Notes on the Occurrence and Determination of Carbon Within Gas

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS345 E. 47 St., New York, N.Y. 10017

The Society shall not be responsible for statements or opinions advanced in papers or in dis-cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications.Discussion is printed only if the paper is published in an ASME Journal. Papers are available

SAC from ASME for fifteen months after the meetingPrinted in USA.

88-GT-164

Notes on the Occurrence and Determination of CarbonWithin Gas Turbine Combustors

J. ODGERS & E. R. MAGNANDept. genie mecanique

Universite Laval, Quebec, QC Canada G1 K 7P4

ABSTRACT

Details are presented of two series of experimentsto investigate carbon determination in gas turbinecombustion chambers. The first series employed agravimetric technique to examine carbon distributionwithin the various zones of a combustor with the aim ofidentifying zones of formation and oxidation.

In the second series a fairly comprehensiveinvestigation of the technique of measuring SmokeNumber was made with the objective of obtaining detailsrelevant to its accuracy and applicability. Mixtures ofiso-octane and benzene were used as fuel, therebypermitting the effects of hydrogen content to beestablished. The results are correlated with othersomeobtained previously.

NOMENCLATURE

A/F air/fuel mass ratioC carbon content - ug/LF/A fuel/air mass ratioFree C % of original fuel found as carbon (soot)h hydrogen mass fraction in fuelK a constantm total mass of gas passing through filter - gn a constantNA data not availablep 3 combustor inlet pressure - Pa or MPaR correlation coefficientSN Smoke NumberT 3 combustor inlet temperature - KT„ combustor outlet temperature - KX, SN correlation parameter =

[1/(A/F+1)][P3(1-h)3/(A/Fxh2)]2,7 T48,66

INTRODUCTION

Within the Combustion Laboratories of LavalUniversity over the past several years a considerableamount of work has been carried out on the measurementand prediction of exhaust smoke in gas turbines [1 -^ 6]especially with regard to fuel effects. The presentpaper has two major objectives; the first is a shortreview of the state of the art of the measurement and

prediction of exhaust carbon; the second is aconsideration of recent experimental work on thedetermination of Smoke Number in gas turbine exhausts.

2. A SHORT REVIEW OF WORK CONCERNED WITH THE SMOKENUMBER DETERMINATION IN GAS TURBINE COMBUSTOR EXHAUSTS

2.1 Definition of Smoke NumberThe Smoke Number generally used in the gas turbine

industry is the SAE Smoke Number [7]. It involvesfiltering a predetermined mass of exhaust gas through awhite filter paper. The reflectance of the filter paperis determined before and after the collection of thestain. The Smoke Number SN is then determined as 100 xthe change in reflectivity divided by the originalreflectivity. In a recent paper [8], Girling haspublished a correlation between SN and the smoke asdetermined gravimetrically. Figure 1 gives theseresults and a comparison with an earlier correlationgiven in [4]. The relationship may be expressed as anexponential function, and taking both sets of data(i.e. [4 & 8]) into account, evaluates as -

Carbon [pg/L] = 0,5194x10O,0283xSN (1)

102

x [4)

+ [81o [121o [13al / +• [13b)

e.,4 ^

mo

a^o

Xo

o/

10 20 30 40 50 60 70

SN (SAE)

Fig. 1 Gravimetric - Smoke Number Relationships

10 1

Carbon yg/L

100

10 1

Presented at the Gas Turbine and Aeroengine CongressAmsterdam, The Netherlands—June 6-9, 1988

Copyright © 1988 by ASME

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Equation 1 would appear to have a maximum error ofabout ± 10 % of the mass concentration for the range ofSN from 0 to 50. This is considered to be a reasonablysatisfactory agreement. The effects of other publisheddata [12 & 13] upon Eqn. 1 will be considered later(Smoke Number Calibration Tests). A feature of Eqn. 1is that it suggests a practical limit upon the maximumvalue of the determined Smoke Number since at highvalues a very small change in SN will result in a largechange in the gravimetric concentration (i.e. degreeof pollution), although the relative error remainssensibly constant at about 7%. This is illustratedbelow.

TABLE I

EFFECTS OF A UNIT CHANGE OF SNUPON THE SOOT MASS CONCENTRATION

SN 10 30 40 50 60 70 80 90Soot ug/L 1,0 3,8 7,4 14 28 54 105 204

SN Variation ±1ASoot ug/L 0,1 0,3 0,5 1,0 2,0 4,0 7,0 14

Obviously, the cut -off point will depend upon theaccuracy of the smoke measurement itself. Champagne[9] was among the first to address both the accuracy ofthe filtration technique and a comparison of the twomethods of determination (filtration and impingement).His results suggest that the filter paper techniquegives a repeatability of about ±10 % in terms of massper unit volume but that the two different techniquescould yield a three-fold difference in concentration.Girling [8] has also addressed the accuracy of the SNtechnique. He states that there can be considerableloss of particulates within the sampling line. Thus,with the maximum permissible length of line (25 ft)losses of about 25 % could occur due to particulatediffusion to and impaction on the sample line walls.Any bends in the line will exacerbate the situation. Hefurther states that for typical gas turbineparticulates (0,02 to 0,9 pm) the filtration medium isonly about 80 % efficient. Additional errors areattributable to batch variations of the filter papersand, unless the papers are carefully aligned within theholders, some 10 % error can occur in the readings. Allthis suggests possible cumulative errors of some 50 %in the determined Smoke Number. In addition, he pointsout that this technique gives no estimate of theparticle sizes and their distribution, a factor whichseems to be of rising importance if erosion is to berelated to particulate concentration. Despite all theselimitations, he concedes that it is very likely thatthe SN will be a much -used tool for at least the nextten years. Repeatability and reproducibility of SN, asdetermined in the Laval combustion laboratories, willbe discussed in section 3.

Wittig and Feld [10] measured the particle sizewithin a gas turbine exhaust, using a Multiple-Ratio-Single-Particle-Counter, and found a mean particle sizeof 1,3 pm, a value which is somewhat larger than thatsuggested by Girling [8] (above). For this mean sizeone might expect a somewhat improved filtrationefficiency compared to that cited by Girling.

2.2 A short consideration of smoke formation andburn-out within typical gas turbine combustors

2.2.1 Supposed zone behaviour. If, somewhatarbitrarily, one divides a gas turbine combustor intothree distinct zones (primary, secondary, dilution) one

may cogitate about the manner of soot formation andremoval. Since conditions within the primary zone areover-rich in many of its sub -regions, then this zonemay be regarded as the formation zone, per se. Thesecondary zone may generally be regarded as one oftransition. Depending upon the overall operatingconditions, this zone may have several or few richpockets, but it may generally be regarded as a burn-outregion. Without doubt, the dilution zone, with itslarge excess of oxygen, is a true burn-out regionproviding the temperature is sufficiently high (Carbonhas a negligible rate of combustion below 1200 K).

2.2.2 Some practical measurements - Two similarcombustors. Very little work has been published withregard to measurements of the soot distribution withinthe various zones of a gas turbine chamber. However,some 20 years ago, one of the authors was involved withsome preliminary experiments of this nature [11].Measurements of soot concentration were made at variousdiameters within two experimental combustors using afiltration technique which involved gravimetricdetermination. The results are not considered to have ahigh accuracy, but they do exhibit an interestinginsight as to behaviour within a real system. The twocombustors were operated at the same condition(T 3 = 667 K, p 3 = 0,79 MPa, A/F = 62,5) and therelative planes were - Plane 2 - Second row of primaryholes; Plane 3 - Secondary holes; Plane 4 - Dilutionholes; Plane 5 - Combustor outlet. The combustordiameter was 0,248 m. The two experimental combustorswere designed for the same duty and only had smalldifferences in combustor geometry (small variations inhole diameters and placement).

A comparison of the fuel/air distribution of thetwo units is given in Figs. 2 to 4. Figure 2 gives themean fuel/air distribution for the two units and showsthat combustor A has a considerably weaker primary zonethan combustor B, and this may well account for thelower carbon content found in combustor A. Past Plane 2combustor A is slightly richer than combustor B, andthe higher temperatures involved could well mean anincrease in the burn-out of the carbon.

0,2

Mean F/A at F

® Comb. AComb. B

0,1

0,0

3 Plane 4

Fig. 2 Mean Fuel/Air Distribution for two Combustors

The radial distributions of the fuel/air ratio(Figs. 3 & 4) are also interesting. Both combustorshave a fairly uniform distribution at Plane 2, but atPlane 3 combustor A indicates a hot core whereascombustor B suggests a cool core. For both units Plane4 has a hot core whilst Plane 5 is relatively uniform.On the basis of the fuel/air distribution one mightanticipate that the exhaust carbon content of combustorA would be less than that of combustor B. That this isso is shown in Figs. 5 to 7. The term 'free carbon' isdefined as the percentage of the original fuel which is


B Plane 2• Plane 3• Plane 4 •o Plane 5

0

•

0.15

0.10

F/A

0,05

0,00

20

R Free C

10

0

10_i

2 3 4 5

6Plane

Fig. 7 Carbon Distribution - Mean Values

102

10 1R Free C (al

100

10-1

10-2

y = 0.1439 " 10(9,4662x) R = 0,79

❑ ❑ /❑

data) ❑ ❑,^

cPAj

❑❑3 ❑ 6, 16®❑_m m

1 0 R Free C

Plane 2

-90 -55 -30 0 30 55 90Red. Dist. mm

Fig. 3 Fuel/Air Distribution - Combustor A

0,2

-90 -55 -30 0 30 55 90Pad. Dist. mm

Fig. 6 Carbon Distribution - Combustor B

• Plane 2

❑ Plane 3 10

I D Plane 4 Mean Frei

F/A © Plane 5

0,1

100

0 ,0 M].1 N:1.'1 tT4 , tti1:'I N9A , N1'1 N9

-90 -55 -30 0 30 55 90

Red. Dist. mm

Fig. Fuel/Air Distribution - Combustor B

•

•

❑ Comb. A• Comb. B

❑

'^—o

❑a,

4

R Free Carbor

3

2

1

0

a

o Plane 2

• Plane 3

■ Plane 4•

0 Plane 5

o ❑

-90 -55 -30 0 30 55 90

Red. Dist. mm

Fig. 5 Carbon Distribution - Combustor A

found as carbon (by mass) for any given measurementpoint. Both combustors indicate that the major burn -outof the carbon takes place between Planes 3 & 4 (i.e. inthe secondary zone). This would suggest that the majorfactor contributing to the burn-out is the combinationof the secondary dilution with the relatively hightemperatures associated with this region, althoughcombustor A clearly indicates additional burn -outdownstream of the dilution jets. What is not clear iswhether the lower carbon content at Plane 2 (forcombustor A) is due to reduced formation or to thecommencement of burn-out caused by the weaker fuel/airratio. However, both sets of results generally supportthe hypothesis put foreward in Para. 2.2.1.

10-2 10-1 t00

F/A All Data

Fig. 8 Relationship between Carbon and Fuel/Air Ratio

It seems obvious that the quantity of carbon foundin any zone has at least some dependency upon the localequivalence ratio. Figure 8 plots all the data in theform of the percentage free carbon versus thedetermined fuel/air ratio. Although there is a strongfunction (which is exponential in form) there is alsoscatter of an order of magnitude between the line andthe experimental values. The equations relating thefree carbon to the fuel/air ratio at the conditions ofoperation are -

3


Both Combustors - %Cfree = 0,144 x 109,47oF/A (2)

R = 0,79

Combustor A - %Cfree = 0,105 X 109,62-F/A (3)

R = 0,81

Combustor B - %Cfree = 0,201 x 109,21xF/A (4)

R = 0,80

It is not thought that there is any significantdifference in the accuracy of the three equations, andit is felt that, as a first approximation, Eqn. 2 wouldserve equally for both units.

3. SMOKE NUMBER CALIBRATION TESTS

It is obvious from Fig. 1 that the various workershave obtained considerably different results relatingthe SN to the gravimetric smoke content within theexhaust. Based upon all of the results given in Fig. 1the following equation (as distinct from Eqn. 1 whichwas based on the initially available data) was derivedfor SN values from 0 to 60 -

C = 0,62 x 100,0261xSN ug/L R = 0,92 (5)

This Equation has a standard deviation of 67 % anda maximum error of 211 %. At first consideration thiswould suggest the accuracy of determination to be verypoor indeed. However, if one examines the data ofFig. 1 there is a trend that the large particles giverise to high gravimetric values for any value of SN.This would suggest that a correction factor is neededto incorporate the size. However, for most routinesmoke number tests the size of the soot particles isunknown. Hence, it would appear to be dangerous toattempt to predict gravimetric smoke concentrationsfrom Smoke Number measurements unless a priorcalibration has been obtained for the specificequipment and fuel. In [12] Eckerle et al. suggest aform of equation for the relationship between sootconcentration and SN -

C = 0.177 SN1,234 R = 0,95 (6)(100 - SN)

This equation adequately describes the lowest curve ofFig. 1 and extends it to cover all values of SN from 0to 100. Obviously the real form of the curves of Fig. 1is sigmoidal, and Eqn. 6 gives the correct shape, andit is theoretically more correct than Eqn. 5 which islimited to values of SN up to 60. No matter whichequation is used, at high values of SN a small changein SN yields a very large change in the gravimetricvalue. This emphasizes the need to assess the accuracyof the technique throughout the gamut of possiblevalues of SN, and it poses the question as to whetheror not an improved accuracy is possible by changing thesampling conditions. The experimental programmedescribed here has been specifically aimed at thislatter question.

3.1 Experimental3.1.1 Paper variations and blank determinations.a) Variations due to different batches of paper.

Unfortunately, for the present work all the filterpapers available came from the same batch, so thiseffect could not be assessed here. However, Girling [8]suggests that errors due to this cause, plus those dueto poorly defined reflectance measurements, could be of

the order of ±10 %.b) Measurements on five different papers from the

same batch. Five virgin papers were marked with anominal N-pole which was aligned with a correspondingmark on the paper-holder of the reflectometer (PacificScientific RG-4600, 45° illumination, 90° measurement).Measurements of the reflectivity were made by rotatingthe paper at 30 0 intervals; the same measurements werethen repeated on the reverse side of the paper. Theresults are shown in Figs. 9 & 10. The angles ofrotation in both figures have been adjusted so as tobring the results in Fig. 9 approximately into phase.

-a PaperA+ Paper B

Paper C+ Paper Df Paper E

-6

0 100 200 300 400ANGLE

Fig. 9 Apparent SN obtained by rotating 5 filterpapers - Face-Up

0 100 200 300 400ANGLE

Fig. 10 Apparent SN obtained by rotating 5 filterpapers - Reverse Side-Up

Clearly the variation of apparent SN is cyclic(almost a sine function), and examination of the filtersurface showed a structure which could readily givethis effect. These variations certainly prove thenecessity of identifying the orientation of the blankpaper prior to experiment. The results also explainsome of the discrepancies noted when a singlemeasurement is taken. Foe instance, the maximumdifference between any two measurements taken on thesame face of the paper is approximately 9 in SmokeNumber. However, if the results are averaged for eachpaper the difference reduces to about 0,2.

c) Blank test runs. Prior to actual experimentalmeasurements with combustion, a series of tests wererun to see whether the air contained any particulatematter which might interfere with the determinations.The equipment and sampling technique were used exactly

4

SN Face

-2

-4

SN Back

2

0

-2

-4

-a Paper A+ Paper B

DE

4


as would be during a combustion run.Figure 11 gives a schematic of the sampling

equipment. It is reasonably conventional except that,in this case, the length of sampling line is equal tothe length of the probe and, therefore, losses due tothis cause are minimized. Also, there are no bendsbetween the probe and the filtration system. Previouswork on gas analysis had shown that the gases werereasonably well mixed at the sampling plane, and it wasassumed that, at the same plane, the smoke would alsobe reasonably well distributed.

RotameterVacuum Pump

TABLE II

NOMINAL OPERATING CONDITIONS FOR SMOKE MEASUREMENTS

mair,rig = 0,235 kg/s A/F = 75

T3 = 320 K p3 = 101 kPa

a) Constant sampling time (3 min 45 s):Sample mass flow g/min 5,20 7,63 10,2 12,5 14,9Total sample g 19,5 28,6 38,1 46,7 56,0

b) Constant sampling rate (7,63 g/min):Sampling time min 1,00 2,50 3,75 5,00 7,00 10,0Total sample g 7,63 19,1 28,6 38,1 53,4 76,3

y = 0,9509 " x0,5515 R = 0.99 08,6 x

x /0ps i+

/• eOAI / x

0 20% benzeneA 40% benzenex 60% benzene

x 0 80% benzene+ 100 R benzene

Thermocouple

Combustor

2

SN/SN 2

1

0Fig. 11 Schematic of Sampling System

Two procedures were used for the test measurements- a) the sampling rate was held constant (7,63 g/min),but the sampling time was varied (1 to 10 min).- b) The time was held constant (3 min 45 s), but thesampling rate was varied (5,2 to 14,8 g/min). Thenominal standard sample was 7,63 g/min for 3 min 45 s,that is a total of 28,6 g of exhaust gases through thefilter (calculated as air).

Passing air through the filters at the variousconditions described above yielded approximate valuesof SN < 1. It was decided that these amounts were sosmall (they showed no trends of any sort, neither withrate or sampling nor time of sampling) that they couldbe neglected. Consequently, no corrections were appliedto the tests described below.

3.1.2 Combustion tests for exhaust smoke content.The equipment and techniques used were exactly the sameas described above. Each test series was performed atthe nominal operating conditions given in Table II. Inorder to correct for minor variations of conditionsduring the tests, the correlation formula developed in[6] was applied -

1 p3 (1 - h) 3 2,7 T -8,66SN = f { x x } ( 7)A/F + 1 A/F x h2 4

The results were expressed in the form of

SN at m (g) sample sample mass m (g)versus

SN at 28,6 g sample 28,6 g

and Fig. 12 gives a plot of all the points other thanthose for pure iso-octane. The latter values were sosmall that the scatter had no significance. With theother results it was found that the smaller smokenumbers had greater relative errors than the higherones.

0 1 2 3m Air/28,6

Fig. 12 Effect of total Sample Size upon SN

The best-fit curve for the results, given inFig. 12, was found to be a logarithmic one -

SN m /SN28,6 = K (m/28,6) n(8)

which for all the data worked out as -

SN m/SN28,6 = 0 , 95 (m/28,6)0,552 R = 0,99 (9)

The statistical data for Eqn. 9 were as follows -Number of points = 50; an = 12,9 %.

For the individual mixtures, the values of K, n, and Rin Eqn. 8 were -

% benzene 20 40 60 80 100K 0,83 0,84 0,94 0,98 0,99n 0,89 0,51 0,70 0,64 0,55R 0,96 0,95 0,94 0,98 0,99

Bearing in mind the limited experimental accuracy, itwas decided to accept Eqn. 9 rather than attempt tofind complex functions of K and n which, probably,might not be meaningful.

As far as the present results indicate, thereappears to be no significant difference between the twotechniques of changing total sample flow (i.e. massflow constant, time varying - mass flow varying, timeconstant). One might anticipate that an increased flowthrough the filter paper could reduce the efficiencyof the filter. To check this, a series of tests weredone using two filter papers in series within thesampling device. Results measured on the second paperwere within the blank scatter. This would suggest thatany smoke passing through one paper is sufficientlyfine to pass through two.

5


4 • A COMPARISON WITH PREVIOUS WORK

In [6] a correlation group (Eqn. 7) wasestablished which successfully described the effects ofoperating conditions and fuels upon the exhaust carboncontent of a number of gas turbine combustors. It wasdecided to assess the present work against this group.To do so, Eqn. 9 was first used to adjust the measuredSN values to the standard sample of 28,6 g through thefilter. Then the corresponding values of X, werecalculated using Eqn. 7. These values are plotted inthe form of SN versus X, in Fig. 13. For comparison,results are also plotted for a similar combustorpreviously used [6] to examine the effects of differentfuels upon exhaust carbon content.

100 0

o SN 1/380 • • SN 1/2

0 0

60 • 0 os

SN

o

40 • • •20

0

10-16 10 15 10-14 10-13 10-12

X1

Fig. 13 Exhaust Carbon Characteristics of the1/3 & 1/2 Scale Combustors

The combustor used in the present experiments wasa geometrically scaled-up version of the previous one,having a similar air distribution and the same designof Simplex atomizer (same cone angle). Calculation ofdroplet sizes showed that these were maintained at±10 µm for both combustors when operated with the samefuels. Because of the above similarities, it might beexpected that the two performance curves would lie onthe same line. A glance at Fig. 13 clearly shows thatthis is not so, although each unit correlates quitesatisfactorily in its own right. A few of the pointsgiven by the smaller of the two combustors may besuspect, in that they are very close to the limitingsmoke number of SN = 100.

A much wider range of fuels was employed in theearlier tests than in the present experiments. However,26 points of the earlier data were obtained usingbenzene or benzene mixtures. Because of this, it isbelieved that the different correlation lines representsome form of scale effect, the most likely contributorbeing a function of the increased residence timeavailable for burn-out in the larger chamber. Basedupon the geometry scale, the gaseous residence timewithin the different zones of the larger combustorwould be 1,5 times that of the smaller combustoroperated at the same Mach-number. That the residencetime function is not linear is suggested by the data(Fig. 13) which approach each other as the amount ofsmoke diminishes. The data also suggest that the carbonformation is much less influenced than the burn-out,and hence that the time available for the latter ismuch more important in defining the exhaust smokecontent.

This effect of scaling on exhaust carbon couldhave considerable practical importance, and aliterature search shows that it apparently has not been

investigated to any degree, certainly not for realcombustion systems. Because of this, it is proposed tocontinue the examination using the present combustorsand, possibly, to include results from an even larger,geometrically similar combustor.

5. CONCLUSIONS

5.1 Limited experimental data suggest that, asexpected, carbon forms within the primary zone of thecombustion chamber, and that major burn-out occurstowards the end of the intermediate section and beforethe dilution holes. Relatively small amounts of carbonare consumed downstream of the dilution holes. Theamount of carbon present shows a strong relationshipwith the local air/fuel ratio, especially when themixture is richer than stoichiometric.

5.2 For two combustors having different airdistributions (but for the same engine) the free carbonpresent in any zone can be crudely estimated by -

%Cfree = 0,144 x 109,4 7xF/A

5.3 The relationship between the Smoke Number andthe carbon mass concentration shows wide discrepancieswhen the results of one worker are compared with thoseof another. Probably, at least a part of this is due todifferences in particle size. Based upon published datafor the two techniques, the following relationship hasbeen established -

C (ug/L) = 0,62 x 100,026xSN

This Equation has a standard deviation of 67 % andestimates can be out by a factor of two. It is onlyrecommended for SN from 0 to 60.

5•4 Examination of the filter paper used tocollect the soot particles shows definite effects ofpaper structure upon the reflectivity readings. Toobtain the best possible accuracy of SN measurement itis not only necessary to ensure that the same side ofthe paper is used to measure reflectivity before andafter filtration, but it is also necessary to maintainthe angular orientation of the paper with respect tothe reflectometer. If this precaution is not taken itis possible that an error can occur of as much as nineunits of SN. By observing these precautions,satisfactory blanks were obtained (SN ±1).

5.5 For very low or very high values of SN it maybe necessary to use larger or smaller (respectively)quantities of sample gas than the standard. Experimentshere have shown this technique to be satisfactory. Theamounts can be varied, either in terms of rate or time,and the following equation gives a satisfactoryprediction for the standard SN within a standarddeviation of 13 % (within the experimental rangeinvestigated) - 0,552

SNm/SN 28,6 = 0,95 (m/28,6)

5.6 Comparison of the present results with thoseobtained on a small scale version of the combustor,having similar geometry, air distribution and injectionsystem, shows that carbon formation is stronglyinfluenced by volumetric reaction scaling.

ACKNOWLEDGEMENTS

The authors wish to thank the Natural Sciences andEngineering Research Council of Canada for the researchgrant which made the work possible.


REFERENCES

[1] J.Odgers & P.Fortier; The Effects of FuelComposition upon Carbon Formation in a Gas TurbineCombustor; Laval University, Dept. Mech. Engrg,Report jo 91, March 1980.

[2] J.Odgers & D.Kretschmer; The Prediction of GasTurbine Combustor Performance due to Changes inFuel, II I Carbon Formation; Laval University,Dept. Mech. Engrg., Report jo 123, October 1983.

[3] J.Odgers; Study on Combustion of Tar Sands TypeGas Turbine Fuels - Part III, 9th Progress ReportLaval University, Dept. Mech. Engrg., Report jo174, August 1987.

[4] J.Odgers & D.Kretschmer; "Some Fuel Effects onCarbon Formation in Gas Turbine Combustors";Canadian Aeronautics & Space J., 28, No. 4,pp 327/338, December 1982.

[5] P.Sampath, M.Gratton, D.Kretschmer, & J.Odgers;"Fuel Property Effects on Exhaust Smoke and WeakExtinction Characteristics of the Pratt & WhitneyPT6A-65 Engine"; J. Engineering for Gas Turbines& Power, 108, pp 175/181, January 1986.

[6] D.Kretschmer & J.Odgers; Exhaust Carbon p TheEffects of Fuel Composition; 8th Int. Symp. onAir Breathing Engines, Cincinnati, 15- 19 June1987.

[7] Aircraft Gas Turbine Smoke Measurement, SAEARP 1179A.

[8] S.P.Girling; Gas Turbine Smoke Measurement: ASmoke Generator for the Assessment of Current andFuture Techniques; AGARD Conference Proceedings422, Paper 20, Chania, 19 -23 Oct. 1987.

[9] D.L.Champagne; Discussion to Paper 74 - 1; TheCombustion Institute, Central States Section,Madison, 1974

[10] S.Wittig & H.J.Feld; Particle Size Measurementsin Sooting Combustion Systems; AGARD ConferenceProceedings 422, Paper 21, Chania, 19 -23 Oct 1987.

[11] S.R.Jackson, Joseph Lucas Research Laboratories,personal correspondence, March 1969.

[12] W.A.Eckerle & T.J.Rosfjord; Soot Loading in aGeneric Gas Turbine Combustor; AIAA Paper87-0297, 25th Aerospace Sciences Meeting, Reno,12- 15 January 1987.

[13] D.L.Champagne; Standard Measurements of AircraftGas Turbine Engine Smoke; ASME Paper 71 -GT- 88,Houston 28 March-1 April 1971.


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Notes on the Occurrence and Determination of Carbon Within Gas