Jet Propulsion: Fuel

1. Jet Propulsion
Fuel

2. Recap
• What are the two basic classifications of
turbine engine lubrication systems?
• What are the two types of dry-sump
lubrication systems?
• Briefly Explain the difference between them.
• What are the three basic sub-systems?
• Briefly explain them?

3. What are the two basic classifications of
turbine engine lubrication systems?
• Wet-sump and Dry-sump
What are the two types of dry-sump lubrication
systems?
• Hot-tank system
• Cold-tank system

4. Briefly Explain the difference between them.
• In a Hot-tank system, the oil is cooled before
lubricating.
• In a Cold-tank system, the oil is cooled before
re-entering the tank

7. What are the three basic sub-systems?
• Pressure system
• Scavenge system
• Breather/Vent system
Briefly explain them?
• Pressure system – This is the pressurised oil being
pumped to the bearings.
• Scavenged system – This is the return oil after it has
done its lubricating.
• Breather/Vent system – This the steady airstream
which has come from the bearings. This has been
contaminated with lubrication oil during operation
and must be de-oiled with a component called de-oiler.

10. Fuel System
• The Fuel Distribution system supplies ice-free filtered
fuel at the pressure and flow rates necessary to meet
all engine operating requirements.
• The fuel distribution system permits fuel to flow from
the aircraft fuel tank through the engine fuel pump to
the fuel metering unit.
• The fuel control unit then supplies metered fuel to the
fuel injectors for combustion.
• Fuel not sent to the fuel control unit goes to the servo
fuel heater to supply servo fuel pressure for engine
component actuation.

12. The LP Stage
• The LP fuel pump has a one stage centrifugal
impeller with an axial inducer.
• It has sufficient capacity to supply the HP fuel
pump through all rates of HP pump output.
• The impeller/inducer is installed on a driveshaft
which is held in precision bearings. These
bearings are lubricated and kept cool with a flow
of fuel from downstream of the impeller/inducer.
• This flow of fuel is supplied through a flow
cleaned strainer. The aircraft supply goes into the
pump at the centre of the impeller.

13. • When the impeller/inducer is turned, the fuel is
caused to flow radially (because of centrifugal
force) and axially through the pump. This also
increases the speed of the flow.
• At the pump outlet the speed of the flow is
decreased which increases the fuel pressure.
• This increase in pressure is necessary to prevent
cavitation of/or a fumes blockage in the supply to
the HP fuel pump.
• The fuel then flows at this low pressure to the
fuel oil heat exchanger.

14. LOW PRESSURE PUMP
PUMP
IMPELLOR
PUMP
INPUT
DRIVE
LP
FUEL
IN

15. The HP Stage
• The HP fuel pump is a positive-displacement
spur-gear type pump. It has sufficient capacity to
supply the fuel control for all rates of metered
flow.
• Two spur gears are turned with a driveshaft
which is held in precision bearings. The same as
the LP stage.
• The driveshaft is installed to the LP pump
driveshaft and its related output shaft in the
external gearbox module. Therefore, the
mechanical power to turn the LP pump is
transmitted through the HP pump driveshaft.

16. • A dry area isolates the pumps from the external
gearbox module. Seals around the HP pump
driveshaft and the external gearbox output
shaft keep the area dry. A usually dry drain
connects the area to the power plant drains
system.
• Leakage from this drain gives a visual indication
that one of the shaft seals has become
defective.

17. • The LP supply goes into the open spaces
between the teeth of the adjacent spur gears.
• When the gears are turned, the fuel is caused
to flow between the teeth and the pump
housing. The rate of flow is in proportion to
the speed of the gears.
• At the pump outlet the speed of the flow is
decreased which increases the fuel pressure.
The fuel then flows at this high pressure to the
fuel control unit.

18. FLOW
OUT
‘SPUR’
GEARS
PUMP FLOW AND RESTRICTION TO FLOW IN
CONTROLLER CAUSES PRESSURE TO INCREASE
Flow
Controller
GEAR TYPE PUMP

19. Multi Plunger (Swash-plate) Pump
• A Positive variable displacement pump, which
means that flow is proportional to pump rpm
and camplate angle, and if the pump stops
rotating, the fuel flow stops as well.
• The pump consists of a rotating body which
has a number of pistons or plungers, typically
in jet engines 7 or 9 depending on the pump
size.

20. • Each plunger works the same as a bicycle
pump, when it extends it sucks fuel in; when it
is compressed, fuel is pushed out under
pressure.
• Each piston has a ‘slipper pad’ on a ball joint
which is in contact with the camplate, also
called a ‘swash-plate’. The camplate does not
rotate, but its angle can be changed by servo
pressure moving the servo piston.
• Pump flow can be changed at a fixed rpm by
changing the camplate angle, or by changing
the pump rpm at a constant camplate angle.

21. FUEL DRAWN IN
FUEL PUMPED OUT
MULTI PLUNGER (SWASH-PLATE) PUMP
MECHANICAL
INPUT DRIVE
‘SWASH’ PLATE SERVO (CONTROL) PRESSURESERVO PISTON
OPERATING
PISTON
FUEL DRAWN IN
FUEL PUMPED OUT
KIDNEY
PLATE
KIDNEY
PORT

22. Multistage Fuel Pump

23. Fuel-Oil Heat Exchanger
• Fuel flows directly
through the tubes
in the cooler, and
engine oil flows
around the tubes.
Heat from the oil
warms the fuel, and
the fuel cools the
oil.
Oil Inlet (Oil outlet not visible)
Flange for mounting on the fuel pump
Fuel in
Fuel out

24. FUEL/OIL HEAT EXCHANGER AND FUEL FILTER
FCOC PRESSURE
RELIEF VALVE
FUEL COOLED OIL
COOLER (FCOC)
LP FUEL
FILTER
FILTER
PRESSURE
RELIEF
VALVE
FUEL
TUBES
OIL BAFFLE
PLATES
COLD LP
FUEL IN
HOT LP
FUEL OUT
COOLED
OIL OUT
HOT OIL
IN
FILTER PAPER
ELEMENT

25. Fuel Control Unit
• The purpose of the fuel control is to maintain a
correct combustion zone air-to-fuel mixture ratio
of 15:1 by weight. This ratio represents weight of
combustor primary air to weight of fuel.
• All fuels require a certain proportion of air for
complete burning, but at rich or lean mixtures
the fuel will burn but not completely. The ideal
proportion for air and jet fuels is 15:1, and it is
called the Stoichometric (chemically correct)
mixture.

26. Spill Flow/Icing
• In some systems, the spill fuel flow can be used to help
prevent icing in the fuel system and tanks by passing it
through another control valve back to the fuel tanks.
• When the fuel has passed through the LP and HP
pumps and through the Fuel-oil heat exchanger, it is
heated to very high temperatures. In certain
conditions, this hot fuel can be returned to the tanks to
counter the cold temperatures flown in at high
altitude, particularly in passenger type aircraft.
• At certain flight phases, such as take off, the return to
tank flows are prevented. This is to ensure that faults
do not starve the engine at a critical stage of the flight.

27. Fuel Nozzles
• The end point of the turbine engine fuel
system is the fuel nozzles.
• In order for the liquid fuel to release its
energy, it must be vaporized so it will mix
with the air to form a combustible mixture.

28. Simplex Nozzle
• Fuel under pressure from the fuel control
forces the check valve off its seat and enters
the nozzle.
• This fuel then passes through a series of
tangential flutes, or grooves, and sprays out
through the single discharge orifice in very
tine droplets in a cone-shaped pattern.

29. Duplex Nozzle
• Two types of duplex nozzles are used on modern engines.
These are: single-line and dual-line nozzles
• Single-line duplex nozzles are supplied with fuel from the
fuel control through a single fuel line or manifold.
• These nozzles incorporate a flow divider valve that allows
the fuel to spray from a central orifice in a widespray
pattern for starting and idling.
• When the fuel control meters sufficient pressure to open
the flow divider,
fuel flows to the secondary orifice. The large volume of the
secondary fuel and the high pressure at which it leaves the
nozzle narrow the spray pattern and force the fuel farther
down the combustor

30. Housings for
flow divided
valve and
check valve
Flange for
attachment on
combustion
casing
Nozzle tube
2 spray nozzle tip
Fuel inlet
Simplex
Nozzle
Single-line Duplex Nozzle
Dual-line Duplex Fuel Nozzle