The optical and probe measurement of no: A comparative study

Eighteenth Symposium (International) on Combustion

The Combustion Institute, 1981

T H E O P T I C A L A N D P R O B E M E A S U R E M E N T O F NO: A COMPARATIVE

STUDYt

M. F. ZABIELSKI, L. G. DODGE,* M. B. COLKET, III AND D. J. SEERY United Technologies Research Center, East Hartford, CT 06108

Experimental facilities used in comparing the performance of optical and probe sampling methods for measuring NO are described. These measurements were made on flame systems fueled with methane, propane, and Jet-A. Both turbulent and nonturbulent subsonic flows were produced in these systems at temperatures up to 1900 K and a pressure of 1 atm. Optical absorptions by NO in the ~ (0, 0) b a n d (--2265A) were monitored in both high and low resolution. The high resolution (Ah = 0.015A) measurements were made only on flat flames (CH4-Oz-Nz) using a high pressure Xe lamp. Low resolution (Ah = 1.5 A) measurements were performed with a hollow cathode lamp (NO resonant) on flat flame, swirl burner and jet combustor exhausts. Optical data were reduced using a first principles spectral model and a multiple zone treatment of the opitical path. A comparison of NO measured optically with that measured after sampling with metallic and quartz water-cooled probes indicated agreement to within 25%. Similar agreement was observed only in lean methane flames with an uncooled metallic probe while in rich flames up to 80% of the NO was lost in the uncooled probe. A discussion of the studies done elsewhere which showed large discrepancies (x2-6) between the two techniques, and recent related studies, which did not show large discrepancies, is provided.

Introduction The study of nitric oxide (NO) formation via the Zeldovich process "~ or from fuel b o u n d nitrogen requires reliable measurement techniques. The reliability of existing probe methods, however, has been questioned because of ultraviolet (2265A region) NO absorption measurements (~'3'4) which yielded concentrations that were factors of 1.5-6 higher than those determined with probes. These discrepancies have been a concern not only to those studying combustion but also to those modeling the atmosphere. ~5~McGregor, Few and colleagues concluded that the discrepancies resulted from processes occurring within the probe which destroyed NO. Infrared gas correlation measurements by Gryvnak and Burch(6) made along with one of the ultraviolet measurements,(4~ however, indicated agreement with

t T h i s work funded by DOT-FAA Contract FA77WA-4081. ~Present Address: Southwest Research Institute, San Antonio, TX.

the probe concentrations to within typically 35%. More recently, Meinel and Krauss ~7~have reported ultraviolet differential absorption measurements which were in agreement to within 20-30% with probe determined concentrations being greater. Falcone et. al. (s~have reported measurements employing an infrared tunable diode laser which indicated agreement to within 20% with the optical concentration being higher. The probes used in these recent studies, however, were water-cooled and uncooled quartz, respectively, while in the original work, the probes were metallic. Moreover, the recent studies were made with fiat-flames while the original work employed jet combustors. The results which will be presented here were obtained in subsonic turbulent and nonturbulent media generated from both gaseous and liquid fuels. The probes employed were quartz and metallic, cooled and uncooled. The optical measurements were made in the ultraviolet with narrow-line (resonant) and continuum lamps. The purpose of these measurements was to investigate whether systematic errors biased the results of these measurement methods over a wide range of conditions.

1591

1592

COMBUSTION DIAGNOSTICS Apparatus

0

Z

1.0

o

Combustors Three combustors were employed. The first was a rectangular (17.5 • 9.2 cm) flat flame burner with a water-cooled, sintered-bronze top. Atmospheric pressure CH4--O2--N 2 flames were produced at stoichiometries of~b = 0.8, 1.0, 1.2. A typical temperature profile along the optical axis is given in Fig. 1. Temperatures were determined with I r / 6 0 % Ir40% Rh thermocouples whose readings were corrected for radiative losses. The temperature gradient present at the edge of the burner (8.75 cm) was due to the penetration of the exhaust stream by cold nitrogen which was used to purge NO from a trapped volume in front of the optical windows. To insure a significant optical absorption, the flame was seeded with NO. Figure 2 gives normalized distributions of NO determined with a water-cooled, metallic probe for lean and rich flames. The seed levels were 850 ppm on a wet basis. The second combustor was a swirl stabilized burner modeled after that described by Be6r and Chigier. ~) It consisted of a central fuel nozzle and an annular air supply. A moveable vane block arrangement provided variable swirl intensities from S = 0 to S = 2.5. The swirl number S is defined as the ratio of the tangential to axial momentum divided by the radius of the exit quarl. This burner was mounted in an atmospheric pressure, cylindrical expansion chamber which was configured to allow optical access. The optical path and probe tips were located 87.5 cm downstream of the quarl exit. P r o p a n e / a i r flames were produced at d~ = 0.8, 1.0, and 1.2 with swirls of S = 0.63 and 1.25. Temperatures along the optical axis were determined with an aspirated Pt/Pt-13% Rh thermocouple probe. A typical temperature distribution is given in Fig. 3. The diameter of the expansion chamber was ~ 5 6 cm. Windowless access ports were attached. Temperatures determined beyond the expansion chamber wall were measured with chromel-alumel thermocouples. To insure an adequate optical adsorption, NO was added to the air flow. Typical normalized

A

2000

u.i 1600

~ 1200

~. 800 400 10

-8

-6

-4

POSITION

-2 FROM

0

2

4

6

CENTERLINE

FIc. 1. Horizontal temperature CH4--O2--N 2 flat flame: ~b = 0.8.

8

10

(CM)

profile

w 0.8 uJ oo o.e Z

#

0,4

~

0.2 -10

-8

- 6

-4

-2

0

2

4

6

8

10

P O S I T I O N F R O M C E N T E R OF B U R N E R (CM)

FIc. 2. Normalized nitric oxide profiles over CH4---O2--N2--NO Flat Flame: - (d) = 0.8), .... ((~ = 1.2).

1400

A

1200 1000

\

800

t t |

600 /

400 ,.C - 4(

-30

i

j

-20

-10

0

i

i

10

20

9

i

30

I I I

-j

i

40

POSITION F R O M C E N T E R L I N E (CM)

FI(;. 3. Temperature profile across swirl combustor operating at ~b = 0.8 and S = 1.25: O ( P t / P t - 1 3 % Rh aspirated thermocouple probe); [] (0.010 in. chromel-alumel thermocouple).

concentration profiles obtained with a water-cooled, metallic probe are given in Fig. 4. The nominal seed value was 155 p p m on a wet basis. The third combustor was a single modified FT12 (Pratt & Whitney) b u r n e r which was fueled with Jet-A. This burner was mounted in the same expansion chamber used with the swirl burner. The air flow was seeded with NO. The thermocouples and probes used on the swirl burner were also used on this burner. The burner was operated at three simulated aircraft conditions: idle [f/a* = 0.0106], cruise [f/a = 0.0143], and maximum continuous [f/a = 0.0152]. Figures 5 and 6 give typical temperature and normalized concentration profiles, respectively, which were obtained 78 cm downstream from the combustor exit. NO r is also given. Probe measurements beyond the expansion chamber diameter were made with an uncooled stainless steel probe.

over

*f/a = fuel-air ratio.

OPTICAL AND PROBE MEASUREMENT OF NO r SWlRL=1.25 ~ - - - ' 1 r 1"0' SWIRL = 1"25t

1.2 u~ 1.0

~ 0.8F

r= 1.2, SWIRL = 1.2511 -"~1

IJ

o.oF

1.0

,,.__._:

,~ 0.8

,,,,~-,--..~

7 / I

/

,';i,

1593 \

\

~0.4

~ o0.0 . ~ ~ -40

-30

-20

10 20 3O 40 0

-10

POSITION FROM CENTERLINE (CM)

FIc. 4. Normalized nitric oxide profiles across swirl combustor: O (EPA probe); [] (1/16 in. S.S. tube, uncooled); 9 (reference probe at 180 torr); 9 (reference probe at 400 torr).

Probes/Sample Analysis A detailed description of the probes and operating conditions employed in this study is given by Colket et. al.; ~~ hence, only a brief summary will be given here. For the flat flame burner measurements, both water-cooled quartz and stainless steel probes (one with a copper tip) were used, each with an orifice diameter of 635 microns. In addition, an uncooled stainless steel probe was used for a limited number of measurements. A detailed fluid dynamic model ~~ indicated that the water-cooled probes quenched the gas sample primarily by convection. No aerodynamic quenching could be obtained despite pressure ratios (probe backpressure to flame pressure) as low as 0.05. For the large scale combustors, two water-cooled stainless steel probes were used. Each of these had an orifice diameter of 2 mm. One probe, which quenched reactions convectively,~~ was designated the EPA probe because it satisfied the present EPA enforced criteria for jet engine sampling. The second probe, which could quench reactions aerodyamically, if its backpressure was below 13.3 kPa (100 torr), m~ was designated the reference probe. Aerodynamic quenching was predicted by the fluid mechanical model and verified experimentally.

I

A 1000

i

n S _ ~ ~

800 600 4

0

0

_ L;o

~ o

II

t

~ I -

PosITION FROM

10 ;ENTERLINE

I I ~5 20 30 (CM)

40

F1c. 5. Temperature profile downstream of FT12 combustor: 9 (idle); 9 (idle); [] (cruise); 9 (cruise); ~, A (cruise, chromel-alumel).

/

0.2 -40

I

-30

-20

-10

10

20

30

40

POSITION FROM CENTERLINE (CM)

FIG. 6. Normalized nitric oxide profiles across optical axis for FT12 combustor: A (NO, EPA probe, idle); 9 (NOx, EPA probe, idle); 9 (NO, EPA probe, cruise); 9 (NOx, EPA probe, cruise); [] (NO, uncooled probe, cruise); 9 (NOx, uncooled probe, cruise). Backpressures for both probes were 53.2 kPa (400 tort) or less for all measurements. During the flat flame burner measurements, a Thermo Electron Corporation (TECO) Model 10AR chemiluminescent N O / N O analyzer was used. A TECO Model 300 Molybdenum Converter was employed for NO~ determinations. For the large combustor measurements, a Scott Model 125 chemiluminescent NO/NO xanalyzer was employed. A Scott Model 119 Exhaust Analyzer provided concentration data on CO, CO2, 02 and total hydrocarbons. All samples were dried before analysis.

Optical Figure 7 is a schematic representation of the optical equipment employed. With the fiat flame burner, the light sources were: (1) a hollow cathode resonant lamp which was designed after that of Meine]; ~jz~and (2) a high pressure Xe lamp (ConradHanovia 976C-0010) which provided a continuum source of radiation through the -~(0, 0) band of NO. The NO ~/(0, 0) narrow-line radiation, which consisted of discrete Doppler-broadened spectral lines, was produced in an air glow discharge (25 ma, 400 Pa). The spectrometer was a Jobin-Yvon (J-Y) 1.5 m Czerny-Turner spectrometer with a 2400 g/mm holographic grating. The photomultiplier was a Hamamatsu R-166 (solar-blind) cooled to -30~ in a Products for Research TE-177 thermoelectrically cooled housing. A Hewlett-Packard 7100B strip chart was used to record the data. For the large combustor measurements, the spectrometer was a SPEX 0.5 m Czerny-Turner. The photomultiplier was also a Hamamatsu R-166. Only the hollow-cathode lamp was employed for these measurements. The spectra were signal-averaged on

1594

COMBUSTION DIAGNOSTICS

WATER-COOLED PROBE HOLLOWCATHODE '~1

0.5 M or 1.5 M CZERNY-TURNER

(NO)p/(NO)., = In r c/ln'r 2 for the hollow cathode lamp and by (NO),/(NO)c, = lnr / l n ~

i

I ~r

U/ST/STREAM~ r-I

COOLEDPHOTOMUILTIPLIER-~"

]

II

i~

]

Fie. 7. Schematic diagram of optical apparatus.

a Northern Scientific NS575 Averager and recorded on 7-track digital tape (Northern Scientific 408F Interface, Wang Mod 7 Tape Transport).

(1)

(2)

for the continuum lamp. In order to determine Tm, it was necessary to account for intensity changes due to beam steering, scattering by particulates, continuum-type absorption by other molecules, etc., especially on the large scale combustor measurements. This was accomplished by monitoring "reference" bands emitted by the hollow-cathode lamp, i.e., NO ~/(3, 4) and ~/(2, 2). No appreciable absorption by NO occurs in this bands because they are not significantly populated at temperatures up to 2000 K.

Results Data Reduction The probe determined concentrations of NO were obtained on a dry basis to avoid changes in analyzer calibration from viscosity and quenching phenomena associated with HzO. Calibration gases used were gravimetrically prepared and certified to within 1%. The optical data were reduced using a first principles computer model for the ~/(0, 0) of NO (A~E§ -X2II). This model is described in detail elsewhereJ TM To compare NO measurements determined optically with those obtained by probe chemiluminescent analysis, it is important to note that the optical method determines the number of molecules per unit volume for an optical path under isothermal conditions. The probe method, on the other hand, gives its result in mole fraction irrespective of the temperature and pressure at the probe orifice. If the temperature is known along the optical path, then it is straightforward to effect a comparison. In practical combustion systems, however, gradients in temperature and pressure are encountered which require an approach developed by Gryvnak and Burch. ~6~In this approach, the optical path is divided into isothermal regions. The mean value of the NO number density is computed from the probe determined mole fraction, temperature, and static pressure for each of the isothermal zones. This information is then used to compute an effective optical transmission for each zone. The total transmission is determined by multiplying the zonal transmissions together. For the results presented, the transmissions calculated from the probe values are represented by "rc. The transmissions that are optically measured are represented by "rm. Quantitative comparison between the probe and optical results is defined by

Flat Flame Burner

Measurements were obtained on the CH4---O2--N 2 flames using water-cooled quartz, water-cooled stainless steel, and water-cooled stainless steel with a copper tip probes. Within the precision of the data (_+10%), all of these probes gave the same results for all stoichiometries. The purpose of the copper-tipped probe was to improve the cooling at the tip. Qualitatively, this was confirmed by the fact that there was no visible emission from the copper tip but considerable emission from the stainless steel tip. Both probes were of identical geometry and operated at the same backpressures. In addition, an uncooled stainless steel probe of geometry similar to the cooled probes was operated at the same backpressures. For the lean flame, the results were the same as those of the cooled probes. However, for the rich flame the NO concentration was only 20% of that obtained with the cooled probes. Two distinct types of optical measurements were made on the flat flame burner. The first type was made with the hollow cathode lamp. With the spectral model, which includes parameters describing both emitter and absorber characteristics, the results presented in TABLE I were obtained. The spectra were low resolution (Ah = 1.46A). Transmissions were determined for first and second bandheads of the ~/(0, 0) band (only two bandheads appear in low resolution). The precision indicated in the table and all subsequent tables indicate only the precision of the transmission measurement. If all of the uncertainties in the measurements, e.g., the spatial distribution of temperature along the optical path, are considered, it is estimated that the overall accuracy is +20-25%. The second type of measurement employed a

OPTICAL AND PROBE M E A S U R E M E N T OF NO

1595

TABLE I Comparison of nitric oxide results obtained with water-cooled probes and narrow-line ultraviolet absorption: Methane flat flames x(NO) centerline (wet) (ppmV)

1st bandhead %,

1st bandhead T

2nd bandhead T,,,

2nd bandhead ~c

[NO]p [NO]~ (Ave.)

0.8

1977

0.772 0.787

0.780

0.713 0.727

0.698

1.05 _+ 0.7

1.0

1862

0.821 0.817 0.824

0.794

0.758 0.755 0.760

0.721

1.16 _+ 0.03

1.2

1673

0.843 0.853

0.807

0.787 0.782

0.736

1.27 + 0.04

continuum lamp which provided a nearly constant intensity in the spectral region of interest. Since the 1.5 m spectrometer is capable of a resolution of 0.015A at 2260A in second order, it was possible to select absorption line pairs, and, in one case, a group of three lines. Measurements of single line pairs in high resolution provide an excellent confirmation of the spectral theory upon which the computer model is based and yield fundamental spectroscopic data required for reducing the hollow cathode lamp data. "4~ The lines used are given in TABLE II. TABLE III lists the comparison of the probe and continuum lamp measurements.

Large-Scale Combustors For any given condition of either combustor, the EPA and reference probes gave essentially the same value (+ 10%) of NO. Moreover, the results obtained by the reference probe whether operated in the aerodynamic or convective modes of quenching were in agreement (<10%). The optical measurements were made only with the hollow cathode lamp. The principle reason for this was that the 1.5 m instrument was not suitable for the harsh environment of a large combustor test cell.

A comparison of probe and optical results for the swirl burner is given in TABLE IV. The indicated precision is that associated with the measurement of the optical transmission. The sensitivity of the optical measurement to experimental uncertainties should be noted. For the case where ~b = 1.2, S = 1.25, and • = 103 ppm, a deviation in measured transmission of less than 3% represents a - 4 0 % discrepancy in NO concentration. A comparison of probe and optical results for the FT12 combustor is given in TABLE V. The agreement between the probe calculated transmission and the measured optical transmission is within the expected accuracy. It is important to mention that strong continuum type absorption (-80%) was observed during these measurements, especially under idle conditions. The precise cause of this absorption is not known. Without the use of the signal averaging technique, the interpretation of these spectra for the idle condition may not have been possible.

Discussion An analysis of the original work, (2'3'4~which indicated large discrepancies, has revealed seriouus difficulties. The first of these optical measurements,

TABLE II Spectral lines used in NO measurements in methane flat flames Group assignment

1

2

3

Line Identification

P2~(15.5) Q 12(15.5)

Q22(8.5) R 12(8.5) P~(26.5)

P22(16.5) Q12(16.5)

4 Q2z(9.5) R,2(9.5)

5

6

Pzz(17.5) Q2e(17.5)

Q2e(lO.5) R12(10.5)

1596

COMBUSTION DIAGNOSTICS FABLE III C o m p a r i s o n of n i t r i c oxide results o b t a i n e d w i t h w a t e r - c o o l e d p r o b e s a n d c o n t i n u u m u l t r a v i o l e t a b s o r p t i o n : M e t h a n e fiat f l a m e s •

qb = 0.8 G r o u p no. "rc "rm [NO] , / [ N O ]

,,,

1

2

0.744 0.764

0.748 0.760

0.745 0.741

1.10

1.05

0.98 •

(b = 1.0 G r o u p no.

1

"rc "r m

[NO] p / [ N O ] ,,p

2

5

6

0.754 0.757

0.747 0.739

0.739 0.722

1.01

0.97

0.93

= 1830 p p m c e n t e r l i n e (wet) 3 4

NOp/NOop (AVE.)

1.01 + 0.06

5

0.768 0.800

0.773 0.804

0.769 0.785

0.777 0.813

0.771 0.802

0.764 0.766

1.18

1.18

1.18

1.22

1.18

1.01

1.14 _+ 0.80

0.834 0.864 1.25

1.16 +_ 0.15

• qb = 1.2 G r o u p no. "rc Tm INO] p / [ N O ] ,,p

= 1923 p p m c e n t e r l i n e (wet) 3 4

1

2

--

0.839 0.875 1.32

-

-

--

= 1184 p p m c e n t e r l i n e (wet) 3 4 0.838 0.840 1.01

0.839 0.867 1.23

5 0.842 0.840 0.99

T A B L E IV C o m p a r i s o n of n i t r i c oxide results o b t a i n e d w i t h w a t e r - c o o l e d p r o b e s a n d n a r r o w - l i n e u l t r a v i o l e t absorption: Swirl combustor Centerline T • (NO) (K) ppmv

1st bandhead "rm

1st bandhead r,.

2nd bandhead "r

2nd bandhead "rc

NOp NO,, t Ave.

(b

Swirl

0.8

0.63

1200

192

0.827 0.813

0.816

0.772 0.768

0.749

1.07 + 0.06

1.0

0.63

1280

152

0.897 0.866

0.868

0.845 0.823

0.817

1.13 + 0.15

1.2

0.63

1220

103

0.924 0.924

0.903

0.894

0.864

1.32 + 0.05

0.8

1.25

1200

212

0.802 0.808

0.804

0.757 0.752

0.734

1.05 __+ 0.06

1.0

1.25

1280

156

0.847 0.855

0.867

0.824 0.823

0.815

0.97 __+ 0.10

1.2

1.25

1220

103

0.925 0.932

0.901

0.897 0.902

0.861

1.41 __+ 0.06

1.2

1.25

1220

135

0.882 0.861

0.872

0.845 0.819

0.822

1.04 +__ 0.11

OPTICAL AND PROBE M E A S U R E M E N T O F NO

1597

TABLE V Comparison of nitric oxide results obtained with water-cooled probes and narrow-line ultraviolet absorption: FT12 combustor

Condition

Centerline T • (NO) (K) ppmv

1st bandhead "rm

1st bandhead %:

2nd bandhead

2rid bandhead

v,~

x~

NOp NO,~ (Ave.)

Idle 1 Idle 2

580 580

120 175

0.789 0.621

0.792 0.711

0.690 0.595

0.725 0.625

0.93 0.82 set 0.87 1.03 1.07 set 1.05

-4- 0.08 _+ 0.13 + 0.11 _+ 0.06 + 0.00 _+ 0.05

Cruise 1 Cruise 2

870 870

240 378

0.750 0.661

0.755 0.641

0.697 0.568

0.680 0.545

900

285

0.747

0.709

0.669

0.623

1.18 _+ 0.00

900

445

0.635

0.606

0.553

0.502

1.13 _+ 0.04 set 1.16 -4- 0.04

Max.

continuous 1 Max continuous 2

which was made on a jet engine exhaust, ~2> was interpreted by using a room temperature calibration procedure. This procedure was inadequate especially given the inhomogeneities of an afterburning jet engine exhaust. Given the p u b l i s h e d information, it is not possible to assess the adequacy of the probe measurements. The second of these optical measurements TM was interpreted with a spectroscopic model. Unfortunately, that model had major spectroscopic errors ~5''"~ and difficulties in the experimental procedures used to verify the model have been identifiedJ ~7~ Moreover, there is evidence to suggest that the probe procedures used in these second measurements were also inadequate for a supersonic flow, i.e., a stagnation zone in front of the probe) ~~ The third set of measurements ~4~made in parallel with the infrared gas correlation measurements, was interpreted with the faulty model. Selected data from these measurements have been reanalyzed with a correct model and have yielded concentrations within 20% of the probe and infrared values. ~'~ These third measurements were made on subsonic flows.

to infer an intrinsic deficiency in the probe technique.

Acknowledgments The authors wish to acknowledge the contributions of the following staff: Mr. D. L. Kocum and Mr. R. P. Smus for experimental aspects; Mrs. B. Johnson and Mr. R. E. LaBarre for data reduction; Mr. P. N. Cheimets, Mr. M. E. Maziolek, Mr. W. T. Knose and Mr. M. Cwikla for facilities support. In addition, we wish to thank Mr. J. D. Few and his colleagues at Arnold Research Organization for providing their original spectral model which formed the basis for the authors' revised model and for several helpful discussions. F u n d i n g for this work was provided by an Interagency Committee representing the Federal Aviation Administration (FAA), Air Force, Navy, National Aeronautics and Space Administration (NASA), and the Environmental Protection Agency (EPA).

REFERENCES

Conclusions The results of the present study plus the reanalysis of the original work indicate that no major discrepancies (>25%) related to processes occurring in probes have been identified. In fact, the evidence indicates that good agreement can be expected between results obtained from properly made and interpreted probe and optical measurements of NO in subsonic exhaust streams at temperatures up to 2000 K. Moreover, for supersonic exhaust streams, it is not possible to use the original measurements ~z'z~

ZELDOVICH, YA. B., Acta Physicochim. USSR 21, 577 (1946). 2. MCGREGOR, W. K., SEIBE~, B. L., AND FEW, J. D., Proceedings Second Conf. Climatic Impact Assessment Program (A. Broderick, Ed.), p. 214, Cambridge, Mass., November 1972. 3. FEW, J. D., BRYSON, R. J., McGREGOR, W. K., ANDDAVIS, M. G., Evaluation o f Probe Sampling Versus Optical In Situ Measurements o f Nitric Oxide Concentrations in a let Engine Combustor 1.

1598

4.

5.

6.

7.

8.

9.

10.

COMBUSTION DIAGNOSTICS

Exhaust. Paper presented at Third Int. Conf. on Environmental Sensing and Assessment; also available as AEDC-TR-76-180, January, 1977. FEW, J. D., MCGREGOR, W. K., AND GLASSMAN, H. N., Experimental Diagnostics in Gas Phase Combustion Systems (B. T. Zinn, Ed.), p. 187, AIAA, 1977. OLIVER, R. C., BAUER, E., AND WASYLKIWSKYJ,W., Recent Developments in the Estimation o f Potential Effects o f High Altitude Aircraft Emission on Ozone and Climate. FAA ALE-78-24, October, 1978. GRYVNAK,D. A. AND BURCH, D. E., Experimental Diagnostics in Gas Phase Combustion Systems (B. T. Zinn, Ed.), p. 205, AIAA, 1977. MEINEL, H., AND KRAUSS, L., Combustion and Flame 33, 69 (1978). FALCONE, P. K., HANSON, R. K., AND KRUGER, C. H., Measurement o f Nitric Oxide in Combustion Gases Using a Tunable Diode Laser. Paper presented at Western States Meeting/Combustion Institute, October 1979. BEI~R, J. M., AND CH1GIER, N. A., Combustion Aerodynamics (J. M. Be6r, Ed.), John Wiley and Sons, Inc., 1972. COLKET, M. B., ZABIELSKI,M. F., CHIAPPETTA, L. J., DODGE, L. G., GUILE, R. N., AND SEERY, D. J., Nitric Oxide Measurement Study: Probe Methods, Task II Report. Report prepared by United Technologies Research Center for DOT

11.

12. 13.

14.

15. 16.

17.

FAA under Contract FA77WA-4081, November 1979. Colket, M. B., Chiappetta, L. J., Guile, R. N., Seery, D. J., and Zabielski, M. F., Aerodynamic Behavior of Gas Sampling Probes. Paper presented at Eastern States Meeting/Combustion Institute, November 1979. MEINEL, H., Naturforsch. 30a, 323 (1975). DODGE, L. G., COLKET, M. B., ZARIELSKI,M. F., DUSEK, J., AND SEERY, D. J., Nitric Oxide Measurement Study: Optical Calibration, Task I Report. Report prepared by United Technologies Research Center for DOT-FAA under Contract FA77WA-4081, May 1979. DODGE, L. G., DUSEK, J., AND ZABIELSKI, M. F., Line Broadening and Oscillator Strength Measurements for the Nitric oxide y (0, O) Band. Paper accepted for publication in Journ. Quant. Spec. and Rad. Trans. DODGE, L. G. ANDDUSEr, J., Journ. Quant. Spec, and Rad. Trans. 23, 523 (1980). McGREGOR, W. K., FEW, J. D., KEEVER, D. R., LOWRY,H. S. III, ANDDAVlS,M. G., Journ. Quant. Spec. and Rad. Trans. 23, 529 (1980). Zabielski, M. F., Dodge, L. G., Colket, M. B., and Seery, D. J., Nitric oxide Measurement Study: Comparison o f Optical and Probe Methods, Task I l l Report. Report prepared by United Technologies Research Center for DOT-FAA under Contract FA77WA-4081, January 1980.

COMMENTS I. W. Daily, University o f California, USA. Would you briefly describe the deficiencies in the earlier published analyses. Author's Reply. The deficiencies in the earlier published analyses (see text references 2, 3, 4) are discussed in detail in references 10, 13, 15, and 17 of the text. Briefly, the most significant sources of difficulty in the spectroscopic theory were: (1) the equation relating band oscillator strength to line oscillator strength gave line oscillator strengths

which were too small by a factor of 4; (2) a sign in the equation for the H6nl-London factor for the Qll lines was in error; and (3) the equation for the number density in a rotational sublevel of the electronic ground state was incorrect. Unfortunately, absorption cell data were used to validate the faulty spectra model; therefore, questions concerning gas handling, optical, and electronic procedures also arose.