SECTION A
(a) The table below shows the firing order of a complete cycle for a four-
cylinder, four-stroke engine.
Cylinder |
Firing Order |
|||
|
1 |
3 |
4 |
2 |
1 |
Power |
|
Induction |
|
2 |
|
Induction |
|
Power |
3 |
Compression |
|
|
Induction |
4 |
Induction |
Compression |
|
|
Complete the cells under the firing order with the missing strokes.
(b) Explain the following terms, as applicable to four-stroke compression ignition engine:
(i) induction stroke; (ii) power stroke.
(c) What is the name of the automobile engine valve that has larger diameter?
Observation
Candidates who attempted this question did appreciably well. The attempt on the
question was good; however, the respondents could not fare well in 4(b).The solution to the poorly answered question is given below.
- (i) Induction Stroke
During this stroke, the inlet valve opens the piston
move down to bottom dead centre, creating a partial
vacuum that draws air into the cylinder.
(ii) Power Stroke
In the power stroke of a compression ignition engine, both valves are closed and fresh air charge is compressed, which results to increased temperature and pressure. The fuel is sprayed at high pressure and combustion starts. The high increase of temperature and pressure forces the piston down during the power stroke.