Engine Fuel and Fuel Metering System

Float-type carburetors which are equipped with economizers are normally set for

their leanest practical mixture delivery at cruising speeds and enriched by means of the economizer system at higher power settings.

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

Add or remove shims under the needle-valve seat.

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

set idle RPM and maximum speed or EPR.

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

No wind and low moisture.

What is the purpose of the carburetor accelerating system?

Temporarily enrich mixture when the throttle is suddenly opened.

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

a rich mixture.

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

from the idle discharge nozzle.

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

It supplies and regulated the addition fuel required for all engine speeds above cruising.

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.

A rotary-vane pump is best described as a

positive-displacement pump.

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

The pressure is inversely proportional to the velocity.

(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.

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

Venturi.

Excessively rich or lean idle mixtures result in

incomplete combustion.

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.

(1) A nonpositive-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.

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

increase.

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

After the main discharge nozzle and venturi.

In a supervisory EEC system, any fault in the EEC that adversely affects engine operation

causes an immediate reversion to control by the hydromechanical fuel control unit.

An aircraft engine continuous cylinder fuel injection system normally discharges fuel during which stroke(s)?

All (continuously).

If an engine equipped with a float-type carburetor backfires or misses when the throttle is advanced, likely causes is that the

accelerating pump is not operating properly.

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

is held constant throughout the entire engine operating range.

The device that controls the volume of the air-fuel mixture to the cylinders is called a

throttle valve.

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 e increased.

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

Automatic mixture control suck in the extended position.

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

The manufacturer's recommendations.

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

vapor lock.

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.

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

Acceleration pump.

Boost pumps in a fuel system

provide a positive flow of fuel to the engine pump.

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

Replace the needle valve and seat.

Which type of pump is commonly used as a fuel pump on reciprocating engines?

Vane.

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

slightly lower than the discharge nozzle outlet.

Reciprocating engine power will be decreased at all altitudes if the

humidity is increased.

What occurs when a back suction type mixture control is placed in IDLE CUTOFF?

The float chamber will be vented to a negative pressure area.

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

Backfiring.

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

accelerating system.

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

rise, and enrich the mixture.

Kerosene is used as turbine engine fuel because

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

Which statement is true regarding proper throttle rigging of an airplane?

The throttle stop on the carburetor must be contacted before the stop in the cockpit.

The fuel pump relief valve directs excess fuel to the

inlet side of the fuel pump.

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

primer while the mixture control is positioned at IDLE CUTOFF.

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.

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

use water injection.

The back-suction mixture control system operates by

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

The purpose of the back-suction mixture control in a float-type carburetor is to adjust the mixture by

regulating the pressure on the fuel in the float chamber.

How often should float carburetors be overhauled?

At engine overhaul.

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.

Fuel crossfeed systems are used in aircraft to

maintain aircraft stability.

Prior to performing engine trimming, you should

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

A mixture ratio of 11:1 normally refers to

1 part fuel to 11 parts air.

On a carburetor without an automatic mixture control as you ascend to altitude, the mixture will

be enriched.

Generally, the practice when trimming an engine is to

turn all accessory bleed air off.

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

2

Fuel boost pumps are operated

to provide a positive flow of fuel to the engine.

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

No relationship since they operate independently.

At what engine speed does the main metering jet actually function as a metering jet in a float-type carburetor?

All RPM's above idle range.

Under which of the following conditions would an engine run lean even though there is a normal amount of fuel present?

Incomplete fuel vaporization.

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.

Detonation occurs when the air-fuel mixture

burns too fast.

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.

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

booster pump.

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

To obtain maximum thrust output when desired.

The throttle valve of float-type aircraft carburetors is located

between the venturi and the engine.

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

An adjustable throttle stop or linkage.

It is necessary to control acceleration and deceleration rates in turbine engines in order to

prevent blowout or die-out.

Which of the following causes a single diaphragm accelerator pump to discharge fuel?

An increase in manifold pressure that occurs when the throttle valve is opened.

Where is the engine fuel shutoff valve usually located?

Aft of the firewall.

A fuel pressure relief valve is required on

engine-driven vane-type fuel pumps.

The desired engine idle speed and mixture setting

is adjustable with engine warmed up and operating.

Which of the following is NOT a function of the carburetor venturi?

Regulates the idle system.

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.

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

150 percent of the takeoff fuel consumptions of the engine.

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.

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

Has little or no effect.

What should be checked/changed to ensure the validity of a turbine engine performance check if an alternate fuel is to be used?

Fuel specific gravity setting.

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.

In turbine engines that utilize a pressurization an 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 engines shutdown) .

What causes the fuel divider valve to open in a turbine engine duplex fuel nozzle?

Fuel pressure.

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.

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

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

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

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

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

Velocity increases, temperature decreases, and pressure decreases.

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

At the lowest point in the fuel system.

A fuel strainer or filter must be located between the

tank outlet and the fuel metering device.

The economizer system in a float-type carburetor

increases the fuel/air ratio at high power settings.

When a new carburetor is installed on an engine,

and the engine is warmed up to normal temperatures, adjust the idle mixture, then the idle speed.

The primary condition(s) that allow(s) microorganism to grow in the fuel in aircraft fuel tanks is (are)

the presence of water.

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

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

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

Rotary vane-type fuel pump.

A full-authority electronic engine control (EEC) is a system that receives all necessary data for engine operation and

develops the commands to various actuators to control engine parameters.

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

relief valve adjusting screw.

If an engine is equipped with a float-type carburetor and the engine runs excessively rich at full throttle, a possible cause of the trouble is clogged

main air bleed.

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

engine will not idle.

(1) The mixture used at rated power in air cooled reciprocating engines is richer than the mixture used through the normal cruising range.

(2) The mixture used at idle in air cooled reciprocating engines is richer than the mixture used at rated power.

Regarding the above statements,

both 1 and 2 are true.

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

Hydromechanical or electronic

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

air velocity.

An excessively lean air-fuel mixture may cause

an increase in cylinder head temperature.

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 cylinder to provide proper cooling.