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50 years of Engine Improvements

Baldev K MehtaTechnical Fellow at Boeing Company

[email protected]

Pacific North West AIAA SymposiumNovember 2009, Seattle

mailto:[email protected]


800% Higher Thrust• 13,500 lbs (Model 707/JT3C-6 in 1958) • 120,000 lbs (Model 777/GE90-115B in 2004)• 1 engine does what 8 engines used to do 50 years ago

Lower Fuel Burn• TSFC about 0.8 in 1958 • TSFC about 0.5 in 2006• Modern engines roughly twice as efficient as 50 years ago

Lower Emissions• Modern combustors do not emit smoke • Modern engines permit quiet airport operations

Thrust/Engine Weight modest increase

Performance Retention /Maintainability

50 years of Engine Improvements747-100/ PWA’s JT9D engines and 777-Trent 800 engine #2

50 years of Engine Improvements747-100/ PWA’s JT9D engines and 777-GE90 engine #2

50 years of Engine Improvements747-100/ PWA’s JT9D engines and 777-GE90-115B engine #2


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• How have these improvements been achieved

• Engine Overall Efficiency

Thrust Specific Fuel Consumption (TSFC)-pounds of fuel per pound of thrust- ability to convert heat energy of fuel into kinetic energy of gases

Propulsive Efficiency- ability to convert kinetic energy of gases to propellant force on the aircraft


• TSFC improvements• Higher thermal Efficiency requires high pressures and high turbine

inlet temperatures to develop increase power per pound of airflow• Variable geometry stators

High overall pressure ratio results in high rotor speeds and creates high variations in operating lines between design point and off design conditions

• Internal turbine blade cooling/ceramic blade coatingHPC air is injected inside the turbine blades to cool turbine blade

surfaces and to remain within temperature limits of turbine/diskmaterial. Complex multiple pass cooling system have reduced theamount of cooling flow and improved performance. New improved ceramic coatings on blades

• Improved performance fan bladesFan efficiency was improved by: removing inlet guide vanes, reduction in number of fan blades, using non-shrouded wider chord/swept fan blades

• Tighter running tip clearancesAchieved by using abradable rub strips, spraying cold air on theoutside of hot cases thus shrinking off cases, reducing losses and improving fuel efficiencyCeramic abradable outer air seals in HPT reduce operating clearances and improve efficiency

• Improved Design Techniques-3 D airfoil3-d Airfoils introduced in compressors and turbines-airfoils designed with thicker leading and trailing edges to provide uniform aerodynamic flow (no separation) throughout blade areaRadial gradient vanes designed to improve turbine aerodynamic efficiency by substantially reducing end wall losses



• Propulsive Efficiency• Propulsive efficiency is the ratio of available useful power (net thrust

x free-stream velocity) to the kinetic energy imparted to the engine mass airflow

• Eff =Fn x Vo/M(Vj-V)/2= 2/1+Vj/Vo= 2/2+(Fn/W)g/VoM= engine weight airflow, Vj= exhaust jet velocity, Vo=free-stream velocity, Specific thrust= Fn/W

• Propulsive Eff. Increasesdecrease in specific thrust (Fn/W)decrease in amount of energy wasted in the jet velocity dissipationAs the speed of aircraft increases


• High Bypass Ratio Engines• In turbojet engines, all the air that enters the inlet, passes through

the engine and exits with high temperature and high jet velocity• In high bypass ratio engines, a portion of air goes through the core

and exits with high temperature and high jet velocity but a large amount of air (10 times the amount going through core) bypasses the engine core and is imparted a relatively low velocity and low temperature.

• The ratio of bypassed airflow to the engine core flow is called Bypass Ratio (BPR).

• BPR increases, the specific thrust (Fn/W) decreases and TSFC improves.

• As BPR increases, mean jet velocity is lowered and propulsive efficiency improves and jet noise is reduced


• The high pressure compressors, combustion chambers and turbines in high BPR engines can be smaller, lighter, shorter for a given level of thrust as they are required to handle only a portion of total airflow.

• High BPR engines require a larger diameter fan, a larger fan case, and a larger diameter nacelle and these result in increased weight and increased nacelle drag and hence the need for composite materials.

50 years of Engine ImprovementsMulti-Variant Engine Installation Optimization

Optimization Requires Consideration of All Factors, a Multi-Disciplined Effort, a "Working Together Approach"

Bypass Ratio - BPR

TSFC,Noise Drag, Loads, Structural Difficulty,

Thrust Capability, Weight

1% Airplane Cruise Drag ≈• 1% TSFC• 3500 lbs EOEW• 5,000 lbs Fuel @ 8000 n.mi.• 1.3% Takeoff Thrust Reduction

5.0 20.0Bypass Ratio - BPR

UninstalledTSFC

Installed Engine, Nacelle, Strut, EBU TSFC, Drag & Weight

Optimum

Mach = Cruise

Optimum Airplane Efficiency Achieved By Optimizing Installed Drag, Weight, TSFC, Noise

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• Engine Weight ImprovementsLighter weight materials-steel/titanium/CompositeReduced number of fan blades, reduced number of turbine blades/statorsModel 707/PWA’s JT3C-6-steel fan bladesModel 777/hollow titanium fan blades (Trent 800), composite fan blades(GE90)Kevlar in fan case (belt wrapped Al structure) is 700 lbs lighter in PW4084(777 engine) relative to a steel caseGEnx engine (787)- composites for fan blades, engine’s one piece forward fan case, engine’s variable bleed ducts at exit of booster stage

• Engine Nacelle Weight ImprovementsInlet, Fan Cowl, Fan Thrust reverser is made of composite materials

50 years of Engine ImprovementsFan blade comparison

50 years of Engine ImprovementsGE90/777-200ER, GE90-115B/777-300ER, GEnx/787


• Engine Performance Retention /Maintainability Features• Full Authority Digital Electronic Control

Improves fuel efficiency, provides precise thrust management, provides redline (rotor speeds) protection, prevents inadvertent over boosting of engine with resulting engine deterioration

• Improved Structural IntegrityIncreased engine case stiffness and additional bearings added toreduce case bending and to improve performance retention. Load sharing cowling designed to increase overall stiffness and reduce performance loss due to case bending


• Turbine Blade/Disc Manufacturing Technology improvementsTurbine blades glow red hot and are designed to be strong enoughfor centrifugal loads and air loads. Turbine blades must be resistant to fatigue and thermal shock as well as to corrosion and oxidation. Over time turbine blades slowly grow-It is called creep. Manufactured blades show a myriad of crystals and are oriented in all directionsTurbine blade service has been improved by :Directionally solidified blades ( aligning the crystals to form columns along blade length), Single crystal blading and blade coatings for improved oxidation/corrosion protection


Blade creep


• Emissions Improvement• Oxides of Nitrogen (NOx) production increase exponentially as gas

temperature increases• 787/Trent 1000 engine –Tiled combustor improves fuel burn and

reduces oxides of Nitrogen (NOx) by 30 %• 787/GEnx engine-Twin Annular Premixing Swirler (TAPS) in

combustor will lower combustor temperatures to reduce NOxemissions ( 30% improvement relative to 747 engine)

• TAPS-fed by two annular fuel/air swirlers- a central swirler for idle and taxi and a main (outside) swirler for take-off, climb and cruise.


• 777/PWA’s PW4084 Engine• Thrust 84,600, 7% improved TSFC

relative to 767/PW4060• 112 inch fan diameter, 22 fan blades-

wide-chord, shroud less • BPR 6.8, OPR 37:1• Fan, 6 stage LPC, 11 Stage HPC,

Burner, 2 stage HPT, 7 Stage LPT


• 777/GE90 Engine• Thrust 84,700, 9% TSFC improvement

relative to 767/GE CF6-80C2• 123 inch fan diameter, composite

wide chord blades with titanium leading edge, Blade- 43 in span, 24 in chord and weighs 32 lbs

• BPR 6.8, OPR 37:1• Fan, 3 stage LPC, 10 Stage HPC,

Burner, 2 stage HPT, 6 Stage LPT


• 777/Trent 800 Engine• Thrust 90,00, 7.5% improved TSFC

relative to 767/RB211• 110 inch fan diameter, new swept

wide-chord hollow titanium fan blades• BPR 6.5, OPR 40:1• Fan, 8 stage IPC, 6 Stage HPC,

Annular 24 Burners, 1 stage HPT, I stage IPT, 5 Stage LPT


• 787 Engines (GEnx and Trent 1000 Engine)• Efficiency improved 6-7% relative to 777 engine

15 % relative to 747 engine• High BPR greater than 9:1• Non-engine bleed system- engine bleed will not be used for cabin

conditioning• Non engine bleed starting system- Engine will be started electrically

with APU/Engine starter generator• Air cycle machines for cabin conditioning will be powered electrically

by APU/Engine generators


• 787-8/GEnx Engine• Thrust 53,000 to 75,000 lbs, • Efficiency improved 6.9% relative to 777 engine (Av Week 4/17)• 111.1 inch fan diameter, 18 composite fan blades-wide chord, new

swept, one piece composite forward fan case• BPR 9.2, OPR 41.4• Fan, 4 stage LPC, 10 Stage HPC, Burner, 2 stage HPT, 7 Stage

LPT


• 787-8/Trent 1000 Engine• Thrust 50,600 to 70,000, • Efficiency improved 6-7% relative

to 777 engine• 112 inch fan diameter, 22 fan

blades, wide-chord, new swept blades

• BPR 9.6, OPR 40.3:1• Fan, 8 stage IPC, 6 Stage HPC,

Burner, 1 stage HPT, 1Stage IPT. 6 stage LPT

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