Question 2
The camshaft idling speed of a six cylinder four stroke cycle engine is 450 r.p.m.
- Determine the speed of the engine in one minute.
- How many power strokes would be done by the engine in one minute?
- Calculate the angle through which the crankshafts will rotate to open and close the valve, if the exhaust valve opens 350 before bdc and closes 100 after tdc.
- Determine the firing intervals for the following:
(i) four cylinder engine;
(ii) six cylinder engine.
- Name one type of camshaft drive.
Observation
This question was very difficult for the candidates, as they could not provide the required responses to the various parts of the question. The required responses to the various parts of the questions are:
(a) Camshaft speed = twice crankshaft speed
Crankshaft speed = 2 x 450 r.p.m.
= 900 r.p.m.
Crankshaft speed = engine speed
= 900 r.p.m.
- For a four stroke cycle, two revolutions of the crankshaft = one power stroke per cylinder.
900 revs = x
If 2 revs = 900 revs per cylinder or 900 power strokes per cylinder
1 rev = power strokes per cylinder
2
= 450 power strokes
For six cylinders = 450 x 6
= 2700 power strokes
(C)
(e) The types of camshaft drive are:
- chain drive;
- gear drive;
- belt draive.