VAlve and ignition timings of internal combustion engine

Valve and ignition timings

1. IGN TIMING

2. IGN TIMING
“TIMING OF SPARK AT THE SPARK
PLUG GAP IN RELATION TO THE
PISTON Position”
PISTON Position AT ANY Point IN TIME IS SEEN IN
TERMS OF Degree OF CRANKSHAFT Revolution

3. TDC
TDC
BDCBDC
POWER
EXHAUST INTAKE
COMPRSSION
360/ 0 DEG
180 DEG
90 DEG270 DEG

4. TDC
TDC
BDCBDC
B
T
D
C
A
T
D
C

5. TDC
TDC
BDCBDC
10
10
10
10
10 DEG ATDC
80 DEG BBDC
10 DEG BTDC
80 DEG ABDC

6. TDC
TDC
BDCBDC
10

7. TDC
TDC
BDCBDC

8. TDC
TDC
BDCBDC
10

9. IGN TIMING
•IDEAL SIT – SPARK AT COMPRESSION
TDC
•
REAL SIT – ?
TDC
TDC
BDCBDC
POWER
EXHAUST INTAKE
COMPRSSION

10. IGN TIMING CONSIDERATOINS
•TIME REQ TO BURN THE FUEL
COMPLETELY
•TIME REQ FOR EXHAUST GASES TO
RAISE THE PRESSURE

11. IGN TIMING CONSIDERATIONS
•HAVE SPARK AT AN INSTANT WHICH
GIVES MORE TIME FOR
–FUEL TO BURN
–BURNT GASES TO RAISE THE PRESSURE
TO THE MAX AS THE PISTON REACHES
TDC
MAX DOWNWARD PUSH TO PISTON

12. LATE SPARK
•SPARK AT OR ATDC
–INCOMPLETE FUEL BURNING
–LESS BURNT GASES PRESSURE
–REDUCED DOWNWARD PUSH
–MORE POWER LOSSES

13. ADV SPARK
•SPARK BTDC
–MORE TIME FOR FUEL
BURNING
–MORE BURNT GASES
PRESSURE
–MORE DOWNWARD PUSH
–MAX POWER OUTPUT

14. TDC
TDC
BDCBDC
POWER
EXHAUST INTAKE
COMPRSSION
?

15. OPTIMIZATION
•NIETHER TOO EARLY NOR TOO LATE
•VERY EARLY SPARK CAUSES
DETONATION

16. DETONATION
BURNING
BEFORE TDC

17. ENGINE SPEED AND IGN TIMING
CONSIDERATION
MORE SPEED – LESS TIME FOR FUEL
TO BURN
TIMING SHOULD GRADUALLY ADV WITH THE INC IN
SPEED

18. VALVE TIMING

19. VALVE TIMIING
•AT WHAT INSTANT SHOULD A VALVE
OPEN?
•FOR HOW LONG SHOULD IT REMAIN
OPEN?
•MAX POWER OUTPUT CAN BE
ACHIEVED FROM AN ENGINE AT
DIFFERENT SPEEDS BY DIFFERENT
VALVE TIMINGS

20. CONSIDERATIONS
•PISTON SPEED IS NOT UNIFORM
DURING A COMPLETE REV
–DEAD AT TOP/ BOTTOM (30 – 40 DEG)
–FASTEST IN THE MIDDLE
•THE DEAD PDS ARE UTILIZED IN DEV
OF TIMING SEQ

21. CRANKSHAFT ROTATIONAL PD
BDC
TDC

22. TDC
TDC
BDCBDC
INTAKE OPEN
INTAKE
CLOSE
EXHAUST
OPEN
EXHAUST
CLOSE
INTAKE
COMPRESSIONPOWER
EXHAUST

23. BDC
TDC
28
71
DURATION 279 DEG
FOR INTAKE VALVE
INTAKE
COMPRSSION

24. BDC
TDC
45
78
DURATION 303 DEG FOR
EXHAUST VALVE
EXHAUST
POWER

25. 45
28
TDC
INTAKE OPENS
EXHAUST
ALREADY
OPEN
EXHAUST CLOSES
INTAKE REMAINS
OPEN
73

26. AT UPPER TDC
•OPENING INTAKE VALVE BEFORE
EXHUAST VALVE IS CLOSED
–MIXTURE IS SUCKED IN DUE TO VACCUM
GEN BY THE EXHUST GASES THUS INC
VOL EFFICENCY
–INTAKE MIXTURE COMING IN ALSO
SWEEPS THE EXHUAST GASES
–OVERLAP TAKES PLACE DURING ONE OF
THE DEAD PDS THUS CAUSES NO
EXHAUST GASES TO BE PULLED BACK IN

27. SPEED, VALVE TIMING AND
POWER
•BY INC THE VALVE DURATION AND
OVERLAP ENGINE CAN BE MADE TO
PRODUCE MAX POWER AT HIGHER
SPEEDS
•HOWEVER THE SAME ENGINE WILL
RUN POOR AT LOW SPEED DUE TO
TENDENCY TO PULL THE EXHAUST
GASES BACK IN

28. VALVE TIMING DIAGRAM