Chapter 7 Flashcards
What are some of the sources used to heat the fuel in a turbine engine fuel system?
Bleed air and engine lubricating oil.
What are the most common types of fuel metering systems used on small reciprocating engines?
Float-type carburetors, pressure-injection carburetors and direct fuel injection systems.
What function does the mixture control perform?
Controls the fuel/air mixture.
What generally causes spark plug fouling?
Operating the engine with an excessively rich mixture at idle.
What is the purpose of an accelerating system?
It provides an immediate but brief increase in fuel flow in the venturi to enrich the mixture.
What is a carburetor economizer system?
It is a power enrichment system that provides a richer mixture at high power settings, where the excess fuel aids in engine cooling. This system functions at throttle settings above cruise power settings.
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.
Why should engine R.P.M be accelerated peiodically when making carburetor adjustments?
To clear the engine.
What maintains the fuel pressure in a pressure-injection carburetor?
An engine driven fuel pump.
What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cutoff position?
The engine stops.
How does an automatic mixture control (AMC) function?
A sealed brass bellows connected to the fuel metering system, expands and contracts with changes in pressure and temperature, adjusting the mixture accordingly.
What are some of the advantages of fuel injection systems over carburetor systems?
Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy, reduced overheating of individual cylinders.
What purpose do turbine engines fuel control units serve?
They automatically meter fuel to the engine.
What are the two basic types of turbine engine fuel control units?
Hydromechanical and electronic.
What are the engine variables detected by the fuel control unit?
Power lever position, engine RPM, compressor inlet temperature, compressor inlet pressure, compressor discharge pressure, burner pressure.
What are the two major components of a supervisory electronics engine control?
The electronic control unit (computer), and the hydromechanical fuel control.
What are some of the advantages of a full authority digital engine control (FADEC) over a hydromechanical fuel control?
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.
What do turbine engines fuel spray nozzles do?
They inject fuel into the combustion area.
What are the different engine indications used for trimming a turbine engine?
Either EPR or RPM is used depending on the particular engine.
What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?
Specific gravity for fuel, idle RPM, and maximum RPM (or maximum EPR).
What type of pump can vary the amount of fuel discharged regardless of speed?
A variable displacement pump.
What is used to keep water, sediment, and foreign matter out of the carburetor?
The main fuel strainer.
What is the purpose of a pressure relief valve in a constant displacement pump?
It returns excess fuel that is not required by the engine to the inlet side of the pump.
What type of engine driven fuel pump is widely used other than gear or piston pumps?
A rotary vane type.
