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Question

Difficulty: MediumFuel and Air Intake Systems

For complete combustion in a standard gasoline engine, what is the ideal stoichiometric air-to-fuel ratio by weight?

  1. A
    14.7 parts fuel to 1 part air
  2. B
    1 part fuel to 14.7 parts exhaust gas
  3. 14.7 parts air to 1 part fuelAnswer
  4. D
    1 part air to 1 part fuel

Answer

14.7 parts air to 1 part fuel
The chemically balanced (stoichiometric) ratio for gasoline is 14.7:1 by weight, meaning 14.7 parts of air are required to completely burn 1 part of fuel with minimal unburned hydrocarbons and optimal catalytic converter efficiency.

Step-by-Step Solution

1
Identify the chemical requirement for stoichiometric combustion in gasoline engines.
Stoichiometry is the chemically ideal ratio where all oxygen in the air and all fuel are consumed without excess of either.
Understanding the baseline air-fuel mixture is essential for diagnosing engine fuel metering.
2
Determine the mass proportion of air needed per unit of gasoline.
Gasoline requires approximately 14.7 units of air by mass for every 1 unit of fuel (14.7:1).
Air is much less dense than gasoline, requiring a significantly larger mass and volume of air to achieve complete combustion.

Key Concept

Stoichiometric Air-Fuel Ratio
Estimated Time:45s
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Topics

Fuel and Air Intake Systems

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