Ignition system

Ignition systems have changed over the past four or five decades.

• The ignition system provides the spark to ignite the air/fuel mixture, which facilitates combustion.
• The spark must occur at the correct moment to ensure complete combustion and smooth, economical running.
• It is the job of the ignition system is to provide a consistent spark precisely when needed.

• The conventional system (sometimes called the points ignition system) consists of battery, ignition switch, ignition coil, distributor, high tension leads, spark plugs.
• The spark plugs require a voltage of approximately 20,000 volts to ignite the air/fuel mixture and as the conventional vehicle electrical system uses a 6 or 12 volt battery this creates a problem. The ignition coil overcomes this problem by acting as a transformer.
• The battery supplies current to the ignition switch (12 volts usually).
• When the ignition switch is turned on, it supplies current to the positive or switch side of the coil. The coil has two circuits, the low tension or primary circuit and the high tension or secondary circuit. The current runs from the ignition switch through the coil primary windings to earth when the ignition contact points in the distributor are closed. This sets up a magnetic field in the coil.
• When the contact points open the current in the primary circuit stops flowing and the magnetic field collapses.
• This induces a high voltage in the secondary windings, which flows through the rotor and distributor cap, through the spark plug leads and into the spark plugs.
• The high voltage jumps the electrode gap in the spark plugs and creates the spark to ignite the air/fuel mixture.

• The distributor was the first thing to change with the advent of electronic ignition.
• A number of different devices now replace the points and condenser.
• They all do the same job as the points - they switch the current on and off at the coil - but they do this electronically.
• This arrangement is better than the old system because there are no contact points to wear out.
• The spark quality is better, which results in a more efficient and environmentally friendly engine.

• The ignition system has been further developed to take advantage of the latest computer technology.
• Most cars now do not have a distributor.
• The control unit or computer uses transistors to switch the current at the coil.
• Some vehicles do not have high-tension leads; they have a small coil sitting on the top of each spark plug, which is controlled by the computer.
• The big advantage of this system is that it allows for a more accurate control over spark timing and there are fewer moving parts, which means less wear and more reliability.