dcp 626 gas turbines web

7/28/2019 Dcp 626 Gas Turbines Web

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Marine Gas Turbines


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Objectives

Major parts and terminology of a gas

turbine Theory of Gas Turbine Operations

Major parts of the LM2500


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Uses of Gas Turbine

Engines Aircraft Engines

Main Propulsion

Arliegh Burke, OHP, Tico, Spruance,

LCACS

Auxiliary Applications

Electric generators


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Advantages of GTEs

Weight reduction of 70%

Simplicity

Reduced manning requirements

Quicker response time

Faster Acceleration/deceleration

Modular replacement

Less vibrations

More economical


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Disadvantages of GTEs

Many parts under high stress

High pitched noise

Needs large quantities of air

Large quantities of hot exhaust (target)

Cannot be repaired in place


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Bernoullis Theory

Convergent Divergent

Pressure Increases

Velocity DecreasesPressure Decreases

Velocity Increases


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Thermodynamic Cycle/

Engine Type

Brayton Cycle (steady-flow cycle, 5

parts of thermo cycle?) Open Cycle:

Working substance is taken in, passed

through engine once and is discharged Unheated Engine:

Energy is added in one place and work is

done in another


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3 Major GTE

Components Compressor

Combustion Chamber

Turbine


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Brayton Cycle

Compressor draws air from the atmosphere

Air passes through the compressor, and the

pressure increases and the volume decreases

Combustion occurs at constant pressure-air

heats up-volume increases

The gases pass through the turbine rotor

The rotor turns KE and ThermE to ME.

Gases are released through the exhaust

stack to the atmos here.


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JET ENGINES


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Single Shaft

Efficiently operates at constant speeds

Used in GTGS (gas turbine generator

systems)


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Split Shaft

Best where speeds and loads vary

Used in LM-2500

Power shaft is decoupled from compressor

Allows both to operate at efficient speeds

(not the same)


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Compressors

Purpose: Pressurize intake air

Two basic types Centrifugal Compressor (Radial Flow)

Axial Compressor (Axial Flow)


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Centrifugal

Compressors Radial Flow- Air is accelerated outward by

centrifugal force

Components: Impeller - Radially accelerates air

Diffuser - KE PE

Compressor Manifold - radial to axial air flow

Lower compression ratio

Lower efficiency

Lower cost


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Rad ial Flow


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Axial Compressors Axial Flow- Air flows over vanes parallel to

the rotor

Components:

Rotor - Axially accelerates air

Stator - KE PE

High pressure and low pressure sections

permit greater efficiency

Multistage axial compressors have large

compression ratio (20:1)

Very expensive


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Ax ial Flow


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Combustors Purpose - Mixes compressed air with

injected fuel and burns the mixture toproduce hot combustion gases.

Types

Can (centrifugal compressor)

Can-annular (axial compressor)

Annular (axial compressor) Compressed Air Uses

Primary- supports combustion process

Secondary- cool gases to desired turbine inlettemperature (prevent heating damage to turbines)


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Turbines

Purpose - utilize hot combustion gas to

create mechanical energy, i.e. produce

torque to drive load (shaft) or output to a

nozzle (jet engine).

Fixed blades (nozzles) - stator

convert heat/pressure energy to velocity energy

Moving blades

convert velocity energy to mechanical energy


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HP Turbine

Follows combustor

Hottest air

Connected to compressor shaft

Drives the compressor


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Power Turbine

Lower temperature air

Power output

drive prop


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Turbojet


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LM2500


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Turboprop


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Ramjet Engine


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Accessory Drive

Assembly Purpose - Provides motive force for driving

the accessories required for operation andcontrol of engine

Attached Accessory Equipment

Fuel oil pump Lube oil pump

Starter (pneumatic, electric, hydraulic)


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Summary

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