Lecture 11. Turbulent Combustion in Gas Turbine Engines

Lecture 11. Turbulent Combustion in Gas Turbine Engines X.S. Bai TC in Gas Turbines Content • • • • • Development of gas turbine Types of gas tur...
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Lecture 11. Turbulent Combustion in Gas Turbine Engines

X.S. Bai

TC in Gas Turbines

Content • • • • •

Development of gas turbine Types of gas turbines Gas turbine cycle Gas turbine combustor New gas turbine combustors for clean environment

X.S. Bai

TC in Gas Turbines

History of gas turbine/jet propulsion engine Hero of Alexandria, Egypt 130 BC

Chinese solid fuel rocket, 1000 AD Leonardo Da Vinci’s chimney jack, 1500 Giovanni Branca, Italy, 1629

Isaac Newton’s steam wagon, 1687 Johan Barber made first patent, 1791 X.S. Bai

TC in Gas Turbines

Gas turbine for modern aviation Frank Whittle, 1930, UK, submitted a patent for a gas turbine for jet propulsion Power Jets Ltd got contract from Air Minsistry In May 1941, the Whittle W1 engine made its first flight

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TC in Gas Turbines

Gas turbine for modern aviation

Gloster Whittle E28

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TC in Gas Turbines

Gas turbine for modern aviation Hans von Ohain and Max Hahn, 1936, Germany, submitted a patent for a gas turbine for jet propulsion Ernst Heinkel Aircraft Company made first true jet propulsion aircraft in 1939, Aug - Sept

Secundo Campiri, Italy, made a gasturbine engine for the CC-2 aircraft, 1940 American (with the help of the British) made W.IX engine in 1941, GE Later Westinghouse Corporation made contiuous development

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TC in Gas Turbines

Gas turbine for modern aviation

Ohain

Whittle

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TC in Gas Turbines

Rolls-Royce Today • • • • •

aero-engines marine propulsion systems energy business Annual sales of over £4.5 billion Orders of over £13 billion

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TC in Gas Turbines

Newton’s 3rd Law: principle of propulsion

MV

Equilibrium

Reaction

Action

Thrust = Mass x Velocity (MV)

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TC in Gas Turbines

Propeller versus Jet Propulsion Mvjet

Propeller - moves LARGE MASS of air at low velocity Mvaircraft

Thrust = M(vaircraft - vjet)

Thrust = m(Vaircraft - Vjet)

mVjet mVaircraft

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Jet - moves small mass of gas at HIGH VELOCITY

TC in Gas Turbines

Jet Engine Layout Compressor

Combustion Chamber

Exhaust Nozzle

mVaircraft mVjet

Shaft

Turbine

’Straight-through’ configuration

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TC in Gas Turbines

Different Jet Engine Types Civil turbofan Trent

Military turbofan EJ200

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TC in Gas Turbines

Reverse Thrust Net 25% to 30% thrust

85% thrust 15% thrust

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TC in Gas Turbines

Gas turbine cycle: Brayton cycle

40

Pressure (atmospheres)

Expansion/ Power 0 1500

Temperature (degrees C) 0 intake X.S. Bai

compression combustion

exhaust

TC in Gas Turbines

Gas turbine cycle: Brayton cycle

TR: temperature ratio a-b PR: pressure ratio a-b

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TC in Gas Turbines

Trend of gas turbine development

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TC in Gas Turbines

Gas turbine running conditions

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TC in Gas Turbines

Gas turbine combustor • • • •

Stright pipe Diffuser Flame stabilization Optimal air supply

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TC in Gas Turbines

Combustor Operation

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TC in Gas Turbines

Jet Engine Layout Can combustor

Whittle W1 engine, 1941

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TC in Gas Turbines

Turbulent flame shape and flame height (3) order of estimation

During time Δt, fuel molecule is convected from inlet to the tip of flame at a speed U, and oxygen molecule is transport by turbulence from air stream to the flame tip at a speed u’.

R

u’

U

H Δt ∝

2R ⇒H∝

H R ∝ U u' RU R ∝ u' I

I=u’/U: intensity of turbulence X.S. Bai

TC in Gas Turbines

Recall: Laminar flame shape and flame height - order of estimation

During time Δt, fuel molecule is convected from inlet to the tip of flame at a speed U, and oxygen molecule is diffused from air stream to the flame tip. D is diffusion coef.

R

U 2R

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H

H R2 Δt ∝ ∝ U D R 2U ⇒H∝ D

TC in Gas Turbines

Dependence of flame height on injection speed

U 2R

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TC in Gas Turbines

Dependence of flame height on burner diameter

laminar

H

turbulent

U R 2R ...

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TC in Gas Turbines

Jet Engine Layout Annular

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cannular

TC in Gas Turbines

Combustor Operation Primary zone Dilution zone Intermediate zone

Fuel spray nozzle

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Reverse flow combustor

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TC in Gas Turbines

Development of modern gas turbine for clean environment

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TC in Gas Turbines

General consideration 30

temperature range for low emissions

80

25 20

60

NOx 15

CO 40

10 20

5

0

0 1600

1700

1800

1900

2000

primary temperature, K

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TC in Gas Turbines

oxides of nitrogen, ppmv

carbon monoxide, ppmv

100

Other cocnepts • Variable geometry • Dry low NOx (DLN) combustion & lean prevaporized premixed (LPP) combustion • Humid air combustion • Rich burner, quick quench, lean burn (RQL) (premixed) • Catalytic combustion • Flameless combustion

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TC in Gas Turbines

Diffusion Flames

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TC in Gas Turbines

FLOX

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TC in Gas Turbines

Flameless: air staged combustion

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TC in Gas Turbines

Flames and flameless

flames

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FLOX

TC in Gas Turbines

Flames and FLOX

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TC in Gas Turbines

Flames and flameless

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TC in Gas Turbines