Knowledge about Spark Plug

Automobile spark plug electric part generating sparks to ignite an internal combustion engine.

Ceramic insulator: pottery support for the parts that conduct electricity.

Terminal: place where a current-conducting wire is attached.

Spline: hollow channel.

Resistance: device that controls the strength of the current.

Ground electrode: current device that unites the electrodes.

Spark plug gap: space separating the current conductors.

Center electrode: central current conductor.

Gasket: spot where two part join together.

Spark plug body: metal part of the spark plug.

Hex nut: hexagonal piece of metal used to screw in a spark plug.

PROBLEM
A typical spark plug requires 5000 to 25000 volts from the ignition coil before it will fire. The exact firing voltage depends on the plug gap (the wider the gap, the higher the voltage required) and the electrode condition (wear increase voltage requirements) and the operating temperature (a cold plug requires more voltage to fire than a hot one). The spark must occur to coincide with the piston position as it approaches top dead center on its compression stroke. If the spark occurs too soon (over advanced timing), cylinder pressures rise too quickly and peak too early in the cycle resulting in power loss. This can also cause "detonation" to occur. If the spark occurs too late, cylinder pressures peak too late in the cycle also resulting in a loss of power. The by- product of increased compression is the increase in cylinder temperatures. These high temperatures must be managed by suitable plug designs.

SPARK PLUG

HEAT RANGE

The "heat range" of a spark plug determines how hot the plug runs during normal operation. If the heat range is correctly matched to the engine application, the plug will run hot enough under normal driving conditions to burn off fouling deposits before they can cause problems. Likewise, the plug will not get too hot and become a source of ignition causing engine-damaging pre-ignition and detonation. If the heat range is too cool for the application, though, fouling deposits may build up faster than they are burned off. For this reason, always follow the vehicle manufacturer or plug supplier heat range recommendations when selecting a spark plug for a particular application. Two spark plugs may appear to be identical on the outside but have entirely different heat ranges.

There are situations, though, that may require a slightly hotter or colder plug than the one normally recommended. Switching to a slightly hotter plug can help reduce fouling in an older engine that uses oil, for an engine that spends a lot of time idling or is used for short trip stop-and-go driving. But a hotter plug should not be used unless an engine is experiencing a fouling problem because of the increased risk of pre-ignition and detonation. For performance applications (racing, or engines that are run under heavier than normal loads or at high rpm for sustained periods of time), switching to a slightly colder plug can minimize the risk of pre-ignition and detonation. Even so, a colder plug can increase the risk of fouling with extended idling and low speed operation.

Many of today's spark plugs have a very broad heat range because the plug manufacturer uses a copper core or platinum center electrode. Copper is an excellent conductor of heat, so the insulator can be designed to run hotter and burn off fouling deposits without it getting too hot under increased load to cause pre-ignition or detonation. A solid platinum center electrode will also carry heat away from the tip, but not if the electrode only has a platinum tip.

PERFORMANCE ENGINE

Modified engines like nitrous oxide injection, smaller-chambered and free-flowing cylinder heads, engines with high compression ratio or force induction usually necessitate changing plug types or heat ranges. Specific electrode/tip combinations, electrode materials and colder heat ranges to remove the heat can provide measurable gains in power. For example: running extreme boost (more than 18 psi), a big shot of nitrous (more than 100 hp) or high compression (more than 11:1) the cold plug must be selected and plug gaps should be adjusted smaller to ensure proper ignitability with a much denser air;/fuel mixture. The smaller gap withe stock ignition loses a little power but this can mitigate problems until you change to a better ignition coil.

For every 75 to 100 hp you add to your engine, you may go to the next colder step. A hotter heat range is not usually recommended except when severe oil or fuel fouling is occurring. The difference from one full heat range to the next is the ability to remove 70 degrees C to 100 degrees C from the combustion chamber.

COLD and HOT PLUG

A "hot plug" has longer porcelain insulator nose which exposes more surface area to dissipate heat more slowly. The plugs electrodes must stay hot enough to burn away and self-clean fouling carbon deposits. This keeps the plug temperature higher overall which is ideal for low speed and city driving conditions. However, a plug that is too "hot" can overheat, also causing power loss, detonation, pre-ignition and possible engine damage.

A "cold" plug can be identified by a shorter porcelain insulator nose that minimizes the amount of surface area exposed to the combustion gases therefore having a shorter path to conduct heat out of the electrode and out of the cylinder chamber quickly. For engines with increased cylinder pressures, higher temperatures and greater horsepower, switching to a slightly colder plug can minimize the risk of pre-ignition and detonation if the plug becomes too hot. However the spark plug must achieve its "self-cleaning" temperature where it can burn off fuel and carbon deposits.