SWIRLER

Abstract

A swirler including a plate normal to a central axis of the swirler, a plurality of vane cross-sections arranged on the plate and radially positioned about the central axis and a plurality of twisted vanes is provided. The twisted part of each vane is twisted around the central axis wherein the cross section of the twisting vane is normal to the central axis. In one aspect, each vane has an essentially triangular cross section.

Description

FIELD OF INVENTION

The invention relates to a fuel injection system and improvements for the further diminishment of air pollutants such as nitrogen oxides (NO_x).

BACKGROUND OF THE INVENTION

Air pollution is a worldwide concern and many countries have enacted stricter laws further limiting the emission of pollutants from gas turbine engines or offer fiscal or other benefits for environmentally sound installations. Although the prior techniques for reducing the emissions of NO_x from gas turbine engines are steps in the right direction, the need for additional improvements remains.

There are two main measures by which reduction of the temperature of the combustion flame can be achieved. The first is to use a fine distribution of fuel in the air, generating a fuel/air mixture with a low fuel fraction. The thermal mass of the excess air present in the reaction zone of a lean premixed combustor absorbs heat and limits the temperature rise of the products of combustion to a level where thermal NO_x is not excessively fowled. The second measure is to provide a thorough mixing of fuel and air prior to combustion. The better the mixing, the fewer regions exist where the fuel concentration is significantly higher than average, the fewer the regions reaching higher temperatures than average, the lower the fraction of thermal NO_x will be.

Usually the premixing of fuel and air in a gas turbine engine takes place by injecting fuel into an air stream in a swirling zone of a combustor which is located upstream from the combustion zone. The swirling produces a mixing of fuel and air before the mixture enters the combustion zone.

SUMMARY OF THE INVENTION

An object of the invention is to provide a swirler, allowing for a better pre-mixing of gaseous fuel and compressor air to provide a homogeneous fuel/air mixture and thereby reduce formation of NO_x. Another objective is to provide a burner with an improved swirler. Still another objective is to provide a gas turbine with an improved swirler.

These objectives are achieved by the claims. The dependent claims describe advantageous developments and modifications of the invention.

An inventive swirler incorporates a modified radial swirler assembly. The modification is best described by a partly twisted radial swirler.

Unlike axial swirlers where the air inflow is predominantly entering the swirler and being deflected by the action of an aerofoil, air is admitted to the swirler over the entire length of the swirl slot or vane section, where it is deflected into a swirling motion.

The added advantage of such a configuration is that the twisted vane ensures that the air entry flow is ‘tumbled’ and hence provides a means for enhanced fuel air mixing.

None of the prior art is targeting the generation of turbulent secondary flows along the swirl vanes with the specific aim of assisting fuel air mixing.

In an advantageous arrangement the twisted vanes comprise straight parts at the base portions of the twisted vanes. This feature provides a well defined shear layer region for any reverse flow into the swirler assembly. This is advantageous because it increases the stability of any flame in that region. The height of the straight parts should not exceed 50% of the twisted vanes' height in order to benefit from the turbulent secondary flows generated in the twisted parts. Therefore it is also advantageous to twist the vanes by an angle of up to 120°. However, twisted vanes with angles differing considerably from 120° will also provide desirable turbulent secondary flows.

By such a design a better pre-mixing of gaseous fuel with compressor air and a homogeneous fuel/air mixture is achieved to reduce formation of NO_x.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a prior art radial swirler,

FIG. 2 shows a perspective view of a swirler in accordance with the present invention, and

FIG. 3 shows another perspective view of a swirler with twisted vanes in accordance with the present invention.

In the drawings like references identify like or equivalent parts.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a typical prior art radial swirler 1 is shown. The turning vanes 9 of a radial swirler 1 are arranged on a first plate 2 that is normal to the central axis 3 of the swirler 1 body. The vanes 9 are of pie slice type with substantially triangular cross-sections 4 (see FIG. 3) and rectangular side faces 13 and a slightly curved outer surface 10. The turning vanes 9 are fixed to a second plate 8 with their sides showing away from the first plate 2. Swirler passages 14 are formed by opposing side faces 13 of swirler vanes 9, by the surface of the first plate 2 and by a surface of the second plate 8. The second plate 8 is connected to a combustion pre-chamber 11.

This configuration of the swirler 1 forces the airflow (as shown by the arrows) to move within the passages 14 radially inwardly towards the central axis 3 of the swirler 1 body. Already with this simple prior art straight vane geometry, a radial swirler 1 is capable of creating strong swirl and thorough mixing with little concern of the problem of aerodynamic wake flows.

FIG. 2 shows the view of an embodiment of the inventive swirler 1. Respective base portions 6 of the turning vanes 9 are arranged on a first plate 2 that is normal to the central axis 3 of the swirler 1 body and the cross-sections 4 (see FIG. 3) of the vanes 9 are of substantially triangular shape. Unlike prior art, the vanes 9 are twisted and will be referred to as twisted vanes 5. The embodiment of FIG. 2 comprises twisted vanes 5 with straight base portions 6 and twisted parts 7. The straight base portions 6 have a shape described by a translation of the vane cross-sections 4 (see FIG. 3) parallel to the central axis 3 of the swirler 1, whereas the twisted parts 7 have a shape described by a further translation of the vane cross-sections 4 along the central axis 3 superimposed by a rotation of the vane cross-sections 4 about the central axis 3.

With reference to FIG. 3, an inventive swirler 1 is shown without second plate 8 and combustor pre-chamber 11 (see FIGS. 1 and 2) where the twisted vanes 5 are arranged on a first plate 2. The substantially triangular vane cross-sections 4 can be seen very clearly in this view. FIG. 3 shows the turbulent secondary flows 12 generated along the twisted vanes 5, improving fuel/air mixing.

Claims

1.-8. (canceled)

9. A swirler, comprising: a first plate normal to a central axis of the swirler;a second plate; anda plurality of vanes arranged between the first plate and the second plate and radially positioned around the central axis,wherein each vane has a straight base portion which is arranged at the first plate, and a twisted part arranged between the straight base portion and the second plate, andwherein the twisted part of each vane is built by twisting the vane around the central axis, andwherein a cross-section of the respective vane is normal to the central axis, over a first height of the respective vane is the same at every height of the respective vane.

10. The swirler as claimed in claim 9, wherein each vane has an essentially triangular cross-section.

11. The swirler as claimed in claim 9, wherein each vane comprises three longitudinal sides extending between the first plate and the second plate.

12. The swirler as claimed in claim 9, wherein an angle of rotation of the twisted part of each vane is less than or equal to 120°.

13. The swirler as claimed in claim 9, wherein a second height of each straight base portion is equal to or less than 50% of the first height of the vane.

14. The swirler as claimed in claim 9, wherein each swirler passage of a plurality of swirler passages are formed by opposing side faces of adjacent vanes, by the first plate, and by the second plate.

15. A burner, comprising: a swirler, comprising: a first plate normal to a central axis of the swirler,a second plate, anda plurality of vanes arranged between the first plate and the second plate and radially positioned around the central axis,wherein each vane has a straight base portion which is arranged at the first plate, and a twisted part arranged between the straight base portion and the second plate, andwherein the twisted part of each vane is built by twisting the vane around the central axis, andwherein a cross-section of the respective vane is normal to the central axis, over a first height of the respective vane is the same at every height of the respective vane.

16. The burner as claimed in claim 15, wherein each vane has an essentially triangular cross-section.

17. The burner as claimed in claim 15, wherein each vane comprises three longitudinal sides extending between the first plate and the second plate.

18. The burner as claimed in claim 15, wherein an angle of rotation of the twisted part of each vane is less than or equal to 120°.

19. The burner as claimed in claim 15, wherein a second height of each straight base portion is equal to or less than 50% of the first height of the vane.

20. The burner as claimed in claim 15, wherein each swirler passage of a plurality of swirler passages are formed by opposing side faces of adjacent vanes, by the first plate, and by the second plate.

21. A turbine engine, comprising: a burner, comprising: a swirler, comprising: a first plate normal to a central axis of the swirler,a second plate, anda plurality of vanes arranged between the first plate and the second plate and radially positioned around the central axis,wherein each vane has a straight base portion which is arranged at the first plate, and a twisted part arranged between the straight base portion and the second plate, andwherein the twisted part of each vane is built by twisting the vane around the central axis, andwherein a cross-section of the respective vane is normal to the central axis, over a first height of the respective vane is the same at every height of the respective vane.

22. The turbine engine as claimed in claim 21, wherein each vane has an essentially triangular cross-section.

23. The turbine engine as claimed in claim 21, wherein each vane comprises three longitudinal sides extending between the first plate and the second plate.

24. The turbine engine as claimed in claim 21, wherein an angle of rotation of the twisted part of each vane is less than or equal to 120°.

25. The turbine engine as claimed in claim 21, wherein a second height of each straight base portion is equal to or less than 50% of the first height of the vane.

26. The turbine engine as claimed in claim 21, wherein each swirler passage of a plurality of swirler passages is formed by opposing side faces of adjacent vanes, by the first plate, and by the second plate.