Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
ATA 73 – ENGINE FUEL AND CONTROL 0
TABLE OF CONTENTS 1 1.1 1.2 1.3 1.4 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3 3.1 3.2 3.3 3.4 3.5 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 5.6
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Fuel system Purpose Fuel system components Fuel additives and limitations Input requirement Fuel pump Purpose Description Typical pump capacity @ 100% N2 Inlet filter Outlet filter Filter bypass valve Maintenance FCU (hydraulic section) Purpose High pressure relief valve Metering valve Bypass valve Motive flow valve FCU (pneumatic section) Purpose Bellows Governor Enrichment valve Back-up valve T2 temperature compensation sensor Step modulator (JT15D-1 and 4 series) Flight idle solenoid (JT15D-5 series) Operation Flow divider Purpose Fuel shut-off and wind milling bypass valve Minimum pressurising and flow divider valve Spill valve Dump valve Operation
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 6 6.1 6.2 6.3 6.4 7 7.1 7.2 7.3 7.4
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Automatic shut-off valve Purpose Construction Operation Maintenance Fuel nozzles Purpose Construction Operation Maintenance
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 1
FUEL S YSTEM
1.1
Purpose The fuel system provides the engine with clean fuel at the required flow rate to permit control of engine power Supply high pressure fuel to the bleed valve actuator (JT15D-5 series)
1.2
Fuel system components Fuel pump Motive flow valve Bleed valve actuator (Ref ATA 72 Sect 6.4 – JT15D-5 series) FCU Flow meter (airframe supplied) Fuel cooled oil cooler Flow divider valve Automatic shut-off valve Fuel nozzles
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 1.3
Fuel, additives and limitation Refer to SB 7144 for complete listing of approved fuel and additives Use of AVGAS limited to 50 hours between any TBO amount of AVGAS Hours operating = average fuel consumption
1.4
Input requirements Power lever position P3, compressor discharge pressure N2, high pressure rotor speed
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 2
FUEL PUMP
2.1
Purpose Provide clean fuel under pressure to the fuel control unit.
2.2
Description: The pump is a one stage gear-type pump (JT15D-1 and 4 series) The fuel pump is a two-stage pump consisting of a centrifugal first stage, and a gear-type second stage (JT15D-5 series) Two filter elements protect downstream components against contamination A bypass valve allows unfiltered fuel to flow to the engine in the event of filter blockage by allowing fuel to bypass the filter
2.3
Typical pump capacity @ 100% N 2 3935 pph @ 580 psi (JT15D-1 and 4 series) 4100 pph @ 580 psi (JT15D-5 series)
2.4
Inlet filter 74 micron metallic type Self bypassing at 9 -12 psid Cleanable
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 2.5
Outlet filter 10 micron Paper type filter Disposable
2.6
Filter bypass valve Ball type bypass valve Open at 40 - 60 psid if filter is restricted
2.7
Maintenance Inspect and clean inlet filter electrosonicaly every minor airframe inspection Inspect and replace outlet filter every minor airframe inspection Replace pump if fuel leakage is detected
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 3
FCU (H YDRAULIC SECTION)
3.1
Purpose Provide the engine with the required fuel flow according to the power lever position and P3 pressure.
3.2
High pressure relief valve Prevents build up of excess P1 and P2 pressure in the fuel system. This valve is normally closed until P1 pressure overcomes the spring tension and allows P1 fuel to dump into P o. It opens at 1260 psid.
3.3
Metering valve The metering valve travels between a maximum and a minimum fuel flow position and determines the amount of fuel going to the engine fuel nozzles. The metering valve is mechanically linked to the pneumatic bellows in the FCU by torque tubes; spring loaded upwards to W f (min.). JT15D-1 and 4 series
POSITION
FUEL FLOW
Wf (min)
UP
155-160 pph
Wf (max)
DOWN
1600-1640 pph
POSITION
FUEL FLOW
JT15D-5 series Wf (min)
UP
160-165 pph
Wf (max)
DOWN
2170-2260 pph
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 3.4
By-pass valve The bypass valve returns fuel in excess of engine requirements to Po. Actuated by means of a diaphragm and spring, the valve maintains a constant P 1 - P2 differential (delta P) of 15-24 psid.
3.5
Motive flow valve Open at 120 psid supply P 1 pressure to the airframe fuel ejector pump (JT15D-1 and 4 series). Open at 240 psid to supply P1 pressure to the airframe fuel ejector pump (JT15D-5 series).
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 4
FCU (PNEUMATIC SECTION )
4.1
Purpose The function of the N 2 governor is to vary engine compressor speed (N2) in order to obtain the desirable thrust (target N1 speed).
4.2
Bellows Senses Px and Py air pressures. Movement of the bellows assembly is transmitted to the metering valve assembly via torque tube assembly.
4.3
Governor Sense N2 speed in order to control the amount of bleed of Px and Py pressure.
4.4
Enrichment valve Allows optimisation of engine acceleration. Above 85% N2 speed, Px and Py pressure are boost in order to increase acceleration rate.
4.5
Back-up valve Allow bleeding P y pressure when actual N2 is higher than selected N2 (approx 9%).
4.6
T2 Temperature Compensation Sensor Modify the fuel schedule to maintain acceleration constant under any ambient temperature.
4.7
constant when engine anti-ice is selected in order to maintain acceleration time constant. It is energised when ignition is ON.
Step modulator (JT15D-1 and 4 series) Fitted to all JT15D-4 and JT15D-1 POST SB 7124. It keeps the P 3 pressure
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 4.8
Flight idle solenoid (JT15D-5 series) Provide higher idle speed (flight idle) to give better respond time on acceleration. NOTE:
4.9
The T2 compensator is matched with the FCU and must be changed as a set.
Operation As the pilot move the power lever, this puts tension on the governor spring. It causes the governor lever to pivot and restricting P y bleed. Py increases in the bellows, causing the bellows section to go down. This downward motion causes the metering valve to move down, therefore increasing Wf . As W f increases, the engine accelerates, increasing rotation of the governor drive shaft. An increase in drive shaft rotation causes the flyweights to spread, which lifts the drive shaft table. As it lifts, the governor spring is overcome, pivoting the governor lever to open the governor orifice again. Once equilibrium between flyweight force and spring tension is obtained, the engine speed is maintained constant.
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL Above 85% N 2 the enrichment lever pivots, which opens the enrichment valve. This boosts Px pressure going to the bellows, therefore increase the rate of acceleration. If N2 is higher than selected power lever setting (approx. 9%), the governor force opens a back-up valve in addition to opening the governor orifice. This rapid bleed of P y causes the bellows to travel upwards, which in turn causes the metering valve to reduce W f and therefore limit an over speed condition. A variable orifice, controlled by bimetallic disks in the sensor, controls the quantity of P x air bleed to atmosphere. This sensor effectively modifies the fuel schedule to maintain engine acceleration constant throughout various outside temperatures. The T2 compensator is located under the engine nacelle.
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 5
FLOW DIVIDER
5.1
Purpose Divide flow between primary and secondary fuel manifolds and dumps fuel from the manifolds on shutdown.
5.2
Fuel shut-off and wind milling bypass valve Prevent fuel to flow to nozzles on cut-off position. Permit fuel to bypass if engine is wind milling.
5.3
Minimum pressurising and flow divider valve In the absence of metered fuel pressure, the minimum pressurising valve prevents flow to the fuel nozzles Ensures proper operating fuel pressures within the fuel system during the starting sequence Divides the metered fuel flow between the primary and secondary fuel manifolds
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 5.4
Spill valve Reduces FCU minimum fuel flow to a level suitable for the starting sequence
5.5
Dump valve Purges fuel remaining in fuel nozzles and manifolds during shutdown
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 5.6
Operation
5.6.1 Starting position As the power lever is moved from cut-off to the start/run position, the shut-off and wind milling valve allow metered fuel from the FCU to flow inside the flow divider. When the metered fuel reaches 75 psid, the minimum pressurising valve opens and allows fuel to flow to the dump valve and spill valve. Metered fuel pressure causes the dump valve to close at 5 psi and fuel flows to the primary fuel manifold and the bleed jet. A bleed jet allows a small amount of metered fuel to prime the secondary manifold.
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL The spill valve opens and diverts a certain amount of metered fuel into the bypass system. This reduction of fuel to the primary manifold is necessary to optimise the starting characteristics of the engine. Once combustion takes place, the engine begins to accelerate towards idle, the spill valve closes under the influence of the increasing P3 air pressure (30 psi).
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
5.6.2 Running position When the pilot sets N 2 above 60%, increased fuel pressure causes the flow divider to open and allow fuel flow to the secondary fuel manifold.
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
5.6.3 Shut-off position As metered fuel pressure is cut-off by the shut-off and wind milling valve, spring tension acting upon the minimum pressure valve causes it to close off the primary and secondary manifold inlet ports. The lack of fuel pressure within the flow divider also allows the dump valve to open. This connects the primary and secondary manifold to the fuel dump port. Fuel remaining in the fuel manifold system drains out of the dump port, which is connected to the airframe waste fuel system.
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 6
AUTOMATIC SHUT-OFF VALVE (JT15D-1, 4 and 5 series)
6.1
Purpose Automatically cut off fuel in the event low pressure rotor shafts decoupling.
6.2
Construction Actuator rod and bell crank Wire rope Tripper mechanism Shut-off valve
6.3
Operation In the event of low pressure rotor shafts decoupling, the turbine shaft moves rearward and contacts the automatic shut-off valve plunger located in the no. 4 bearing cover. This causes the shut-off valve to trip and shut-off the supply of fuel to the nozzles. NOTE:
6.4
An axial displacement of the low pressure turbine shaft of 0.070" is required to trip valve.
Maintenance Set gap between tripper and housing, and between bell crank and no. 4 bearing cover Reset the tripper mechanism when system tripped
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL 7
FUEL NOZZLES (JT15D-1, 4 and 5 series)
7.1
Purpose Deliver and atomise fuel into the combustion chamber.
7.2
Construction Dual orifice type 12 nozzle adapters 12 nozzle sheaths 12 nozzle tips 24 transfer tubes
7.3
Operation Two offset slots on the nozzle distributor impart a swirl motion to the fuel which emerges as a finely atomised spray in the combustion chamber. Slots in the sheath allow compressor discharge air to pass through the sheath and over the nozzle tip for cooling the tip and atomisation of the fuel.
7.4
Maintenance Flow test at 22 and 60 psi Pressure test for cross manifold leakage at 170 - 200 psi Leak test at 500 psi once installed on low turbine support case
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
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Pratt & Whitney JT15D Series (CAT C) ATA 73 – ENGINE FUEL AND CONTROL
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