How Ignition System Works

The ignition system in a gasoline engine generates an electric spark to ignite the fuel-air mixture in the cylinders, which then produces the motive force for the engine. This system typically involves components like the ignition coil, distributor (or a coil-on-plug system), and spark plugs. The ignition system's primary function is to create a high-voltage spark at the precise moment needed to ignite the fuel-air mixture, ensuring efficient combustion and optimal engine performance.

1. Low Voltage and High Voltage: 

• The system starts with a low-voltage input from the car battery.

• This low voltage is then transformed into a high voltage (thousands of volts) by the ignition coil.

2. Ignition Coil: 

• The ignition coil is essentially a transformer, converting low-voltage electricity into a high-voltage spark.

• It consists of two coils: a primary winding that receives low voltage from the battery and a secondary winding that produces the high voltage.

3. Distributor (or Coil-on-Plug): 

• The distributor (or a coil-on-plug system) is responsible for delivering the high voltage from the coil to the correct spark plug at the right time for each cylinder. 

• In a traditional distributor, a rotating rotor arm directs the high voltage to the appropriate spark plug. 

• Coil-on-plug systems have individual ignition coils mounted directly on each spark plug, eliminating the need for a distributor. 

4. Spark Plugs:

• Spark plugs are the devices that create the spark to ignite the fuel-air mixture. 

• They are designed to withstand the high voltage and heat of the combustion process. 

5. Ignition Timing:

• The ignition system must fire the spark at the correct moment, known as the ignition timing. 

• This timing is crucial for efficient combustion and engine performance. 

• Distributors typically include mechanical and vacuum advance mechanisms to adjust the timing based on engine speed and load. 

• Electronic ignition systems use an engine control unit (ECU) to calculate and control the ignition timing. 

6. Primary and Secondary Circuits:

• The ignition system is often divided into two circuits: the primary and secondary. 

• The primary circuit carries the low-voltage current from the battery to the ignition coil. 

• The secondary circuit carries the high-voltage current from the coil to the spark plugs. 

7. Components and Functionality:

• Ignition switch: Controls the flow of power to the ignition system. 

• Breaker points (in older systems): A mechanical switch that interrupts the primary circuit to trigger the spark. 

• Electronic control module (ECU): In electronic ignition systems, the ECU controls the ignition timing and spark generation. 

• Ignition coil: Converts low-voltage to high-voltage. 

• Distributor (or coil-on-plug): Distributes the high voltage to the spark plugs. 

• Spark plugs: Create the spark to ignite the fuel-air mixture. 

• Reluctor ring and magnetic sensor: Used in electronic ignition systems to determine engine speed and position. 

Lesson Summary:

The ignition system in a gasoline engine is responsible for igniting the air-fuel mixture in the engine's combustion chambers. This system begins with a low-voltage current from the battery, which is transformed into a high-voltage current by the ignition coil—a step-up transformer. This high-voltage electricity is either sent through a distributor or directly via a coil-on-plug system to the appropriate spark plug, which then generates the spark needed for combustion.

The system is divided into two circuits:

• The primary circuit carries low voltage from the battery to the ignition coil.
  
  

• The secondary circuit carries the high-voltage output from the coil to the spark plug.
  
  

Ignition timing is a crucial factor, ensuring the spark occurs at the precise moment for maximum engine efficiency. Older systems use mechanical and vacuum advance mechanisms, while modern systems rely on electronic control modules (ECUs), magnetic sensors, and reluctor rings for accurate timing based on engine speed and load.

The ignition system's effectiveness directly impacts engine performance, fuel efficiency, and emissions, making it an essential topic for automotive technology students.