Jeppesen Chapter 7 - Engine Fuel and Fuel Metering (37 items) Flashcards
Q2. What are most common types of fuel metering system’s used on small reciprocating engines?
A2. Float-type carburetors, pressure -injection carburetors, and direct fuel injection systems.
Q3. What function does the mixture control perform?
A3. Controls the fuel/air mixture.
Q4. What generally causes spark plug fouling?
A4. Operating the engine with an excessively rich mixture at idle.
Q5. What is the purpose of an accelerating system?
A5. It provides an immediate but brief increase in fuel flow in the Venturi to enrich the mixture.
Q6. What is the carburetor economizer system?
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.
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?
The idle mixture is set correctly.
Q8. Why should engine r.p.m. be accelerated periodically when making carburetor adjustments?
A8. To clear the engine.
Q9. What maintains the fuel pressure in a pressure-injection carburetor?
A9. An engine-driven fuel pump.
Q10. What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cut-off position?
A10. The engine stops.
Q11. How does an automatic mixture control (AMC) function?
A11. A sealed brass bellows connected to the fuel metering system, expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly.
Q12. What are some of the advantages of fuel injection systems over carburetor systems?
A12. Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy, reduced overheating of individual cylinders.
Q13. What purpose do turbine engine fuel control units serve?
A13. They automatically meter fuel fuel to the engine.
Q14. What are the two basic types of turbine engine fuel control units?
A14. Hydromechanical and electronic.
Q15. What are the engine variables detected by the fuel control unit?
A15. Power level position, engine r.p.m., compressor inlet temperature, compressor inlet pressure, compressor discharge pressure, burner pressure.
Q16. What are the two major components of a supervisory electronics engine control?
A16. The electronic control unit (computer), and the hydromechanical fuel control.
Q17. What are some of the advantages of a full-authority digital engine control (FADEC) over a Hydromechanical fuel control?
A17. 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;e engine transients.
Q18. What to turbine engine fuel spray nozzles do?
A18. They inject fuel into the combustion area.
Q19. What are the different engine indications used for trimming a turbine engine?
A19. Either EPR or r.p.m. is used depending on the particular engine.
Q20. What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?
A20. Specific gravity for fuel, idle r.p.m., and maximum r.p.m. (or maximum EPR).
Q21. What type of pump can vary the amount of fuel discharged regardless of speed?
A21. A variable displacement pump.
Q22. What is used to keep water, sediment, and foreign matter out of the carburetor?
A22. The main fuel strainer.
Q23. What is the purpose of a pressure relief valve in a constant displacement pump?
A23. It returns excess fuel that is not required by the engine to the inlet side of the pump.
Q24. What type of engine-driven fuel pump is widely used other than gear or piston pumps?
A24. A rotary vane type.
Q25. What function do fuel boost pumps perform?
A25. They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.
