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The purpose of the Ignition System is to create a high voltage electrical spark, much like a bolt of lightning, directed into the individual cylinders to ignite or burn the highly compressed air and fuel mixture inside the individual cylinders. As this air and fuel mixture burns, it creates a rapidly expanding gas that pushes against the top of the piston and provides rotational force called torque to the crankshaft.
The voltage can vary from 5,000 to 8,000 volts direct current (DC) per cylinder when the engine is idling, to over 40,000 volts per cylinder when the engine is working hard during acceleration. Many modern ignition systems are capable of 80,000 to 100,000 volts DC during periods of absolute peak output such as when a vehicle operator 'floors' the accelerator on a cold engine in cold weather.
There are two basic types of ignition systems.
- The Distributed Ignition System uses a single, centralized ignition coil.
- The Direct Ignition System uses several very powerful ignition coils, sometimes one per cylinder. This allows for more precise control over each individual cylinder firing. Each cylinder's firing can be finely tuned and timed in the actual firing order in real time while the engine operates. It creates a more powerful and responsive engine that burns cleaner.
Regardless of the type of ignition system utilized, the system is divided into two sections, the primary ignition system and the secondary ignition system.
The Primary Ignition System actually begins with the battery. When a vehicle is first started, it needs the 12 volts from the battery to begin the process of creating the spark that will eventually fire or 'ignite' the cylinders. The battery voltage is directed to the ignition coil by the operation of the ignition switch. Once the engine fires, the vehicle's charging system takes over and provides the electrical energy needed to sustain the operation of the ignition system.
Components of the Primary Ignition System are;
Mechanics Corner: More Technical Detail
Noise suppression is an important part of the primary ignition system. The ignition system produces radio frequency interference that, left unchecked, would cause so much buzzing in the audio speakers it would be impossible to listen to music inside a vehicle. To remedy this, noise suppression diodes, of various designs, are wired into the circuitry of the ignition system. These diodes electrically 'shock absorb' all the on-off switching and accompanying voltage spikes that are done by the ignition module to the ignition coil. These diodes also protect the sensitive semi-conductor circuits in the ignition module.
The operation of the alternator in the charging system produces an alternating current (AC) signal that can be transferred to the ignition system and will create a buzz in the audio speakers. To remedy this, there are additional diodes in the charging system that isolate it from the ignition system for the same purpose of voltage surge protection and noise suppression.