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Question

Difficulty: MediumIgnition System

An automotive technician is troubleshooting an engine that cranks normally but will not start due to a lack of spark at the cylinders. Which of the following functions must the ignition system perform to produce the necessary spark across the spark plug gaps?

  1. A
    Direct alternating current from the alternator directly to the starter solenoid during cranking
  2. Transform low battery voltage into high secondary voltage through electromagnetic inductionAnswer
  3. C
    Discharge electrical current to ignite the cylinder when the piston reaches bottom dead center on the exhaust stroke
  4. D
    Increase the proportion of liquid fuel in the intake runner to reduce electrical resistance across the combustion chamber

Answer

Transform low battery voltage into high secondary voltage through electromagnetic induction
The correct response accurately states that the ignition system uses electromagnetic induction in the ignition coil to transform low primary battery voltage (12 volts) into high secondary voltage (typically 20,000 to 50,000 volts). This high voltage is essential to ionize the gap between the spark plug electrodes under high cylinder pressure.

Step-by-Step Solution

1
Identify the electrical potential needed to bridge a spark plug gap under cylinder compression
Recognize that ionizing the compressed air-fuel gap requires between 20,000 and 50,000 volts, far exceeding standard 12V automotive battery voltage.
Air and atomized fuel under high pressure act as electrical insulators that require high dielectric breakdown voltage.
2
Determine the operating principle of the ignition coil
The ignition coil functions as a step-up transformer, utilizing electromagnetic mutual induction between primary and secondary windings when primary current is interrupted.
Rapid collapse of the primary magnetic field induces high voltage in the secondary winding with many more turns of wire.
3
Match the core function to the correct system requirement
The primary requirement of the ignition system is transforming 12V battery power into high-voltage secondary pulses delivered at the proper timing.
Without this voltage step-up, no spark can jump the electrode gap to initiate combustion.

Key Concept

Ignition Coil Voltage Step-Up via Electromagnetic Induction
Estimated Time:1m 0s
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Topics

Ignition System

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