1. Gas Turbines

2. References Required Principles of Naval Engineering (pp 106-115)
Optional
Introduction to Naval Engineering (Ch 12).

3. Objectives
A. Comprehend the thermodynamic processes occurring in a gas turbine. B. Comprehend the basic operation, key components, and safety considerations of gas turbine engines (single and split shaft) and propulsion plants, including support systems. C. Know the features of shipboard gas turbine plant arrangements, including main propulsion and auxiliary machinery configuration on the CG-47 class ships. D. Know the features of intake and exhaust duct systems in a typical gas turbine plant. E. Know the propulsion plant lineup variations for a 4 engine, 2 shaft gas turbine plant.

7. Background
Aircraft turbojet/turbofan engines are precursors to gas turbines
Installed for propulsion in:
FFG’s
DD’s
DDG’s
CG’s
M-1 tanks
Also used for electrical generation & auxiliary applications

8. Background Advantages of GTE Disadvantages High power to weight ratio
Smoothness of operation
Less radiated noise compared to Diesel Engine
Fuel economy is comparable to Diesel Engines
Efficient at high speeds
Disadvantages
Large quantities of air necessary (contaminated air can cause damage)
Loud high pitched noises can cause hearing loss
High exhaust heat makes the susceptible to anti-ship missiles
Major casualties are not easily repaired on board.
Maintenance is complicated and costly if performed incorrectly
(a pencil mark on a blade or a finger print in the wrong place can cause failure)

9. Brayton Cycle Unlike diesels, operate on STEADY-FLOW cycle
Open cycle, unheated engine
Engine Nacelle
Fan
Low pressure compressor
High Pressure Compressor
Combustion Chamber
High Pressure Turbine
Low Pressure turbine
Exhaust cone

10. Basic Components

11. Basic Components

12. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it.
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load

13. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load

14. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load

15. Compressor Supplies high pressure air for combustion process
Compressor types
Radial/centrifugal flow compressor
Axial flow compressor

16. Compressor Radial/centrifugal flow Axial flow
Adv: simple design, good for low compression ratios (5:1)
Disadv: Difficult to stage, less efficient
Axial flow
Good for high compression ratios (20:1)
Most commonly used

17. Compressor Controlling Load on Compressor Compressor Stall
To ensure maximum efficiency and allow for flexibility, compressor can be split into HP & LP sections
Vane control: inlet vanes/nozzle angles can be varied to control air flow
Compressor Stall
Interruption of air flow due to turbulence

18. Use of Compressed Air Primary Air (30%) Secondary Air (65%)
Passes directly to combustor for combustion process
Secondary Air (65%)
Passes through holes in perforated inner shell & mixes with combustion gases
Film Cooling Air (5%)
Insulates/cools turbine blades

19. Combustion Chambers Where air & fuel are mixed, ignited, and burned
Spark plugs used to initially ignite fuel
Types
Can: for small, centrifugal compressors
Annular: for larger, axial compressors (LM 2500)
Can-annular: for really large turbines

20. Combustion Chambers
Annular
Can-Annular

21. Turbines
Consists of one or more stages designed to develop rotational energy
Uses sets of nozzles & blades
Single shaft
Power coupling on same shaft as turbine
Same shaft drives rotor of compressor and power components

22. Gas Turbine Systems Fuel System Lubrication System
Uses either DFM or JP-5
Regulates the speed of the engine during steady state and transient conditions. Controls acceleration.
Lubrication System
Supply bearings and gears with oil
Provides source of hydraulic power for controls

23. Gas Turbine Systems Air System
Air intakes are located high up & multiple filters
Exhaust discharged out stacks

24. Air Intake & Exhaust Must minimize space and weight
Must keep air inlet losses to a minimum to ensure maximum performance
Intake has screens/filters to ensure clean, filtered air at all times

25. Air Intake & Exhaust Exhaust generates thermal and acoustic problems
Possible damage to personnel & equipment
Increased detection & weapons guidance from heat (IR signature)
Silencers and eductor nozzles used to silence and cool exhaust

26. Air Intake & Exhaust

27. Air Intake & Exhaust

28. Gas Turbine Systems Starting System Power Transmission System
To get compressor initially rotated, HP air used (can use electrical also)
Once at certain RPM, fuel injected and spark ignited
Power Transmission System
Reduction gears used to transfer torque
With split shaft, turbines can different speeds

29. Split Shaft Design Split Shaft Gas generator turbine drives compressor
Power turbine separate from gas generator turbine
Power turbine driven by exhaust from gas generator turbine
Power turbine drives power coupling

30. LM 2500 In DDG’s and CG’s, have 4 engines In FFG’s, have 2 engines
Engines are shock mounted to minimize noise and allow for protection
Advantages of LM 2500
Compact & light
Easy to maintain & repair
Quick start time (~ 1 min)

31. LM 2500

32. LM 2500 Components Starter Compressor
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

33. LM 2500 Components
Combustion Chamber
Annular design
30 fuel nozzles

34. LM 2500 Characteristics Stage efficiency = 92.5%
R&D: 30,000+ hrs of op-testing
Two versions available:
LM (22,500 shp)
LM (30,000 shp) – USN warships

35. LM 2500 Engine Control Speed Governor Overspeed Trip
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%)

36. CRP Propeller & Propulsion Shafting
Shaft is hollow to provide flow of oil to propellers
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

37. CRP Propeller & Propulsion Shafting
In order to go faster than 11 kts, shaft RPM increased
In order to go astern, pitch varied to reverse flow
Overall purpose
Controllable pitch to improve efficiency
Reversible to allow for ahead/astern flow with single direction rotation of shaft

38. Plant Lineups Disadvantage of gas turbine
VERY poor partial load fuel economy
LM 2500’s connected to reduction gears via pneumatic clutch
Three possible lineups
Full Power
Split Plant
Trail Shaft

39. Full Power Line Up 4 2 Reduction Gears Reduction Gears 3 1 PORT Shaft
Clutch
Clutch
Clutch
Reduction Gears 3 1
PORT
Shaft
STBD
Shaft

40. Split Plant Line Up 4 2 Reduction Gears Reduction Gears 3 1 PORT Shaft
Clutch
Clutch
Clutch
Reduction Gears 3 1
PORT
Shaft
STBD
Shaft

41. Trail Shaft Line Up 4 2 Reduction Gears Reduction Gears 3 1 PORT Shaft
Clutch
Clutch
Clutch
Reduction Gears 3 1
PORT
Shaft
STBD
Shaft

42. Plant Lineups Full Power Lineup Split Plant Lineup Trail Shaft Lineup
2 turbines/shaft with 2 shafts (4 turbines)
Max speed > 30+ kts
Split Plant Lineup
1 turbine/shaft with 2 shafts (2 turbines)
Max speed = 30 kts
Trail Shaft Lineup
1 turbine/shaft with 1 shaft (1 turbine)
Other shaft windmilling
Max speed = 19 kts

43. Take Away Give the advantages and disadvantages to GT propulsion
Draw a one-line diagram of a gas turbine and explain the Brayton cycle
Describe purpose/advantage of split shaft vs. single shaft GTE
Describe the various methods of power transmission and speed control for GTE
List and describe the various plant lineups used with GT propulsion plants

44. Questions?