Ex.No: Date:
VALVE TIMING DIAGRAM OF A SINGLE CYLINDER
4- STROKE COMPRESSION IGNITION
ENGINE
Aim: To draw the valve timing diagram of the four
stroke compression ignition engine.
Brief
Theory of the Experiment:
The valve timing diagram gives an idea about how various operations are
taking place in an engine cycle. The four stroke diesel engines have inlet
valve to supply air inside the cylinder during suction stroke and an exhaust
valve to transfer exhaust gas after combustion to the atmosphere. The fuel is
injected directly inside the cylinder with the help of a fuel injector. The
sequence of events such as opening and closing of valves which are performed by
cam- follower-rocker arm mechanism in relation to the movements of the piston
as it moves from TDC to BDC and vice versa. As the cycle of operation is
completed in four strokes, one power stroke is obtained for every two
revolution of the crankshaft.
The suction, compression, power and exhaust processes are expected to
complete in the respective individual strokes. Valves do not open or close
exactly at the two dead centers in order to transfer the intake charge and the
exhaust gas effectively. The timing is set in such a way that the inlet valve
opens before TDC and closes after BDC and the exhaust valve opens before BDC
and closes after TDC. Since one cycle is completed in two revolutions i.e 720
degrees of crank rotations, various events are shown by drawing spirals of
suitable diameters. As the timing plays major role in transfer of the charge,
which reflects on the engine performance, it is important to study these events
in detail.
Equipment's Required:
1. Cut section engine,
2. Measuring tape/thread-measuring scale,
3. Feeler gauge / paper strip
4. Chalks
Procedure:
1.
Mark the direction of rotation of the flywheel.
Always rotate only in clockwise direction when viewing in front of the
flywheel.
2.
Mark the Bottom Dead Center (BDC) position on the
flywheel with the reference point when the piston reaches the lowermost
position during rotation of the flywheel.
3.
Mark the Top Dead Center (TDC) position on the
flywheel with the reference point when the piston reaches the top most position
during the rotation of flywheel.
4.
Identify the four strokes by the rotation of the
flywheel and observe the movement of inlet and exhaust valves.
5.
Mark the
opening and closing events of the inlet and exhaust valves on the flywheel.
6. Measure the circumferential distance of the above events either from TDC or from BDC whichever is nearer and calculate their respective angles.
7. Draw the valve timing diagram and indicate the valve opening and closing periods
Formula:
Angle = (L x 360) / X degrees
Where, L - Distance from nearest dead center in mm and
X-
Circumference of the flywheel in mm
Observations:
|
S.No. |
Event |
Position of
crank w.r.to TDC or BDC |
Distance in mm |
Angles in Degrees |
|
1 |
IVO |
|
|
|
|
2 |
IVC |
|
|
|
|
3 |
EVO |
|
|
|
|
4 |
EVC |
|
|
|
Example: (Theoretical Values)
Pre Lab Questions
1.
Define
valve timing?
2.
Differentiate
valve and port?
3.
Define
mechanism of valve operation?
4.
How
do you identify an engine is working on two stroke or four stroke principle?
5.
What
are the advantages of four stroke engines over two stroke engines?
6.
Define
compression ratio.
7.
How
do you identify an engine whether it is petrol or diesel engine?
Post Lab Questions
1.
What
are the position of inlet vale opening and closing?
2.
What
are the exhaust valve opening and closing positions?
3.
Indicate
the injection/ignition period in the diagram?
4.
What
do you mean by valve overlap? What are their effects in SI engines?
5.
How
the cylinder numbers assigned in multi-cylinder I.C. engines?
6.
Explain
the lubrication system of four stroke engines.
7.
Give
firing order for a four and six cylinder engines.
8. Explain how the
correct direction of rotation is found before starting the valve timing
experiment.
Conclusion:
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PO Attainment: |
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Composed By:
R.Satheesh, M.E., Asso.Prof.,
