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11. Read the title of the text and guess what it is about. Choose between the following variants
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11. Read the title of the text and guess what it is about. Choose between the following variants
a) Main elements of the combustion engine.
B) Inventor of the internal combustion engine.
C) Evolution of the internal combustion engine.
D) Engine operation
Look through the text and guess the meanings of the underlined words. Read the text and the questions to it. Cross out the questions to which there is no answer in the text
The Four-Stroke Cycle
The engine cycle begins with the intake stroke as the piston is pulled towards the crankshaft. The intake valve is open, and fuel and air are drawn through the valve and into the combustion chamber. The exhaust valve is closed and the electrical contact switch is open. The fuel-air mixture is at a relatively low pressure (near atmospheric). At the end of the intake stroke, the piston is located at the cylinder bottom and begins to move back towards the top. The cylinder and combustion chamber are full of the low-pressure fuel-pair mixture and, as the piston begins to move upward, the intake valve closes.
With both valves closed, the combination of the cylinder and combustion chamber form a completely closed vessel (сосуд) containing the fuel-air mixture. As the piston is pushed upward, the volume is reduced and the fuel-air mixture is compressed during the compression stroke. As the volume is decreased because of the piston’s motion, the pressure in the gas is increased, as described by the laws of the thermodynamics. To produce the increased pressure, we have to do work on the mixture, just as you have to do work to inflate (накачать) bicycle tire (шина) using a pump.
At the beginning of the power stroke, the electrical contact is opened. The sudden opening of the contact produces a spark in the combustion chamber which ignites the fuel-air mixture. Rapid combustion of the fuel releases heat, and produces exhaust gases in the combustion chamber. Because the intake and exhaust valves are closed, the combustion of the fuel takes place in a totally enclosed (and nearly constant volume) vessel. The combustion increases the pressure in the combustion chamber. The high pressure of the gases acting on the face of the piston causes the piston to move downward which initiates the power stroke. Unlike the compression stroke, the hot gas does work on the piston during the power stroke. The force on the piston is transmitted by the connecting rod to the crankshaft, where the reciprocating motion of the piston is converted to rotary motion of the crankshaft. During the power stroke, the volume occupied by the gases is increased because of the piston motion. As the volume increases because of the piston’s motion the pressure and temperature of the gas decrease.
The purpose of the exhaust stroke is to clear the cylinder of the spent exhaust gases in preparation for another ignition cycle. As the exhaust stroke begins, the cylinder and combustion chamber are full of exhaust products at low pressure. Because the exhaust valve is open, the exhaust gas is pushed through the valve and exits the engine. The intake valve is closed.
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1. What is the first stroke of the four-stroke cycle?
2. What valve is open during the intake stroke?
3. Where is fuel mixed with air before entering the cylinder?
4. Is the exhaust valve open or closed during the intake stroke?
5. Where is the piston located at the end of the suction stroke?
6. At what pressure is fuel-air mixture during the intake stroke?
7. What is fuel-air mixture compressed by?
8. Where is fuel-air mixture contained during the compression stroke?
9. Why does the pressure increase?
10. Does the temperature of fuel-air mixture increase during the compression stroke?
11. How is fuel-air mixture ignited?
12. What process initiates the power stroke?
13. How is reciprocating motion of the piston converted into rotary motion of the crankshaft?
14. What is the volume of the cylinder?
15. What is the purpose of the exhaust stroke?
16. At what pressure are the exhaust products during the exhaust stroke?
17. What is the temperature of the exhaust gases?
Listening
12. You will hear a part of a lecture about operation of internal combustion engines. While listening, complete the gaps in the sentences
1. In a four-stroke engine a piston makes _________________ strokes: two strokes ________________ the cylinder head and two strokes downward.
2. During the first stroke the intake valve is ___________________.
3. The mixture of fuel and air is sucked into _________________________.
4. During the compression stroke the volume of the combustion chamber is at a __________________.
5. At the end of the power stroke the pressure of gases is _____________ to ______________ kg/cm².
6. When the exhaust gases are driven out of the combustion chamber, the cylinder is _________________ to repeat the cycle.
Speaking
13. Describe each picture in turn and define the type of the stroke
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