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
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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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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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Different Jet Engine Types Civil turbofan Trent
Military turbofan EJ200
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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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Trend of gas turbine development
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Gas turbine running conditions
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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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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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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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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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Diffusion Flames
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FLOX
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Flameless: air staged combustion
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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