Combustion, combustion chamber, compression

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(1) Process by which an engine produces power by igniting a fuel mixture.

(2) Area at the top of the cylinder above the piston head where the fuel mixture is ignited.

(3) Process of reducing the volume within a cylinder and therefore increasing the pressure on a fuel mixture within that cylinder.

Exercise 3

Read the text and be ready to answer the questions

1) What does a four-stroke cycle mean?

2) What happens during the induction stroke?

3) What kind of stroke is called compression stroke?

4) What is ignition (firing) stroke?

5) What happens during the exhaust stroke?

THE FOUR-STROKE CYCLE OF ENGINE OPERATION

Most modern car engines operate on a four-stroke cycle. This means that each piston travels down twice and up twice after each ignition of petrol/air mixture, making four strokes in all. To simplify the operating sequence, we will assume that our engine has only one cylinder.

(1) Induction. This begins with the piston at the top of its stroke and the inlet valve open. As the piston goes down it draws the petrol/air mixture into the cylinder past the open inlet valve.

(2) Compression. When the piston has completed its down-stroke, the inlet valve closes. The revolving crankshaft then pushes the pistons up again, and the mixture now in the cylinder is compressed upward into the combustion chamber. At the top of the stroke it is fully compressed.

(3) Ignition (Firing). At this point a spark occurs between the electrodes of the sparking plug. This ignites the air/petrol mixture. The heat from the explosion causes high pressure on the top of the piston which is thus forced downward.

(4) Exhaust. At the end of this down-stroke, the exhaust valve opens and during the following up-stroke the products of combustion are pushed past the valve and out of the engine. This cycle is constantly repeated so long as the engine is running.

Exercise 4

Match the processes with the names of the cycles during which they happen

A) Induction B) Compression C) Ignition D) Exhaust

1) The heat from the explosion causes high pressure on the top of the piston which is thus forced downward.

2) The piston is at the top of its stroke and the inlet valve is open.

3) The exhaust valve opens and during the following up-stroke the products of combustion are pushed out of the engine.

4) When the piston has completed its down-stroke, the inlet valve closes.

5) The mixture in the cylinder is compressed upward into the combustion chamber.

6) A spark ignites the air/petrol mixture.

LESSON 17