Engine Fuel Systems

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Engine Fuel Systems

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航空

Engine Fuel Systems

Typical Oral Questions

1. What is the purpose of the bypass valve in an engine-driven fuel pump?

The bypass valve allows fuel to flow around the engine-driven pump for starting and for emergency operation if the engine-driven pump should fail.

2. On which side of the firewall is the engine fuel shutoff valve located?

The shutoff valve must be on the side of the firewall away from the engine.

3. What are three purposes for the boost pumps in an aircraft fuel system?

To provide fuel pressure for starting the engine, to pressurize the fuel lines to prevent vapor lock, and to transfer fuel from one tank to another.

4. What kind of boost pump is used in most aircraft fuel systems?

Electrically operated centrifugal pumps.

5. Where does an engine-driven fuel pump direct the excess fuel from its pressure relief valve?

Back to the inlet side of the pump.

6. What causes a vapor lock in an aircraft fuel system?

The fuel becomes hot enough that it boils. Vapors are released from the liquid fuel, and these vapors block the fuel lines so the liquid fuel cannot flow to the engine.

7. What is done in most aircraft fuel systems to prevent vapor lock?

Boost pumps in the fuel tank pressurize the fuel in the lines and force the fuel into the fuel metering system.

8. What is meant by a compensated relief valve in an engine-driven fuel pump?

A pressure relief valve that is acted upon by a diaphragm as well as a spring. Atmospheric pressure acting on the diaphragm varies the pump discharge pressure so that it will remain a given amount higher than the pressure of the air entering the carburetor.

9. What is the purpose of the pressurizing and dump valve in the fuel system for a turbine engine?

For normal engine operation, the pressurizing and dump valve acts as a flow divider, directing the fuel into the main or pilot manifold so it will be discharged from the proper orifice in the duplex fuel nozzle.

When the engine is shut down, the dump function of the valve dumps all of the fuel from the manifold.

10. What should be done to an aircraft reciprocating engine if it has been operated on turbine engine fuel?

All of the turbine fuel should be drained out and the system filled with the proper grade of aviation gasoline. The engine should be given a compression check, and all of the cylinders should be inspected with a borescope. The oil should be drained and the filters carefully examined. The engine should be given a complete run-up check.

11. What are the two basic types of turbine engine fuel?

Jet A and A-1, which are a special type of kerosine-base fuel. This is similar to military JP-5.

Jet B is a gasoline-base fuel similar to military JP-4.

12. Why do some turbine engine fuel systems incorporate a fuel heater?

The fuel heater keeps the fuel warm enough that any water that precipitates out of the fuel will not freeze on the filters.

13. What are two reasons Prist is used in turbine engine fuel?

Prist is an antifreeze agent that lowers the freezing point of any water that precipitates out of the fuel. It also acts as a biocidal agent that kills the microbial growth that forms scum in fuel tanks. This scum traps and holds water against the aluminum alloy in the fuel tanks and causes corrosion.

14. Why do some aircraft fuel filters have a built-in relief valve?

This relief valve will open and allow unfiltered fuel to flow to the fuel control device if the filter should become plugged with ice or other contaminants.

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Engine Fuel Systems