Spark plug construction

Spark plug construction

Spark plug is a device that generates electric spark to the combustion chamber of a spark-ignition engine to ignite the compresses air-fuel mixture. Spark plug should be strong and durable. Spark Plugs have the best thermal properties. The normal work of spark plug is providing by use next insulate materials: alumina (Al2O3), and a very hard ceramic material with high dielectric strength. There are used diverse materials for the produce of spark plugs: special nickel-based alloys and copper-core, silver, platinum, iridium, titanium.

Spark plugs

Spark plug construction

A – Construction of the spark plug; B – hot plug; C – cold plug; 1 – tip body;  2 – lead-out; 3 – contact spring; 4 – resistor; 5 – contact; 6 – check spring; 7 – central electrode rod; 8 – insulator; 9 – sealing powder; 10 – plug body; 11 – copper washer; 12 – copper asbestos washer; 13 – skirt; 14 – side electrode; 15 – center electrode; 16 – contact nut; 17 – insulator of plug; 18 – conductive glass sealant.

Spark plug construction

Spark plug consist of insulator 8 with central electrode 15 and body 10 with side electrode 14, connects to the mass. There is creating a spark between electrodes when the spark plug has a high voltage. This spark ignites the working mixture in the cylinder. There is the special thread on the spark plug to install in engine head. Thermal characteristic of spark plug depends by length of thermal insulator.

Spark plugs, which has a short thermal cone (length 7,5 mm) has name cold spark plugs.  These spark plugs are used on engines with high compression ratio and high temperature work.

Spark plugs with longer thermal cone (length 16 mm), has a more thermal out.  These spark plugs have named hot spark plugs.

Also you can hear the term «Incandescent number».  Incandescent number of spark plug is conditional value proportional to the average indicator pressure.

Electrode gap

Electrode gap is the shortest distance between the central and earth electrodes on the spark plug. The electrode gap should be optimum. It is important to have maintaining maximum precision of electrode gap. For example: if the electrode gap is very small this may cause misfiring, poor exhaust gas quality levels and noisy idling. If the electrode gap is very large, this may lead to misfiring.

seat sealing spark plug

The spark plug screwed into the cylinder head so that it provides gas-tight. There
are two different types of seal:
– Flat seat;
– Taper seat.

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