The document discusses valve timing in internal combustion engines, including the benefits of valve overlap and how variable valve timing (VVT) uses computer control and oil pressure to advance or retard cam timing and change valve duration, overlap, and lift while the engine is running, allowing for optimization of valve timing under different operating conditions. VVT has been widely adopted by Japanese and European automakers since the 1990s and more recently by some American automakers.

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2. Catalytic conveter

3. Introduction:
Acatalytic convertor is a vehicle emission control device that converts toxic pollutants in exhaust gas
to less toxic pollutants by catalyzing a redox reaction.
Catalytic convertors are used in internal combustion engines fueled by either petrol(gasoline) or diesel.
Invented by:
Eugene Houndry
Year of invention:
1950
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4. Construction:
The catalyst support:
The core is usually a ceramic monolith with a honey comb structure.
The Wash coat:
A wash coat is a carrier for the catalytic materials & is used to disperse the
materials over large surface area.
The catalysts:
The catalyst itself is made up of mixtures of
palladium, rhodium etc…
Rhodium is used as reduction catalyst.
Palladium is used as oxidation catalyst.
Platinum is used as both for reduction & oxidation
Catalyst.
precious metals such as platinum,
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5. Working:
Due to partial combustion, gases such as oxides of nitrogen, carbon monoxide
& un burnt hydrocarbons enter the catalytic convertor through the exhaust valve.
There are basically two ceramic blocks,
ceramic block 1 contains platinum & rhodium and ceramic block 2 contains platinum and
palladium as catalyst.
1st 1stAs toxic gases enter
1. 2NOx xO2 +N2
ceramic block oxides of nitrogen are to react.
2nd
1.
The N2,O2,CO,HC enters the
2CO+O2 2CO2
ceramic block.
2. HC + O2 H2O + CO2
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6. Types:-
Two-way:
Involves two types of oxidation reaction
1. Oxidation of carbon monoxide to carbon-di-oxide
2CO+O2 2CO2
2. Oxidation of hydrocarbons
CxH2x+2+ [(3x+1)/2] O2 xCO2+(x+1) H2O (combustion reaction)
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7. Three-way:-
Oxidation-reduction reaction’s
1. Reduction of oxides to nitrogen & oxygen:
2NOx – xO2 +N2
2. Oxidation of carbon monoxide to carbon-di-oxide:
2CO+O2 – 2CO2
3. Oxidation of un burnt hydrocarbons:
CxH2x+2 + [(3x+1)/2] O2 – xCO2 + (x+1) H2O
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8. Installation:
Many vehicles have a close-coupled catalytic converter located near
the engine's exhaust manifold.
This unit heats up quickly due to its proximity to the engine,
and reduces cold-engine emissions by burning off hydrocarbons from
the extra-rich mixture used to start a cold engine
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9. Damage :
Catalyst poisoning occurs when the catalytic convertor is exposed to exhaust containing
substance that coat the working surfaces, encapsulating
the catalyst so that it cannot contact & treat the exhaust.
The most notable contaminant is lead.
Vehicles equipped with catalytic Convertor can be run only
on unleaded fuels.
Vehicles equipped with OBD-II diagnostic systems are designed to alert
The driver the misfire condition by means
Light on the dashboard.
of flashing the check engine
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10. Environmental impact:
Catalytic convertors have proven to be reliable & effective in reducing of
toxic emissions. However, these also have adverse environmental impacts in production.
If a three-way catalyst must run at the stoichiometric point, means the
Fuel is consumed than in the lean burn engine.
This means app. 10% more CO2 is emitted.
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11. IGNITION ADVANCE
METHODS
CONVENTIONAL IGNITION SYSTEMS

12. IGNITION ADVANCE

13. IGNITION RETARD

14. NEED OF ADVANCE/RETARD

15. IGNITION ADVANCE - METHODS
 Mechanical
o Octane selector
 Automatic
o Centrifugal advance
o Vacuum advance
o Centrifugal and vacuum
combination
o Complete vacuum control
o Computerised advance control

16. Mechanical Ignition advance

17. Octane selector

18. • Controlled by hand only by means of a lever at the dash board
• The distributor has a provision that contact breaker base plate can be rotated within a
certain degree
• Turning the breaker plate in cam’s direction of rotation results retardation, opposite
direction turning results advanced ignition
Advantage
• Useful for the ‘pre-setting of ignition advance when different fuels may be used’
Disadvantage
• However the timing of ignition is not satisfactory, because adjustment is normally done
after the engine gives poor performance and not at the proper time

19. Automatic Ignition advance
1.CENRIFUGAL ADVANCE

23. Automatic Ignition advance
2.VACUUM ADVANCE

27. Automatic Ignition advance
3.CENTRIFUGAL AND VACUUM COMBINATION

30. Automatic Ignition advance
4.COMPUTERISED ADVANCE CONTROL

31. • Modern technology
Basic components
• A memory
• Timing map(contains spark advance values for all combinations of speed, load and
other conditions)
Based upon the signals received from various sensors, the computer ECU sends a signal
to the ignition coil at the precise moment indicated in the timing map, which fires the
spark plug at the instant.
In the most of the original systems, the timing map and hence the timing advance curve
can’t be modified. However aftermarket ECUs allow the changes to be made later in the
timing map.

32. VALVE TIMING
In a piston engine, the valve timing is the precise timing of the opening and closing
of the valves. In an internal combustion engine those are usually poppet valves and in a steam engine they are
usually slide valves or piston valves.
In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is
controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine
operation by variable valve timing. It is also affected by the adjustment of the valve mechanism, and
particularly by the tappet clearance. However, this variation is normally unwanted.

34. Valve overlap
With traditional fixed valve timing, an engine will have a period of "valve overlap" at the end of
the exhaust stroke, when both the intake and exhaust valves are open. The intake valve is
opened before the exhaust gases have completely left the cylinder, and their considerable
velocity assists in drawing in the fresh charge. Engine designers aim to close the exhaust valve
just as the fresh charge from the intake valve reaches it, to prevent either loss of fresh charge or
unscavenged exhaust
gas. In the diagram, the valve overlap
overlap of the red and blue arcs.
Key:
TDC = Top dead centre BDC = Bottom
dead centre IO = Inlet valve opens
IC = Inlet valve closes
EO = Exhaust valve opens
EC = Exhaust valve closes
periods are indicated by the

35. The Inner Workings of Variable Valve Timing
Variable Valve Timing (VVT) is a way to advance/retard valve timing, and change duration, overlap
and even lift in some applications while the engine is running.
VVT is computer-controlled and typically uses oil pressure to change the
position of a phaser mechanism on the end of the camshaft to advance or retard cam timing.
VvT has been used on numerous Japanese (Honda, Nissan and Toyota) and European (Audi, BMW,
Mercedes and VW) engines since the late 1980s and early 1990s, but only in the last decade or so on
domestic engines (such as Ford 4.6L V8s, Chrysler 2.4L and 3.6L VVT engines, Chevy 2.4L Ecotec,
etc.).
On overhead cam engines where there are separate cams for the intake and exhaust valves, changing
the timing of one cam also changes the effective duration and overlap, and on engines where VVT
also involves activating extra cam lobes or changing the rocker arm fulcrum point, VVT can also
change total valve lift.