Propane annular combustor for use in miniature gas turbine engine for wind tunnel

Burnett, M.

English

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DEVELOPMENT OF A 
PROPANE BURNING ANNULAR COMBUSTOR 
FOR USE I N  A 
MINIATURE GAS TURBINE E N G I N E  
B y  M a c k e n z i e  B u r n e t t  
P r e p a r e d  under  NASA C o n t r a c t  N A S I - 7 2 6 1  by 
TECH DEVELOPMENT, INC.  
D a y t o n ,  O h i o  
for LangZey R e s e a r c h  C e n t e r  
https://ntrs.nasa.gov/search.jsp?R=19700020081 2020-03-12T01:59:32+00:00Z
SUMMARY 
This  r e p o r t  covers  t h e  completed work of NASA Modi f i ca t ion  
of c o n t r a c t  Number NAS1-7261 d a t e d  2 2  J u l y  1969 on t h e  develop- 
ment of a  Propane Burning Annular Combustor f o r  u s e  i n  a  Minia- 
t u r e  Gas Turbine  Xngine f o r  wind t u n n e l  t e s t  programs. The 
purpose of  t h i s  program was t o  de te rmine  t h e  minimum l e n g t h  of 
burner  s i m i l a r  i n  concep t  t o  t h a t  developed f o r  t h e  hydrogen 
burner  which could  o p e r a t e  s a t i s f a c t o r i l y  u s i n g  propane a s  t h e  
f u e l .  By t e s t i n g  it was determined t h a t  i t  i s  n o t  f e a s i b l e  t o  
use  propane a s  a f u e l  i n  a  c o n f i g u r a t i o n  such a s  was developed 
f o r  hydrogen a s  a  f u e l .  The d i f f e r e n c e s  between propane and 
hydrogen a r e  c o n s i d e r a b l e .  Propane flame v e l o c i t y  a t  atmospher- 
i c  p r e s s u r e  i n  a i r  i s  l e s s  t h a n  one f i f t h  t h a t  o f  hydrogen. The 
f u e l / a i r  mix tu re  a t  which propane w i l l  burn i s  i n  t h e  range  of 
2 . 3 7 %  t o  9 . 5 %  by volume w h i l e  hydrogen w i l l  burn i n  t h e  much 
l a r g e r  range of  4 %  t o  7 4 . 2 %  by volume. It  i s  t h i s  wr i te r ' s  
op in ion  t h a t  t h e  burning volume must be i n c r e a s e d  beyond r e a l i s -  
t i c  p r o p o r t i o n s  f o r  t h e  s m a l l  d iamete r  combustor proposed b e f o r e  
s u c c e s s f u l  o p e r a t i o n  of  a  propane f u e l e d  eng ine  cou ld  be  accom- 
p l i s h e d .  
INTRODUCTION 
Following t h e  s u c c e s s f u l  development of  a  combustor f o r  a  
m i n i a t u r e  g a s  t u r b i n e  e n g i n e  u s i n g  hydrogen a s  a  f u e l  (Ref.  1) 
an a t t e m p t  t o  develop a  s i m i l a r  burner  u s i n g  propane a s  a  f u e l  
was made on t h e  r e f e r e n c e  NASA c o n t r a c t .  One reason  hydrogen 
was o r i g i n a l l y  used was t o  keep eng ine  l e n g t h  a s  s h o r t  a s  p o s s i -  
b l e .  Th i s  development program was i n i t i a t e d  t o  de te rmine  how 
much l o n g e r  a  burner  must be u s i n g  propane a s  a  f u e l .  T h i s  pro-  
gram made use  of  e x i s t i n g  hardware used on t h e  hydrogen burner  
program. The c o n f i g u r a t i o n s  t o  be t e s t e d  were l i m i t e d  by t h e  
requ i rements  t h a t  t h e  b u r n e r  be u s a b l e  i n  a  m i n i a t u r e  g a s  t u r -  
b i n e  eng ine  on ly  of  somewhat longer  l e n g t h .  Four d i f f e r e n t  
burner  l e n g t h s  were made a v a i l a b l e  f o r  t e s t .  The s h o r t e s t  was 
t h e  same burner  used i n  t h e  hydrogen burner  development program. 
The l o n g e s t  was 2 .86  t i m e s  t h e  l e n g t h  of t h e  s h o r t e s t .  The 
d i a m e t r i c a l  dimensions w e r e  t h e  same on a l l  c o n f i g u r a t i o n s .  
TEST INSTALLATION 
The a i r  supply  f o r  t h i s  program was provided by a  S o l a r  
Model T-300-J-3 g a s  t u r b i n e  S t a r t  C a r t .  The a i r  was p iped  t o  
t h e  t e s t  s e c t i o n  by a  3.5 i n c h  p i p e  and was cooled  e n r o u t e  by 
two p a r a l l e l  s i n g l e p a s s  w a t e r  h e a t  exchangers .  A i r  f low was 
measured in the air line by use of an orifice plate. The liquid 
propane was stored in a GOO gallon tank. A propane fueled heat- 
er under the tank gasified the propane and maintained a constant 
pressure of 180 psig. A heated-insulated fuel line brought the 
f u e l  to the test cell. The burner section was mounted in a hor- 
izontal position in a test cell which was open at both ends. 
Remote controls for operating the test were located in a control 
room. Figure 1 shows the general layout of the test set up. 
Instrumentation 
Airflow rates were measured by a square-edged orifice in- 
stalled according to ASME specifications. The AP across the 
orifice plate was read on a mercury " U "  tube manometer. Air 
temperature for the flow calculations and for the combustion 
chamber inlet was measured with Iron-constantan thermocouples 
and read on a Honeywell multi-channel dial type instrument. 
Combustor exit air total tempzrature was measured with Chromel- 
Alumel ceramic insulated thermocouples on a recording chart type 
"Honeywell-.Brown Electronik" instrument. 
Propane temperature for the flow calculations was measured 
with an Iron-Constantan thermocouple on a Honeywell multi- 
channel dial type instrument. Inlet air total pressure was 
measured with a three-tube equal-area rake and read on standard 
dial type gages, 
CALCULATIONS 
The characteristics of the combustor are calculated as 
follows and the results are presented in Table 1. 
Combustion efficiency was defined as the ratio of actual 
temperature rise to theoretical temperature rise 
- 
AT (actual) 
nc AT (theoretical) 
Where T (theoretical) = 
AH 
-- 
(mCp) excess air + ( m ~ ~ ) ~ ~ ,  + (mCp)~,0 + (mCp)~, 

alld t h e  v a l u e s  f o r  ( m )  a r e :  
mexcess air = (mair  - l 5 . 5 8 )  l b s .  a i r / l b s .  f u e l  
m ~ O  = 3 l b s .  C 0 2 / l b s .  f u e l  
m = 1.6  l b s .  H O/lbs.  f u e l  
2 
m 
N2 
= (75 .5%) ((95.58) = 11.76 l b s .  N / l b s .  f u e l  
2 
The r e f e r e n c e  v e l o c i t y  used i n  t h i s  r e p o r t ,  which i s  a 
common term i n  t h e  g a s  t u r b i n e  i n d u s t r y ,  i s  based on maximum 
c r o s s  s e c t i o n a l  a r e a  of  combustor housing f low p a t h  and t h e  
s t a t i c  p r e s s u r e  and t empera tu re  a t  t h e  i n l e t  t o  t h e  combustor.  
The c a l c u l a t i o n s  a r e  based on r e f e r e n c e  2 .  
COMBUSTORS 
The combustion l i n e r  ( F i g u r e  2)  used on t h e  hydrogen burn- 
e r  program was used f o r  t h e  f i r s t  t r i a l  w i t h  propane a s  a f u e l .  
The n e x t  l i n e r  t o  be  used was t h e  l o n g e s t  l i n e r  ( s e e  F ig .  3)  
made. A w i r e  s c r e e n  was i n s e r t e d  a f t  of  t h e  f u e l  i n l e t  i n  a n  
a t t e m p t  t o  p r o v i d e  a f lame h o l d e r .  A i r  h o l e s  i n  t h e  l i n e r  were 
provided b o t h  f o r e  and a f t  of  t h e  s c r e e n  w i t h  t h e  a r e a  i n  pro-  
p o r t i o n  t o  t h e  expec ted  a i r  r e q u i r e d  f o r  combustion ahead of t h e  
s c r e e n  and t h e  remainder  a f t  of  t h e  s c r e e n .  The on ly  o t h e r  b a s i c  
c o n f i g u r a t i o n  t e s t e d  was t h a t  of  adding a t a i l  p i p e  t o  t h e  burner  
( s e e  F i g u r e  4 .  ) . 
RESULTS AND DISCUSSIONS 
The s h o r t  "hydrogen" burner  ( F i g u r e  2 )  u s i n g  propane was 
e n t i r e l y  u n s u c c e s s f u l  i n  t h a t  no burning took p l a c e  i n s i d e  t h e  
l i n e r .  The f lame a t t a c h e d  i t s e l f  a t  t h e  burner  e x i t  nozz le .  
The long b u r n e r  ( F i g u r e  3 )  was t h e n  i n s t a l l e d .  The same 
r e s u l t s  o c c u r r e d  a s  i n  t h e  s h o r t  burner .  I n  an  e f f o r t  t o  e n r i c h  
t h e  f u e l - a i r  m i x t u r e  two t h i r d s  of t h e  a i r  h o l e  a r e a  forward o f  
t h e  s c r e e n  was blocked o f f .  The run  was r e p e a t e d  w i t h  i d e n t i c a l  
r e s u l t s .  Up t o  t h i s  p o i n t  t h e  s p a r k  p lug  had been l o c a t e d  a t  
t h e  r e a r  o f  t h e  burner  i n  t h e  nozz le  s i m i l a r  t o  t h a t  of  F i g u r e  2 .  
The p l u g  was moved t o  a p o i n t  j u s t  a f t  of  t h e  s c r e e n  a s  i s  shown 
i n  F i g u r e  3 .  With t h e  s p a r k  p lug  i n  i t s  new p o s i t i o n  combustion 
SPARK PLUS 
-7 
FUEL INLET 7 
3 .500  D I A .  
~ 2 . 5 3 0  DIA. 
FIGURE 2 

/ I 
I !, ( ' I  
took  lace i n  t-Ile Surner. 
The I? r e s s u r e  r a t i o  and weight  f2sw f o r  this cor id i t io l~  vas 1.013 a.nd -066& lb/sec.,  respect ively ,  
Attempts t o  r a i s e  f u e l  flow and a i r  f low,  however, r e s u l t e d  i n  
pushing t h e  f l m e  o u t  o f  t h e  combustor and a t t a c h i n g  t o  t h e  back 
end of t h e  b u r n e r ,  Next t h e  covered a i r  h o l e s  w e r e  uncovered ,  
t h u s  r e t u r n i n g  t o  t h e  o r i g i n a l  d e s i g n  c o n d i t i o n s  and e s s e n t i a l l y  
t h e  same r e s u l t s  occur red .  Data f o r  t h e  maximum tempera tu re  and 
f low f o r  t h e  l a s t  two runs  a r e  shown i n  t h e  foPPowing t a b l e .  
TABLE 1 
A i r  f low- lbs . / see .  
A i r  Holes A i r  Holes 
Covered Uncovered 
,0675 -0664 
Propane flow-lbs./sec. 0038 .Oil38 
Ai r / fue% r a t i o  l4.459 17.186 
T h e o r e t i c a l  AT 351g°F 3566°F 
Ac tua l  Average AT 889OF 1175.33 
Combustion e f f i c i e n c y  33.9% 40.6% 
Average e x i t  t empera tu re  P06g°F %3Qfj°F 
Average i n l e t  t e m p e r a t u r e  180°P 190gF 
I n l e t  t o t a l  p r e s s u r e  15,815 p s i a  14 .774  p s i a  
Reference V e l o c i t y  18.3 f t . / s e c .  18.6 f t . / s e c .  
P r e s s u r e  r a t i o  1.033 1,033 
The maximum a i r  f low a t t a i n a b l e  w i t h  combustion i n  t h e  
burner  i s  c o n s i d e r a b l y  lower t h a n  t h e  g o a l  of  1 - 8 7  bbs./see. 
One l a s t  a t t e m p t  t o  keep t h e  f l m e  i n s i d e  t h e  burner  was 
made by i n s t a l l i n g  an e x h a u s t  p i p e  behind t h e  b u r n e r .  (See 
F i g u r e  4 ) .  The e x h a u s t  p i p e  made no a p p r e c i a b l e  d i f f e r e n c e .  
A t  t h i s  point,  t h e  program sras halted since it was f e l t  t h a t  
f u r t h e r  development o f  a  b u r n e r  o f  t h e  r e s t r i c t e d  s i z e  shown 
i n  F i g u r e  3  u s i n g  propane a s  a  f u e l  would be  unproduc t ive .  
CONCLUDING REMARKS 
T e s t i n g  o f  t h e  4 .00  i n c h  d i a m e t e r  a n n u l a r  combus tor  h a s  
i n d i c a t e d  t h a t  p ropane  f u e l  c a n n o t  be  burned  i n  t h e  s i z e  b u r n e r  
d e s c r i b e d  i n  t h i s  r e p o r t  a t  t h e  p r e s s u r e  r a t i o ,  mass f l o w  and 
t e m p e r a t u r e  r i se  d e s i r e d .  The propane  b u r n i n g  r a t e  and r a n g e  of  
f u e l - a i r  r a t i o s  i n  which it b u r n s  i s  such  t h a t  a  b u r n e r  o f  t h e  
s i z e  and d e s i g n  t e s t e d  i s  n o t  f e a s i b l e  f o r  p ropane  f u e l  a s  it 
was f o r  hydrogen  f u e l .  I t  i s  n o t  recommended t h a t  p ropane  f u e l  
be  c a n s i d e r e d  f o r  u s e  i n  a p p l i c a t i o n s  s i m i l a r  t o  t h o s e  r e p o r t e d  
on i n  t h i s  r e p o r t .  
REFERENCES 
1.- B u r n e t t ,  Mackenzie:  Development of A Hydrogen-Burning 
Annular  Combustor f o r  U s e  i n  A M i n i a t u r e  Gas Turb ine  
Engine.  NASA CR-66362, 1 9 6 9  NASA C o n t r a c t  NAS1-7261 
by Tech Development,  I n c .  
2 , -  P r e n t i c e  H a l l ,  Mooney, David A :  Mechan ica l  E n g i n e e r i n g  
Thermodynamics 


Development of a propane burning annular combustor for use in a miniature gas turbine engine

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