Electronic Ignition Components

• The ignition system is one of the most complex systems in an internal combustion engine. Monkey Business Images Ltd/Valueline/Getty Images

  The ignition system of an internal combustion engine solves two complex tasks. The first task is to deliver a brief spark to exactly the right point at exactly the right time--thousands of times a second. The second task is to deliver a spark that is thousands of volts from a 12-volt battery--thousands of times a second. Both of these issues are solved using only a few simple components.

What the Spark Does

• The spark plug is the final component in the ignition system--in other words, everything leads up to the spark plug. When the spark plug goes off it ignites the atomized gasoline mixture delivered by the carburetor to the cylinder. This spark is very brief but has thousands of volts. The part of the spark plug that is inside the cylinder has a carefully controlled gap. When a voltage of thousands of volts is delivered to one side of the gap a spark jumps across the gap to produce the explosion that drives the piston down. This is the first step in delivering power to the wheels of the vehicle.

Producing the Spark

• When a coil and a capacitor (some auto mechanics still use the old word--condenser--for these) are connected they set up a "resonance" if the values of the coil and capacitor are exactly right. Coils produce magnetic fields when current is applied. Capacitors store a charge temporarily. The coil builds up a magnetic field that collapses when the current abates; the collapsing magnet field produces a surge of current. The current is briefly stored on the capacitor and then it is sent back to the coil. As this process continues, the magnet field gets stronger and stronger. At exactly the right moment, a pair of contacts called the "points" separates and the final magnetic field collapses to produce a brief spark that has thousands of volts. These three components--the coil, the capacitor and the points--work together to turn 12 continuous volts into a brief spark with thousands of volts.

Distributing the Spark

• Newer cars use a solid state device to create a spark but on classic cars there is a mechanical device--driven by the engine--that rotates a wiper that sweeps over six or eight contacts (depending on whether the engine is a straight 6 or a V8). At the exact moment that the wiper of the distributor reaches a contact the spark is delivered from the coil and routed to the proper spark plug.