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Difficulty: MediumIgnition System

A technician is tracing the pathway of electrical energy in a conventional distributor-based ignition system. In what chronological sequence does electrical energy travel from the low-voltage source to ignite the cylinder's air-fuel mixture?

  1. 112-volt battery current flows through the ignition switch and coil primary winding to establish a magnetic field.
  2. 2The primary circuit switch opens, suddenly halting current flow and causing the magnetic field to collapse rapidly.
  3. 3The collapsing magnetic field induces a high-voltage surge in the secondary winding that travels to the distributor cap.
  4. 4The distributor rotor directs the high-voltage pulse through a spark plug wire to jump the spark plug electrode gap.

Answer

The correct chronological sequence is: (1) 12-volt battery current flows through the primary winding to build a magnetic field, (2) The primary circuit switch opens to collapse the magnetic field, (3) High voltage is induced in the secondary winding and travels to the distributor cap, and (4) The distributor rotor directs the high voltage across the spark plug wire to fire the spark plug.
In a conventional distributor ignition system, low-voltage current from the battery first energizes the primary coil windings to build a magnetic field. When the switching mechanism opens, the current stops and the magnetic field collapses instantly. This rapid collapse induces tens of thousands of volts in the secondary coil windings. The high-voltage surge enters the distributor cap, where the rotating rotor directs it to the correct spark plug wire, jumping the spark plug gap to ignite the compressed air-fuel mixture.

Step-by-Step Solution

1
Identify the primary circuit energizing stage.
Low-voltage current from the battery flows through the primary coil winding, creating a strong magnetic field around the iron core.
An ignition coil must store electrical energy in a magnetic field before it can be stepped up to firing voltage.
2
Identify the triggering event that releases stored magnetic energy.
The contact points or switching transistor opens the circuit, abruptly interrupting primary current flow.
High-voltage induction requires a rapid rate of change in the magnetic lines of force.
3
Trace the step-up voltage transformation in the secondary circuit.
The collapsing magnetic lines cut through the secondary winding, inducing a surge of 20,000 to 50,000 volts that exits through the coil tower.
The high ratio of secondary turns to primary turns steps up the collapsing field energy into high voltage.
4
Trace the mechanical distribution to the combustion chamber.
The distributor rotor turns toward the cylinder's cap terminal, routing the surge through the plug wire to spark across the electrode gap.
The distributor mechanically times and directs the high voltage to the cylinder ready for combustion.

Key Concept

Ignition coil primary magnetic saturation, field collapse induction, and high-voltage distributor delivery
Estimated Time:1m 0s
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Topics

Ignition System

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