EP0496016A1 - High pressure spray nozzle - Google Patents

Abstract

For optimum atomisation of liquid materials, a high pressure atomising nozzle is proposed, with a nozzle body (1) in which a turbulence chamber (11) is formed and is connected via a nozzle bore (4) to an external space and has feed channels (8) through which the liquid to be atomised can be fed under pressure. The cross-sectional surfaces of the feed channels (8) opening into the turbulence chamber (11) are larger by a factor of 2-10 than the cross-sectional surface of the nozzle bore (4). In this manner a portion of the pressure available before the nozzle is used to produce a high degree of turbulence in the fluid to be atomised. The production of turbulence is achieved by means of a sudden widening (Carnot diffusor) in the turbulence chamber located before the nozzle hole proper. The resulting spray of droplets is distinguished by its small spreading angle and very small droplet sizes (in the case of atomisation of water </= 20 mu m above pre-pressures >/= 150 bar). <IMAGE>

Description

TECHNICAL AREA

The invention relates to a high-pressure atomizing nozzle, comprising a nozzle body, in which a turbulence chamber is formed, which is connected to an outside space via at least one nozzle bore, and has at least one feed channel for the liquid to be atomized, through which said liquid can be supplied under pressure .

The invention refers to a state of the art, as it results for example from the book "LUEGER - LEXIKON DER ENERGIETECHNIK UND KRAFTMASCHINEN", DVA Stuttgart 1965, p.600, under the keyword "atomizer burner".

TECHNOLOGICAL BACKGROUND AND PRIOR ART

In atomizing burners, the oil that comes to the combustion is mechanically finely divided, ie broken down into small droplets of about 10 to 400 µm in diameter (oil mist), which evaporate and burn in the flame when mixed with the combustion air. In addition to atomizer types such as injection and rotary atomizers, so-called pressure atomizers are used for this. Here, the oil is fed under high pressure to an atomizing nozzle which is attached to a nozzle body by means of a feed pump. The oil enters a swirl chamber via essentially tangential slots or channels and leaves the nozzle via a nozzle bore. Through the tangential Inflow is achieved that the oil particles receive two motion components, an azimuthal and an axial. The fluid rotation in the vortex chamber causes the formation of an air funnel, the tip of which extends into the vortex chamber. The oil film emerging from the nozzle bore as a rotating hollow cylinder expands due to the centrifugal force into a hollow cone, the edges of which become unstable in vibration and tear into small oil droplets. The atomized oil forms a cone with a more or less large opening angle.

• die Tröpfchen müssen sehr klein sein, sodass sie vor der Verbrennung verdampfen können;
• der Oeffnungswinkel (Ausbreitungswinkel) des Oelnebels sollte bei bestimmten Brennertypen, insbesondere bei Verbrennung unter erhöhtem Druck klein sein (z.B. Dieselmotor,Gasturbine;
• die Tropfen müssen eine sehr hohe Geschwindigkeit haben, um (auch unter der z.B. in einer Gasturbinen-Brennkammer um den Faktor 5 erhöhten Dichte) noch weit genug in den Verbrennungsluftstrom eindringen zu können.

The low-emission combustion of mineral fuels in modern burners places special demands on atomization, which are roughly as follows:

• the droplets must be very small so that they can evaporate before combustion;
• the opening angle (angle of spread) of the oil mist should be small for certain types of burners, especially when burning under increased pressure (eg diesel engine, gas turbine;
• the drops must have a very high speed in order to be able to penetrate the combustion air flow far enough (even under the density increased by a factor of 5, for example in a gas turbine combustion chamber).

Swirl nozzles of a known type are less suitable for this because they do not allow small angles of spread.

SUMMARY OF THE INVENTION

The invention is based on the object of specifying a high-pressure atomization nozzle which has a simple construction, very small angle of propagation and optimal beam decay is possible even at comparatively low pressures.

This object is achieved according to the invention in that the cross-sectional area (s) of the feed channel or channels opening into the turbulence chamber is (are) larger by a factor of 2 to 10 than the cross-sectional area of the nozzle bore. For atomizing water with nozzle bores of 0.5 mm, about four times the nozzle outlet area is useful as a turbulence chamber inlet area.

In this way, part of the available nozzle pressure is used to generate high levels of turbulence in the fluid to be atomized. The turbulence is achieved by means of an abrupt expansion (Carnot diffuser) into the turbulence chamber located in front of the actual nozzle hole. The fluid flowing into the turbulence chamber is practically not forced into any tangential velocity components in the turbulence chamber, but is only put into strong turbulence, which is excited by shear forces. The inflow into the turbulence chamber can take place via one or more feed channels, preferably essentially radially to the axis of the nozzle bore, or else axially and coaxially to the nozzle bore. In the limit case, the feed channel is an annular gap. In contrast to the known swirl nozzle, where the drops are formed by the disintegration of a thin liquid film downstream of the nozzle opening, the fuel jet emerging from the nozzle bore also has essentially no tangential speed components which would lead to a conical expansion of the fuel. The consequence of this is that the fluid jet is brought to rapid decay by the turbulence generated in front of the nozzle bore. The resulting drop spray is characterized by small angles of spread and very small drop sizes (in the case of atomization of water ≦ 20µm above admission pressure ≧ 150 bar).

Compared to simple perforated nozzles, jet decay occurs at much lower pressures. Compared to diesel injectors, the turbulence generator in front of the spray hole results in better atomization quality.

Exemplary embodiments of the invention and the advantages which can be achieved thereby are explained in more detail below with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

Fig.1

einen Längsschnitt durch ein erstes Ausführungsbeispiel einer Hochdruckzerstäubungsdüse mit radialer Zuströmung in die Turbulenzkammer;

Fig.2

einen Querschnitt durch die Hochdruckzerstäubungsdüse gemäss Fig.1 längs deren Linie AA;

Fig.2a

einen Querschnitt durch eine Abwandlung von Fig.2 mit Zufuhrkanälen, die als Spalte ausgebildet sind;

Fig.3

ein Diagramm zur Veranschaulichung der Abhängigkeit der Tröpfchengrösse vom Druck einer Hochdruckzerstäubungsdüse gemäss Fig.1 bzw. 2 bei der Zerstäubung von Wasser;

Fig.4

ein Ausführungsbeispiel einer Hochdruckzerstäubungsdüse mit axialer Zuströmung im Längsschnitt;

Fig.5

ein einen Querschnitt durch die Hochdruckzerstäubungsdüse gemäss Fig.4 längs deren Linie BB.

Fig.6

ein Diagramm zur Veranschaulichung der Abhängigkeit der Tröpfchengrösse vom Druck einer Hochdruckzerstäubungsdüse gemäss Fig.4 bzw. 5 bei der Zerstäubung von Wasser.

Exemplary embodiments of the invention are shown schematically in the drawing, namely:

Fig. 1

a longitudinal section through a first embodiment of a high pressure atomization nozzle with radial inflow into the turbulence chamber;

Fig. 2

a cross section through the high pressure atomization nozzle according to Figure 1 along the line AA;

Fig.2a

a cross section through a modification of Figure 2 with feed channels which are formed as a column;

Fig. 3

a diagram illustrating the dependence of the droplet size on the pressure of a high-pressure atomizing nozzle according to Figure 1 or 2 when atomizing water;

Fig. 4

an embodiment of a high pressure atomization nozzle with axial inflow in longitudinal section;

Fig. 5

a cross section through the high pressure atomization nozzle according to Figure 4 along the line BB.

Fig. 6

a diagram illustrating the dependence of the droplet size on the pressure of a high pressure atomization nozzle according to Fig. 4 or 5 when atomizing water.

WAYS OF CARRYING OUT THE INVENTION

The high-pressure atomization nozzle according to FIG. 1 comprises a nozzle body 1, consisting of a tube 2, which is closed at the bottom by a conical cover 3. In the middle of the cover 3 there is a nozzle bore 4, the longitudinal axis of which is designated 5. In the tube 2, a second tube 6 is inserted, which reaches up to the cover 3 and rests on it. The annular space 7 between the tubes 2 and 6 serves to supply the fluid (water, liquid fuel). The end of the tube 6 resting on the cover 3 is provided with four radial slots 8, the longitudinal axes of which are designated by 9. The four longitudinal axes 9 of the slots 8 intersect with the longitudinal axis 5 of the nozzle bore 4. In the interior of the second tube 6, a filler piece 10 is inserted and fastened therein. This filler 10 is spaced from the upper edge of the slots 8. In this way, a space 11 is formed between the cover 3 and the filler 10, which serves as a turbulence chamber.

The fluid to be atomized passes under pressure via the annular space 7 through the slots 8 into the turbulence chamber 11. The jets - four in the case of the example - enter the turbulence chamber 11 essentially radially and produce by the intensive shear and by their deflection in the axial direction and by the collision of the rays a very high level of turbulence. This high level of turbulence does not subside on the short path to the point where it emerges from the nozzle. The liquid jet is brought to rapid decay by the turbulence generated in front of the nozzle bore 4 (after leaving the nozzle bore 4), with angles of propagation of 20 ° and less resulting in the exterior. The cross section of the nozzle and the slots 8 results from the desired throughput (depending on the admission pressure) taking into account sufficiently high Reynolds numbers in the nozzle bore 4 and the slots 8.

Die erfindungsgemässe Hochdruckzerstäubungsdüse kann abweichend vom dargestellten Ausführungsbeispiel auch mit weniger oder mehr Schlitzen 8 versehen sein, oder die Schlitze können sich, wie es in Fig.2a veranschaulicht ist, über nahezu den gesamten Umfang des inneren Rohres 6 erstrecken. Die einzelnen Zuführungskanäle 8 sind dann nur noch durch schmale Stege 8a, die als Distanzierung des Rohres 6 vom Deckel 3 dienen, voneinander getrennt Im Grenzfall unendlich vieler Schlitze ergibt sich ein Ringspalt als Zuströmkanal in die Turbulenzkammer 11.The diagram shown in Figure 3 illustrates the dependence of the droplet diameter d _T on the form p for different limit diameters of the drop mass distribution Q₃, measured at a distance of about 200 mm from the nozzle. D _X denotes, for example, the limit diameter that X mass% of all particles fall below. D _S denotes the Sauter diameter. The high pressure atomization nozzle on which the diagram is based was charged with water and had the following essential parameters (see Fig. 1):

${\text{d}}_{\text{L}}{\text{= 0.3 mm, i.e.}}_{\text{t}}{\text{= 0.5 mm, h}}_{\text{t}}{\text{= 0.3 mm, i.e.}}_{\text{K}}\text{= 2 mm}$

In contrast to the exemplary embodiment shown, the high-pressure atomization nozzle according to the invention can also be provided with fewer or more slits 8, or the slits can extend over almost the entire circumference of the inner tube 6, as illustrated in FIG. The individual feed channels 8 are then separated from one another only by narrow webs 8a, which serve as a spacing of the tube 6 from the cover 3. In the limit case of an infinite number of slots, an annular gap results as an inflow channel into the turbulence chamber 11.

Even with a single radially extending slot 8, the desired effect of extremely high turbulence formation in the turbulence chamber 11 results.

Instead of a radial inflow into the turbulence chamber 11 according to FIGS. 1 and 2, the desired turbulence can also be achieved by an axial inflow, as the embodiment according to FIGS. 4 and 5 shows. There, a metallic insert 13 is soldered into a tube 12, which seals the tube 12 to the right. The interior 14 of the tube serves to supply the fuel. A blind hole 15 is incorporated in the insert 13, which is connected via a radially running bore 16 to a recess 17 in the form of a cylindrical section in the metallic insert 13. This recess 17 forms the turbulence chamber and corresponds to the space 11 in FIG. 1, while the bore 16 corresponds to the slots 8 in FIG. The tube 12 is provided with a nozzle bore 18 coaxial with the bore 16. The longitudinal axis of the nozzle bore 18 is designated 19, the longitudinal axis of the bore 16 is designated 20. Both axes 19 and 20 coincide. Although in the embodiment of a high-pressure atomization nozzle according to FIGS. 4 and 5 there is no deflection of the liquid jet flowing into the turbulence chamber 17, the inflow into the "cavity" (turbulence chamber 17) alone generates a sufficiently high level of turbulence, which continues in the nozzle bore 18 and that Fluid in the outside space decays. This also makes it possible to achieve an angle of spread of the drop spray of 20 ° and less in the exterior.

The diagram according to FIG. 6 illustrates the dependence of the droplet radius d _T on the admission pressure p for different and at the same time gives an impression of the comparatively small dependence of the droplet radius d _T on the nozzle diameter d _L compared to FIG. As in the diagram according to FIG. 3, D _X denotes the limit diameter that X mass% of all particles fall below. D _S denotes the Sauter diameter.

The high pressure atomizing nozzle on which the diagram is based was charged with water and had the following key parameters: Diameter of the nozzle bore d _L : 0.12 mm Length of the nozzle bore = wall thickness of the tube 12: 0.35 mm Volume of the turbulence chamber: about 0.4 mm³ Bore 16 diameter: 0.3 mm

Claims (7)

High-pressure atomizing nozzle, comprising a nozzle body (1; 12), in which a turbulence chamber (11; 17) is formed, which communicates with an outside space via at least one nozzle bore (4; 18), and at least one supply channel (8; 16) for the liquid to be atomized, through which said liquid can be fed under pressure, characterized in that the cross-sectional area (s) of the feed channel or feed channels (8; 8a; 16) opening into the turbulence chamber (11; 17) around the Factor 2 to 10 is (are) larger than the cross-sectional area of the nozzle bore (4). High-pressure atomizing nozzle according to claim 1, characterized in that the nozzle bore (4) is arranged in the cover (3) of a first tube (2), in which a second tube (6) of smaller outside diameter is inserted, which extends to the said cover (3) , and that at least one radially extending slot (8, 8 a) is provided in the end of the second tube, which connects the annular space (7) between the first and the second tube with a turbulence chamber (11), from which turbulence chamber the nozzle bore (4 ) leads into the outside area. High-pressure atomizing nozzle according to claim 1, characterized in that the nozzle bore (4) is arranged in the cover (3) of a first tube (2), into which a second tube (6) of smaller outside diameter is inserted, which leaves an annular gap up to the said cover (3) is sufficient, which annular gap the annular space (7) between the first and the second tube with one Turbulence chamber (11) connects from which turbulence chamber the nozzle bore (4) leads into the outside space. High-pressure atomizing nozzle according to claim 2 or 3, characterized in that the turbulence chamber (11) essentially limited by said cover (3) and by a filler (10) in the second tube (6) and optionally laterally by the protruding from the filler (10) End of the second tube (6) is limited. High-pressure atomizing nozzle according to claim 1, characterized in that the nozzle bore is designed as a radial bore (16) in the wall of a tube (12), in which tube a metallic insert (13) is fastened, that in this insert a recess in the region of the nozzle bore (17) is designed as a turbulence chamber which is connected to the interior of said tube (12) via a bore (16) running radially in the insert (13) and an axially extending bore (15) adjoining it, the axes of the Bore (16) in the insert (13) and the bore in the tube (12) run approximately parallel or collapse in the limit case. High-pressure atomizing nozzle according to claim 4, characterized in that said recess in the insert (13) has the shape of a cylinder section which is incorporated in the insert from the outside. High-pressure atomizing nozzle according to one of claims 1 to 6, characterized in that the axis (s) (9; 20) of the feed channel (8; 16) or the feed channels intersect the axis (5; 19) of the nozzle bore (4; 18) or in the borderline case coincide with the latter.

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