Atomization of fuel oil

ATOMIZATION OF FUEL OIL

by

Nicholas Hobson Wheless jr.

Submitted in Partial Fulfillment of the

Requirements for the Degree of Bachelor

or Science

from the

Massac iusetts Institute of Technology

1938

Signature Redacted

NOW U I

-IV

f

Department of Chemical Engineering, May 19, 1938

Professor in Charge of Research

484 Beacon Street Boston, Mass.

May 19, 1938

Professor George W7. Swett

Secretary of the Faculty

Massachusetts Institute of Technology Cambridge, Massachusetts

Dear Sir:

In accordance with the requirements for the degree of Bachelor of Science in Chemical

Engi-neering, I herewith submit a thesis entitled,

"Atom-ization of Fuel Oil."

Respectfully submitted,

Signature Redacted

-__4

A cknowledgment

The aut nor wishes to express his appreciation for the assistance given by Professor Hoyt C. Hottel in -ne carrying out or this thesis.

TABLJ OF JONT INTS

Summary . . . 1

Introduction and Literature Survey. . . . 4

Development or Transmissivity . . . . . Equation. . . . * . * . . .

i1

Apparatus . . . 0 . . .0 .0 0 0

.*16

Procedure . . . . 0 . . 0 0 0 . . 0 0

*19

Results . . . 0 0 0 0 0 * 0 0 0 0 0 0 21 Discussions or Results . * . . . .26 Conclusions .. *... . - . 34 Recommendations . * * * * * * *

*36

Appendix 0 0 0 0 0 0 0 - 38 A.Supplementary Apparatus Drawings 39 B.Summerized Data. .0 * . . . .42

C.Sample

Calculations . * * . 45

-4

:1

2

SUMMARY

The purpose or tnis thesis was to study a method

involving the transmissivity or a lignt beam through a

cloud or fuel particles as a means or determining drop

size.

The roilowing equation was derived and used to

calculate the mean drop diameter;

() 7 x I xA l

(1,~~ p oe

D30 -/:g.T

In this equation Q is the oil volume per secon per unit area normal to drop motion, X is the distance of

penetration of the fuel spray in tne direction of the

Light beam, u is the viscosity of air, D is the mean

drop diameter, V Is the drop velocity at the point where measurements are taken, p is the density of the fuel, and Tr is the transmissivity.

Work was carried on using nozzles furnished by the Monarch Mfg. Works. Pressure ror atomization

was secured by means of nitrogen under pressure. The

ruel was _{atomized into a chamber constructed or wood,}

since no burning was done. Transmissivity readings were taken through slip tubes fitted into the sides

or the chamber. A Weston Photronic cell was used to

record these readings. Measurements were taken far

velocity had been attained. Flow was measured at the

nozzle. Wiatn or tne spray wtis determined by direct

measurement. Results snow a drop size of .OOU4

inones to .005 inches, depending upon the pressure for

a nozzle or l.3 gallons per hour capacity using

Esso-neat No. 2 ruel oil. There is a definite decrease in

drop size with increasing pressure.

It is recommended tnat further work be carried on using this method or determining drop size.

4

5.

l1TRODUTION

It is the purpose of this thesis to study a method involving transmissivity o light as a means o deter-mining droplet size in a fuel spray resulting from the atomization process of a heavy fuel oil. The purpose of

the study of droplet size is to furnish data for the

determination of combustion space requirements for

fur-naces burning heavy fuel oil. A recent survey made by Snuggs indicates arop size determination to be an

edrly step in the combustion space study. Drop size

will be used as the method of studying theatomization process.

The importance of the atomization process can best

be shown by showing its relation to combustion.

Com-bustion in fuel oil rurnaces is dependent on breaking tne fuel into the smallest possible drops and then pro-jecting these drops into the combustion space in such a way as to give thorough mixing with air. The process

of breaking the fuel into small drops is termed

atom-ization.

The theory or atomization as set forth by Castlemaz)

is based on the ligament theory. This theory can be

applied equally well to solid injection, that is

6.

considers the two processes to be essentially the

sane. _{In the case of carburetion for internal}

combus-tion engines, a high velocity air stream is passed

over a still body of fuel while in the case of

atom-ization of a jet, a hign velocity fuel stream is

in-jeoted into a relatively still mass of air; thus the

relative motion or air and fuel is the same in both

cases.

Castieman's theory of atomization is that first

ligaments are formed, which become unstable due to their geometrical shape and break down giving

parti-oles which assume spherical form due to surface

ten-sion. It can be argued mathematically that the drops

depart rrom the spherical form, but for all practical purposes they may be considered spherical.

The foundation or this theory resulted from a study or high speed photographs of the atomization process, since the process occurs so rapidly that to

the naked eye atomized particles appear to come

di-rectly from the jet. It is possible to account for

this very rapid breakdown of the ligaments by using Raleigh's method of calculation.

As stated previously, combustion and the size

or the drops in the spray formation are very closely

7.

fine atomization and to have the drops of uniform size;

it is necessary to have an even and constant distribu-tion of drops in the spray cone; and it is necessary to have even penetration into the combustion space to give

good mixing with the air.

The distribution or the fuel within a spray may be

regulated by nozzle design and operating conditions. Dispersion, the ratio of spray volume to original

vol-ume of fuel, is also controlled by the nozzle design. It may be stated nere that nozzles of the seme type and dimensions often give different characteristics, a slight scratch being sufficient to cause the differ-ence. Thus the characteristics of any given nozzle

have to be determined experimentally.

The atomization process has many variables. Two

of the most important factors affecting it are injec-tion pressure and viscosity of the fuel. Fineness of atomization increases with increasing pressure. It is

cnown that fineness or atomization increases with a decrease in viscosity, but there is little data avail-able regarding tne permissible variations in

viscos-ity without change, or with minor changes only, of

injection system adjustments. A method of determining

particle size would make a study of this phase

8.

Several possible methods of determining particle size nave been tried. The first that will be

dis-cussed depends on the relation of drop size to free

railing velocity, a relation known as Stokes law,

when the drops are surfioiently small. A drop of

radius r falling with a velocity v through a fluid

with viscosity n encounters a rorce equal to 6"nrv.

Also f = mg u 4/3 r2dg where d is density. Therefore:

2/Wr2gd

(l~v n

The size or drops formed in atomization is well within

the limits required by Stoke's law, but the great variety of drop sizes encountered makes this method

extremely tedious. There is in addition the difficult

problem of obtaining a representative sample on which to make observations.

If all the drops were the same size, use could be

made of the fact that a beam of light is diffracted

on passage through cloud particles. The variation in

drop size, however, would cause overlapping of the rings produced, which would result in obscuring them.

High speed photographs have been tried. Lee and

(.3)

Spencer used this method. Each drop in a certain

area of the spray was measured and a curve plotted to

is that many or the drops are out of focus and that

it is possible that many small drops do not show up at all so that a representative sample of the spray as a whole Is not obtained.

(7,8)

Von Sauter developed a method or using light

ab-sorption through a spray of particles as the basis for his calculations. His method is derived for use with

an air injection system. However, as had been pointed out the atomization obtained is independent of whether

air or solid injection is used. This absorption method

is based upon defining average fineness so that instead or considering the actual mixture of air and droplets

including droplets of widely varying diameters, a substitute mixture is introduced which has the same

volume of fuel (Volume in cubic centimeters) as the droplets actually present and the same total surface area (0 in square centimeters) as the material contained

in the mixture measured. In this substitute mixture

rm = ₆V/0(om) = average radius in actual mixture, Let

B be the amount of fuel in cubic centimeters per second

passing an observation post, w equals velocity in

oen-timeters per second, and U equal the amount of light absorbed by the liquid flowing in front of the

obser-vation post as a fraction of the beam of light going

10.

a constant of the apparatus and u is a function ofU. This equation assumes that all particles travel with

a velocity of w. This would mean taking the

observa-tion post at a great distance from the nozzle.

The method used in this study was similiar to that used by von Sauter, whose method may be outlined

briefly as follows: Air injection was used. The fuel

was atomized into a chamber equipped with windows through which a beam of light could be projected, en-abling him to measure the amount of light absorbed by the liquid flowing in front of the observation post as a percentage of the beam of light going through the

fuel tube. The cell arrangement used enabled him to

read the fraction of light absorbed directly. The

arrangement required numerous reflecting surfaces

which it is desirous to avoid. The beam of light

passing through the fuel spray is essentially circular. Nothing has been found regarding any results that

might have been obtained using von Sauter's method.

11.

DAVELOPMSNT Ot' TRAN6=S8VVITY

120

II

DEVELUPkOF1 OF TRANSLUSSIVITY EQUA TIUI

The problem involved is that or evaluating the

frac-tion or a beam or light stopped by passage through a

(9)

cloud or particles. Hottel and Hasiam have evaluated

tnis for the passage or a beam of light through a cloud

of coal particles. The following is the equation which

they derived:

(1) F e-oxB

F is the rraction of light absorbed, C is the

concentra-tion or particles in the cloud, X is the thickness or the cloud in the direction of penetration of the beam, and B is the average cross sectional or projected area or a particle.

In deriving this equation it was assumed that an individual particle is opaque to any radiation ralling upon It. This holds true ror ruel particles.

The transmissivity, Tr, determined by the photo cell

is equal to i-F. Thererore,

(2) Ty : "-xB

STr

(3)

B __D

4

Where D is the mean particle diameter

13.

Furthermore:

(5) C - -_iD3 - 0

6

Where w is the oil volume flowing per second through

a unit cross section of path normal to the direction

of drop motion and V is the velocity of the particles

at the point in the cloud where the transmissivity

measurenants are taken. Substituting this relation

yields

(6) Tr e= 2 D V

All the quantities with the exception of D can be measured.

The presence of velocity in this equation Is per-haps hard to conceive. At first glance it is hard to

see what effect the velocity of the particles has on the amount or light that gets tlrough the spray. In order to clear up this point, consider two sprays having particles of the same size and delivering fuel at the same total rate. The number of particles

pro-duced per unit time will consequently be the same.

If the average distance between particles were the

same in the two sprays, then obviously the number of particles in suspension, and consequently in the path

-4,

14.

the sprays differ in drop velocity at the point of

observation or transmissivity (due either to the

im-parting of higher kinetic energy to the drops in one

case than in the other, or to the observation of the two systems at different distances from the nozzle), then the time of passage of the drops through the

field of view will differ; and since the number passing will be the same, the fraction of the space

occupied by the drops will depend on tie drop

veloo-ity. It is this fraction of space occupied upon

which the transmissivity depends.

The Q/y term is a concentration. If a cylinder with top and bottom which can be opened and shut

simuttaneously is placed in the spray with the top

and bottom open, left long enough to minimize the effects of its position in the spray, then closed suddenly and removed from the spray, the ratio of

the volume or the fuel present to the volume of the

cylinder represents the (/V term.

The derivation of the original equation (7) Tr U

is based on the assumption that any particle can

15.

as long as separate particles are small comparted to the cross section of the beam of light , and as long

as the spray is not so dense as to interfere with the

ability of a particle-position to be determined

com-pletely by chance, (i.e., in a tightly packed system

or spheres eOx*'v is not quite zero, but we know

.hat Tr is.*)

in oalcuLating the mean drop size, Stoke's Law

is used to determine the average velocity or the par-tioles. The reasons for using this law and the

valid-ity or the assumption that it is correct will be dis-cussed later.

D2 (Is-fa) g

(8) Stokes Law 2 V g

In this equation V is the particle velocity, D is the mean particle aiameter,Cs is the particle density, Pa is the density of air, and u is the viscosity of air.

(9) Therefore:

r

D

3

(,s.,a)g

(10) _{2 & I A a}

logeT

16.

17

16a.

FIG.

-Z:fk*-SECTION

A A OF

wm,F-

FNC

DIAGRAM

THER SLIDING ROD PROJECTION LAMP AIR EXHAUST 77 F/ , 4 IN. PIPE MOCOUPLES LAGGING STEEL SUPPORT AIR HEATER FILTER STABILIZER CONE CATCH BASIN SLIP T UBES LE NS

0

GLASS PLATE LENS PHOTO-ELECTRIC COVER TUBE -5 SLIP TUBE -- F

ILT

ER SCALE-3/4 IN- I FT. J.S. 5-38 ,/-/ '/ '/I/ I/ I/,/

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APPARATUS

For sketches of _{the apparatus see Fig.1 on page 16a}

and supplemntary crawings in the Appendix. The

sketches show Ine apparatus designed for a complete study or the atomization process of which the study of drop size is but a part. Thererore, only portions

of the apparatus pertinent to this study will be

discussed.

The principal piece of apparatus was the

atomiza-tion chamber. It was constructed of wood, since in

the study no burning was done. The cross section of

the chamber was made large enough to avoid spraying of the fuel upon the sides, the heigit of the chamber wbs designed to allow the drops in the spray to reach the free settling velocity. Approximate dimensions

are 4' in diameter by 5' in height.

Fuel was stored in a fuel chamber above the

atom-ization chamber. Its capacity was approximately one

gallon. Pressure for injection was obtained by using nitrogen under pressure. Pressures of from 0 to

175#/ could be obtained.

The nozzles used were furnished by the Monarch

Mfg. Co. Those available had 600 spray angles with

capeoities of 1.2, 2, 3, and 4 gallons per hour.

Those of different capacities were interchangeable on the apparatus.

18.

The apparatus was equipped with an air blower.

Air was sucked through the chamber by means of a

vacuum cleaner motor. The outlet was equipped with

an orifice to measure the flow₀

For the purpose of taking transmissivity measure-ments, slip tubes were placed on diametrically oppo-site sides of the chamber. These tubes had a diameter

of 1-5/8 inches and were placed at one foot intervals

down the length of the chamber starting approximately

6 inches from the nozzle. The lenses for directing

the light beam were fitted into tubes or l" inside

diameter, which telescoped into the slip tubes. The

purpose of the slip tubes was to make possible the use

of only one set of lenses and to make possible varia-tions or distance between lenses. The lenses used

were double convex lenses or e66 m.m. focal length. The insides of the lens tubes were blackened with

paint and carbon to minimize reflection effects. Illumination was obtained by means of a 200 watt projection lamp. 115 volt a-c current was used; voltage control was attained by means of a variable resistance in the line.

Transmissivity measurements were taken by using

19.

_ ----4

20.

PROCSDUR-The oelL reading with the fuel spray off was

first taken. The spray was turned on and the

pressure adjusted to the proper value. Flow was

measured by the graduate and stop watch method. The length of the spray in the direction or

pene-tration or the light beam was measured and the

cell reading taken.

Readings were taken at various pressures and with varying distances between lenses.

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I -, I -. -r '_' . '_ . . . : I N . --41- , . I -. : * .-- I . . . i . , , . -__ I 4-, -' , 4 . -_ I -. -' - . -, , -t f 7 -_ * ! r -+ * -' -I --. I . . , . I : -! ...- -I -- -." ---1 _3 -,. . ' I -_i : . ' ' , -. -I --, * : I ! I " .. . I I I -4 1 " + L " , t I -!-- , ! ii l '_:' . ' _. _': , I I I I -_ . _-.-. -, -- -, -, ,. lli zi .' ' ' ' -- -i i_' .-A _ 1 .. 4 -. . 1. T ' ' ' ' ' . I . -I 11 -I -- , I .... --' -_ .I _: : .'_ _ --4- -- -f I . ' -i : : : : ; _- I , ... -.-__ -J. -i --' -_ . _ I'l +_T. -. I _ ' , -q -- -I -I -.-. -. -.- --- -I . -I . . --- I _ , : -' .. -_-1-:i .-I. -_. I _-_--.t_ -t --r. -_ -_4 i _. _l -- _.' -t L_ _1 -! -I I , " , -.. f -I- -: .- * , -- -r-- . . . I * I , _ -" j : --1 -++ -, --. " -L -I -1 . -. I . I I ___ I i , I N ' Z! I--. . I : " -I i - --, I + J--' + --, __ ". -' . -I . i . -It .- . -, --t -11, I -.. I i I .I I I ir. , . -. -. : , I , : 1. := .- _' '-i , t I . + I . ' ,,, I : -f---!--, " -T-t : ' --- , 4 .4 3 , --; T , -.- I . ' ' -' . , --- i-J-1 ' -I , 1 '- t . -- " -- ' '_ -+ . -' -' -1 , _-, -' ' -T + . -' -I- . t -7 . . I ' L -7 _' r, ._ --:- , -. :, 4 , I -1 I ._. -I -' :1 1. -1 .I 1 * I --; ._- I , -, i " . -. -I q , , il . I -, -, , : -L " . := -. i _ I .-4-, + .' .' :. .1 1, ' _ + -- t- --; -I . 1 ; I I .I- " i t4 -:' ..- _ ! ' _ ii _' _t _ _. -' -_ ' LL T _ _ i : -1 -I : i o Ili -I : ,4 "_ -" . -i , -. ' : 4- . . IL i ' * -I- ' +:' ' I _'J ; 1 -. -, -. -... + -. 0." ' -I t i .. --t I _: , . , ;_; 1; --1 _' f- -; 11 . .. 1 : , ; 4 _: , I 1 ' 41, + j , '. -11 + " --_ ,--t . , .. I _ ---t-4-1- -. -I- -. . , ' 11 I . _. . . -. -'.: . I . I -E / . . 4 , -. . ,,,- :'-_;.' 1. _ I -t . -, ... __ ._'.. . , _ -t: ; .-..-I -.. ' . , -* ' : :' _: 4 ' ' _ _ -. . : ' . : t -: -1 -* I . I ' r ." ' " -I .-, -, t , 1-4-. -. . i , 4 . r I ; , . -1. .- i , l ; -: : ;4 T , -4 -l ,: --I .1 -. -1 _. .-4-' -. I ;-. . I I , I . -I . 4 -: - --;- _ _: _: r -__._ -.! ,-.- I , -j . z -t- -I +-t -T ' i 4-j+ I, --7 -t r I -" -+ i , ' " --t -t --- , --4- .4- -- i -,- f 4 _t I . , ..1 4 -_; .- 7-t-I +-- , ---1 t -+ -. -4 .4 I4 4 , -' I ., , : f -. _ _ _ --1 ..-, . i 4 ' -i -I I "* . _ I ---- -t 44 . .--..I .. -:_ __. I _. I : , I -T ' ; *1 ., I -. _ I , -_ , I- _.- I-,-+- . I . -T , I- I .I -4 ... _ I _+ ' -, I- + -P.6'j-+ _ _' . ' ' ; ' + . : , , -. _ . ;-i 4 -* -_4'l _ : -_ . t-, , --.I -A- I I I _*71. : -;t -' , I '-- T:a --' , --t ' -1 . + --I -f-.1 i. r -L-1- -I I _ -1 --+ -___--f 7' i . ti I ,4- I , 4- ----_'W I .I I ' t -I .-f E 14 tT t- t: -I- -1 . -: --L_ -" ! 1. ,-I--. r , T I -' t I'- --1 ':' . , , + I -I T ' A "-14 1 ' iN '. 7 . . 1 . . . . + -._:' --4 14 ' I . ---:- 7 -, -. -. -I lk t I ILL: -' f , I I " -L _' -_ _ .. ' -.1 -_ _L I .-, '- -t --,-: -14 .---, , .4% -', "- --., __ _ __' tl I I -__ . _.. I -. _I -. . .. . , :_ -. . -1- -; ,-;- -,- ,_ -Zi. 41: 4 _. ! -I.. AI .11 I 1-1- -I.- --T ._'_'_Z: I I "4J 1 -4 ,' 1- ','- '. " L -' -f '- -- -+ " -7 -" '_; ;_ __ , 4- -4 + -. + :4 t ,_ ' , -'t ' : .: -_ -+ : , ..I . _ __ ; i ': ' : , I -. . : 4 , _1 -. .. . _ ' ' 4 -' t -t-+- 14 7 -__4_ '_u . -1 I- --;_4 _ -.--- --- .t + " r ..'. ..' i -1 4 -, i-- ---: f -.I 1 .7 r -.' i: ' " -;t , -., 4. k , '. -, * I .1 Af _. 'N _i t, ._. .1: -,-H E .- I 4 ;:i I I I I ' -4 1 ' -i_ ", ,-. I 4 ,r -_ I -t-- . ; .. -, . -I -I+- , I I ' i i -.-I , '__ -+ f-i _ + -4i * 17 ;__ , f -, __:__7__:_.7 4 .-t" -i , ..-t _ -' I .1 A. ' . 4 f ll " i_ . , 4 -7 . . I , _ -I~ -,_: I-! 4 1 .-. . ,. , I ; , .-'. -I -D, I -4-- I -I- T; F -I --I -. I I . , I I I . I ' I . I + 4- -+ -.- , I .--_ .--_ 14 ! I I I I I +1 I ---+_ , .., , t ., .r , : : , .1 , -4- t -' , ..- -7 .' -. -ij 4- -., -* ' L , , I , -' ! , : . .' I -: * ' -. . Alk -I . -4 4 -.- -, I , , . --1 I . . 4444 i -. + -- , , + -I -. ' ' , , L_ .. _ I I ----I __ .., . . , -, -, -, .;_; :1 ;__- + 4. --t , -, L -I -I -. _ , , ' , , 4 , + I i , , . I -I --! -4- -14 ;- I -, -I , -, : -, , ... _'. : : 1 .I . , + ..., I . I -:- -.- I , , : , --I -U . i .' , , -.-+ , . ' E _I.i , . ! I .- I I ' -' , -_: , , , --' I -: : -- i . ' --, I -7 _- _ . ' '- -J ; : -. " , .-' , 4 '- -, .- 17: ' -, , I ' ' , -I __ -!-, I -'__ ." -1 .--- -4-. . . " t-. i -. : 1-:_ -: 4- '- 1 -7 ! g l I -, -1 I I I I -,-: ' -i -. -. . .- , -,-T-* , . , -. I I I -. ., i , , -4 -_. --, .. .1 l -I''''-I . , T i , I -. I -, -'__ -' . , t '.. , -..-. I , -I l T , --+-! I _ I -I . . -. I . .1 .. I , . ! ; -, : , :_ -:' i ; 4 . -. -14 _. .. -" "I -I ; I ' _: ' , _r , .-1 ' -l : _' --I -I t -' , i-: --* t .- r -I I , ' * , ' -_ .1. 4 .'_;'4 : _ _' '_ . -, q 1-7 4- , -__ , . I ! ' ' . ! ' : -, _.L ' I , , 4 .17 !, -1 I L ; . -, . I --7 ' -1 I . ' . I I : L' : I .L .... ; .., --- .f 1, . T -, , -, . I -- i ' -,- . I -. , . -+ -4 . -.- _; -11 -. -.' . i .4- , -I . I ..I ..._. _ . . , --I . -a , . . -I -, __ . . _1 -1 I -i , . -.I I H ---' " ' -f ' : -I : -1 ' -* ' 4 ; -. .. ?_ I I . "' ! , -, ; I .1 1 -. 4 L . --- , , ' . . : -" 1 * 14- -I- M- , i . 'N -I . _I .:t . 1 4 : t -I I ! -I . .: ; -.' -, ' 1 -4 1 -.. -f -i I , I --I I -' . .-. -. ; . . . . -.-- I -T-! I I . I I F , ,. ---, I .. I I I ' i -, I , . n- --T: -+ , . . -. I I ._-. r 4 -, ..-, I- . 6 -.1 . 1 '_ I ' -I . . I I -a I -..-: .I I .. . I . -17 , -Z , I r . I -1 : . ' __ I 4 -1 . I I .1 I- . , :N '_! 4 " -. . . -. ; : . -+.. ,. I '_. 4_ --I -., , I , -, -_ 1 4 .--. ..1 1 -: --i --4 4 , , -: = , t -I . . . -. ..I , -.I -' . , , , , , ; I _ f + : ' -. i . -m T . . . I . -, -. I -. .- . . . -. I ; , : --, , -I __ --. _ I : + , 4 -. , , , -, , r * ___ ___ _ . _ , j 'r ' I I . -.: -.- + -I . , -- . -. -I : I -' ; . I ..r . * -* 1 '. _' .' -r , --V -I . , . .;_ . _ , t' : , _ 7- -, I -I -. L -: ' I -, _ : . I I , . , . I . I .. -__ I I -.f t -.. I , -. i 'r , -I -, , .-' -.____ -.-t-I _i , : _ _ _ J__ , , . f i -.-, +-_ . t . , 'A , : _ -: .' .- I . -: I -. I . _ _ _ ,I , . r . I -. I _ _. I t , . 'f -_" . -4 r. ' , 4 : ' , -, : -r . . I -t I : -. ' , -;- --I . ; . I I _ . . . -, : 1 : -. . , : i. I -1, --- -..--.. -I : -. ' ' , .: ' , -!- --- '. I , !'o . u . I -, . - .-I __ . -: I . . I -. . . . ..---I I t + I -.-, i 'l-, -, * ; -, ;-T- . -1 , r . I , -r I . -, . .- . I -, 'rl. , , 1 ., : ..: t 4_ llf _+ 4 , , --- , . . . . I -; / _ -, , , , -, , i , I I .* * t I -I I . . -. r d I I , .--I I _ --.-r -.. , : . ' I -, 4 --'_ f 1 .. , ' ' ' T I I 11 .- J -. _ '_- I . . .. -'.' I t I -. -1 -.- . _4_'. -. -. 1 I- '_. , -i . --I -_ . , I _ -* ' . 4 to -. .. . , .. ,I , i --, -" . ' ' I , T --t I -1 4::: __ --t t -I ' -i-I --.! -, , I I .,,, 4-- --! --t _ -I .- I ' -,__ . 1+ -...--I -...--I . I ' -" ' -i .-I. .-. I . I -, -: I , I _j I, I -, 1 , -1 4 4 -.__ _'v _: I '_ '_ -_: . -1 !-; 4 + 4r ' "I I I -I I -_ : .. .I I .: I -1 I t -'- 7 -, -. '_. -1 ' -' I I r '- ,-I- i -I.i 1 .-.1 7 1 1 .1 I -, . . i . _ -4 ,- '-t -1- I . --f . -. -! , -I -t ." -: -. --; I I '_ . ' -, -i -4 : ',-' . --f I -j --T-.- , -, _ _: -, '-' : : I . : . ;4' , .._' -I _ '4 -"'. ' -. : , T , : , t L , I~ r! -' I , . I I * I . . __ + , _ r , ---I -1 I .; i I I + --'_ --.. T -' I i i ' -"r_'._"_ "r': :; I !* , -I . I . . _ . '_ . , I- -I .i _.' + j' -q. -4 I -.; 4 ---. ' _ , r . __

.""

0

26.

27.

DI6CUSSIUN

Berore taking up the results that were obtained, 1i might be well to discuss the diri'iculties that were encountered.

The Q, which appears in the equation, it will be

remembered, is an oil rate divided by an area. The

oli rate was measured by catching the fuel at the

nozzle for a known length of time. The area which

determines Q at the point where the measurements are

taken is the cross sectional area taken in by the entire spray at that point normal to drop motion.

In order to determine this area it is necessary to

measure the thickness of the spray in the direction or penetration of the beam of light which is

pro-jected through it. This distance, x, also appears

in tne equation.

The measurement or this distance presents

defi-nite difficulties. Upon observation of the spray it is difficult to escertain just at what point the actual spray leaves off and the mist which is pre-sent in the chamber begins. The apparatus used was not equipped so that the lenses could be placed

definitely within the limits of the spray. Had this been possible, the distance, x, and the area would have been accurately fixed. If this were done,

28.

however, something about the distribution of the fuel in tne spray would have to be known. Unless the dis-tribution of particles in the spray were uniform, (i.e. the stime ratio of particles to area in the out-side limits of the spray as in the center) the value of Q/A would be in error. The value or the oil rate

for this fixed area might be measured, however, by collecting the particles which fall on a plate, the size or which just covers the area in question.

The measurement of velocity of the particles is also a subject for discussion. It was first thought that it might be possible to determine the velocity either by a microscopic study or by photographic

means. The first method would have involved focusing

on a drop and measuring the time required for it to go

a certain distance by following it down.

The second method would have involved photograph-ing a small portion of the spray, leavphotograph-ing the shutter open for a known length of time. From the length of paths of the drops as shown by the photograph the velocity was to be computed.

Observation of the resulting spray, however, ruled out these two methods. The drops do not come

down straight - some angle in one direction, others

-4

29.

motion is prevalent. Besides this, the spray is

com-posed or drops or varying diameters so that in order to obtain a good average velocity a large number of

drops mould have to be observed.

The next nmthod which was tried was to take measurements at a distance of 4-4- ft. from the nozzle and to assume that at this distanoe the velocity of the particles was equal to the air velocity as given

by the orifice attached to the blower. This

assump-tion would have been a good one had the free settling velocity or the particles been small compared to the air velocity. However, it was found that drops of

diameter as given by calculations based on this

assump-tion have a free settling velocity many times the

ve-locity of the air in the chamber. The air velocity

in the chamber is .05 rt. per second while the rree settling velocity or a particle .005 inches in

diame-ter is 2.7 ft. per second.

If, now, we take the measurements at a point were the spray has assumed a substantially

oylindri-cal shape (that is the lateral velocity imparted to many or the drops at the nozzle and causing a conical shaped beam has been lost) it is sare to assume that the free settling velocity has been obtained.