Supersonic Combustion
Theresita Buhler
Sara Esparza
Cesar Olmedo
10/29/2009
NASA Grant URC NCC NNX08BA44A
Supersonic Outline
•
•
•
•
•
•
•
•
Purpose & Goals
Introduction to combustion
Engine parameters
Jet Engine
Ramjet
Scramjet
Jet Engine vs. Scramjet
Model
•
•
•
•
– Materials
– Design Specifications
•
Installation in the wind tunnel
– Location
– Fuel lines and ignition wires
– Hydrogen safety
•
•
•
•
History
Cost
Acknowledgements
Questions
– Reference stations
•
•
Analytical approach
Compressible flow
– Shockwaves
•
Inlet: Diffuser design
– COSMOSWorks design
10/29/2009
Engine: Cowl design
Combustion schemes & fuels
Exhaust: Expansion
Prototype design
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Hypersonic Vehicle
• High speed travel
– Commercial flight
• Reaction engines
– Circumnavigation in four hours
• NASA Goals
NASA X-43 Vehicle
– Global reach vehicle
– Reduced emissions
• Challenges
–
–
–
–
Shockwaves
High heat
Combustion instability
Flight direction control
NASA X-51 Testing
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Combustion
• Fuel
• Air
• Heat
• High pressure flow, at high compression
• Quickly changing conditions
• Temperature difficulties
– Frictional heating
– High forced convection
• Highly turbulent
• Shock
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Engine Parameters
Fit engine to aerospace system
Jet Engines – Low orbit, max Mach 3
Ramjets – High altitude, supersonic flight, subsonic combustion
Scramjets – High altitude, hypersonic flight, supersonic combustion
10/29/2009
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Jet Engines
• Combustion chamber
• Inlet design
– Feed air into chamber
• Compressor blades
– Increase pressure of flow
10/29/2009
– Introduce fuel
– House combustion
• Turbine blades
– Capture expansion of exhaust
gases
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Ramjet
•
•
•
•
Vehicle travels at supersonic
speed
Simplest air-breathing engine
No moving parts
Compression of intake achieved
by supersonic flow – inlet speed
reduction
– Shockwave system
•
Relatively low velocity
10/29/2009
• Combustions at subsonic speeds
• Very high reduction in speed
– High drag
– High fuel consumption
– Temperature at 3000 K (4940°F)
• Diffuser
–
–
–
–
Exit plane contracts
Exhaust at supersonic speed
Travel: M = 3
Combustion: M= 0.3
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Scramjet
• Hypersonic flight
• No moving parts
• Combustion at Supersonic speed
– Flow ignites supersonically
– Fuel injection into supersonic air
stream
– Steer clear of shock waves
• Is Aerodynamically challenged
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Scramjet
Boeing
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Then and Now
10/29/2009
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What is Supersonic Combustion
Combustion maintained at supersonic speed
How is it achieved?
Design
Shockwave
Fuel Injector
Detonation Combustion
10/29/2009
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Shock Waves
• Normal shocks
• Mach number decreases
• Pressure, temperature, and density
increase
• Creates subsonic region in front of
nose
• Detached
10/29/2009
• Oblique shocks
• Mach number decreases
• Pressure, temperature, and density
increase
• Attached to vehicle
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Shock Waves
• Oblique shock
• Mach number decreases
• Pressure, temperature, and density
increase
10/29/2009
• Expansion wave
• Mach number increases
• Pressure, temperature, and density
decrease
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Diffuser Development
• Wind tunnel specifications
– Inlet speed
• Mach 4.5
– Cross-sectional area
• 6 x 6 in
– Length of test section
• 10 in
10/29/2009
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Design of Diffuser
• Initial design of diffuser
• Use manifold design to
introduce fuel
• Diffuser was designed in to two
separate pieces
18°
28.29°
19.67°
10/29/2009
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Goal Seek
Design of Diffuser
• Top part of the diffuser
• Has machined holes for fuel
and ignition wires.
• Also four holes for securing the
base of the diffuser
10/29/2009
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Design of Diffuser
10/29/2009
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2D Shockwaves
10/29/2009
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Inefficient Designs
Bow Shock – Cowl Interference
10/29/2009
Oblique Shock – Cowl Spillage
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Cosmo Flowork Analysis
10/29/2009
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Cosmos Flowork Analysis
Velocity Profile
10/29/2009
Mach Speed Profile
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Cosmos Flowork Analysis
10/29/2009
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Pressure Contours
Inlet Mach = 4.5
Cosmos Flowork Analysis
10/29/2009
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Temperature Contours
Inlet Mach = 4.5
Cosmos Flowork Analysis
10/29/2009
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Ramp Fuel Injections
Ramped Outward
Ramped Inward
10/29/2009
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Cosmos Flowork Analysis
10/29/2009
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Cosmos Flowork Analysis
10/29/2009
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Cosmos Flowork Analysis
10/29/2009
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Cosmos Flowork Analysis
10/29/2009
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Combustion
•
Combustion Stoichiometry
–
•
Ideal fuel/ air ratio
Recommended fuel for scramjets
–
Hydrogen
–
Methane
–
Ethane
–
Hexane
–
Octane
•
Only Oxidizer is Air
•
Maximum combustion temperature
–
•
Hydrocarbon atoms are mixed with air so
•
Hydrogen atoms form water
•
Oxygen atoms form carbon dioxide
Most common fuel for scramjets
–
Hydrogen
•
In scramjets, combustion is often incomplete due to the very short combustion period.
•
Equivalence ratio
–
Should range from .2 -2.0 for combustion to occur with a useful time scale
–
Lean mixture ratio below 1
–
Rich mixture ratio above 1
10/29/2009
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Combustion
Parallel Mixing
Fuel- Air Mixing at mach speeds
Gas phase chemical reaction occurs by the exchange of atoms between molecules as a results of
molecular collisions.
The fuel and air must be mixed at near-stoichiometric proportions before combustion can occur
Parallel Mixing of Fuel- Air
U1
Mixing
Layer
δm
U2
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Combustion
Parallel Mixing
•
Zero shear mixing
–
–
Both air and fuel velocities are equal
•
Shear stress doesn’t exist between streams
•
Coflow occurs
Lateral transport
•
Occurs by molecular diffusion
–
•
At fuel – air interface
No momentum or vorticity transfer
–
Axial development of cross –stream profiles of air mole fraction YA in Zero shear (U1=U2)
–
Fuel Mole fraction Profile is YF=1-YA
•
Mirror Image
Ya
Ya
U1
δm
U2
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Combustion
Parallel Mixing
•
•
Molecular diffusion
jA   DFA .
Fick’s Law
C A
y
– Air molecular transport rate into fuel
• Proportional to the interfacial area times the local concentration gradient.
– Proportionality constant
• DFA = molecular diffusivity
,
– Where DFA*ρ is approximately equal to molecular viscosity μ for most gases
Ya
Ya
U1
δm
U2
10/29/2009
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Combustion
Parallel Mixing
• Fick’s law for diffusion
jA   DFA .
YA
C A
y
j A is the net molar diffusive flux in the y direction
 C A 

  is the lateral concentrat ion gradient

y


CA

C A  CF
DFA x
Uc
m  8
YA 
1
2
C A  Concentrat ion of air

1  erf

erf  x  
10/29/2009
2

 m  Mixing layer thic kness
 4y


 m




YA  Mole Fraction of Air
 exp  t  dt
x
2
0
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Combustion
Parallel Mixing
Differenti ating the molar concentrat ion equation
YA 
 4 y 
1
1  erf  
2
  m 
YA 
 y 

y 0
4
m

1.772
m
, m  0
The results demostrate that th e maximum mixing rate
decreases inversely with the square root of x
Ya
Ya
U1
δm
U2
10/29/2009
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Combustion
Parallel Mixing
• Steepest concentration gradient at x = 0
• Mixing layer reaches the wall at x=Lm the air mole fraction still varies
from 1.0 at y=B1 and 0 at y= -B2
y
•
•
•
More mixing is needed
2Lm is recommended by experiment
enables complete micro-mixing
B1
Ya
Ya
U1
x
δm
U2
-B2
B1+B2
10/29/2009
X=0
X=Lm
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Combustion
Parallel Mixing
Mixing layer thickness equation
m  8
DFA x
Uc
Estimate injector height, B1+B2=B
 m  2b
to reduce mixing length, Lm
Solving for
x  Lm
U Cb2
Lm 
16 DFA
y
B1
Ya
Ya
U1
x
δm
U2
-B2
B1+B2
10/29/2009
X=0
X=Lm
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Combustion
Parallel Mixing
Manifolding idea
Multiple inlets
Reduce mixing length
Tradeoff: Inefficient design
Adds bulk and volume
B
Air
δm
Fuel
Air
δm
Fuel
10/29/2009
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Combustion
Laminar Shear Mixing
• Molecular diffusion alone cannot
meet the requirements of rapid
lateral mixing in supersonic flow
• Solution shear layer between both
layers
• U1>U2 , Uc=0.5(U1+U2 )
• Velocity ratio r =(U1/U2 )
• Velocity Difference Δ U= (U1-U2 )
U1  U 2
(U  U 2 )
Uc  1
2
u
1 r   4 y 
 1 
erf  
uc
1 r    
U 
r   1 
U2 
 8
1 r 
U  (U 1  U 2 )  2uc 

1 r 



μ: dynamic viscosity
ν: kinematic viscosity
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x
uc
8
2x  1  r 


u  1  r 
Combustion
Turbulent shear mixing
•
As we further increase the velocity
difference delta U
•
Shear stress causes the periodic
formation of large vortices
•
The vortex sheet between the two
streams rolls up and engulfs fluid
from both streams and stretches the
mixant interface.
•
Stretching of the mixant interface
increases the interfacial area and
steepens the concentration gradients
•
Shear mixing increases molecular
diffusion
10/29/2009
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Combustion
Turbulent shear mixing
Fuel wave
10/29/2009
Fuel vortex
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Micro-mixing
Combustion
Turbulent Shear Mixing
• Mean velocity profile combines
– Prandtl’s number
– Turbulent kinematic viscosity
– Time average characteristics of turbulent shear
3

U
1

r
y
y

     
 1 
3   4  
Uc
 1  r        
Fuel wave
10/29/2009
Fuel vortex
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Micro-mixing
Combustion
Turbulent Shear Mixing
Shear layer width – Two methods
Local shear layer width for turbulent
shear mixing
1 r 
x
1 r 
 m  6B 2 
B
10/29/2009
Recent research
Cδ is a experimental constant
1 r 
 m  C 
x
1 r 
lm

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Combustion
Turbulent Shear Mixing

s 1
2
P1 
1
1
1 u1 2  P2   2 u2 2
2
2
U1  U1  U c
U 2  U c  U 2
• Density effects on shear layer
growth – compressible flow
• Based on constant but different
densities
• A density ratio, s, is derived
• s can be calculated once
stagnation pressure and stream
velocities are known
P1  P2
1
2
s 
10/29/2009
U 1 U 1  U c

U 2 U c  U 2
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Combustion
Turbulent Shear Mixing
U1  s1/ 2U 2
Uc 
1  s1 / 2
  1 1
2
M C1 
1 
2


• Convective velocity for the vortex
structures
1
 1 1
M C1 
U1  U c
a1
MC2 
U c  U 2
a2
10/29/2009
  1
2
 1  2
MC2 
2


2
 2 1
• With compressible flow using
isentropic stagnation density
equation changes to
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Combustion
Turbulent Shear Mixing
• Density correct expression for shear layer growth including compressibility
effects

1  s1 / 2 r 
1/ 2

1/ 2
m


 1  r  1  s r 
1

s
r


 .49 f ( M c1 )C 
1



1/ 2


x
2
 1  s r 
 1  1.291  r  

1  r  

f ( M c1 )  .2  .8e 3 M c1
2
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Combustion
Turbulent Shear Mixing
10/29/2009
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Only applies to box cowl
Combustion
Turbulent Shear Mixing
Based on what we know the angle of our hydrogen injection should be
To produce a hydrogen rich mixture
Lm , F
• Fuel
air
Lm , A
10/29/2009
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Diffusion Combustion
Mixing Controlled Combustion
• High mixture temperature
• High reaction rates
• Limiting feature: mixing
Reaction Rate Controlled
• Low mixture temperature
• Adequate mixing
• Limiting feature: reaction rates
– Rate of heat release
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Diffusion Combustion
• Symmetric flame
• Stoichiometric ratio
– Varies across flame
• Flame center
– Highest temperature, fuel
• Air lost around edges
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Conductive Combustion
• Diffusion and premixed combined
• Stoichiometric ratio
– Determined by pre-mixture
• Flame center
– Highest temperature, fuel
• Air lost around edges
10/29/2009
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Supersonic Wind Tunnel
Commission of pressure tank
Team
Assistant dean Don Maurizio
Technician Sheila Blaise
Professor Chivey Wu
Wind tunnel team : Long Ly, Nhan Doan
10/29/2009
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Apparatus
10/29/2009
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Fuel Supply
• Follows test rig of wind tunnel
• Stainless steel lines
– Leak proof
– Tank pressure
10/29/2009
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Hydrogen
Scramjet X-43
2H2  O2  2H2O
Expensive fuel
Much less emissions than hydrocarbons
Dangerous
Invisible flame
Detailed analysis
Calculations & numerical
Safety procedures
Experimental
Safety analysis
10/29/2009
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Hydrogen Safety Equipment
Tank
Carbon fiber, non-burst tank
Liquid check valve
Gas flashback arrestor
Infrared camera
FLIR Thermacam
$3,500.0
10/29/2009
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Materials
Hastelloy
Nickel Steel
Reinforced carbon-carbon
BMI
Stainless steel 430
10/29/2009
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Costs
Group
Item
Price
Fuel
Hydrogen + Regulator $275.
Catalyst - Silane
$125.
Steel
$400.
Materials
Manufacturing
In-house
Wind Tunnel Retrofit
Gauges, Channels,
$350.
View Windows
2 Sapphire 1” x 0.375” $700.
10/29/2009
Total
NASA Grant URC NCC NNX08BA44A
$1,850.
Future Work
• Analytical study
–
–
–
–
Compressible flow
Gas dynamics
Diabatic flow
Chemical kinetics in supersonic
flow
• Numerical analyses
– FLUENT
• Supersonic wind tunnel
• Manufacturing
• Compressible flow class with Dr.
Wu
• Document calculations
10/29/2009
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Dramatic Quotes
Sustaining supersonic combustion is
“like trying to light a match in a
hurricane”
“There is currently no conclusive
evidence that these requirements
can be met: nevertheless, the
present study starts with the basic
assumption that stable supersonic
combustion in an engine is possible”
-Richard J. Weber
10/29/2009
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Textbook References
Anderson, J. “Compressible Flow.”
Anderson, J. “Hypersonic & High Temperature Gas Dynamics”
Curran, E. T. & S. N. B. Murthy, “Scramjet Propulsion”
AIAA Educational Serties,
Fogler, H.S. “Elements of Chemical Reaction Engineering” Prentice Hall
International Studies. 3rd ed. 1999.
Heiser, W.H. & D. T. Pratt “Hypersonic Airbreathing Propulsion”
AIAA Educational Searies.
Olfe, D. B. & V. Zakkay “Supersonic Flow, Chemical Processes, & Radiative
Transfer”
Perry, R. H. & D. W. Green “Perry’s Chemical Engineers’ Handbook”
McGraw-Hill
Turns, S.R. “An Introduction to Combustion”
White, E.B.
10/29/2009
“Fluid Mechanics”.
NASA Grant URC NCC NNX08BA44A
Journal References
Allen, W., P. I. King, M. R. Gruber, C. D. Carter, K. Y Hsu, “Fuel-Air Injection Effects on Combustion in Cavity-Based
Flameholders in a Supersonic Flow”. 41st AIAA Joint Propulsal. 2005-4105.
Billig, F. S. “Combustion Processes in Supersonic Flow”. Journal of Propulsion, Vol. 4, No. 3, May-June 1988
Da Riva, Ignacio, Amable Linan, & Enrique Fraga “Some Results in Supersonic Combustion” 4 th Congress, Paris,
France, 64-579, Aug 1964
Esparza, S. “Supersonic Combustion” CSULA Symposium, May 2008.
Grishin, A. M. & E. E. Zelenskii, “Diffusional-Thermal Instability of the Normal Combustion of a Three-Component Gas
Mixture,” Plenum Publishing Corporation. 1988.
Ilbas, M., “The Effect of Thermal Radiation and Radiation Models on Hydrogen-Hydrocarbon Combustion Modeling”
International Journal of Hydrogen Energy. Vol 30, Pgs. 1113-1126. 2005.
Qin, J, W. Bao, W. Zhou, & D. Yu. “Performance Cycle Analysis of an Open Cooling Cycle for a Scramjet” IMechE, Vol.
223, Part G, 2009.
Mathur, T., M. Gruber, K. Jackson, J. Donbar, W. Donaldson, T. Jackson, F. Billig. “Supersonic Combustion
Experiements with a Cavity-Based Fuel Injection”. AFRL-PR-WP-TP-2006-271. Nov 2001
McGuire, J. R., R. R. Boyce, & N. R. Mudford. Journal of Propulsion & Power, Vol. 24, No. 6, Nov-Dec 2008
Mirmirani, M., C. Wu, A. Clark, S, Choi, & B. Fidam, “Airbreathing Hypersonic Flight Vehicle Modeling and Control,
Review, Challenges, and a CFD-Based Example”
Neely, A. J., I. Stotz, S. O’Byrne, R. R. Boyce, N. R. Mudford, “Flow Studies on a Hydrogen-Fueled Cavity FlameHolder Scramjet. AIAA 2005-3358, 2005.
Tetlow, M. R. & C. J. Doolan. “Comparison of Hydrogen and Hydrocarbon-Fueld Scramjet Engines for Orbital Insertion”
Journal of Spacecraft and Rockets, Vol 44., No. 2., Mar-Apr 2007.
10/29/2009
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Acknowledgements
•
•
•
•
•
Dr. H. Boussalis
Dr. D. Guillaume
Dr. C. Liu
Dr. T. Pham
Dr. C. Wu
•
•
•
SPACE Center Students
Combustion Team
Wind Tunnel Team
– Nhan Doan
– Long Ly
•
•
•
•
Sheila Blaise
Don Roberto
Cris Reid
Dr. D. Blekhman
– Cesar Huerta
– Celeste Montenegro
•
Dr. C. Khachikian
–
•
10/29/2009
Keith Bacosa
D. Maurizio
NASA Grant URC NCC NNX08BA44A