Lesson 1. The Diesel Engine

DIESEL ENGINE

The diesel engine is an internal combustion engine which ignites the fuel by injecting it into high hot pressure air in a combustion chamber. The diesel engine has either a four-stroke or a two-stroke cycle. A stroke is a travel of the piston between its extreme points.

The four stroke cycle consists of inlet (or suction), compression, power (or working stroke) and exhaust. This cycle is completed in two revolutions of the crankshaft. At the top dead centre (TDC) the inlet valve opens and fresh air is drawn in as the piston moves down – suction stroke. At the bottom dead centre (BDC) the inlet valve closes and the air in the cylinder is compressed as the piston rises – compression. Fuel is injected as the piston reaches top dead centre and combustion takes place producing very high pressure in the gases. There gases force the piston down and at bottom dead centre the exhaust valve opens. The final stroke is the exhausting of the burnt gases as the piston rises to top dead centre.

The two-stroke cycle is completed in the two strokes of the piston during one revolution of the crankshaft: the upstroke (scavenge and compression) and the downstroke (power and exhaust stroke). Instead of valves holes known as “ports” are used which are opened and closed by the sides of the piston as it moves. When the piston is forced down on its working stroke it uncovers (opens) the exhaust ports. The burnt gases then begin to exhaust and the piston continues down until it opens the inlet or scavenge ports. Pressurized air then enters and drives out the remaining exhaust gases. The piston on its return stroke closes the inlet and exhaust ports. The air is then compressed as the piston moves to the top of its stroke.

I. Complete the sentences.

1. The diesel engine has either ___.

2. At the top dead center the inlet valve opens and ___.

3. A stroke is ___.

4. There gases force the piston down and ___.

5. The two-stroke cycle is completed in ___.

II. Answer the questions.

1. What is a diesel engine?

2. What cycle does a diesel engine have?

3. What does the four-stroke cycle consist of?

4. When is the air in the cylinder compressed?

5. What is the final stroke of the four-stroke cycle?

6. What is used instead of valves in the two-stroke diesel engines?

7. When are the exhaust ports uncovered?

8. When are the exhaust ports closed?