Engine Fuel And Metering

Question 1

What are some of the sources used to heat the fuel in a turbine engine fuel system?

Answer 1

Bleed air and lubricating oil.

Question 2

What are the most common types of fuel metering systems used on small reciprocating engines?

Answer 2

Float carbs, pressure injection carbs and direct fuel injection.

Question 3

What function does the mixture control perform?

Answer 3

Controls fuel air mixture.

Question 4

What generally causes spark plug fouling?

Answer 4

Operating with excessively rich mixture at idle.

Question 5

What is the purpose of an accelerating system?

Answer 5

Provides immediate brief increase of fuel flow in venturi to enrich mixture.

Question 6

What is a carburetor economizer system?

Answer 6

Power enrichment system that provides richer mixture at high power settings where excess fuel aids engine cooling, functions as throttle setting above cruise power.

Question 7

When the mixture is placed in the idle cut off position a slight rise in RPM is noted prior to the engine decelerating what does this indicate?

Answer 7

Idle mixture is set correctly.

Question 8

Why should engine RPM be accelerated periodically when making carburetor adjustments?

Answer 8

To clear the engine.

Question 9

What maintains the fuel pressure in a pressure injection carburetor?

Answer 9

Engine driven fuel pump.

Question 10

What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cut off position?

Answer 10

Engine stops.

Question 11

How does an automatic mixture control AMC function?

Answer 11

Sealed brass bellows expand and contract with pressure and temperature changes adjusting the mixture accordingly.

Question 12

What are some of the advantages of fuel injection systems over carbureted systems?

Answer 12

Less induction icing, better acceleration, better fuel distribution, better fuel economy, reduced individual cylinder overheating.

Question 13

What purpose do turbine engine fuel control units serve?

Answer 13

Automatically meter fuel to engine.

Question 14

What are the two basic types of turbine engine fuel control units?

Answer 14

Hydromechanical and electronic.

Question 15

What are the engine variables detected by the fuel control unit?

Answer 15

Power lever position, engine RPM, compressor inlet temperature, compressor inlet pressure, compressor discharge pressure, burner pressure.

Question 16

What are the two major components of a supervisory electronics engine control?

Answer 16

Computer and fuel control.

Question 17

What are some of the advantages of a full authority digital engine control FADEC over a hydro-mechanical fuel control?

Answer 17

Better fuel economy, improved starts, requires no engine trimming, engine limit protection, constant idle speeds regardless of atmospheric conditions or bleed air requirements, fully modulates active clearance control and allows more repeatable engine transients.

Question 18

What do turbine engine fuel spray nozzles do?

Answer 18

Inject fuel into combustion area.

Question 19

What are the different engine indications used for trimming a turbine engine?

Answer 19

EPR or RPM depending on the engine.

Question 20

What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?

Answer 20

Specific gravity for fuel, idle RPM and maximum RPM or maximum EPR.

Question 21

What type of pump can vary the amount of fuel discharged regardless of speed?

Answer 21

Variable displacement pump.

Question 22

What is used to keep water sediment and foreign matter out of the carburetor?

Answer 22

Main fuel strainer.

Question 23

What is the purpose of a pressure relief valve in a constant displacement pump?

Answer 23

Returns excess fuel not required by engine to inlet side of pump.

Question 24

What type of engine driven fuel pump is widely used other than gear or piston pumps?

Answer 24

Rotary vane type.

Question 25

What function do fuel boost pumps perform?

Answer 25

Supply pressurized fuel to fuel pump, prevents vapor lock and cavitation.

Question 26

What is a commonly used type of fuel boost pump?

Answer 26

Centrifugal type.

Question 27

What causes vapor lock and why is it a concern?

Answer 27

Low fuel pressure, high fuel temperatures, excessive fuel turbulence which may block fuel flow resulting in engine failure.

Question 28

What function does the engine driven pump on a turbine engine perform?

Answer 28

Provides continuous supply of fuel at proper pressure while engine is running.

Question 29

Name the two categories of turbine engine pumps.

Answer 29

Constant and variable displacement.

Question 30

What category is a gear type pump classified in?

Answer 30

Constant displacement.

Question 31

When performing an external inspection of an engine driven fuel pump what should you look for?

Answer 31

Leaks and security of mounting.

Question 32

What is the purpose of a sheer section of the drive shaft in a dual element constant displacement pump?

Answer 32

If one of the elements seize, the other element continues the operation.

Question 33

Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?

Answer 33

Fuel filter, a fuel heater that consists of a heat exchanger using either engine oil or bleed air to warm the fuel.

Question 34

What is the purpose of a bypass valve and an engine fuel system micron filter?

Answer 34

Safety feature that allows fuel to flow to engine if filter becomes blocked.

Question 35

What is the purpose of a duplex fuel nozzle?

Answer 35

Discharges two spray patterns, spray pattern is wider during startup / acceleration and narrows when engine speed increases above idle.

Question 36

What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?

Answer 36

Pressurizing portion provides primary and secondary fuel flow to duplex nozzles and dump portion allows fuel to drain from manifolds after engine shut down.

Question 37

What purpose do fuel selector valves serve?

Answer 37

Allow tank and engine selection, provide a means for shutting off fuel flow.