Spark and Ignition (2)

Spark and Ignition (2)

 

Imagine a electric wire with 220 Volt electricity flowing it. Now, assume you cut it some point of the wire and keep the gap around 1 mm, then of course the current stops to flow and connected electric devices stop working. The reason that the current stops is the electric resistance of air is much higher than those of copper wire. Then how can we overcome this resistance ? The easiest way is to connect the copper wire again to remove the air gap between the wire and the second possible way is to increase the voltage implied in the wire. If you increase the voltage more and more, one you can have a quick one time flow of the current with a form of spark. The same way is used to make spark ignition in the gasoline engine combustion chamber.

 

Then, how high the voltage should be to get a proper amount of energy to initiate the burning of air-fuel mixture ? In the air, we need 2,000 volts to 3,000 volts to get a spark with the gap of 1 mm distance. (Based on the air conditions, such as, humidity, air density, etc., the required voltage can be different.) When the boundary conditions change from normal atmosphere condition to those of combustion chamber, the required voltage will be much higher, because the air has been already pressurized by piston movement and air density is much higher than those of normal air condition. Normally the required voltage inside combustion chamber can reach 20,000 volts to 30,000 volts to get a spark between the two poles of spark plug.

 

 

It is understandable that if we think the spark as an acceleration of charge. To accelerate a charge in the higher density of air, we need to supply more energy. The energy of this electric spark gives the energy which is required for ignition of air-fuel mixture inside combustion chamber. The where in a vehicle can we find a device which generates that much high voltage like 20,000 – 30,000 volts ? We have only 12 Volt battery to turn start motor in our car, what other device can make and supply this high voltage of electricity ?

 

To be continued at part (3)

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