Unit 11 GT & Misc PropulsionGas Turbine Propulsion:

Engine types:Aircraft-derivative Gas Turbines(“marinized” jet engines) light weight (1 lb/SHP) reliable, familiar to (aircraft)

maintenance staff off-the-shelf design gas generator change-out for

maintenance quick starting (1-2 minute

warm-up) burns jet fuel (JP-4 or JP-5) or

DFM

Industrial (Heavy Duty) Gas Turbines heavier (15 ibs/SHP) custom design with numerous

heat recovery devices (intercoolers, regenerators, reheaters, etc.)

must be maintained in place slower starting (15-20 minute

warm-up) burns cheaper residual fuel

The LM2500 series engine was selected in the early 1970's as the prime mover for propulsion on the Spruance (DD 963) Class ships. Different configurations of this engine have since been used on each new class of Surface Combatants including the Oliver Hazard Perry (FFG 7) Class, the Ticonderoga (CG 47) Class, the Kidd (DDG 993) Class, the Arleigh Burke (DDG 51)/Oscar Austin (DDG 79) Class as well as the AOE 6 Class supply ships.

Notes:

PS 111. Professional Studies Unit 11: GT & Misc Propulsion

GT Basic Components:

GAS GENERATOR

provides working fluid (combustion gas) at high temperature and pressure to be expanded through power turbine; consists of compressor (centrifugal or axial type) combustion chamber (can type, annular or can-

annular type) (compressor) turbine: alternate rows of nozzles (or

nozzle vanes) and blades (of impulse, reaction or hybrid type cooled by air in internal air passages)

single-spool gas generator: compressor & turbine mounted on single shafttwin-spool gas generator: LP compressor & LP rotor on inner, slower shaft; HP compressor & turbine on outer, faster shaft for increased efficiency

POWER (FREE)TURBINE

mounted on a separate shaft from the gas generator (i.e. “split shaft) the power turbine is connected to the load (reduction gears and propeller). Coupled aerodynamically, but not mechanically to the gas generator, the power turbine is “free” to spin at varying RPM while the gas generator rotates at constant speed. On smaller units such as electric generator applications, the power turbine may be mounted on the same shaft as the gas generator (“single shaft”)

ACCESSORIES

normally driven by a reduction gear connected to HP compressor shaft and provided with engine: fuel oil boost pump : delivers fuel nozzles in

combustors lube oil pump : delivers LO to bearings and gears deaerator : removes entrained air starting motor : electric, hydraulic, or air driven to

bring engine up to self-sustaining speed during engine start sequence (spark plugs fired in combustion chamber for starting only)

control equipment : hydraulic pumps, governors, speed switches, tachometers, etc.

MANEU-VERING & REVERSING

The speed at which the power turbines operates is determined by the quantity of hot gasses it receives from the gas generator and the load placed on the propeller. This is termed power control rather than speed control of the free turbine. Thus the control of the fuel and air to the combustors determines, ultimately, ship speed

Gas turbines are inherently irreversible. Reversal of propeller thrust must be accomplished by external means such as:

1. electric drive 2. controllable pitch (CP) propeller3. reversing gears (with hydraulic,

electric or friction type clutches)

Notes:

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PS 111. Professional Studies Unit 11: GT & Misc Propulsion

Advantages of Electric Drive: Ease of control, flexibility of arrangement and adaptability to multiple use of prime mover generator sets

Applications: Ferries, icebreakers, tugs oceanographic vessels, and cable-

layers which require a high degree of maneuverability self-unloaders, fireboats, dredges, drill ships and tenders which

have extensive electric power requirements not coincident with maximum propulsion power requirements

Cruise ships with a large hotel loads Vessels using non-reversing, high-speed and/or multiple

prime movers (e.g. gas turbine powered vessels)

Basic Components:

AC Electric Drive Arrangements: AC motors are usually used in applications above 10,000hp “classical” plant comprised of dedicated variable speed

propulsion generator to power propulsion motor (at sea) or cargo pumps (in port)

F

F

F

R

R

R

Special Purpose(variable frequency)Non-propulsion LoadsCargo Gear, etc.

Prime-moverReductionGear

PropulsionGenerator

PropulsionMotor

Switchgear:Fwd/Stop/Rev

PropulsionBus

Notes:

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PS 111. Professional Studies Unit 11: GT & Misc Propulsion

tendency in modern plants to utilize solid state controlled AC drives and induction motors

PropulsionMotors

60HzBus

ConverterNo.2

ConverterNo.1

GenSets

Propulsion Auxiliariesand Hotel Loads

Generator Bank:60 Hz AC power produced by various combinations of generator sets. No. of units determined by demandother arrangements:Some GenSets dedicated to propulsion and special service, others to ship service.

Propulsion Motors: Typically induction type AC motors

controlled by variable frequency output of converters

propeller reversal accomplished electronically by converters

occasionally combined with CP propellers (maneuvering at min. pitch via converter output then increasing pitch at 60Hz to obtain sea speed)

Other Propulsion Drive Trains applicable to Non-Reversing Engines:

Controllable-Reversible Pitch (CRP) PropellerContain mechanism within propeller hub that can be operated remotely to change pitch (by rotating blades about their radial axis). Advantageous in the following situations:

where maximum thrust requirements at widely varying operations (Tugs, Trawlers, etc.)

where unidirectional rotation is beneficial/required (e.g. non reversing engines, highly skewed propellers, operating in ice covered water, etc.)

where extensive low speed maneuvering and/or rapid response to thrust reversal is required

where constant shaft rpm is required (i.e. shaft-driven generators)

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PS 111. Professional Studies Unit 11: GT & Misc Propulsion

CRP PropellerReversing Gears

AHEAD and ASTERN clutches are interlocked to prevent simultaneous engagement

Propeller Shaft often fitted with a shaft brake that is activated when BOTH clutches are disengaged

Clutch mechanism may beMechanicalHydraulicElectro-magnetic, orpneumatic

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PROPELLER SHAFT

Reversing Gear

AST

AHD

Astern Clutch Aster

n PinionAhead Pinion

Ahead Clutch

ENGINE

Reduction Gear

PS 111. Professional Studies Unit 11: GT & Misc Propulsion

Drive Train Components:

REDUCTION GEARSProblem: Turbines (steam or gas) are high speed, low torque devices (Re: HP = torque x rpm), while propellers are high torque, low speed (relatively) devices for the same HP. How can the two be connected?Solution: Reduction Gears

Single Reduction:in equilibrium (constant speed) F1 = F2 and pinion torque T1 = F1 x r1 while rd. gear torque, T2 = F2 x r2then

T1/T2 = r1/r2and since

rpm1/rpm2 = r2/r1 then

T1/T2 = rpm2/rpm1FinallyP1 = T1 x rpm1 = T2 x rpm2 = P2

i.e. Pinion Power = Red. Gear Powerbut speed is traded for torque !

Double reduction:LS pinion radius = r32nd reduction gear radius = r4butLS Pinion mechanically joined to 1st Reduction Gear thusrpm2/rpm3 = r4/r3henceT1/T3 = rpm3/rpm4 = [r1/r2]x[r3/r4]

Maximum limit for single reduction is approx. 10:1for double reduction, 100:1

For TSES at full power (17,500 HP)HP turbine = 5600rpmLP turbine = 3600rpmHP 1st red. gear = 755 rpmLP 1st red gear = 755 rpmshaft = 104 rpm

Thus HP HS pinion:shaft = [5600:755] x [755:104] =[7.4:1] x [7:3:1] = 53.8:1

and LP HS pinion:shaft =[3400:755] x [755:104] =[4.5:1] x [7.3:1] = 32.7:1

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PS 111. Professional Studies Unit 11: GT & Misc Propulsion

TSES VI Reduction Gears:Double input (HP & LP turbines), Single Output, Cross-Compounded, Articulated

MAIN THRUST BEARING

Notes:

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LP

HP

LP Flex Coupling

HP Flex Coupling

Quill Shafts

HP, HS Pinion

HP, 1st Reduction Gear

HP, LS Pinion

LP, HS Pinion

HP, 1st Reduction Gear

HP, LS Pinion

Line Shaft (“SPRING”)

Bearing2nd Reduction (“BULL”)Gear

Main THRUST

Bearing

PS 111. Professional Studies Unit 11: GT & Misc Propulsion

LINE SAFT BEARINGS.

STERN TUBE BEARINGSWater Lubricated Lignum Vitae (wood!) – TSES VI Synthetic/composite

Oil Lubricated

Notes:

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PS 111. Professional Studies Unit 11: GT & Misc Propulsion

Combined Cycle Propulsion Plants

COmbinedDieselSteamGasNuclear

AndOr

GasSteam

COGAG COGOG

Small gas turbines used for cruising mode and large units for maximum power (since GT’s are most efficient at near their full power rating). A COGAG arrangement would utilize both the large and small turbines together for maximum power situations. In a COGOG arrangement, the larger GT(s) would replace the smaller ones during high power operation.

CODAG CODOG

Combine diesels (usually medium speed) for increased range at low power while maintaining high speed capability with gas turbines. A CODAG arrangement would utilize both Diesel and GT’s at full power. In a CODOG arrangement the diesel engines would be disconnected and secured when the GT is in operation

COGESThe LM2500 is also available as a Combined Gas Turbine Steam and Electric System (COGES). High-pressure, superheated steam is produced from exhaust gas, which is used to power the steam turbine generator set. This arrangement increases system thermal efficiency by 10 to 20 percent.

CONAGA thought experiment, combining the immense range properties of nuclear propulsion with gas turbines for burst power. No such plant exists today.

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“Waste Heat” Boiler

PS 111. Professional Studies Unit 11: GT & Misc Propulsion

The Engine Order Telegraph is the electrical/mechanical means by which the bridge communicates to the propulsion control station the desired engine speed. With a manually operated system, the engine orders are recorded in Bell Book at the propulsion station and (a second copy is maintained on the bridge). These records are extensions of the official log and should be treated as such. The following standard shorthand is used for the corresponding maneuvering speed:

STANDBY STOP

D DEAD SLOW AHEAD

D DEAD SLOW ASTERN

SLOW AHEAD SLOW ASTERN

HALF AHEAD HALF ASTERN

FULL AHEAD FULL ASTERN

E EMERGENCYFULL AHEAD

E EMERGENCYFULL ASTERN

When other than standard maneuvering speeds are required by the bridge, the ordered RPM is recorded in lieu of the standard symbol

In automated plants, speed changes are recorded by a Bell Logger interfaced with the control station console. The printout of the Bell Logger supplants the Bell Book.

Maneuvering Modes:

Bridge Control: The bridge console engine order telegraph is actually the throttle, ship speed and direction is initiated by bridge personnel.

Engine Room (automated) Control: Engine console engine order telegraph is actually the throttle, ship speed and direction as indicated by bridge telegraph position is matched by engine telegraph position. Control is transferred by bridge request acknowledge by engine room. Engine room control may be assumed at any time in an emergency.

Engine Room (manual) Control: Telegraph used to communicate engine speed/direction order (as on TSES). Telegraph order acknowledge by engine room personnel by matching pointer position and engines maneuvered independently.Notes:

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