Практическая работа № 11

Four-stroke engine

1. Match the phrases with the Russian equivalents:

Answer:1-____,2-____,3-____,4-____,5-____,6-____, 7-____,8-____,9-____,

10-____,11-____

2. Translate international words:Motor, function, compression, cylinder, cycle, operation, product, revolution.

3. Put the appropriative word(s) :

1) The space between the piston and the cylinder head is …

a. the working cylinder b. the combustion chamber c. exhaust valve

2) At the very beginning of the return stroke … closes, and the charge is compressed.

a. inlet valve b. exhaust valve c. combustion chamber

3) The process requires four piston strokes is called … .

a. two-stroke cycle b. four-stroke cycle

4.Read and translate the text:

All cars and larger motor-cycles use 4-stroke engines. In the hot-air motor the combustion piston performed its function in two strokes: suction of a fresh charge on the forward stroke and compression on return. The expansion piston likewise completed its duty in two strokes: expansion on its forward stroke and exhaust of the spent charge on return.

By merging the two cylinders in one, the same functions are retained, so that now the cycle of operation includes four strokes of piston. This is the way it is done: We have now one cylinder with a piston reciprocating therein. The space between the piston and the cylinder head is the combustion chamber. The first stroke is forward. With a valve (called the inlet valve) open a fresh charge is sucked into the cylinder from the outside by the receding piston. At the very beginning of the return stroke the inlet valve closes, and then the charge is compressed. Just before the end of this stroke ignition is made. On the next forward stroke the combustion is completed and the products of combustion expand. This is the working or power stroke. Last the exhaust valve is opened, and the piston on returning a second time pushes out the spent or waste charge. The piston then is back where it started, and the operation is repeated.

This process requires four piston strokes (two crankshaft revolutions) and is, therefore, called four-stroke cycle, or just four-cycle.

5. Answer the questions:

1) What kind of land vehicles do four-stroke engines use?

2) How many strokes of piston does the cycle of operation include in one cylinder now?

3) What kind of strokes did compete its duty the expansion piston in a hot-air motor in?

4) What is the combustion chamber?

5) Is the inlet valve closed or open at the very beginning of the return stroke ?

6) Where is ignition made?

7) Why is this process called four-stroke cycle?

Практические работы № 12-13.

The Gasoline Engine

1. Read and translate the texts. Make a title to each letter:

a) If the fuel (gas, oil) burns inside an engine cylinder, it is then called an internal combustion engine. A gasoline engine is the perfect example. There are two types of gasoline engines – the two-cycle and four-cycle engines. Both types have pistons that move up and down in cylinders.

One cycle (or stroke) is one up movement or one down movement of a piston. In a two-cycle engine, each piston goes down once and up once every time the spark plugs ignite the fuel. Two-cycle engines are used where the machine needs to be light in weight. A power lawn mower usually has a two-cycle engine. So does a model airplane engine. Speed and efficiency are not too important.

Most larger gasoline engines, such as those in automobiles, are four-cycle. In these four-cycle engines, each piston goes down twice and up twice while the fuel is ignited once. A starter mechanism sets the pistons in motion. Once started, explosions resulting from the spark plugs igniting the fuel help keep the pistons moving. Each piston is connected by a rod to a crankshaft which transfers the power to the wheels of the machine.

Every piston goes down twice and up twice (four cycles) to every explosion. The strokes are called (1) intake, (2) compression, (3) power, and (4) exhaust. As the drawing show, one down stroke draws in fuel (intake); one up stroke compresses or squeezes the fuel into the top of the cylinder where it is ignited by the spark plug (compression); a second down stroke uses the power of the explosion to turn the crankshaft (power); a second up stroke drives the burned gases out the exhaust valve (exhaust). This operation is, of course, repeated over and over in every cylinder. The four strokes in one cylinder are completed in a fraction of a second.

There are usually six or more pistons in a four-cycle engine. To get the most power the explosions are timed to go off at different times in each cylinder.

A title-

b)The diesel engine is also an internal combustion engine. It works on the same cylinder and pistons principal as a gasoline engine. There are, however, two main differences between the diesel and gasoline engine. A diesel engine uses a special grade of fuel oil – not gasoline. Hot compressed air – not the spark from a spark plug – ignites this fuel oil.

There are two-cycle and four-cycle diesel engines. Let’s look at the operation of the one cylinder in a four-cycle diesel engine:

A starter gets the piston moving. As the piston moves downward, it draws air into the cylinder through an air valve. (In some engines, air is forced in by a blower called a supercharger.) That completes one cycle (or stroke). The piston then moves up compressing or squeezing the air into the top of the cylinder. As the air is squeezed, its temperature is increased to about 900° F. this completes the second cycle. Next the oil intake valve opens and oil is sprayed into the cylinder. The heat from the air (like the spark in a gasoline engine) ignites the oil. The resulting explosion forces the piston dawn ward. This third cycle is the power stroke; it turns the engine drive shaft. Finally, as in a burned engine, the piston comes back up and forces the burned or exhaust gases out of the cylinder through an escape valve. This all takes only seconds and occurs in all the cylinders at timed intervals.

A diesel engine gets more energy out of its fuel than any other type internal combustion engine. It is more efficient than a steam engine. The fuel is cheaper, too, requiring less refining than gasoline. Much progress has been made in the design of diesel engines in recent years so more and more of them are in use today. This is especially true among automobiles and light trucks.

A title-

Answer the questions.

1. How do engines help you in your living?

2. What types of engines do you know?

3. What is an internal combustion engine?

4. What types of gasoline engines do you know?

5. Where are two-cycle engines used?

6. What is the function of four-cycle engine?

7. What is the stroke?

8. How many pistons are there in a four-cycle engine?

9. What is the difference between diesel and gasoline engine?

10. Is diesel engine an internal combustion engine?