Lesson 10 - Gas Turbines II

8/11/2019 Lesson 10 - Gas Turbines II

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Gas TurbineApplications

LM 2500,

Allison 501,

The Plant


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Objectives

LM 2500 Gas Turbine Engine - specificcomponents, specifications, systems

Allison 501 Gas Turbine Generator Set -purpose and operation

Interrelationship of supporting systems

and operations Engineering plant lineups


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Gas Turbine Power Plants

Gas generator section

Compressor

Combustion chamber Gas generator turbine

Power section Power turbine


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LM 2500

In DDGs and CGs, have 4 engines

In FFGs, have 2 engines

Engines are shock mounted to minimizenoise and allow for protection

Advantages of LM 2500

Compact & light Easy to maintain & repair

Quick start time (~ 1 min)


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LM 2500


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LM 2500 Components

Starter Pneumatic - driven by pressurized air

Compressor

16-stage, axial flow (17:1 compression ratio) Has some controllable pitch vanes to

provide proper air flow and prevent stall


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LM 2500 Components

Combustion Chamber

Annular design

30 fuel nozzles


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LM 2500 Components

Gas Generator

Turbine HP Element only

High speed

Power Turbine Split shaft to allow varying output speeds

while maintaining constant generation ofenergy

6 sets of nozzles and blades

Lower speed than GGT


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LM 2500 Engine Control

Gas Generator Turbine

Produces energy available for power turbine

Controlled by throttles - alters fuel flow Runs at set continuous RPM

Power Turbine

Speed depends on quantity of exhaust gases from gas

generator turbine & propulsion load

Double helical, double reduction, locked trainreduction gears


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LM 2500 Characteristics

Stage efficiency = 92.5%

R&D: 30,000+ hrs of op-testing

Two versions available: LM 2500-20 (22,500 shp)

LM 2500-30 (30,000 shp) USN warships


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LM 2500 Engine Control

Speed Governor

Used to prevent power turbine from

exceeding speed limit (104%) Reduces fuel to gas generator section which

reduces gases to power turbine

Overspeed Trip If governor fails, trip secures fuel to LM 2500

to shut it down (108%)


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CRP Propeller &Propulsion Shafting

Shaft is hollow to provide flow of oil topropellers

LM 2500 cannot operate at < 5,000 RPM(corresponds to ~11 kts for DDG)

Pitch of blades controlled hydraulically

through pistons and gears Pitch must be adjusted to go slower than 11

kts


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In order to go faster than 11 kts, shaft RPMincreased

In order to go astern, pitch varied toreverse flow

Overall purpose

Controllable pitch to improve efficiency Reversible to allow for ahead/astern flow with

single direction rotation of shaft

CRP Propeller &Propulsion Shafting


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Plant Lineups

Disadvantage of gas turbine VERYpoor partial load fuel economy

LM 2500s connected to reduction gearsvia pneumatic clutch

Three possible lineups

Full Power Split Plant

Trail Shaft


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Plant Lineups

Full PowerLineup 2 turbines/shaft with 2 shafts (4 turbines)

Max speed > 30+ kts

Split PlantLineup 1 turbine/shaft with 2 shafts (2 turbines)

Max speed = 30 kts

Trail ShaftLineup 1 turbine/shaft with 1 shaft (1 turbine)

Other shaft windmilling

Max speed = 19 kts


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Air Intake & Exhaust

Must minimizespace and weight

Must keep air inletlosses to a minimumto ensure maximumperformance

Intake hasscreens/filters toensure clean, filteredair at all times


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Exhaust generates thermal and acousticproblems

Possible damage to personnel & equipment

Increased detection & weapons guidancefrom heat (IR signature)

Silencers and eductor nozzles used tosilence and cool exhaust


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Allison 501 Gas Turbine

Generator Set (GTGS) Used to generate electricity

Three 2000KW GTGS

Any two can supply electrical needs of ship Separated by 3 water-tight bulkheads to minimize

potential battle damage

Single Shaft

Waste Heat Boiler

Uses heat of exhaust to generate low pressure steamfor auxiliary purposes


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Allison 501


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Safety Features

Automatic Shutdown on: High Vibration

Cooling System Failure Module Fire (UV Flame Detection)

High Turbine Inlet Temp

Low Lube Oil Pressure

Power Turbine Overspeed

Battle Override


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Ship Layout


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Operating Stations


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Propulsion PlantComparisons


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Introduction

Overall, various different propulsiondesigns - to choose, must consider:

Operational requirements Construction requirements

Manpower requirements

Thermodynamic efficiency


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Design Considerations

Minimal size and weight

Reliable & easy to maintain

Cost efficiency & budget

Fuel efficiency over wide power range

Shock resistant to handle stress

Quiet & safe

Manpower & training


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Conventional Steam Plant

Advantages:

Efficiency @ cruising speeds

Reliability

Good performance @ partial loading

Usefulness for auxiliary functions

Disadvantages

Large & bulky w/ large manpower reqs

Long start-up time

Large fuel storage & low endurance


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Nuclear Power Plant

Advantages

Endurance, reliability, speed

No air required for combustion

No NBC warfare problem

Disadvantages

High costs & weight for shielding

Long startup time

Manpower & training requirements

Radiological problems


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Diesel Plant

Advantages

High efficiency @ all loads

Low initial cost and specific fuel cost (SFC)

Reliability

Few operators needed

Disadvantages

Capacity limitations & space considerations High maintenance & overhaul

High lube oil consumption

Noise


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Gas Turbine Plant

Advantages

Light weight & compact

Short startup time

Reliable & quiet

High full-load efficiency

Disadvantages

Large quantities of air (NBC problems)

Large fuel storage

Low efficiency @ partial loads


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Hybrid Plants

Overall goal: small, more fuel efficientengines for normal ops while retainingability to shift to high power units whenneeded

Examples:

CODAG, CODOG: (Diesel and/or GT)

COGAS (RACER): (GT & Steam )

CODAS: (Diesel & Steam)


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Summary

Diesel plant is a hacker! Most efficient

Easy to construct and operate Good versatility

Gas Turbine with CRP screws is awinning combo

Efficient and reliable

Good for mass-production missile sponges


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Summary

Most versatile is nuclear plant

Tremendous endurance overcomes

inefficiency Saves space and energy

If you consider fuel storage for other plants, it

is actually lighter & less expensive


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Questions?

Lesson 10 - Gas Turbines II

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