1

Previous lectures

• §2.1 Thermodynamic cycles of gas turbine engines1. Ideal cycle

2. Real cycle

• §2.2 Thrust generation1. Propulsion power and efficiency

2. Total efficiency

3. Parameter evolution along air passage

4. Thrust distribution in the components

2

§2.3 Characteristics and specification of engine performance

1. Characteristics of performancea ． Thrust F

• Thrust is the most important character.

• Unit: N (Newton) or daN

• Hundreds to >10’s k daN

3

1. Characteristics

a ． Thrust F

• For jet engines, thrust cannot be directly equivalent to power.

• Roughly P= 450m/s F.

22)(

20909

09

20

29 vv

Fvv

vvqvv

qP mm

4

1. Characteristics

b ． Specific thrust Fs

• Thrust over air mass flow.

daN.s/kg

• On test bed, v0=0, v9 is specific thrust.

0909 )(

vvq

vvq

q

FF

m

m

ms

5

1. Characteristics

b ． Specific thrust Fs

• It’s important.• Mass flow determines dimension and weight o

f an engine. For a certain size and weight, the bigger Fs is, the bigger is the total thrust. 。

• In general, at test bed, Fs of a jet-engine is aro

und 60~75daN.s ／ kg at full power.

6

1. Characteristics

3 ． Ratio of thrust/weight

• FW, On ground (zero speed), ratio of the thrust at maximum power over the weight of engine .

7

1. Characteristics

3 ． Ratio of thrust/weight• This ratio is an important characterist

ic which represents design quality of aerodynamics, thermodynamics and structure of an engine.

• Turbojet——3.5~4• Turbojet afterburner——5~6• Turbofan afterburner——8• Fourth generation——10

8

1. Characteristics

4 ． Frontal area thrust• Ratio of total thrust over biggest frontal area

of the engine, FA 。• The area determines drag. • Unit: N/m2 ， or daN/m2.

• 8000 ～ 10000daN/m2 。• Important for fighters

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1. Characteristics

5 ． SFC (Specific Fuel Consumption)• Consumption of fuel per hour to generate 10 New

ton of trust. This is an economic characteristic.

（ 2-26 ）

here ： qmf—consumption of kerosene ， kg ／ s 。 sfc: kg ／ h·daN or kg ／ h·N 。Under ground, turbojet: 0.8~1.0kg ／ h·daN ， Tur

bofan: 0.5~0.6kg ／ h·daN ， even less 。

F

qsfc mf3600

10

1.5 ． sfc

• Using f=qmf/qm, ratio of fuel and air, then

sF

fsfc

3600

11

1.5 ． sfc

• Lower heating value of kerosene LHV ，J ／ kg ，

here ： q1——heat added to 1 kg of air ，J ／ kg.

then

1qqLHVq mmf

s

m

FLHV

q

FLHV

qqsfc

11 36003600

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1.5 ． sfc

• According to total efficiency q1/fs=v0/0 ，we have

c0 ——local sound speed

M0 ——flying Mach number

0

00

0

0 36003600

M

LHV

c

LHV

vsfc

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1.5 ． sfc

• C0 depends on local T. T C0 sfc

• Given M0, sfc reversely proportional to total efficiency. sfc is function of flying speed.

0

00

0

0 36003600

M

LHV

c

LHV

vsfc

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1. Characteristics

– Total thrust satisfies ONLY requirement of the airplane.

– Other 4 characteristics evaluate performance of engine, also that of airplane. They are all specific. For one daN of thrust:• 1 ／ Fs ——Air flow• 1 ／ FW ——Weight• 1 ／ FA ——Frontal area• sfc ——Consumption per hour

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1. Characteristics

• Other characteristics– Starting process

– Acceleration

– Stability

– Reliability

– Etc.

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§2.3 Characteristics & Specifications

• 2. Specifications– High ratio of thrust over weight

– Small frontal area

– Low sfc

– Stable

– Reliable

– Low cost

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2. Specifications

1 ． FW, FA

• The greater is the diameter, the heavy is the engine. Two parameters are considered together, but FW is more important.

• Specially for military use

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2. Specifications

1 ． FW, FA

• Fighter no longer high altitude, fast; but good maneuverability.

• Maneuverability depends on the thrust and weight of airplane where the engines are installed.

• Engine’s weight influences airplane’s weight.

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2. Specifications

1 ． FW, FA

• Nowadays, fighters with good maneuverability have ratio of thrust over weight greater than 1.1. This requires that engine has the ratio of greater than 8. If ratio is 5, airplane will be heavier (40%~80%) than 8 for the same distance.

• Next generation FW >10.

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2. Specifications

1 ． FW, FA

• FW depends on aerodynamics and thermodynamics design, new materials and reasonable structure design.

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2. Specifications

2 ． sfc

• Lower sfc, less consumption, more economic.

• Petrol will be exhausted, price increases

• For fighters, longer distance and time in air. It may be decisive for a combat.

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2. Specifications

2 ． sfc

For civilian airliners or transporters, this is more important. Longer distance and time in air, more charge, lower cost.

• Therefore, we always try to lower sfc.

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2. Specifications

3 ． stability

• Stability is from point of view of aerodynamics and thermodynamics.

• Engine may go out of the surge line. Airflow oscillation may stop the engine. Parts may be overheated, etc.

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2. Specifications

3 ． stability

• Starting and accelerating could enter in surge range.

• For fighters, flight envelop map means aircraft’s performance. Maneuvers depend also on engine’s stability.

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2. Specifications

4 ． reliability

Reliability is based on structural strength, integrity.

–Life

–Time between shop visits

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2. Specifications

4 ． reliability

–Time between shop visits

For fighter, 100-400h. Too long may reduce other performance.

For civilian, 5k-10kh.

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2. Specifications

4 ． reliability

• With development of detection technologies, many sensors are installed in engines. They can give us an accuracy information for maintenance or replacements of parts.

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2. Specifications

4 ． reliability

We must say: no one of transportations is absolute safe. Normally reliability includes 2 parts:• Accident ratio, number of accidents due to

engine failure in one million working hours;• Ratio of unpredicted replacements (Short

er life).

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2. Specifications

5 ． Cost

• Kerosene (fuel)

• Price

• Maintenance （ hours, materials, parts, equipments, etc. ）

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2. Specifications

– There are relations among above points

– Trade-off design according to requirements.

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§2.3 Characteristics and specification

• 3. Development tendency– Insure stability and reliability

– Increase engine’s performance Fs

sfc

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3. Development tendency

– From formula

– We obtain

–W →Fs

09 vvFs

2

20

29 vv

W

0202 vvWFs

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3. Development tendency

– Formula

– We obtain

)( *2

*3

'

1 TTc

qb

p

sHuF

qsfc 13600

sb

p

HuF

TTcsfc

)(3600 *2

*3

'

34

3. Development tendency

– Work

– where

11

1

)()(

1

01*3

'

0*29

*3

'

TcTc

TTcTTcW

pp

pp

0

*2p

p

35

3. Development tendency

–Let

–then

–and

1

e0

*3T

T

110 e

eTcW p

eTT

T

T

TTTT

0

0

*2

0

*3

0*2

*3

36

3. Development tendency

– here ， b ——combustion efficiency

0200 )1)(1(2 vv

eeTcF ps

0200

0

)1)(1(2

3600

vve

eTc

e

Hu

Tcsfc

pb

p

1

e0

*3T

T

37

3. Development tendency

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3. Development tendency

– T3*↑Fs↑

– For given T3*， exists an optimal to minimize sfc.

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3. Development tendency

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F135

• Pratt & Whitney F135 – Power for the Lockheed Martin F-35 Joint Strike Fighter (JSF) which will replace the F-16 Fighting Falcon, A-10 Thunderbolt II, AV-8B Harrier, and F/A-18 Hornet.

• Thrust – 40 000 lb

• No afterburner

• Production deliveries of the engine will begin in 2008.

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F135

• An evolution of the F119 that powers the F/A-22 Raptor, the F135 will serve the U.S. Air Force, Navy, Marines and Britain's Royal Navy and Air Force, as well as other international customers.

• The same F135 engine will be able to power the aircraft in all of its variants – conventional takeoff and landing (CTOL), carrier variant (CV), and short takeoff/vertical landing (STOVL).

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F119

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F135• The F135 engine will cost 35 percent less

to own than legacy systems. • It will require 30 to 50 percent fewer

maintenance technicians and 50 percent fewer airlift assets in deployment. The F135 is also designed to reduce the time for fault detection and repair by 94 percent and increase the time between shop visits by 225 percent over legacy systems. And it’s designed for growth and flexibility for decades.

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F135

• The F135 has a unique Integrated Lift Fan Propulsion System (ILFPS) for the STOVL variant of the JSF.

• The F135 will power the flights of all three variants of the F-35. Over 2,500 aircraft could be produced over the life of the program.

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F135