fuel must be pulverized before entering the cylinder.
8. Fuel used in petrol engines is more expensive than that of diesel engines.
22. Read the text “Diesel Engines” and a plan to it
a) Look through the text and find the definitions of the terms “scavenging” (продувка) and “glow plug” (запальная свеча)
b) Divide the text into paragraphs according to the plan
1. General description
2. The inventor and his invention
3. How diesel engines work
4. Important elements
5. Classification
Diesel Engines
The diesel engine is a type of internal combustion engine; more specifically, a compression ignition engine, in which the fuel is ignited by the high temperature of a compressed gas, rather than a separate source of energy (such as a spark plug).
It was invented and patented by Rudolf Diesel in 1892. Diesel intended the engine to use a variety of fuels including coal dust. He demonstrated it in the 1900 World’s Fair using peanut oil.
When a gas is compressed, its temperature rises; a diesel engine uses this property to ignite the fuel. Air is drawn into the cylinder of a diesel engine and compressed by the rising piston, at much higher compression ratio than a spark-ignition engine. At the top of the piston stroke, diesel fuel is injected into the combustion chamber at high pressure, through a pulverizing nozzle, mixing with the hot, high-pressure air. The resulting mixture is ignited and burns very rapidly. This explosion causes the gas in the chamber to expand driving the piston down with considerable force and creating power in a vertical direction. The connecting rod transmits this motion to the crankshaft which is forced to turn, delivering rotary power at the output end of the crankshaft. Scavenging (driving the exhausted gas out of the cylinder, and drawing in a fresh charge of air) is done either by ports or valves. An important component of any diesel engine system is the governor, which limits the speed of the engine by controlling the rate of fuel delivery. In very cold weather, the compression itself cannot heat the air enough to ignite it.
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Glow plugs are electrical heaters inside the cylinder to help warm the air. Once the engine is started and warmed up, the glow plugs are no needed and may be turned off.
There are two types of diesel engines: two-stroke and four-stroke. Many larger diesels operate on the two-stroke cycle. Smaller engines generally use the four-stroke cycle.
23. Look through the text and find the definitions of the terms “compression ratio”, “engine knock”, “glow plug”
Analysis of the Otto cycle engine shows that its efficiency is mostly dependent (зависит) on the compression ratio, that is, the ratio of maximum compression of the fuel-air mixture to atmospheric pressure. The greater the compression ratio, the more efficient the engine.
However, the Otto cycle engine is limited on the level of compression it can obtain, since at high compression the temperatures and pressures will cause the fuel-air mixture to ignite spontaneously before the piston reaches the top of its travel. This phenomenon is known as engine knock.
The diesel cycle engine does not have this problem. It has the same general four-stroke operational cycle as the Otto-cycle engine, but uses a fuel injection system to spray fuel directly into the cylinder at the end of the compression stroke, allowing higher compression ratios. The diesel engine uses heavier fuels than the Otto cycle engine. It does not use spark plugs, instead using glow plugs that are heated and ignite the fuel-air mixture when the compression reaches the proper level.
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