3. Air gap:
The quenching effect between the electrodes is the work of the electrodes absorbing the heat and
extinguishing the flame, if it greater than the flame core heat generation action, the flame core is
extinguished and the combustion stops. If the plug gap is wide, the flame core is larger and the
quenching effect is smaller, so reliable ignition can be expected, but if the gap is too wide, a large
discharge voltage becomes necessary, the limits of the coil performance are exceeded, and discharge
becomes impossible.
4. Air gap:
Both new and used spark plugs should have their air gaps set to
manufacturer’s specifications. Always use round wire gauges when
checking and setting the gap.
The model names tell you the installation thread diameter,
heat range, reach, and shape. Car manufacturers select
appropriate spark plugs for the engine and vehicle type,
so use the specified spark plugs.
5. Heat Range
The heat that the electrode section of the spark plug
receives due to combustion is dispersed through the path in
the figure. The degree to which a spark plug disperses the
heat it receives is called its "heat range".
Spark plugs with a high degree of heat dispersion are called
high heat range (cold type) and those with a low degree of
heat dispersion are called low heat range (hot type).
This is largely determined by the temperature of the gas
inside the combustion chamber and the spark plug design.
6. Heat Range
Low heat range plugs have long insulator leg sections and the surface area affected by the flame and the gas
pocket capacity are large. Also, since the heat release path from the insulator nose to the housing is long, heat
dispersion is low and the temperature of the center electrode rises easily.
On the other hand, high heat range plugs have short insulator nose and the surface area affected by the flame
and the gas pocket capacity are small.
Pre- ignition
Temperature
Self cleaning
Temperature
7. Electrode Wear:
The electrode wears from the locations that discharge
easily with spark discharge, since the center electrode
reaches high temperatures, it oxidizes and wears.
The amount of electrode wear varies with electrode
material, strength, hardness.
In order to reduce the amount of this wear, nickel alloys, platinum, iridium, and other such materials are
used for the electrodes and service lives are also extended with fine electrodes. Also, the wear varies
with the engine type and usage conditions, but for normal nickel alloy plug, it is approximately in the
range of 0.10-0.15 mm for each 10,000 km driven.
8. Effect of Electrode Wear:
Rise in required voltage
The required voltage rises in proportion to the
distance driven. This rise in the required voltage
is large until the sharp section at the end of the
center electrode is worn round to some degree
(about 4,000 km). After that, the main factor is
the enlargement of the gap due to electrode wear
and the rise in the required voltage is smaller.
Misfiring
Failure due to sparks not discharging between the electrodes of the sparkplug this occurs when the volage
generated by the ignition coil is lower than the voltage required by the spark plug.
9. Sparkplug Materials:
Copper/Nickel Spark Plugs:
Sometimes referred to as "standard" or "normal", copper spark plugs actually
Copper/nickel spark plugs are lower in cost
Generally, have a shorter lifetime (30,000 – 60,000 km)
Performs well under high-compression or turbocharged conditions
Requires high voltage
10. Sparkplug Materials:
Platinum Spark Plugs:
A single platinum spark plug is similar to a copper/nickel spark plug, except that its ground electrode has a
platinum disc welded to the tip instead of only nickel alloy.
Expensive spark plugs.
Generally, have a long lifetime up to 150000 km
Easley overheat in some conditions.
Reduces carbon buildup
Hard material with low electrode wear rate
11. Sparkplug Materials:
DoublePlatinum Spark Plugs:
Double platinum spark plugs have platinum coating both the center and ground electrodes. This is more
efficient and longer-lasting which makes these plugs a great choice for a wasted spark ignition system,
which exerts more wear on both electrodes than do other ignition systems.
Expensive spark plugs.
Generally, have a long lifetime up to 150000 km
Improve engine power
Reduces carbon buildup
12. Sparkplug Materials:
IridiumSpark Plugs:
Iridium is said to be six times harder and eight times stronger than platinum with a 700° higher melting
point. Iridium spark plugs have extremely fine electrodes while retaining excellent wear characteristics.
The most expensive type of spark plugs.
Have a long lifetime
Improve engine power
Improve fuel efficiency
Requires less voltage
high corrosion resistance
13. Carbon Fouling:
The insulator foot section and electrode
covered with dried, soft black carbon.
section are
This is due to repeat short-distance driving (driving with the
engine cool), incorrect choking (overly rich air-fuel mixture),
injection timing delay, plug heat range too high.
Sparkplug Diagnosing:
14. Oil Fouling:
The insulator section and electrode section is black and lustrous with
wet oily deposits.
This is due to Oil leaking due to piston ring, cylinder, or valve guide
wear (occurs easily to new engines and engines that have just been
overhauled), high oil content in air-fuel mixture (2-stroke engines).
Lead Fouling:
The insulator leg section has yellow or yellowish-brown burnt on
deposits or is covered with a glossy surface.
This is due to use of bad fuel or fuel with much lead.
15. insulator directly above the
housing This occurs due to
electrical stress in the air near
the insulator. (This is not a
spark plug gas leak, for which
it is sometimes mistaken.)
Insulator breakage:
The Insulator cracked which happened due to spark plug
removed/installed incorrectly (spark plug turned too far with spark
plug wrench, excess tightening torque, or other inappropriate work).
16. Recommended Tightening Torque:
1) Use the correct wrench for the hex on the plug, and be careful not to damage the insulator.
2) When changing, make sure that the oil, on the outside of the plug does not enter the engine interior.
3) When putting plugs in, clean engine side of the flange
4) Make sure the plugs are vertical, and tighten them by hand until they cannot be tightened any further.
5) Then, use a plug wrench to tighten them accurately to the torque.
