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Why fuel injection reduces induction icing

Aviation Mechanic Powerplant (AMP) practice question 9 of 20 on Engine Fuel and Fuel Metering Systems. ACS element AM.III.I.K4 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA continuous-flow fuel-injection system has less danger of induction system icing than a carburetor system because

  1. Athe injector has no venturi of any kind
  2. Bfuel vaporizes in or near the cylinder
  3. Cfuel is heated before it is metered
Show the answer and explanation

Correct answer: B. fuel vaporizes in or near the cylinder

  • A — incorrect The injector airflow section does use a venturi to sense airflow; the venturi is not what is removed, and its presence is not what causes carburetor icing.
  • B — correct The handbook attributes the reduced icing risk to the temperature drop from fuel vaporization taking place in or near the cylinder rather than in the induction air passage.
  • C — incorrect Reciprocating engine injection systems do not heat the fuel before metering; fuel heaters are described for turbine engine fuel systems, not for continuous-flow injection.

BACKGROUND

The fuel-injection system has several advantages over a conventional carburetor system. There is less danger of induction system icing because the drop in temperature caused by fuel vaporization takes place in or near the cylinder instead of in the carburetor throat. Acceleration is improved because of the positive action of the injection system, and fuel distribution is better, which reduces the overheating of individual cylinders caused by uneven mixture. Fuel economy also improves, because a carbureted engine must run most cylinders richer than necessary so that the leanest cylinder still operates properly. In the Bendix continuous-flow arrangement, one air bleed discharge nozzle is located in each cylinder head with its outlet directed into the intake port.

STUDY TIP

Group the four standard advantages of injection together: less induction icing, better acceleration, better distribution, and better fuel economy. Each one traces back to fuel being delivered at the cylinder rather than upstream.

KEY POINTS

  • Fuel injection reduces induction icing because vaporization cooling happens in or near the cylinder.
  • Injection also improves acceleration, cylinder-to-cylinder distribution, and fuel economy.
  • One discharge nozzle per cylinder sprays into the intake port from the cylinder head.

SOURCES

  • amp-powerplant/ch02.txt "Fuel-Injection Systems"
  • amp-powerplant/ch02.txt "Fuel Discharge Nozzles"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.