Catalytic combustors have demonstrated the ability to operate efficiently over a much wider range of fuel air ratios than are imposed by the flammability limits of conventional combustors. Extensive commercial use however needs the following: (1) the design of a catalyst with low ignition temperature and high temperature stability, (2) reducing fatigue due to thermal stresses during transient operation, and (3) the development of mathematical models that can be used as design optimization tools to isolate promising operating ranges for the numerous operating parameters. The current program of research involves the development of a two dimensional transient catalytic combustion model and the development of a new catalyst with low temperature light-off and high temperature stablity characteristics

Bracco, F. V.

Bruno, C.

Royce, B. S. H.

Santavicca, D. A.

Sinha, N.

Stein, Y.

English

NASA Technical Reports Server

COUPLING OF TRANSPORT AND CHEMICAL PROCESSES 
I N  CATALYTIC COMBUSTION 
F.V. Bracco, C. Bruno, B.S.H. Royce, D.A. Santav icca  
N. S inha  and Y. S t e i n  
P r i n c e t o n  U n i v e r s i t y  
P r i n c e t o n ,  New J e r s e y  08540 
C a t a l y t i c  combustors have demonstra ted t h e  a b i l i t y  t o  o p e r a t e  e f f i -  
c i e n t l y  o v e r  a  much wider  range of f u e l  a i r  r a t i o s  t h a n  a r e  imposed by t h e  
f l ammabi l i ty  l i m i t s  of  c o n v e n t i o n a l  combustors. Ex tens ive  commercial u s e  
however a w a i t s  f u r t h e r  p r o g r e s s  i n  t h e  a r e a s  of i )  t h e  d e s i g n  of a c a t a l y s t  
w i t h  low i g n i t i o n  t empera tu re  - and h i g h  t empera tu re  s t a b i l i t y ,  ii) r e d u c i n g  
f a t i g u e  due t o  the rmal  s t r e s s e s  d u r i n g  t r a n s i e n t  o p e r a t i o n  and,  iii 1 t h e  
development of mathemat ical  models t h a t  can  be used a s  d e s i g n  o p t i m i z a t i o n  
t o o l s  t o  i s o l a t e  p romis ing  o p e r a t i n g  ranges  f o r  t h e  numerous o p e r a t i n g  
parameters .  
The c a t a l y t i c  combustion program a t  P r i n c e t o n  r e f l e c t s  t h e s e  needs f o r  
f u r t h e r  resea rch .  The c u r r e n t  program of r e s e a r c h  i n v o l v e s  t h e  development 
o f  a  two-dimensional t r a n s i e n t  c a t a l y t i c  combustion model and t h e  develop- 
ment of a  new c a t a l y s t  w i t h  low tempera tu re  l i g h t - o f f  and h i g h  t empera tu re  
s t a b i l i t y  c h a r a c t e r i s t i c s .  
A r e c e n t l y  developed two-dimensional t r a n s i e n t  model h a s  been 
used  t o  s t u d y  t h e  i g n i t i o n  of C O / A i r  mix tu res  i n  a p la t inum c o a t e d  c a t a l y -  
t i c  honeycomb. T h i s  model i n c l u d e s  c o u p l i n g  between t h e  g a s  and s u b s t r a t e ,  
r a d i a t i v e  h e a t  1 o s s . t o  t h e  o u t s i d e  and  r a d i a l  h e a t  l o s s e s  p r o v i d i n g  s o l u -  
t i o n s  f o r  t h e  two-dimensional t empera tu re  f i e l d  i n  t h e  s u b s t r a t e  and t h e  
two-dimensional temperature ,  composi t ion and  v e l o c i t y  f i e l d  i n  t h e  gas. 
The model h a s  been used t o  p r e d i c t  t h e  t r a n s i e n t  and steady'  s t a t e  u s i n g  
i n l e t  c o n d i t i o n s  f o r  which s t e a d y  s t a t e  exper imenta l  d a t a  i s  a v a i l a b l e .  I n  
t h e  c a l c u l a t i o n  t h e  i n l e t  c o n d i t i o n s  f o r  v e l o c i t y  and t empera tu re  a r e  s e t  
and  t h e  t r a n s i e n t  beg ins  by i n j e d t i n g  f u e l .  R e s u l t s  showing t h e  t r a n s i e n t  
behav ior  of t h e  s u b s t r a t e  and t h e  gas  a r e  p resen ted .  Th is  model i s  p a r -  
t i c u l a r l y  u s e f u l  f o r  p r e d i c t i n g  t h e  t empera tu re  g r a d i e n t s  i n  t h e  s u b s t r a t e  
which i n  t u r n  can  be used t o  p r e d i a t  t h e  the rmal  s t r e s s e s  i n  t h e  c a t a l y s t  
https://ntrs.nasa.gov/search.jsp?R=19830020959 2020-03-22T00:49:13+00:00Z
dur ing  t h e  t r ans i en t .  S ince  t r a n s i e n t  measurements a r e  no t  a v a i l a b l e  t h e  
ca l cu l a t ed  s teady  s t a t e  r e s u l t s  a r e  compared t o  s teady  s t a t e  measurements. 
The p red i c t ed  s teady  s t a t e  c a t a l y s t  temperature p r o f i l e  and t h e  exhaus t  gas 
composition a r e  found t o  agree  very w e l l  with measurements over  a  range of 
i n l e t  v e l o c i t i e s  and equivalence r a t i o s .  
Operat ing temperatures  of c a t a l y t i c  combustors o f t e n  exceed 1500 K, 
r e s u l t i n g  i n  unacceptably s h o r t  l i f e t i m e s  f o r  s tandard  c a t a l y s t s .  A new 
c a t a l y s t  has  been designed t o  e x h i b i t  long l i f e t i m e  a t  high temperatures  
and adequate i g n i t i o n  c h a r a c t e r i s t i c s  a t  low temperatures.  The c a t a l y s t  i s  
a  modified pe rovsk i t e  based on La (Cro,  5 ARo.5) 03. This  ceramic has  been 
doped t o  make i t  e l e c t r i c a l l y  conduct ive and consequently i t  can be 
r e s i s t i v e l y  heated t o  b r i n g  t h e  c a t a l y s t  up t o  t h e  requi red  l i gh t -o f f  tem- 
pera ture .  I n  add i t i on ,  plat inum has  been incorpora ted  i n t o  t h e  c r y s t a l  
s t r u c t u r e  t o  g ive  improved low temperature  l igh t -of f  while  having a  low 
platinum vapor p re s su re  a t  high ope ra t i ng  temperatures.  This  c a t a l y s t  can 
be  used i n  powdered form, by washcoating it onto  a h igh  temperature ceramic 
s u b s t r a t e ,  o r  a s  s i n t e r e d  monoly t h i c  s t r u c t u r e s ,  e. g. p l a t e s .  The advan- 
t a g e  of u s ing  t h e  c a t a l y s t  i n  t h e  form of p l a t e s  is  t h a t  they can be 
r e s i s t i v e l y  heated t o  a s s i s t  l i gh t -o f f .  However, t h e  c a t a l y s t  is  more 
r e a d i l y  a v a i l a b l e  i n  powdered form and t h e r e f o r e  t h e  f i r s t  tests wi th  t h e  
new c a t a l y s t  have been made wi th  i t  washcoated on a  honeycomb subs t r a t e .  
The s u b s t r a t e  used was mu l l i t e ,  t h r e e  inches  long wi th  1/16 i nch  square  
c e l l s .  Resu l t s  of experiments u s ing  a  pu re  platinum washcoat and a  
pe rovsk i t e  powder wi th  nominal 1.0% (by weight)  plat inum washcoat a r e  
presented.  The t e s t s  c o n s i s t  of e s t a b l i s h i n g  t h e  l igh t -of f  temperature and 
low temperature performance f o r  s e v e r a l  equivalence r a t i o s  and i n l e t  velo- 
ci t ies,  a f t e r  which t h e  c a t a l y s t  i s  "aged" f o r  s e v e r a l  hours a t  1500 O K  and 
then  t h e  l igh t -of f  and low temperature  experiments repeated. Prel iminary 
r e s u l t s  a r e  very encouraging i n d i c a t i n g  very l i t t l e  change i n  su r f ace  a c t i -  
v i t y  when used wi th  propane fue l .  T e s t s  wi th  hydrogen however i n d i c a t e  a 
poisoning e f f e c t  which quick ly  reduces t h e  a c t i v i t y  of t h e  c a t a l y s t .  
Resu l t s  from these  tests w i l l  be used a s  a guide i n  t h e  s e l e c t i o n  of t h e  
optimum platinum conten t ,  i n  terms of both adequate low temperature  l i g h t -  
o f f  and minimal high temperature aging, t o  be used i n  t h e  c a t a l y t i c  p l a t e s  
which w i l l  be produced and t e s t e d  i n  t h e  near  fu tu re .  
T R A N S I E N T  C A T A L Y T I C  COMbUST lON MODEL 
.................................... 
SOLVES COMPLETE COUPLED 2 - D  T R A N S I E N T  C O N S t K V A T l O N  E Q U A T I O N S  I N  
S O L I D  AND GAS 
+ P R E D I C T S  T R A N S I E N T  AND STEADY STATE, 2 - D  TEMPERATURE I N  S U B S T K A l t ,  
2 - D  V E L O C I T Y / C O M P O S I T I O N / T E R P E K A T U R E  I N  GAS 
I N C L U D E S  HADIAT1UI . I  W I T t l l N  C A l A L Y S T  BED Akb F k O H  F K U N l / B A L K  T U  
UP/DOWN STREAM CUi lBUSTUK WALLS 
I N C L U D E S  R A D I A L  HEAT L O S S E S  ( 1  s t .  N U N - A D I A B A T I C )  
HAS B E E N  USED TO P K E U I C T  T R A N S l E N T  AND STEADY S T A T E  C O / A I K  C A T A L Y l l C  
COMBUSTION I N  P L A T I N U M  COATELl HUNEYCOMB C A T A L Y S T S  U S I N G  ONE S T E P  
O V E R A L L  R E A C T I O N  FOR GAS AND WALL  R E A C T I O N S  
I N L E T  C O N D I T I O N S  FOR T R A N S I E N T  C A L C U L A T I O N  
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" THE I N I T I A L  HEAT RELEASE OCCURS NEAR THE ENTRANCE AT THE 
GAS-SOLID INTERFACE A$D I S  CONTROLLED BY HETEROGENEOUS 
REACTIONS. 
LARGE SPATIAL AND TEMPERAL TEMPERATURE GRADIENTS OCCUR I N  
THE SOLID i4EAR THE ENTRANCE CONTROLLED MOSTLY BY THE 
AVAILABIL ITY  OF FUEL, 
THE TEMPERATURE OF Ti iE SOLID NEAR THE ENTRAliCE ACHIEVES AUIOST 
I T S  F I N A L  VALUE BEFORE SIGNIFICANT HEATING OF THE BACK, 
HETEROGENEOUS REACTIONS AllD THE GAS HEATED UP FRONT A ~ D  FLOWING 
DOWNSTREAM HEAT THE BACK OF THE SOLID. 
THE OVERALL TRANSIENT TIME I S  CONTROLLED BY THE THERMAL INERTIA 
OF THE SOLID AND BY FORCED CONVECTION, 
RADIATION SIGN1 F I  CANTLY INFLUENCES BOTH TRANSIENT AND STEADY 
STATE PARTICULARLY NEAR THE ENTRANCE. 
THE OXIDATION OF CO OCCURS MOSTLY ON THE CATALYST AlJD SOON INTO 
THE TRANS1 ENT BECOMES DIFFUSION CONTROLLED, 
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K 
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AXIAL POSITION (MA) 
D E V F l  O P M t N T  OF NEW C A T A L Y S T  F O R  H I G H  TFHP O P E H A T I O N  
I) T w o  OBJECTIVES 
A )  LOW TEMPERATURE LIGHT-OFF; PT Ili C R Y S T A L  STRUCTURE 
8)  HIGH TEMPERATURE STABILITY, PARTICULARLY AGAINST LOSS O F  PT 
CRYSTAL S T R U C l U R E  
A P P R O X ~ M A T E L Y  C U B 1  c 
E A S Y  S U B S T ~ T U T I O N  O F  ~ M P U R I T I E S  
AT  A AND B SITES 
To C O N T R O L  PROPERTIES 
1) PEROVSKITES H A V E  BEEN EVALUATED A S  MHU MATERIALS,  AND H A V E  P R O V E N  HIGH 
TEMPERATURE ENDURANCE A N D  C A T A L Y T I C  A C T I V I T Y  
2 )  THE M A T E R I A L  I S  E L E C T R I C A L L Y  C O N D U C T I V E  AND MAY B E  H E A T E D  B Y  A P P L I E D  
VOLTAGE, E N A B L I N G  P R E C I S E  L I G H T - O F F  CONTROL 
3 )  PLATINUM DOPANT ADDED FOR LOW TEMP. L I G H T - O F F  C A P A B I L I T Y ;  T H E  PT I S  
C H E M I C A L L Y  BOUND I N  T H E  C R Y S T A L  STRUCTURE FOR S T A B I L I T Y  A N D  ENDURANCE 
4) MONOLYTHIC D E S I G N  OVERCOMES DRAWBACKS OF l N E R T  S U B S T R A T E  + A C T I V E  
C O A T I N G  C A T A L Y S T S  
MADE BY TRANSTECH AND SUPPIED BOTH A S  A ~ O W D E R  F O R  S L I P  C O A T I N G  A N D  
AS MONOLYTHIC P L A T E S  AND SPACERS FOR PARALLEL P L A T E  REACTOR 
MADE B Y  P R O F .  H A R L A N  A N D E R S O N ,  U N I V E R S I T Y  OF M I S S O U R I ,  AND S U P P L I E D  
AS A  POWDER S U I T A B L E  FOR S L I P  C O A T I N G  
D A T A  FROM 
MEADOWCROFT,  D-b. 
B R I T .  J. APP.  P H Y S  ;! ( 1 9 6 9 )  1225 
-1 I I 0 0.1 0.2 0.3 
Sr CONTENT. X 
A1 CONTENT. X 
Lo, (M9, Cr,, Al,), 0, 
ATM: pO = 16' otm 
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3 80 Ha' 
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- I 17A0°C 
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Weight loss (~glcm'lh) .of La., CHg.nsCr AT) -rrOt.r, r o  
function of Al content: Temperature - ii16*~; At.: Flovlng 
tas pixture (0.001 8 t m  02+0.1 atm Hz(HN2); Flov rate - 1 
D A T A  FROM 
PROF.  H.O. A N D E R S O N  
0 1 4 '  Lb "0.8 1% 
V )  TEST CONFIGURATIONS 
A )  SLIP COATED ONTO A  SUBSTRATE. A L 2 0 3  I S  A  PREFERRED S U B S T R A T E  FOR 
H I G H  TEMPERATURE OPERATION.  FOR L I G H T - O F F  TESTS,  M U L L I T E  MAY B E  
U S E D -  
D I S A D V W  P H A S E  DIAGRAM PROBLEMS; N O  DIRECT ELECTRICAL HEAT ING 
FOR L I G H T - O F F  CONTHOL-  
TAGFS PERMITS R A P I D  T E S T  OF M A T E R I A L  UNDER COMBUSTION 
C O N D I T I O N S  
B )  MONOLYTHIC STRUCTURES - POWDERS M A Y  B E  S INTERED T O  P R O D U C E  MONOLYTHIC  
MATERIALS IN T H E  F O R M  O F  PLATES.  DENSITIES BETWEEN 75% AND 95% 
T H E O R E T I C A L  ARE A C H I E V A B L E  AND P R O V I D E  A D E Q U A T E  P L A T E  STRENGTH. 
J I S A D V A N T A U  THERMAL S H O C K  C R A C K I N G  O F  M O N O L Y T H S  ( N E E D  T O  C O N T R O L  
D E N S I T Y  A N D  C O M P O S I T I O N  T O  M I N I M I Z E  THIS.) 
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PVANTAGES ELECTRICAL H E A T I N G  POSSIBLE FOR REACTION INITIATION. 
OOD E X P E R I M E N T A L  ACCESS. E S P E C I A L L Y  FOR L A S E R  PROBES. 
Distance from Catalyst lnlet (mm) 
AGING OF PURE PLATINUM CATALYST 
PROPANE FUEL, EQUIVALENCE RATIO = 0.42 
INLET TEMP. = 688 K, INLET VELOCITY = 9.9 
1400 - 
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1200 - 
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- 1000 
Distance from Catalyst Inlet (mm) 
PURE PLATINUM CATALYST 
HYDROGEN FUEL, EQUIVALENCE RATIO = 0.1 
INLET TEMP. = 590  K, INLET VELOCITY = 10.2 m/s 
Distance f rom Catalyst Inlet (mm) 
1400 
1200 
n 
Y 
c i  
- $ loo0 800 
I- 
6oo 
PURE PLATINUM CATALYST 
PROPANE FUEL, EQUIVALENCE RATIO = 0.28 
INLET TEMP. = 589 K, INLET VELOCITY = 10.1 m/s 
BEFORE AGlNG 
I $ AFTER AGING 4 HRS. 
- 1 
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I 1ST AGING 2 HRS. 
A 2ND AGING 7 HRS. 3RD AGlNG 10 HRS. $ 4TH AGING 1 2  HRS. 
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0 50 100 150 200 
4 0 0 0 " " ~ " ~ " ~ " " ~ " " 1  50 100 150 200 
Distance from Catalyst Inlet (mrn) 
PEROVSKITE WITH NOMINAL 1 % BY WEIGHT 
PLATINUM CATALYST 
HYDROGEN FUEL, EQUIVALENCE RATIO = 0.10 
INLET TEMP. = 591 K, INLET VELOCITY = 10.1 m/s 
PEROVSKITE WITH PIOMINAL 1% BY WEIGHT 
PLATINUM CATALYST 
PROPANE FUEL, EQUIVALEPICE RATIO = 0.30 
INLET TEMP. = 698 K, INLET VELOCITY = 6.0 m/s 
- - - - - - - - - - - - - - - - - - 1 s  AND 3RD AGING WITH PROPANE EA-J-A C Y S ~  2ND AND 4TH AGING WITH PROPANE AND HYDROGEN 
1400 
1200 
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I $ 1 9  AGING 2 HRS. 
I A 2FID AGING 7 HRS. 
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Distance from Catalyst Inlet (mm) 


Coupling of Transport and Chemical Processes in Catalytic Combustion

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