Engine Fuel and Fuel Metering Systems

Powerplant (AMP) ASA Prepware Questions with ENGINE FUEL AND FUEL METERING SYSTEMS

Maximum power is normally considered to be developed in a reciprocating engine with a air-fuel mixture ratio of approximately

12:1

Fuel is discharged for idling speeds on a float-type carburetor

from the idle discharge nozzle.

An aircraft carburetor is equipped with a mixture control in order to prevent the mixture from becoming too

rich at high altitudes.

What is the possible cause of an engine running rich at full throttle if it is equipped with a float-type carburetor?

Clogged main air bleed.

The function of the altitude compensating, or aneroid valve used with the Teledyne-Continental fuel injection system on many turbocharged engines is to

prevent an overly rich mixture during sudden acceleration.

A punctured float in a float-type carburetor will cause the fuel level to

rise, and enrich the mixture.

A fuel strainer or filter must be located between the

tank outlet and the fuel metering device.

What corrective action should be taken when a carburetor is found to be leaking fuel from the discharge nozzle?

Replace the needle valve and seat.

If a float-type carburetor becomes flooded, the condition is most likely caused by

a leaking needle valve and seat assembly.

When troubleshooting an engine that will not idle, what would be a probable cause?

Economizer valve not operating correctly.

Fuel pump relief valves designed to compensate for atmospheric pressure variations are known as

balanced-type relief valves.

Kerosene is used as turbine engine fuel because

kerosene has more heat energy per gallon and lubricates fuel system components.

Select the correct statement concerning the idle system of a conventional float-type carburetor.

The low pressure between the edges of the throttle valve and the throttle body pulls the fuel from the idle passage.

What factor is not used in the operation of an aircraft gas turbine engine fuel control unit?

Mixture control position.

What precaution should be taken when putting thread lubricant on a tapered pipe plug in a carburetor float bowl?

Engage the first thread of the plug, then put a small amount of lubricant on the second thread and screw the plug in.

If the idling jet becomes clogged in a float-type carburetor, the

engine will not idle.

The purpose of the diaphragm in most vane-type fuel pumps is to

compensate fuel pressures to altitude changes.

The density of air is very important when mixing fuel and air to obtain a correct fuel-to-air ratio. Which of the following weighs the most?

100 parts dry air.

(Refer to Figure 7.) What is the purpose of the fuel transfer ejectors?

To assist in the transfer of fuel from the main tank to the boost pump sump.

To determine the float level in a float-type carburetor, a measurement is usually made from the top of the fuel in the float chamber to the

parting surface of the carburetor.

A major difference between the Teledyne-Continental and RSA (Precision Airmotive or Bendix) continuous flow fuel injection systems in fuel metering is that the

Continental system uses fuel pressure only as a metering force.

Which of the following best describes the function of an altitude mixture control?

Regulates the richness of the fuel / air charge entering the engine.

The use of less than normal throttle opening during starting will cause

a rich mixture.

Fuel pressure produced by the engine-driven fuel pump is adjusted by the

relief valve adjusting screw.

Generally, the practice when trimming an engine is to

turn all accessory bleed air off.

What is the final authority for the details of carburetor overhaul?

The manufacturer’s recommendations.

The economizer system of a float-type carburetor performs which of the following functions?

It supplies and regulates the additional fuel required for all engine speeds above cruising.

What is the purpose of the flow divider in a turbine engine duplex fuel nozzle?

Creates the primary and secondary fuel supplies.

What method is ordinarily used to make idle speed adjustments on a float-type carburetor?

An adjustable throttle stop or linkage.

When air passes through the venturi of a carburetor, what three changes occur?

Velocity increases, temperature decreases, and pressure decreases.

Prior to performing engine trimming, you should

obtain a true temperature reading comparable to that of the air that enters the engine.

Where physical separation of the fuel lines from electrical wiring or conduit is impracticable, locate the fuel line

below the wiring and clamp the line securely to the airframe structure.

What could cause a lean mixture and high cylinder head temperature at sea level or low altitudes?

Automatic mixture control stuck in the extended position.

An aircraft should be facing into the wind when trimming an engine. However, if the velocity of the wind blowing into the intake is excessive, it is likely to cause a

false high compression and turbine discharge pressure, and a subsequent low trim.

Most large aircraft reciprocating engines are equipped with which of the following types of engine-driven fuel pumps?

Rotary vane-type fuel pump.

The Federal Aviation Regulations require the fuel flow rate for gravity systems (main and reserve) to be

150 percent of the takeoff fuel consumption of the engine.

The fuel metering force of a conventional float-type carburetor in its normal operating range is the difference between the pressure acting on the discharge nozzle located within the venturi and the pressure

acting on the fuel in the float chamber.

What component is used to ensure fuel delivery during periods of rapid engine acceleration?

Acceleration pump.

What is the relationship between the accelerating pump and the enrichment valve in a pressure injection carburetor?

No relationship since they operate independently.

Which statement is correct regarding a continuous-flow fuel injection system used on many reciprocating engines?

Fuel is injected at each cylinder intake port.

Where is the engine fuel shutoff valve usually located?

Aft of the firewall.

A mixture ratio 11:1 normally refers to

1 part fuel to 11 parts air.

When trimming a turbine engine, the fuel control is adjusted to

set idle RPM and maximum speed or EPR.

A carburetor is prevented from leaning out during quick acceleration by the

accelerating system.

What carburetor component limits the maximum airflow into the engine at full throttle?

Venturi

How often should float carburetors be overhauled?

At engine overhaul.

The economizer system in a float-type carburetor

increases the fuel / air ratio at high power settings.

It is desirable that fuel lines have a gentle slope upward or downward and not have sharp curves or sharp rises and / or falls in order to

prevent vapor lock.

The fuel pump relief valve directs excess fuel to the

inlet side of the fuel pump.

What is the purpose of the carburetor accelerating system?

Temporarily enrich the mixture when the throttle is suddenly opened.

Under which of the following conditions will the trimming of a turbine engine be most accurate?

No wind and low moisture.

The desired engine idle speed and mixture setting

is adjusted with engine warmed up and operating.

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

To prevent a damaged or inoperative pump from blocking the fuel flow of another pump in series with it.

(1)A non-positive-displacement pump produces a continuous flow, but due to lack of a positive internal seal against slippage, its output will drop as pressure increases. (2) In a positive displacement pump, slippage is negligible compared to the pump’s volumetric output flow. If the output port were plugged, pressure would increase, and the pump pressure relief valve would open. Regarding the above statements

both number 1 and number 2 are true.

What are the principal advantages of the duplex fuel nozzle used in many turbine engines?

Provides better atomization and uniform flow pattern.

A nine-cylinder radial engine, using a multiple-point priming system with a central spider, will prime which cylinders?

1, 2, 3, 8, and 9.

During the operation of an aircraft engine, the pressure drop in the carburetor venturi depends primarily upon the

air velocity

An indication that the optimum idle mixture has been obtained occurs when the mixture control is moved to IDLE CUTOFF and manifold pressure

decreases and RPM increases momentarily before the engine ceases to fire.

Which of the following is least likely to occur during operation of an engine equipped with a direct cylinder fuel injection system?

Backfiring

A rotary-vane pump is best described as a

positive-displacement pump.

An aircraft engine equipped with a pressure-type carburetor is started with the

primer while the mixture control is positioned at IDLE CUTOFF.

If an aircraft engine is equipped with a carburetor that is not compensated for altitude and temperature variations, the air-fuel mixture will become

richer as either the altitude or temperature increases.

Which of the following best describes the function of an automatic mixture control (AMC)?

It compensates for change in the air density due to temperature and altitude.

(Refer to Figure 6.) Which curve most nearly represents an aircraft engine’s air-fuel ratio throughout its operating range?

2

What is the relationship between the pressure existing within the throat of a venturi and the velocity of the air passing through the venturi?

The pressure is inversely proportional to the velocity.

On an engine equipped with a pressure-type carburetor, fuel supply in the idling range is ensured by the inclusion in the carburetor of

a spring in the unmetered fuel chamberto supplement the action of normal metering forces.

Excessively rich or lean idle mixtures result in

incomplete combustion

What effect does high atmospheric humidity have on the operation of a jet engine?

Has little or no effect.

Why must a float-type carburetor supply a rich mixture during idle?

Because at idling speeds the engine may not have enough airflow around the cylinders to provide proper cooling.

One of the things a metering orifice in a main air bleed helps to accomplish (at a given altitude) in a carburetor is

better fuel vaporization and control of fuel discharge, especially at lower engine speeds.

The metered fuel pressure (chamber C) in an injection-type carburetor

is held constant throughout the entire engine operating range.

The back-suction mixture control system operates by

varying the pressure acting on the fuel in the float chamber.

If the volume of air passing through a carburetor venturi is reduced, the pressure at the venturi throat will

increase

An excessively lean air-fuel mixture may cause

an increase in cylinder head temperature.

During idle mixture adjustments, which of the following is normally observed to determine when the correct mixture has been achieved?

Changes in RPM or manifold pressure.

During engine operation, if carburetor heat is applied, it will

decrease the air density to the carburetor.

One of the best ways to increase engine power and control detonation and preignition is to

use water injection.

When an electric primer is used, fuel pressure is built up by the

booster pump.

What will occur if the vapor vent float in a pressure carburetor loses its buoyancy?

The amount of fuel returning to the fuel tank from the carburetor will be increased.

The fuel level within the float chamber of a properly adjusted float-type carburetor will be

slightly lower than the discharge nozzle outlet.

The primary purpose of the air bleed openings used with continuous flow fuel injector nozzles is to

aid in proper fuel vaporization.

Where is the throttle valve located on a float-type carburetor?

After the main discharge nozzle and venturi.

Which method is commonly used to adjust the level of a float in a float-type carburetor?

Add or remove shims under the needle-valve seat.

Which of the following turbine fuel filters has the greatest filtering action of any present day filter type?

Micron filter.

How will the mixture of an engine be affected if the bellows of the automatic mixture control (AMC) in a pressure carburetor ruptures while the engine is operating at altitude?

It will become richer.

When checking the idle mixture on a carburetor, the engine should be idling normally, then pull the mixture control toward the IDLE CUTOFF position. A correct idling mixture will be indicated by

an increase of 10 to 50 RPM before decreasing.

What are the positions of the pressurization valve and the dump valve in a jet engine fuel system when the engine is shut down?

Pressurization valve closed, dump valve open.

During what period does the fuel pump bypass valve open and remain open?

When the boost pump pressure is greater than fuel pump pressure.

Boost pumps in a fuel system

provide a positive flow of fuel to the engine pump.

Where is the main fuel strainer located in the aircraft fuel system?

At the lowest point in the fuel system.

What is a function of the idling air bleed in a float-type carburetor?

It aids in emulsifying / vaporizing the fuel at idle speeds.

For what primary purpose is a turbine engine fuel control unit trimmed?

To obtain maximum thrust output when desired.

Which of the following statements concerning a centrifugal-type fuel boost pump located in a fuel supply tank is NOT true?

The centrifugal-type pump is classified as a positive displacement pump.

Which of the following is NOT an input parameter for a turbine engine fuel control unit?

Ambient humidity.

Fuel lines are kept away from sources of heat, and sharp bends and steep rises are avoided to reduce the possibility of

vapor lock

If fuel is found running from the carburetor with the engine not running, the likely cause is that the

float needle valve is not seated properly.

What is a characteristic of a centrifugal-type fuel boost pump?

It separates air and vapor from the fuel.

In turbine engines that utilize a pressurization and dump valve, the dump portion of the valve

drains the engine manifold lines to prevent fuel boiling and subsequent deposits in the lines as a result of residual engine heat (at engine shutdown).

A fuel pressure relief valve is required on

engine-driven vane-type fuel pumps.

Which type of fuel control is used on most of today’s turbine engines?

Hydromechanical or electronic.