I - Engine Fuel and Fuel Metering Systems (Powerplant)

Gasoline and other liquid fuels do not burn at all unless they are mixed with what other element

Gasoline and other liquid fuels do not burn at all unless they are mixed with air

Where are the fuel spray nozzles located in a turbine engine

Located either externally or internally on the combustion chamber in such a way that fuel can be sprayed into the combustion area

Name the heat sources for the operation of fuel heaters used in turbine engines

Turbine engines use heat exchangers to heat the fuel and prevent the possibility of ice crystal formations. Fuel lines are routed through the fuel heater, which uses a heat source, either bleed air, or engine lubricating oil. If bleed air is used as a heat source it is called an air to liquid heat exchanger. When oil is used, it is a liquid to liquid heat exchanger.

What engine variables are sensed by a hydro mechanical fuel control

The fuel control senses power level position, rpm compressor inlet pressure temperature, burner pressure, or compressor discharge pressure, and EGT or TIT

In an electrical fuel control system, what are the two input components

Electrical and Fuel

What are the two most commonly used carburetors is small reciprocating engines

Float type carburetor, pressure type carburetor

What type of fuel control unit is used in a turbine engine

Both hydro mechanical and electronic fuel control units are in use today. However, the most common fuel control unit is the hydro mechanical type

What is meant by trimming a turbine engine

Adjusting the fuel control for the proper specific gravity of the fuel and for the proper idle and full throttle RPM

When should a turbine engine be trimmed

Whenever there is a loss in engine power, or the manufacturer specifies

What specifications are used to trim a turbine engine

The data plate on the engine typically contains the trimming specifications

What are the three types of fuel controls for turbine engines

Supervisory EEC (electronic engine control) , FADEC ( full authority digital electronic control) and Mechanical

What is a FADEC

A full authority digital electronic control. It is a high precision digital electronic fuel control that utilizes an electronic engine control and the flight management computer to measure the fuel nozzle that prevent over speed and over temp conditions. This is FADEC also sends info to indication systems for the aircraft crew

Does a turbine engine controlled by a FADEC require manual trimming

No FADEC is self trimming

What is the purpose of a mixture control in a float type carburetor

It is to control the fuel air mixture as air density changes with altitude changes.

What is the purpose of an accelerating system on a float type carburetor

When throttle is opened rapidly, the fuel air mixture will lean out momentarily. To overcome this tendency, a charge or fuel from the accelerating pump will temporarily enrich the mixture in the Venturi

Describe the purpose and operation of a Venturi

Venturi in a carburetor is an example of Bernoulli’s principle, which states “as the velocity of gas or liquid increases, the pressure decreases “ the Venturi performs three function. It proportions the fuel air mixture, lowers the pressure at the discharge nozzle, and limits airflow at full throttle. The principle operation of the carburetor depends on the differential between the atmospheric pressure, and the decreased pressure offered by the Venturi

What is the function of a metering jet

Purpose is to limit the fuel flow when the throttle valve is wide open. The main metering jet is placed in the fuel passage between the float chamber and the discharge nozzle

What is the fuel metering force in a float type carburetor

It is a differential pressure between the pressure in a float chamber and at the nozzle

What will be the result of using excessively rich idle mixtures

Excessively rich idle mixtures will cause carbon fouling of the spark plug

What is the purpose of the economized system in a float carburetor

Economizer is essentially a valve which is closed at throttle settings below 60 - 70 percent of rated power, but provides additional fuel for engine cooling to prevent detonation at higher throttle settings above 60 - 70

where does a pressure injection carburetor obtain fuel pressure

it obtains fuel pressure from the boost pump for starting and from the engine driven fuel pump for normal operations

what operates an automatic mixture control (AMC) on a pressure carburetor

the AMC contains sealed bellows that expand or contract with changes in atmospheric pressure. The movement of the bellow operates a tapered needle that controls the impact air pressure into the “A” chamber of the carburetor

In what position do you place the mixture control of a pressure injection carburetor to stop the engine

in the idle cutoff position

what rpm indication should result when the mixture control is placed in the idle cutoff position when the idle mixture is set correctly

there should be a slight increase in rpm, followed by a rapid drop of rpm to zero

what is the purpose of filling a pressure injection carburetor full of fuel and allowing it to soak for a period of about 8 hours prior to installation

to soften the diaphragms and make them as pliable as possible as they were when the carburetor was originally calibrated

what are three types of carburetor icing

throttle, impact, and fuel evaporation icing

what is the typical fuel pressure in a float type carburetor

3 to 5 psi

name some advantages of direct fuel injection systems over conventional carburetor systems

less danger of induction system icing, improved acceleration, fuel distribution, reduced overheating of individual cylinders, better fuel economy

what is the purpose of filters in a fuel system

to prevent foreign matter from entering the carburetor

why do carburetors in aircraft have a mixture control

because air density changes with altitude, which effects the air fuel mixture. mixture control provides a means to adjust for the correct mixture at different altitudes

what two items are adjusted when setting idling conditions on a float carburetor

throttle stop for idling rpm, idle mixture through idle needle valve

what is the purpose of a fuel selector valve

a means of shutting off fuel flow, cross feed for tank and engine selection and for fuel transfer

what should be looked for when inspecting an engine driven fuel pump

look for fuel leaks and security of mounting

what is the purpose of an engine driven fuel pump

the engine driven fuel pump always delivers a continuous supply of fuel at the proper pressure during engine operation

what type of fuel pump is generally used with large reciprocating engines

positive displacement rotary vane type pump

what happens to the excess fuel not required by the engine in a constant displacement pump

pressure relief valve opens, and the fuel is routed back to the inlet side of the pump

what is the most common type of fuel boost pump

the electrically driven centrifugal type pump

what are the functions of the boost pump

during starting supplies fuel, maintain pressure in the fuel lines to prevent from boiling off at altitude, and they are a backup if engine driven pump fails

what is the purpose of the bypass valve in the engine driven fuel pump

the bypass valve provides a path around the pump vanes for starting the engine, and to allow fuel to bypass the pump in case of a pump failure

what is the purpose of using boost pumps in a fuel system

keep the pressure on the suction side of the engine driven pump from becoming low enough to permit the fuel to boil when operating at high altitudes

what are the three general causes of vapor lock

low fuel pressure, high fuel temp, excessive fuel turbulence

turbine engine fuel pumps may be divided into what two distinct system categories

constant displacement and variable displacement

what category is a turbine engine driven gear type pump

constant displacement

what type of fuel pump can be made to vary the fuel flow at any speed

variable displacement pump

what part of a gas turbine engine fuel system is very susceptible to the formation of ice

the fuel filters

how is the engine fuel system protected from ice formation

fuel heaters

why is a micron filter provided with a bypass valve as necessary safety factor

small openings in this type of filter make it very susceptible for clogging

where are filters located

fuel pump, in line with the system; last chance filter screens are in fuel controls

can you use automotive gasoline in reciprocating engine in place of avgas

yes, if you have an ATC

what is the purpose of the pressurizing portion of a pressurizing dump valve

provide primary and secondary fuel flow to dual line duplex nozzles

what do the divided fuel flows of a turbine engine duplex fuel nozzle produce in the fuel

two spray patterns

what is stoichiometric ratio

15:1