Fuel System and Fuel Measurement - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 65

Fig. 4.6 Fuel system of an fuel level gages

(in cockpit)

fuel supply
pressure gage
(in cockpit)

airplane

main
tank

auxillary
tank 1

auxillary
tank 2

tank
selector
valve
transfer
pump

submerged
boost
pump

defuel or
refuel valve

system
selector
valve

flowmeters or
fuel pressure
gages
(in cockpit)

engine
selector
valve

defuel or
refuel line filters

engine-driven
supply pumps

left
engine

right
engine

carburetor or
jet controls

Gear wheel or piston pumps are used for the high pressure circulation system. The
fuel regulator unit provides the flow that corresponds to the load. The fuel nozzles
distribute the fuel into the combustion chamber. Their number varies according to the
construction of the combustion chamber and the size of the jet engine [ 27 ].
The fuel is preheated downstream to the low pressure pump to prevent water
contained in the fuel from crystallizing into ice which could clog the filters and the
regulation valves. The main fuel filter stops particles bigger than 0.03 mm or
1.18 9 10 -3 inches [ 28 ].
Certain nozzles are used for the starting process and for the higher load ranges.
Double channel burners have a primary and a secondary fuel nozzle. The primary
nozzle delivers fuel during the start and the idle phases. Above these load ranges,
the secondary nozzle takes over the supply of fuel. The diameter of the droplets is
0.05-0.10 mm (1.96 9 10 -3 -3.94 9 10 -3 in). Primary and secondary nozzles
spray droplets into the combustion chamber with an intensive whirl [ 29 ].

4.2.2 Fuel Regulation

The regulator of a gas turbine has to provide the proper amount of fuel required
under any operating conditions and has to prevent thermal or mechanical overload.
Operations had to be simplified when flight engineers were excluded from the
cockpit, because there were more input signals to be controlled by two pilots. This
required computers to take over the monitoring function. Fuel management
became more complicated due to the permanent increase of requirements
regarding jet engines as a whole. The earlier hydro-mechanical regulators have