Workings Of Spark Plug
(Last Updated On: March 12, 2018)

A spark plug is one of the simplest and also one of the most important components in a vehicle. It’s only job is to create an electrical spark that will power up the engine. That spark is very small yet very powerful and is an essential in the combustion process within an engine’s cylinder. The spark which ignites the air/fuel mixture in the cylinder has very high voltage and the voltage is anywhere between 20,000 and 100,000 volts this figure will give you an idea of the power of the spark produced by such a simple component.

Thermal Performance Spark Plugs

We have to be clear on one thing that the spark plug is there in the engine to produce a spark and nothing else. The spark plug does not sustain the spark but it does help in transmitting the heat out of the cylinder. This ability, assisting of heat transmission out of the cylinder by the spark plug is determined by the ‘heat range’. This temperature of the firing end of the spark plug has to be just right. The temperature has to be high enough to prevent fouling and not low enough to cause pre-ignition. This phenomenon is referred by the manufacturers as thermal performance. Thermal performance has nothing to do with the energy passed on from the ignition system but it is just a heat range that allows for the spark plug to function in, thermally.

Cold Spark Plugs

Now onto cold spark plugs, these spark plugs have shorter heat flow path resulting in quick heat transfer. The insulator nose on these spark plugs is short and has a smaller surface area compared to thermal performance spark plugs these in return lead to less heat absorption.

The hot spark plugs have longer insulator nose and longer heat transfer path. This causes slower heat transfer out of the cylinder.

The main point to consider here is the heat range, this has to be spot on to create optimal thermal performance. The heat range that is not optimum will lead to performance issue and will affect the lifespan of the spark plug as well. The best range for the firing end of the spark plug is between 900 and 1,450 degrees anything less than that will cause carbon deposit issues and the spark plug will not live up to it’s lifespan and anything more will cause overheating issues.

Spark Plug Voltage Rise

The spark plug is connected to the ignition system via ignition coil which transfers the voltage required for the spark plug to produce a spark. That electricity flows through the coil and a voltage difference start to develop between the electrodes of the spark plug.

As we have discussed in other publications that spark plug and the piston have a gap in between in the cylinder which is the space for the air and fuel mixture to come in and act as a insulator so without the air/fuel mixture the spark cannot be generated, it will be useless without the air and fuel mixture present there.

The electricity from the coil coming in steadily increases the voltage and when the power hits the 20,000 volt mark a spark is produced by the firing end of the spark plug. This spark ignites the air and fuel mixture. The timing of the spark is synchronized with the air/fuel intake and when the spark is produced you will hear a clicking sound as well. If you are looking through into the cylinder somehow you will be able to see the spark if the conditions are dark enough.

The clicking sound is produced due to the production of spark and you can say that the spark is somewhat of a miniature form of lightning.

The spark produced between the gap of piston and spark plug creates a fireball at first and that expands into a small explosion which completes the process of combustion in the cylinder.

We hope you find this publication useful.

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