ATOMIZER FOR GAS TURBINE ENGINE

Abstract

An atomizer provides a high-quality fuel-air mixture to a gas turbine engine, by combining air input from an engine compressor and fuel input from a single low-pressure fuel supply pump. The atomizer includes an atomizer body, a main vortex chamber, a secondary vortex chamber for improving quality of the fuel-air mixture, and a fuel sleeve providing fuel to the secondary vortex chamber. The main vortex chamber includes a main outlet nozzle in fluid communication with a combustion chamber inlet of the gas turbine engine. The secondary vortex chamber includes a secondary outlet nozzle in fluid communication with the main vortex chamber. The fuel sleeve has a blind channel with a longitudinal axis and a fuel tip. The same atomizer may be used for startup mode and for all operational modes of the gas turbine engine.

Claims

1. An atomizer providing atomization of a fuel-air mixture flowing into a gas turbine engine, the atomizer receiving air input from an engine compressor and fuel input from a low-pressure fuel supply pump, the atomizer comprising an atomizer body, a main vortex chamber comprising a main outlet nozzle in fluid communication with a combustion chamber inlet of the gas turbine engine; a secondary vortex chamber for improving an atomization quality of the fuel-air-mixture, the secondary vortex chamber comprising a secondary outlet nozzle in fluid communication with the main vortex chamber; and a fuel sleeve providing fuel to the secondary vortex chamber, the fuel sleeve comprising a blind channel with a longitudinal axis and a fuel tip.

2. The atomizer of claim 1 further configured to provide an atomized fuel-air mixture to the gas turbine engine, both for engine startup and for all operational modes of the engine.

3. The atomizer of claim 1 wherein the main vortex chamber comprises one or more tangential channels.

4. The atomizer of claim 1 wherein the secondary vortex chamber comprises one or more tangential orifices.

5. The atomizer of claim 1 wherein the fuel sleeve further comprises at least one radial orifice and/or at least one fuel nozzle.

6. The atomizer of claim 1 wherein the secondary vortex chamber and the fuel sleeve are coaxial.

7. The atomizer of claim 1 wherein a position of the main and secondary vortex chambers with respect to the fuel sleeve is fixed by a threaded nut.

8. The atomizer of claim 1 comprising an air cavity and grooves on a surface of the main vortex chamber which supply air to the air cavity.

9. The atomizer of claim 1 further comprising an airflow tip and/or an air collector.

10. The atomizer of claim 1 wherein a ratio of a mass flow rate of the air input to a mass flow rate of the fuel input has a value in a range of two to six.

11. The atomizer of claim 1 wherein an atomization quality, as determined by a distribution of fuel droplet diameters in the fuel-air mixture, is substantially the same for engine startup and for all operational modes of the engine.

12. The atomizer of claim 1 wherein a ratio of a secondary outlet nozzle outer radius (r.sub.b.sup.a) to a main output nozzle radius (r.sub.n) is greater than or equal to the square root of a nozzle threshold parameter (1−φ).

13. The atomizer of claim 1 wherein a ratio of a fuel sleeve outer radius (r.sub.b) to a secondary outlet nozzle radius (r.sub.n.sup.a) is greater than or equal to the square root of a nozzle threshold parameter (1−φ).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention is described herein, by way of example only, with reference to the accompanying drawings, wherein:

[0035] FIG. 1 is a conceptual drawing of air and fuel flow into an atomizer, according to the principles of the present invention;

[0036] FIG. 2 is a cross-sectional drawing of an atomizer according to an embodiment of the present invention;

[0037] FIG. 3A, FIG. 3B, and FIG. 3C are cross-sectional drawings of the main vortex chamber of the atomizer embodiment of FIG. 2;

[0038] FIG. 4A and FIG. 4B are cross-sectional drawings of the secondary vortex chamber of the atomizer embodiment of FIG. 2;

[0039] FIG. 5A and FIG. 5B are cross-sectional drawings of two alternative embodiments of a fuel sleeve of the atomizer, according to the principles of the invention; and

[0040] FIG. 6A and FIG. 6B are exemplary histograms of particle diameter distributions for air-water mixtures produced by a prototype atomizer according to the principles of the invention.

DETAILED DESCRIPTION

[0041] The invention is an atomizer for providing a high-quality fuel-air mixture to a gas turbine engine, for use during engine start-up and during all operational modes of the engine. The principles and practical use of the invention may be better understood with reference to the drawings and the accompanying description.

[0042] FIG. 1 shows a conceptual drawing of air and fuel flow into an atomizer 100, according to the principles of the present invention. Fuel enters atomizer 100 via fuel line 103 which receives fuel from a fuel supply pump, which provides fuel at a low pressure, for example in a pressure range of 2 to 10 bar. Air enters atomizer 100 via air line 102, which receives air from a compressor of the gas turbine engine (not shown). The arrows indicate the direction of airflow. The atomizer 100 mixes air and fuel to form a fuel-air mixture which flows in the axial Z-direction into a combustion chamber of the engine. Typically, the ratio of air mass flow rate to fuel mass flow rate is in a range of two to six.

[0043] FIG. 2 shows a cross-sectional drawing of atomizer 100 according to an embodiment of the present invention. Two-phase fuel-air mixtures are formed in a main vortex chamber 105 having a main outlet nozzle 114 and in a secondary vortex chamber 108 having a secondary outlet nozzle 119, respectively. Both outlet nozzles provide fuel-air mixtures which flow into a combustion chamber of the turbine engine.

[0044] An airflow tip 107 introduces an airflow which passes through an opening in atomizer body 104 and into the main and secondary vortex chambers. Air enters into main vortex chamber 105 through tangential channels 106 and into secondary vortex chamber 108 through tangential orifices 109. The positions of the two vortex chambers are fixed relative to the atomizer body 104 by means of compressive force applied to sealing rings 113 and 110.

[0045] A fuel sleeve 112 receives fuel from fuel line 103 (shown in FIG. 1) and supplies it to the secondary vortex chamber. The fuel sleeve 112 contains a blind channel 120, having a longitudinal axis 120A, and a fuel tip 122. The fuel sleeve is held in place by a threaded nut 111. In the exemplary embodiment of FIG. 2, the fuel sleeve 112 and the secondary vortex chamber 108 are coaxial.

[0046] Air collector 115 supplies air to tangential channels 106. Grooves 116 on the surface of the main vortex chamber, on the side facing the threaded nut 111, supply air to air cavity 117, which is located between the main vortex chamber 105 and the threaded nut 111. Air cavity 117 is sealed by O-ring 118.

[0047] FIGS. 3A, 3B, and 3C show exemplary cross-sectional drawings of the main vortex chamber of the atomizer shown in FIG. 2, together with relevant geometric parameters. The main outlet nozzle 114 of the main vortex chamber 105 provides outflow of the fuel-air mixture into a premix zone of the combustion chamber. FIG. 3A shows a detail of the main outlet nozzle 114; FIG. 3B shows a detail of the tangential channels 106; and FIG. 3C shows a detail of the grooves 116.

[0048] FIGS. 4A and 4B show exemplary cross-sectional drawings of the secondary vortex chamber 108 of the atomizer shown in FIG. 2, together with relevant geometric parameters. FIG. 4A shows a detail of the secondary outlet nozzle 119 in the secondary vortex chamber 108; and FIG. 4B shows a detail of tangential orifices 109.

[0049] FIGS. 5A and 5B show exemplary cross-sectional drawings of two alternative embodiments of the fuel sleeve, denoted 112A and 112B, together with relevant geometric parameters. In FIG. 112A, fuel tip 122 contains radial orifices 121 through which fuel flows to the secondary vortex chamber 108. In the embodiment of FIG. 5B, fuel nozzles 123 are added in order to prevent clogging under conditions of low fuel flow.

[0050] The maximum ratio between tangential and axial components of the air velocity leaving the vortex chambers is determined by the geometric parameters R, r.sub.n, r.sub.t, L.sub.n, L.sub.t of the main vortex chamber 105, as defined in FIGS. 3A and 3B, and by the geometric parameters R.sub.a, r.sub.n.sup.a, r.sub.t.sup.a, L.sub.n.sup.a, L.sub.t.sup.a for the secondary vortex chamber 108, as defined in FIGS. 4A and 4B. All of the abovementioned geometric parameters have units of length.

[0051] In order to relate the parameters of the main vortex chamber 105 to those of the secondary vortex chamber 108 and of the fuel sleeve 112, it is useful to define three dimensionless parameters—A, A.sub.a and φ—by the equations:

[00001]$\begin{array}{cc}A=\frac{R.Math.r_n}{n.Math.r_t^2}& \left(\mathrm{Equation}1\right)\end{array}$$\begin{array}{cc}{A}_a=\frac{R_a.Math.r_n^a}{{n\left(r_t^a\right)}^2}& \left(\mathrm{Equation}2\right)\end{array}$$\begin{array}{cc}{A}_a=\frac{\sqrt{2}}{\phi \sqrt{\phi }}\left(1-\phi \right)& \left(\mathrm{Equation}3\right)\end{array}$

The radius (r.sub.v) at which the tangential velocity of the swirling vortex flow reaches its maximum value is then determined by:

[00002]$\begin{array}{cc}\frac{r_v^2}{r_n^2}=1-\phi .& \left(\mathrm{Equation}4\right)\end{array}$

The number (n) of tangential channels 106 (and of tangential orifices 109) appearing in equations 1 and 2, is typically in a range of 4 to 8. The geometric parameters (A) and (A.sub.a) determine the ratio of tangential and axial flow velocities in the main and secondary output nozzles; their empirical values are typically in a range of 3 to 6. Equations 1-4 are a consequence of maximizing flow through a cylindrical chamber, for fluid flow in a swirling vortex regime. For any given value of A.sub.a, the value of φ is found by solving equation 3, and the value of r.sub.v is then found by solving equation 4. Henceforth, the parameter (1−φ) will be referred to as a “nozzle threshold parameter”.

[0052] To optimize the tangential air flow velocity in the main and secondary vortex chambers, and thereby to improve the atomization quality, the atomizer geometric parameters typically satisfy the following relationships: [0053] a) the outlet nozzle length-to-radius ratio, equal to L.sub.n/r.sub.n for the main outlet nozzle and to L.sub.n.sup.a/r.sub.n.sup.a for the secondary outlet nozzle, is in a range of 1 to 2; [0054] b) the tangential length-to-radius ratio, equal to L.sub.t/r.sub.t, for the tangential channels 106 of the main vortex channel and equal to L.sub.t.sup.a/r.sub.t.sup.a for the tangential orifices 109 of the secondary vortex channel, is greater than or equal to 1.5; [0055] c) the outlet nozzle transition ratio, equal to r.sub.f/r.sub.n for the main outlet nozzle and to r.sub.f.sup.a/r.sub.n.sup.a for the secondary outlet nozzle, is in a range of 0.2 to 0.3. [0056] d) the ratio of the secondary outlet nozzle outer radius, r.sub.b.sup.a, to the main output nozzle radius, r.sub.n, is greater than or equal to the square root of the nozzle threshold parameter, 1−ϕ; and [0057] e) the ratio of the fuel sleeve outer radius, r.sub.b, to the secondary outlet nozzle radius, r.sub.n.sup.a, is greater than or equal to the square root of the nozzle threshold parameter, 1−φ.

[0058] As a consequence of angular momentum conservation, the tangential velocity of air in the secondary vortex chamber increases with decreasing radius, and reaches its maximum value at a radius equal to the fuel sleeve outer radius, r.sub.b. The outflow is confined to an annular ring, limited by the radius r.sub.n.sup.a and the radius at which the pressure is equal to the pressure in the combustion chamber.

[0059] The value of the pressure drop on the radial orifices 121 of the fuel sleeve is just large enough to enable fuel to exit from the fuel chamber and enter into the secondary vortex chamber. This permits the radial orifices 121 to be large enough to prevent them from becoming contaminated.

[0060] In FIG. 5B, the installation of fuel nozzles 123 into channel 120 causes a decrease in the pressure drop across radial orifices 121, and an increase in the radial orifice diameters at low fuel consumption. It should be noted that the increase in orifice diameter is facilitated by the outflow of fuel into the secondary vortex chamber, where the presence of airflow having a high tangential velocity reduces the flow rate coefficient. The low pressure of the fuel supply at engine startup ensures that the atomizer only requires a single fuel supply pump for both engine startup and for all operational modes, a fact which greatly simplifies engine operation.

[0061] FIG. 6A and FIG. 6B show exemplary histograms of particle diameter distributions of air-fluid mixtures produced in a prototype atomizer constructed according to the principles of the present invention. In the prototype, the fluid used is water instead of fuel. The following table lists the values of the air pressure (P.sub.air), the air mass flow rate (m.sub.air), the fluid mass flow rate (m.sub.f), and the root-mean-square droplet diameter (D.sub.rms) corresponding to each of the figures.

TABLE-US-00001 TABLE 1 P.sub.air m.sub.air m.sub.f D.sub.rms (bar) (grams/sec) (grams/sec) micrometers (μm) FIG. 6A 0.04 6.2 4.0 29.4 FIG. 6B 0.06 6.1 1.2 27.6
Based upon the results of prototype experiments, the ratio of the air mass flow rate (m.sub.air) to the fuel mass flow rate (m.sub.f) should typically be in a range of 2 to 6. Within this range, the atomizer of the invention provides a high-quality liquid-air mixture in which the diameter of liquid droplets is less than or equal to 30 μm. When the ratio is below 2, the liquid droplets become larger, and their diameters exceed 30 μm. Conversely, when the ratio is above 6, the increase in airflow does not appear to reduce the droplet diameters, or to improve the quality of liquid-air mixture.

[0062] It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims. Furthermore, many other configurations of the atomizer, besides the exemplary embodiment explicitly shown in FIG. 2, will be readily apparent to those skilled in the art of gas turbine engines, based upon the principles disclosed herein.