GB2252400A

GB2252400A - Air swirl generator

Info

Publication number: GB2252400A
Application number: GB9101849A
Authority: GB
Inventors: Shyh-Ching Yang
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 1991-01-29
Filing date: 1991-01-29
Publication date: 1992-08-05
Anticipated expiration: 2011-01-29
Also published as: GB9101849D0; GB2252400B

Abstract

An air swirl generator for a combustion chamber comprises a series of parallel overlapping axial curved blades 14 extending from an inner cylinder 1 with a closed end to adjacent a co-axial outer cylinder 2 with a divergent quarl 3 connection to the combustion chamber. A method of determining the shape of each blade 14 is set out. <IMAGE>

Description

A SWIRL GENERATOR WITH AXIAL VANES The present invention relates generally to a swirl generator, and particularly to a swirl generator with improved axial vanes.

A burner is one of the most important parts in a combustion system. The performance of the burner not only greatly influences the combustion efficiency but also closely relates to the stability of combustion flame, the effective utilization of the fuel, and the discharge of pollutants. Improper combustion technology and improper selection of burners not only influences the effective use of energy, but also results in air pollution due to emission of large amount of hazardous matters .such as NOx on account of undue combustion.

A conventional burner usually feeds air into the combustion chamber by means of a fan or a compressor having blades of fixed radial type to mix the air with the fuel for burning. However, it is found that the performance of the burner will become very poor if the pressure drop is too large and the turbulence intensity is too high when the air flows through the blades of fixed radial type in the conventional burner for forming swirling flow which is required for combustion.

In order to improve the performance of the burner by decreasing the amount of NOx formed in the combustion process and increasing the stability of the combustion flame, it is necessary to reduce the peak temperature of the flame and the residence time of combustion gas, and to form local fuel-rich combustion.

It is therefore a primary purpose of this invention to provide a swirl generator, for the burner, adapted to produce a swirling flow having low pressure drop and low turbulence intensity, and being capable of controlling local fuel-rich combustion, lowering the peak temperature of combustion flame, controlling the residence time of combustion gas, and improving combustion flame stability.

In accordance with this invention, a swirl generator, adapted to produce swirling air flow required for a combustion chamber, comprises a hollow cylinder having an outer radius Ri and including a flat bluff body at one end, a hollow cylindrical casing having an inner radius R2 and coaxially sleeved around the cylinder and connecting with the combustion chamber through a divergent quarl, and a plurality of axial vanes formed in parallel with each other along the periphery of the cylinder and overlapping each other, each axial vane including a diametrically inner edge fixed to the outer periphery of the cylinder and a diametrically outer edge closely adjacent to the inner periphery of the casing, each axial vane axially extending from an upstream end, including a first point P1 at the inner edge and a second point P2 at the outer edge, through a curved surface to a downstream end, the curved surface having a radius of curvature ri along the inner edge thereof and a radius of curvature r2 along the outer edge thereof, the shape of each axial vane being determined as follows: (A). Determining the values for Ri and R2 according to the desired fuel and air flow rate; (B). Determining a proper radius of curvature ri for the inner edge of the axial vane, and calculating the radius of curvature r2 for the outer edge of the axial vane according to the below formula: r2 = rl* (R2/R1) (C). Determining the outlet angle 9 of the axial vane according to the required swirl number S; (D).Taking a first reference plane tangent to the outer periphery of the cylinder at the first point, and a second reference plane parallel to the first reference plane and including the second point, (E). Equally dividing the curved surface of the axial vane into N consecutive parts, each subtending an angle i/N with respect to the curvature center thereof and having a length H1 at the inner edge thereof and a length H2 at the outer edge thereof, then H1 = 2r1* sin(i/2N) H2 = 2r2* sin(i/2N) (F).Denoting the distance of the inner edge of the n-th part of the axial vane from the first reference plane by Dln, and the distance of the outer edge of the n-th part of the axial vane from the second reference plane by D2n, and calculating Dln and D2n as follows:

(G). Defining the positions of the N consecutive points on the developed inner edge of the axial vane by taking n * H1 and R1-Dln ( n=1, 2, 3, ---11) as abacissas and ordinates, respectively, and defining the positions of the N consecutive points on the developed outer edge of the axial vane by taking n * H2 and R2-D2n ( n=1, 2, 3, ---11) as abacissas and ordinates, respectively; (H).Forming the thus obtained developed shape of the axial vane into a final shape in which the radii of curvature at its inner and outer edges conform to the predetermined values Ri and R2.

The present invention can be more fully understood by reference to the following description and accompanying drawings, which form an integral part of this invention: Fig. 1 is a fragmentary sectional view schematically showing part of the swirl generator in accordance with the present invention; Fig. 2 is a fragmentary perspective view showing the construction of the main portion of the swirl generator illustrated in Fig. 1, including a cylinder and a plurality of axial vanes formed thereon; Fig. 3 is an end view of portion of swirl generator shown in Fig. 2; Fig. 4 is a fragmentary perspective view schematically showing the geometric shape of a axial vane on the periphery of the cylinder and three reference planes for analysis purpose;; Fig. 5 is a perspective view showing the contours of the diametrically outer and inner edges of a axial vane developed, respectively, on two of the references planes illustrated in Fig. 4; -Fig. 6 is a plan view for analyzing the geometric shape of the inner edge of a axial vane developed on a reference plane; Fig. 7 is a view for analyzing the geometric shape of the inner edge of a axial vane by observing the projection of its dividing points on a cross-sectional plane of the cylinder; Fig. 8 is a view showing an example of the shape of a developed axial vane obtained by calculation.

As can be seen from Figs. 1 to 3, in accordance with this invention, a swirl generator adapted to produce swirling air flow required for a combustion chamber (not shown), comprises a hollow cylinder 1 having an outer radius R1 and including a flat bluff body 1A at one end, a hollow cylindrical casing 2 having an inner radius R2 and coaxially sleeved around the cylinder 1 and connecting with the combustion chamber through a divergent quarl 3, and a plurality of axial vanes 10 formed in parallel with each other on the periphery of the cylinder 1 and overlapping each other ( see Figs. 2 and 3).

Referring now to Fig. 2 or 4, each axial vane 10 includes a diametrically inner edge 11 fixed to the outer periphery of the cylinder 1 and a diametrically outer edge 12 closely adjacent to the inner periphery of the casing 2 (see also Fig. 1). Each axial vane 10 axially extends from an upstream end 13, including a first point P1 at inner edge and a second point P2 at outer edge, through a curved surface 14 to a downstream end 15.

For facilitating further explanation of the geometric shape of the axial vane 10, it is convenient to take (see Fig. 4) a first reference plane Qi tangent to the outer periphery of the cylinder 1 at the first point Pi, a second reference plane Q2 parallel to the first reference plane Q1 and including the second point P2, and a third reference plane Q3 including the axis S-S of the cylinder 1 and perpendicular to the first reference plane Qi.

In Fig. 5, the inner edge of the curved surface 14 (see also Fig. 4) is developed, on the first reference plane Qi, into a circular curve 11' having a radius of curvature ri. Similarly, the outer edge of the curved surface 14 is developed, on reference planes Q2 , into a circular curve 12' having a radius of curvature r2 . In order to obtain the same exit angle o( at the inner and outer edges of the axial vane, r2 and ri must be related as follows: r2 = ri* (R2/R1) --------- (1) Suppose we equally divide the curved surface 14 of the axial vane 10 into N consecutive parts to facilitate the description of its geometric shape.The shape of the developed inner edge 11' will now be analyzed by referring to Fig. 6 which shows the plan view of the developed inner edge 11' of the axial vane divided into N consecutive parts at E1 1 E2 , E3 ---, En-i, En ---. As shown in Fig. 6, the N consecutive parts of the developed inner edge 11' have lengths denoted by H11, H12 , H13, , H1n , ---, respectively, ( H11= H12 = H13 = --- = H1n = --- =H1), and subtends an angle denoted by #α1, #α2, #α3,-- #αn,--, respectively, (#α1 = #α2 = #α3 = --- = #α@= α/N), with respect to the curvature center 0 thereof.

Similarly, though not shown, the N consecutive parts of the developed outer edge 12' have lengths denoted by H21, H22, H23, --, H2n, --, respectively, (H21= H22 = H23 = --- = H2n = --- =H2), and subtends an angle denoted by α/N with respect to the curvature center thereof.If we take an N large enough and refer to Fig. 6, Hln can be expressed by the below formula: H1n = 2r1* sin(#αn/2) = 2r1*sin(α/2N)-------(2) Similarly, H2n can be expressed by the below formula: H2n = 2rz* sin(α/2N) ------------------------(3) Now, if we denote the components1 in the direction perpendicular to reference plane Q3 or in the direction of line OP1 , of the distance of each pair of adjacent dividing points on the developed inner edge 11' by Y11, Y12 , Y13 , ---, Y1n , ---, then Y1n can be expressed as follows::

Now, referring to Figs. 7 and 6, and denoting the distance of the n-th dividing point of the developed inner edge 11' from the first reference plane Q1 by Dln, and the distance of the same n-th dividing point from the third reference plane Q3 by Tln, then we can express them by:

and thus

Similarly, if we denote the distance of the n-th dividing point of the developed outer edge 12 2 from the second reference plane Q2 by D2n, and the distance of the same n-th dividing point from the third reference plane Q3 by T2n, then we can express these two distances by:

and

In fact the required geometric shape of the axial vane is decided by the following steps: (A).Deciding Ri and g2 according to the desired fuel and air flow rate and also the design of fuel gun, of which the outer diameter is R1; (B). Deciding outlet angle of the axial vane according to the required swirl number S; (C). Deciding a proper N so as to make sufficiently small which makes the geometrical shape of the axial vane smooth enough; (D). Deciding a proper radius of curvature ri for the inner edge of the axial vane, and calculating the radius of curvature r2 for the outer edge according to formula ( 1 ); (E). Calculating D1n , D2n for n = 1, 2, 3, ---, N so as to decide the geometrical shape of the whole axial vane.

Now taking, for an example, the values for h , 2, and R2 as 75mm, 150mm, 48mm, and 94mm, respectively, and the values for α and #α@as 59 and 5 , respectively, and calculating the values of Dln, D2n for n = 1, 2, 3, ---, 11 by using the above formulas, we obtain:: H1 =6. 6 H2 = 12.8 D11 = 0.003 D21 = 0.008 D12 = 0.03 D22 = 0.07 D13 = 0.12 D23 = 0.29 D14 = 0.33 D24 = 0.82 D15 = 0.74 D25 = 1.83 D16 = 1.44 D26 = 3.6 D17 = 2.54 D27 = 6.36 Dis = 4.20 D28 = 10.6 D19 = 6.60 D29 = 16.9 Duo 9.90 D210= 26.6 D111= 14.7 D211= 43.1 Taking Hli = n * H1 and R1-D1n ( n=1, 2, 3, ---11) as abacissas and ordinates, the curve for the developed inner edge is drawn in Fig. 8. Similarly, taking H21=n* H2 and R2-D2n ( n=1, 2, 3, ---11) as abacissas and ordinates, the curve for the developed outer edge is also drawn in the same Fig. The thus obtained developed shape of the axial vane must be further formed into the-desired shape so that the radii of curvature at its inner and outer edges conform to the predetermined values.

Claims

1. A swirl generator adapted to produce swirling air flow required for a combustion chamber, comprising a hollow cylinder having an outer radius Ri and including a flat bluff body at one end, a hollow cylindrical casing having an inner radius Rz and coaxially sleeved around the cylinder and connecting with the combustion chamber through a divergent quarl, and a plurality of axial vanes formed in parallel with each other along the periphery of the cylinder and overlapping each other, each axial vane including a diametrically inner edge fixed to the outer periphery of the cylinder and a diametrically outer edge closely adjacent to the inner periphery of the casing, each axial vane axially extending from an upstream end, including a first point P1 at the inner edge and a second point P2 at the outer edge, through a curved surface to a downstream end, the curved surface having a radius of curvature ri along the inner edge thereof and a radius of curvature r2 along the outer edge thereof, the shape of each axial vane being determined as follows: (A). Determining the values for R1 and R2 according to the desired fuel and air flow rate; (B). Determining a proper radius of curvature ri for the inner edge of the axial vane, and calculating the radius of curvature r2 for the outer edge of the axial vane according to the below formula: rz. = ri* (R2/R1) (C). Determining the outlet angle of the axial vane according to the required swirl number S; (D).Taking a first reference plane tangent to the outer periphery of the cylinder at the first point', and a second reference plane parallel to the first reference plane and including the second point1 (E). Equally dividing the curved surface of the axial vane into N consecutive parts, each subtending an angle /N with respect to the curvature center thereof and having a length H1 at the inner edge thereof and a length H2 at the outer edge thereof, then H1 = 2ri* sin(α/2N) H2 = 2r* sin(α/2N) (F).Denoting the distance of the inner edge of the n-th part of the axial vane from the first reference plane by Dln, and the distance of the outer edge of the n-th part of the axial vane from the second reference plane by D2n, and calculating Dln and D2n as follows:

(G). Defining the positions of the N consecutive points on the developed inner edge of the axial vane by taking n * H1 and R1-D1n ( n=l, 2, 3, ---N) as abacissas and ordinates, respectively, and defining the positions of the N consecutive points on the developed outer edge of the axial vane by taking n * H2 and R2-D2n ( n=1, 2, 3, --- N ) as abacissas and ordinates, respectively; (H). Forming the thus obtained developed shape of the axial vane into a final shape in which the radii of curvature at its inner and outer edges conform to the predetermined values Ri and R2.

2. A swirl generator as claimed in claim 1, wherein each pair of adjacent axial vanes overlap each other by an overlapping angle of about 20 to about 45 in a plane formed by developing the outer periphery of the cylinder.

3. A swirl generator as claimed in claim 2, wherein the overlapping angle is about 30 .

4. A swirl generator substantially as hereinbefore described with reference to Figures 1 through 8.