10/29/2009NASA Grant URC NCC NNX08BA44A Supersonic Combustion Theresita Buhler Sara Esparza Cesar...

10/29/2009 NASA Grant URC NCC NNX08BA44A

Supersonic Combustion

Theresita Buhler

Sara Esparza

Cesar Olmedo


Supersonic Outline

• Purpose & Goals• Introduction to combustion• Engine parameters• Jet Engine• Ramjet• Scramjet• Jet Engine vs. Scramjet• Model

– Reference stations• Analytical approach• Compressible flow

– Shockwaves• Inlet: Diffuser design

– COSMOSWorks design

• Engine: Cowl design• Combustion schemes & fuels• Exhaust: Expansion• Prototype design

– Materials– Design Specifications

• Installation in the wind tunnel– Location– Fuel lines and ignition wires– Hydrogen safety

• History• Cost• Acknowledgements• Questions


Hypersonic Vehicle

• High speed travel– Commercial flight

• Reaction engines

– Circumnavigation in four hours

• NASA Goals– Global reach vehicle– Reduced emissions

• Challenges– Shockwaves– High heat– Combustion instability– Flight direction control

NASA X-43 Vehicle

NASA X-51 Testing


Combustion

• Fuel

• Air

• Heat

• High pressure flow, at high compression

• Quickly changing conditions

• Temperature difficulties– Frictional heating

– High forced convection

• Highly turbulent

• Shock


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


Jet Engines

• Inlet design– Feed air into chamber

• Compressor blades– Increase pressure of flow

• Combustion chamber– Introduce fuel– House combustion

• Turbine blades– Capture expansion of exhaust

gases


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

• 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


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


ScramjetBoeing


Then and Now


What is Supersonic Combustion

Combustion maintained at supersonic speed

How is it achieved?

Design

Shockwave

Fuel Injector

Detonation Combustion


Shock Waves

• Oblique shocks

• Mach number decreases

• Pressure, temperature, and density increase

• Attached to vehicle

• Normal shocks



• Creates subsonic region in front of nose

• Detached


Shock Waves

• Oblique shock



• Expansion wave

• Mach number increases

• Pressure, temperature, and density decrease


Diffuser Development

• Wind tunnel specifications– Inlet speed

• Mach 4.5

– Cross-sectional area• 6 x 6 in

– Length of test section• 10 in


Design of Diffuser

• Initial design of diffuser• Use manifold design to

introduce fuel• Diffuser was designed in to

two separate pieces

Goal Seek18° 28.29°

19.67°


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


Design of Diffuser


2D Shockwaves


Inefficient Designs

Bow Shock – Cowl Interference Oblique Shock – Cowl Spillage


Cosmo Flowork AnalysisCosmo Flowork Analysis


Cosmos Flowork AnalysisCosmos Flowork Analysis

Velocity Profile Mach Speed Profile



Pressure ContoursInlet Mach = 4.5



Temperature ContoursInlet Mach = 4.5


Cosmos Flowork Analysis


Ramp Fuel InjectionsRamp Fuel Injections

Ramped Outward

Ramped Inward










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


CombustionParallel Mixing

Fuel- Air Mixing at mach speedsGas 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

Mixing Layer

δmU1

U2



• 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

δmU1

U2

Ya

Ya



• Molecular diffusion

• Fick’s Law

– 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

δmU1

U2

Ya

Ya

y

CDjA AFA

.



• Fick’s law for diffusion

dttxerf

yerfY

U

xD

CC

CY

y

CDjA

x

mA

c

FAm

FA

AA

AFA

0

2 exp2

41

2

1

8

.

Air ofFraction Mole Y

knesslayer thic Mixing

air ofion Concentrat

gradiention concentrat lateral theis

directiony in theflux diffusivemolar net theis

A

m

A

A

A

C

y

C

j


Combustion Parallel Mixing

δmU1

U2

Ya

Ya

xofroot square with theinversely decreases

rate mixing maximum e that thdemostrate results The

0,772.14

41

2

1

equation ion concentratmolar theatingDifferenti

0

mmmyy

A

mA

Y

yerfY



• 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

• More mixing is needed

• 2Lm is recommended by experiment

• enables complete micro-mixing

δmU1

U2

Ya

Ya

B1+B2X=Lm

B1

-B2

y

x

X=0



FA

Cm

m

m

c

FAm

D

bUL

Lx

b

U

xD

16

for Solving

2

8

2

Mixing layer thickness equation

δmU1

U2

Ya

Ya

B1+B2X=Lm

B1

-B2

y

x

X=0

Estimate injector height, B1+B2=B

to reduce mixing length, Lm



Manifolding idea

Multiple inlets

Reduce mixing length

Tradeoff: Inefficient design

Adds bulk and volume

Fuel

FuelAir

AirB δm

δm


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 )

1

12)(

2

)(

21

2

1

21

21

r

ruUUU

U

Ur

UUU

UU

c

c

r

r

u

x

u

x

yerf

r

r

u

u

c

c

1

1288

4

1

11

μ: dynamic viscosityν: kinematic viscosity


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


Combustion Turbulent shear mixing

Micro-mixingFuel vortexFuel wave


CombustionTurbulent Shear Mixing

• Mean velocity profile combines– Prandtl’s number

– Turbulent kinematic viscosity

– Time average characteristics of turbulent shear

3

431

11

yy

r

r

U

U

c

Micro-mixingFuel vortexFuel wave



Shear layer width – Two methods

m

m

lB

xr

rB

1

16 2

Local shear layer width for turbulent shear mixing

xr

rCm

1

1

Recent researchCδ is a experimental constant



• 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

2

1

2

12

1

21

22

11

2222

2111

2

1

2

1

2

1

UU

UU

U

Us

PP

UUU

UUU

uPuP

s

c

c

c

c



• Convective velocity for the vortex structures

• With compressible flow using isentropic stagnation density equation changes to

2

22

1

11

1222

212

11

2/12

2/11

2

1

1

2

11

2

11

1

a

UUM

a

UUM

MM

s

UsUU

cC

cC

CC

c



• Density correct expression for shear layer growth including compressibility effects

213

1

2/1

2/1

2/1

2/11

8.2.)(

1129.1

1

11

12

1

1

1)(49.

cMc

cm

eMf

rrrsrs

rs

rs

rCMf

x



Only applies to box cowl



Based on what we know the angle of our hydrogen injection should be

To produce a hydrogen rich mixture

• Fuel

air

Lm, A

Lm, F


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


Diffusion Combustion

• Symmetric flame

• Stoichiometric ratio– Varies across flame

• Flame center– Highest temperature, fuel

• Air lost around edges


Conductive Combustion

• Diffusion and premixed combined

• Stoichiometric ratio– Determined by pre-mixture

• Flame center– Highest temperature, fuel

• Air lost around edges


Supersonic Wind TunnelSupersonic Wind Tunnel

Commission of pressure tank

Team

Assistant dean Don Maurizio

Technician Sheila Blaise

Professor Chivey Wu

Wind tunnel team : Long Ly, Nhan Doan


ApparatusApparatus


Fuel Supply

• Follows test rig of wind tunnel

• Stainless steel lines– Leak proof

– Tank pressure


HydrogenHydrogen

Scramjet X-43

Expensive fuel

Much less emissions than hydrocarbons

Dangerous

Invisible flame

Detailed analysis

Calculations & numerical

Safety procedures

Experimental

Safety analysis

O2HO2H 222


Hydrogen Safety EquipmentHydrogen Safety Equipment

Tank

Carbon fiber, non-burst tank

Liquid check valve

Gas flashback arrestor

Infrared camera

FLIR Thermacam$3,500.0


Materials

Hastelloy

Nickel Steel

Reinforced carbon-carbon

BMI

Stainless steel 430


Costs

Group Item Price

Fuel

Hydrogen + Regulator

Catalyst - Silane

$275.

$125.

Materials

Steel $400.

Manufacturing

In-house

Wind Tunnel Retrofit

Gauges, Channels, $350.

View Windows

2 Sapphire 1” x 0.375” $700.

Total $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


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


Textbook ReferencesTextbook 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. “Fluid Mechanics”.


Journal ReferencesJournal 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 Flame-Holder 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.


AcknowledgementsAcknowledgements

• Dr. H. BoussalisDr. H. Boussalis

• Dr. D. GuillaumeDr. D. Guillaume

• Dr. C. LiuDr. C. Liu

• Dr. T. PhamDr. T. Pham

• Dr. C. WuDr. C. Wu

• SPACE Center StudentsSPACE Center Students• Combustion TeamCombustion Team• Wind Tunnel TeamWind Tunnel Team

– Nhan DoanNhan Doan– Long LyLong Ly

• Sheila BlaiseSheila Blaise• Don RobertoDon Roberto• Cris ReidCris Reid• Dr. D. BlekhmanDr. D. Blekhman

– Cesar HuertaCesar Huerta– Celeste MontenegroCeleste Montenegro

• Dr. C. KhachikianDr. C. Khachikian– Keith BacosaKeith Bacosa

• D. MaurizioD. Maurizio

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10/29/2009NASA Grant URC NCC NNX08BA44A Supersonic Combustion Theresita Buhler Sara Esparza Cesar...

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