Hydromechanical and Electric Turbine Engine Fuel Systems

Posted on February 13, 2020 Josh Parker Aircraft Component

Since the creation of the turbine engine, hydromechanical fuel controls have served on many engines, and remain in use to this day. Despite this, their popularity is dwindling due to the rise of electronic based control systems. To ensure proper flow of fuel to the engine, fuel controls systems have two sections: computing and metering. A standard hydromechanical fuel control lacks an electronic interface to assist in computing and metering fuel flow. Once an accurate determination of fuel flow has been made by the computing section, the metering section delivers fuel to the engine via cams and servo valves.

Operating procedures of hydromechanical fuel controls are particularly intricate, but fuel metering is still not as accurate as that of an electronic fuel control because electronic controls receive inputs with greater accuracy. It was common for early hydromechanical fuel systems to use hydromechanical control with an added electronic system to provide supplemental information and fine tune the metering. This configuration was the next step in the evolution of turbine engine fuel controls and became known as the hydromechanical/electronic fuel control.

This type of system generally uses a remote EEC power relay to adjust the fuel flow. The basic function of this fuel system is to pressurize fuel, meter fuel flow, and deliver atomized fuel to the combustion section of the engine. The engine fuel control system is comprised of five parts including:

1) The vane fuel pump assembly: a fixed displacement fuel pump that provides high pressure fuel to the engine control system.

2) The filter bypass valve: a valve in the fuel pump that allows fuel to bypass the fuel filter when the filter experiences an excessive pressure drop.

3) The hydromechanical fuel control: an assembly that provides the fuel metering function of the electronic fuel control unit.

4) The flow divider and drain valve assemble: funnels that provide fuel to the engine fuel nozzles.

5) The fuel manifold assembly: a matched set consisting of primary and secondary manifold as well as the fuel nozzle assemblies.

Each of these components has a crucial role within the fuel control system and the turbine engine as a whole. Whatever engine components you are in need of, Just NSN Parts is here to help.

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