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Produced by the NASA Center for Aerospace Information (CASI)
t

NASA Contractor Report 168279 10 ^^'1v"ir

S yg ,p v^

R ^.

ar 1

EXPERIMENTAL STUDY OF THE OPERATING CHARACTERISTICS

` OF PREMIXING—PREVAPORIZING FUEL/AIR MIXING PASSAGES

David A. Rohy and J. G. Meier

Solar Turbines Incorporated Y

San Diego, California

w 

iA AJA°CR°= Vi°v27^) ,'Y► Fin.2clEii`. Ai ^T[ll3A Z'iC TH E

i:84° t414^

OPERATING CHARACTERISUIC,S OF

PREMIXING-PREVAPORIZI*1G FUEL/A:IF MIXING

PASSAGES Final Report (Solar Zur.bines Unclas 

It tern ational) 60 p HC A04/MF A01 CSCL 21E G3/07 42761

4 

November 1983

r 

{L 

^ 

Prepared for j 

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Lewis Research Center

Under Contract NAS3-20662
i

TABLE OF CONTENTS

Section Page

GLOSSARY iii

1 INTRODUCTION 1

2 EXPERIMENTAL DESIGN 2

2.1 Design Philosophy 2

2.2 Rig Design 3

2.3 Rig Control and Control Instrumentation 7

2.4 LDV Technique 10

2.4.1 LDV Operating Procedure 10

2.4.2 LDV Data Recording Procedure 16

2.4.3 Definition of Size and Velocity Parameters 16

2.5 Special Instrumentation 18

2.5.1 Temperature Uniformity in Measurement Plane 18

2.5.2 Fuel Injection Plane Measurement Probe 18

2.5.3 Probe for Flow Uniformity and Spillover

Measurements 20

2.6 Fuel Evaluation Tests 21

3 MEASUREMENTS 22

3.1 Preliminary Rig Measurements 22

3.1.1 Temperature Uniformity 22

3.1,2 Flow Uniformity+

24

3.2 Measurements With Fuel in Flow Field 25 

3.2.1 Spillover Measurements 26

3.2.2 Description of Graphs and Tables 28

3.2.3 Data Collection Summary 28

4 CONCLUSIONS 34 

APPENDIX A - Details of Size Determination by LDV 35

APPENDIX B - Vaporization Computer code, 55

i
G LOSSARY

A.

(= NASA - National Aeronautics and Space Administration

y ALEC - Advanced Low Emission Combustor

LPP - Lean Premixed, Prevaporized

t LDV - Laser Doppler Velocimeter

SDL - Spectron Development Laboratories

k

PRECEDING PAGE BLANK NOT FILMED

PAGE-_4L-IWTENT10NALLY BLANK
1

1

INTRODUCTION

The program described in this report had as a goal the characterization of

fuel sprays to be utilized in calibrating and verifying an analytical model

of a premixing-prevaporizing passage of a lean burning combustor.

NASA's Advanced Low Emission Combustor Program (ALEC) was initiated to apply

modern techniques of combustion science and Analysis to the problems of

achieving significant reductions in gas turbine pollutant emissions while

maintaining high performance and durability for a wide range of aviation

fuels. From this program, the lean premixed-prevaporized (LPP) combustor has

evolved as the primary candidate for the program goals.

The LPP combustor is similar to conventional combustor concepts except that,

prior to combustion, the fuel and air are mixed and the fuel vaporized in a

fuel preparation section; hence the term premixed and prevaparized. This

premixing and pevaporization is necessary to achieve the uniformity and control over local stoichiometry for low pollutant emissions, and low levels of

flame radiation and pattern factors conducive to improved durability and

performance for a variety of fuels.

In order to assist the design of the LPP combustor and reduce the a.seoriated 

development risks, an analytical model of the fuel preparation process is

desirable. Such a model would permit low cost computer screening of premixing 

passage concepts and reduce time consuming, expensive experimental evaluation

of high potential candiates. Such a model is currently being developed. The

model computes the fuel-air distribution, degree of fuel vaporization, residual dropsize, distribution and air velocity pressure and temperature profiles at the exit of the fuel preparation section, given the inlet air flow

conditions and fuel spray characteristics.

Under the present program, data was collected on fuel spray and air flow

characteristics at several points within a fuel preparation duct to calibrate

and verify this analytical model. A well controlled test rig capable of

producing repeatable fuel sprays was utilized in the research program. The

rig was designed to operate to pressures of 10 atmospheres and to inlet

temperatures of 750K.

The use of advanced non-intrusive (optical) measurement techniques for fuel

v spray characterization is seen as a significant contribution of this program.

The data set obtained is the first acquired by this method at high pressures 

and temperature and is significantly more detailed than any previously

obtained.
EXPERIMENTAL DESIGN

2.1 DESIGN PHILOSOPHY

Combustion research, relating to the operational characteristics of both

innovative systems and the more well-established devices such as gas turbine

combustors, requires instrumentation which can provide measurements in extremely severe environments. In an environment where pressures may reach 600

psi and temperatures over a thousand degrees Celcius, mechanical devices

such as hot wire anemometers designed to function in much less severe conditions quickly fail or become highly inaccurate. Furthermore, instrumentation

requiring a mechanical sampling technique perturb the environment which is

to be measured. This perturbation reduces their accuracy and reliability.

One particular area where instrumentation needs have become critical is in

the measurement of particle (droplet) size and velocity for fuel sprays

during fuel/air preparation and combustion. Devices which utilize optical

measurements of the desired parameters are non-intrusive and thus can operate

in severe environments with no perturbation of the flow field. v

An instrument which has undergone extensive development during the past ten

years, and has shown its utility in a wide variety of applications, is the

Laser Doppler Velocimeter (LDV). Using a laser as a coherent light source, 

this instrument has been used to measure particle velocities in fluids.

These applications have ranged from low speed water flows through supersonic

wind tunnels to large oil and gas flames. The velocity measurement is

obtained by determining the Doppler shift of light scattered from particles

passing through the laser beam, This program has used a well-developed 

version of one type of Laser Doppler Velocimeter (LDV) optical system which

incorporated highly refined signal analysis and electronic instrumentation

to determine not only particle velocity but also particle size. This system

has been tested with excellent results in small wind tunnels for the measurement of droplets in water sprzsys.

The primary use of the LDV instrumentation is to characterize the spray from

various fuel injectors at several sets of operating conditions. The spray is

characterized by measuring the droplet size and velocity at a set of points in

several planes downstream of the injector. In order to achieve data that is

meaningful, the test conditions (air .flow ( temperature, pressure, etc.) must

remain constant during the measurement period and be repeatable from one

test session to the next. This type of stability is especially important

when comparing spray distributions from different injectors. The rig must

also provide access for complete instrumentaton to allow for flow measurement.

The completed rig, as described below, allows for repeatability and stability.

In addition, it has provision for instrumentation txad fuel burnoff.

2
2.2 RIG DESIGN

The "rig" includes the fuel/air preparation section, burnoff combustor, air

pressure regulation valve and supporting subassemblies. Basically the constraints were:

The air inlet preparation section has been designed to produce uniform flat profiles of total pressure, total temperature and velocity

at the inlet plane to the fuel injection section.

r

The fuel injection section and fuel/air mixing section have a rectangular cross section with ,inside dimensions of 7.62 cm by 7.62 am.

The fuel injection section is designed to produce uniform flat profiles of total pressure, total temperature and velocity immediately

upstream of the fuel injector location. It is also designed to

accommodate various types of fuel. injectors. ( The injectors are

mounted on a spool piece (2.5 cm high) and inserted into the flow

path.)

The fuel/air mixing section is designed to avoid autoignition and

flashback over the conditions of the tests. It was designed to

allow for optical measurements 7.5 cm, 15 cm, and 30 cm downstream

of the fuel injector. This was accomplished with a. stationary

window and the addition of bland; spool pieces to move the injector.-

; and fuel/air mixJ, ng section further upstream of the window. The

spools were 7.5 cm, 15 cm and 30 cm high. 

The rig is designed to operate at temperatures of 450 to 750K, 20.0

yto 80. 0 m/sec reference velocity, equivalence ratios of 0.3 to 0.5 

and pressures up to 10 atm.

Flow distortions due to ports and instrumentation were minimized.

,G The rig was assembled in a manner shown in Figures 1 and 2. An A- frame 

support is used to support the rig vertically so that gravity will not disturb

the radial symmetry of the spray distribution. The major components and

dimensions of the rig are called out in the sketch of the rig in Figure 3. x 

The liquid fuel injector flange assembly is shown in Figure 4 and 5. It was

K?- designed to allow for changes in the type of injector under study. The fuel 

eenters the air strut from both sides to prevent coking. Instrumentation 

ports were installed 180 degrees opposed. The injector for the first test

k i has an ID = 0.085 cm and protrudes about 0.64 cm from the strut. This design 

produced a narrow spray cone and a distribution of fine droplets. Others 

designs without the sharp edge around the injector produced larger droplets

} and a less uniform con;bustion in the afterburner. ( Standard gas turbine

injectors cannot be used vn the rig because the spray angle is generally too

wide. They would have deposited fuel on the wall within centimeters of the

injector.) All optical measurements were made with the injector shown in

Figure 5.

t^ 3 

r

.`.1
i

Of% 

.w 

. .r

OF PUOK QU,^LI TY

Figure 1. overview of Cell Showing LUV, frig, Fuel Cart, and

Air and Fuel Control Console

Figure 2. Rig Installed With inlet and Exhaust Lines

4
AFETY RUPTURE DISC

LOW STRAIGHTENING

ECTION

iUPPORTS FOR TURBULENCE

iENERATORS

IQUID FUEL INJECTOR

'LANGE

ASER WINDOW

A" FRAME .ASSEMBLY

AUXILIARY WINDOW

'LASHBACK

1CREEN ASSEMBLY

IATURAL C;AS

'LANGE

IUTTERFLY VALVE

FLOOR

REF

4

4

v

ORIGINAL PAGE".4 VS

OF POOR QUALITY

Figure 3. Fuel Atomization Rig Mounted on A-Frame

5

.
r

:JI

Fiqure 4. Liquid Fuel Injector Flanqe Assembly

Fiqure 5. Closeup of Fuel Injector Nozzle

6
The laser measurement section is the most complex assembly in the rig. It is

pictured in Figures 6 to 10. This section inoludes the laser beam window

and ports, the laser !ream dump, the off-axis detector window and ports and

two auxiliary optical port for other instrumentation. To prevent major flow

disturbances plates were installed Mush with the Inner walls of the flow

path at each measurement section. Slots were machined in these plates prior

to the optical measurements. The laser Pteasurement section contains pressure

and temperature instrumentation. The W, am dump port served the additional

purpose of being a port for instrumentation rapes.

» The afterburner section (Fig. 11) contains the torch ignitor, natural gas

pilot cone, dilution and cooling air port, combustor, transition duct (square

to round) and water injector for final air cooling.

A standard butterfly valve with an electical actuator was used to eotrol rig

backpressure. Because the valve was rated for .427 0 C service it was necessary

to spray considerable quantities of water into the air stream just ahead of

the valve. A thermocouple was used to monitor air temperature at the valve.

2.3 RIG CONTROL AND CONTROL INSTRUMENTATION

All optical measurements were made at air temperatures of 375°C. Variations

over a six hour run were within 2.E 0 F. Air from high pressure compressors

was directed through a heater to achieve the design operating temperature.

The flow was controlled by a remotely actuated valve. Flow rates were

measured using a standard ASME orifice run.

The fuel subsystem was desi ed to y gn, provide high pressure fuel at the design

flowrate of 0.9 kg/s configurations. The fuel was filtered to prevent

clogging of the fuel injector.

Nitrogen was used to purge the optical window ports and laser beam dump to

maintain clarity. Needle valves were used to adjust nitrogen flow into the

flow section. The total nitrogen flow was minimized to reduce the disturbance

of the air flow in the measurement section. The primary purpose of this

subsystem is to maintain high optical transmission through the quartz windows.

overall rig instrumentation is detailed in Figure 12. Thermocouples in critical locations were routed to limiting pyrometers. Actual instrumentation

channels recorded did not include all instrumentation shown. Many instruments

were monitored by the test engineer to insure rig safety and not recorded.

The control panel with instrumentation readouts is shown in Figures 13 to 15.

7
Figure 6.

Laser Measurement Section

(The laser beam dump will be

installed in the upper port.

Transviiss (toter ports were

welded into the lower ports

at the time of these photos.)

Figure 7.

Top View of Measurement

Section

ORIGINAL PAGE

OF POOR QUALITY

8
ORIGINAL PAGE iS

OF POOR QUALITY

9

is 1 0 

Figure H.

The Two Measurement Window

Flanges Can he Seen in This

View of the Measurement

Section. (Nitrogen purge

tubes are assembled.)

Figure 9.

Apertures for the Laser Beam

are Visible Inside Window

Flange. (The entire rig is

supprted on the brackets

extending from both sides.
OQfOMJ:.:_ '

OF 'POOR

Figure 10. Laser Entry Window With Four Ports

2.4 r r . 'PECHNTQUF.

2.4.1 LDV Operating Procedure

The techn=ques used to obtain size and velocity information differed from

standard LDV practice in one significant way; the detector measured the

scattered lr,er light 90 degrees off axis (the laser heam defines the axis).

t This techique provided smaller probe volumes and fewer incidentr of multiple

droplet measurement. In this technique, two laser beams are used, but only

one component of droplet velocity and size are measured at one time. The lens

F in front of the detector selects the signal from only the central part of the

elipsoid created by the intersecting laser beams. In this manner the probability for multiple droplets in the probe volume is considerably reduced.

M

1 

Data can be taken in regions where the drop density is so high that some

detection techniques would not provide significant data. There was great

concern that the results would be biased if approximately 90 percent of the

data were rejected. Since this rejection does not occur with the off-axis

detector the bias problem was reduced considerably.

SDL was subcontracted to take optical data using their equipment. Spectron

set up the equipment at Solar in early September 1979. That equipment is

10
'

g

OF POOR QUALITY

Figure 11. Afterburner Section. (Torch ignitor port is on the left while

cooling air is introduced via the port on the right.)

represented in the sketch in Figure 16 and shown photographically in Figures

17 and 18. the data consist of size and velocity measurements of fuel droplets and the surrounding air.

11

V490F
OF FOO QUALITY

1

EMERGENCY NOTES: V MEANS INITIALLY CRITICAL)

PRESSURE RELIEF

ASSEMBLY ' 1 APO ORIFICE PRESSURE DROP.

HEATED AIR SUPPLY ( 1), AP TRANS.

• 2 7 , ORIFICE AIR TEMP., HEATED

AIR SUPPLY (1), P,R.T.

5

3 T1 P.R.T.

• • A• AND

D

 5, STATIC PRESS. AP1g (1),

AND P15 4, BOTH: TRANSDUCERS

0 Pit, (1), TOTAL PRESSURE, TRANS.

' 7 TP. ,N TF•OUT, (1 OF EACH), FUEL TEMP,

P,R7.S,

4PLENUM

AIR

INLET ' 8 P28, WALL TAPS IN FUEL BLOCK, (26

5 PRESSURE TRANSDUCERS

0 T2 , (2), C,A, THERMOCOUPLES IN

FUEL BLOCK

10 NF 1

 NF2 (1 OF EACH) LIQUID FUEL

/ TURBOFLOWMETER COUNTS FROM

t

k

i

t

4 "_l

LIQUID FUEL

INJECTOR

1011 12

LASER

WINDOW

17

WATER

CAMERA

WINDOW

f

19 _

20^ 0000

COMBUSTOR

LINER

21

23

THROTTLE VALVE

23 =-^

EXHAUST

PIPE

SHIMMING 1

FUEL CART

LOCATIONS ' 11 TFb Tp2,11 OF EACH) FU E L PRESS. 2

ON CART, PRESS. TRANSDUCER,

---TEST SECTION

12

ON CART4PRESS, TRANSDUCERSS

W: 13141518

13 P3 , WALL TAPS IN LASER P L ANE, (2)

WATER COOLED ANTI• ONTO PRESSURE TRANSDUCERS

FLASHBACK SCREEN

14 T3A,WALL MAGPACKS (C,A, THERMOER J COUPLES) (2)

SCREENWATUMENTATION

URAL GAS IN

15 P3 1 , ARRAY OF 24 ON REMOVABLE

 PILOT CONE PLUG, TOTAL PRESSURE, TRANS,

16 T313, ARRAY OF 13 ON REMOVABLE

PLUG, C,A, THERMOCOUPLES

CH 17 T WINDOW FLANGE TEMP (2)

C.A, THERMOCOUPLES

18 Pw, WINDOW N2 BUFFER PRESS,

ONTO AP GAGE WITH P35-

19 T4 (1), FLASHBACK INDICATOR;

C.A, THERMOCOUPLE ONTO PYROM,

-COOLING WATER 20 T5 (1), C.A. THERMOCOUPLE ONTO

INJECTOR PYROMETER, OPTIONAL TO 20

22 Ty (1), C,A, THERMOCOUPLE ONTO

PYROMETER

THROTTLE

VALVE 24 23 PES, EXHAUST STATIC PRESSURE,

AOTUATOR GAGE

24 THROTTLE VALVE POSITION INDICATOR

ONTO PANEL METER

26 INSTRUMENTED BLOCK, P2T (6) KIEL PROBES

P2S (2) WALL TAPS, AND T2 (8) C.A, TIIERMO.S

Figure 12. Liquid Fuel Premix Rig Instrumentation

Mf 6

NEW

^4

12
Of'•2lWIAL P:.UL I

OF POOR QUALITY

Figure 13. Main Control Panel for Test Rig

Figure 14. LDV Signal Conditioning and Control

13
OF POOR Q„ALITY

Figure 15. overall Control Panel With View Into Test Cell

a. L, G L7

M M

h

1, I?

FUEI SPRAY RIG

Tt EPl I

vv

^ bP ` ^ M I

L ----- ----1

M

POWER SUPPLY

DG DIFFRACTION GRATING F SCIL LOSCOPE

L, L213 TRANSMITTING LENSES PMT

L, LS COLLECTING LENSES

M MIRROR SDL VP1000 PROCESSOR

PMTPNOTOMULTIPLIER TUBE

3 v PROBE VOLUME

i SDl DMS DATA

MANAGEMENT SYSTEM

Figure 16. Diagram of SDL Equipment for Off-Axis Measurement

i

14
^, 1

Figure 17. Optical Bench for SDL Tests

OF POOR QUALI FY OR'GINAL R7 13

1.

Figure 18. Signal Processor for SDL Tests

15
Two types of measurements were made: visibility and Dopple% 0.eriod (see

Appendix A for description). These were then converted to size and velocity

of individual particles or droplets. From this information, several important parameters were then obtained. They are: linear mean diameter, size

standard deviation, surface mean diameter, kurtosis, mean velocity, and

turbulence intensity. These parameter as defined below.

In an effort to understand the interaction between the fuel droplets and the

surrounding air, the velocities of both media were measured. The velocity of

the air was obtained by seeding it with 3 11m glass beads using a fluidized

bed and subsequently measuring the bead velocity.

2.4.2 LDV Data Recording Procedure

The positions where the measurements were taken are identified by the indices

(i,j) where i corresponds to the abscissae (x) axis, and j corresponds to the

ordinate ( y) axis as specified in Figure 19. 

w The data of each task are presented in matrix form where the position, mean

velocity, turbulence intensity, and linear mean diameter are specified. In 

the SPRAY series, the velocity and size distributions are also provided. 

The heading of the test data matrix indicates the series and the position of

the run. For instance, SPRAY 1 RUN 2-1 indicates that the measurements were

taken at 30 cm plane and the position 2, 1). The histogram that follows,

plots the frequency of the particle of a certain size versus the corresponding

size. This frequency is obtained by dividing the number of particles of a

certain size by the total number collected. That is, frequency fi = Ni/N.

;. The maximum frequency of the ordinate is then indicated. Typically, it is 

j- 0.1. The ordinate is then divided into five equal numbers of intervals.

The table below the graph shows the values that were used to construct the

graph: the diameters of the particles and the number of particles with this

diameter ( count). Finally, there is a list of the size and velocity parameters of interest for this test.

The next graph shows the velocity versus size distribution. The maximum

iF velocity ( ordinate) is indicated, and again the ordinate is divided into five

equal intervals. The table below indicates the velocity and turbulence

intensity corresponding to each size.

The data and graphs are included in Section 3.

2.4.3 Definition of Size and Velocity Parameters

h

i Let: 

Di = diameter of droplet i, 

M 16

r.:

ws;»'^"'•FP7E.R9't`

C
ORIGINAL. PAGE 1c.1

OF POOR QUALITY

c1 N M .'i N M

RECEIVING -OPTICS

SERIES: SPRAY 1 - 30 cm DOWNSTREAM NOZZLE PLANE

SPRAY 2 - 15 cm DOWNSTREAM NOZZLE PLANE

SPRAY 3 - 7.5 cm DOWNSTREAM NOZZLE PLANE

RUN 16 / PLANE AT LOCATIONS ( REC, TRANS)

Figure 19. Test Matrix

Ni = number of i droplets collected,

Ui = velocity of droplet i, and

N = total collected droplets + ENi.

i<

r€

17

_ - 11

5.0 cm

4.15

3.333

2,5

1.667

0.85

0

3.0

2.5

CIO 2.0 0

U

z C

L 1.5

y

1.0

0.5

0

0

^ o ^ oo r ^ ^n

cv ri c cry' o ^+ c^
r

R

The following can then be defined;

Linear mean diameter: D10 . E Ni Di/N

Surface mean diameter: D20 CE Ni Di 2 /N] 1/2

volume mean diameter; D30 . CE N i Di'/N]1/3 1

Sauter mean diameter: D32 - E Ni Di 3/ E Ni Di2

Standard deviation: S . [E Ni (Di - D10 )2/N]1/2

Kurtosis: ENi ( Di - D10( 3 /N / CENi ( Di - D10)2IN]3/2

Mean velocity: U E Ni Ui/N

Turbulence intensity: T = [ E Ni (Ui - -) 2/N3 1/2

2.5 SPECIAL INSTRUMENTATION

Several special instrumentation probes were built to measure the performance

of the rig prior to the fuel droplet measurements. Data obtained from the

probes are presented in Section 3.

2.5.1 Temperature Uniformity in Measurement Plane

The optical droplet measurements were made in a plane perpendicular to the

flow axis. That plane was called the measurement plane. Air temperature

and pressure measurements were made in that plane to assure uniformity.

Art instrumentation rake was built to install in the rig at the measurement

plane. It contained 13 thermocouples to measure total gas temperature. The

thermocouples were arranged in a cross pattern (see Fig. 20). They were

routed through a cruciform shaped airfoil to reduce the disturbance of the

air flow.

2.5.2 Fuel Injection Plane Measurement Probe

A probe was designed to measure pressure and temperature at the fuel injection

plane. The basic design is shown in Figure 21. This probe was installed in

a spool section and replaced the fuel injector module. The probe spool piece

was equipped with wall pressure and temperature probes.

18
ORIGINAL PAGE IF;

OF POOR QUALITY

rigure 20. Measurement Plane Probe

1.00

0.90

O

(0-=

Figure 21. Pressure/Temperature Probe for Fuel Plane

19
2.5.3 Probe for Plow uniformity and Spillover Measurement s

OF POOR 0"I'L14Y

A sampling probe was designed and built for the flow uniformity and spillover

measurements. The probe replaced the laser beam dump and received samples of

the air or air / fuel mixtures at the laser measurement plane. Six samples

could be made with the rig at operating conditions without moving the probe.

The probe could be positioned into a total of four slots to achieve the 24

point grid (Fig. 22).

In order to measure the percent of fuel vaporized in the measurement plane

Solar followed the technique of Tacina l . A catalytic reactor was built which

was patterned after a design supplied by NASA. The catalyst used was 0.5

percent Pt on Gamma Alumina. The basic design was reasonably successful with

problems occurring only in the heater. The electric_ heater element for the

reactor was manufactured straight. To fit the reactor, the element was

wound into a helical shape and inserted into the shell. The actual bend

radius was smaller than that tolerated by the element resulting in an open

t circuit failure after each cycle. The design was altered by removing the

strip heater and surrounding the core with a clamshell heater.

0 0 0

O $ 0 00 p

rh

h^^

$ 0 0)0

y^

C

i

T

t COVER BLOCK (31 REO'D

Figure 22. Sampling Probe

1 Tacina, Robert R., "Degree of vaporization using an Airblast Type Injector

for a Premixed-Prevapori zed Combustor", NASA TM-78835, presented at First

International Conference on Liquid Atomization and Spray Systems, Tokyo,

Japan, August 28-31, 1978.

20
i

t,

ORIGINAL PA04E I:3!

OF POOR QUALITY

2.6 FUEL EVALUATION TESTS

All Fuel used during this study was drawn from a single 3800 1 tank. Only

this program used the fuel in that tank. The tank was pumped empty and then

filled with commercial Jet A at the beginning of the test in June 1979. A

sample of that fuel was taken on three separate occasions and rested in the

Solar Chemistry Laboratory. The results of those three evaluations are

shown in Table 1. There is some variation in the measured properties and

these cannot be explained fully. it is possible that some fuel evaporation

occurred between the first test and the subsequent two evaluations. The test

rig had not been operated for a period of months when the third evaluation was

made. A complete distillation curve was not measured during the second test*

All chemistry testings were performed by the same personnel using the same

equipment and techniques.

Table 1

Fuel Sample Evaluation

#1

7/79

#2

11/79

#3

4/80 Units

Kinematic Visocisty 1.55 1.46 1.55 (centistokes @ 100OF)

Gravity 43 . 2 43.7 40.3 Degrees API 0 60 'F

Pour Point - 80 -72 88.6 OF

Flash Point 140 170 160 OF

Distillation BP 357 356 OF

10 390 379 OF

20 403 386 OF

50 430 409 OF

90 484 455 460 OF

End PT 548 505 510 OF

Recovery 9805 98 95 $

Carbon Residues 0.28 0.08 0.095 $

21
k

3

MEASUREMENTS

The results presented in this section are divided into two sections] measurements of the rig flow characteristics without fuel droplets, and measurements

concerning droplets in that flow Meld.

3.1 PRELIMINARY RIG MEASUREMENTS

This subsection describes the measurements of the flow temperature and uniformity of the rig without fuel being present. (The inlet air was preheated

in an external heat exchanger.)

3.1.1 Temperature Uniformity

The air temperature was measured at the optical (LDV) measurement plane using

the probe described in Section 2.5.1. The conditions for that test were:

air temperature 744K

air pressure 507 kPa

. reference velocity 40 m/sec

No fuel was injected during this test. The data from the thermocouples is

shc;m in Table 2. The thermocouple numbers are referenced in Figure 23.

one thermocouple failed, but the remainder indicated that an extremely uniform

temperature distribution in the measurement plane had been achieved.

Temperatures were also measured at the fuel injection plane using the probe

described in Section 2.5.2. The conditions at the time of that test were:

air temperature 650K ( nominal)

air pressure 507 kPa

reference velocity 40 m/sec.

Data from that test are shown in Figure 24. The mean temperature was 656K

with a standard deviation of 0.44K.

22
OF POOR QUALITY

Table 2

Thermocouple Data

Thermocouple

Number

Temperature

(°K)

1 741

2 741

3 Trailed

4 741

5 741

6 741

7 741

8 742

9 741

10 741

11 742

12 742

13 742

DETECTOn

I

Figure 23. Diagram of Measurement With Thermocouple Numbers

23

3C AM

E
LASER PORT

DETECTOR PORT

57.7 PSIQ

Tp2.3°F

58.4 PSIQ

41 703,2 F

512 PSIQ 58.4 PSI4 702.7'F

703.5'F 57.0 PSIQ 57.9 PSIQ

703'F

68.2 PSIQ

705' F

58,0 PSIQ

TORCH

Figure 24. Temperature and Pressure in Fuel Plane

3.1.2 Flow Uniformity

The uniformity and symmetry of the air flow in the mixing section was determined by injecting methane into the rig at a point in the center of the fuel

injection plane. A probe (Fig. 25) was constructed in a square spool piece

which replaced the fuel injector. Methane was injected into rig while the

rig was being operated at

Air temperature 650K

. Air pressure 5 atm.

. Reference velu_ity 40 m/s

A sampling probe ( Fig. 22) was constructed for use at the measurement plane. 

The rectangular mounting plate of that probe replaced the laser beam dump,

180 degrees opposed to the laser port. Each of the six probes could be

sequentially attached to ,a, hydrocarbon analyzer. When the rig was shut

down the probe could be moved to any of four different positons. In this

manner a grid of 24 measurement points was constructed in the optical measurement plane. Unburned hydrocarbons were measured at each of the 24 points.

The methane injector was positioned at three different planes to measure the

distribution of the methane at 7.5, 15 and 30 cm downstream of the injector.

4 

The results of the 72 point survey are shown in Figure 26. The data indicates that the distx i bution is slightly skewed toward one side. This is

probably a result of a slight skew in the injector. Taking this into account,

the concentration profiles show the flow uniformity within the tset section

is acceptable. Background levels of CH 4 were subtracted out before pl^Ooentation. The sensitivity of the CH4 measurement is + 1 ppm overall range. Data

gathering was repeated for the right hand column of the 30 cm plane.

24
BRAZE PER

STD, SHOP

PRACTICE

126 DIA. TU6E

.

25

ORIGINAL It:' .^ `.

OF POOR QLI(.;At-Y

AIR PLOW 376

ALL

i n

Figure 25. Methane Injection Probe for Flow Uniformity Test

Several pressures were measured at the fuel injection plane using the probe

described in Section 2.5.2. The conditions at the time of the test were:

air temperature 650K

air pressure 507 kPa (5 atm)

reference velocity,

40 m/sec

The pressure measurements had a mean of 400 kPa (gauge) with a standard

deviation of 3.3 kPa. The pressure data slats exhibited good uniformity. The

data are shown in Figure 24.

3.2 MEASUREMENTS WITH FUEL IN FLOW FIELD

All tests were accomplished with a Jet A fuel and except for one characterization test were performed at one set of operating conditions. These conditions

were:

air temperature - 750K 

air pressure - 75 psia

air velocity = 40 m/sec

mean equilibrium ratio = 0.4

The operation set points to achieve these conditions are shown in Table 3.

The variations described the tolerance that the rig operator could maintain
Table 3

Set Points for Operating Conditions

Inlet temperature

Rig Pressure

Orifice Temperature

Orifice Pressure

AP Orifice

Downstream Throttle Temperature

Fuel flow In

Fuel Flow Total

Nitrogen Window Pressure

Fuel Nozzle Pressure

Fuel Pump Pressure

Cooling Air Pressure

Pilot Light Off T.C.

Rig Overtemperature T.C.

Combustor Exit Temperature

7000E

58.2 psig

727 OF

70 psig

11.8 in. Hg

280"F

133 Hz

88 Hz

78 psig

300 psig

580 psig

65 psig

1700°F

450°F

In excess of 2200OF

3.2.1 Spillover Measurements 

The test were performed in the 7.5 cm measurement plane with the rig at the 

set position:

air temperature = 650K 

air pressure 5 atm.

reference velocity = 40 m/s

equivalence ratio - 0.4

The probe shown in Figure 22 was used to collect the samples. This probe was 

used only in the middle two of the four possible positions. This was done 

primarily because of the narrow spray angle and the proximity of the probe to

the fuel injector. The sample location numbering grid is shown in Figure 27.

The conditions of the rig and the emissions data received are shown in Table

4 for position B. Rig conditions are only printed out when changes in conditions were recorded. This order of presentation is the order in which the

data was taken. The computer code used to generate the results in snown in

Appendix B.

Problems were encountered on several occasions. The existance of the problems 

limited the amount of data available. Iii some positions, primarily probe

positon C, insufficient flow as obtained to go past the isokinetic velocity.

High "percent vaporized" numbers resulting from these data are not realistic

and are excluded. The raw data are shown in Table 5 and 6.

26

xt

^.,-.:.`::W°"d:rilYr.': .._ ,^w ,<•'r..^.^.^-.^.i ^^.. f^f?v.3i
30 CM PLANE

DETECTOR

WINDOW

7.5 CM PLANE

DETECTOR

WINDOW

LASER WINDOW

3 20 0 0

85

I

315 62 0

175 640 180 9

200 700 210 8

135 442 100 0

10 37 8 0

15 CM PLANE

DETECTOR

WINDOW

130 225 125 15

195 350 208 35

210 390 220 40

220 400 208 40

210 360 190 35

150 250 130 15

145 200 140 43

170 215 140 52

175 220 130 47

180 215 125 49

180 210 128 55

155 185 110 54

FLOW

UNIFORMITY TEST.

DATA IS PPM

OF CH4 AT 

EACH LOCATION

WITH BACKGROUND

SUBTRACTED OUT. 

TORCH

Figure 26. Flow Uniformity Test Results

27
ORICINAL

V3

LASER WINDOW OF POOR QUALITY

DETECTOR

WINDOW 06 I

05

x

04

C 03

02

1

I N

01

^' A B C D

Figure 27. Probe Numbering When Viewed from Top of the Rig

3.2.2 Description of Graphs and Tables

The data of the various series is prese,tted in matrix form. The numbers

indicated in each element correspond to the position, mean velocity, mean

droplet diameter, and turbulence intensity, as appropriate. The corresponding positions in the combustor are indicated in Figure 19

t

3.2.3 Data Collection Summary

The velocity, size, and related statistical parameters of the selected conditions studied in this research program are presented in this section.

{ They are given in entirity in the Comphensive Data Report.

(1) Air Velocity_Uniformity Check: 13 points taken along both centerlines

` of test section at 30 cm plane.

Series: VELOCITY

h

vf^

28

`f
ORIGINAL MaE IS

OF POOR QUALITY

4

Table 4

Vaporization Data Via spillover Technique

' 1 4 (11, 1 ^,- t I: F F111)

T Ei :r,

1: q"f

J F, rrrw

F r l q la F PAG

00 R a41 1 i " .: tMo 51.1. 411

PJF.1 F*1 ol,l 111H r,lf.*L AIR to

fil, l I t1f I

► 1.

0: F, HF,

I

'4101 p i IfIG

MH

lip"

F" 11'1^" V ri L F;- 11r L

I F H In H T I jJ R T 10

Cii 4 1:

5 0

AF

I

L I C L JIF: I F f F I,kF,I F II; E

EMP P F: I) F L 7'A P T C. 1. 1 P P F^ 1. r I K; F

;

t. I A.T. R 1-1 L 1`11-1 :;1) 111F',,I I

Ej 'j

A T 10 .T] O F I TY4 C I

i[INPI I 1JG

T 71 H

I.t

I, ITU B 1, 1 ri

PF1111 PF 1'^, I I 10 1''A] 10

l 

0 4 4 1

Q 2r a w.

I'L 11

1

1 r It C= 1.L L A PCI R I Z' E 1I

II I-Ir-1lill"'

C A 1-114

r t F.' PH

P: 

FI F,

FRI A I" I I) R'171 T I

0 1..' 181 5

fl:."' -:0

01'.5

29
i

A

OF Poo 4 J° Table 4 (Continued)

F,FFtT'f4T 

11F- Ff-IEL VAPORIZED

OP11- Ii:.E: "PIF Ii.;1 IfRiFIGE RIG RIG

• I"FMf' F^'I?F.:' ' DELTA F' TEMP F'F'E'3'-1

r"hL R

r.N,41 11. 1133 f10 5'^.,ii

f IIEL FLOW Flip FI-4)W FUE'L..,"RIF' MEAN I'-: of'.114 '1 Ic

l E'^'F!F` 1, E; HF? PAT 10 VEL.Ot ITYs FT , riCl';

t i;. ', ;^ r x'1„1';. i_1 0.02026 30. f

f1MF'LING

I.fll,,ATTON

i

6ri: "ELw. I T '

FiT FTI ON TIP iWi4 1 1JId F^•'H E0JIVAL-•EN1W F

F, T ,,'SCC F''F'M F''F'11 F°HTII) C,AT10

42 1 6 1r. ► i 11 t3 t1tlr 1J;, 0.080 

i'f r .^ 1 "!.. rt3

w,. rt»1 »% 1 1.;^'^1 ^^'^^L^ ? 11. 1L^iw^j i 1^.094

-^` 4:I.',3 1.5' 0, vf ^ J.1]F47"^1^f f's.11ta 

I'E R,.' t`H T 11F FUEL 'VA F 1 R12ED 7

HhiF'l.. TNG

LGG'Fi'1"I0t•i 

w-- Iti: t Y Y EL1 ii' I'F r'

11T F'ROBf. TIP 1 11jL- r 1-1 I,44t, «„

j• f 'aE^1:^

F^ hi [^ ^i.l E HLEfjr,^.C"

F'F'M t='FI'1 RAT1 0 R, AT

FQ 1 I F1. 1 ^9. 0 ,' Q. 0 ti 149 0r4a2r' 1 12. «'...J 41 1 a G1. U j

0.00207 0. (130 

.1 ? ki G 1.: a 1ri I k1 r f3 1 F; 0.027 I

:•

,. 

F'EF.i.,MNT OF FUEL 1-MIPORI' ED

^ 1irlF^l I rn:, 

!_.1a C H 1 I r f•I

E1-1 

VEL1:nw'IT^

1'1T 1 , R 08L. T II.,, 

T IJ N 1-. F Fi EIPl_I SEf.". F'FM FFhi F;1=i TI: 1;J FS FIT i1J 

. 

^, }1 .^ c1 11. I:^ 11 0. 00 111 0 . r 1. 6

iJ . 4i 10 0 r 0 431, 9 t' . 0 r 1„,1 1 4

t ♦ I1;i

fff 

a

t 

30 

WL

,
Table 5

Spillover Tests - Gas Analysis

OF POOR QUALITY

Flow Meter Gas Analysis

Flow

Probe Meter Temperature Pressure CO2 CO UHC

Date Time Location Reading (°F) in. Hg (b) (ppm) (ppr)

2/14/80 1216 B-1 59 70 +1.8 0.67 0 54

1222 B-1 45 70 +1.2 0.51 0 30

2/15/80 1028 D-3 58 70 +1.7 6.85 6.0 14

1030 0-3 45 70 +1.3 7.47 5.0 18

1030 B-3 30 70 +0.6 8.55 3.0 0

1040 B-3 15 70 -0.5 9.97 0 0

1044 B-4 55 70 +114 5.65 0 12

1047 B-4 45 70 +1.1 5.65 0 10

1051 B-4 30 70 +0.6 7.02 0 6

1055 B-4 15 70 -0.2 7.95 0 4

1100 B-4 so 70 +1.3 5.22 0 5

1105 B-2 57 70 +1.6 1.78 0 6

1107 B-2 42 70 +1.2 1.78 0 4

1110 B-2 30 70 +0.6 1.86 0 2

1116 B-2 15 70 -005 2.24 0 12

1121 B-5 60 70 +:r.1 1.26 0 11

1126 B-5 45 70 +1.5 1.26 0 8

1129 B-5 29 70 +0.7 1.34 0 7

1132 B-5 15 70 -0.7 1.57 0 5

1136 B-6 62 70 +2.3 0.31 0 8

B-6 30 70 +0.8 0.43 0 5

B-6 15 70 -0.8 0.39 0 5

1147 B-6 45 70 +1.8 0.27 0 6

1200 B-1 65 70 +3.0 0.23 0 11

20 70 +0.3 0.20 0 10

1527 C-3 34 70 +0.2 1.38 5 610

1531 C-3 15 70 -3.3 1.22 5 12

1535 C-4 36 70 +0.1 1.30 6 Soo

1538 C-4 15 70 -3.0 1.34 5 10

1605 C-2 37 70 +0.1 0.53 3 8o

C-2 15 70 -3.2 0.39 3 10

Recalibrated with 0-59 CO

2/15/80 1632 C-5 39 70 +0.2 0.26 0 150

C-5 25 70 +0.05 0.26 0 100

1637 C-5 15 70 -2.9 0.24 0 10

1646 C-1 44 70 +0.4 0.10 0 250

(too low)

ti

1649 C-6 42 70 +0.3 0.10 0 120

1708 C-4 39 70 +0.2 0.71 0 120

C-4 25 70 +0.1 0.70 0 100

1715 C-4 15 70 -2.8 0.62 0 120

C-3 41 70 +0.2 0.80 0 120

C-3 20 70 0.0 0.80 0 120
Of U'a

Table 6

Spillover TeSt Rig Data

Temperature Orifice Rig Catal tic Reactor Tem araturos

Orifice Lnlet Press. AP Presa, Fuel Flaw

Dare Time "F or PSIG HG PSIG CPS Top Mid 130tt. Care

2-14-80 11115 6800 7206 65 1108 59.5 136.7

111130 6800 7200 65 11.0 60.0 135.9

11145 680 0 7200 65 12.1 59.0 13509

32115 6800 720° 66 012.1 60.0 135.7

2-15-00 10330 6800 7000 66 11.8 59.8 134.6 1903 out 1183 7000

10145 685• 7000 66 12.0 58.5 135.9 1751 Out 1207 792

11100 6900 7150 66 12.0 56.5 135.8 1056 out 1304 845

11115 6900 7200 66 11.8 59.5 135.7 643 Out 1255 768

11130 6900 7200 66 11.8 $9.5 135.2 475 Out 1309 6515

11145 6950 7200 66 11.8 59.5 134.8 345, Out 1047 530

3115 6950 725" 66 11.8 64.0 328.6 553 Out 1170 826

3130 690 0 7250 63 11.55 60.0 129.7 602 Out 1503 932

4130 6900 7250 66 11.8 59.9 129.8 513 out 1279 761

5115 699 0 7250 67 11.55 60.0 129.6 595 Out 1375 647

32
(2) Air Velocity: 16-point rectangular matrix

Series: AXAIR 1 - 30 cm plane

AXAIR 2 - 15 cm plane

AXAIR 3 - 7.5 cm plane

(3) Radial Air Velocity: 16-point matrix.

Series: RADAIR 1 - 39 cm plane

RADAIR 2 - 15 cm plane

f

RADAIR 3 - 7.5 cm. plane

r (4) Droplet Velocity/Size: 16-point matrix.

Series: SPRAY 1 - 30 cm plane

{ SPRAY 2 - 15 cm plane

SPRAY 3 - 7.5 cm plane

Qt{}.

nit

(5) Radial Droplet Velocity: 16-point matrix

# H

-, Series: RADVEL 1 - 30 cm plane

RADVEL 2 - 15 cm plane

RADVEL 3 - 7.5 cm plane

_4

s+

33
4

CONCLUSIONS

A new method of measuring fuel droplet size and velocity was developed during

the mid 1970's. The significant factors in this method are the (1) simultaneous measurement of size and velocity and (2) the capability to measure the

droplets in situ with no flow disturbing probes. The measuring instrument is

based on the laser doppler velocimeter (LAV) principles.

While applications of this instrument can be found in many technical areas,

the area of particular interest to gas turbine engines is the study of fuel

sprays during fuel/air preparation and combustion in liquid fueled gas turbine

engines. Once the fuel size and velocity characteristics are measured in an

^• engine environment, combustion engineers will gain a more basic understanding

of the fuel atomization process. The desired goal of this understanding is

w the production of low emission gas turbine combustors. The results could be

applied to gas turbine combustors burning various types of heavy oils or 

a^

synfuels. 

Fuel spray characterization data was needed to calibrate and test an analyti-

„- cal model of lean premixed, prevaporized (LPP) combustors. To obtain data

useful in the model development, a new measurement technique was developed. 

In order to obtain the data, it was necessary to design and build a test rig 

^. with well-defined and controlled conditions. The rig was sucessfully completed and run for extended periods of time.

Optical measurements were successfully performed using a rig described above.

r The optical measurements included drop size and velocity distributions made

z at 30 points in three planes. The data were plotted and are consistent with

expectations. This is the first known application of this technique to 

combustor fuel preparation investigations.
f

j

APPIENDIX A

DETAILS OF SIZE DETERMINATION BY LDV 

METHODS OF LDV CALIBRATION

Pea

^i

w

Y

4

r

{

35

.. .«r - .. ... v $fn... _ „wXeWs`^f-':i r2 ^" " _ ""°-"—Y^ch. ^"":!:•..+.r!^.:...^
LDV MEASUREMENT CAPABILITIES

Spectron Development 'Laboratories (SDL) in clone collaboration with John C.

Meier of Solar, has developed an instrument for combustion research in gas

turbine combustion system. The LDV instrument is unique in its capabilities

of measurment of droplet size and two component velocities in the severe

environment of an operating gas turbine combustor system. The instrument

incorporates the following capabilities:

. Measurement of a two-dimensional velocity vector with a range of

+(0.01-200 m/sea)

. Measurement of particle size when the particles and in the velocity

rango of 5-30 m

Specification of probe volume position coordinates with a high

degree of accuracy (+0.5 mm)

Immediate on-line data checks

. Rapid computer storage of acquired data

w The optical system of the LDV was constructed based qn proven designs. The

optial system is designed so the instrument can be used in the backscatter

observation mode or 90 degrees off axis. The electronic, system was built

' around an existing design which is capable of:

measuring s 9 ig9n

nal visibility (propPoortional to particle size) for

each velocity component

Measuring signal time period (proportional to particle speed and

velocity) for each velocity component

Sorting data ,pertinent to particle size or velocity for each 

velocity component 

Producing the particle size and velocity data in a format compatible with digit&1 computer recording systems

The optical system is mounted on a moveable platform which provides environmental protection and allows the oeprator to specify the position of the

sample ,space with high accuracy. The system is designed for remote oepration.

Table A-1 shows the general capabilities and system advantages.

Signal Analysis for Determination of Particle Size

;f 

^ 

A brief review of the basic principles which must be used to determine particle

size from a measurement of signal shape in the LDV.

36

.F 

^t

^::

 _ ..^+-.+ _.^^e mow• ,

r..r.^, -tv.,-' !^ ' ^.. +w`»
w D

Table A-1

LDV General Description

I. The LDV determines particle size over n 10:1 size range via the

relative magnitude of light scattered from particles ,passing

through crossed laser beans interference fringes, and determines

particle velocity over a 10 5 :1 range (not simultaneously)

2. The system is capable of measuring particle size, number density

and velocity at a rate of 20,000 particles/soc for particles from

5 Am to 300 Am in diameter and +1 cm/sec to +200 m/sec.

3. Requires no material probes and therefore performs perturbationless measurements.

4. Calibration for particle composition not required since size

determination is not dependent on absolute measurement of

radiation intensity.

5. High quality receiving optics not required.

6. With calibration LDV can be used to directly determine particle

mass concentration.

Two equal-intensity, well-collimated, coherent light beams intersect at a

common origin (geometric renter) with an included angle, (rig. A-1).

Huygen's diagram of the wavefronts shows that planar interference fringes are

generated which are perpendicular to the plane defined by the beam centerlines

and are parallel to the bisector between the beams. The distance between the

periodio (rings, d, is given by.

a = t\[2 tin (a/2)] (1)

where X is the wavelength of the coherent light. When a particle (assumed

spherical) much less than a in diameter crosses the fringe pattern, it can be

assumed to be uniformly illuminated at allpoints along its path through the

fringe pattern, and the light which is scattered by the particle is proportional to the observable flux illuminating it. Thus, measurement of the

time period, T, of the scattered light is related to the velocity, v, of the

particle through the relationship;

V = a/T (2)

As the size of the scattering particle increases relative to a, the illumination of the particle is no longer uniform and must be averaged over the

cross-sectional area of the particle. The nonuniform illumination of the

particle results in a reduction in the contrast or visibility of the scattered

37
R

0 R I MA1. VP,C"- Iw

OF POOR QUALITY

Dcam Iti'ava

,.e""'" modulation ontour

K l^

'^._ `•,, 2b

Fronts

2b a

Figure A-1. Huygen's Diagram of Interference Fringe Generation

in PM Probe Volume

light signal. Let Imax by the maximum value in intensity in a period of

the scattered light from a particle and Imin the next successive minimum.

The visibility, V, and then be defined as:

V „ Imax - I min (3)

Imax + Imin

It is straightforward to show that V is fully equivalent to the ratio of AC

amplitude divided by the DC amplitude of the scattered light signal. Henceforth, the high frequency " Doppler" portion of the signal will be referred to 

as the "AC", It usually has many cycles of information relative to that of

the DC component, which refers to the Gaussian shaped low frequency terms

describing the signal. Analytically, the visibility may be written as:

Io cos (2 7ft/ b)dAP

fA V

JAP op

where Ap is the cross-sectional area of the particle; To is the intensity

distribution across one of the illuminating beams and y is the coordinate 

ormal to the fringe planes When I o is a Gaussian function ( TEM00 laser

beam), it can be shown that Equation ( 4) is an accurate approximation over a

depth of field, 1, given by:

Q 0.8 b/ , ( 5)

where b is the radium of the a-2 intensity point in the illumination beam.

For depthe of field greater than 1, the signal visibility is a function of

particle size and position in the illumination. To simplify Equation (4) 

for Guassian beams and st i ll maintain accuracy, it is required that the particle diameter, D, satisfy the relationship:

38
D < 0.2 b (6)

And for a to satisfy:

a < 0.2 b (7)

Under these conditions, V for a sphere can be written as:

V = 2AJ, (7rp/6)/(7'D/6), (S)

where A71 is a vessel function of the first kind. For a cylinder, V can be

written as

V n-- sin(ML/6)/(Mi6). (9)

Equations (S) and (9) aroa plotted in Figure A-2 to illustrate the salient

features of the visibilty in particle size measurement.

Determination of particle size using a visibilty measurement has a number of

advantages over other optical techniques. Among the more important is the

fact that:

High quality, scattered-light-collecting systems are not required.

A visibility measurement can determine particle size to, at least,

10 times better than the resolution limit of the transmitting lens.

True particle flux rate, i.e., mass concentration, may be determined with the LDV system.

Size measurements may be made from backscattered light.

On the other hand, disadvantages in using this technique are also apparent.

For example, application of the LDV system must account for the fact that:

Size measurement is particle shape dependent.

High quality, transmitting optical systems are required.

Particle size measurement of spheres is limited to approximately a

15:1 size variation range for a given fringe period.

High quality spatially coherent light is required for good interference fringe quality.

The particle size measuring ability is limited by the frequency

response of the signal process in electronics.

The last item results from the fact that the signal frequency is velocity

dependent. Hence, an instrument which measures signal visibilty is limited

to the measurement of particle with velocities which are less than those which

produce a signal frequency greater than the frequency response limit of the

instrument.

39
ORIGINAL MCC1, 0 OF POOR QUAD 'ry

t

0,9 major

Of Fri S

+`^ $ A 0{

0.8 2'^

0.7

0,6

H

U)

0,5

Z

14

0.4 \ 

O \ 

W

\ 

E-4

0.3 +

Z

0,2 + \\ ,,^'"^

o , ► 1 /.y t

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1,6 l.8 2.A

Figure A-2. Visibility as a Function of D/a for Two Particle Shapes

A summary of the principles of operation of the LDV is provided in Table A-2. 

A schematic representation and interpretation is summarized in "fables A-3 and 

A-4.

Siqnal Processin q Considerations

To minimize error in the estimate of particle size, it is of utmost importance

that signal visibility be measured with high accuracy and precision. This is

due to the fact that signal visibility error and particle size error are not

linearly related. For spherical particles, Figure A-3 illustrates the particle diameter uncertainty for several different values of visibility. As

the figur^ . .;,s show, where the ratio of particle diameter D to fringe period 6 is

near 1, the particle diameter uncertainty is the same as the visibility un40
^/^' L____J

V/ir.1t1111.

oi I of .V1110Ml M 001

ORIGINAL PAGE IS

Table A-2 OF POOR QUALITY

Principle of LDV Operation

1. Two equal intensity, coherent light beams are mixed at an angle.

2. A well-defined set of equally spaced interference fringes is

formed by interference of the two beams.

3. Light scattered by a particle traversing the fringe set is modulated according to size and position of the particle.

4. Particle size is determined from the ratio of the amplitudes of

(1) the modulated scattered intensity to (2) the average scattered

intensity.

5. Particle velocity is determined by measurement of the signal time

period.

r

v

IDIWI.D /t 1111. /

:t

111111V111fiN MODI r

.MI rlMl

vnocrrr nn

PA II TICLI HZI AC/DC

Figure A-3. Interferometric Measurement of Velocity and Particle Size

41
oRICINAL PAGE W

Table A-3 OF POOR QUALMY

Signal. Description

4

t

T

w

N

_ ^AC

a ,^

^ D

MN

TIME

1. The signal contains two components in amplitude

• the modulated scattered intensity of ac component

• the average scattered intensity of do component

2. The time period, T, of the modulated scattered intensity is a function of particle velocity,

Table A-4

Signal Parameters and Particle Characteristics

1. Particle velocity v is computed from

v = a 1

2. Particle size is computed from signal visibility

V = ac/dc

3. For spherical particles of diameter D

V = 2J 1 (7rD/4) / (7rD/6 )

J 1 ( ) is a first order Bessel function of first kind

f

42
UNCERTAihTY iN YISIdis.iTY —

0,)D

ORIGINAL. PAGE M

OF POOR QUALITY

f 1

f 1O

NCERTAINTY IN VISIB16ITY

I• ,

ACCURACY LiN,iTEZ BY WIDTH OF 8 Biz

 DIGITAL WORD t '/256

^&

10_3 ^ , s r L

^

0.1 012 0.3 0,4 015 0,6 0.7 0,8 0.9

K Figure A-4. Uncertainty in Spherical Particle Diameters for Various

Values of Uncertainty in the Visibility

certainty is the same as the visibility uncertainty. However, as D/a decreases, particle diameter uncertainty rapidly increases. Thus, when D/b is

small, the error in particle size will be much greater than that in the

visibility. An instrument which measures signal visibility must seek to

minimize errors in the visibilty measurements if an accurate particle size

measurement is to be o); ir-t-Uned.

ti

Potential Sources of Error in a Signal Visibility Measurement

In examining the LDV signal, a number of potential error sources are evident

which could produce considerable error in a visibilty measurement. Among the

most important error sources are:

Signal noise

Asymmetric signal shapes

Variations in the signal visibility

Signals insulting from more than one particle.

43
Signal noise may result from any number of sources but is usually either broad

band, Gaussian-distributed noise occurring during the entire duration of the

signals single, very-high—frequency spikes which occur randomly in the signals

or periodic amplitude variations which mix with the signal. The first two

forms of noise are u& . ,ially evident when signal magnitudes are low. The third

form usually results frim a radiative pickup from high-power consuming or generating instruments operc:ting across the entire frequency spectrum. Asymmetric signal shapes result form particles with trajectories that do not pass

through the optical axis of the probe volume. Such signals can also arise

through turbulence induced distortions in the signal (Fig. A-5). Variations

in signal visibilty occur when D16 is near 1, and the AC component of the

signal has only a few cycles of information relative to that of the DC component. Signals resulting from more than one particle usually generate

aperiodic signals of skewed shapes. The LDV optical designs account for the

possibility of multiple particle signals by generating a probe volume which is

small enough to produce a low probability of observing more than one particle.

Certain types of error logic may also be used in the signal processing electronics to reject such signals.

Visibility From Signal Integration. To minimize the errors which may result

from "real world" LDV signals, it is most desirable to observe and measure as

much of the signal as possible. One method of satisfying this requirement is

through integration of the entire signal (within preset limits). Consider a

particle whose trajectory, passes through or near the geometric center of the

probe volume. It can be shown that the visibility obtained by computing the

integral of the DC component, and the integral of the full-wave rectified

value of the AC component, and by dividing the integrated DC into the integrated AC is (to within a known numerical factor) identical to that measured

for a single cycle measured at the center of the signal. Integration of the

signal is most desirable because the noise components previously listed will

contribue very little to an integral value of the signal. For example,

Gaussian-distributed white noise and periodic noise have zero or nearly zero

values for an integration, and high-frequency-noise spikes contribute very

little to the overall integral value. Furthermore, integration of asymmetric

signals tends to reduce the effects of the asymmetry by producing an overall

signal average. The primary difficulty in using a signal integration to

determine the signal visibility resides in the fact that the dynamic response

of an integrator will be affected by large frequency variations in the signal

input. Thus, without design precautions, an integator could ,produce considerable error in attempting to measure particle size in turbulent flows where

there are considerable velocity variations.

Signal Amplitude Constraints. While a visibilty measurement is independent

of signal magnitude, detailed considerations must be given to relative signal

amplitude in order for a visibility measuring instrument to have a sufficient

dynamic range in amplitude response.

For particles of identical index of refraction and of a size greater than

about 511m, i.e., for particles with scattering gain coefficients independent

of particle size, the signal amplitude can be expected to vary by a factor of

100 over the measurable size range. Probable volume intensity variations can

44
Time 1,10 μs/Div.)

ORIGINAL FAG:: 13

OF POOR QUALITY

0

a

'O

C

7+

1 H

Figure A-5. Example of LDC Signal Distortions Resulting

From Flame Turbulence

be expected to range over facrors of 10 in each of two orthogonal probe volume

dimensions. Thus, an instrument must be capable of responding to relative

signal amplitude variations of at least 10 3 :1 and, more reasonably, 104:1.

Linear amplifiers can cover a linear dynamic range of approximately 10 2 for a

single-range setting. The designer is thus faced with the difficulty of producing an instrument which at one range setting can cover sufficient dynamic

range to eliminate instrumental bias in particle size measurements.

One technique to overcome the dynamic range limitation is the use of logarithmic amplifiers. For example, if an integration technique is used to determine

45
N

the signal visibilty from a logarithmically amplified signal, it can be shown

that the visibility is given by;

V a sech ( fln (1AC ) - .fjn ( iDC) ) . (10)

where fi nUAC ) is the integrated logarithmically amplified AC component of the

signal and j',OniD.) is the integrated DC component. Logarithmic amplifiers can

easily cover a dynamic range of 10 4 :1 for low frequency signals, making an

instrument much more sensJ,tive to small particle signals. The primary difficulty with such amplifiers is that their sensitifity is a strong function of

signal frequency and quickly decreases as the frequency increases, making

their effectiveness questionable at the carrier frequencies involved with the

laser flame analyzer.

Another solution to this limitation is obtained in using the integration

approach to visibility measurement. An integrator can be designed to cover a

10:1 dynamic range visibility processor designed by SDI, personr.al utilizes

four parallel integration circuits each overlapping the other in range so

that for a given signal frequency a dynamic amplitude range of 10 4 :1 with

three-digit accuracy can be covered. Duch accuracy gives an acceptable error

in particle size determined by a visibility measurement even when the particle

size is small.

LDV CALIBRATIONS

The LDV is a recently developed instrument and as such requires attention to

the methodology of calibration. Four separate experimental procedures were

developed to achieve a high confidence level in the calibration and therefore

in the data from the instrument. The experiments are the wionodispersed

droplet generator, the spinning disc velocity calibrator, the nitrogen tunnel

for simultaneous particle size and velocity measurements and comparison with

data from a calibrated spray nozzle. (A second method would be used to

calibrate the spray nozzle.)

Monodispersed Droplet Generator

A droplet generator was successfully designed, built and tested on non-program

funds. The generator produces a stream of liquid droplets (water) of uniform

diameter in the range 20-300 microns. A built-in deflection circuit allows

the experimenter to divert one droplet (minimum diameter 40 micron) at regular

intervals. The diversion of a single droplet is critical to calibration since

the LDV probe volume can only contain that one droplet without signal dropout.

Optical verification techniques (photomicrographs) of the same drop being

measured by the LDV will give the LDV user confidence in the size data. A

photograph of the stream of droplets produced by the Solar monidispersed

generator is in Figure A-6. The deflection of one droplet can be seen in

that photo.

46
ORIGINAL PAGE IS

OF POOR QUALI f Y

Figure A-6. Monodispersed Droplet Stream (100 Microns)

An overall view of the equipment used to make the droplets is shown in Figure

A-7. Basically, the droplets are formed by the passage of the liquid through

a vibrating orifice plate. Pulsed deflection plates downstream of the orifice

deflect the chosen droplet if the liquid has been lightly doped with an

electrolyte. The entire droplet generating head is mounted on the XY7. micropositioning translator.

Spi nning Disc

The spinning disc calibration consists of a motor driven disc with one wire

protruding radially from its circumference. The circumference of the wheel

is known. The rotational speed of the wheel is accurately measured by a

frequency counter. Thus the wire passes through the probe volume at a precisely known translational velocity. Velocities can be controlled up to

100 m/g . The equipment is pictured in Figure A-8. A scope trace taken

F

after the passage of the wire through probe volume is shown in Figure A-9.

The characteristic LDV signal trace is seen there.

The LDV was successfully calibrated for velocity accuracy using this technique. The calibrations were performed for four fringe periods at one transmitter focus, 40 inches, and one scan distance, 20 inches. Two channels of

the LDV were calibrate; at the four fringe periods and the entire calibration

was performed a second time in reverse order to check for systematic errors.

At each fringe period, the instrument was checked at six different velocities.

F ive separate sets of one hundred measurements were made at each velocity.

In total, 48,000 measurements were made during the fringe period (velccity)

calibration. The data from the fringe period calibration exists on several

pages. A typical data sheet is reproduced in Figure A-10. A statistical

analyses of that data is shown near the bottom of that figure.

47
ORIGRi't F;:,F: '1!

Or POUR QUA I A I Y

Figure A-7. Monodispersed Droplet Generator Mounted on XYZ Positioner

1

•1

t

I

TIMING GEAR

DRIVE MOTOR 11z HP \

MOTOR SPEED CONTROL

5006000 RPM

(MAX 10,000)

TACH SIGNAL TO COUNTER

(20 PULSES/REVOLUTION)

/!

SPINNING DISC

(TARGET 1M CIRCUMFERENCE)

( 1 RPM ? 1 MISEC)

TARGET SLIT HOLES

MAGNETIC PICKUP

Figure A-8. LDV Spinning Disc With Target for Velocity Calibration

48
49

OF POOR QUALITY

Figure A- Scope of Trace of LDV Signal

A surmnary of all data points is shown in Figure A-11. The standard deviations

are less than one percent and most are less than 0.5 percent of the fringe

period.

Nitrogen Tunnel

The nitrogen tunnel experiment was designed, built, calibrated and tested on

non-program funds (Solar). The purpose of this device is to calibrate the

LDV for size and velocity simultaneously. Particles or beads of a known size

are injected into an airstream of known and controlled velocity. The LDV

measures the size and velocity of the group of particle as they exit the

tunnel. A catch basin is provided to remove the spent particles from the

atmosphere. The gas used is pure, high pressure nitrogen, boiled from an

LN 2 supply. That uniform gas enters the test tunnel from the top (see

Fig. A-12), passes through flow straighteners, and encounters a throttle.

Gas pressure and temperature are measured just above the throttle. Three

throttle plates were built. Each was calibrated in the tunnel by the Co,orado

Experimental Station in Boulder, Colorado. The gas passing the plate enters

a venturi section in which the particles are injected. To insure uniform

distribution of the particles in the air stream, they are fed from a fluidized

bed into six ports placed symmetrically around the tunnel just above the

venturi. For small particles the six injectors are perpendicular to the gas

stream. For heavier particles a second set of injectors pointing 15 degrees

upstream is used. The calibrator is totally operational.

^. 
I 2

Calculated D 1sc

3 4

Calculated Fringe

Run Disc Frequency Velocity (1 t 20) Period (2 + 3)

Number (counts) m/s) measured (u

1 172 8,6o 12,17 70,67

2 172 8,60 12,16 70.72

3 171 0055 12,13 70.49

4 171 8155 12,10 70.66

5 171 8,55 12,15 70 +37

6 403 20415 28,71 70,18

7 404 20,20 28,62 70,50

8 412 20.60 29.17 70.62

9 417 20.85 29.67 70,27

10

,

I 428 21,40 30.49 70,19

26

27

28

29

30

1210

1207

1209

1208

1210

60,50

60435

60,45

60.40

60,50

82,99

84.34

85,22

82.81

84,00

72,90

71,56

70.93

72.94

72,02

Vmeasured

a 1

° T - T - (measured

A AVcalibration

-

Vcallbration

dmea sured dmea cured

STATISTICAL ANALYSIS

Number of data points n - 30 runs of 100 replications each

Mean fringe period x n 70.78 68.59.1 x l < 72.92

Standard deviation Sx - 0.73 i3Q - 12.19

Standard deviation of mean ax - 0.13

True value of x n 70.78 ±0,13

OPERATING PARAMETERS

Lens Number Setting

L - 2 0,96

L-3 685

L-4 3070

L-5 6.o

Transmit 60.11

Receiver 3.420

Powar 750 mV

PMT 300 V

Line N 7

Figure A-30. Typical Fringe Period Calibration Data Sheet

vim''

50

_.... rn.. _. .'*a:wrrc...y...x ,, ..,.^ ...,,,.,n,,.« ....Y,...^-..-.^.,.„ -._ +"s-:-.-Y...1--..,....•... ..>...^.y ,.,.,,.: sw3...w, :+^.._,.i:, ;:'.X' ^. _.
Figure A-12.

Nitrogen Tunnel Experiment

OF HOUR t4 n' r

Channel A

Fringe Period

Horizontal

Velocity Standard

Compression Deviation

82 0.1

105 0.4

160 0.4

278 1 .4

Channel S

Fringe Period

Vertical

Velocity

Compression

56

70

105

179

Standard

Deviation

0.6

0.3

0.1

0.4

Figure A-11. Summary of Fringe Period Calibration Data

51

l
52

Calibrated SRray Nozzle

The intent of this experiment is to measure the droplet size and velocity

distributions from a pressure atomizing spray nozzle calibrated by another

method and compare the data from the two methods. This was not accomplished

during the period of the reported effort.

d^

t
53

APPENDIX B

VA!', ORIZATION COMPUTER CODE
pUDR ijUAWY

1000 REM CAUCUALTION OF DEGREE OF VAPORIZATION

1010 REM HASH — SOLAR LASER RIG

1020 REM TPILLOYER TECHNIQUE

1030 DIM R$E2t53iVSC2t53tCSC2e53tMSC2s53tHSC2o53fA$C83tB$CS3

1031 DIM BSr5p53wNSE5w53xC$C8J

1032 PRIHT TA8Q1"HSSA — LEWI3/S0LAR LASER RIG''

1032 PRINT TAB14"VAPORIZATION DATA 

VIA 

SPILLOVER TECHNIQUE''

103 41 DISP TABS" INPUT DATE AND FUEL" ;

1035 INPUT A$v8$

1036 PRINT

1,037 PRINT TAB22"DATE:"A&TAb40"FUEL: "B$

1038 PRINT

1040 DISP TABS"INPUT RIG DATA";

1050 TH P UT T1oT201010201

1060 REM RIG DATA IS AS FOLLOWS

1070 REM Tl=ORIFICE TEMP wDEG F

1080 REM Pl=ORIFICE PRESSP PSIG

1090 REM DI=ORIFICE PRESS. DROPs IN HG

1100 REM T2=RIG TEMP wDEG F

1110 REM P2=RIG PRESS. p

PSIG

1120 REM CI=CYCLESISEMI; FUEL FLOW

1.130 REM CALCULATION OF AIR DENSITY AT ORIFIC&== Rl

1140 R42.7023*01+14.71/40+460,

1150 REM CALCULATION OF AIR FLOW RATE R2

1160 R2=4606.09*SQR(Rl*Dl)

100 REM CALC OF FUEL FLOW RATE == Fl

1180 FI=0.99t*CI+4

1190 REM CALC OF ISOKINETIC VELOCITY IN RIG == VO

1200 REM CAL ► OF AIR DENSITY AT RIG GONDITIONS==R3

1210 R3=2,7023*(P2+14.7)/KT2+460:'l

1220 V00.00326402/6-3

1221 REM CALL OF RIG FUEL/RIR RATIO

1222 R00102

1230 PRINT TA89"ORIFICE ORIFICE ORIFICE RIG

1240 PRINT TAE IO"TEMP PRESS DELTA P TEMP

1250 PRINT TABil"F PSIG IN HG F

1260 FORMAT 9XtF4.Oi14:,1XtF5.tt6SiF5.146XtF4.O96XoF5.1,

1270 WRITE (10126045PIrD1nT202

1280 PRINT

1290 PRINT

1300 PRINT TAB9"F ► EL FLOW AIR FLOW FUEL/AIR

1310 PRINT TA89"LB/HR LB/HR RATIO

1320 FORMAT 9XPF6.IoSXoF7.lp6XoF8.5sl4XiF6.i

1330 WRITE (150320)FIO2PRO&O

1..34 PRINT

1340 REM INPUT DATA FOR EACH SAMPLING POINT

1350 DISP "INPUT NO. OF PTS AND LOCATION";

1360 INPUT PoC$

1364 PRINT

1365 PRINT TAB4"SAMPLING"

1366 PRINT TAB4"LOCATION''

JIG"

f ESS"

ofir.

MEAN ISOKINETIC"

VELocITYP FT/SEC

54
ORIOIi IAL PAC, is i.%

OF POOR QUALITY

1,167 PRINT TA85PC$

1370 DI$P "INPUT ROTAMETER AND GAS ANLA • SIS DATA";

1380 FOR J = l TO P

1390 INPUT ME KJJPHE 1a0sBE hJJwBC4vJJvBE5wJ)

1391 REM M(h&= ROTAMETER READING a DIVISIONS 605 TUBE v SS FLOAT

1392 REM H?lvJ)= ROTAMETER PRESSUR&

IN 

HG

1400 NEXT J

1402 GO SUB 4000

1403 GOSUB 5000

140! GOS ► B 7001

1412 GO-UB 6000

1413 DISP "NEW RIG DATA 11YES) O(NO)";

1414 INPUT A

1415 IF A=l THEN 1040

1416 GOTO 1350

1453 END

09 99 STOP

4000 REM SUBROUTINE FOR CAL ► OF FUEL/AIR RATIO::.^-

4010 REM B(19J) m PERCENT CO2

4020 REM 8 (of 5J) m PPM CO

4030 REM B(5aJ) = P PM UHC

4040 REM AW FUEL RATIO H/1.'

4041 A8=1 . 9

4050 REM N(I,J)= F/A RATIO EMISSIONS

4060 REM H(00 = EQU IVALENCE RATIO EMISSI O NS

4070 81=34.3719616-274.219526/(12POI+AS)

4080 FOR J=l TO P

4090 N1=(0.0001*(BE41J3—BEIP J 3*0.68)+BEIPJ3)*(1+88/2*10t(-S)*BE5 pJJ ,,I

4100 N2=100+AS/4*BCIsJ3+(0.0001*(BC4pJ 3—BtloJ3*6 .68)*(R$/4-0.5),,,,I

4110 NE10301*02.01+88028.8902

4111 RE WKNE IPJ I

4120 NE 2 p J VNE 19 J 3*8 1.

4121 NEXT J

4141 RETURN

4150 END

4999 S TOP

5 000 REM SUBROUTINE FOR CALC OF V( IPJ) S AMPLING V EL AT PROBE TIP

5010 FOR J m l TO P

5020 REM FI RST CA LC SAMPLING RATE SCFM AT STP= C( 0 4)

5030 CEIiJ3=(0.2903*MEIPJ3-0a871)*SQRC129-92+HEIoJ3)V29.92)* 0 .0 00588!. 

5040 YE:[tJ3=CEIPJ3*1515.62*(T2+460)/IP2+14.7)

5041 NEXT J

5060 RETURN

5070 END

5999 S T 0 1""

6000 REM SUBROUTINE FOR CALC OF DEGREE OF YAPORIZATIOI

6010 REM BASED ON LEAST SQUARES FIT OF DATA

6020 W I

6030 X I

6040 Y 14.4

6050 zim".

6060 FOR J=l TO P

55
N

K._

Y ^

1#

6 0 7 0 W 1A If( a,, W / V L I F

 J J ) .r. w

6 080 X 011+00/010 3 :,,

6090 Yl=Yl+(REloJ3/R@)

6100 ZI=Z1+(Y0 /Y E h J 3)*(RC i, J 3•r'RQ)

6110 NEXT „I

6 12 0 REM SOLVE OF DEGREE OF VAP

6140 NNY100=1

6141 E =B E,+M) x;10@

61 42 PRINT

6151 PRI NT TAB24"PERCENT OF FUEL, VAPORIZED''

6152 FORMAT =08.3

6 153 WRITE (1501520

6160 RETURN

6 17 0 END

7000 '_:TOP

7001 REM SUBROUTINE FOR DATA PRINTING

7120 PRINT

71 22 PRINT TA B5" GAS VELOCITY''

7123 PRINT TM85"HT PROBE TIP CO2 co ► „I H C F '' H EQUIVA LENCE"

7124 PRINT' TA "FT/ EC PPM PPM RATIO RATIO'' 

71:; :^' 

FOR

R J =1 TO P

—7

r, , , ,., i,^ •-^ r, i„^ •. L.

,-, ,•^^ 4,.^ C: ^ wi try ^.,J ^•1._, `^ FO^' f'1 A I'1^tFI' . 2o6X9F5 n 2t 2 PY !F5^ 1 g2fh7f"6NO14,•y F N Y6 4

F6Nμi 7

1 3

5 WRITE 415 0 1 4)VE19•_3PBE1 p 0sBL0•m► a015, "J]0C1!• 3PNE203

7140 NEXT .,„►

7141 RETU RN

1 43 END

()F po ()R

56

,