Fuel Metering Systems Oral (JEPP+ASA)

What is the purpose of using boost pumps in a fuel system?

-Supply fuel to a pressure carburetor during engine starting. -Incase of engine-driven pump failure. -Maintain pressure on vacuum side of main pump to prevent fuel from boiling at higher altitudes. (Answer from book indicates the main purpose is to maintain pressure so fuel doest boil at higher altitudes)

What are two basic types of fuel controls for aircraft turbine engines?

Hydropneumatic and electro-hydromechanical

In what position is the mixture control placed for starting an engine that is equipped with a pressure carburetor? (simple Qstn-format: Mixture Control placed for starting a Press. Carb?)

Idle Cutoff position. & The engine is started with fuel from the primer system

What is adjusted when the fuel control unit of a turbine engine is trimmed? (Engine Trimming)

Idle Speed. Maximum Thrust.

Does the fuel-air mixture provided by a float carburetor become richer or leaner as the aircraft goes up in altitude?

If the mixture is not adjusted, it will become richer as the aircraft gains in altitude

In which direction relative to the wind should a turbine-powered aircraft be positioned when the fuel control is being trimmed?

If wind is Below 10 MPH - Face anywhere. If wind is 10-25 MPH - Face into the wind Above 25 MPH DO NOT-TRIM.

In what position is the carburetor heat control placed when starting an aircraft engine?

In the Cold position

What are two purposes of the manifold valve (or flow divider) in the fuel injection system of a horizontally opposed aircraft engine?

It provides a constant discharge fuel pressure for idling, and it provides a positive shutoff for the fuel when the engine is shut down

What should be looked for when inspecting an engine-driven fuel pump?

Look for fuel leaks and security of mounting.

What are the three general causes of vapor lock?

Low fuel pressure. High fuel temperatures. Excessive fuel Surge.

Where is the fuel from a Continuous-Flow fuel injection system discharged?

Low pressure fuel, discharged through injector nozzles installed next to the intake valve.

Why must the diaphragms of a pressure carburetor be soaked before the carburetor is ready for flight?

Soaking the diaphragms of a pressure carburetor restores them to the condition of flexibility that they had when the carburetor was calibrated

What is the function of the derichment valve in a pressure carburetor used on an aircraft engine with an anti-detonation injection system?

The derichment valve automatically closes to lean the fuel-air mixture when ADI fluid is flowing As soon as the ADI fluid stops flowing, the derichment valve opens and the mixture returns to its rich condition

What is the function of the economizer system in an aircraft engine carburetor? (Power Enrichment)

The economizer (or power enrichment) system allows the engine to operate with an economically lean mixture. Under FULL THROTTLE condition the Economizer permits fuel Enrichment.

What is the most common type of fuel boost pump?

The electrically driven centrifugal-type pump

What is the purpose of an engine-driven fuel pump?

The engine-driven fuel pump must deliver a continuous supply of fuel at the proper pressure at all times during engine operation.

What is controlled by the adjustment of the orifice in the fuel pump of a Teledyne-Continental fuel injection system?

The high unmetered fuel pressure

Does the fuel-air mixture provided by a float carburetor become richer or leaner when carburetor heat is applied?

The mixture becomes richer when carburetor heat is applied

What would happen to the fuel-air mixture ratio in a float carburetor if the main air bleed were to become plugged?

The mixture would become excessively rich

What happens to the excess fuel not required by the engine in a constant displacement pump?

The pressure relief valve opens and the fuel is routed back to the inlet side of the pump.

What two things are adjusted when adjusting the idling of a reciprocating engine?

The throttle stop, to get the proper idling RPM. The idle mixture control screw, to get the smoothest operation

What is the significance of the letters that are stamped on the flats of a fuel injection nozzle?

These letters designate the relative size of the orifice in the injector nozzle The lower the letter in the alphabet, the smaller the amount of fuel the nozzle will flow

What is the purpose of strainers in a fuel system?

They are used to prevent foreign matter from entering the carburetor.

What is the purpose of fuel selector valves?

They provide a means of shutting off fuel flow, for tank and engine selection, for crossfeed, and for fuel transfer.

Where does the fuel metering system of a turbine engine discharge its fuel?

Through Spray Nozzle into Combustion Chamber.

What is the function of a float carburetor?

To measure airflow through the induction system and dispense vaporized fuel in the correct ratio. (Better Answer) (Original Answ: The float carburetor's function is to measure airflow through the engine induction system and dispense the appropriate amount of gasoline into the airflow for all engine operating perimeters and conditions It must also provide the fuel in a state that is as vaporized as possible by the time ignition occurs in the engine cylinders)

When does the acceleration system operate on an aircraft carburetor?

When the throttle is suddenly opened

How does the mixture control change the fuel-air mixture ratio on the Teledyne-Continental fuel injection system?

While in Full Rich position, all fuel goes to the manifold valve. When it is in the Idle Cutoff position, all fuel is returned to the pump inlet. Intermediate positions vary the amount of fuel that goes to the engine

What type fuel pump can be made to vary the fuel flow at any speed?

A Variable Displacement pump (Also referred to as : Centrifugal Pump/Centrifugal Boost Pump or Non-Displacement Pump) (This is also the pump that keeps a positive fuel pressure on the main pump)

What type of fuel pump is generally used with large reciprocating engines?

A positive-displacement rotary vane-type pump

How does the exhaust gas temperature of a reciprocating engine tell anything about the fuel-air mixture being burned by the engine?

A stoichiometric mixture (a mixture in which all of the constituents of the fuel-air mixture are burned) produces the highest exhaust gas temperature The mixture is adjusted to get the highest EGT, and then it is enriched to place it on the rich side of stoichiometric

How does the automatic mixture control in a pressure carburetor keep the fuel-air mixture constant as the aircraft changes altitude?

Automatically through bellows, a needle sits on the orifice and restricts the air force. This leans the mixture as the aircraft goes up in altitude.

Why is a micron fuel filter provided with a bypass valve as a necessary safety factor?

Because the small openings in this type filter make it very susceptible to clogging.

Why is an aircraft reciprocating engine killed by Placing the mixture control in the Cutoff position, rather than by using the magneto switch?

By shutting off the fuel to the cylinders, the combustion chambers are left full of air with no fuel This makes the engine less likely to fire if the propeller is pulled through with the ignition switch accidentally on

What are two locations water may be injected into a turbine engine?

Compressor Inlet. Diffuser Inlet.

What category is a turbine engine-driven gear-type pump?

Constant displacement

Turbine engine fuel pumps may be divided into what two distinct systems categories?

Constant displacement (Positive Displacement) & Variable displacement (Centrifugal Boost Pump)

What is meant by a duplex nozzle in a turbine engine fuel metering system?

Duplex nozzle has two ports of discharge, primary and secondary. The fuel is discharged at low pressure, when demand rises the second port opens. (There are two Duplex Nozzle systems: Single Line and Dual Line. Single Line syst. is fed from one fuel line. Dual Line has two lines that feed the nozzle and operate based on demand from the system)

What engine parameters are sensed by the fuel control unit of a turbine engine?

Engine RPM, inlet air pressure, compressor dis-charge pressure, burner can pressure, and inlet air temperature

What part of a gas turbine engine fuel system is very susceptible to the formation of ice?

Fuel Filter

How is the engine fuel system protected from ice formation?

Fuel Heaters and Anti-Ice additive.

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

The bypass valve provides a path around the pump vanes for starting the engine and to allow fuel to bypass the pump in case of pump failure.