ASVAB · Vehicle Systems

What component ignites the air-fuel mixture in a gasoline engine?

Correct answer

The spark plug

  1. A The piston
  2. B The fuel injector
  3. C The muffler
  4. D The spark plug

Why this is the answer

The SPARK PLUG ignites the air-fuel mixture in a gasoline engine, creating the spark that causes combustion during the power stroke. ASVAB Auto Information tests ignition. The spark plug receives high voltage (from the ignition coil) and produces a spark across its gap, igniting the compressed air-fuel mixture. (DIESEL engines have no spark plugs — they ignite fuel by compression heat.) Other parts: FUEL INJECTOR (delivers fuel); PISTON (moves in the cylinder). Knowing the spark plug ignites the mixture in a gas engine is commonly tested.
Source: ASVAB Auto Information — Ignition System

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About this topic: Vehicle Systems

Vehicle systems questions ask how the major subsystems work together — fuel, ignition, cooling, lubrication, electrical, exhaust and drivetrain — and what symptom points to which system. You do not need mechanic-level depth, just the function of each part and the common failure signs. This is one of 9 Auto Information questions on vehicle systems, each with a full explanation on a single study page.

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