Engine Fuel and Fuel Metering 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?
It 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 setting where the excess fuel aid in engine cooling. This system functions as throttle setting above cruise power setting.
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?
The idle mixture is set correctly
What maintains the fuel pressure in a pressure injector carburetor?
An engine driven fuel pump
Why should engine rpm be accelerated periodically when making carburetor adjustments?
To clear the engine
What happens if the manual mixture control of a pressure injector carburetor is moved to the idle cut off position?
The engine stops
How does an automatic mixture control function?
A sealed brass bellows connected to the fuel metering system expands and contracts with the changes in pressure and temperature, adjusting the mixture accordingly
What are some of the advantages of fuel injection systems over carbureted systems?
Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy and reduced overheating of individual cylinders
What purpose do turbine engine fuel control units serve?
They automatically meter fuel to the engine
What are the two basic types of turbine engine fuel control units?
Hydro mechanical 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 and burner pressure
What are the two major components of a supervisory electronics engine control?
The electronic control unit computer and the hydro mechanical fuel control
What are some of the advantages of a full authority digital engine control over a hydro mechanical 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 engine 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 hydro mechanical 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 is widely used other than geared or piston pumps?
A rotary vane type
