studies on a pressurized swirl injector bi-propellant

8/17/2019 Studies on a Pressurized Swirl Injector Bi-Propellant

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Studies on a Pressurized Swirl Injector Bi-Propellant

Used in Rocket-motor

L. Rocco Jr.1, R.F.B.Gonçalves2, J.A.F.F. Rocco3 and K. Iha4

Departamento de Química - Instituto Tecnológico de Aeronáutica - CTA,

São José dos Campos – CEP 12228-901 - S.P. – Brasil

The process of fuel injection in combustion chambers is of vital importance, under several

aspects, for the ideal operation of each motor. The responsible element for the introduction

of liquid and gaseous propellants in the combustion chamber of rockets and for the

transformation of liquid masses in sprays is the injector, that converts the potential energy of

the propelants in kinetic energy, for the pressure fall in its interior, forming a jet or liquid

sheet that dissolves in drops. Swirl type pressurized injectors, mono or bipropelants, are

object of constant studies to understand its operation in rocket-motor with liquid propelant,

because they produce conical liquid sheets and present a serie of differences in relation to the

axial type in terms of improvement of the combustion process as a whole. The fast formation

of a high number of drops, of convenient diameters, distributed in an extensive area, favors

the vaporization mechanisms due to the high surface of all, that quickly vaporize and enter

in combustion. Its production is a challenge for the techniques of conventional fabrication,because of the complexity, dimensions, work conditions and its fixation in the injection head.

Injectors production from preexistent designs and the assembly of a structure which allowed

the tests of the same, was the object of this work, that generated pieces in brass which

allowed cold tests with the fluids kerosene and cut oil to confirm the formation of the hollow

conical spray and hot tests with melted paraffin to confirm the formation of spherical drops

of several sizes, which were measured in a profile projector, and analyzed by the process of

test sieving, revealing the existence of drops within the range of those already found in

literature.

Nomenclature

ß max = wave growthλ opt/ 2 = half wavelengthDL = ribbon diameter filament

SMD = mean diameter of drop Sauterλ

* = axial wavesd1 = toroidal ligaments of diameterλ 1 = circumferential wavesΔD = strip of drops diameterΔ Ni = number increment inside of Δ DiΔ Qi = volume increment inside of Δ DiDi = mean diameter of the range of size i

Di1 e Di2 = upper and under limits in the Δ Di

Ni = number of drops in the range of size i

Vi = volume of measured liquid of the class ii = number of classes of drop size or size of the considered field

a and b = any value corresponds to the investigated effect

a + b = called of order of the mean diameter

1 PhD Candidate, Chemistry Department, [email protected] AIAA member2 PhD Candidate, Chemistry Department, [email protected] AIAA member

3 Professor, Chemistry Department, [email protected] AIAA member4 Professor, Chemistry Department, [email protected] AIAA member

1American Institute of Aeronautics and Astronautics

45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit2 - 5 August 2009, Denver, Colorado

AIAA 2009-549

Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


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D32, or SMD = mean diameter of the drop SauterVesf = (4/3) π r 3 = volume of the sphere where r is the ray of the spherePesf = Vesf. ρ = weigh of the sphere where ρ it is the specific massAesf = 4 π r 3 = area of the sphere

I.

Introduction

The complete understanding of the phenomena involved in the operation of pressurized swirl atomizers isstill a challenge for the researchers due to great complexity of the phenomena involved in the atomization

process.The main factors that determines the quality of atomization of these atomizers are the properties of the

injected liquids, the physical properties of the gas in which this liquid is injected, the pressure of injection ofthe liquid, the dimensions of the nozzle, and principally the final diameter of the exit hole on whichtheoretical foresee, and experiments confirm, that the size of the mean drop is proportional to the thethickness of the liquid sheet [1].

It is necessary a minimum speed of the sheet for its enlargement against the force of surface tension thattends to contract the surface. As larger is the speed, the sheet expands and is elongated until a main extremityis formed, where balance exists between the surface tension and the inertial forces. Its disintegration canhappen with or without perforations in the liquid sheet.

The generation of a wave movement in the sheet through the one which has areas corresponding to one orhalf wavelength of the complete oscillation, will be torn before the extremity is reached. These torn areas,when don't suffer disintegration for the action of air or turbulence, contract quickly under the action of thesurface tension, forming a net of lines.

Lefebvre [1] showed that the regularity of the disintegration process and the uniformity of production oflines have a big influence in the drop size distribution. Perforations that happen in the sheet at the samedistance of the nozzle have a similar formation and the drop sizes are very constant in the disintegration of

perforated sheet. The disintegration of the wavy sheet is highly irregular, and consequently the drop sizes aremuch more varied.

Atomizers that unload the liquid in the form of a sheet are usually capable to exhibit all the three mannersof sheet disintegration. Sometimes two different manners happen simultaneously, and its relative importancecan influence a lot, so much in the drop size, as in the distribution of its size.

Lefebvre [1] used an improved photographic technique and an especially projected source to combine a

discharge and intense illumination with short duration, and established that the ligaments are caused, mainly,for perforations in the liquid sheet. If the perforations are caused by attrition with the air, the ligamentsseparate very quickly. However, if the same ones are created through other means, as turbulence in thenozzle, the ligaments break up more slowly. They ended that liquid sheets with high surface tension andviscosity are more resistant to the breaking and the effect of the liquid density in the sheet disintegration isvery small.

Lefebvre [1] observed that the interaction between liquid and air produces waves that are unstable andthey dissolve in fragments that contract in ligaments and break up in drops. These drops are minors to highvelocity airstreams, because the ligaments are finer and they are formed closer to the nozzle.

The initial thickness of the liquid sheet, that it is directly proportional to the size of the injector nozzle, itis important to determine the drop medium size produced, because it was observed that thicker films

produces thicker ligaments and larger drops.The comparison among the magnitude of the wavelength of the disturbances that cause rupture of the

liquid sheet with its thickness is used by Lefebvre [1] to classify the liquid sheets in two groups.In the first case, when the magnitude of the wavelength of the disturbances in the liquid surface is of thesame order of the sheet thickness, the rupture process begins closer to the nozzle exit and extends along thesheet and the ligaments. The formed great structures and drops are unstable and they break up in smallerdrops than they tend to be wide of the order of the sheet thickness.

In the second case, when the magnitude of the wavelength of the disturbances in the liquid surface issmaller than the sheet thickness, suface liquid disturbances are confined to a small area close to the surfaceand as the disturbances grow, fine ligaments and small drops are removed of the surface. This disintegration

process happens in further areas of the nozzle.



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A. Liquid sheets

Instability and wave formation in the interface among the continuous and discontinuous phases are themain factors in the rupture of a liquid sheet in drops plane in liquid sheets moving in the air. Forces ofsurface tension try to do the protuberances return to their original position, but the local air static pressuredecreases (corresponding to the local increase in speed) and tends to enlarge the more distant external

protuberance. This corresponds to the pattern of instability for induced wind, where the forces of surfacetension are opposed in any movement of the interface of its initial plan and try to reestablish the balance,while aerodynamics forces increases any interface divergence and promote the instability.

To formulate the problem, Lefebvre [1] considered an infinite two-dimensional liquid sheet of finitethickness with air on both sides, without viscous effects and flow on rotational.Using calculated velocities by Bernoulli equation, the pressure then can be evaluated and the displacementsdeterminated. As in the case of a liquid jet, an exponential increase in the wave amplitude happens undercertain conditions.

The growth tax has a defined maximum for a certain Weber number, especially to high Weber numbersand the disturbance with this wavelength will dominate the interface and quickly disintegrate the sheet.

Lefebvre [1] proposed an expression for drops sizes produced by the rupture of a sheet with low viscosityin form of fan. His model assume that the fastest wave growth (ß max) is separated from the border in theform of a ribbon with the width of half wavelength (λ opt/ 2). This ribbon immediately contracts in a diameterfilament DL, which subsequently dissolves in drops of equal diameter.

The medium diameter of drop Sauter (SMD) is the drop diameter that has the volume proportion andsurface area like the same of the total spray.

For a real case, where the liquid has finite viscosity and the thickness of the sheet decreases with themovement as it increases the distance of the injector nozzle exit, Dombrowski and Johns [2] related themeasurements of the medium diameter Sauter of their works for a nozzle fan spray theoretically, for a lowviscosity flow, empirically correlating liquid sheet thickness, the distance of the nozzle, liquid dynamicviscosity, its pressure and the sheet speed.

The theory of rupture of conical sheets produced by pressurized swirl injector nozzles is not totallydeveloped, but there are evidences that the ray of cone curvature has a desestabilized effect in the flotations.

Three different manners came from the sheet disintegration, described as ring, wave and perforated sheet.In the ring way, as illustrated in Figure 1, occurs an unbalance in the extremity liquid sheet free owed the

unbalance between the surface tension forces and viscous forces that tend to unite the liquid and the forcesthat tend to separate it, forming a margin breaks up for a mechanism that corresponds to the disintegration of

a free jet.The resulting liquid continues moving in the direction of the original flow, staying fixed to the surface to put thin lines (ligaments) that also quickly fracture in rows of drops. This disintegration way is very prominent where the viscosity and surface tension of the liquid are high and produce big drops, withnumerous small drops around.

Figure 1. Hollow conical liquid sheet disintegration in ring and ligaments [1].

In the case of the waves, these are formed close to the nozzle and the wavelength for the maximumgrowth causes periodic thickening of the liquid sheet towards the normal flow. Rings break outside of theconical sheet, and the liquid volume contained in the rings can be dear as the volume of a ribbon cut out ofthe sheet with a thickness same to the one of the sheet in the rupture distance and a width same to a



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wavelength. These cylindrical ligaments dissolve then in drops, in agreement with the mechanism ofRayleigh.

The formation mechanisms, stabilization and disintegration of conical liquid sheets also studied by Mao,Kuo [3], and Figure 2 illustrate surface waves dominating the disintegration of a conical hollow liquid sheetwhat under ideal conditions, the axial waves λ * are they responsible for the creation of toroidal ligaments ofdiameter d1 that possesses circumferential waves λ 1 what drive to the formation of the drops.

Figure 2. Hollow conical liquid sheet disintegration in waves [3]

In the disintegration of perforated sheet as shown by Inamura and Miyata [4], as show in Figure 3, holesthat show up in the sheet are delineated by formed margins of the liquid inside of which was formed initially,that grow quickly in size until the margins of adjacent holes and they are founded to produce ligaments in anirregular way that break up in drops of varied size.

Figure 3. Hollow conical liquid sheet disintegration in perforated sheet [4]

These disintegration manners can happen in a same hollow conical liquid sheet produced by a pressurized swirl injector under several conditions of injection as low or high pressure or with or without itinfluences of movement of the adjacent air.

B. Thickness of the liquid sheet

In swirl pressurized atomizers, the thickness of the liquid film in the end of the discharge hole is directlyrelated with the area of the nucleus of air.

Theory and practice indicate [1] that as higher the injection differential pressure, thinner the producedliquid sheet and better the quality of the atomization. This is usually attributed to the increase of the speed ofdischarge of the liquid, or also, partly, for the decrease of the thickness of the liquid film caused by theincrease of the differential pressure.



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An increase in the diameter of the final nozzle hole leads to a thicker film, because it reduces thedischarge coefficient. The thickness of the film increases with the increase of the area of the tangentialentrance holes of the liquid, because the flow increases in the nozzle, and it results in a thicker film. Theeffect of a reduction in the diameter of vortex camera is the increase of the thickness of the liquid film. Thisis attributed to the lowest action of the vortex that reduces the diameter of the nucleus of air inside the end ofthe discharge hole. The effects of nozzle length and of the length of vortex camera in the thickness of thefilm are quite small.

The thickness of the liquid film increases with the dimensions of the nozzle, liquid flow rate and viscosityof the liquid and decreases with the increase in the density of the liquid and in the injection pressure.

The surface tension represents an important paper in the subsequent collapse of the liquid sheet inligaments and drops and the viscosity of the liquid is very important in the atomization process, because theviscous forces oppose the atomization increasing the initial thickness of the film and resisting to thedisintegration of the liquid sheet in drops.

The effect of the density of the liquid in the thickness of the film is very small and probably theinfluences in the atomization quality should be also small, and that is confirmed by the results of measures ofmedium size of drop for swirl pressurized atomizers.

C. Drops diameters in conical sheets of a swirl pressurized injector

The average mean diameter of droplets for the same pressure drop and liquid flow rate is 2.2 to 2.5

smaller than that of jet injectors [5]The mean drop diameter produced in conical sheets of swirl pressurized atomizers is calculated with base

in the thickness of the sheet and in the wavelength for the maxim growth rate.Lefebvre [1] thought the sheet model plain infinite used in the theoretical analysis didn't represent the

conical spray of his experiences sufficiently.For modulation dilatation of the liquid conical sheet, the effect of the change of the number of Weber in

the length and in the time of rupture of the sheet it is determined by the relative importance of the curvatureray in the main direction of the flow. For the sinuous modulation the rupture of the film happens due to the

joining no lineal with the way dilatation and the length. The time of rupture of the sheet due to changes in thenumber of Weber is influenced by the way no lineal of joining and for the behavior lineal dilatation and nolineal.

For conical films, increases in the deviations of the liquid film drive it tuning and small drops soon standout of the fine ligaments and soon afterwards the film dissolves in agreement with Rayleigh’s mechanisms

rupture of jet.Lefebvre [1] proposed an equation for the mean diameter of drop Sauter (SMD) produced by swirlatomizers based in the notion that the disintegration of a liquid jet or sheet that leaves a nozzle is not causedonly by aerodynamic forces, but also and partly for the turbulence or other disruptive forces inside of theliquid. These disturbances inside of the flow have a strong influence in the sheet disintegration, especially inthe first phase of the atomization. Subsequently, and even certain point simultaneously, the relative speed

between the liquid and the adjacent gas has an important paper in the atomization for its influence in thedevelopment of the surface waves initially smooth and the production of unstable ligaments. Any increase inthis relative speed cause a reduction in the size of the ligaments, so that, when they dissolve many smallerdrops are produced. As the atomization process in swirl nozzles is highly complex is convenient to subdivideit in two main phases. The first phase represents the generation of instabilities in the surface due to thehydrodynamic effects and forces aerodynamics combined. The second phase is the conversion of the surface

protuberances in ligaments and then drops. It is recognized that this subdivision of the total process of

atomization in two separate and different phases, represents a simplification of the involved mechanisms,however, it allows the formulation of an equation for SMD as:

SMD = SMD1 + SMD2

In the equation SMD1 represents the first phase of the atomization process. Its magnitude depends partlyon the Reynolds number of which supplies a measure of the disruptive forces inside of the liquid sheet.These forces increase for increments in the speed of the liquid and in the thickness of liquid sheet anddecrease for an increase in the viscosity of the liquid. SMD1 is also influenced by the Weber number thatgoverns the development of capillary waves (undulations) in the liquid surface. The tax of growth of these



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disturbances in big projections is enough to break in the form of ligaments, depending on the relationship ofthe aerodynamic forces among the interface liquid / air that its are opposed to the forces of superficial tensionthat is Weber number.

The term SMD2 represents the final phase of the atomization process in the which the relative high-speedinduced to the interface of I liquidate / air, generated by the fast involvement of the conical sheet, it takes tothe separation of the surface protuberances generated in the first phase that it break up and they formligaments that break up in drops.

Couto, Carvalho and Neto [6] obtained an expression in which, leaving of the expression of Dombrowskiand Johns [2] for plane liquid sheets in fan, was considered the conical format and the axial components andtangential speed of one of a hollow conical spray, produced by an atomizer pressurized of the type swirl.

D. External properties of the spray

The atomizer should fraction the liquid in small drops that should be distributed in the surrounding gas inthe form of a symmetrical and uniform spray.

The liquids sheet dissolves quickly in drops that tend to maintain the direction of the movement obtainedto the exit of the nozzle. Under the effect of the resistance of the air, the formed drops lose the pulse, mainlythe ones that are in contact with the adjacent gas forming a cloud of drops, finely atomized, suspendedaround of the main body of the spray.

When the liquid is injected in inactive gas, currents of gas generated by the action of the own sprayinfluence in its physical structure and any increase of the angle of the spray cone will increase the extensionof this exposition, leading to a better atomization, reason for the which the angle of the cone of a spray isvery important.

In efficient dispersions the liquid mixtures happen quickly with the adjacent gas, and the evaporationtaxes are high. In pressurized swirl atomizers, the dispersion is governed mainly through other characteristicsof the spray, as the cone angle, mean size of the drop and distribution of drop size. The penetration, that isthe maxim distance reached by a spray when injected in stagnated air is determine for the magnitudes of theforces contrary of the kinetic energy of the initial liquid jet and of the resistance aerodynamic of the adjacentgas. The first formed drops give up it kinetic energy for the adjacent gas that it begins moving with the spray,offering smaller resistance then for the following drops that consequently penetrate far away. The penetrationof the spray drives the introduction of fuel in areas of the combustion chamber according to the needs, as inthe walls, where vortexes of hot air are present, or it can still harm when the inadequate penetration results ina mixture fuel-oxygen unsatisfactory.

The radial distribution of the liquid measures the radial volumetric symmetry of the fluid of the spray andthe distribution circunferential measures the circunferential volumetric symmetry of the fluid of the spray,and they can also be done with base in the sizes of drops. The quality of the nozzle is important and thedistribution of the spray can be harmed to put bad superficial finish, imperfections in the hole, obstructionsor contaminations in the passages of the flow.

E. Distribution of the drops sizes in spray

The spray can be considered as a spectrum of drops sizes distributed under some medium value definedarbitrarily and besides the mean drop size, other important parameter for the definition of a spray is in thedrop sizes distribution that the spray contains. The graphic representation of the drop sizes distribution can

be made in a histogram of drop size in which each ordinate represents the number of drops whose dimensionthis among the limits D - ΔD/2 e D + ΔD/2 , where ΔD is the strip of drops diameter that subtract and add to

the nominal drop diameter supplies the under and upper limit.It is not always possible to count the number of drops, so the volume can be used (or the superficial area)

of the spray that corresponds to a range of drop sizes among D - ΔD/2 and D + ΔD/2 and is the resultingdistribution skewed to the right, shown in Figure 4, due to the weighting effect of the larger drops.

The histogram of the Figure 4 assumes the form of a frequency curve for values of small ΔD and a largenumber of samples. The values of the ordinates can be of several alternative manners as the number of dropswith a certain diameter. The relative number or fraction of the total, or the fraction of the total number forsize class, and in this case the area under the curve of frequency distribution, it should necessarily be equal to1 Inclusions in the frequency plans can be made directly of the data of distribution of the drop sizes drawing



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Δ Ni / N Δ Di , for D or Δ Qi / Q Δ Di , for D where Δ Ni it is the number increment inside of Δ Di e Δ Qiit is the volume increment inside of Δ Di [2].

Δ Qi = Δ Ni ( π / 6 ) [ 0,5 ( Di1 + Di2 ) ]3 (1)

where Di1 e Di2 they are the limits upper and under in the Δ Di (i nr) classes of drop size.

NUMBEROF DROPS DROP

VOLUME

ΔD DROPS DIÂMETER

Δ N / ΔDor

ΔQ / ΔD

Figure 4 - Drop size histogram based on number and volume [1]

F. Mean diameters

The concept of mean diameter was generalized and standardized by Mugele & Evans [1] and in manycalculations of mass transfer and flow processes are convenient to work only with average or meandiameters, instead of the complete distribution of drop size.

The equationDa b = [ Σ Ni Di

a / Σ Ni Di b ] 1/ ( a – b ) (2)Vi = Ni (4/3) π (Di/2) 3 (3) Ni = 3 Vi / 4 π (Di/2) (4)

where a and b can assume any value corresponds to the investigated effect, the sum of a + b is called of orderof the mean diameter, i represents the size of the considered field, Ni is the number of drops in the range ofsize i, Di is the mean diameter of the range of size i and Vi is the volume of measured liquid (of the class i)for the unit of volume, therefore a percentage.

D32, (SMD) it is the medium diameter of the drop Sauter whose proportion of the volume for thesuperficial area is the same of the total spray, in the case of spherical drop format:Volume of the sphere : Vsph = (4/3).π.r

3 where r represents the ray of the sphere (5)Weigh of the sphere : Psph = Vsph.ρ where ρ represents the specific mass (6)Area of the sphere : Asph = 4.π.r

3 (7)



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G. Representative diameters

It is important to distinguish the concept among a representative diameter and a diameter that it suppliesan indication of atomization quality.

D 32 or SMD it can indicate correctly and adequately the "refinement" of the spray of the combustion point of view, where many small drops are necessary to promote high initial evaporation taxes for a fastignition, because it has special significance for applications of transfer of heat and mass, but as any otherrepresentative diameter can lead to erroneous conclusions on the delicacy of the spray.

Aspects as space and temporary sampling, sample size, saturation, evaporation and adhesion of dropsand collection point influence in the measurement of drop size and should be considered to guarantee that thetechnique of measurement of size of chosen drop incurs the least possible mistakes than in practice arealready known.

Although a spray contains a larger proportion of small drops than great drops, are these few big dropsthat prevail, determining the mean of diameter of drop of the spray, and then if a sample of drops is trulyrepresentative as an all of the spray is important that the big drops are included.

H. Methods to measure sizes of drops.

Laser

A laser beam divided in two coherent laser beams of equal intensity and parallel polarization that areguided in cross way, they form a control area through where passes the spray with drops to be measured.These drops spread the light that is received then by an outline optical collector that sends the images of thecontrol area for the opening of a sensor one where the signs of the drops are registered.

They are equipments relatively easy to use with good flexibility of introduction of the sample and fastmeasurement, but that demand knowledge for manipulation of data and they operate with restrictions indense means.

Based on the light scattering theories of Fraunhofer and Lorenz Mie, the equipment calculates a statisticsof distribution of size of a population of particles and it doesn't measure individual particles.

Melted wax technique

The paraffin wax is heated up to an ideal temperature above it fusion point, when it has close physical

properties of the aviation kerosene oil (density, 780 kg/m3

; surface tension 0,027 kg/s2

, kinematic viscosity1,5 x 106 m2/s) and it is injected then in the atmosphere, cooling and solidifying quickly, as proposed byJoyce [1]

The wax drops solidified can be appraised and measures with the aid of optical instruments asmicroscopes or profile projectors.

The analysis of a significant quantity of solid paraffin drops was conducted in the present work by usinggranulometric sieves with brided metallic wires, in which the wax drops are separated in groups ofcompatible diameters by the meshes openings.

The distribution of cumulative volume and medium diameter of mass will be measured directly and thehigh number of drops in a sample turns the accurate procedure.

Besides the limitation in the choice of the material for test, other disadvantage of this technique ischanges in the physical properties of the wax drop that it cools quickly after leaving the atomizer, so that theformation processes and secondary recombination cannot be reproduced accurately and for this reason the air

close to the nozzle or in the area where the fundamental process of atomization is happening, it should bewarm to the same temperature of the melted wax.

II.

Experimental Procedures

A double and concentric swirl injector was used by Rocco [7], manufactured in brass for cold tests withsynthetic oil and kerosene oil, and hot ones with melted paraffin.

A milling cutter was used with digital marker, divide plate and drills to obtain the tangential holes of the"swirl", besides a mechanical lathe with cut tools and drills.



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To guarantee the close fitting of the vortex chambers, the injectors were projected to use O-ring ofnitrilic rubber, ideal for derived of petroleum and work temperatures among - 50 and 120 0 C, guaranteeinglike this the gasket of the ensemble.

Figure 5 shows the internal injector, that it is longer and the external injector, that it is shorter.Figure 6 shows the adapter that unites the ensemble injector to the injector head.

Figure 5. Internal injector, (longer) and Figure 6. Adapter that unites the ensemble

external injector, (shorter). injector to the injector head.

The angles of the formed cones can be altered by factors, as format of the vortex chamber and injection pressure among others.

The tests equipment of fluids injection is composed by a pump of gears of straight teeth worked byelectric motor, manometer and valve of spheres to control the fluids flow, tank and system for maintenanceof the temperature of the paraffin wax melted to 700 C.

The bench of tests was used for the tests with cut oil for automatic lathes, commercial kerosene oil andmelted paraffin and Figures 7 and 8 shows the external and internal injectors no simultaneously, forminghollow conical liquid sheets of kerosene with pressure below 1 atm.

Figure 7. External injector conical liquid sheets Figure 8. Internal injector conical liquid sheets

Figure 9 shows the external and internal injectors operating simultaneously without interaction, formingseparated hollow conical liquid sheets of kerosene with pressure below 1 atm.



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Figure 10 shows the external and internal injectors operating simultaneously with interaction, formingunited hollow conical liquid sheets of kerosene with pressure below 1 atm.

Figure 10. External and internal sheets united

Figure 9. External and internal sheets separated

The paraffin melted to 70o

C was injected at a pressure of 5 atm in both injectors. In the external injectorthe mass flow was of 140 g/s and the cone angle of 118 0 and in the internal injector the mass flow was of183 g/s and cone angle of 78o.

For the test sieving with wire cloth test sieve it was utilized an equipment to shake these sieves withmeshes 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 100, 120, 140, 170, 200, 30, 270, 325, 400 e 500manufactureted and calibrated according to ASTM E11.

For each injector a sample of 250 g of paraffin drops solidified was removed with which were made thesieving tests and made registrations of drops images in the profile projector.

This material kept in each mesh was weighed then in analytical weighing and starting from the nominalopening of each one, the number of particles was made calculations kept inside of each class, allowing likethis the calculation of SMD that resulted in SMD INT 5 = 0,214 mm for the internal injector and SMD EXT 5 = 0,296 mm for the external injector.

Figure 11 shows the external injector design and Figure 12 shows the angle of the cone formed by the

external injector with paraffin melted to 5 atm.



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118 0

Figure 12. The angle of the cone formed by the external

injector with paraffin melted to 5 atm.

Figure 11: External injector design

Figure 13 shows the solid paraffin wax (5 atm) on the collector (external injector) and Figure 14 showsthe solid paraffin wax (5 atm) on the perfil projector table

Figure 13. Solid paraffin wax (5 atm) on Figure 14. Solid paraffin wax (5 atm) on the

the collector (external injector) profile projector table

Figure 15 shows the internal injector design and Figure 16 shows the angle of the cone formed by theinternal injector with paraffin melted to 5 atm.



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78 0

Figure 15. Internal injector design Figure 16. Angle of the cone formed by the external

injector with paraffin melted to 5 atm.

Figure 17 shows the solid paraffin wax (5 atm) on the collector (internal injector) and Figure 18 showsthe solid paraffin wax (5 atm) in the profile projector screen.

Figure 17. Solid paraffin wax (5 atm) Figure 18. Solid paraffin wax (5 atm) in the

on the collector (internal injector) profile projector screen

III. Results and conclusions

The manufacturing process of the injectors and injector head was considered efficient and satisfactory, because it allowed the production of the necessary pieces and with good finish, making possible all the testsaccomplished inside of a good reliability pattern.

In several circumstances, in other words, varying the injected fluids and the work pressures, the coneswere formed in the external injector and in the intern and inside of the formation theories and disintegrationof hollow conical liquid sheets, found in the literature.

In the initial observations of the injected melted paraffin, done in the profile projector, it was possible toidentify that besides producing drops in the spherical format, as it would be of waiting, the same ones

presented different diameters.



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The rehearsals with wire cloth sieves made possible the calculations to determine the medium diameter ofdrop Sauter (SMD):

In agreement with Rocco [7], the formation of the liquid sheet already feels to low pressures and flows,so much for the internal injector as for the external.

The increase of the injection pressure doesn't have great effect in the angle of close spray to the exit ofthe nozzle, but it causes significant alteration in the curvature of the spray, in the length of the liquid sheetthat it decreases as the pressure increases until not being more visibly identified and probably in the size ofthe produced drops, therefore to high injection pressures it was formed a fine fluid fog.

Perforations are not observed in the liquid sheets in the area between the nozzle and strip of dropformation, not evidencing the existence in the way sheets perforated proposed by Fraser and Eisenklam [1].

In the strip where happens the formation of the drops it is not clear enough to affirm that in it doesn'thappen perforations and aren’t clear enough to see rings, but ligaments seem to exist.

It is possible to observe ondulations in the liquid sheets that they evidence the development of dissociatestructures of the same ones that end for promoting the rupture of which results the drops.

In the area where already the drops are observed, the same ones come willing of such a form, aligned inway vertical or oblique, indicating a process of rupture of ligaments.

The accomplished calculations revealed that the dimensions of the injector and mainly the angles of the produced cones are compatible with the literature and the project methodology.

The particles imagery of solidified paraffin and accumulated in the collectors, so much for the externalinjector as intern, indicated that there were a radial homogeneous distribution and circunferential of the

particle in the spray.

IV. Acknowledgements

CNPQ Conselho Nacional de Desenvolvimento Científico e TecnológicoCAPES Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

V. References

[1] LEFEBVRE, A. H. Atomization and sprays. West Lafayette: Purdue University, 1989.

[2] DOMBROWSKI, N.; JOHNS, W. R. The aerodynamic instability and disintegration of viscous liquidsheets. Chemical Engineering Science, v.18, n. 2, p. 203 -214, 1963.

[3] KUO, K. K. Recent advances in spray combustion: spray atmomization and drop burning phenpmena.University Park: Pennsylvania State University, 1996. v.1 v.2

[4] INAMURA, T.; MIYATA, Spray characteristics of swirl coaxial injector and its modeling , K. HirosakiUniversity, Hirosaki, TAMURA H., SAKAMOTO, H., National Aerospace Laboratory, Kakuda, Japan,AIAA Paper 2001-3570, A01-34284.

[5] BAZAROV, V.; YANG, V.; PURI, P. Liquid rocket thrust chambers: aspects of modeling, analysis, anddesign vol. Lexington 200, Progress in Astronautics and Aeronautics, Massachusetts, 2.004 . Cap. 2, p.19 - 103.

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studies on a pressurized swirl injector bi-propellant

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