The document discusses valve timing diagrams for both four-stroke and two-stroke engines, detailing the opening and closing sequence of intake and exhaust valves. It contrasts theoretical and actual valve timing, highlighting the importance of precise timing to optimize engine performance and prevent issues such as knocking. Key aspects, including the degrees of valve operations and the influence of inertia on timing, are described to illustrate the practical workings of engine cycles.

1. Presented To:
Presented By:

2.  Introduction
 Why we need Valve Timing Diagram?
 Theoretical Valve Timing Diagram
1. For Four Stroke Engine
2. For Two Stroke Engine
 Actual Valve Timing Diagram
1. For Four Stroke Engine
2. For Two Stroke Engine
Theoretical vs Actual Valve Timing Diagram

3. A valve timing diagram is a graphical representation of the opening
and closing of the intake and exhaust valve of the engine.
The valve timing diagram comprises of a 360 degree figure which
represents the movement of the piston from TDC to BDC in all the
strokes of the engine cycle, Which is measured in degrees and the
opening and closing of the valves is controlled according to these
degrees.

4. The normal engine completes around 100000 cycles per minute, as we
know there are number of processes involve in a single cycle (from the
intake of the air-fuel mixture to the exhaust of the combustion
residual) of a internal which makes it necessary to be equipped with an
effective system that can enable –
1. Ideal timing for the opening and closing of the inlet and outlet valve
which in turn protect the engine from defects like knocking or
detonation.
2. A high compression ratio required to combust the fuel especially in
case of diesel engine by overlapping the closing of the valve.
3. Synchronisation between the steps of a cycle of the engine from
intake of air-fuel ratio to the exhaust of combustion residual.

5. 1. For Four-stroke Cycle Engine :

6. 1. For Two-stroke Cycle Engine :

7. TDC : Top Dead Centre
BDC : Bottom Dead Centre
IVO : Inlet valve opens ( 100 - 200 before TDC )
IVC : Inlet valve Closes( 300 - 400 after BDC )
IGN : Ignition (200 - 300 before TDC )
EVO : Exhaust valve opens( 300 - 500 before BDC )
EVC : Exhaust valve Closes( 100 - 150 after TDC )
1. For Four-stroke Cycle Engine :

8. 1. For Four-stroke Cycle Engine :
TDC : Top Dead Centre
BDC : Bottom Dead Centre
IVO : Inlet valve opens ( 100 - 200 before TDC )
IVC : Inlet valve Closes( 250 - 400 after BDC )
FVO : Fuel Valve Opens (100 - 150 before TDC )
FVC : Fuel Valve Closes (150 - 200 after TDC )
EVO : Exhaust valve opens( 390 - 500 before BDC )
EVC : Exhaust valve Closes( 100 - 150 after TDC )

9. 1. For Two-stroke Cycle Engine :
TDC : Top Dead Centre
BDC : Bottom Dead Centre
EPO : Exhaust Port opens( 350 - 500 before BDC )
TPO : Transfer port opens ( 300 - 400 before BDC )
TPC : Transfer Port Closes( 300 - 400 after BDC )
EPC : Exhaust port Closes( 350 - 500 after TDC )
IGN : Ignition (150 - 200 before TDC )

10. 1. For Two-stroke Cycle Engine :
TDC : Top Dead Centre
BDC : Bottom Dead Centre
FVO : Fuel valve opens ( 100 - 150 before TDC )
FVC : Fuel valve Closes( 150 - 200 after TDC )
EPO : Exhaust Port Opens (350 - 500 before BDC )
TPO : Transfer Port Opens(300 - 400 before BDC )
TPC : Transfer Port Closes( 300 - 400 after BDC )
EPC : Exhaust Port Closes( 350 - 500 after BDC )

11. Sr.
No.
Actual Valve Diagram Theoretical Valve Timing
1.
The inlet valve starts opening 10 degrees to 30
degrees before the beginning of suction stroke
(TDC) and closes after 30 degrees to 40 degrees at
the end of the stroke (BDC)
The inlet valve opens exactly at the beginning of suction
stroke (TDC) and closes at the end of the stroke (BDC)
2.
The exhaust valve starts opening 30 degrees to 60
degrees before the beginning of exhaust stroke
(BDC) and closes after 8 degrees to 10 degrees at
the end of the stroke (TDC)
The exhaust valve opens exactly at the beginning of
exhaust stroke (BDC) and closes at the end of the stroke
(TDC)
3.
The inertia of the valve operating mechanism is
considered
Inertia of the valve operating mechanism is not
considered
4.
Time for the charge to fill completely into the
cylinder is considered
Time for the charge to fill completely into the cylinder is
not considered
5.
Time for the exhaust gases to escape out of the
cylinder is considered
Time for the exhaust gases to escape out of the cylinder
is not considered
6.
The inlet valve is closed when the piston reaches a
point in its next stroke at which the pressure in the
cylinder equals the pressure outside.
The inlet valve is closed when the piston reaches TDC
7. The valves are opened or closed slowly. The valves are closed or opened instantaneously
8. There is valve overlap. There is no valve overlap.