BURNERS AND COMPONENTS FOR USE IN BURNERS

Abstract

A high excess air burner includes a housing including a generally tubular body enclosing an air chamber, a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body, a fuel inlet configured to supply a variable volumetric flow rate of fuel, an air inlet configured to supply air to the air chamber, a first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, and a third combustion cavity having a third inlet opening communicating with the second combustion cavity for receiving the second fuel-air mixture. The burner including one or more components (e.g., nozzle, rear cover) to improve flame characteristics, such as flame stability or consistency, and/or one or more components or features to improve flame detection capability.

Description

BACKGROUND

Technical Field

This disclosure relates generally to gas burners and components for use in gas burners and, more specifically, to components which are particularly suitable for use in a high excess air burner that operates over a relatively wide range of fuel flow rates and a relatively wide range of air flow rates.

Description of the Related Art

A nozzle for use in a high excess air burner of the type described herein can be constructed with multiple combustion cavities. Each combustion cavity has an inlet opening for receiving a fuel-air mixture from a previous or upstream cavity and typically has additional passages for receiving additional combustion air. Combustion air is staged through axially-spaced passages to allow the nozzle to operate over a range of fuel flow rates. For example, as the flow of fuel increases and the fuel-air mixture becomes fuel-rich in one combustion cavity, the flame front moves forward or downstream into the next combustion cavity where additional air is delivered to the flame through additional openings. The additional air brings the volumetric fuel-to-air ratio of the mixture in the downstream combustion cavity to within the flammability limits of the fuel. Further, as the flow of fuel decreases and the fuel-air mixture becomes fuel-lean in one combustion cavity, the flame front moves upstream into the previous combustion cavity where one less set of openings delivers air to the mixture. In a similar manner, if the flow of air delivered to the flame increases to a point where the fuel-air mixture becomes fuel-lean in one combustion cavity, then a flame front transitions upstream into the previous combustion cavity. During normal operation of a high excess air burner, the flame front transitions throughout the nozzle as the volumetric flow rate of either the air or the fuel varies within predefined operating limits of the burner.

Successful operation of a nozzle having more than one combustion cavity requires that the flame smoothly transition between adjacent combustion cavities. In the absence of provisions for a smooth flame transition, there tends to be a region of unstable operation where the flame is unable to establish itself in either of the adjacent combustion cavities. This instability is substantially due to the turbulent nature of the fuel-air mixture as it flows through the inlet opening of the downstream combustion cavity and tends to cause the flame front to jump back and forth between the two adjacent combustion cavities. Under extremely turbulent conditions at high flow rates, this instability may cause the flame to be extinguished.

BRIEF SUMMARY

A high excess air burner may be summarized as comprising: a generally tubular body enclosing an air chamber; a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body; a fuel inlet configured to supply a variable volumetric flow rate of fuel; an air inlet configured to supply air to the air chamber; a first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity; and at least a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, the second combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity, wherein the second combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the second combustion air inlets is perpendicular to central axes of the second combustion air inlets.

A nozzle for use within an air chamber of a high excess air burner may be summarized as comprising: a combustion cavity having an inlet opening communicating with an upstream combustion cavity of the high excess air burner for receiving a fuel-air mixture, the combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the combustion cavity having combustion air inlets communicating with the air chamber so that the fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the combustion cavity, wherein the combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the combustion air inlets is perpendicular to central axes of the combustion air inlets.

A high excess air burner may be summarized as comprising: a generally tubular body enclosing an air chamber; a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body; a fuel inlet configured to supply a variable volumetric flow rate of fuel; an air inlet configured to supply air to the air chamber; a first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity; a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, the second combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity; and a third combustion cavity having a third inlet opening communicating with the second combustion cavity for receiving the second fuel-air mixture, the third combustion cavity having third combustion air inlets communicating with the air chamber so that the second fuel-air mixture is mixed with supplemental combustion air to form a third fuel-air mixture in the third combustion cavity, wherein the third combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the third combustion air inlets is perpendicular to central axes of the third combustion air inlets.

A nozzle for use within an air chamber of a high excess air burner may be summarized as comprising: a first combustion cavity having a first inlet opening communicating with an upstream combustion cavity for receiving a first fuel-air mixture, the first combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the first combustion cavity having first combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the first combustion cavity; and a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the second fuel-air mixture, the second combustion cavity having second combustion air inlets communicating with the air chamber so that the second fuel-air mixture is mixed with supplemental combustion air to form a third fuel-air mixture in the second combustion cavity, wherein the second combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the second combustion air inlets is perpendicular to central axes of the second combustion air inlets.

A high excess air burner may be summarized as comprising: a housing including a generally tubular body enclosing an air chamber, and including an air inlet with an air inlet axis oriented perpendicular to a longitudinal axis of the high excess air burner; a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body; a rear cover coupled to the generally tubular body and to the nozzle, where the rear cover encloses an upstream end of the air chamber, and wherein the rear cover is configured to be coupled to the housing in incremental rotational orientations; a fuel inlet configured to supply a variable volumetric flow rate of fuel; an air inlet configured to supply air to the air chamber; a first combustion cavity provided within the rear cover, the first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity, and wherein the first combustion air inlets extend at oblique angles to the air inlet axis of the air inlet of the housing; and at least a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity.

A rear cover configured to be coupled to a housing of a high excess air burner in incremental rotational orientations may be summarized as comprising: combustion air inlets that extend at oblique angles to an air inlet axis of an air inlet of the high excess air burner.

A high excess air burner may be summarized as comprising: a housing including a generally tubular body enclosing an air chamber; a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body; a rear cover coupled to the generally tubular body and to the nozzle, where the rear cover encloses an upstream end of the air chamber; a fuel inlet configured to supply a variable volumetric flow rate of fuel; an air inlet configured to supply air to the air chamber; and a first combustion cavity within the rear cover, the first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity, wherein the rear cover includes a flame sensor passage for receiving a flame sensor, and wherein an ultraviolet-limiting device is positioned or provided in the flame sensor passage, the ultraviolet-limiting device having surface features that reduce interference with measurements made by the flame sensor by absorbing or redirecting a portion of ultraviolet light entering the flame sensor passage.

An ultraviolet-limiting device configured for use in a flame sensor passage of a rear cover configured to be coupled to a housing of a high excess air burner in incremental rotational orientations may be summarized as comprising: surface features that reduce interference with measurements made by a flame sensor by absorbing or redirecting a portion of ultraviolet light entering the flame sensor passage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a high excess air burner of the prior art.

FIG. 2 illustrates an exploded view of a high excess air burner, including a nozzle, a rear cover, and an ultraviolet-limiting connector thereof.

FIG. 3 illustrates a perspective view of the nozzle of the high excess air burner of FIG. 2.

FIG. 4 illustrates a cross-sectional view of the nozzle of the high excess air burner of FIG. 2.

FIG. 5A illustrates a cross-sectional view of the rear cover of the high excess air burner of FIG. 2 taken along a downstream section of the rear cover that extends into an air chamber of the high excess air burner.

FIG. 5B illustrates a cross-sectional view of components of another high excess air burner for purposes of comparison with FIG. 5A.

FIG. 6 illustrates a cross-sectional view of the ultraviolet-limiting connector of the high excess air burner of FIG. 2.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with the burner technology have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.

By way of background, FIG. 1 shows a high excess air burner 11 known in the art, which includes a nozzle 10. High excess air burners are useful in applications where it is desirable to have a high-velocity discharge from the burner. For example, in a high temperature furnace where the high-temperature discharge from the burner is to be mixed with additional air in a chamber downstream of the burner and where a mixing fan is not available, the high velocity of the discharge from the burner provides turbulent means for mixing the high-temperature discharge with the additional air. For this purpose, excess air, i.e., air in excess of the air that is necessary for combustion of the fuel, flows around the nozzle and discharges through the exit of the burner.

The burner 11 includes a generally cylindrical body or burner housing 12, a cylindrical combustion tube 13 which is secured to the downstream end of the burner housing 12, and a rear cover 14 which is secured to the upstream end of the burner housing 12 and which closes off the upstream end of the burner 11 from an outside environment. The burner housing 12 and the upstream end portion of the combustion tube 13 are formed with cylindrical interior surfaces having the same diameter. The upstream end portion of the combustion tube 13 is secured in a recess 15 formed in the downstream end portion of the burner housing 12 so that the interior surface of the combustion tube 13 extends forwardly from the downstream end of the interior surface of the burner housing 12 to define a generally cylindrical air chamber 16. The downstream end portion of the combustion tube 13 is formed with a radially inwardly converging internal surface which defines a converging burner exit 17. A radially outwardly projecting mounting flange 18 is formed integrally with the downstream end of the burner housing 12 for mounting the burner 11 to a furnace.

The nozzle 10 is located in the air chamber 16 and, for purposes of illustration, includes three coaxial combustion cavities 20, 21, and 22. The first combustion cavity 20 is defined in a forwardly projecting portion of the rear cover 14. The second and third combustion cavities, 21 and 22 respectively, are defined in a nozzle housing 23 which is secured to the forwardly projecting portion of the rear cover 14. A radially outwardly extending flame retention ring 24 is integrally formed at the downstream end of the nozzle housing 23. Axially and radially inwardly extending slots 25 are formed in the outer flame retention ring 24 and are circumferentially spaced around the flame retention ring 24. The base of each of the slots 25 defines a surface which slopes radially inwardly upon progressing toward the burner exit 17.

Gaseous fuel is supplied to the upstream or inlet end of the first combustion cavity 20 through an inlet tube 27 formed in the rear cover 14. The fuel flows forwardly in the nozzle 10 where combustion air is mixed with the fuel to form a combustible fuel-air mixture. A spark plug 28 is threaded into the rear cover 14 so that an electrode of the spark plug 28 extends into a slot formed in the first combustion cavity 20 for ignition of the combustible mixture therein. Adjustable means may be used to control the volumetric flow rate of the fuel entering the nozzle 10.

Gas is supplied to the burner 11 through a fitting or port 29 located in the rear cover 14. The air enters the upstream end of the air chamber 16 through internal passages in the rear cover 14 and flows forwardly in the air chamber 16 and along the length of the nozzle housing 23 toward the converging exit 17 of the burner 11. A relatively small percentage of the air enters the nozzle 10 from the air chamber 16 through passages 30, 31, 32A, and 32B for mixing with the flow of fuel in the nozzle 10. A velocity of the remaining excess air increases as it flows through the converging exit 17 of the burner 11, resulting in a desired high-velocity discharge from the burner 11. Adjustable means may be used to control the volumetric flow rate of the air entering the burner 11.

The passage 30 is formed in a sidewall of the forwardly-projecting portion of the rear cover 14 and communicates with the air chamber 16 to supply combustion air to be mixed with the fuel in the inlet tube 27 directly upstream of the first combustion cavity 20. A centerline of the passage 30 is generally perpendicular to, and lies in a plane which is parallel to and displaced outwardly from, a central longitudinal centerline of the inlet tube 27 so that the combustion air entering the inlet tube 27 has a tangential velocity component with respect to the flow of fuel in the inlet tube 27. The tangential velocity component of the combustion air entering the inlet tube 27 results in a swirling fuel-air mixture at the inlet of the first combustion cavity 20.

The upstream end of the first combustion cavity 20 is formed with a gradually increasing cross-sectional flow area defined by an outwardly expanding frustoconically-shaped interior surface or sidewall 33A extending from the inlet end 20A. The remainder of the first combustion cavity 20 is formed with a generally cylindrical interior surface 33B extending from the downstream end of the frustoconical surface 33A. This construction insures that the forward velocity of the fuel-air mixture in the first combustion cavity 20 is greatest at the inlet of that cavity 20 in order to prevent a flame from flashing back into the inlet tube 27 and to insure that the swirling of the mixture is not interrupted in the first combustion cavity 20.

The second combustion cavity 21 is formed with a back wall 34 and an interior surface or sidewall 35 having a circular cross-section. The second combustion cavity 21 is located adjacent and downstream of the first combustion cavity 20 so that the downstream or exit 20B of the first combustion cavity 20 defines an inlet opening to the second combustion cavity 21, the inlet opening of the second combustion cavity 21 being located in the back wall 34. The cross-sectional flow area at the upstream end of the second combustion cavity 21, as defined by the interior surface 35 at the back wall 34, is substantially greater than the cross-sectional flow area at the inlet opening of the second combustion cavity 21. As a result of this abrupt increase in flow area, the fuel-air mixture expands and its forward velocity substantially decreases as the mixture enters the second combustion cavity 21, thereby providing for flame retention at the inlet opening of the second combustion cavity 21. The passages 31 extend from the air chamber 16 through the back wall 34 and are located radially outwardly from the inlet opening of the second combustion cavity 21. The air flowing through the passages 31 enters the upstream end of the second combustion cavity 21 in a generally axial direction and mixes with the expanding fuel-air mixture therein.

The third combustion cavity 22 is formed with a back wall 36 and a cylindrical interior surface or sidewall 37. The third combustion cavity 22 is located adjacent and downstream of the second combustion cavity 21 so that the exit end of the second combustion cavity 21 defines an inlet opening to the third combustion cavity 22, the inlet opening of the third combustion cavity 22 being located in the back wall 36. The cross-sectional flow area at the upstream end of the third combustion cavity 22, as defined by the interior surface 37, is substantially greater than the cross-sectional flow area at the inlet opening of the third combustion cavity 22. As a result of this abrupt increase in flow area, the fuel-air mixture expands and its forward velocity decreases substantially as the mixture enters the third combustion cavity 22, thereby providing for flame retention at the inlet opening to the third combustion cavity 22. The passages 32A, 32B extend from the air chamber 16 radially inwardly through the sidewall 37. Air flows through the passages 32A, 32B for mixing with the fuel-air mixture in the third combustion cavity 22.

Combustion air is supplied to each of the combustion cavities 20, 21 and 22 and to the outer flame retention ring 24 to accommodate the flammability limits of the fuel. If the flame is located in an upstream cavity, for example the second combustion cavity 21, and the volumetric flow rate of the fuel increases to the point where the fuel-air mixture in the second combustion cavity 21 becomes fuel-rich, i.e., the volumetric fuel-to-air ratio exceeds the maximum flammability limit of the fuel, then the flame front transitions into the downstream or third cavity 22 where additional air is supplied to the mixture through passages 32A, 32B. The additional air brings the fuel-to-air mixture ratio in the third combustion cavity 22 to within the flammability limits of the fuel. Alternatively, if the flame front is in the third combustion cavity 22 and the volumetric flow rate of the fuel is decreased to the point where the fuel-air mixture in the third combustion cavity 22 becomes fuel-lean, then the flame transitions upstream to the second combustion cavity 21 where the passages 32A, 32B are no longer delivering air to the mixture at the flame. In a similar manner, if the flow of air delivered to the flame in the third combustion cavity 22 increases to a point where the fuel-air mixture becomes fuel-lean, then the flame transitions upstream into the second combustion cavity 21.

The nozzle 10 is designed to support combustion, i.e., to retain a flame, in each of the combustion cavities 20, 21 and 22 and at the outer flame retention ring 24. If the volumetric flow rate of the fuel being supplied to the nozzle is at a predetermined minimum operating condition, then a stable flame front will establish itself near the upstream end of the first combustion cavity 20. Alternately, if the volumetric flow rate of the fuel being supplied to the nozzle is at a predetermined maximum for a given volumetric flow rate of air (a so-called high-fire condition), then the flame front will be located on the outer flame retention ring 24. A radially inwardly extending restriction 38 is integrally formed at the exit end of the third combustion cavity 22 to enhance stability of the flame when the flame is located on the outer flame retention ring 24. For a given flow rate of air, the second and third combustion cavities 21 and 22 support combustion of the fuel as the flow rate varies between the predetermined minimum and maximum.

Successful operation of the nozzle 10 requires that the flame smoothly transition between the combustion cavities 20, 21 and 22 as the flow rate of the fuel varies. In the absence of provisions for a smooth flame transition, there tends to be a region of unstable operation where the flame is unable to establish itself in either of two adjacent combustion cavities. This instability is substantially due to the turbulent nature of the fuel-air mixture as it flows through the inlet opening of the downstream combustion cavity and tends to cause the flame front to jump back and forth between the two adjacent combustion cavities. Under extremely turbulent conditions at high flow rates, this instability may cause the flame to be extinguished.

The flame transitions smoothly between the first combustion cavity 20 and the second combustion cavity 21 by virtue of the swirling fuel-air mixture at the exit end of the first combustion cavity 20. Since the flow rate of the fuel-air mixture in the first combustion cavity is relatively low, this swirling mixture has negligible effect on the efficiency of the nozzle 10. However, the flow rate of the fuel-air mixture is relatively high when the flame front is located in the second combustion cavity 21. If a swirling mixture were provided at the exit of the second combustion cavity 21, then the swirling mixture would detrimentally affect the efficiency of the nozzle 10.

Thus, the second combustion cavity 21 can be configured so that the flow area in the second combustion cavity 21 smoothly decreases upon progressing toward the exit end of the second combustion cavity 21. As a result, the base of the flame smoothly transitions between the second combustion cavity 21 and the third combustion cavity 22 as the volumetric flow rate of the fuel varies between the operating ranges of the second and third combustion cavities 21, 22.

More specifically, the sidewall 35 of the second combustion cavity 21 defines a frustoconical cavity which converges radially inwardly upon progressing forwardly or downstream from the back wall 34 toward the exit end of the second combustion cavity 21. The outer periphery of the back wall 34 is preferably formed with an internal radius 34A so that the back wall 34 smoothly merges with the sidewall 35. The exit end of the second combustion cavity 21 also is preferably formed with an external radius 22A so that the sidewall 35 smoothly merges with the inlet opening of the third combustion cavity 22.

Substantial turbulence is created in the fuel-air mixture as the mixture expands at the upstream end of the second combustion cavity 21. This turbulence enables the combustion air entering the second combustion cavity 21 through the passages 31 to mix thoroughly with the fuel-air mixture flowing from the first combustion cavity 20. The smoothly and gradually decreasing flow area of the second combustion cavity 21, as defined by the sidewall 35, causes the velocity of the fuel-air mixture in the second combustion cavity 21 to increase at a relatively constant rate as the mixture flows toward the exit end of the second combustion cavity 21. As a result, the velocity profile of the fuel-air mixture at the exit end of the second combustion cavity 21 is relatively constant so as to enable the base of the flame to smoothly transition between the second combustion cavity 21 and the third combustion cavity 22. The smoothly converging flow area in the second combustion cavity 21, which is capable of operating with relatively high fuel flow rates, provides for a smooth flame transition between the second combustion cavity 21 and the third combustion cavity 22. Accordingly, the nozzle 10 is capable of stable operation over a wide range of relatively high fuel flow rates.

FIG. 2 illustrates an exploded view of a high excess air burner 100 according to an embodiment of the present invention, including a nozzle 102 that may have similarities to the nozzle 10 of the known burner 11 of FIG. 1, a rear cover 104 that may have similarities to the rear cover 14 of the known burner 11 of FIG. 1, and an ultraviolet-limiting connector 106. The nozzle 102, rear cover 104, and ultraviolet connector 106 are circled in FIG. 2 for clarity. In some embodiments, any or all of the features described for the high excess air burner 11 of FIG. 1 and its respective components, including the nozzle 10 and the rear cover 14, can be combined with the features of the high excess air burner 100 and its respective components, including the nozzle 102 and the rear cover 104.

FIGS. 3 and 4 illustrate a perspective view and a cross-sectional view, respectively, of the nozzle 102 of the high excess air burner 100 of the illustrated embodiment of FIG. 2. As illustrated in FIGS. 3 and 4, the nozzle 102 has an outer surface that, in contrast to the outer surface of nozzle 10, is more complex and less closely resembles a simple cylindrical shape. In particular, the nozzle 102 has a plurality of passages 108 that extend through the side wall of the nozzle 102 from the outer surface thereof to the inner surface thereof. In some embodiments, any or all of the features described for the passages 32A, 32B, can be combined with the features of the passages 108. For example, the passages 108 may extend from an air chamber surrounding the nozzle 102 and a forwardly-projecting portion of the rear cover 104 (comparable to the air chamber 16) radially inwardly through the sidewall of the nozzle 102 (comparable to the sidewall 37). Air flows through the passages 108 for mixing with a fuel-air mixture within a combustion cavity within the nozzle 102 (comparable to the second combustion cavity 21 and/or the third combustion cavity 22).

As the passages 108 extend radially inwardly through the sidewall of the nozzle 102, they also extend in a downstream direction relative to a fluid flow through the interior of the nozzle 102. That is, central longitudinal axes of the passages 108 are arranged at an oblique angle relative to a central longitudinal axis of the nozzle 102, where the oblique angle can be greater than 10°, 20°, 30°, or 40°, and/or less than 50°, 60°, 70°, or 80°, or about 45°. In some embodiments, central longitudinal axes of a first subset of the passages 108, such as an upstream subset of the passages 108, are arranged at a first oblique angle relative to the central longitudinal axis of the nozzle 102 and central longitudinal axes of a second subset of the passages 108, such as a downstream subset of the passages 108, are arranged at a second oblique angle relative to the central longitudinal axis of the nozzle 102. In some embodiments, the first oblique angle may be smaller than the second oblique angle. The first oblique angle may be less than 60, 70, 80, or 90 percent of, and/or more than 10, 20, 30, or 40 percent of, the second oblique angle, or about 22.5 degrees.

Furthermore, the outer surface of the nozzle 102 can be configured such that, at a radially-outermost end of each of the passages 108, the outer surface of the nozzle 102 is arranged at an angle relative to the central longitudinal axis of the passage 108, where the angle can be greater than 50°, 60°, 70°, or 80°, and/or less than 100°, 110°, 120°, or 130°, or about 90° or perpendicular thereto. Orienting the outer surface of the nozzle 102 perpendicular, substantially perpendicular, or approximately perpendicular to the central longitudinal axes of the passages 108 can improve control over air flow into the passages 108 from the chamber surrounding the nozzle 102 and the forwardly-projecting portion of the rear cover 104. The outer surface of the nozzle 102 can have a generally cylindrical shape or stepped cylindrical shape, with distinct downstream cylindrical portions having larger diameters than distinct upstream cylindrical portions. Further, at an upstream end of each of such distinct portions, the outer surface of the nozzle 102 can include a respective circumferential ridge or protraction to accommodate the features described herein with respect to the passages 108.

In some embodiments, the passages 108 can all have the same size, while in other embodiments, the passages 108 can have different sizes, such as different diameters. Similarly, each of the passages 108 that are coupled directly to any one of the combustion cavities 20, 21, or 22 can all have the same size, while in other embodiments, such passages 108 can have different sizes, such as different diameters. For example, in some embodiments, a largest one of any of the sets of the passages 108 discussed herein has a diameter that is 4 times, 3 times, or 2 times larger than a diameter of the smallest one of the passages 108 in the set of passages. Providing the passages 108 with different diameters can vary air penetration depth into the respective combustion cavity and thereby make mixing intensity less uniform. This can further increase flame stability over a larger operating range.

FIG. 5A illustrates a cross-sectional view of the rear cover 104 of the high excess air burner 100 of the illustrated embodiment of FIG. 2, where the cross-section is taken on a plane perpendicular to a central longitudinal axis of the rear cover 104, the high excess air burner 100 as a whole, and of a combustion cavity within the rear cover 104 (comparable to the first combustion cavity 20) in a downstream portion of the rear cover 104 that extends into the air chamber of the burner 100 within housing 120. As illustrated in FIG. 5A, the rear cover 104 includes an igniter passage 110 for receiving a spark plug or igniter, an inlet tube or combustion cavity 112 (which may be referred to simply as a combustion cavity herein, but may also be an inlet tube, and which may be comparable to the inlet tube 27 and/or the first combustion cavity 20), and a flame sensor passage 114 for receiving a flame sensor, arranged in that order along a reference axis that extends perpendicular to, and that intersects, the central longitudinal axis of the combustion cavity 112.

As further illustrated in FIG. 5A, the rear cover 104 includes first and second air flow passages 118 extending from an outer surface of the rear cover 104 to an inner surface of the rear cover 104 and the combustion cavity 112 therein. For example, the air flow passages 118 may extend from the air chamber surrounding the nozzle 102 and a forwardly-projecting portion of the rear cover 104 radially inwardly through the sidewall of the rear cover 104. Air flows through the air flow passages 118 for mixing with a fuel-air mixture within the combustion cavity 112 therein. The first and second air flow passages 118 each have a respective central longitudinal axis that extends at an oblique angle to the reference axis and perpendicular to the central longitudinal axis of the combustion cavity 112, where the oblique angle can be greater than 10°, 20°, 30°, or 40°, and/or less than 50°, 60°, 70°, or 80°, or about 45°. The respective central longitudinal axes of the first and second air flow passages 118 are also offset from and do not extend through each other or through the central longitudinal axis of the combustion cavity 112. Thus, air travelling through the first and second air flow passages 118 has a tangential velocity component with respect to the flow of fuel in the combustion cavity 112. The tangential velocity component of the combustion air entering the combustion cavity 112 can improve mixing of the fuel-air mixture.

As illustrated in the cross-sectional view of FIG. 5A, each of the first and second air flow passages 118, and their respective central longitudinal axes, are offset from each other in a rotational direction, such that the air flow passages collectively have rotational symmetry about the central longitudinal axis of the combustion cavity 112. Referring back to FIG. 2, the high excess air burner 100 includes a burner housing 120 having features similar to the burner housing 12, where the burner housing 120 includes an air inlet 122 in a sidewall thereof, through which air can be introduced into the air chamber surrounding the nozzle 102 and a forwardly-projecting portion of the rear cover 104. FIG. 2 also illustrates that a central longitudinal axis of the air inlet 122 is aligned with or parallel to the reference axis extending through the igniter passage 110, the combustion cavity 112, and the flame sensor passage 114, as illustrated by the arrow labeled 124 in FIG. 5A, and such that air flows into the high excess air burner 100 nearest to the flame sensor passage 114 in the orientation of the rear cover 104 shown in FIG. 2.

Thus, with reference to FIG. 5A again, air flow will generally enter from the left, as illustrated by the arrow labeled 124, and travel around the body of the rear cover 104 toward the right. Because the first and second air flow passages 118 are oriented at about 45 degrees with respect to the reference axis in the illustrated embodiment, rather than perpendicular thereto, air flow can enter at least one of the first and second passages 118 more directly than it could if the passages were oriented perpendicular to the inlet direction illustrated by arrow labeled 124. This can improve control over air flow into the passages 118. This can be seen in particular by comparing the features illustrated in FIG. 5A with those of FIG. 5B, in which air flow can enter at least one of the first and second passages only after travelling 90 degrees or a quarter of the way through the annular space, because the passages are oriented perpendicular to the inlet direction. Furthermore, the rear cover 104 may be coupled to the rest of the system (e.g., housing 120) in different rotational orientations (that is, it could be clocked in different orientations, such as 90, 180, or 270 degrees relative to that illustrated in FIG. 2), such that, for example, the reference axis is arranged at different angles to the air inlet 122. In such cases, provision of the first and second air flow passages 118 can reduce the effects of switching between these different orientations on air flow through the passages 118, by providing at least one air flow passage 118 that is aligned at an oblique angle to the inlet direction illustrated by the arrow labeled 124 and generally at the same relative orientation with respect to the inlet direction irrespective of the clocked position of the rear cover 104.

FIG. 6 illustrates a cross-sectional view of the ultraviolet-limiting connector 106 of the high excess air burner 100 of FIG. 2. As illustrated in FIG. 6, the ultraviolet connector 106 has an overall hollow cylindrical or annular shape, with a first end thereof having an ultraviolet-limiting device 130, such as an internal threaded surface, a thread-like surface, a grooved surface, or a stepped surface, and a second end thereof having, for example, a smooth and generally cylindrical inner surface, within which a flame sensor, such as an ultraviolet flame sensor, may be positioned. In some embodiments, the features of the ultraviolet-limiting device 130, such as the threads, grooves, steps, or other features thereof, may be formed by machining them directly into the inner surface of the ultraviolet-limiting connector 106 and then installing the ultraviolet-limiting connector 106 within the flame sensor passage 114. In other embodiments, the features of the ultraviolet-limiting device 130, such as the threads, grooves, steps, or other features thereof, may be formed by machining them directly into the flame sensor passage 114 itself. In some embodiments, the ultraviolet-limiting device 130 of the ultraviolet connector 106 may be coated with an optically-, light-, or ultraviolet-reflective or optically-, light-, or ultraviolet-absorbent material.

When the high excess air burner 100 is assembled, the ultraviolet connector 106 can be positioned within the flame sensor passage 114 with the first end thereof closest to the combustion cavity 112. When the high excess air burner 100 is in operation, the ultraviolet connector 106, and particularly the ultraviolet-limiting device 130 thereof, can act to trap or prevent stray ultraviolet light from interfering with measurements made by the flame sensor, such as, for example, stray ultraviolet light that may arise from the ignitor during a lighting sequence and enter the flame sensor passage 114. In this way, the flame sensor can more reliably detect the presence of a flame, that is, that the burner 100 is in operation, while minimizing interference resulting from light generated by the igniter, for example, because light generated by the igniter is reflected and/or absorbed by the features of the ultraviolet-limiting device 130 described herein.

While the ultraviolet-limiting connector 106 is shown and described as being used in connection with the high excess air burner 100, it will be understood that the ultraviolet-limiting connector 106 can be used in other embodiments with other types of burner nozzles, including any burner nozzle that uses ultraviolet detection for flame monitoring.

U.S. Pat. No. 5,647,739 is hereby incorporated herein by reference in its entirety. Features and aspects of the embodiments described herein can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.

Claims

1. A high excess air burner, comprising: a generally tubular body enclosing an air chamber;a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body, the nozzle having first and second combustion cavities;a fuel inlet configured to supply a variable volumetric flow rate of fuel; andan air inlet configured to supply air to the air chamber;wherein the first combustion cavity has a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity;wherein the second combustion cavity has a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, the second combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity, wherein the second combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the second combustion air inlets is perpendicular to central axes of the second combustion air inlets.

2. The high excess air burner of claim 1 wherein each of the first combustion air inlets has the same diameter.

3. The high excess air burner of claim 1 wherein a largest one of the first combustion air inlets has a first diameter and a smallest one of the first combustion air inlets has a second diameter, wherein the first diameter is at least two times the second diameter.

4. The high excess air burner of claim 1 wherein a largest one of the first combustion air inlets has a first diameter and a smallest one of the first combustion air inlets has a second diameter, wherein the first diameter is four times the second diameter.

5. The high excess air burner of claim 1 wherein each of the second combustion air inlets has the same diameter.

6. The high excess air burner of claim 1 wherein a largest one of the second combustion air inlets has a first diameter and a smallest one of the second combustion air inlets has a second diameter, wherein the first diameter is at least two times the second diameter.

7. The high excess air burner of claim 1 wherein a largest one of the second combustion air inlets has a first diameter and a smallest one of the second combustion air inlets has a second diameter, wherein the first diameter is four times the second diameter.

8. The high excess air burner of claim 1 wherein the oblique angle at which the second combustion air inlets extend is greater than 20 degrees and less than 25 degrees.

9. The high excess air burner of claim 1 wherein the outer surface of the nozzle has a generally stepped cylindrical shape.

10. The high excess air burner of claim 1 wherein an upstream end of a portion of the outer surface of the nozzle that surrounds the second combustion cavity includes a circumferential ridge and the second combustion air inlets extend through the circumferential ridge.

11. The high excess air burner of claim 1 wherein a flow of air between an inner surface of the generally tubular body and the nozzle flowing in a direction parallel to the central longitudinal axis of the nozzle is impeded by projecting portions of the outer surface of the nozzle located in an intermediate portion of the nozzle between opposing ends of the nozzle.

12. A high excess air burner, comprising: a generally tubular body enclosing an air chamber;a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body;a fuel inlet configured to supply a variable volumetric flow rate of fuel;an air inlet configured to supply air to the air chamber;a first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity;a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, the second combustion cavity having a sidewall that converges radially inwardly in a downstream direction, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity; anda third combustion cavity having a third inlet opening communicating with the second combustion cavity for receiving the second fuel-air mixture, the third combustion cavity having third combustion air inlets communicating with the air chamber so that the second fuel-air mixture is mixed with supplemental combustion air to form a third fuel-air mixture in the third combustion cavity, wherein the third combustion air inlets extend through a side wall of the nozzle at an oblique angle to a central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the third combustion air inlets is perpendicular to central axes of the third combustion air inlets.

13. The high excess air burner of claim 12 wherein the oblique angle is greater than 40 degrees and less than 50 degrees.

14. The high excess air burner of claim 13 wherein the second combustion air inlets extend through the side wall of the nozzle at a shallow angle to the central longitudinal axis of the nozzle, and wherein an outer surface of the nozzle at a radially-outermost end of each of the second combustion air inlets is perpendicular to central axes of the second combustion air inlets.

15. The high excess air burner of claim 14 wherein the shallow angle is less than the oblique angle.

16. The high excess air burner of claim 15 wherein the shallow angle is greater than 20 degrees and less than 25 degrees.

17. The high excess air burner of claim 12 wherein the outer surface of the nozzle has a generally stepped cylindrical shape.

18. The high excess air burner of claim 17 wherein an upstream portion of the outer surface of the nozzle that surrounds the second combustion cavity has a smaller diameter than a downstream portion of the outer surface of the nozzle that surrounds the third combustion cavity.

19. The high excess air burner of claim 12 wherein an upstream end of a portion of the outer surface of the nozzle that surrounds the third combustion cavity includes a circumferential ridge and the third combustion air inlets extend through the circumferential ridge.

20. The high excess air burner of claim 12, wherein a flow of air between an inner surface of the generally tubular body and the nozzle flowing in a direction parallel to the central longitudinal axis of the nozzle is impeded by projecting portions of the outer surface of the nozzle located in an intermediate portion of the nozzle between opposing ends of the nozzle.

21. A high excess air burner, comprising: a housing including a generally tubular body enclosing an air chamber, and including an air inlet with an air inlet axis oriented perpendicular to a longitudinal axis of the high excess air burner;a nozzle located in the air chamber and spaced radially inwardly of the generally tubular body;a rear cover coupled to the generally tubular body and to the nozzle, where the rear cover encloses an upstream end of the air chamber, and wherein the rear cover is configured to be coupled to the housing in incremental rotational orientations;a fuel inlet configured to supply a variable volumetric flow rate of fuel;an air inlet configured to supply air to the air chamber;a first combustion cavity provided within the rear cover, the first combustion cavity having a first inlet opening communicating with the fuel inlet for receiving the variable volumetric flow rate of fuel, the first combustion cavity having first combustion air inlets communicating with the air chamber so that fuel is mixed with combustion air to form a first fuel-air mixture in the first combustion cavity, and wherein the first combustion air inlets extend at oblique angles to the air inlet axis of the air inlet of the housing; andat least a second combustion cavity having a second inlet opening communicating with the first combustion cavity for receiving the first fuel-air mixture, and the second combustion cavity having second combustion air inlets communicating with the air chamber so that the first fuel-air mixture is mixed with additional combustion air to form a second fuel-air mixture in the second combustion cavity.

22. The high excess air burner of claim 21 wherein the oblique angles are greater than 40 degrees and less than 50 degrees.

23. The high excess air burner of claim 21 wherein central longitudinal axes of the first combustion air inlets are not coincident with one another, are offset from one another, and are parallel to one another.

24. The high excess air burner of claim 21 wherein the rear cover is configured to be coupled to the housing in incremental rotational orientations of ninety degrees, and wherein, irrespective of the incremental rotational orientation of the rear cover, the first combustion air inlets extend at oblique angles to the air inlet axis of the air inlet of the housing.

25. The high excess air burner of claim 21, wherein the rear cover includes an igniter passage for receiving a spark plug or igniter and a flame sensor passage for receiving a flame sensor, wherein the igniter passage and the flame sensor passage are arranged along a reference axis that extends perpendicular to and intersects a central longitudinal axis of the first combustion cavity, and wherein the first combustion air inlets extend at oblique angles to the reference axis.

26. A burner, comprising: a nozzle;a fuel inlet configured to supply a fuel;an air inlet configured to supply air;a flame sensor passage for receiving a flame sensor; andan ultraviolet-limiting device positioned or provided in the flame sensor passage, the ultraviolet-limiting device having surface features that reduce interference with measurements made by the flame sensor by absorbing or redirecting a portion of ultraviolet light entering the flame sensor passage.

27. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are threads.

28. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are grooves.

29. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are steps.

30. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are coated by an ultraviolet-reflective material.

31. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are coated by an ultraviolet-absorbent material.

32. The high excess air burner of claim 26 wherein the surface features of the ultraviolet-limiting device are configured such that ultraviolet light traveling parallel or generally parallel to a longitudinal axis of the ultraviolet-limiting device continue uninterrupted through the flame sensor passage toward the flame sensor, and such that a substantial portion of ultraviolet light traveling obliquely to the longitudinal axis of the ultraviolet-limiting device is absorbed or redirected out of the flame sensor passage away from the flame sensor.

33. The high excess air burner of claim 26 wherein the ultraviolet-limiting device is provided in the form of a component that is removeably insertable in the flame sensor passage.