U.S. patent application number 09/960588 was filed with the patent office on 2002-03-21 for fuel injection nozzle and method of use.
Invention is credited to Ganan-Calvo, Alfonso M..
Application Number | 20020033422 09/960588 |
Document ID | / |
Family ID | 27443927 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020033422 |
Kind Code |
A1 |
Ganan-Calvo, Alfonso M. |
March 21, 2002 |
Fuel injection nozzle and method of use
Abstract
Atomized particles within a desired size range (e.g., 1 micron
to about 5 microns) are produced from two immiscible fluids, the
first a fuel source containing the formulation to be atomized, and
a second fluid source which is contained in a pressure chamber
surrounding at least the area where the first liquid is to be
provided. The invention provides a method for the formation of
small, relatively uniform fuel particles for use in internal
combustion engines and a nozzle-type apparatus for providing the
particles to a combustion chamber.
Inventors: |
Ganan-Calvo, Alfonso M.;
(Sevilla, ES) |
Correspondence
Address: |
Karl Bozicevic
Bozicevic, Field and Francis LLP
Suite 200
200 Middlefield Road
Menlo Park
CA
94025
US
|
Family ID: |
27443927 |
Appl. No.: |
09/960588 |
Filed: |
September 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09960588 |
Sep 21, 2001 |
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09604935 |
Jun 27, 2000 |
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09604935 |
Jun 27, 2000 |
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09191787 |
Nov 13, 1998 |
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6189803 |
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Current U.S.
Class: |
239/5 ; 239/410;
239/411; 239/8 |
Current CPC
Class: |
F23D 11/106 20130101;
F02M 69/08 20130101; B05B 7/066 20130101; F02M 43/04 20130101; A61M
2202/064 20130101; B05B 1/02 20130101; C40B 60/14 20130101; F02M
69/047 20130101; B82Y 30/00 20130101; B01F 25/30 20220101; B05B
7/0884 20130101; B01F 23/232 20220101; B01J 2219/00378 20130101;
B05B 7/0475 20130101; B05B 7/061 20130101; G01N 2015/1409 20130101;
A61M 15/025 20140204; A61M 15/0065 20130101; B01F 33/3011 20220101;
B05B 7/065 20130101; G01N 21/01 20130101; F02M 67/10 20130101; G01N
2015/1406 20130101 |
Class at
Publication: |
239/5 ; 239/8;
239/410; 239/411 |
International
Class: |
F02D 001/06; F02D
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 1997 |
ES |
PCT/ES97/00034 |
May 13, 1996 |
ES |
P9601101 |
Dec 17, 1997 |
ES |
P9702654 |
Claims
What is claimed is:
1. A liquid fuel stream characterized by forming a stable capillary
microjet over a portion of the stream, wherein the stable capillary
microjet is formed by a surrounding gas flowing in the same
direction, said gas having a greater velocity than the liquid.
2. The fuel stream of claim 1, wherein the fuel is a hydrocarbon
fuel.
3. The fuel stream of claim 2, wherein stable capillary microjet
comprises a diameter d.sub.j at a given point A in the stream
characterized by the formula: 20 d j ( 8 l .PI. 2 P g ) 1 4 Q 1 2
wherein d.sub.j is the diameter of the stable microjet,
.apprxeq.indicates approximately equally to where an acceptable
margin of error is .+-.10%, .rho..sub.1 is the density of the
liquid and .DELTA.P.sub.g is change in gas pressure of gas
surrounding the stream at the point A.
4. The fuel stream of claim 1, wherein d.sub.j is a diameter in a
range of about 1 micron to about 1 mm, and the stable capillary jet
portion has a length in a range of from about 1 micron to about 50
mm, and wherein the stable capillary microjet is maintained, at
least in part, by tangential viscous stresses exerted by a gas on a
surface of the jet in an axial direction of the jet.
5. The fuel stream of claim 2, wherein the microjet is further
characterized by a slightly parabolic axial velocity profile.
6. A monodisperse aerosol of fuel particles in air, the particles
characterized by having the same diameter with a deviation in
diameter from one particle to another in a range of from about
.+-.3% to about .+-.30%.
7. The aerosol of claim 6, wherein a given particle in the aerosol
has a diameter in a range of about 5 microns to about 500 microns
and other particles in the aerosol have the same diameter as the
given particle with a deviation of about .+-.3% to about
.+-.30%.
8. A fuel injection nozzle comprising: a means for providing fuel,
said means comprising a fuel entrance port and a fuel exit port;
and a pressure chamber for providing a pressurized fluid to an area
surrounding the fuel exit, the pressure chamber having an exit
opening aligned with the fuel exit port; and a means for providing
a second fluid in the pressure chamber, the means comprising a
second fluid entrance and an exit opening.
9. The device of claim 8, wherein the first means for providing the
fuel is a feeding needle having a cylindrical channel therein
whereby the first fluid entrance port and first fluid exit port are
each circular.
10. The device of claim 8, wherein the first means for providing a
fuel is a planar channel created between a first planar member
surface and a second planar member surface positioned parallel to
the first planar member surface and wherein the pressure chamber
comprises a plurality of pressure fluid exit ports.
11. The device of claim 9, wherein the feeding needle exit port has
a diameter in the range of from about 0.01 mm to about 2 mm, and
the pressure chamber exit port has a diameter in the range of about
0.01 mm to about 2 mm, and wherein the exit opening of the first
means for providing fuel is positioned at a point in the range of
about 0.01 mm to about 1.0 mm from the second fluid exit port of
the pressure chamber.
12. The device of claim 8, having inserted therein fuel having a
dynamic viscosity in the range of from about 10.sup.-4 to about 1
kg/m/sec and wherein the fuel is a hydrocarbon.
13. A fuel injection apparatus comprising the fuel injection nozzle
of claim 8.
14. An internal combustion engine comprising the fuel injection
apparatus of claim 13.
15. A method for producing atomized fuel, comprising the steps of:
forcing a fuel through a channel of a feeding source in a manner
which causes the liquid to be expelled from an exit opening;
forcing a second fluid through a pressure chamber in a manner which
causes the gas to exit the pressure chamber from an exit orifice in
front of a flow path of the liquid expelled from the exit opening
of the feeding source; wherein a stable fluid-fluid interface is
maintained and the first fluid forms a stable capillary jet focused
on the exit orifice of the pressure chamber by the second
fluid..
16. The method of claim 15, wherein the fuel is a liquid and the
second fluid is a gas, and wherein the liquid has a viscosity in a
range of from about 10.sup.-4 to about 1 kg/m/sec.
17. The method of claim 16, wherein the liquid has a viscosity in a
range of from about 0.3.times.10.sup.-3 to about 5.times.10.sup.-2
kg/m/sec, and wherein the liquid is forced through the channel at a
rate in a range of about 0.01 nl/sec to about 100 .mu.l/sec, and
wherein the gas is forced through the opening of the pressure
chamber at a rate in the range of from about 100 to 500 m/sec.
18. The method of claim 16, wherein the liquid is forced through
the channel at a rate in a range of about 1 nl/sec to about 10
.mu.l/sec, and wherein the gas is forced through the opening of the
pressure chamber at a rate in the range of from about 50 m/sec to
about 2000 m/sec.
19. The method of claim 16, wherein the feeding source is a
cylindrical channel and the liquid is expelled from an exit opening
having a diameter in the range of from about 0.1 mm to about 0.4 mm
and wherein the opening in the pressure chamber has a diameter in
the range of about 0.1 mm to 0.25 mm and is positioned directly in
front of the exit opening of the channel.
20. The method of claim 16, wherein the fuel particles formed are
uniform in size to the extent of having a relative size deviation
in a range of from about .+-.3% to about .+-.30%.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to a fuel injection
apparatus, and specifically to fuel injection nozzles for use in an
internal combustion engine.
BACKGROUND OF THE INVENTION
[0002] A number of different types of fuel injectors are known in
the art, and these devices generally use conventional fuel
injection nozzles to introduce droplets of fuel into the combustion
chamber of an engine, thus increasing the surface area of fuel
available for reaction. Increasing the surface area of the fuel
affords a more efficient combustion reaction in internal combustion
engines.
[0003] A number of improvements have been made to the fuel
injection process in internal combustion engines that allow such
fuel injection devices to function more efficiently within the fuel
injection system. For example, U.S. Pat. No. 5,020,498 describes a
fuel injection apparatus designed to provide a direct connection to
supply lines or pressure lines to avoid pressure waves that may
arise in the supply line network, which can have a disruptive
effect on the injection quantity. In this device, a direct line
connection with fuel supply lines is avoided during the injection
event, the result being that pressure waves that develop in the
lines cannot affect the injection event. In another example,
British patent No. 2,099,078A describes the use of a compound
rotary valve to control the timing and duration of opening the
intensifier cavity to either the high pressure actuation fluid or
to the low pressure fuel drain. In a further example, U.S. Pat. No.
5,697,341 describes fuel injectors that are hydraulically actuated,
with fuel pressurized by a plunger driven by an intensifier piston.
Fuel in the hydraulically actuated devices can be metered into the
injector either by biasing the plunger with a return spring, or by
pressurizing the fuel to hydraulically push the plunger in a
retracting direction between injection events.
[0004] Although the quantity and quality of injection in the fuel
injection apparatus have been improved by altering the method and
route of fuel delivery to the device, these improvements have not
addressed the efficiency limitations of the nozzle mechanism per
se. Each of the above-described systems, which have enhanced
delivery of fuel, use a conventional VOP type of needle check and
nozzle. Examples of conventional nozzles can be found in: U.S. Pat.
Nos. 4,662,338; 4,603,671; and 4,363,446. Such methods of delivery
through conventional nozzles have technological limitations, such
as limits on the minimum size of the expelled fuel droplets, the
amount of energy transfer necessary to produce the fuel droplets,
and clogging of the nozzle due to build up of residue left by the
fuel composition.
[0005] There is a need in the art for a method of more efficient
injection of fuel into an internal combustion engine or other
similar device, e.g. by decreasing the size of the fuel droplet
thus increasing the surface area available for the combustion
reaction. Accordingly, there is a need in the art for a nozzle to
improve the efficiency of fuel delivery in a fuel injection
system.
SUMMARY OF THE INVENTION
[0006] A fuel injection nozzle for use in a fuel injection
apparatus of an internal combustion engine is provided. The fuel
injection nozzle of the present invention has a unique fuel
delivery system comprised of a pressure chamber and a fuel source.
Atomized fuel particles within a desired size range (e.g., 5 micron
to about 500 microns, and preferably between 10 and 100 microns)
are produced from a liquid fuel formulation provided via a fuel
supply opening. The fuel may be provided in any desired manner,
e.g., forced through a channel of a feeding needle and expelled out
of an exit opening of the needle. Simultaneously, a second fluid
contained in a pressure chamber which surrounds at least the area
where the formulation is provided, e.g., surrounds the exit opening
of the needle, is forced out of an opening positioned in front of
the flow path of the provided fuel, e.g. in front of the fuel
expelled from the feeding needle. Various parameters are adjusted
to obtain a stable fuel-fluid interface and a stable capillary
microjet of the fuel, which allows formation of atomized fuel
particles on exiting the opening of the pressurized chamber.
[0007] Fuel injectors of the invention have three significant
advantages over prior injectors. First, fuel never contacts the
periphery of the exit orifice from which it is emitted because the
fuel stream is surrounded by a gas (e.g. air) which flows into the
exit orifice. Thus, clogging of the orifice is eliminated or
substantially reduced. Second, the fuel exits the orifice and forms
very small particles which are substantially uniform in size,
thereby allowing faster and more controlled combustion of the fuel.
Third, by using the methods described herein, the amount of energy
needed to produce aerosolized particles of fuel is substantially
less than that required by other methods.
[0008] An object of the invention is to provide a device for
efficient delivery of a fuel to a combustion chamber of an internal
combustion engine.
[0009] Another object is to provide a method of creating an fuel
aerosol of consistent particle size, which increases the surface
area available for a combustion reaction.
[0010] A feature of the invention is that the diameter of the
opening from which fluid is expelled, the diameter of the opening
from which fluid is expelled and the distance between they two
openings is adjustable and is adjusted to obtain a stable
fuel-fluid interface which results in a stable capillary microjet
being formed by the fuel expelled, which microjet is focused on an
exit opening by the flow of surrounding fluid (e.g. air).
[0011] An advantage of the invention is that it consistently
produces fuel particles within a desired particle diameter
range.
[0012] Another advantage of the invention is that the method of
aerosolization of the fuel discourages agglomeration of the
particles upon entering the combustion chamber.
[0013] An advantage of the invention is that fuel injection using
the device of the invention is energy efficient.
[0014] Another advantage is that the structure of the device and
its use are simple.
[0015] Another advantage is that clogging of the exit opening of
the pressure chamber is substantially eliminated because the fuel
is kept out of contact with the surface of the exit opening by a
surrounding focused funnel of fluid, which flows out of the
pressure chamber exit opening.
[0016] Yet another advantage is that particles produced are
substantially smaller in size than would be expected based on the
diameter of the exit opening of the pressure chamber due to
focusing the flow of the fuel with the flow of surrounding
fluid.
[0017] An aspect of the invention is a fuel injection nozzle that
is one element of a fuel injection device and system.
[0018] Another aspect of the invention is a device which provides
for the rapid engagement and disengagement of the aerosolization
process.
[0019] These and other aspects, objects, features and advantages
will become apparent to those skilled in the art upon reading this
disclosure in combination with the figures provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view showing the basic components of
one embodiment of the invention with a cylindrical feeding needle
as a source of formulation.
[0021] FIG. 2 is a schematic view of another embodiment of the
invention with two concentric tubes in a single feeding needle unit
as a source of formulation.
[0022] FIG. 3 is a schematic view of yet another embodiment showing
a wedge-shaped planar source of formulation. FIG. 3a illustrates a
cross-sectional side view of the planar feeding source and the
interaction of the fluids. FIG. 3b show a frontal view of the
openings in the pressure chamber, with the multiple openings
through which the atomizate exits the device. FIG. 3c illustrates
the channels that are optionally formed within the planar feeding
member. The channels are aligned with the openings in the pressure
chamber.
[0023] FIG. 4 is a schematic view of a stable capillary microjet
being formed and flowing through an exit opening to thereafter form
a monodisperse aerosol.
[0024] FIG. 5 is a graph of data where 350 measured valves of
d.sub.j/d.sub.o versus Q/Q.sub.o are plotted.
[0025] FIGS. 6a and 6b are schematic views of an exemplary use of
the embodiment of FIG. 1 in an injection apparatus.
[0026] FIGS. 7a and 7b are schematic views of an exemplary use of
the embodiment of FIG. 3, in which the injection device is
comprised of circular feeding elements positioned in multiple,
concentric pressure chambers.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] Before the present device and method are described, it is to
be understood that this invention is not limited to the particular
components and steps described, as such may, of course, vary. It is
also to be understood that the terminology used herein is for the
purpose of describing particular embodiments only, and is not
intended to be limiting, since the scope of the present invention
will be limited only by the appended claims.
[0028] It must be noted that as used herein and in the appended
claims, the singular forms "a", "and," and "the" include plural
referents unless the context clearly dictates otherwise. Thus, for
example, reference to "a particle" includes a plurality of
particles and reference to "a fuel " includes reference to a
mixture of fuels, and equivalents thereof known to those skilled in
the art, and so forth.
[0029] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
any methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
All publications mentioned herein are incorporated herein by
reference to disclose and describe the methods and/or materials in
connection with which the publications are cited.
[0030] The publications discussed herein are provided solely for
their disclosure prior to the filing date of the present
application. Nothing herein is to be construed as an admission that
the present invention is not entitled to antedate such publication
by virtue of prior invention. Further, the dates of publication
provided may be different from the actual publication dates which
may need to be independently confirmed.
DEFINITIONS
[0031] The terms "particles", "atomized particles" and "atomized
particles of formulation" are used interchangeably herein and shall
mean particles of formulation that have been atomized using the
device and method of the invention.
[0032] The terms "formulation" and "fuel formulation", as used
herein interchangeably, refer to any matter which is desired to be
atomized. The formulation may be any fluid used to initiate and/or
participate in a combustion reaction, preferably a solution
comprised of hydrocarbon alkanes, e.g. gasoline or kerosene. The
formulation is preferably presented in the method of the invention
as the first fluid, although it may be presented as the second
fluid. Formulations can also be a combination of fuels, either in
solution, suspension or an emulsion.
[0033] The terms "air", "particle free air" and the like, are used
interchangeably herein to describe a volume of air which is
substantially free of other material and, in particular, free of
particles intentionally added such as particles of formulation. The
term means that the air does not include particles of formulation
which have been intentionally added but is not intended to imply
that the normal surrounding air has been filtered or treated to
remove all particles although filtering can take place. Air may be
filtered for use in the invention, or alternatively another gas may
be used.
DEVICE IN GENERAL
[0034] The present invention can be applied to the creation of
particles for any number of uses. The present disclosure focuses on
use of general technology in delivering fuel to internal combustion
engines, e.g. volumetric and spark engines. The invention is not to
be limited to such uses, however, as related uses of the method and
device of the present invention, such as delivery of combustible
materials in gas turbines, burners, heaters and the like will be
applicable and readily seen by those skilled in the art.
[0035] The technology of the invention comprises (1) a means for
supplying a first fluid; and (2) a pressure chamber supplied with a
second fluid. The first fluid is generally a liquid and preferably
a hydrocarbon fuel comprised of alkanes. The second fluid is
generally either a gas, preferably air, or a hydrophilic liquid.
The critical property of the fluids is that the first and second
fluid are sufficiently different from each other so as to allow for
the formation of a stable microjet of the first fluid moving from
the supply means to an exit port of the pressure chamber.
Notwithstanding these different combinations of gas-liquid,
liquid-gas, and liquid-liquid the invention is generally described
with a liquid formulation being expelled from the supply means and
forming a stable microjet due to interaction with surrounding air
flow focusing the microjet to flow out of an exit of the pressure
chamber.
[0036] Formation of the microjet and its acceleration and ultimate
particle formation are based on the abrupt pressure drop associated
with the steep acceleration experienced by the first fluid (e.g., a
liquid) on passing through an exit orifice of the pressure chamber
which holds the second fluid. On leaving the chamber the flow
undergoes a large pressure difference between the first fluid
(e.g., a liquid) and the second fluid (e.g., a gas), which in turn
produces a highly curved zone on the first fluid (e.g., liquid)
surface near the exit port of the pressure chamber and in the
formation of a cuspidal point from which a steady microjet flows
provided the amount of the first fluid (e.g., the liquid) withdrawn
through the exit port of the pressure chamber is replenished. Thus,
in the same way that a glass lens or a lens of the eye focuses
light to a given point, the flow of the gas surrounds and focuses
the liquid into a stable microjet. The focusing effect of the
surrounding flow of gas creates a stream of liquid which is
substantially smaller in diameter than the diameter of the exit
orifice of the pressure chamber. This allows liquid to flow out of
the pressure chamber orifice without touching the orifice,
providing advantages including (1) clogging of the exit orifice is
virtually eliminated, (2) contamination of flow due to contact with
substances (e.g. undesirable particulates) on the orifice opening
is virtually eliminated, and (3) the diameter of the stream and the
resulting particles are smaller than the diameter of the exit
orifice of the chamber. This is particularly desirable because it
is difficult to precisely engineer holes which are very small in
diameter. Further, in the absence of the focusing effect (and
formation a stable microjet) flow of liquid out of an opening will
result in particles which have about twice the diameter of the exit
opening. An additional advantage is that the particles are not
prone to agglomeration following exit from the chamber.
[0037] Specific embodiments of aerosol creation devices are now
described.
EMBODIMENT OF FIG. 1
[0038] A first embodiment of the invention where the supply means
is a cylindrical feeding needle supplying liquid into a pressurized
chamber of gas is described below with reference to FIG. 1.
[0039] The components of the embodiment of FIG. 1 are as
follows:
[0040] 1. Feeding needle--also referred to generally as a fluid
source and a tube.
[0041] 2. End of the feeding needle used to insert the liquid to be
atomized.
[0042] 3. Pressure chamber.
[0043] 4. Orifice used as gas inlet.
[0044] 5. End of the feeding needle used to evacuate the liquid to
be atomized.
[0045] 6. Orifice through which withdrawal takes place.
[0046] 7. Atomizate (spray)--also referred to as aerosol.
[0047] D.sub.0=diameter of the feeding needle; d.sub.0=diameter of
the orifice through which the microjet is passed; e=axial length of
the orifice through which withdrawal takes place; H=distance from
the feeding needle to the microjet outlet; P.sub.0=pressure inside
the chamber; P.sub.a=atmospheric pressure.
[0048] A fuel injection nozzle of the invention may be any size but
is preferably sized for use in a conventional fuel injection
apparatus. Although the device can be configured in a variety of
designs, the different designs will all include the essential
components shown in FIG. 1 or components which perform an
equivalent function and obtain the desired results. Specifically, a
fuel injection nozzle of the invention will be comprised of at
least one source of formulation (e.g., a feeding needle with an
opening 2) into which a liquid flowable formulation can be fed and
an exit opening 5 from which the formulation can be expelled. The
feeding needle 1, or at least its exit opening 5, is encompassed by
a pressure chamber 3. The chamber 3 has inlet opening 4 which is
used to feed gas into the chamber 3 and an exit opening 6 through
which gas from the pressure chamber and liquid formulation from the
feeding needle 3 are expelled creating an aerosol.
[0049] In FIG. 1, the feeding needle and pressure chamber are
configured to obtain a desired result of producing an aerosol
wherein the particles are small and uniform in size. Preferably the
particles have a size which is in a range of 0.5 to 500 microns,
more preferably 10 to 100 microns. Particles of less than 1 micron
in diameter can be produced via the present invention, should that
size be found to be desirable for fuel injection. The particles of
any given aerosol fuel will have about the same diameter with a
relative standard deviation of 10% to 30% or more preferably 3% to
20%. Stating that particles of the aerosol have a particle diameter
in a range of 10 to 100 microns does not mean that different
particles will have different diameters and that some will have a
diameter of 10 microns while others of 100 microns. The particles
in a given aerosol will all (preferably about 90% or more) have the
same diameter .+-.3% to .+-.30%. For example, the particles of a
given aerosol will have a diameter of 25 microns .+-.3% to
.+-.10%.
[0050] Such a monodisperse aerosol is created using the components
and configuration as described above. However, other components and
configurations will occur to those skilled in the art The object of
each design will he to supply formulation so that it creates a
stable capillary microjet which is accelerated and stabilized by
tangential viscous stress exerted by the gas on the liquid surface.
The stable microjet created by the gas leaves the area of the
pressurized gas (e.g., leaves the pressure chamber and exits the
pressure chamber orifice) and splits into particles which have the
desired size and uniformity.
[0051] The aerosol created is a monodisperse aerosol meaning that
the size of the particles produced are relatively uniform in size.
The relative standard deviation in particle size is in the range of
from about 10% to about 30%, preferably 3% to 10% and most
preferably 3% or less. The size of aerosolized particles useful for
combustion may range anywhere from 10 nm to 10 microns.
[0052] For purposes of simplicity the remainder of the detailed
description of the operation of the device of FIG. 1 will refer to
the first fluid as liquid and the second fluid as gas. The
parameter window used (i.e. the set of special values for the
liquid properties, flow-rate used, feeding needle diameter, orifice
diameter, pressure ratio, etc.) should be large enough to be
compatible with virtually any liquid (dynamic viscosities in the
range from 10.sup.-4 to 1 kg m.sup.-1s.sup.-1); in this way, the
capillary microjet that emerges from the end of the feeding needle
is absolutely stable and perturbations produced by breakage of the
jet cannot travel upstream. Downstream, the microjet splits into
evenly shaped drops simply by effect of capillary instability (see,
for example, Rayleigh, "On the instability of jets", Proc. London
Math. Soc., 4-13, 1878), similar in a manner to a laminar capillary
jet falling from a half-open tap.
[0053] When the stationary, steady interface is created, the
capillary jet that emerges from the end of the drop at the outlet
of the feeding point is concentrically withdrawn into the nozzle.
After the jet emerges from the drop, the liquid is accelerated by
tangential sweeping forces exerted by the gas stream flowing on its
surface, which gradually decreases the jet cross-section. Stated
differently the gas flow acts as a lens and focuses and stabilizes
the microjet as it moves toward and into the exit orifice of the
pressure chamber.
[0054] The forces exerted by the second fluid (e.g., a gas) flow on
the first fluid (e.g., a liquid) surface should be steady enough to
prevent irregular surface oscillations. Therefore, any turbulence
in the gas motion should be avoided; even if the gas velocity is
high, the characteristic size of the orifice should ensure that the
gas motion is laminar (similar to the boundary layers formed on the
jet and on the inner surface of the nozzle or hole).
STABLE CAPILLARY MICROJET
[0055] FIG. 4 illustrates one example of the interaction of a
liquid and a gas to form atomizate using the method of the
invention. The feeding needle 60 has a circular exit opening 61
with an internal radius R.sub.0 which feeds a liquid 62 out of the
end, forming a drop with a radius in the range of R.sub.0 to
R.sub.0 plus the thickness of the wall of the needle. The exiting
liquid forms an infinite amount of liquid streamlines 63 that
interact with the surrounding gas to form a stable cusp at the
interface 64 of the two fluids. The surrounding gas also forms an
infinite number of gas streamlines 65, which interact with the
exiting liquid to create a virtual focusing funnel 66. The exiting
liquid is focused by the focusing funnel 66 resulting in a stable
capillary microjet 67, which remains stable until it exits the
opening 68 of the pressure chamber 69. After exiting the pressure
chamber, the microjet begins to break-up, forming monodispersed
particles 70.
[0056] The gas flow, which affects the liquid withdrawal and its
subsequent acceleration after the jet is formed, should be very
rapid but also uniform in order to avoid perturbing the fragile
capillary interface (the surface of the drop that emerges from the
jet).
[0057] Liquid flows out of the end of a capillary tube and forms a
small liquid drop at the end. The tube has an internal radius
R.sub.0. The drop has a radius in a range of from R.sub.0 to
R.sub.0 plus the structural thickness of the tube as the drop exits
the tube, and thereafter the drop narrows in circumference to a
much smaller circumference as is shown in the expanded view of the
tube (i.e. feeding needle) 5 as shown in FIGS. 1 and 4.
[0058] As illustrated in FIG. 4, the exit opening 61 of the
capillary tube 60 is positioned close to an exit opening 68 in a
planar surface of a pressure chamber 69. The exit opening 68 has a
minimum diameter D and is in a planar member with a thickness L.
The diameter D is referred to as a minimum diameter because the
opening may have a conical configuration with the narrower end of
the cone positioned closer to the source of liquid flow. Thus, the
exit opening may be a funnel-shaped nozzle although other opening
configurations are also possible, e.g. an hour glass configuration.
Gas in the pressure chamber continuously flows out of the exit
opening. The flow of the gas causes the liquid drop expelled from
the tube to decrease in circumference as the liquid moves away from
the end of the tube in a direction toward the exit opening of the
pressure chamber.
[0059] In actual use, it can be understood that the opening shape
which provokes maximum gas acceleration (and consequently the most
stable cusp and microjet with a given set of parameters) is a
conically shaped opening in the pressure chamber. The conical
opening is positioned with its narrower end toward the source of
liquid flow.
[0060] The distance between the end 61 of the tube 60 and the
beginning of the exit opening 68 is H. At this point it is noted
that R.sub.0, D, H and L are all preferably on the order of
hundreds of microns. For example, R.sub.0=400 .mu.m, D=150 .mu.m,
H=1 mm, L=300 .mu.m. However, each could be 1/100 to 100.times.
these sizes.
[0061] The end of the liquid stream develops a cusp-like shape at a
critical distance from the exit opening 68 in the pressure chamber
69 when the applied pressure drop .DELTA.P.sub.g across the exit
opening 68 overcomes the liquid-gas surface tension stresses
.gamma./R* appearing at the point of maximum curvature--e.g. 1/R*
from the exit opening.
[0062] A steady state is then established if the liquid flow rate Q
ejected from the drop cusp is steadily supplied from the capillary
tube. This is the stable capillary cusp which is an essential
characteristic of the invention needed to form the stable microjet.
More particularly, a steady, thin liquid jet with a typical
diameter d.sub.j is smoothly emitted from the stable cusp-like drop
shape and this thin liquid jet extends over a distance in the range
of microns to millimeters. The length of the stable microjet will
vary from very short (e.g. 1 micron) to very long (e.g. 50 mm) with
the length depending on the (1) flow-rate of the liquid and (2) the
Reynolds number of the gas stream flowing out of the exit opening
of the pressure chamber. The liquid jet is the stable capillary
microjet obtained when supercritical flow is reached. This jet
demonstrates a robust behavior provided that the pressure drop
.DELTA.P.sub.g applied to the gas is sufficiently large compared to
the maximum surface tension stress (on the order of
.gamma./d.sub.j) that act at the liquid-gas interface. The jet has
a slightly parabolic axial velocity profile which is, in large
part, responsible for the stability of the microjet. The stable
microjet is formed without the need for other forces, i.e. without
adding force such as electrical forces on a charged fluid. However,
for some applications it is preferable to add charge to particles,
e.g. to cause the particles to adhere to a given surface. The
shaping of liquid exiting the capillary tube by the gas flow
forming a focusing funnel creates a cusp-like meniscus resulting in
the stable microjet. This is a fundamental characteristic of the
invention.
[0063] The fluid stream flowing from the tube has substantially
more density and develops substantially more inertia as compared to
the gas, which has lower viscosity than the liquid. These
characteristics contribute to the formation of the stable capillary
jet. The stable capillary microjet is maintained stably for a
significant distance in the direction of flow away from the exit
from the tube. The liquid is, at this point, undergoing
"supercritical flow." The microjet eventually destabilizes due to
the effect of surface tension forces. Destabilization results from
small natural perturbations moving downstream, with the fastest
growing perturbations being those which govern the break up of the
microjet, eventually creating a uniform sized monodisperse aerosol
70 as shown in FIG. 4.
[0064] The microjet, even as it initially destabilizes, passes out
of the exit orifice of the pressure chamber without touching the
peripheral surface of the exit opening. This provides an important
advantage of the invention which is that the exit opening 68 (which
could be referred to as a nozzle) will not clog from residue and/or
deposits of the liquid. Clogging is a major problem with very small
nozzles and is generally dealt with by cleaning or replacing the
nozzle. When fluid contacts the surfaces of a nozzle opening some
fluid will remain in contact with the nozzle when the flow of fluid
is shut off. The liquid remaining on the nozzle surface evaporates
leaving a residue. After many uses over time the residue builds up
and clogging takes place. The present invention substantially
reduces or eliminates this clogging problem.
MATHEMATICS OF A STABLE MICROJET
[0065] Cylindrical coordinates (r,z) are chosen for making a
mathematical analysis of a stable microjet, i.e. liquid undergoing
"supercritical flow." The cusp-like meniscus formed by the liquid
coming out of the tube is pulled toward the exit of the pressure
chamber by a pressure gradient created by the flow of gas.
[0066] The cusp-like meniscus formed at the tube's mouth is pulled
towards the hole by the pressure gradient created by the gas
stream. From the cusp of this meniscus, a steady liquid thread with
the shape of radius r=.xi. is withdrawn through the hole by the
action of both the suction effect due to .DELTA.P.sub.g, and the
tangential viscous stresses .tau..sub.s exerted by the gas on the
jet's surface in the axial direction. The averaged momentum
equation for this configuration may be written: 1 z [ P 1 + 1 Q 2 2
2 4 ] = 2 s , ( 1 )
[0067] where Q is the liquid flow rate upon exiting the feeding
tube, P.sub.1 is the liquid pressure, and .rho..sub.1 is the liquid
density, assuming that the viscous extensional term is negligible
compared to the kinetic energy term, as will be subsequently
justified. In addition, liquid evaporation effects are neglected.
The liquid pressure P.sub.1 is given by the capillary equation.
P.sub.1=P.sub.g+.gamma./.xi.. (2)
[0068] where .gamma. is the liquid-gas surface tension. As shown in
the Examples, the pressure drop .DELTA.P.sub.g is sufficiently
large as compared to the surface tension stress .gamma./.xi. to
justify neglecting the latter in the analysis. This scenario holds
for the whole range of flow rates in which the microjet is
absolutely stable. In fact, it will be shown that, for a given
pressure drop .DELTA.P.sub.g, the minimum liquid flow rate that can
be sprayed in steady jet conditions is achieved when the surface
tension stress .gamma./.xi. is of the order of the kinetic energy
of the liquid .rho..sub.1Q.sup.2/(2.pi..sup.2.xi..sup.4), since the
surface tension acts like a "resistance" to the motion (it appears
as a negative term in the right-hand side term of Eq. (1)). Thus, 2
Q m i n ~ ( d j 3 1 ) 1 / 2 ( 3 )
[0069] For sufficiently large flow rates Q compared to Q.sub.min,
the simplified averaged momentum equation in the axial direction
can be expressed as 3 z ( 1 Q 2 2 2 4 ) = P g z + 2 s , ( 4 )
[0070] where one can identify the two driving forces for the liquid
flow on the right-hand side. This equation can be integrated
provided the following simplification is made: if one uses a thin
plate with thickness L of the order or smaller than the hole's
diameter D (which minimizes downstream perturbations in the gas
flow), the pressure gradient up to the hole exit is on the average
much larger than the viscous shear term 2.tau..sub.s/.xi. owning to
the surface stress. On the other hand, the axial viscous term is of
the order O[.mu..sup.2Q/D.sup.2d.sub.j.sup.2], since the hole
diameter D is actually the characteristic distance associated with
the gas flow at the hole's entrance in both the radial and axial
directions. This term is very small compared to the pressure
gradient in real situations, provided that
.DELTA.P.sub.g>>.mu..sup- .2/D.sup.2.rho..sub.1 (which holds,
e.g., for liquids with viscosities as large as 100 cpoises, using
hole diameters and pressure drops as small as D.about.10 .mu.m and
.DELTA.P.sub.g.gtoreq.100 mbar). The neglect of all viscous terms
in Eq. (4) is then justified. Notice that in this limit on the
liquid flow is quasi-isentropic in the average (the liquid almost
follows Bernoulli equation) as opposed to most micrometric
extensional flows. Thus, integrating (4) from the stagnation
regions of both fluids up to the exit, one obtains a simple and
universal expression for the jet diameter at the hole exit: 4 d j (
8 1 2 P g ) 1 4 Q 1 2 , ( 5 )
[0071] which for a given pressure drop .DELTA.P.sub.g is
independent of geometrical parameters (hole and tube diameters,
tube-hole distance, etc.), liquid and gas viscosities, and
liquid-gas surface tension. This diameter remains almost constant
up to the breakup point since the gas pressure after the exit
remains constant.
MONODISPERSE PARTICLES
[0072] Above the stable microjet undergoing "supercritical flow" is
described and it can be seen how this aspect of the invention can
be made use of in a variety of industrial
applications--particularly where the flow of liquid through small
holes creates a clogging problem. An equally important aspect of
the invention is obtained after the microjet leaves the pressure
chamber.
[0073] When the microjet exits the pressure chamber the liquid
pressure P.sub.1 becomes (like the gas pressure P.sub.g) almost
constant in the axial direction, and the jet diameter remains
almost constant up to the point where it breaks up by capillary
instability. Defining a Weber number We
=(.rho..sub.g.nu..sub.g.sup.2d.sub.j)/.gamma..congruent.2.DELTA-
.P.sub.gd.sub.j/.gamma. (where .nu..sub.g is the gas velocity
measured at the orifice), below a certain experimental value
We.sub.c.about.40 the breakup mode is axisymmetric and the
resulting droplet stream is characterized by its monodispersity
provided that the fluctuations of the gas flow do not contribute to
droplet coalescence (these fluctuations occur when the gas stream
reaches a fully developed turbulent profile around the liquid jet
breakup region). Above this We.sub.c value, sinuous nonaxisymmetric
disturbances, coupled to the axisymmetric ones, become apparent.
For larger We numbers, the nonlinear growth rate of the sinuous
disturbances seems to overcome that of the axisymmetric
disturbances. The resulting spray shows significant polydispersity
in this case. Thus, it can be seen that by controlling parameters
to keep the resulting Weber number to 40 or less, allows the
particles formed to be all substantially the same size. The size
variation is about .+-.3% to .+-.30% and move preferably .+-.3% to
.+-.10%. These particles can have a desired size e.g. 0.1 microns
to 50 microns.
[0074] The shed vorticity influences the breakup of the jet and
thus the formation of the particles. Upstream from the hole exit,
in the accelerating region, the gas stream is laminar. Typical
values of the Reynolds number range from 500 to 6000 if a velocity
of the order of the speed of sound is taken as characteristic of
the velocity of the gas. Downstream from the hole exit, the
cylindrical mixing layer between the gas stream and the stagnant
gas becomes unstable by the classical Kelvin-Helmholtz instability.
The growth rate of the thickness of this layer depends on the
Reynolds number of the flow and ring vortices are formed at a
frequency of the order of .nu..sub.g/D, where D is the hole
diameter. Typical values of .nu..sub.g and D as those found in our
experimental technique lead to frequencies or the order of MHz
which are comparable to the frequency of drop production (of order
of t.sub.b.sup.-1).
[0075] Given the liquid flow rate and the hole diameter, a
resonance frequency which depends on the gas velocity (or pressure
difference driving the gas stream) can be adjusted (tuned) in such
a way that vortices act as a forcing system to excite perturbations
of a determined wavelength on the jet surface. Experimental results
obtained clearly illustrates the different degree of coupling
between the two gas-liquid coaxial jets. In one set of experimental
results the particle sizes are shown to have a particle size of
about 5.7 microns with a standard deviation of 12%. This results
when the velocity of the gas has been properly tuned to minimize
the dispersion in the size of droplets resulting from the jet
breakup. In this case, the flow rate of the liquid jet and its
diameter are 0.08 .mu.l s.sup.-1 and 3 .mu.m, respectively. Data
have been collected using a MASTERSIZER from MALVERN Instruments.
As the degree of coupling decreases, perturbations at the jet
surface of different wavelengths become excited and, as it can be
observed from the size distributions, the dispersion of the spray
increases.
[0076] It is highly desirable in a number of different industrial
applications to have particles which are uniform in size or to
create aerosols of liquid particles which are uniform in size. For
example, particles of a liquid formation containing a hydrocarbon
could be created and designed to have a diameter of about 10
microns .+-.3%. These particles could be injected into the
combustion chamber of an engine. Moreover, particle size can be
adjusted to increase fuel efficiency, thus wasting less fuel in the
combustion reaction.
[0077] The gas flow should be laminar in order to avoid a turbulent
regime-turbulent fluctuations in the gas flow which have a high
frequency and would perturb the liquid-gas interface. The Reynolds
numbers reached at the orifice are 5 Re = v g d 0 v g ~ 4000
[0078] where .nu..sub.g is the kinematic viscosity of the gas. Even
though this number is quite high, there are large pressure
gradients downstream (a highly convergent geometry), so that a
turbulent regime is very unlikely to develop.
[0079] The essential difference from existing pneumatic atomizers
(which possess large Weber numbers) and the present invention is
that the aim of the present invention is not to rupture the
liquid-gas interface but the opposite, i.e. to increase the
stability of the interface until a capillary jet is obtained. The
jet, which will be very thin provided the pressure drop resulting
from withdrawal is high enough, splits into drops the sizes of
which are much more uniform than those resulting from disorderly
breakage of the liquid-gas interface in existing pneumatic
atomizers.
[0080] The proposed fuel injection nozzle system obviously requires
delivery of the fuel to be aerosolized and the gas to be used in
the resulting spray. Both should be fed at a rate ensuring that the
system lies within the stable parameter window. Multiplexing is
effective when the flow-rates needed exceed those on an individual
cell. More specifically, a plurality of feeding sources or feeding
needles may be used to increase the rate at which aerosols are
created. The flow-rates used should also ensure the mass ratio
between the flows is compatible with the specifications of each
application.
[0081] The gas and liquid can be dispensed by any type of
continuous delivery system (e.g. a compressor or a pressurized
valve system. If multiplexing is needed, the liquid flow-rate
should be as uniform as possible among cells; this may entail
propulsion through several capillary needles, porous media or any
other medium capable of distributing a uniform flow among different
feeding points.
[0082] Each individual injection nozzle should consist of at least
one feeding point (a capillary needle, a point with an open
microchannel, a microprotuberance on a continuous edge, etc.)
0.002-2 mm (but, preferentially 0.01-1.2 mm) in diameter, where the
drop emerging from the microjet can be anchored, and a small
orifice 0.002-2 mm (preferentially 0.01-1.0 mm) in diameter facing
the drop and separated 0.01-2 mm (preferentially 0.2-0.75 mm) from
the feeding point. The orifice communicates the withdrawal gas
around the drop, at an increased pressure, with the zone where the
atomizate is produced, at a decreased pressure. The injection
nozzle can be made from a variety of materials (but preferably a
material that is not reactive with fuel, metal, polymers,
etc.).
[0083] FIG. 1 depicts a tested prototype where the liquid to be
atomized is inserted through one end of the system 2 and the gas in
introduced via the special inlet 4 in the pressure chamber 3. The
prototype was tested at gas feeding rates from 100 to 2000 mBar
above the atmospheric pressure P.sub.a at which the atomized liquid
was discharged. The whole enclosure around the feeding needle 1 was
at a pressure P.sub.0>P.sub.a. The liquid feeding pressure,
P.sub.1, should always be slightly higher than the gas propelling
pressure, P.sub.0. Depending on the pressure drop in the needle and
the liquid feeding system, the pressure difference
(P.sub.1-P.sub.0>0) and the flow-rate of the liquid to be
atomized, Q, are linearly related provided the flow is
laminar-which is indeed the case with this prototype. The critical
dimensions are the distance from the needle to the plate (H), the
needle diameter (D.sub.0), the diameter of the orifice through
which the microjet 6 is discharged (d.sub.0) and the axial length,
e, of the orifice (i.e. the thickness of the plate where the
orifice is made). In this prototype, H was varied from 0.3 to 0.7
mm on constancy of the distances (D.sub.0=0.45 mm, d.sub.0-0.2 mm)
and e-0.5 mm. The quality of the resulting spray 7 did not vary
appreciably with changes in H provided the operating regime (i.e.
stationary drop and microjet) was maintained. However, the system
stability suffered at the longer H distances (about 0.7 mm). The
other atomizer dimensions had no effect on the spray or the
prototype functioning provided the zone around the needle (its
diameter) was large enough relative to the feeding needle.
WEBER NUMBER
[0084] Adjusting parameters to obtain a stable capillary microjet
and control its breakup into monodisperse particle is governed by
the Weber number and the liquid-to-gas velocity ratio or .alpha.
which equal V.sub.l/V.sub.g. The Weber number or "We" is defined by
the following equation: 6 We = g V g 2 d
[0085] wherein .rho..sub.g is the density of the gas, d is the
diameter of the stable microjet, .gamma. is the liquid-gas surface
tension, and V.sub.g.sup.2 is the velocity of the gas squared.
[0086] When carrying out the invention the parameters should be
adjusted so that the Weber number is greater than 1 in order to
produce a stable capillary microjet. However, to obtain a particle
dispersion which is monodisperse (i.e. each particle has the same
size .+-.3 to .+-.30%) the parameters should be adjusted so that
the Weber number is less than 40. The monodisperse aerosol is
obtained with a Weber number in a range of about 1 to about 40 when
the breaking time is sufficiently small to avoid non-symmetric
perturbations. (1<We<40)
OHNESORGE NUMBER
[0087] A measure of the relative importance of viscosity on the jet
breakup can be estimated from the Ohnesorge number defined as the
ratio between two characteristic times: the viscous time t.sub.v
and the breaking time t.sub.b. The breaking time t.sub.b is given
by [see Rayleigh (1878)] 7 t b ~ ( l d 2 ) 1 2 . ( 2 )
[0088] Perturbations on the jet surface are propagated inside by
viscous diffusion in times t.sub.v of the order of
t.sub.v.about..rho..sub.id.sup.2/.mu..sub.1, (3)
[0089] where .mu..sub.1 is the viscosity of the liquid. Then, the
Ohnesorge number, Oh, results 8 Oh = 1 ( l d ) 1 2 . ( 4 )
[0090] If this ratio is much smaller than unity viscosity plays no
essential role in the phenomenon under consideration. Since the
maximum value of the Ohnesorge number in actual experiments
conducted is as low as 3.7.times.10.sup.-2, viscosity plays no
essential role during the process of jet breakup.
[0091] Formation of the microjet and its acceleration and ultimate
particle formation are based on the abrupt pressure drop associated
with the steep acceleration experienced by the first fluid (e.g., a
gas) on passing through an exit orifice of the pressure chamber
which holds the second fluid. On leaving the chamber the flow
undergoes a large pressure difference between the first fluid
(e.g., a liquid) and the second fluid (e.g., a gas), which in turn
produces a highly curved zone on the first fluid (e.g., liquid)
surface near the exit port of the pressure chamber and in the
formation of a cuspidal point from which a steady microjet flows
provided the amount of the first fluid (e.g., liquid) withdrawn
through the exit port of the pressure chamber is replenished. Thus,
in the same way that a glass lens or a lens of the eye focuses
light to a given point the flow of the gas surrounds and focuses
the liquid into a stable microjet. The focusing effect of the
surrounding flow of gas creates a stream of liquid which is
substantially smaller in diameter than the diameter of the exit
orifice of the pressure chamber. This allows liquid to flow out of
the pressure chamber orifice without touching the orifice. This
provides advantages including (1) clogging of the exit orifice is
virtually eliminated, (2) contamination of flow due to contact with
substances on the orifice opening is virtually eliminated (3) the
diameter of the stream and thus the resulting particles is smaller
than the diameter of the exit orifice of the chamber, (4) the
particles are not prone to agglomeration following exit from the
chamber. This is particularly desirable because it is difficult to
precisely engineer holes which are very small in diameter. Further,
in the absence of the focusing effect a flow of liquid out of an
opening will result in particles which have about twice the
diameter of the exit opening.
[0092] In summary, the fluid 2 flow, which effects the liquid
withdrawal and its subsequent acceleration after the jet is formed,
should be very rapid, but also uniform, in order to avoid
perturbing the fragile capillary interface (the surface of the drop
that emerges from the jet) and hence its breaking. Therefore, the
dynamic forces exerted by the fluid 2 should never exceed the
surface tension (drop and microjet) at any time during the process.
In terms of non-dimensional fluid dynamics numbers, the Weber
number (i.e. the dynamic to surface tension force ratio) should not
exceed unity during the process. The Weber number for the microjet
will inevitably be unity because the pressure drop in the fluid 2
is similar in magnitude to the effect of the surface tension: 9 2 d
j ~ 1 2 v g 2
[0093] where .gamma. and .rho. are the surface tension and liquid
density, respectively; and d.sub.j and .nu..sub.g are the
characteristic diameter of the jet and characteristic velocity of
the fluid 2. Also, the velocity of the fluid 2 around the drop that
produces the jet must be related to that across the orifice via the
areas, i.e. V.sub.gD.sub.0.sup.2.about..n- u..sub.gd.sub.0.sup.2,
where V.sub.g is the velocity of the fluid 2 around the drop, and
D.sub.0 and d.sub.0 are the diameters of the feeding point and
orifice, respectively. Since the maximum possible fluid 2 velocity
at the orifice is similar to the speed of sound, one has 10 V g ~ (
d 0 D 0 ) 2 .times. 320 m / s
[0094] and, for the jet diameter, 11 d j ~ 4 g v g 2 ~ 4 .times. 2
.times. 10 2 1.2 .times. 320 2 ~ 5 m ( ~ 2 .times. 10 2 N / m 2 for
n - heptane )
[0095] This indicates that micrometric drop sizes in the range of 1
to 10 microns in diameter or even less than 1 micron in diameter
can be obtained.
[0096] At the smallest diameters possible with this system (similar
to the thickness of the boundary layer), the kinetic energies per
unit volume of the liquid and fluid 2 should be of the same order.
The resulting liquid velocity will be 12 V l ~ ( g 1 ) 1 2 v g ~ 10
m / s
[0097] where .rho..sub.1 is the liquid density. From the previous
equation, the liquid flow-rate turns out to be
Q.sub.1.about.d.sub.j.sup.2.nu..sub.1.about.10.sup.-11m.sup.3/s
[0098] at the smallest drop sizes.
[0099] The fluid 2 flow should be laminar in order to avoid a
turbulent regime--turbulent fluctuations in the fluid 2 flow, which
has a high frequency, would perturb the liquid-fluid 2 interface.
The Reynolds numbers reached at the orifice are 13 Re = v g d 0 v g
~ 4000
[0100] where .nu..sub.g is the kinematic viscosity of the fluid 2.
Even though this number is quite high, there are large pressure
gradients downstream (a highly convergent geometry), so a turbulent
regime is very unlikely to develop.
[0101] The essential difference from existing pneumatic atomizers
(which possess large Weber numbers) is that the aim is not to
rupture the liquid-fluid 2 interface but the opposite, i.e. to
increase the stability of the interface until a capillary jet is
obtained. The jet, which will be very thin provided the pressure
drop resulting from withdrawal is high enough, splits into drops
the sizes of which are much more uniform than those resulting from
disorderly breakage of the liquid-fluid 2 interface in existing
pneumatic atomizers.
EXEMPLARY USES OF THE FIRST EMBODIMENT
[0102] The first embodiment of the invention can be employed in a
nozzle-type injection device to inject a more fine and evenly
distributed liquid particle, e.g. to an internal combustion
chamber. Since each injection will involve the injection a
relatively small volume of liquid, due to the fine nature of the
particles formed, it is desirable to have multiple injection points
in each device. Accordingly, the device may have a plurality of
feeding needles in a single injection device, preferably at least
10, more preferably at least 100, even more preferably at least
500, and even more preferably at least 1000. The injection points
may be spatially arranged in the device in any manner that allows
the efficient production of particles, and preferably the injection
points are arranged in a configuration to decrease the tendency for
agglomeration once the particles enter the combustion chamber, e.g.
evenly spaced in a parallel manner in the device. The gas and
liquid used for fuel can be dispensed to the feeding needles by any
type of continuous delivery system, e.g. a compressor or a
pressurized tank for gas delivery and a volumetric pump or a
pressurized bottle the latter for liquid delivery. The dispersion
of the gas and/or liquid may be controlled using any mechanism
known in the art, for example through the use of a valve that
controls the entrance of the gas and/or liquid into the inlet tubes
leading to the injection device. The housing of the device and the
feeding needle can be made from a variety of materials (metal,
plastic, ceramics, glass), and preferably from materials that do
not react with the fluids used in the device.
[0103] FIG. 6 illustrates a generalized, schematic view of an
exemplary use of the embodiment of FIG. 1 in an injection
apparatus. In the device of FIG. 6, a plurality of evenly spaced
feeding needles 84 are housed in a pressure chamber 80, and the
fuel is atomized multiple exit openings 81 in the pressure chamber
80. FIG. 6A is a side view of the internal portion of the device,
with multiple injection needles 84 housed inside a single pressure
chamber 80. The pressure chamber should be such that the pressure
is approximately equivalent throughout the chamber, allowing the
efficient production of stable focusing cusps for each separate
feeding needle. Alternatively, each feeding needle could have its
own, compartmentalized pressure chamber, with each chamber
individually controlled to have approximately equal pressure and
in-flow of fluid.
[0104] The fuel is supplied to the feeding needles through an inlet
opening 82, and the in-flow of fuel is preferably controlled by a
mechanism within the fuel injector. e.g. a valve controllably
opened by the use of a computer signal to the fuel injector. See
e.g. U.S. Pat. Nos. 4,984,552 and 5,697,341 which are both
incorporated herein by reference. In the example of FIG. 6, the
fuel is supplied to each separate needle from a single source via a
fuel feeding tube 83 positioned above and connected to each of the
feeding needles 84. Other methods of introducing fuel to the
individual feeding needles, such as separate fuel feeding tubes
stemming from either a single fuel source or multiple fuel sources,
can also be employed. Should multiple sources be employed, they are
preferably synchronized and/or modulated to control of the quantity
of fuel injected.
[0105] The second fluid used to focus the first is provided through
at least one separate inlet opening 86. FIG. 6B is a view from the
bottom of the device, showing the multiple exit openings 81 in the
pressure chamber 80. Although FIG. 6 illustrates a single pressure
chamber, multiple pressure chambers may be used to increase the
efficiency of the device. Fluid to these separate chambers may be
provided from a single outlet source, or from multiple sources.
[0106] In another example of the embodiment of FIG. 1, the fuel may
be provided as the second fluid of the invention, and a gas,
preferably air, is used as the first fluid. The gas is then fed
through the feeding needles, with the fuel formulation introduced
into the pressure chamber. The fuel is used to focus the gas, and
the gas is expelled in particle form. The fuel, as the second fluid
will coat the gas particles as the fluids exit the pressure
chamber. Expulsion of the gas bubbles contained in the liquid
stream into a gaseous environment results in the production of
highly disperse fuel globules with a gas core, preferably an air
core. This use of the injection nozzle may increase the surface
area of the fuel formulation available for reaction while
conserving the fuel composition.
EMBODIMENT OF FIG. 2
[0107] A variety of configurations of components and types of
fluids will become apparent to those skilled in the art upon
reading this disclosure. These configurations and fluids are
encompassed by the present invention provided they can produce a
stable capillary microjet of a first fluid from a source to an exit
port of a pressure chamber containing a second fluid. The stable
microjet is formed by the first fluid flowing from the feeding
source to the exit port of the pressure chamber being accelerated
and stabilized by tangential viscous stress exerted by the second
fluid in the pressure chamber on the surface of the first fluid
forming the microjet. The second fluid forms a focusing funnel when
a variety of parameters are correctly tuned or adjusted. For
example, the speed, pressure, viscosity and miscibility of the
first and second fluids are chosen to obtain the desired results of
a stable microjet of the first fluid focused into the center of a
funnel formed with the second fluid. These results are also
obtained by adjusting or tuning physical parameters of the device,
including the size of the opening from which the first fluid flows,
the size of the opening from which both fluids exit, and the
distance between these two openings.
[0108] The embodiment of FIG. 1 can, itself, be arranged in a
variety of configurations. Further, as indicated above, the
embodiment may include a plurality of feeding needles. A plurality
of feeding needles may be configured concentrically in a single
construct, as shown in FIG. 2.
[0109] The components of the embodiment of FIG. 2 are as
follows:
[0110] 21. Feeding needle--tube or source of fluid.
[0111] 22. End of the feeding needle used to insert the liquids to
be atomized.
[0112] 23. Pressure chamber.
[0113] 24. Orifice used as gas inlet.
[0114] 25. End of the feeding needle used to evacuate the liquid to
be atomized.
[0115] 26. Orifice through which withdrawal takes place.
[0116] 27. Atomizate (spray) or aerosol.
[0117] 28. First liquid to be atomized (inner core of
particle).
[0118] 29. Second liquid to be atomized (outer coating of
particle).
[0119] 30. Gas for creation of microjet.
[0120] 31. Internal tube of feeding needle.
[0121] 32. External tube of feeding needle.
[0122] D=diameter of the feeding needle; d=diameter of the orifice
through which the microjet is passed; e=axial length of the orifice
through which withdrawal takes place; H=distance from the feeding
needle to the microjet outlet; .gamma.=surface tension:
P.sub.0=pressure inside the chamber: P.sub.a=atmospheric
pressure.
[0123] The embodiment of FIG. 2 is preferably used when attempting
to form a spherical particle of one substance coated by another
substance. The device of FIG. 2 is comprised of the same basic
component as per the device of FIG. 1 and further includes a second
feeding source 32 which is positioned concentrically around the
first cylindrical feeding source 31. The second feeding source may
be surrounded by one or more additional feeding sources with each
concentrically positioned around the preceding source.
[0124] The process is based on the microsuction which the
liquid-gas or liquid-liquid interphase undergoes (if both are
immiscible), when said interphase approaches a point beginning from
which one of the fluids is suctioned off while the combined suction
of the two fluids is produced. The interaction causes the fluid
physically surrounded by the other to form a capillary microjet
which finally breaks into spherical drops. If instead of two fluids
(gas-liquid), three or more are used that flow in a concentric
manner by injection using concentric tubes, a capillary jet
composed of two or more layers of different fluids is formed which,
when it breaks, gives rise to the formation of spheres composed of
several approximately concentric spherical layers of different
fluids. The size of the outer sphere (its thickness) and the size
of the inner sphere (its volume) can be precisely adjusted.
[0125] The method is based on the breaking of a capillary microjet
composed of a nucleus of one liquid or gas and surrounded by
another or other liquids and gases which are in a concentric manner
injected by a special injection head, in such a way that they form
a stable capillary microjet and that they do not mix by diffusion
during the time between when the microjet is formed and when it is
broken. When the capillary microjet is broken into spherical drops
under the proper operating conditions, which will be described in
detail below, these drops exhibit a spherical nucleus, the size and
eccentricity of which can be controlled.
[0126] In the case of spheres containing two materials, the
injection head 25 consists of two concentric tubes with an external
diameter on the order of one millimeter. Through the internal tube
31 is injected the material that will constitute the nucleus of the
microsphere, while between the internal tube 31 and the external
tube 32 the coating is injected. The fluid of the external tube 32
joins with the fluid of tube 31 as the fluids exit the feeding
needle, and the fluids (normally liquids) thus infected are
accelerated by a stream of gas that passes through a small orifice
24 facing the end of the injection tubes. When the drop in pressure
across the orifice 24 is sufficient, the liquids form a completely
stationary capillary microjet, if the quantities of liquids that
are injected are stationary. This microjet does not touch the walls
of the orifice, but passes through it wrapped in the stream of gas
or funnel formed by gas from the tube 32. Because the funnel of gas
focuses the liquid, the size of the exit orifice 26 does not
dictate the size of the particles formed.
[0127] When the parameters are correctly adjusted, the movement of
the liquid is uniform at the exit of the orifice 26 and the
viscosity forces are sufficiently small so as not to alter either
the flow or the properties of the liquids; for example, if there
are biochemical molecular specimens having a certain complexity and
fragility, the viscous forces that would appear in association with
the flow through a micro-orifice might degrade these
substances.
[0128] FIG. 2 shows a simplified diagram of the feeding needle 21,
which is comprised of the concentric tubes 30, 31 through the
internal and external flows of the fluids 28, 29 that are going to
compose the microspheres comprised of two immiscible fluids. The
difference in pressures P.sub.0-P.sub.a (P.sub.0>P.sub.a)
through the orifice 26 establishes a flow of gas present in the
chamber 23 and which is going to surround the microjet at its exit.
The same pressure gradient that moves the gas is the one that moves
the microjet in an axial direction through the hole 26, provided
that the difference in pressures P.sub.0-P.sub.a is sufficiently
great in comparison with the forces of surface tension, which
create an adverse gradient in the direction of the movement.
[0129] There are two limitations for the minimum sizes of the
inside and outside jets that are dependent (a) on the surface
tensions .gamma.l of the outside liquid 29 with the gas 30 and
.gamma.2 of the outside liquid 29 with the inside liquid 28, and
(b) on the difference in pressures .DELTA.P=P.sub.0-P.sub.a through
the orifice 26. In the first place, the jump in pressures .DELTA.P
must be sufficiently great so that the adverse effects of the
surface tension are minimized. This, however, is attained for very
modest pressure increases: for example, for a 10 micron jet of a
liquid having a surface tension of 0.05 N/m (tap water), the
necessary minimum jump in pressure is in the order of 0.05
(N/m)/0.00001 m=.DELTA.P=50 mBar. But, in addition, the breakage of
the microjet must be regular and axilsymmetric, so that the drops
will have a uniform size, while the extra pressure .DELTA.P cannot
be greater than a certain value that is dependent on the surface
tension of the outside liquid with the gas .gamma.l and on the
outside diameter of the microjet. It has been experimentally shown
that this difference in pressures cannot be greater than 20 times
the surface tension .gamma.l divided by the outside radius of the
microjet.
[0130] Therefore, given some inside and outside diameters of the
microjet, there is a range of operating pressures between a minimum
and a maximum; nonetheless, experimentally the best results are
obtained for pressures in the order of two to three times the
minimum.
[0131] The viscosity values of the liquids must be such that the
liquid with the greater viscosity .mu..sub.max verifies, for a
diameter d of the jet predicted for this liquid and a difference
through the orifice .DELTA.P, the inequality: 14 max Pd 2 D Q
[0132] With this, the pressure gradients can overcome the
extensional forces of viscous resistance exerted by the liquid when
it is suctioned toward the orifice.
[0133] Moreover, the liquids must have very similar densities in
order to achieve the concentricity of the nucleus of the
microsphere, since the relation of velocities between the liquids
moves according to the square root of the densities
v1/v2=(.rho.2/.rho.1).sup.1/2 and both jets, the inside jet and the
outside jet, must assume the most symmetrical configuration
possible, which does not occur if the liquids have different
velocities (FIG. 2). Nonetheless, it has been experimentally
demonstrated that, on account of the surface tension .gamma.2
between the two liquids, the nucleus tends to migrate toward the
center of the microsphere, within prescribed parameters.
[0134] When two liquids and gas are used on the outside, the
distance between the planes of the mouths of the concentric tubes
can vary, without the characteristics of the jet being
substantially altered, provided that the internal tube 31 is not
introduced into the external one 32 more than one diameter of the
external tube 32 and provided that the internal tube 31 does not
project more than two diameters from the external tube 32. The best
results are obtained when the internal tube 31 projects from the
external one 32 a distance substantially the same as the diameter
of the internal tube 31. This same criterion is valid if more than
two tubes are used, with the tube that is Surrounded (inner tube)
projecting beyond the tube that surrounds (outer tube) by a
distance substantially the same as the diameter of the first
tube.
[0135] The distance between the plane of the internal tube 31 (the
one that will normally project more) and the plane of the orifice
may vary between zero and three outside diameters of the external
tube 32, depending on the surface tensions between the liquids and
with the gas, and on their viscosity values. Typically, the optimal
distance is found experimentally for each particular configuration
and each set of liquids used.
[0136] Each atomizing device will consist of concentric tubes 31,
32 with a diameter ranging between 0.05 and 2 mm, preferably
between 0.1 and 0.4 mm, on which the drop from which the microjet
emanates can be anchored, and a small orifice (between 0.001 and 2
mm in diameter, preferably between 0.1 and 0.25 mm), facing the
drop and separated from the point of feeding by a distance between
0.001 and 2 mm, preferably between 0.2 and 0.5 mm. The orifice puts
the suction gas that surrounds the drop, at higher pressure, in
touch with the area in which the atomizing is to be attained, at
lower pressure.
EXEMPLARY USES OF SECOND EMBODIMENT
[0137] The embodiment of the second invention is very similar to
that illustrated in FIG. 6, with the difference in that
multi-formulation particles may be injected into the combustion
chamber. This may allow the surface of a molecule to have a certain
component of the overall fuel composition accessible to the
surface, with the remaining components of the composition in the
nucleus of the liquid particle. For example, in a diesel fuel
formulation containing ether, kerosene, castor oil and isopropyl
nitrate, it may be desirable to have the kerosene as a coating and
the other three molecules in the nucleus of the particle.
Accordingly, the formulation containing ether, castor oil and
isopropyl nitrate would be introduced into the inner tube of the
feeding needle, and the formulation of kerosene (or kerosene
dissolved in ether) would be introduced into the external tube of
the feeding needle. This would produce an atomization of fuel
particles with a kerosene coating, which may increase the surface
area available for combustion reaction with the kerosene component
of the fuel composition. This embodiment may be used for any fuel
composition in which it is desirable to have one or more components
of the composition coating the fuel particle and the remaining
components positioned in the nucleus of the same particle.
[0138] A nozzle-type injection device utilizing the second
embodiment would be very similar to FIG. 6, with a plurality of
feeding needles positioned within either a single pressure chamber
or within multiple pressure chambers. The major difference is that
the fuel composition would be introduced to the feeding needle
using separate sources for the formulation of the coating of the
particle and the formulation of the nucleus of the particle.
EMBODIMENT OF FIG. 3
[0139] The embodiments of FIGS. 1 and 2 are similar in a number of
ways. Both have a feeding piece which is preferably in the form of
a feeding needle with a circular exit opening. Further, both have
an exit port in the pressure chamber which is positioned directly
in front of the flow path of fluid out of the feeding source.
Precisely maintaining the alignment of the flow path of the feeding
source with the exit port of the pressure chamber can present an
engineering challenge particularly when the device includes a
number of feeding needles. The embodiment of FIG. 3 is designed to
simplify the manner in which components are aligned. The embodiment
of FIG. 3 uses a planar feeding piece (which by virtue of the
withdrawal effect produced by the pressure difference across a
small opening through which fluid is passed) to obtain multiple
microjets which are expelled through multiple exit ports of a
pressure chamber thereby obtaining multiple aerosol streams.
Although a single planar feeding member as shown in FIG. 3 it, of
course, is possible to produce a device with a plurality of planar
feeding members where each planar feeding member feeds fluid to a
linear array of outlet orifices in the surrounding pressure
chamber. In addition, the feeding member need not be strictly
planar, and may be a curved feeding device comprised of two
surfaces that maintain approximately the same spatial distance
between the two pieces of the feeding source. Such curved devices
may have any level of curvature, e.g. circular, semicircular,
elliptical, hemi-elliptical, etc.
[0140] The components of the embodiment of FIG. 3 are as
follows:
[0141] 41. Feeding piece.
[0142] 42. End of the feeding piece used to insert the fluid to be
atomized.
[0143] 43. Pressure chamber.
[0144] 44. Orifice used as gas inlet.
[0145] 45. End of the feeding needle used to evacuate the liquid to
be atomized.
[0146] 46. Orifices through which withdrawal takes place.
[0147] 47. Atomizate (spray) or aerosol.
[0148] 48. first fluid containing material to be atomized.
[0149] 49. second fluid for creation of microjet.
[0150] 50. wall of the propulsion chamber facing the edge of the
feeding piece.
[0151] 51. channels for guidance of fluid through feeding
piece.
[0152] d.sub.j=diameter of the microjet formed; .rho..sub.A=liquid
density of first fluid (48); .rho..sub.B=liquid density of second
fluid (49); .nu..sub.A=velocity of the first liquid (48);
.nu..sub.B=velocity of the second liquid (49); e=axial length of
the orifice through which withdrawal takes place; H=distance from
the feeding needle to the microjet outlet; P.sub.0=pressure inside
the chamber;
[0153] .DELTA.p.sub.g=change in pressure of the gas;
P.sub.a=atmospheric pressure; Q=volumetric flow rate
[0154] The proposed dispersing device consists of a feeding piece
41 which creates a planar feeding channel through which a where a
first fluid 48 flows. The flow is preferably directed through one
or more channels of uniform bores that are constructed on the
planar surface of the feeding piece 41. A pressure chamber 43 that
holds the propelling flow of a second liquid 49, houses the feeding
piece 41 and is under a pressure above maintained outside the
chamber wall 50. One or more orifices, openings or slots (outlets)
46 made in the wall 52 of the propulsion chamber face the edge of
the feeding piece. Preferably, each bore or channel of the feeding
piece 41 has its flow path substantially aligned with an outlet
46.
[0155] Formation of the microjet and its acceleration are based on
the abrupt pressure drop resulting from the steep acceleration
undergone by the second fluid 49 on passing through the orifice 46,
similarly to the procedure described above for embodiments of FIGS.
1 and 2 when the second fluid 49 is a gas.
[0156] When the second fluid 49 is a gas and the first fluid 48 is
a liquid, the microthread formed is quite long and the liquid
velocity is much smaller than the gas velocity. In fact, the low
viscosity of the gas allows the liquid to flow at a much lower
velocity; as a result, the microjet is actually produced and
accelerated by stress forces normal to the liquid surface, i.e.
pressure forces. Hence, one effective approximation to the
phenomenon is to assume that the pressure difference established
will result in the same kinetic energy per unit volume for both
fluids (liquid and gas), provided gas compressibility effects are
neglected. The diameter d.sub.j of the microjet formed from a
liquid density .rho..sub.1 that passes at a volumetric flow-rate Q
through an orifice across which a pressure difference
.DELTA.P.sub.g exists will be given by 15 d j ( 8 l 2 P g ) 1 4 Q 1
2
[0157] See Gan-Calvo, Physical Review Letters, 80:285-288
(1998).
[0158] The relation between the diameter of the microjet, d.sub.j,
and that of the resulting drops, {overscore (d)}, depends on the
ratio between viscous forces and surface tension forces on the
liquid on the one hand, and between dynamic forces and surface
tension forces on the gas on the other (i.e. on the Ohnesorge and
Weber numbers, respectively) (Hinds (Aerosol Technology, John &
Sons, 1982), Lefevre (Atomization and Sprays, Hemisphere Pub.
Corp., 1989) and Bayvel & Orzechowski (Liquid Atomization,
Taylor & Francis, 1993)). At moderate to low gas velocities and
low viscosities the relation is roughly identical with that for
capillarity instability developed by Rayleigh:
{overscore (d)}=1.89d.sub.j
[0159] Because the liquid microjet is very long, at high liquid
flow-rates the theoretical rupture point lies in the turbulent zone
created by the gas jet, so turbulent fluctuations in the gas
destabilize or rupture the liquid microjet in a more or less uneven
manner. As a result, the benefits of drop size uniformity are
lost.
[0160] On the other hand, when the second fluid 49 is a liquid and
the first fluid 48 is a gas, the facts that the liquid is much more
viscous and that the gas is much less dense virtually equalize the
fluid and gas velocities. The gas microthread formed is much
shorter; however, because its rupture zone is almost invariably
located in a laminar flowing stream, dispersion in the size of the
microbubbles formed is almost always small. At a volumetric gas
flow-rate Q.sub.g and a liquid overpressure .DELTA.P.sub.1, the
diameter of the gas microjet is given by 16 d j ( 8 l 2 P l ) 1 4 Q
g 1 2
[0161] The low liquid velocity and the absence of relative
velocities between the liquid and gas lead to the Rayleigh relation
between the diameters of the microthread and those of the bubbles
(i.e. d=1.89d.sub.j).
[0162] If both fluids 48, 49 are liquid and scarcely viscous, then
their relative velocities will be given by 17 v A v B = ( B A ) 1
2
[0163] The diameter of a microjet of the first liquid at a
volumetric flow-rate of A Q.sub.A and an overpressure of
B.DELTA.P.sub.B will be given by 18 d j ( 8 A 2 P B ) 1 4 Q A 1
2
[0164] At viscosities such that the velocities of both fluids 48,
49 will rapidly equilibrate in the microjet, the diameter of the
microjet of the first liquid will be given by 19 d j ( 8 B 2 P B )
1 4 Q A 1 2
[0165] The proposed fuel injection nozzle system obviously requires
delivery of the fluids 48, 49 to be used in the dispersion process
at appropriate flow-rates. Thus:
[0166] (1) Both flow-rates should be adjusted for the system so
that they lie within the stable parameter window.
[0167] (2) The mass ratio between the flows should be compatible
with the specifications of each application. Obviously, the gas
flow-rate can be increased by using an external means in special
applications, since this need not interfere with the aerosolization
operation.
[0168] (3) If the flow-rates are altered, the characteristic time
for the variation should be shorter than the hydrodynamic residence
times for the liquid and gas in the microjet, and smaller than the
reciprocal of the first natural oscillation frequency of the drop
formed at the end of the feeding piece.
[0169] (4) Therefore, the gas and liquid can be dispensed by any
type of continuous delivery system.
[0170] (5) The housing of the pressure chamber and the feeding
nozzle can be made from a variety of materials, but preferably
materials that are not reactive with organic solutions (e.g. metal
or plastic).
EXEMPLARY USES OF THE THIRD EMBODIMENT
[0171] FIG. 7 illustrates a generalized, schematic view of an
exemplary use of a modified version of the embodiment of FIG. 3 in
an injection apparatus. In this figure, the planar feeding element
is adapted for use in a cylindrical injection structure. The device
provides for either a single cylindrical feeding elements, or more
preferably a plurality of concentric cylindrical feeding elements,
through which the fuel formulation is introduced for injection.
These feeding elements are housed within a single pressure chamber
(i.e. one or multiple feeding elements within a single pressure
chamber), or each cylindrical feeding element may be housed within
multiple chambers, more preferably a single pressure chamber for
each feeding element. Alternatively, the feeding elements may be
planar, and the device can be comprised from a bank of planar
elements that are configured to approximate the desired shape of
the nozzle.
[0172] FIG. 7A is a side view of the internal portion of a single,
circular feeding element 93 contained within a single pressure
chamber 90. The feeding element preferably has multiple recessed
chambers within the element 92 to the feeding exit ports 93. The
external surface of the exit ports are optionally designed to aid
in directing the surrounding gas to the openings in the pressure
chamber 91, as is pictured in FIG. 7A. The chambers are aligned
with the openings in the pressure chamber to provide better
directional flow to the exit openings and to aid in the formation
of the focusing tunnel and stable microjet. FIG. 7B illustrates the
multiple openings in the pressure chambers of the device containing
the same number of multiple, concentric feeding elements and
pressure chambers 90.
FUEL INJECTION FORMULATIONS
[0173] The compositions used in the invention for producing
particles will depend in part on the chemical nature of the
formulation to be atomized. For example, if a formulation to be
atomized is hydrophobic, e.g. a hydrocarbon, then the solvent
containing the formulation used in the method of the invention is
preferably a solvent suitable for dissolving hydrophobic compounds,
e.g. ether. The hydrophobic components are preferably at least
partially dissolved in the solvent. The second fluid is preferably
either a gas, more preferably air, or a liquid immiscible with the
first.
[0174] Fuel formulations for use in the invention may be comprised
of any composition that can be aerosolized or atomized for use in
an internal combustion reaction delivery. Such formulations
preferably contain mixtures of alkanes obtained from petroleum,
e.g. natural gas, kerosene, gasoline, diesel fuel and jet fuel.
Such formulations, in addition to containing a fuel composition
base of molecules such as hydrocarbons, may contain additives that
enhance fuel performance and/or reduce harmful emissions, e.g.
ethanol. Further examples of fuel compositions may be found in
Riegel's Handbook of Industrial Chemistry, ed. J. A. Kent (1992),
which is incorporated herein by reference. These formulations may
be in any form capable of atomization, such as dissolved in a
solvent, suspended in a solvent, or in the form of an emulsion, a
slurry, etc., provided the dynamics of the form render it capable
of forming a capillary microjet upon exposure to a second
fluid.
[0175] While the present invention has been described with
reference to the specific embodiments thereof, it should be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted without departing from the
true spirit and scope of the invention. In addition, many
modifications may be made to adapt a particular situation,
material, composition of matter, process, process step or steps, to
the objective, spirit and scope of the present invention. All such
modifications are intended to be within the scope of the claims
appended hereto.
* * * * *