On a reciprocating engine, what is the injection carburetor that employs a closed feed system called?

• A. Mechanical-jet carburetor
• B. Electronic fuel injection system
• C. Open-feed carburetor
• D. Hydromechanical fuel control system

Answer: (D)

The injection system that uses a combination of hydraulic and mechanical sensing to meter fuel in a closed loop is the hydromechanical fuel control system. In this arrangement an engine-driven pump delivers pressurized fuel to a metering unit that responds to air flow and engine conditions through diaphragms and mechanical linkages. The metered fuel is then sent to the injectors, while excess fuel is recirculated back, keeping the metering pressure and flow inside a closed circuit. This closed feed design provides precise, stable fuel metering across operating conditions.

The other options describe different fuel delivery concepts. A mechanical-jet carburetor is a carburetor, not an injection system, and relies on jets for metering rather than a closed hydraulic loop. An open-feed carburetor is also a carburetor with no closed fuel circuit. An electronic fuel injection system uses electronic control rather than the hydromechanical metering that defines the closed-feed approach.