Check your Auto Motor Ignition System
How Auto Motor Sparks are Produced
A petrol engine provides power to propel the car by burning a mixture of petrol and air in its cylinders. The ignition system provides the electric sparks that ignite the mixture.
Each cylinder has a spark-plug with two metal points called electrodes, which project into the combustion chamber. When electricity is fed to the spark-plug at a high enough voltage, current jumps across the gap between the electrodes in the form of a spark.
Spark ignition systems are basically the same on all modern cars.
The rest of the ignition system supplies electricity to the spark-plugs at a high enough voltage and at exactly the right moment in each cylinder.
Electricity will not easily jump the gap between the spark-plug’s electrodes. The further apart the electrodes are, the higher is the voltage needed to make a spark. But the spark must be ‘fat’ enough for effective petrol / air burning.
In order to meet tighter emission controls and give better fuel consumption, lean air / fuel mixtures are now used. These require a higher energy spark and a wider gap. Whereas most older vehicles had a gap of 0,6mm, it is now common to have gaps of 0,8mm or larger.
The voltage at the spark-plugs can be as high as 25 000 in later systems with the coil able to generate up to 60 000 volts.
A normal car battery delivers just over 12 volts; this voltage is boosted thousands of times by the coil. Once this increased voltage has been produced, it has to be delivered to each spark-plug at the correct moment in the 4-stroke cycle.
The distributor feeds electricity to each of the cylinders in turn, depending on the firing order. The contact-breaker also works with the coil in generating the necessary high voltage.
The Auto Motor Battery
Electricity is supplied by the battery to the ignition system, the starter motor, the lights, indicators and the rest of a car’s electrical equipment.
The battery is made up of a number of cells, each of just over 2 volts, connected by metal bars. Car batteries have either three or six cells, giving a nominal 6 or 12 volts.
Each cell consists of two sets of plates (the electrodes) in a solution of dilute sulphuric acid (the electrolyte). One electrode is made of lead dioxide and the other of spongy lead.
When the cell is functioning, the acid reacts with the plates, converting chemical energy into electrical energy. A positive charge is built up on the lead dioxide electrode and a negative charge on the other electrode.
Electric current, measured in amperes (amp.), flows from one pole of the battery through the car circuit, back to the battery and then through the electrolyte.
As the chemical reaction goes on, lead sulphate forms on the surface of both electrodes, and the sulphuric acid turns to water. When the surfaces of both plates have turned completely to lead sulphate, the battery is flat. Recharging the cell with an electric current restores the electrodes to their original condition and regenerates the sulphuric acid.
A battery eventually goes dead and cannot be recharged for a number of reasons: the plates become encrusted with sulphate, so that a charge cannot get through to them; they may disintegrate; a leakage between the cells may cause a short circuit.
The heaviest demand is made on a battery when the car is being started. Once the engine is running, the generator provides a flow of current to the battery to recharge it and keep it charged.
In most modern cars the negative terminal of the battery is earthed by connection to the chassis or bodywork.
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