Jeppesen Chapter 7 - Engine Fuel and Fuel Metering (37 items)

Question 1

Q1. What are some sources used to heat the fuel in a turbine engine fuel system?

Answer 1

A1. Bleed air and engine lubricating oil.

Question 2

Q3. What function does the mixture control perform?

Answer 2

A3. Controls the fuel/air mixture.

Question 3

Q4. What generally causes spark plug fouling?

Answer 3

A4. Operating the engine with an excessively rich mixture at idle.

Question 4

Q5. What is the purpose of an accelerating system?

Answer 4

A5. It provides an immediate but brief increase in fuel flow in the Venturi to enrich the mixture.

Question 5

Q6. What is the carburetor economizer system?

Answer 5

A6. It is a power enrichment system that provides a richer mixture at high power settings, where the excess fuel aids in engine cooling. The system functions at throttle settings above cruise power settings.

Question 6

Q7. When the mixture is placed in the idle-cutoff position, a slight rise in r.p.m. is noted prior to the engine decelerating. What does this indicate?

Answer 6

The idle mixture is set correctly.

Question 7

Q8. Why should engine r.p.m. be accelerated periodically when making carburetor adjustments?

Answer 7

A8. To clear the engine.

Question 8

Q9. What maintains the fuel pressure in a pressure-injection carburetor?

Answer 8

A9. An engine-driven fuel pump.

Question 9

Q10. What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cut-off position?

Answer 9

A10. The engine stops.

Question 10

Q11. How does an automatic mixture control (AMC) function?

Answer 10

A11. A sealed brass bellows connected to the fuel metering system, expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly.

Question 11

Q12. What are some of the advantages of fuel injection systems over carburetor systems?

Answer 11

A12. Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy, reduced overheating of individual cylinders.

Question 12

Q13. What purpose do turbine engine fuel control units serve?

Answer 12

A13. They automatically meter fuel to the engine.

Question 13

Q14. What are the two basic types of turbine engine fuel control units?

Answer 13

A14. Hydromechanical and electronic.

Question 14

Q15. What are the engine variables detected by the fuel control unit?

Answer 14

A15. Power level position, engine r.p.m., compressor inlet temperature, compressor inlet pressure, compressor discharge pressure, burner pressure.

Question 15

Q16. What are the two major components of a supervisory electronics engine control?

Answer 15

A16. The electronic control unit (computer), and the hydromechanical fuel control.

Question 16

Q17. What are some of the advantages of a full-authority digital engine control (FADEC) over a Hydromechanical fuel control?

Answer 16

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

Question 17

Q18. What do turbine engine fuel spray nozzles do?

Answer 17

A18. They inject fuel into the combustion area.

Question 18

Q19. What are the different engine indications used for trimming a turbine engine?

Answer 18

A19. Either EPR or r.p.m. is used depending on the particular engine.

Question 19

Q20. What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?

Answer 19

A20. Specific gravity for fuel, idle r.p.m., and maximum r.p.m. (or maximum EPR).

Question 20

Q21. What type of pump can vary the amount of fuel discharged regardless of speed?

Answer 20

A21. A variable displacement pump.

Question 21

Q22. What is used to keep water, sediment, and foreign matter out of the carburetor?

Answer 21

A22. The main fuel strainer.

Question 22

Q23. What is the purpose of a pressure relief valve in a constant displacement pump?

Answer 22

A23. It returns excess fuel that is not required by the engine to the inlet side of the pump.

Question 23

Q24. What type of engine-driven fuel pump is widely used other than gear or piston pumps?

Answer 23

A24. A rotary vane type.

Question 24

Q25. What function do fuel boost pumps perform?

Answer 24

A25. They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.

Question 25

Q26. What is a commonly used type of fuel boost pump?

Answer 25

A26. The centrifugal type.

Question 26

Q27. What causes vapor lock and why is it of concern?

Answer 26

A27. Vapor lock is caused by insufficient fuel pressure, high fuel temperatures and excessive fuel turbulence, which may completely block any fuel flow resulting in engine failure.

Question 27

Q28. What function does the engine-driven pump on a turbine engine perform?

Answer 27

A28. It provides a continuous supply of fuel at the proper pressure while the engine is running.

Question 28

Q29. Name the two categories of turbine engine pumps.

Answer 28

A29. Constant and Variable displacement.

Question 29

Q30. What category is a gear-type pump classified in?

Answer 29

A30. Constant Displacement

Question 30

Q31. When performing an external inspection of an engine-driven fuel pump, what should you look for?

Answer 30

A31. Leaks and security of mounting.

Question 31

Q32. What is the purpose of a shear section of the driveshaft in a dual element constant displacement pump?

Answer 31

A32. If one element seizes, a portion of the driveshaft seizes, allowing the other element to continue to operate.

Question 32

Q33. Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?

Answer 32

A33. The fuel filter is most susceptible to ice formation, so a fuel heater is used that consists of a heat exchanger using either engine oil or bleed air to warm the fuel.

Question 33

Q34. What is the purpose of a bypass valve in an engine fuel system micron filter?

Answer 33

A34. It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked.

Question 34

Q35. What is the purpose of a duplex fuel nozzle?

Answer 34

A35. A duplex fuel nozzle discharges two different spray patterns. The spray pattern is wider during start up and acceleration and narrows when engine speed increases above idle.

Question 35

Q36. What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?

Answer 35

A36. The pressurizing portion provides primary and secondary fuel flow to dual-line duplex fuel nozzles, and the dump portion allows fuel to drain from the manifolds after engine shutdown.

Question 36

Q37. What purpose do fuel selector valves serve?

Answer 36

A37. They allow tank and engine selection, and provide a means for shutting off fuel flow.

Question 37

Q2. What are most common types of fuel metering system’s used on small reciprocating engines?

Answer 37

A2. Float-type carburetors, pressure -injection carburetors, and direct fuel injection systems.