Profiles of static temperature and hydroxyl radical concentration were measured in a two-dimensional supersonic combustor test section 22.8 cm downstream of hydrogen injection. A high-pressure gas generator supplied vitiated air to the test section at Mach 2.44, atmospheric pressure, and a total temperature of about 2240 K. Room-temperature hydrogen was injected through a 0.40-cm step slot at Mach 1 and matched pressure. The measurements utilized a noninterfering spectral line absorption technique in which narrow ultraviolet emission lines of the hydroxyl electronic transition are absorbed by the broader absorption lines in the combustion gas. Comparison of the measured temperature profiles with theoretical calculations showed good agreement

Gaugler, R. E.

English

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NASA TECHNICAL
MEMORANDUM
COI
x
NASA TM X-3004
OPTICAL MEASUREMENT OF
STATIC TEMPERATURE AND
HYDROXYL RADICAL PROFILES IN
A HYDROGEN-FUELED SUPERSONIC COMBUSTOR
by Raymond E. Gaugler
Lewis Research Center
Cleveland, Ohio 44135
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • /MARCH 1974
https://ntrs.nasa.gov/search.jsp?R=19740010441 2020-03-23T10:45:14+00:00Z
1. Report No.
NASA TM X-3004
4. Title and Subtitle
OPTICAL MEASUREMENT OF
2. Government Accession No.
STATIC TEMPERATURE AND
HYDROXYL RADICAL PROFILES IN A HYDROGEN-FUELED
SUPERSONIC COMBUSTOR
. 7. Author(s)
Raymond E. Gaugler
9. Performing Organization Name and Address
Lewis Research Center
National Aeronautics and Space Administration
Cleveland, Ohio 44135
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546
3. Recipient's Catalog No.
5. Report Date
March 1974
6. Performing Organization Code
8. Performing Organization Report No.
E-7797
10. Work Unit No.
501-24
1 1 . Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
Profiles of static temperature and hydroxyl radical concentration were measured in a two-
dimensional supersonic combustor test section 22.8 cm downstream of hydrogen injection. A
high-pressure gas generator supplied vitiated air to the test section at Mach 2. 44, atmospheric
pressure, and a total temperature of about 2240 K. Room-temperature hydrogen was injected
through a 0.40-cm step slot at Mach 1 and matched pressure. The measurements utilized a
noninterfering spectral line absorption technique in which narrow ultraviolet emission lines of the2 1 ohydroxyl S - n electronic transition are absorbed by the broader absorption lines in the
combustion gas. Comparison of the measured temperature profiles with theoretical calculations
showed good agreement.
17. Key Words (Suggested by Author(s))
Spectral absorption
Temperature measurement
Supersonic combustion
Hydroxyl concentration
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20. Security Classif. (of this page) 21. No. of Pages
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OPTICAL MEASUREMENT OF STATIC TEMPERATURE AND
HYDROXYL RADICAL PROFILES IN A HYDROGEN-FUELED
SUPERSONIC COMBUSTOR
by Raymond E. Gaugler
Lewis Research Center
SUMMARY
Measurements of static temperature and hydroxyl radical concentration were made
in a two-dimensional supersonic combustor. Vitiated air was supplied to the combustor
at Mach 2. 44, atmospheric pressure, and a total temperature of about 2240 K. Room-
temperature hydrogen was injected through a step slot, parallel to the main stream at
Mach 1. 0 and atmospheric pressure. Data were taken at nine points across the stream
22. 8 centimeters downstream of the hydrogen injection station. The measurements
utilized the spectral line absorption technique in which narrow ultraviolet emission lines
o , p
of the hydroxyl E - -n electronic transition are absorbed by the broader absorption
lines in the combustion gas. Comparison of the results with theoretical calculations
showed good agreement in temperature, but the measured hydroxyl concentration dif-
fered markedly from the theoretical.
INTRODUCTION
The development of advanced, hypersonic aircraft will require airbreathing engines
in which combustion takes place in a supersonic airstream. In order to design effec-
tively the supersonic combustor of such an engine, reliable analytical techniques are
required to describe the mixing and combustion processes. To develop analytical tech-
niques requires that experimental data be available to test the analysis.
Reference 1 presents detailed probe measurements of total temperature, pressure,
and gas composition made for supersonic combustion of hydrogen in a vitiated airstream
using stepped wall injection. The results of a computer program to describe the mixing
with equilibrium combustion are also presented in reference 1.
The purposes of the tests described in this report were to demonstrate a measure-
ment technique which would produce no flow disturbance in a supersonic combustor and
to provide experimental data to check the analysis of Kurkov (unpublished data obtained
at the Lewis Research Center). To this end, profiles of static temperature and hy-
droxyl radical (OH) concentration were measured in the mixing and combustion zone
of the combustor of reference 1.
The measurement technique made use of the spectral line absorption method de-
scribed in references 2 to 4 in which narrow ultraviolet emission lines of the hydroxyl
2 + 22 - TT electronic transition are absorbed by the broader absorption lines in the com-
bustion gas.
Conditions in the combustor were Mach 2. 44, atmospheric pressure, and a total
temperature of about 2240 K. Hydrogen was injected at room temperature, Mach 1. 0,
and atmospheric pressure. Run times were limited to 3 seconds because of the use of
uncooled hardware.
EXPERIMENTAL APPARATUS
Facility
Figure 1 is a schematic of the combustor test section. A detailed description of
the hardware can be found in reference 1. Briefly, upstream of the test section was a
high-pressure hot-gas generator which burned an oxygen-hydrogen-nitrogen mixture.
The proportions were fixed so that the resulting hot-gas stream had an oxygen concen-
tration equal to that of air. The hot gas, with total temperature of about 2240 K, was
expanded through a contoured nozzle which produced a Mach 2. 44 parallel flow stream
at the entrance to the test section. Pressure at the test-section entrance was approxi-
mately atmospheric. The test section at the entrance was 5. 1 centimeters wide and
8. 9 centimeters high.
In the test section, room-temperature hydrogen was injected along the wall, from
behind a 0. 40 centimeter step slot, parallel to the vitiated airstream at Mach 1 and
atmospheric pressure. From the step slot the test-section height increased linearly
from 9. 4 to 10. 1 centimeters at the measuring station.
Runs were limited by the use of heat-sink hardware to a length of 3 seconds.
Optical System
For the OH absorption studies, the downstream test-section windows were re-
placed with brass plates containing a line of 0. 32 centimeter diameter holes, and thus
the windows were eliminated as a source of beam attenuation. Two sets of plates were
fabricated, which enabled measurements to be made on 0. 32 centimeter centers across
the stream 22. 8 centimeters downstream of the slot. The length of the optical path
through the test section L was the test section width, 5.1 centimeters.
The optical system is shown schematically in figure 2. The OH lamp, which is
described in references 3 and 4, was a water-cooled, end-view capillary discharge
tube. Water vapor was supplied to the lamp at a pressure of about 1 torr by pumping
on a sulfuric acid solution which was maintained at 0° C in an ice bath. A power supply
provided 40 milliamperes at about 5000 volts to the lamp for these tests. The emission
from the lamp was chopped and focused on the test-section centerline with a quartz lens.
The beam emerging from the other side of the test section was reflected by a spherical
mirror to a focus on the entrance slit of a 1/2-meter grating monochromater. The
monochromater was used in the second order, and this provided good separation of the/
spectral lines of interest, which were in the 0-0 band starting around 0. 307 micrometer.
The line intensity was measured by a photomultiplier located at the exit slit. The pho-
tomultiplier output was amplified with a lock-in amplifier, and the signal recorded on
an X, Y-recorder.
DATA ANALYSIS
The optical technique used to determine OH concentration and temperature in this
study was developed and used in the work of references 2 and 4. This method relies2 i 2
on the absorption of the narrow ultraviolet emission lines of the OH S - 77 elec-
tronic transition by the broader absorption lines in the combustion gas. The absorption
coefficient a can be computed from the experimental data:
in ^2
a= 1 (1)
where L is the path length in the absorbing gas, which was taken to be the width of the
test section. All symbols are defined in the appendix.
The OH concentration is given in reference 3 as
12NnH = e 2.40x10^ (2)
\Jtl - A rri v '
The Doppler line half -width b~ is determined from reference 5 as
Me2
(3)
A listing of the spectral lines used in calculating NQTT and their related constants is
given in table I.
The OH number density is converted to mole fraction through use of the perfect
gas law:
[OH]=NOH*T (4)
Before equation (2) can be evaluated, the temperature must be determined. This is
done, as described in references 2 and 3, by plotting ln(a/AkTJf T,,) as a function of
hcu>,/k for a number of different spectral lines. Assuming rotational equilibrium, the
resulting straight line has a slope of 1/T. This type of plot is referred to as a Boltzmann
plot. Figure 3 shows a typical Boltzmann plot for an optical path located at y = 1. 85
centimeters from the wall of the test section.
EXPERIMENTAL PROCEDURE
To determine temperature, absorption measurements for a number of different
spectral lines are required. Because of the short run times available, about 3 seconds,
it was necessary to duplicate the same run conditions a large number of times and
change the monochromater setting between runs. A reading of emission line intensity
with no absorbing gas present was recorded before and after each run. If the prerun
and postrun levels were not the same, within about 2 percent, the run was discarded.
During a run, conditions would change slightly because of heating of the test section. In
order to be consistent, the data plot was always read at the same time relative to gas-
generator shutdown.
Figure 4 shows a typical data recording. The top trace was taken immediately
before the run started. The bottom trace is the gas-generator pressure and indicates
when the run began and ended. The middle trace is the measured line intensity after
attenuation in the test section,, The point on the plot marked Read is 0. 5 second before
shutdown and is the point where data are picked off for each run. This procedure is
consistent with the technique used in reference 1.
After a series of runs was completed at one location, the optical system was re-
alined through the next window hole and another series of runs initiated. Because of the
large number of runs required to gather data, 226 for the conditions reported here,
there was not time to investigate other combustor conditions. Overall, data were
collected from nine different locations across the stream, ranging from 0. 6 to 6. 0 cen-
timeters above the wall, all at an axial location 22. 8 centimeters downstream of the
hydrogen injection step.
RESULTS AND DISCUSSION
A Boltzmann plot, like that shown in figure 3, was constructed from the data at
each of the nine locations. The data on each plot were fit to a straight line by using a
least squares technique. The temperature for each location was then determined as
the reciprocal of the sbpe of the line fit to the data. Figure 5 is a plot of static tem-
perature as a function of distance from the wall.
Once the temperature profile was determined, the concentration of the OH radical
could be calculated from equations (2) and (4).
The result of this calculation is figure 6, where OH mole fraction is plotted as a
function of distance from the wall. Included in figures 5 and 6 are curves theoretically
calculated by Kurkov. The calculations include the effects of wall boundary layer in the
free stream, initial nonequilibrium composition, and finite rate chemical kinetics. The
kinetic mechanism considers 18 reactions involving nine species, including HO0 and&
hydrogen peroxide (H2O2). The turbulent Lewis and Prandtl numbers are assumed to be
unity.
There is excellent agreement between theory and experiment in the location of the
peak of the temperature and concentration profiles.
In figure 5 the measured temperature profile shows a slower approach to free-
stream conditions than does the calculated. This difference is probably due to a com-
bination of assumptions in the theory and averaging effects in the experiment. The
theoretical calculations are for two-dimensional flow, whereas the experiment surely
includes three-dimensional effects, particularly within the combustion region. The op-
tical measurements are, effectively, averages over the cross section and along the
length of the beam'. This averaging is weighted heavily toward higher temperature re-
gions.
The cause of the discrepancy in magnitude between predicted and measured OH mole
fraction in figure 6 can be explained primarily as a path length effect. Although the tem-
perature calculation does not depend on the value of the optical path length, the OH con-
centration is inversely proportional to path length. In the experiment, the flow was not
necessarily uniform across the test section. In reality, there was an influence of the
side walls, and possibly the combustion was not uniform. A shortening of the active
optical length by these effects would yield a higher measured value of [OH].
SUMMARY OF RESULTS
The absorption of ultraviolet radiation by the hydroxyl radical was used to measure
the temperature and concentration profiles across a two-dimensional supersonic com-
bustor test section. Measurements were made 22. 8 centimeters downstream of the
point where hydrogen was injected parallel to the free stream and at matched static
pressure. The purpose of these measurements was to demonstrate the technique in a
combustor and to compile data against which to compare analytical calculations. The
results of the temperature measurements showed good agreement with theoretical cal-
culations. The measured hydroxyl concentration profile showed a peak where expected,
but the magnitude was well below that calculated.
Lewis Research Center,
National Aeronautics and Space Administration,
Cleveland, Ohio, November 15, 1973,
501-24.
APPENDIX - SYMBOLS
A. relative transition probability
bD Doppler line half-width
c speed of light
F constant in eq. (2) (from ref. 2); F = 2.0X10"4
h " Planck's constant
I measured line intensity after passing through absorbing gas
I measured line intensity before passing through absorbing gas
k Boltzmann's constant
L active optical length in test section
M mass of OH molecule
NOH number density of OH
[OH] mole fraction of OH
p static pressure
Q. Si.R' V rotation and vibration partition functions
T static temperature
Ty,T,, correction factor for vibration-rotation interaction (ref. 4)
a absorption coefficient per unit length, cm"
v wave number of spectral line, cm"
(t). lower state energy level, cm"
REFERENCES
1. Burrows, Marshall C.; and Kurkov, Anatole P.: Analytical and Experimental Study
of Supersonic Combustion of Hydrogen in a Vitiated Airstream. NASA TM X-2828,
1973.
2. Kaskan, W. E.: Hydroxyl Concentrations in Rich Hydrogen-Air Flames Held on
Porous Burners. Combustion and Flame, vol. 2, no. 3, Sept. 1958, pp. 229-243.
3. Lezberg, Erwin A.; and Buchele, Donald R.: Some Optical Techniques for Tempera-
ture and Concentration Measurements of Combustion in Supersonic Streams. NASA
TND-2441, 1964.
4. Lezberg, Erwin A.; Rose, Charles M.; and Friedman, Robert: Comparisons of
Experimental Hydroxyl Radical Profiles with Kinetic Calculations in a Supersonic
Nozzle. NASA TN D-2883, 1965.
5. Simmons, Frederick S. : Spectroscopic Pyrometry of Gases, Flames, and Plasmas.
ISA Trans., vol. 2, no. 2, Apr. 1963, pp. 168-189.
6. Learner, R. C. M.: The Influence of Vibration-Rotation Interaction on Intensities
in the Electronic Spectra of Diatomic Molecules. I. The Hydroxyl Radical. Proc.
Roy. Soc. (London), ser. A, vol. 269, no. 1338, Sept. 1962, pp. 311-326.
TABLE I. - CONSTANTS USED FOR HYDROXYL ULTRAVIOLET
ABSORPTION DATA REDUCTION
[From ref. 6.]
Rotational
line
Q! 5
Pj'2
Qj'6
<7
Ql,9
Q2, 11
Qo 10<J, 12
o^1, 13
Q, ,,wl, 15
Wave
number,
'"-1
cm
32403.5
32390.9
32381.0
32304.8
32297.4
32189.9
32152.0
32142.7
32045.4
Lower state
energy level,
hcwk
k
K
783.
120
1106
1551
2379
3522
4147
4765
6257
Relative
transition
probability.
Ak
42.2
12.7
50.6
51.0
75.8
84.2
92.5
108.8
125.2
Correction
factor.
TJ'J"
0.978
.998
.969
.969
.938
.926
.912
.881
.847
Entrance
(\\\\
Brass plate-\
Total height,
0.476cm; open
height, 0.400cm
i
Exit
. \\\\V
Hydrogen ,'
injection J
22.8cm-
LNine port
locations
Optical measuring station^
Figure 1. - Schematic side view of combustor test section.
rC hopper
rSpherical mirror
rTest section
Quartz
rOH lamp
CS-66398
Figure 2. - Schematic layout of optical system.
-3
-4
-5
-7
-8
Rotational
line:
0 1000
CS-6640Z
2000 3000 4000
Energy of lower state, K
5000 6000
Figure 3. - Boltzmann plot of hydroxyl absorption measurements
taken 1.85 centimeters from wall 22.8 centimeters downstream of
injection step. Rotational temperature, 1654 K.
10
100,—
S 401—
Time »-
Figure 4. - Typical data recording for Pj ^ l'ne taken 1.52 centi-
meters from wall 22.8 centimeters downstream of injection step.
2000i—
-Experimental
1800
^
Te
mp
era
tur
e,
1200
/I M Theoretical (Kurkov)
- /!\/ i \ \
_ o/o 1 \<J
1 \\
I \ V^
" ' V ^— ^^
 c
1 1 1 1 1
0 1 2 3 4 5 6
Distance from wall, cm
Figure 5. - Temperature profile measured by spectral line ab-
sorption 22.8 centimeters downstream of injection slot.
11
10'f l
,-210
OJ -,
o ICf3
ir/4r-
10',-5
O— Experimental
Theoretical (Kurkov)
Distance from wall, cm
Figure 6. - Hydroxyl mole fraction profile measured by spectral line
absorption 22.8 centimeters downstream of injection slot.
12 NASA-Langley, 1974 E-7797
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Optical measurement of static temperature and hydroxyl radical profiles in a hydrogen-fueled supersonic combustor

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