Method Of Fuel Atomization And A Fuel Atomizer Nozzle Therefor

Abstract

A very fine fuel particle size is obtained by atomization resulting from the intersection of a fuel stream from a fuel nozzle and a gas stream from a gas nozzle with respective velocity vectors forming an angle at least as great as 90.degree., with atomization of an inverse Y-jet type. Preferably, the fuel is jetted with a whirling motion in an axial direction away from the atomizer, and the gas is whirled inwardly at right angles to its whirling axis or axially either in the same direction as or in the opposite direction as the axial direction of movement for the fuel. The fuel and preferably also the gas will be whirled conically, that is with both a radial and axial component of movement with respect to the whirling axis.

Parent Case Text

This is a division, of application Ser. No. 231,702 filed Mar. 3, 1972.

Description

BACKGROUND OF THE INVENTION

The present invention relates to methods of fuel atomization and fuel atomizer nozzles therefor, which are usually employed with the combustion chambers of boilers, gas turbines and the like. In the prior art fuel atomizer nozzles, only a very small percentage of the total kinetic energy of the air is utilized in the atomization of the fuel. In the combustion of atomized fuel, the combustion intensity and efficiency is primarily determined by the average surface area of the fuel particles in contact with the air or other oxidizer. Particularly, with liquid fuels, the time required for the evaporation of the liquid drops or particles is extremely important and generally proportional to the square of the particle diameter. Since combustion efficiency increases with finer atomized fuel particles given off by the atomizer nozzle, if finely atomized fuel is available, high load combustion is possible with a very small combustor. In this respect, the fuel atomizer that determines fuel particle size of the combustor is very important.

Recently, the desired capacity for a combustor has been rapidly increasing, particularly from economical demands. Also, air pollution problems are becoming increasingly serious, and administrative regulations regarding non-combusted hydrocarbons, carbon monoxide, nitrogen oxides contained in the exhaust gas, soot and dust are becoming increasingly severe.

One of the typical prior art atomizer nozzles is of what is termed a parallel type. This type of atomizer nozzle is constructed so that an air jet nozzle is concentric with and before a fuel jet nozzle, with both having the same fluid directions for projection. Since the driving power for atomization of liquid fuel is gained from the relative velocity between the air or gas and the liquid fuel, in this parallel type of atomizer, the relative velocity is so small that the efficiency of atomization by the air is quite low, that is the fuel particle size will be relatively great on the average.

Other prior art atomizer nozzles are what may be termed the Y-jet type, one of which is constructed so that the liquid fuel is injected in the passage of the air within the atomizer nozzle at an angle of about 45.degree. with respect to the direction of the air passage, and thereafter the mixed air and fuel is jetted from the atomizer nozzle. Since the relative velocity, between the fuel and air, for the Y-type of atomizer nozzle is larger than for the parallel type of atomizer nozzle and at the same time the stream of air shears the stream of liquid fuel, the atomization of fuel for the Y-type of atomizer nozzle is considerably better than that obtained with the parallel type of atomizer nozzle.

Further, it is known to provide a right angled type of atomizer nozzle, where the velocity vectors for the air and fuel stream, respectively, meet or intersect at a right angle. Thus, the relative velocity in the direction of air flow is larger than for the Y-jet type of atomizer nozzle.

As the relative velocity between the air and fuel becomes larger, the atomization for the fuel correspondingly is improved. However, the fuel stream increasingly tends to receive the dynamic pressure of the air stream with increased relative velocity to become unstable.

On the other hand, another prior art type of atomizer nozzle jets and whirls the air and fuel, respectively for improving the efficiency of atomization. This type of nozzle is constructed so that the air is jetted toward the stream of whirling fuel, but there is the considerable drawback that the jet angle for the fuel is extremely small.

Thus, although the above-mentioned atomizer nozzle types have been improved as noted, they are still unsatisfactory for high performance and have many drawbacks.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of fuel atomization by a fuel atomizer nozzle, wherein the liquid fuel is atomized by jetting or injecting the fuel and the gas so that the velocity vectors of the fuel stream jetted or injected meet the velocity vectors of the gas stream jetted or injected at angles greater than 90.degree., which will produce excellent particle sizes and stable atomizing characteristics.

This object is primarily accomplished by whirling both the air and fuel, in opposite directions about a common axis, with axial components of movement in the same direction or the opposite direction, or with only the fuel having an axial component of movement, or with neither having an axial component of movement. Further, it is preferable to provide both the whirling gas stream and whirling fuel stream with opposite radial velocity vector components.

BRIEF DESCRIPTION OF THE DRAWING

Further objects, features and advantages of the present invention will become more clear from the following detailed description of the drawing, wherein:

FIG. 1 is a partial cross sectional view taken through one embodiment of an atomizer nozzle according to the present invention;

FIG. 2 is a cross sectional view taken along line II--II in FIG. 1;

FIG. 3 is a view similar to FIG. 1, but showing another embodiment of the present invention;

FIG. 4 is a schematic diagram of the nozzle of FIG. 1 showing the air or gas and fuel stream velocity vectors;

FIG. 5 is a view similar to FIG. 1, but of an additional embodiment of the present invention;

FIG. 6 is a view similar to FIG. 1, but of still another embodiment of the present invention;

FIG. 7 is a view similar to FIG. 1, but of another embodiment of the present invention;

FIG. 8 is a cross sectional view taken along line VIII--VIII of FIG. 7;

FIG. 9 is a cross section similar to that of FIG. 8, but showing a variation thereof;

FIG. 10 classifies various atomizer methods in a chart according to the relation between the air and fuel stream velocity vectors; and

FIG. 11 is a graph showing experimentally obtained values for mean atomized particles diameter plotted against the ratio between air stream speed and fuel stream speed.

DETAILED DESCRIPTION OF THE DRAWING

As shown in FIGS. 1 and 2, the atomizer nozzle includes a nozzle cap 1 assembled concentrically with a nozzle body 2. A vortex chamber 3 is formed by drilling or the like within the nozzle body 2 and connects with a liquid fuel nozzle 4 and a flared fuel guiding surface portion 6, which is generally frusto-conically formed, all of which is annularly symmetrical with respect to a central axis for the cap 1 and body 2. Further, the fuel nozzle body 2 is formed with upstream, to the right in FIG. 1, enlarged chamber portions containing therein the fuel whirling means 8. Preferably, the fuel whirling means 8 is assembled within the body 2 by a threaded connection and contains a central fuel passage 13 delivering fuel to fuel passages 9, which are in turn connected with an annular fuel reservoir 10 for feeding fuel under pressure to the peripherally arranged fuel injection grooves 11. The fuel injection grooves are formed so that the directions of the grooves are along the tangent of the inner surface of the vortex chamber 3.

The downstream end of the nozzle body 2 is formed with a plurality of peripherally arranged helically grooves 5, which form a plurality of gas passages with the nozzle cap 1 constituting the gas nozzle. The annular chamber or space between the inner surface of the nozzle cap 1 and the outer surface of the nozzle body 2 forms a gas delivery chamber for the gas, which is preferably air, oxygen or the like.

The fuel 15 is supplied in the direction of the arrow to the fuel reservoir 10 through the fuel passages 13, 9 under pressure and is thereafter injected into the vortex chamber 3 through the fuel injection grooves 11. Since as mentioned above the grooves 11 are tangent to the inner surface of the vortex chamber 3, the injected fuel within the vortex chamber 3 will whirl about the axis of symmetry for the nozzle in the manner of a vortex, so that whirling fuel is jetted as a vortex or whirling stream through the fuel nozzle 4 into the outer portion A of the atomizer nozzle peripherally closely adjacent the downstream end of the helical grooves 5. The whirling stream of fuel jetted from the fuel nozzle 4 will travel in a generally conical path as guided by the guiding surface portion 6. The gas 14 traveling in the direction of the arrow under pressure within the annular chamber formed between the nozzle cap 1 and nozzle body 2 will pass through the helical grooves 5 to be jetted in a whirling pattern as dictated by the helical grooves to intersect the fuel generally along the peripheral area A for atomizing the same.

With the above-mentioned construction, the atomizer nozzle is not affected by the dynamic pressure of the gas, so that steady state fuel supply will be insured, for general steady state conditions.

As the flare angle .alpha. of the flared or conical surface portion 6 is increased, a transition angle will be reached wherein the whirling fuel stream flow will leave or separate from the surface 6. The threshold angle .alpha..sub.o, that is the above-mentioned angle at which the whirling fuel flow just starts to separate from the surface 6, is determined by the following equation:

.alpha..sub.o = 2tan.sup..sup.-1 {K/.sqroot.1-K.sup.2 }

, where K is generally known as the cavity constant, a parameter representing the intensity of the whirling of the fuel.

In practice, it is most advantageous and therefore preferred to construct the flare angle .alpha. at or slightly greater than the transition angle .alpha..sub.o, because with separation of the whirling fuel from the surface 6 the energy loss due to viscosity of the fuel is substantially less than what it would be for flare angles less than .alpha..sub.o. In operations wherein the flare angle .alpha. is less than the threshold or transition angle .alpha..sub.o, the fuel will be guided along the flared or conical surface portion 6 toward the outlet of the helical grooves 5 of the gas nozzle. This will serve to supply the whirling fuel to where the gas velocity is the greatest. In a construction wherein the flare angle .alpha. is greater than the transition angle .alpha..sub.o, the presence of the flared or conical surface 6 becomes meaningless and generally has no effect. Thus, the atomizer nozzle of FIG. 1 may be constructed as shown in FIG. 3 wherein a cylindrical cavity 6a is formed in the nozzle body 2a in place of the conical surface 6 of FIG. 1. Otherwise, the nozzle cap 1a, nozzle body 2a and fuel whirling means are identical to the corresponding elements of FIG. 1 that have previously been described. Therefore, in the embodiment of FIG. 3 and subsequent embodiments only the differences between the embodiments will be described in detail and it is to be understood that the remaining illustrated structures are identical to those already described with respect to FIG. 1.

In practice, the atomizer nozzle of FIGS. 1 and 3 are of the inverse or reverse Y-jet type according to the chart of FIG. 10. As shown in FIG. 4 with respect to a point of intersection B between the whirling fuel stream along the conical path 7, which would be along the flared or conical surface portion 6 of FIG. 1, it is seen that the directions of the gas and fuel streams are reversed, so that the velocity vector Va of the jetted gas from the helical grooves 5 and the velocity vector Vf of the fuel jetted from the fuel nozzle 4 form an intersection angle substantially greater than 90.degree. of the reverse Y-jet type.

The further modification of FIG. 5 differs from the previous construction of FIG. 1 in that the helical grooves 5b that jet the gas generally lie within a plane perpendicular to the axis of symmetry for the atomizer nozzle and particularly for the fuel axis passing through the fuel nozzle 4b of the nozzle body 2b. Of course, the passages formed by the nozzle cap 1b and the helical grooves 5b will still provide a whirling movement for the exiting gas stream, but there will be no axial component for the gas velocity vector. With the construction of FIG. 5, the angle between the velocity vectors for the gas and fuel at intersection will be substantially larger than for the nozzle of FIG. 1.

According to the further modification of FIG. 6, the gas jet passages formed between the nozzle cap 1c and nozzle body 2c by the helical grooves 5c will whirl the gas with an axial velocity vector component opposite in direction to that of the previously described fuel jet axial velocity vector component, to produce an even greater atomization of the fuel than would be obtained with the previously described embodiments. With the construction of FIG. 6, it is possible to have a velocity vector intersection angle between the gas stream and fuel stream of approximately 180.degree..

While the preceding embodiments have utilized the fuel pressure in forming the whirling fuel stream, the most simple one of the other methods of supplying the fuel is to utilize an annular cavity.

The atomizer nozzle according to FIGS. 7 and 8 includes a nozzle cap 16 concentrically mounted and generally spaced from a nozzle body 17, which is formed with a plurality of angled outlet grooves 18 forming a plurality of gas nozzle passages between the downstream ends of the nozzle cap 16 and nozzle body 17. A fuel supply tube 19 is threadably connected concentrically with the nozzle body 17, and is threadably assembled until the annular projection or flange 20 axially abuts the illustrated interior shoulder of the nozzle body 17 to fix the relative position between the nozzle body 17 and the fuel supply tube 19 by tightening the threads 21. The hollow fuel supply tube 19 forms fuel passage 22 in its interior, and is generally closed at its downstream end, which is the left hand end in FIG. 7. At this downstream end, the fuel supply tube 19 is formed with the plurality of fuel nozzle passages 23 that angularly open through the outer peripheral surface of the fuel supply tube 19. An annular gas supply passage 24 is formed between the inner cylindrical surface of the nozzle cap 16 and the outer cylindrical surface of the nozzle body 17, and provides fluid communication with the gas nozzle passages 18, which passages 18 tangentially open into the annular cavity or chamber 25. The fuel nozzle outlet passages 23 pass through the inner cylindrical surface of the chamber 25, and the gas nozzle passages pass through the outer cylindrical surface of the annular chamber 25.

With the fuel atomizer nozzle of FIGS. 7 and 8, the fuel 27 is supplied in the direction of the arrow within the fuel passage 22 under pressure to the fuel nozzle passages 23 to be jetted or injected into the annular cavity or chamber 25 with a whirling motion having a radial velocity vector component, but without an axial velocity vector component. The gas 26 is supplied in the direction of the arrow through the annular gas passage 24 under pressure to the gas nozzle passages 18 to be injected or jetted with a whirling motion into the annular chamber 25 with an inwardly directed radial velocity vector component, but without any axial velocity vector component. Thus, as particularly seen from FIG. 8 with respect to the angularity of the nozzle passages 18, 23, the jetted gas stream will be whirled in one rotational direction about the axis of symmetry for the atomizer nozzle and the jetted fuel stream will be whirled in the opposite rotational direction about the same axis, and the radial velocity vector components of the gas stream and fuel stream will be opposite so that they will intersect to mix the fuel with the gas and atomize the fuel. The atomized fuel will be diffused toward the left hand end of the annular chamber 25 due to the pressure differential between the open left hand end and the closed right hand end of the annular chamber 25, as seen in FIG. 7, as the atomized fuel whirls by the gas stream. With the nozzle of FIG. 7, the air and fuel stream velocity vectors intersect at an angle greater than 90.degree., that is they form the reverse Y-jet type of atomizer nozzle so that very efficient atomization may be achieved.

The variation of the atomizer nozzle according to FIGS. 7 and 8, which variation is shown in FIG. 9, differs only in that it employs tapered gas nozzle passages 18a, which would be used with subsonic jetted gas flow. With supersonic jetted gas flow, the gas nozzle passages 18 would be flared or tapered in the opposite direction; that is, with subsonic flow, the gas passages would converge, while with supersonic flow, they would diverge.

In FIG. 10, the various types of atomizer nozzles are classified according to the relationship between the velocity vectors for the air and fuel stream. Namely, there are shown the parallel type, the Y-jet type, the normal or right angled type, and the reverse Y-jet type nozzles, proceeding from the left to the right.

FIG. 11 shows the results of experiments conducted with the four types of atomizer nozzles classified in FIG. 10. It is seen that with the right angle type and reverse Y-jet type of atomizer nozzles, particularly the latter, the mean particle diameter of atomized fuel is quite small over a wide range of relative speed, and also it varies less with change in air flow as compared with the remaining two types of atomizer nozzles.

According to the present invention, it is possible to provide atomizer nozzles having excellent atomizing characteristics. Thus, complete combustion of liquid fuel similar to that of gas fuel may be readily achieved. Further, according to the present invention, the exhaust gases will contain practically no unburnt or non-combusted hydrocarbons and carbon monoxide, and the concentration of smoke mainly composed of unburned carbon may be reduced, so that the invention is very useful in the prevention of air pollution or contamination by combustion apparatus. Since the atomizing efficiency of the present invention is excellent, the above objects may be achieved with very little compressing of the air or oxidizing gas, which means a reduction in the driving power of the auxiliary units, particularly the cost and size of a compressor; this is true, because it is well known that the pumping of a liquid requires very little power in comparison with the pumping of a gas. Furthermore, the present invention is particularly useful for gas turbines for vessels or vehicles using low-grade fuel such as C-grade heavy oil, because with such low-grade fuel the attachment of ashes to the walls of the fuel-air mixture passage can be prevented by virtue of the complete combustion.

Since the method of atomizing has been described along with the description of the structure and further illustrated by various diagrams, no separate operation or method description will be given.

While many embodiments of the present invention with variations have been specifically illustrated and described as above, further modifications, embodiments and variations are contemplated within the spirit and scope of the present invention as defined by the following claims.

Claims

What is claimed is:

1. A fuel atomizer nozzle, comprising: a liquid fuel passage, fuel whirling means receiving fuel from said fuel passage and moving the fuel in a whirling pattern about a fuel axis; fuel nozzle means to project the whirling fuel in a conical whirling jet generally in an axial direction with respect to said fuel axis; and gas nozzle means for producing a whirling gas stream downstream of said fuel nozzle means intersecting the whirling fuel jet so that at the points of intersection the gas velocity vector generally forms an angle greater than 90.degree. with the fuel velocity vector.

2. The fuel atomizer nozzle according to claim 1, wherein said gas nozzle means whirls the gas stream about said fuel axis with a radial component of velocity with respect to said fuel axis.

3. The fuel atomizer nozzle according to claim 1, wherein said gas nozzle means whirls the gas stream about the fuel axis and discharges the whirling gas in an axial direction corresponding to the axial direction of movement of the whirling fuel jet.

4. The fuel atomizer nozzle according to claim 1, wherein said gas nozzle means whirls the gas stream about said fuel axis and projects the whirling gas stream in an axial direction opposite to the axial direction of the whirling fuel jet.

5. A fuel atomizer nozzle, comprising: spaced inner and outer annular walls forming therebetween an annular chamber; fuel injection means opening through said inner annular wall for projecting a stream of fuel in a whirling conical path axially into said annular chamber; a fuel passage means for supplying fuel under pressure to said fuel injection means; a gas injection means having gas outlets around said outer annular wall for projecting a whirling gas stream into said annular chamber; gas passage means for supplying gas under pressure to said gas injection means; said gas injection means and said fuel injection means cooperating to intersect the projected gas stream with the projected fuel stream so that at the points of intersection, the gas velocity vector will form an angle with the fuel velocity vector within said annular cavity greater than 90.degree..

6. The fuel atomizer nozzle according to claim 5, wherein said gas injection means gas outlets are each open at one end to said gas passage means and open at the other end generally tangentially to said outer annular wall.

7. The fuel atomizer nozzle according to claim 6, wherein said gas outlets are tapered in cross section from said gas passage end to said outer annular wall end.

8. The fuel atomizer nozzle according to claim 5, wherein said fuel injection means includes a plurality of fuel passages, each opening at one end to said fuel passage means and opening at the opposite end tangentially through said inner annular wall.

9. The fuel atomizer nozzle according to claim 5, wherein said fuel injection means whirls the fuel stream within said annular chamber in one rotary direction about the axis of said annular chamber and said gas injection means whirls the gas stream within said annular chamber in the opposite rotary direction, with respect to the axis of said annular chamber.