Unit III: Ignition System

Ignition System in Internal Combustion Engines

• An ignition system is a crucial component in internal combustion engines, responsible for initiating and controlling the combustion process.
• Its primary function is to generate a high-voltage spark at the right moment to ignite the air-fuel mixture within the engine's cylinders.

Components of an Ignition System

• Battery: Provides electrical power to the ignition system.
• Ignition Switch: Controls the ignition system's operation, allowing the driver to start and stop the engine.
• Ignition Coil: Converts low voltage from the battery into high voltage, which is necessary to create a spark at the spark plugs.
• Distributor (or Ignition Module): Distributes high voltage from the ignition coil to the correct cylinder's spark plug at the precise time.
• Spark Plugs: Devices that create a spark to ignite the air-fuel mixture.

Types of Ignition Systems

• Conventional (Mechanical) Ignition Systems: Older systems that use a mechanical distributor to control spark timing.
• Electronic Ignition Systems: Modern systems that use solid-state electronics and sensors to control ignition timing more precisely, improving efficiency and performance.

Importance of Ignition System

• The efficiency and reliability of an ignition system directly impact engine performance, fuel efficiency, and emissions.
• A well-maintained ignition system ensures smooth engine operation and optimum power output.

Battery Ignition System

• Consists of primary ignition circuit (low voltage), secondary ignition circuit (high voltage), ignition switch, contact breaker, capacitor, and spark plugs.
• The primary ignition circuit supplies low voltage to the ignition coil, which steps up the voltage to generate a high-voltage spark.

Magneto Ignition System

• Uses a magneto to generate electric current for producing spark.
• Main components include frame, permanent magnet, armature, soft iron field, rotor, primary and secondary winding, contact breaker, and condenser.

Ignition Timing

• Refers to the precise moment when the spark plugs fire in the cylinders of an internal combustion engine.
• Timing is crucial because it determines when the fuel-air mixture ignites, which directly affects engine performance, fuel efficiency, and emissions.

Factors Affecting Ignition Timing

• Engine speed, load, and fuel quality.
• Mechanical vs. electronic methods of adjusting ignition timing.
• Advance and retard timing to optimize engine performance.

Ignition Advance Mechanism

• Centrifugal Advance Mechanism:

  • Adjusts ignition timing based on engine speed.
  • Uses centrifugal weights and springs to rotate the distributor shaft and advance the spark timing.

• Vacuum Advance Mechanism:

  • Adjusts ignition timing based on engine load and vacuum pressure.
  • Uses a vacuum sensor to advance the spark timing when the engine is under load.### Ignition Timing

• The amount of advance in ignition timing is designed to compensate for the time it takes for combustion to complete at higher engine speeds, optimizing engine performance.

• Centrifugal advance mechanisms are mechanical and work without additional sensors or electronic controls, making them reliable and effective for adjusting ignition timing based on engine speed variations.

• Vacuum advance mechanisms are used in conjunction with centrifugal advance to optimize ignition timing based on engine load conditions.

• During light throttle or low-load conditions, vacuum advance mechanisms advance the timing to improve fuel efficiency and reduce emissions.

• Under heavy load or full throttle, vacuum advance mechanisms retard the timing to prevent knocking or pre-ignition.

Starting System

• The starting system is responsible for initiating the engine's operation from a stationary position.
• Components of the starting system include:
  • Battery: provides electrical energy to power the starting system
  • Starter Motor: an electric motor specifically designed for high torque output
  • Starter Solenoid: a relay switch that controls the high current needed to operate the starter motor
  • Ignition Switch: controls the flow of electrical power to the starter solenoid and other electrical systems
  • Starter Relay: controls the flow of current to the starter solenoid (in some vehicles)
  • Flywheel or Flex plate: toothed wheel attached to the engine's crankshaft
• Operation of the starting system involves:
  • Initiation: electrical power flows from the battery to the starter motor
  • Starter solenoid activation: the starter relay or ignition switch sends a signal to the starter solenoid
  • Starter motor engagement: the starter motor spins and its drive gear extends to engage with the flywheel or flex plate teeth
  • Cranking the engine: the starter motor cranks the engine by turning the flywheel or flex plate
  • Engine start: the engine fires and begins to run under its own power

Bendix Drive

• The Bendix drive is a type of starter drive mechanism commonly used in automobile starter motors.
• Its primary function is to engage the starter motor with the engine's flywheel ring gear to start the engine.
• The Bendix drive consists of a pinion gear mounted on an overrunning clutch mechanism.
• The pinion gear is typically a helical gear mounted on a shaft connected to the armature shaft of the starter motor.
• The overrunning clutch allows the pinion gear to spin freely in one direction and locks it in the opposite direction, engaging with the flywheel.
• The working process of the Bendix drive involves:
  • Starting process initiation: electrical current flows to the starter solenoid, which activates the starter motor
  • Pinion gear movement: the Bendix drive shaft rotates, moving the pinion gear towards the flywheel due to centrifugal force or a mechanical mechanism
  • Engagement with flywheel: the pinion gear engages with the flywheel ring gear, meshing with the teeth and transferring rotational motion from the starter motor to the engine's crankshaft
  • Engine starting: the engagement allows the starter motor to crank the engine
  • Automatic disengagement: once the engine starts running, the overrunning clutch mechanism allows the pinion gear to spin freely, disengaging it from the flywheel ring gear.