jt15d ata 73

Pratt & Whitney JT15D Series (CAT C)

ATA 73 – ENGINE FUEL AND CONTROL

of 22 FOR TRAINING PURPOSES ONLY © JT15D - ISSUE 1, 2009




ATA 73– ENGINE FUEL AND CONTROL

0 TABLE OF CONTENTS

1 Fuel system 4 1.1 Purpose 4 1.2 Fuel system components 4 1.3 Fuel additives and limitations 5 1.4 Input requirement 5 2 Fuel pump 6 2.1 Purpose 6 2.2 Description 6 2.3 Typical pump capacity @ 100% N2 6 2.4 Inlet filter 6 2.5 Outlet filter 7 2.6 Filter bypass valve 7 2.7 Maintenance 7 3 FCU (hydraulic section) 8 3.1 Purpose 8 3.2 High pressure relief valve 8 3.3 Metering valve 8 3.4 Bypass valve 9 3.5 Motive flow valve 9 4 FCU (pneumatic section) 10 4.1 Purpose 10 4.2 Bellows 10 4.3 Governor 10 4.4 Enrichment valve 10 4.5 Back-up valve 10 4.6 T2 temperature compensation sensor 10 4.7 Step modulator (JT15D-1 and 4 series) 10 4.8 Flight idle solenoid (JT15D-5 series) 11 4.9 Operation 11 5 Flow divider 13 5.1 Purpose 13 5.2 Fuel shut-off and wind milling bypass valve 13 5.3 Minimum pressurising and flow divider valve 13 5.4 Spill valve 14 5.5 Dump valve 14 5.6 Operation 15




6 Automatic shut-off valve 19 6.1 Purpose 19 6.2 Construction 19 6.3 Operation 19 6.4 Maintenance 19 7 Fuel nozzles 20 7.1 Purpose 20 7.2 Construction 20 7.3 Operation 20 7.4 Maintenance 20




1 FUEL SYSTEM

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




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

Hours operating = amount of AVGAS

average fuel consumption

1.4 Input requirements

Power lever position

P3, compressor discharge pressure

N2, high pressure rotor speed




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% N2

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




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




3 FCU (HYDRAULIC 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 Po. 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

JT15D-5 series POSITION FUEL FLOW

Wf (min) UP 160-165 pph

Wf (max) DOWN 2170-2260 pph




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 P1 - P2 differential (delta P) of 15-24 psid.

3.5 Motive flow valve

Open at 120 psid supply P1 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).




4 FCU (PNEUMATIC SECTION)

4.1 Purpose

The function of the N2 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 Py 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 Step modulator (JT15D-1 and 4 series)

Fitted to all JT15D-4 and JT15D-1 POST SB 7124. It keeps the P3 pressure

constant when engine anti-ice is selected in order to maintain acceleration time constant. It is energised when ignition is ON.




4.8 Flight idle solenoid (JT15D-5 series)

Provide higher idle speed (flight idle) to give better respond time on acceleration. NOTE: The T2 compensator is matched with

the FCU and must be changed as a set.

4.9 Operation

As the pilot move the power lever, this puts tension on the governor spring. It causes the governor lever to pivot and restricting Py 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 Wf 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.




Above 85% N2 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 Py causes the bellows to travel upwards, which in turn causes the metering valve to reduce Wf and therefore limit an over speed condition. A variable orifice, controlled by bimetallic disks in the sensor, controls the quantity of Px 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.




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




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




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.




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).




5.6.2 Running position

When the pilot sets N2 above 60%, increased fuel pressure causes the flow divider to open and allow fuel flow to the secondary fuel manifold.




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.




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: An axial displacement of the low

pressure turbine shaft of 0.070" is required to trip valve.

6.4 Maintenance

Set gap between tripper and housing, and between bell crank and no. 4 bearing cover

Reset the tripper mechanism when system tripped




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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jt15d ata 73

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fuel additives

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