Pressure Spray Type Fuel Injection Nozzle Having Air Discharge Openings

Abstract

A fuel injection nozzle of the type which injects fuel from a nozzle opening with pressure in the form of a conical spray of fuel particles, in which air discharge openings are provided around the nozzle opening. The air discharge openings each have an angle of inclination and an angle of torsion to the axis of the nozzle opening and cause a spiral flow of air which contacts from the outside the outer periphery of the conical spray of fuel particles injected into a combustion chamber and thereby divides coarse fuel particles at the outer periphery of the conical spray into smaller particles. These air discharge openings are communicated with a flow passage of combustion air inside a combustion element.

Description

BACKGROUND OF THE INVENTION

This invention relates to a pressure spray type fuel injection nozzle used with gas turbines.

Combustion elements used in gas turbines and boilers are becoming larger and larger in capacity to meet economical demands. On the other hand, fuels used in such combustion elements are changing from more volatile oils, such as kerosine and light oil, to less volatile oils, such as heavy oil, containing a large amount of residual oil, in consideration of effective use of the petroleum resources. These tendencies are aggravating air pollution by the unburned hydrocarbons, carbon monoxide, nitrogen oxides, smoke and dusts contained in the exhaust gases from the combustion elements. In this view, removal of the air polluting substances contained in the exhaust gases is an important problem in increasing the capacity of the combustion elements and in using less volatile oils, and countermeasures are required.

The combustion element of gas turbine, as compared with that of boiler, is extremely narrower in the size of combustion chamber and is used under severer operational conditions, such as quick starting and stopping. Therefore, even if light oil is used as fuel, carbon contained in the fuel is separated in the combustion chamber and the separated carbon is released directly into the atmosphere, which imparts a sufficiently visible black color to the exhaust gas. For the gas turbines which are considered as discharging less amounts of air polluting substances than other heat engines, the suppression of smoke generation is an important problem.

For the suppression of smoke generation, there are known two methods. Namely, one is an indirect method in which a desmoking agent is added to fuel and the other one is a direct method in which the construction of the combustion element is designed best to suppress the generation of smoke. In the former method, manganese and manganese compounds are chiefly used as the desmoking agents. However, since the desmoking agent must be mixed in fuel beforehand, this method has some defects, such as that mixing means is required for mixing the desmoking agent with fuel, that the desmoking agent cannot be mixed uniformly in the fuel, and that the secondary products of the desmoking agent resulting from the combustion are discharged into the atmosphere, causing secondary air pollution, and is rarely being used at the present time.

The generation of smoke, as is well known, is attributable to the presence of local excess fuel regions in the primary combustion region within the combustion chamber, and therefore, can be prevented by eliminating such local excess fuel regions. In order to eliminate directly the source of smoke generation, it is only necessary to encourage mixing of air and fuel and thereby to promote complete combustion of fuel and prevent separation of carbon. As a method, there can be considered to increase the area of a primary air supply opening of the combustion element. This method aims to encourage fuel-air mixing by supplying a large amount of primary air and thereby to eliminate the excess fuel regions. However, the generation of smoke cannot be prevented, simply by supplying the primary air in a large amount, and this is the very fact which makes the subject of combustion complicated and difficult to deal with. In case of a liquid fuel, the evaporation stage of the liquid fuel droplets is important and the diameter of the droplets has a significant influence on the combustion of fuel. It is well known that the evaporation time of a liquid droplet is proportional to the square of the diameter thereof. Therefore, it will be understood that the evaporation time of the fuel particle sprayed into the combustion element becomes longer and the interior thereof is contacted more hardly by air, as the size of said fuel particle (hereinafter referred to as sprayed particle size) becomes larger. A larger sprayed particle size facilitates the occurrence of excess fuel regions in the combustion chamber and is a cause of smoke generation. The sprayed particle size is influenced by the fuel atomizing characteristic of the fuel injection nozzle.

Fuel injection nozzles are classified broadly into two types in terms of spray method. Namely, one is a type of fuel injection nozzle which sprays fuel with pressure (hereinafter referred to as pressure spray type fuel nozzle) and the other one is a type of fuel injection nozzle which sprays fuel by making use of air pressure (hereinafter referred to as air spray type fuel nozzle). In case of the air spray type fuel nozzle, the sprayed particle size is smaller than in case of the pressure spray type fuel nozzle. However, the air spray type fuel nozzle has the serious disadvantage that it calls for a compressor solely for compressing the air used for spraying fuel. Further, with the air spray fuel nozzle, there must be provided, in addition to a fuel flow control system, an air flow control system and an air piping which render the construction of the gas turbine complicated.

In gas turbines, the pressure spray type fuel nozzle is generally being used at the present time, As one type of the pressure spray type fuel nozzle, there is known a spiral spray type fuel nozzle which sprays fuel particles in the form of a spiral flow. This type of fuel nozzle includes a fuel nozzle having dual nozzle openings consisting of a small opening from which fuel is constantly sprayed and relatively large openings which are not opened at the time of ignition (hereinafter referred to as dual opening type spiral fuel nozzle). This duel opening spiral type fuel nozzle has the advantages that the time required from the start of a gas turbine to the rated speed can be shortened, and that the flow rate of fuel can be regulated simply by varying the spray pressure by means of a fuel pump. On the other hand, with the duel opening type spiral fuel nozzle, the fuel particles are sprayed in a conical shape and most of them are concentrated at the peripheral portion of said conical shape, substantially no fuel particles being present in the central portion of the conical shape. Practically speaking, the numbers of fuel particles at the peripheral portion is about 27 times that of fuel particle present in the central portion, with respect to the unit area of the conical shape. Further, the mean sprayed particle size is as large as about 320 microns, and even larger and about 370 microns especially at the peripheral portion. Thus, it will be understood that fuel particles of large diameters are present in a large number at the peripheral portion of the conical spray of fuel. In consideration of the air and fuel concentrations at this portion, it will be readily understood that excess fuel regions occur locally in the combustion chamber, which are obviously the major cause of incomplete combustion and high smoke concentration. For eliminating the excess fuel regions, only increasing the primary air is insufficient and the fuel atomizing characteristic of the fuel nozzle needs to be improved. Such a tendency can be said on all of pressure spray type fuel nozzles.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a novel pressure spray type fuel nozzle which overcomes the disadvantages of the conventional ones and is capable of reducing the sprayed fuel particles.

Another object of the invention is provide a pressure spray type fuel nozzle which suppresses the generation of smoke even when used with a combustion element of gas turbine.

Still another object of the invention is to provide a pressure spray type fuel nozzle which enables even a less volatile oil, such as heavy oil, used as fuel to be burned satisfactorily.

Still another object of the invention is to provide a pressure spray type fuel nozzle which is capable of dividing into smaller particles the coarse fuel particles concentrating to the outer peripheral portion of a conical spray of fuel injected from the nozzle opening and enables a uniform distribution of fuel particles to be obtained.

A further object of the invention is to provide a pressure spray type fuel nozzle which divides the sprayed fuel particles by making use of part of the combustion air being supplied into a combustion chamber and, therefore, is very simple in construction and inexpensive, without requiring an additional air supply source.

The present invention is characterized in that air discharge openings are provided around the opening of a fuel injection nozzle connected to one end of a fuel passage facing the combustion chamber of a combustion element, and each of said air discharge opening is of such construction that air discharged therefrom forms a spiral air flow which contacts from the outside the outer periphery of a conical spray of fuel particles injected into the combustion chamber from the fuel injection nozzle. Therefore, with the fuel injection nozzle of the invention, the outer peripheral portion of the conical spray is disturbed by the spiral air flows. with the result that the coarse fuel particles concentrating to said portion are divided into smaller particles and dispersed uniformly in the combustion chamber, providing for satisfactory combustion of fuel. Further, the spiral air flows are formed by making use of part of the combustion air supplied into the combustion chamber and hence, a special air supply source is not required. This is advantageous in rendering the fuel injection nozzle of the invention very simple in construction and inexpensive.

The objects, set forth above, other objects and the unique features of the present invention will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings. It should be understood, however, that the drawings are only illustrative and not limitative to the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of an embodiment of the pressure spray type fuel injection nozzle according to the present invention;

FIG. 2 is a front elevational view showing in detail the air discharge opening unit shown in FIG. 1;

FIG. 3 is a fragmentary view of the air discharge opening unit, looking in the direction of the arrow III in FIG. 2;

FIG. 4 is a sectional view illustrating diagrammatically spiral air flows and fuel particle flow, formed by the nozzle of the invention, relative to the axis of the nozzle opening;

FIG. 5 is a characteristic graph showing the flow rate distributions of sprayed fuel, of a conventional dual opening type spiral fuel nozzle and the pressure spray type fuel nozzle of the invention;

FIG. 6 is a characteristic chart showing the particle size distributions in the radial direction of fuel particles sprayed by the conventional dual opening type spiral fuel nozzle and the pressure spray type fuel nozzle of the invention; and

FIG. 7 is a vertical sectional view of another embodiment of the fuel nozzle according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown an embodiment of the pressure spray type fuel nozzle according to the invention generally indicated by numeral 11, as mounted in a combustion element (hereinafter thr pressure spray type fuel nozzle of the invention will be referred to simply as fuel nozzle, to distinguish it from conventional pressure spray type fuel nozzles). The fuel nozzle 11 comprises a nozzle body 12 having a fuel passage (not shown) formed therein and a fuel discharge opening 27 provided at the forward end of said fuel passage, a cap 14 surrounding said nozzle body 12 to form an annular air passage 23 therebetween, a spiral passage unit 18 provided at the forward end of the air passage 23 defined by said nozzle body 12 and cap 14 and having air discharge openings 20, and a supporting member 21. The fuel discharge opening 27 is located on the axis 29 of the nozzle body 12 and is of the ordinary one capable of spraying fuel in a conical shape coaxial with the axis 29. The nozzle body 12 is connected to the supporting member 21 by the ordinary means, e.g., screws. The forward end of the cap 14 is so shaped as to define an air discharge openings 20 between the inner surface thereof and the outer surface of the spiral passage unit 18. The cap 14 is connected to the supporting member 21 through screw engagement between external threads formed on the outer surface of the rear end portion of said cap 14 and internal threads formed on the inner surface of the forward end of said supporting member 21. The spiral passage unit 18 is secured between the nozzle body 12 and the cap 14 at the same time when the cap 14 is connected to the supporting member 21. The spiral passage unit 18 may alternatively be connected to the nozzle body 12 by means of screws. The spiral passage unit 18, as shown in FIG. 2, has a plurality of grooves formed in the conical outer surface thereof which form air discharge openings 20 together with the inner surface of the cap 14. Each of the air discharge openings 20 has an angle .alpha. of inclination to the axis 29 of the nozzle body 12 as shown in FIG. 1, and an angle .theta. of torsion to the axis 29 as shown in FIG. 3. The upper and lower surfaces of the air discharge opening 20 are parallel to the air flowing direction, but not necessarily and one of them may be inclined relative to the other so that said air discharge opening may be progressively reduced in cross section toward the downstream of the fuel nozzle 11. The air discharge openings 20 and the fuel discharge opening 27 do not have a common passage at any point within the fuel nozzle 11.

An outer cylinder, generally indicated by numeral 35, of the combustion element is composed of a cylinder 36 and an end plate 37 perpendicular to said cylinder 36. The supporting member 21 supporting the fuel nozzle 11 is fixed to the end plate 37 by means of bolts. In the outer cylinder 35 is disposed a liner 39 which defines a combustion chamber 45 therein and is provided with primary air inlet openings 41, secondary air inlet openings (not shown) and slit-like louvers 43. The outer cylinder 35 and the liner 39 form therebetween a passage 26 for combustion air 51. One end of the liner 39 is closed and the forward end of the fuel nozzle 11 is projecting into the combustion chamber 43, with the cap 14 located at the center of said closed end of the inner 39, to spray fuel into said combustion chamber. The other end of the liner 39 is open for discharging the combustion gas. The cap 14 has a number of apertures 16 formed through that portion thereof which is exposed in the passage 26. The air discharge openings 20 are communicated with the passage 26 through the passage 23 and the apertures 16. The total cross sectional area of the air discharge openings 20 is made smaller than the cross sectional area of the passage 23 and the total cross sectional area of the apertures 16. Between the nozzle body 12 and the spiral passage unit 18 is formed an annular passage 25 which is in communication with the passage 23 and open at the forward end for discharging air along the forward end face of the nozzle body 12.

The coarse fuel particle dividing effect of the present invention is achieved by spiral flows of air discharged from the air discharge openings 20 which contact from the outside the outer periphery of the conical spray of atomized fuel particles injected from the fuel discharge opening 27, where the coarse fuel particles are present in a large number. Namely, the coarse fuel particles are divided into smaller particles by taking advantage of the velocity energy of the spiral air flows. This principle will be described hereunder with reference to FIG. 4.

FIG. 4 is a sectional view diagrammatically showing in side elevation the conical spray 57 of fuel particles injected from the fuel discharge opening 27 and the spiral flows 55 of air discharged from the air discharge openings 20, relative to the axis 29 of the fuel nozzle. The centers of the air discharge openings 20 are located on a circle concentric with the axis 29 of the fuel nozzle, which is a distance t spaced axially from the fuel discharge opening 27 and has a radius a (hereinafter all distances from the air discharge openings 20 are with reference to this circle). At a point a distance h spaced axially downstream from the air discharge openings 20, the coarse fuel particles discharged from the fuel discharge opening 27 at an angle 2.phi. of injection and being present at the outer peripheral portion of the conical spray 57 of fuel particles, are spaced radially from the axis 29 of the fuel discharge opening by a distance R.sub.1 which is represented by the following formula:

R.sub.1 = .+-. (h - t) tan.phi. 8

Here, it should be understood that in FIG. 4 axial distances measured downstream from the fuel discharge opening 27 are regarded as + and radial distances measured upwardly from the axis 29 of the fuel nozzle are regarded as +. At the point the distance h spaced axially downstream from the air discharge openings 20, the spiral flows 55 of air discharged from said air discharge openings pass the points spaced radially from the axis 29 of the fuel nozzle by a distance R.sub.2 which is represented by the following formula:

R.sub.2 = .+-..sqroot.(htan.theta.).sup.2 + (a = htan.alpha.).sup.2 2

wherein .alpha. is the angle of inclination of the air discharge openings to the axis of the fuel nozzle, and

.theta. is the angle of torsion of the air discharge openings to the axis of the fuel nozzle.

The spiral air flows 55 contact the outer periphery of the conical spray 57 of fuel particles at the point the distance h spaced axially downstream from the air discharge openings 20, when equations (3) given below are satisfied:

R.sub.1 = R.sub.2, (dR.sub.1 /dh) = (dR.sub.2 /dh) 3

In the event when the axial position of the air discharge openings 20 are changed with respect to the fuel discharge opening 27, the radius a from the axis 29 of the fuel nozzle is adjusted such that the spiral air flows will not interfere with the conical spray 57 of fuel particles sprayed from the fuel discharge opening 27.

On the contrary, the positions of contact between the spiral air flows 55 and the outer periphery of the conical spray 57 of fuel particles can be optionally changed by selectively changing the angle .alpha. of inclination and angle .theta. torsion of the air discharge openings 20 to the fuel discharge opening 27 which has a specific spray angle.

In formulae (1) and (2), the angle .alpha. of inclination and the angle .theta. of torsion which satisfy equation (3) are subjected to certain limitations in respect of the selectable ranges thereof, for the following reason: namely, when the angle .alpha. of inclination is extremely large or the angle .theta. of torsion is extremely small, the spray angle of the fuel particles 57 becomes undesirably small, with the result that the fuel particles concentrate to the axis 29 of the fuel nozzle and the finely atomized fuel particles join again, forming particles of large diameters. Conversely, when the angle .alpha. of inclination is extremely small, the points of contact between the spiral air flows 55 and the conical spray 57 of the fuel particles move away axially downstream from the air discharge openings 20, so that the velocity energy possessed by the spiral air flows 55 cannot be used effectively for the division of fuel particles into smaller particles. Further, when the angle .theta. of torsion is extremely large, the spiral air flows 55 do not contact the conical spray 57 of fuel particles.

With the spray angle of the fuel discharge opening 27 being 80.degree., a satisfactory result can be obtained when the angle .alpha. of inclination of the air discharge openings 20 is in the range of 30.degree. - 65.degree. and the angle .theta. of torsion thereof in the range of 15.degree. - 50.degree., and the best result can be obtained when the angle .alpha. of inclination is 45.degree. and the angle .theta. of torsion is 25.degree.. Using a fuel nozzle having air discharge openings 20 of which .alpha. = 45.degree. and .theta. = 25.degree., the flow rate distribution and particle size of sprayed fuel were measured at the point of contact between the spiral air flows 55 and the conical spray 57 of fuel particles, namely at a point 140 mm spaced axially downstream from the air discharge openings 20, with the results shown in FIGS. 5 and 6.

FIG. 5 shows the radial distribution of the sprayed fuel particles. It will be seen that, with the fuel nozzle of the invention, the number of fuel particles present in the vicinity of the nozzle axis is larger than with the conventional dual opening type spiral fuel nozzle, and that the number of fuel particles at the portion where the fuel particles concentrate most is only about eight times that at the nozzle axis, with respect to unit area and thus the fuel particles are distributed considerably uniformly.

FIG. 6 shows the particle size distribution of fuel particles in the radial direction. It will be seen that, with the fuel nozzle of this invention, the mean particle size becomes as small as about 230 microns and the particle size difference in the radial direction decreases. Thus, the fuel nozzle of the invention is advantageous in respect of particle size distribution as well as flow rate distribution of sprayed fuel.

The spiral air flows are formed by making use of part of the combustion air passing in the space between the liner 39 defining the combustion chamber and the outer cylinder 35 of the combustion element surrounding said liner 39, to be supplied into said combustion chamber. This part of the combustion air is injected into the combustion chamber from the air discharge openings by virtue of a pressure difference between the interior and exterior of the liner, to form the spiral air flows. Therefore, it is unnecessary to provide an additional compressor which has been required by the conventional air spray type fuel nozzle solely for spraying fuel. With the fuel nozzle of the invention, the atomization of fuel into fine particles is possible, only with the compressor provided for a gas turbine as a combustion air source.

The process in which the fuel is atomized by the fuel nozzle of the invention will be described in greater detail hereunder with reference to FIG. 1. The fuel nozzle of the invention is provided with the air discharge openings 20 each having an angle .alpha. of inclination and an angle .theta. of torsion to the axis of the fuel discharge opening 27 from which the fuel injected in the form of a conical spray having a spray angle .phi.. Now, let it be supposed that the angle of inclination and the angle of torsion to satisfy equations (1) and (2) are x and y respectively, i.e., .alpha. = x and .theta. = y, and the spray angle is .beta., i.e., .phi. = .beta..

The combustion air 51 supplied from the compressor (not shown) of the gas turbine and passing in the passage 26 flows into the combustion chamber 45 from the primary air inlet openings 41, the secondary air inlet openings (not shown) and the louvers 43 formed in the liner 39. In this case, part of the combustion air 51 flows into the passage 23 from the apertures 16 as the air 53 discharged into the combustion chamber 45 from the air discharge openings 20 to form the spiral air flows 55 each having the angle .alpha. of inclination, that is the angle x, and the angle .theta. of torsion, that is the angle y, to the axis 29 of the fuel discharge opening 27. In the conical spray 57 of atomized fuel discharged from the fuel discharge opening 27, the number of fuel particles is small at the portion adjacent the axis 29 and is large at the outer peripheral portion of the conical spray, and the majority of the fuel particles at the outer peripheral portion of the conical spray are large in particle size. The spiral air flows 55 contact the outer periphery of the conical spray 57 of fuel particles at points downstream of the fuel nozzle 11. The large fuel particles present at the outer peripheral portion of the conical spray 57 are further divided by the actions of these spiral air flows 55 into finer particles. The spiral air flows 55 also act to disperse uniformly the fuel particles concentrating to the outer peripheral portion of the conical spray 57. Thus, fine fuel particles and uniform distribution of the fine fuel particles are obtained downstream of the contacts between the conical spray 57 of fuel and the spiral air flows 55, and excess fuel regions are reduced. It is also to be noted that mixing of fuel and air is promoted by the spiral air flows 55. By the action of the spiral air flows 55, the fuel particles are also caused to make a spiral motion, so that the retention time of the fuel particles within the combustion chamber 45 is prolonged and accordingly, the time in which the fuel particles receive heat from the combustion gas formed in said combustion chamber 45 is prolonged, whereby the evaporation of the fuel particles is promoted. As a result, stable combustion is obtained within the combustion chamber 45 and the smoke concentration in the exhaust gas is reduced to an invisible degree.

Part of the air 53 passing in the passage 23 flows into the annular passage 25 formed between the nozzle body 12 and the spiral passage unit 18, at a point upstream of the air discharge openings 20, and discharges along the forward end face of said nozzle body 12 to prevent carbon from attaching to said end face of the nozzle body 12.

In the embodiment described above, the apertures 16 for leading the combustion air 51 into the passage 23 therethrough are formed in the cap 14, it should be understood that these apertures 16 may alternatively be formed in the supporting member 21. In this case, as shown in FIG. 7, the supporting member is provided with a cap mounting portion 61 projecting into the passage 26 through the end plate 37 of the combustion element and a cap 14' is connected to said cap mounting portion 61. The apertures 16 are formed in the cap mounting portion 61 at points upstream of the cap 14', for leading part of the combustion air 51 therethrough into the passage 23. The same effect as has been described above can also be obtained with such construction.

In order to impart the maximum velocity energy to the spiral air flows 55 by taking advantage of the pressure difference between the interior and exterior of the liner 39, it is necessary to locate the air discharge openings 20 as close to the combustion chamber 45 as possible and to make tht total cross sectional area thereof smaller than the total cross sectional area of the passage 23 and the apertures 16. The total cross sectional area of the air discharge openings 20 is preferably 1.0 - 1.5 percent of the total area of the primary air inlet openings 41, the secondary air inlet openings (not shown) and the louvers 43 provided in the liner 39. A larger proportion of the area will result in an instable state of combustion during the transition period from the ignition to the rated output operation phase of the gas turbine. Namely, since the temperature of the combustion air 51 is low during the transition period, supplying an excessively large amount of air from the air discharge openings 20 will promote cooling of the fuel particles sprayed from the fuel discharge opening 27 and retard the evaporation of the fuel particles.

Claims

We claim:

1. A pressure spray type fuel nozzle comprising a fuel discharge opening located at one end of a fuel passage for injecting fuel into a combustion chamber therethrough to form a conical spray of fuel particles, and an air discharge opening provided exteriorly of said fuel passage and adapted to form a spiral air flow within said combustion chamber which contacts from the outside the outer periphery of said conical spray of fuel particles,

in which there are provided a plurality of said air discharge openings which are arranged on a circle concentric with said fuel discharge opening and each of which has an angle of inclination and an angle of torsion to the axis of said fuel discharge opening,

in which with 2 .phi. representing the spray angle of fuel particles discharged from said fuel discharge opening, R.sub.1 = .+-. (h - t) tan .phi. representing the radial distance from the axis of said fuel discharge opening of the fuel particles present at the outer periphery of said conical spray at a point distance h spaced axially downstream from said air discharge openings and R.sub.2 = .+-. .sqroot.(htan.theta.) .sup.2 + (a - htan.alpha.).sup.2 representing the radial distance from the axis of said fuel discharge opening of said spiral air flows at said point, wherein a and t are the radial distance and axial distance of said air discharge openings from the axis of said fuel discharge opening respectively, each of said air discharge openings has an angle .alpha. of inclination and an angle .theta. of torsion to the axis of said fuel discharge opening which satisfy the conditions

R.sub.1 = R.sub.2 and (d.sup.R 1/ dh) = (d.sup.R 2/ dh)

when R.sub.1 and R.sub.2 are both plus or minus values.

2. A pressure spray type fuel nozzle according to claim 1, in which there is provided means for leading to said air discharge opening part of the combustion air passing in a space formed between a liner defining said combustion chamber therein and an outer cylinder of a combustion element surrounding said liner and being supplied into said combustion chamber.

3. A pressure spray fuel type nozzle according to claim 2, comprising a nozzle body having said fuel discharge opening and connected to a supporting member, a cap connected to said supporting member in a manner to surround said nozzle body other than the portion of said fuel discharge opening and to form an annular air passage between it and said nozzle body and formed with apertures for leading said combustion air into said air passage therethrough, and a plurality of said air discharge openings provided at the forward end of said air passage.

4. A pressure spray fuel type nozzle according to claim 2, comprising a nozzle body having said fuel discharge opening and connected to a supporting member, a cap connected to said supporting member in a manner to surround said nozzle body other than the portion of said fuel discharge opening and to form an annular air passage between it and said nozzle body, said supporting member being formed with apertures for leading the combustion air into said annular passage therethrough, and a plurality of said air discharge openings provided at the end of said air passage closer to said fuel discharge opening.

5. A pressure spray type fuel nozzle according to claim 1, comprising a nozzle body having said fuel discharge opening and connected to a supporting member, a cap connected to said supporting member in a manner to surround said nozzle body other than the portion of said fuel discharge opening and to form an annular air passage between it and said nozzle body and formed with apertures for leading said combustion air into said air passage therethrough, and a plurality of said air discharge openings provided at the forward end of said air passage.

6. A pressure spray type fuel nozzle according to claim 1, comprising a nozzle body having said fuel discharge opening and connected to a supporting member, a cap connected to said supporting member in a manner to surround said nozzle body other than the portion of said fuel discharge opening and to form an annular air passage between it and said nozzle body, said supporting member being formed with apertures for leading the combustion air into said annular passage therethrough, and a plurality of said air discharge openings provided at the end of said air passage closer to said fuel discharge opening.