Ignition process

Section 1: Stages of the Ignition Process

  • The ignition process begins with the intake stroke, where the intake valve opens, and the piston moves down, sucking in the air-fuel mixture into the cylinder.
  • The second stage is the compression stroke. Here, the piston moves upwards compressing the air-fuel mixture whilst all valves are closed.
  • Next is the ignition stage, where the spark plug ignites the compressed air-fuel mixture, causing an explosion. The force of this explosion pushes the piston down. This is also known as the power stroke.
  • Lastly, the exhaust stroke occurs. The exhaust valve opens to let the combustion gases exit the cylinder as the piston moves upwards again. Once the gases are expelled, the exhaust valve closes, ready for the next intake stroke.

Section 2: Purpose of Ignition Timing

  • Ignition timing refers to the point at which the spark plug fires during the compression stroke.
  • Advanced ignition timing means the spark plug fires earlier, making the power stroke start sooner. Delayed ignition timing means the spark plug fires later.
  • Correct ignition timing is essential for efficient operation. If ignition timing is off, it can lead to poor engine performance, increased emissions, and even engine damage.

Section 3: Components Involved in the Ignition Process

  • The spark plug is vital in igniting the air-fuel mixture.
  • The distributor controls the routing of high voltage from the ignition coil to the spark plugs in the correct firing order.
  • The ignition coil transforms the battery’s low voltage output to the high voltage needed to create an electric spark in the spark plugs.
  • The ignition switch usually operates in four modes: Off, Accessories, On, and Start. During the ‘Start’ mode, power is sent to the engine’s starter to crank the engine.

Section 4: Ignition Systems

  • There are mainly two types of ignition systems used in most cars today: Distributor Ignition System (DI) and Distributorless Ignition System (DIS).
  • A Distributor Ignition System uses a distributor to route high voltage from the coil to the spark plugs.
  • A Distributorless Ignition System sends the high voltage directly from the coil to the spark plugs without a distributor, reducing the chances of electrical losses and misfire.

Remember, understanding the ignition process and the components involved is integral for anyone studying spark ignition engine systems and operation.