Patent Description:
Gas turbines, also referred to as jet engines, are rotary engines that extract energy from a flow of combustion gas. They have an upstream compressor coupled to a downstream turbine with a combustion chamber in between. There are many different variations of gas turbines, but they all use the same basic principal.

Jet aircraft are usually powered by turbojet or turbofan engines. A turbojet engine is a gas turbine engine that works by compressing air with an inlet and a compressor, mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure gas through a turbine and a nozzle. The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts energy in the fuel to kinetic energy in the exhaust, producing thrust. All the air ingested by the inlet passes through the compressor, combustor, and turbine.

A turbofan engine is very similar to a turbojet except that it also contains a fan at the front of the compressor section. Like the compressor, the fan is also powered by the turbine section of the engine. Unlike the turbojet, some of the flow accelerated by the fan bypasses the combustor and is exhausted through a nozzle. The bypassed flow is at a lower velocity, but a higher mass, making thrust produced by the fan more efficient than thrust produced by the core. Turbofans are generally more efficient than turbojets at subsonic speeds, but they have a larger frontal area which generates more drag at higher speeds.

Turboprop engines are jet engine derivatives that extract work from the hot-exhaust jet to turn a rotating shaft, which is then used to spin a propeller to produce additional thrust. Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds.

Turboshaft engines are very similar to turboprops, differing in that nearly all of the energy in the exhaust is extracted to spin the rotating shaft. Turboshaft engines are used for stationary power generating plants as well as other applications.

One problem associated with gas turbine engines, especially in aircraft, is the possibility of flame-out, which occurs when the flame becomes extinguished within the combustion chamber. One of the causes of flame-out is instability of the flame front within the combustor. Since engine failure during flight is clearly problematic, it would be advantageous to construct a gas turbine engine such that the possibility of flame-out was reduced. For stationary power generating systems there is a need for reduced emissions, primarily NOx, in order to meet newer, more stringent clean air requirements.

Additionally, power burners of various types have been in use for many years. "Nozzle mix" or "gun style" burners are those burners that inject fuel and air separately in some manner so as to provide a stable flame without a ported flame holder component. Other types of power burners use some method of pre-mixing the fuel and air and then delivering the fuel-air mixture to a ported burner "head". These "heads" or "cans" can be made of a variety of materials including perforated sheet metal, woven metal wire, woven ceramic fiber, etc. Flame stability, also referred to as flame retention, is key to making a burner that has a broad operating range and is capable of running at high primary aeration levels. A broad operating range is desired for appliances that benefit from modulation, in which the heat output varies depending on demand. High levels of primary aeration are effective in reducing NOx emissions, but tend to negatively impact flame stability and potentially increase the production of Carbon Monoxide (CO). High levels of primary aeration (also referred to as excess air) also reduce appliance efficiency. There is a need in the art for a fuel burner that reduces the production of NOx while maintaining flame stability. Even more desirable is a burner that produces very low levels of NOx while operating at low levels of excess air.

Prior art is found in <CIT> which generally relates to a combustor.

The invention is set out in the independent claim.

The present invention provides a new and improved method of combustion and a combustor or burner that can be used in a jet engine, as well as other heating/burner applications such as a heating appliance or gas turbine engine.

In accordance with the invention a fuel burner includes an outer tube extending along a central axis from a first end to a second end. The outer tube includes an outer surface and an inner surface defining a passage. The outer tube includes fluid directing structure having a plurality of openings and a guide associated with each opening. An inner tube extends from a first end to a second end and is positioned within the passage of the outer tube. The inner tube includes an outer surface and an inner surface defining a central passage. A fluid passage is defined between the outer surface of the inner tube and the inner surface of the outer tube. The central passage is supplied with a mixture of air and combustible fuel pre-mixed upstream of the inner tube. The inner tube has fluid directing structure for directing the pre-mixed mixture radially outward from the central passage to the fluid passage such that the pre-mixed mixture rotates radially about the central within the fluid passage. The fluid directing structure on the outer tube is supplied with the pre-mixed mixture and directs the pre-mixed mixture radially inward to the fluid passage to mix with the pre-mixed mixture from the fluid directing structure on the inner tube. A first end wall closes the second end of the inner tube in a fluid-tight manner with the first end wall intersecting the central axis. A second end wall secures the first end of the inner tube to the outer tube in a fluid-tight manner such that the fluid directing structure on the inner tube provides the only fluid path from the central passage to the fluid passage.

Additional features and a further understanding of the invention will become apparent by reading the following detailed description made in connection with the accompanying drawings.

The invention relates to a fuel burner and, in particular, relates to a combustor for a heating appliance, gas turbine engine or jet engine that imparts a centrifugal force upon combustion air or a combination of air and fuel. Although some drawings generally depict a turbojet type engine and the specification describes an example use of the present invention in a jet engine, those having ordinary skill will appreciate that the combustor of the present invention described herein is also suitable for use in any of the engine variants described above.

<FIG> illustrate a combustor <NUM> for use in a jet engine <NUM>.

As shown in <FIG>, the jet engine <NUM> extends along an axis <NUM> and includes a housing <NUM> that extends along the axis from a first end <NUM> to a second end <NUM>. A wall <NUM> of the housing <NUM> defines an interior passage <NUM> that extends the length of the housing. A turbine <NUM>, a compressor <NUM>, and at least one combustor <NUM> are positioned within the passage <NUM> of the housing <NUM> and along the axis <NUM>. The compressor <NUM> includes a shaft or connecting member <NUM> that connects the compressor to the turbine <NUM> such that the connecting member and turbine rotate together. The combustor <NUM> is positioned axially between the turbine <NUM> and the compressor <NUM>.

As shown in <FIG>, the combustor <NUM> includes outer and inner tubes <NUM>, <NUM> that are concentric to one another about a central axis <NUM> and secured to one another and the housing <NUM>. The central axis <NUM> of the combustor <NUM> can be coaxial with the axis <NUM> of the engine <NUM> or can be spaced from the axis of the engine (not shown). The connecting member <NUM> extends through the inner tube <NUM> and a shaft seal <NUM> is provided between the connecting member and the inner tube to prevent fluid from passing between the connecting member and the inner tube directly into the turbine <NUM>.

The space between the outer and inner tubes <NUM>, <NUM> defines a fluid passage <NUM> for receiving fuel and air. The periphery of the outer tube <NUM> includes fluid directing structure <NUM> for directing fluid radially inward to the fluid passage <NUM>. More specifically, the fluid directing structure <NUM> is configured to direct fluid to the fluid passage <NUM> in a direction that is offset from the central axis <NUM> of the combustor <NUM> and along a path that is angled relative to the normal of the inner surface (not shown) of the outer tube <NUM>.

The periphery of the inner tube <NUM> includes fluid directing structure <NUM> for directing fluid from the interior <NUM> of the inner tube radially outward into the fluid passage <NUM>. More specifically, the fluid directing structure <NUM> is configured to direct fluid into the fluid passage <NUM> in a direction that is offset from the central axis <NUM> of the combustor <NUM> and along a path that is angled relative to the normal of the outer surface (not shown) of the inner tube <NUM>. The fluid directing structures <NUM>, <NUM> can direct their respective fluid in the same general direction. The fluid directing structure <NUM>, <NUM> can include a series of openings with associated fins or guides for directing the fluid in the desired manner (<FIG>).

The jet engine <NUM> further includes one or more tubular fuel supply members <NUM> that extend into or are otherwise in direct fluid communication with the fluid passage <NUM> of the combustor <NUM> and extend radially outward from the passage, through the wall <NUM> of the housing <NUM>, and to a fuel source (not shown) outside of the housing. The fuel supply members <NUM> thereby deliver fuel directly to the fluid passage <NUM>, as indicated generally by arrows F1. Although six fuel supply members <NUM> spaced radially equidistant from one another are illustrated in <FIG>, it will be appreciated that any number of fuel supply members exhibiting any spacing configuration can be provided.

A ring-shaped wall <NUM> (see <FIG>) is secured to the end of the outer and inner tubes <NUM>, <NUM> closer to the compressor <NUM> in order to seal one end of the fluid passage <NUM> in a fluid-tight manner. The wall <NUM> is provided with openings <NUM> that receive ends of the fuel supply members <NUM> to establish the direct fluid path between the fuel supply members and the fluid passage <NUM>.

In operation, air enters the compressor <NUM> at the first end <NUM> of the housing <NUM> in the direction indicated generally by the arrows D2 (<FIG>) and exits the compressor as compressed air. Some of the compressed air exiting the compressor <NUM> flows directly into the interior <NUM> of the inner tube <NUM> as indicated generally by the arrows D3 and through the fluid directing structure <NUM> in the inner tube <NUM> into the fluid passage <NUM>. Some of the compressed air also flows to the peripheral annular space <NUM> between the outer tube <NUM> and the wall <NUM> of the housing <NUM>, where it flows through the fluid directing structure <NUM> in the outer tube and into the fluid passage <NUM> as indicated generally by arrows D4. A wall <NUM> secured to the end of the outer and inner tubes <NUM>, <NUM> closer to the turbine <NUM> and between the outer tube and the wall <NUM> of the housing <NUM> prevents the compressed air D4 from passing into the turbine without first passing through the combustor <NUM>.

The compressed air D3, D4 is mixed with fuel F1 that is injected into the combustor <NUM> via the fuel supply members <NUM>. Since the ring-shaped wall <NUM> blocks the end of the fluid passage <NUM> adjacent to the compressor <NUM>, the fuel F1 is directed by the fuel supply members <NUM> directly into the fluid passage <NUM>. Accordingly, the fluid directing structures <NUM>, <NUM> of the combustor <NUM> only control the flow of compressed air D4, D3 into the fluid passage <NUM> such that the compressed air mixes with the fuel F1 from the fuel supply members <NUM> within the fluid passage <NUM> in a desired manner. More specifically, as the peripheral air D4 passes through the fluid directing structure <NUM> in the outer tube <NUM> and into the fluid passage <NUM>, the air mixes with the fuel F1 exiting the fuel supply members <NUM>. Due to the configuration of the fluid directing structure <NUM>, the compressed air D4 is imparted with a centrifugal force about the central axis <NUM> of the combustor <NUM> as it enters the fluid passage <NUM>. The swirling air D4 mixes with the fuel F1 to create a swirling air/fuel mixture within the fluid passage <NUM> and about the central axis <NUM> of the combustor <NUM>.

Likewise, the compressed air D3 enters the interior <NUM> of the inner tube <NUM> and passes through the fuel directing structure <NUM> of the inner tube <NUM> and into the fluid passage <NUM>, thereby imparting a centrifugal force upon the compressed air D3 about the central axis <NUM> of the combustor <NUM>. The swirling air D3 mixes with the fuel F1 to create an additional swirling air/fuel mixture within the fluid passage <NUM> and about the central axis <NUM> of the combustor <NUM>. The mixture formed from the fuel F1 and the compressed air D3 mixes with and becomes indistinguishable from the mixture formed from the fuel F1 and the compressed air D4 within the fluid passage <NUM>.

Since the fluid directing structures <NUM>, <NUM> extend around the entire periphery of the outer tube <NUM> and the inner tube <NUM>, respectively, the collective air/fuel mixture within the fluid passage <NUM> is forced generally in a single direction, indicated by arrow R (<FIG>), that is transverse to the central axis <NUM> of the combustor <NUM>. It will be appreciated that the fluid directing structures <NUM>, <NUM> can direct the respective air/fuel mixtures in the same direction, e.g., clockwise relative to the central axis <NUM>, within the fluid passage <NUM>. Consequently, the air/fuel mixture within the fluid passage <NUM> undergoes a rotational, spiraling effect relative to the central axis <NUM> of the combustor <NUM> and within the fluid passage <NUM>. The rotating, spiraling air/fuel mixture is ignited by an ignition device (not shown) of any number of types well known in the art and positioned in any number of suitable locations to light the combustor <NUM>. For example, the wall <NUM> can be provided with an opening (not shown) through which an igniter extends. Flame proving means (not shown) can be positioned in any number of suitable locations to detect the presence of flame.

Due to the continued supply of air and fuel to the combustor <NUM> from the compressor <NUM> and the fuel supply members <NUM>, subsequent spiraling air/fuel mixtures are created within the fluid passage <NUM> prior to complete combustion of prior air/fuel mixtures within the passage such that the spiraling air/fuel mixtures become radially layered within the fluid passage. The swirling or rotation of the air fuel mixture in the passage <NUM> provides thorough mixing of the fuel and air, thereby improving combustion. The swirling pattern imparted to the fuel air mixture contributes to combustion stability and, therefore, reduces the chances of flame out.

As shown in <FIG>, the combustion products from the ignited air/fuel mixture exit the combustor <NUM> rotating about the central axis <NUM> of the combustor <NUM> and the axis <NUM> of the jet engine <NUM> as indicated generally by arrows R2. The combustion products of the air/fuel mixture exit the combustor <NUM> at elevated pressure and velocity and pass through the turbine <NUM>, thereby imparting rotation upon the turbine as indicated generally by arrow R3. The turbine <NUM>, in turn, directs the combustion products out of the jet engine <NUM> in the direction indicated generally by arrows T to provide thrust to the aircraft. Since the connecting member <NUM> rotatably connects the turbine <NUM> to the compressor <NUM>, the rotating turbine drives the compressor.

Each of the fluid directing structures <NUM>, <NUM> can have any configuration suitable for imparting rotation to the compressed air D4, D3, respectively, to form an air/fuel mixture with the fuel F1 and within the fluid passage <NUM> that swirls about the central axis <NUM> of the combustor <NUM>.

<FIG> illustrate one configuration of the fluid directing structure <NUM> of the inner tube <NUM> and those having ordinary skill will appreciate that the fluid directing structure <NUM> of the outer tube <NUM> can have a similar construction to the fluid directing structure <NUM>. Alternatively, the fluid directing structures <NUM> and <NUM> can be dissimilar (not shown). In any case, the fluid directing structure <NUM> is configured to direct fluid radially inward while the fluid directing structure <NUM> is configured to direct fluid radially outward.

As shown in <FIG>, the fluid directing structure <NUM> includes a plurality of openings <NUM> in the inner tube <NUM> for allowing the compressed air D3 to pass radially outward from the central passage <NUM> of the inner tube to the fluid passage <NUM>. Each of the openings <NUM> extends entirely through the inner tube <NUM> from an inner surface <NUM> to an outer surface <NUM>. Each opening <NUM> can have any shape, such as rectangular, square, circular, triangular, etc. The openings <NUM> can all have the same shape or different shapes. The openings <NUM> are aligned with one another along the periphery, i.e., around the circumference, of the inner tube <NUM> to form an endless loop. One or more endless loops of openings <NUM> can be positioned adjacent to one another or spaced from one another along the length of the inner tube <NUM>. Each loop can have any number of openings <NUM>. The openings <NUM> in adjacent loops can be aligned with one another or can be offset from one another. The size, shape, configuration, and alignment of the openings <NUM> in the inner tube <NUM> is dictated by desired flow and performance characteristics of the compressed air D3 flowing through the openings. Although the openings <NUM> are illustrated as being arranged in a predetermined pattern along the inner tube <NUM>, it will be appreciated that the openings can be randomly positioned along the inner tube (not shown).

Each opening <NUM> includes a corresponding fluid directing projection or guide <NUM> for directing the compressed air D3 passing through the associated opening radially outward into the fluid passage <NUM> and in a direction that is offset from the central axis <NUM> of the combustor <NUM>, i.e., a direction that will not intersect the central axis. The guides <NUM> are formed on or integrally attached to the inner surface <NUM> and/or the outer surface <NUM> (not shown) of the inner tube <NUM>. Each guide <NUM> extends at an angle (shown in <FIG>) relative to the outer surface <NUM> of the inner tube <NUM>. The guides <NUM> can extend at the same angle or at different angles relative to the outer surface <NUM> of the inner tube <NUM>. Each guide <NUM> extends at an angle, indicated at α2, relative to an axis <NUM> extending normal to the outer surface <NUM> of the inner tube <NUM>.

Since the fluid directing structure <NUM> on the outer tube <NUM> can be formed similar to the fluid directing structure <NUM> on the inner tube <NUM>, those having ordinary skill in the art will appreciate that guides and openings associated with the fluid directing structure <NUM> (not shown) direct the compressed air D4 passing through the outer tube radially inward toward the central passage <NUM> and in a direction that is offset from the central axis <NUM> of the combustor <NUM>. Similar to the fluid directing structure <NUM> on the inner tube <NUM>, the guides of the fluid directing structure <NUM> on the outer tube <NUM> can be formed in or integrally attached to the inner surface and/or the outer surface of the outer tube (not shown). In the illustrated embodiment, the fluid directing structures <NUM>, <NUM> direct the associated incoming compressed air D4, D3 in the same general direction such that the combined air/fuel mixture swirls within the fluid passage <NUM> around the central axis <NUM> of the combustor <NUM> in the same general direction.

<FIG> illustrate alternative configurations of the fluid directing structure <NUM> in the inner tube <NUM>.

The fluid directing structure 252a-d directs the incoming compressed air D3 radially outward into the fluid passage <NUM> and in a direction that is <NUM>) offset from the central axis <NUM> and <NUM>) angled relative to the normal of the outer surface <NUM> of the inner tube <NUM> such that compressed air mixes with the fuel F1 to form an air/fuel mixture within the central passage <NUM> that exhibits a swirling, rotational path around the central axis while becoming radially layered relative to the central axis. The openings in the fluid directing structure can be randomly positioned along the inner tube <NUM> or can be arranged in any predetermined pattern dictated by desired flow and performance criterion.

<FIG> illustrate alternative configurations of the fluid directing structure <NUM>, <NUM> that can be formed on or integrally attached to the inner and/or outer surface of the respective tube <NUM>, <NUM>.

More specifically, either of the fluid directing structures <NUM>, <NUM> can exhibit any of the configurations shown in <FIG>. In the preferred embodiment, the fluid directing structure <NUM> directs the incoming compressed air D4 radially inward into the fluid passage <NUM> and in a direction that is <NUM>) offset from the central axis <NUM> and <NUM>) angled relative to the normal of the inner surface of the outer tube <NUM> (not shown) such that the compressed air mixes with the fuel F1 to form an air/fuel mixture that exhibits a swirling, rotational path within the central passage <NUM> and around the central axis. Likewise, the fluid directing structure <NUM> directs the incoming compressed air D3 radially outward into the fluid passage <NUM> and in a direction that is <NUM>) offset from the central axis <NUM> and <NUM>) angled relative to the normal of the outer surface <NUM> of the inner tube <NUM> (not shown) such that compressed air mixes with the fuel F1 to form an air/fuel mixture that exhibits a swirling, rotational path within the central passage <NUM> and around the central axis. In each case, the openings in the fluid directing structure <NUM>, <NUM> can be randomly positioned along the respective tube <NUM>, <NUM> or can be arranged in any predetermined pattern dictated by desired flow and performance criterion.

In <FIG>, the fluid directing structure 252a includes a plurality of guides 286a that define openings 284a in the inner tube 244a. The guides 286a are arranged in a series of rows that extend around the periphery of the inner tube 244a. The annular rows are positioned next to one another along the length of the inner tube 244a. The guides 286a of adjacent rows can be radially offset from one another or can be radially aligned with one another (not shown). The guides 286a in each row can be similar or dissimilar to one another. The guides 286a direct the compressed air D3 passing through the openings 284a in a radially inward direction that is offset from the central axis <NUM> and at an angle α2 relative to the axis 287a extending normal to the outer surface 280a of the inner tube 244a. If the guides 286a within a row are fully or partially aligned with one another around the periphery of the inner tube 244a, the compressed air D3 exiting each guide in that row is further guided in a direction offset from the central axis <NUM> by the adjacent guide(s) in the same row.

In <FIG>, the inner tube 244b is formed as a series of steps that each includes a first member <NUM> and a second member <NUM> that extends substantially perpendicular to the first member to form an L-shaped step. The second member <NUM> of each step includes a plurality of openings 284b for directing the compressed air D3 in a direction that is offset from the central axis <NUM> and angled relative to the axis (not shown) extending normal to the outer surface 280b of the inner tube 244b. In particular, the openings 284b in each second member <NUM> direct the compressed air D3 across the first member <NUM> of the adjoining step to impart rotation to the compressed air and, thus, to the air/fuel mixture within the fluid passage <NUM> about the central axis <NUM>.

In <FIG>, the fluid directing structure 252c includes a plurality of openings 284c that extend from the inner surface 282c of the inner tube 244c to the outer surface 280c. The openings 284c extend through the inner tube 244c at an angle relative to the axis 287c extending normal to the outer surface 280c of the inner tube 244c and through the central axis <NUM> of the combustor <NUM>. The openings 284c in the inner tube 244c direct the compressed air D3 and, thus, the air/fuel mixture within the fluid passage <NUM> in a direction that is offset from the central axis <NUM> and at an angle relative to the axis 287c in order to impart rotation to the air/fuel mixture within the fluid passage about the central axis.

In <FIG>, the fluid directing structure 252d is formed by a series of arcuate, overlapping plates <NUM> that cooperate to form the inner tube 244d. Each plate <NUM> has a corrugated profile that includes peaks <NUM> and valleys <NUM>. The plates <NUM> are longitudinally and radially offset from one another such that that peaks <NUM> of one plate <NUM> are spaced between the peaks of adjacent plates. In this configuration, the peaks <NUM> and valleys <NUM> of the plates create passages <NUM> through which the compressed air D3 is directed. Each plate <NUM> directs the compressed air D3 in a direction that extends substantially parallel to the adjoining arcuate plate to impart rotation to the compressed air and, thus, to the air/fuel mixture within the fluid passage <NUM> about the central axis <NUM>. The air/fuel mixture within the fluid passage <NUM> is thereby directed in a direction that is offset from the central axis <NUM> of the combustor <NUM> and angled relative to the axis (not shown) extending normal to the plates <NUM>.

Features in <FIG> that are identical to features in <FIG> have the same reference number as <FIG>, whereas features in <FIG> that are not similar to features in <FIG> are given the suffix "a". <FIG> illustrate a jet engine 200a similar to the jet engine <NUM> of <FIG>. In the jet engine 200a of <FIG>, the fuel being delivered via the fuel pipe 254a is partially mixed with air prior to being injected into the region <NUM>. The partially pre-mixed fuel is indicated by the reference character F3 and, as seen best in <FIG>, the fuel pipe 254a passes through a pre-mix chamber <NUM>'. As seen best in <FIG>, the pre-mix chamber <NUM>' receives compressor air indicated by the reference character D5 through a port (not specifically shown) formed in the pre-mix chamber <NUM>'. Fuel passing through the chamber mixes with the incoming air stream (D5) and is injected to the region <NUM> where it is mixed with additional air D4, D3 delivered through ports <NUM>, <NUM> formed in the members <NUM>, <NUM>, respectively (see also <FIG>).

The jet engine burner shown in <FIG> operates essentially similar to the burner shown in <FIG>, except that the fuel is pre-mixed with some air prior to being injected into the region <NUM>. The fuel and air movement patterns shown in <FIG> are equally applicable to the burner shown in <FIG>. In the jet engine 200a of <FIG>, however, the fuel delivered by the fuel supply members 254a is partially pre-mixed with the incoming compressed air D5 before being discharged into the chamber <NUM>. This partial fuel mixture is further mixed with compressed air D3 and D4 which is injected through the respective fluid directing structure <NUM> and <NUM> and into the fluid passage/combustion chamber <NUM>' where the fully mixed fuel charge is ignited and burned.

The fluid directing structure <NUM> allows the air D3 within the passage <NUM> to be directed radially outward into the fluid passage <NUM>, and the fluid directing structure <NUM> allows the air D4 in the region <NUM> outside of the outer tube <NUM> to be directed radially inward into the fluid passage <NUM>. Either or both of the fluid directing structures <NUM>, <NUM> can have any of the configurations illustrated in <FIG>.

The compressed air D3, D4 mixes with the partial fuel mixture F3 from the fuel supply members 254a to form an air/fuel mixture within the fluid passage <NUM> that swirls around the axis <NUM> of the combustor 240a. Due to the configuration of the fluid directing structure <NUM>, the compressed air D4 is imparted with a centrifugal force about the axis <NUM> of the combustor 240a as it passes into the fluid passage <NUM>. Likewise, the compressed air D3 enters the interior <NUM> of the inner tube <NUM> and then through the directing structure <NUM> of the inner tube <NUM> and into the fluid passage <NUM>, thereby imparting a centrifugal force upon the air/fuel mixture about the axis <NUM> of the combustor 240a.

Those having ordinary skill in the art will appreciate that a mixture of air and fuel is formed in the fluid passage and imparted with a centrifugal force that causes the air/fuel mixture within the fluid passage <NUM> to rotate or spiral around the central axis of the combustor, thus improving and stabilizing combustion.

Features in <FIG> that are identical to features in <FIG> or <FIG> have the same reference number as <FIG> or <FIG>, whereas features in <FIG> that are not similar to features in <FIG> are given the suffix "b". Similar to the jet engine <NUM> of <FIG>, a wall 251b is secured to the end of the combustor 240b closer to the compressor <NUM> and a wall 255b is secured to the end of the combustor closer to the turbine <NUM>. In the jet engine 200b of <FIG>, however, the fuel F4 is injected upstream from the combustor and is completely mixed with compressed air D4' before entering the combustor 240b.

The jet engine 200b of <FIG> includes a fluid mixing element <NUM> secured to the housing <NUM> for pre-mixing the compressed air D4' and fuel F4 exiting the fuel supply members 254b such that the air and fuel is completely mixed prior to entering the combustor 240b. The fluid mixing element <NUM> is positioned along the axis <NUM> of the jet engine 200b between the fuel supply members 254b and the combustor 240b and includes an outer element <NUM> and an inner element <NUM> positioned concentric to one another and the connecting member <NUM>. The outer element <NUM> is ring-shaped and has a generally frustoconical configuration that tapers radially inward in a direction extending towards the combustor 240b, i.e., leftward as viewed in <FIG>. The inner element <NUM> is positioned in the interior of the outer element <NUM> and is secured to or integrally formed with the outer element. The compressor/turbine connecting member <NUM> extends through an opening indicated generally by the reference character 294a in the inner element <NUM>.

An annular gap <NUM> extends between the inner element <NUM> and the outer element <NUM> and tapers inwardly in a direction extending towards the combustor 240b, i.e., the cross-sectional area of the gap along the axis <NUM> decreases in the direction towards the combustor. The fluid mixing element <NUM> is configured such that the compressed air D4' from the compressor and the fuel F4 exiting the fuel supply members 254b must pass through the gap <NUM> in the mixing element in order to reach the combustor 240b. Since the cross-sectional area of the gap <NUM> decreases along the length of the fluid mixing element <NUM>, the compressed air D4' and fuel F4 become mixed together as the air and fuel travel through the fluid mixing element. The air D4' and fuel F4 exit the fluid mixing element <NUM> as a fully pre-mixed mixture, indicated generally as M in <FIG>. Although the fluid mixing element <NUM> is illustrated as having a particular construction, those having ordinary skill will appreciate that any structure or structures can be used that are configured to mix the compressed air D4' and fuel F4 to form a fully pre-mixed mixture M that enters the combustor 240b to be ignited.

The mixture M enters the combustor 240b along two different pathways. Some of the mixture M flows to the region <NUM>, i.e., the exterior of the combustor 240b between the wall <NUM> of the housing <NUM> and the outer tube <NUM>, where it is directed radially inward by the fluid directing structure <NUM> of the outer tube <NUM> into the fluid passage <NUM>. The remainder of the mixture M flows into the interior <NUM> of the inner tube <NUM> where it is directed radially outward by the fluid directing structure <NUM> of the inner tube into the fluid passage <NUM>. The fluid directing structures <NUM>, <NUM> cause the collective mixture M to swirl within the fluid passage <NUM> around the axis <NUM> of the combustor 240b in a manner similar to that illustrated in <FIG>. The mixture M is then ignited within the fluid passage <NUM> by an ignition source (not shown) and the combustion products of the ignited mixture are expelled from the combustor 240b towards the turbine <NUM> in the manner indicated generally by arrows R2 in order to drive the turbine in the manner described.

In the jet engine 200c of <FIG>, a plurality of combustors 240c is arranged about the central axis <NUM> of the jet engine. Each of the combustors 240c can constitute the non-pre-mixed combustor <NUM> of <FIG>, the partially pre-mixed combustor 240a of Figs. <NUM>-6B or the fully pre-mixed combustor 240b of <FIG> or modifications thereof. Features in <FIG> that are identical to features in <FIG> have the same reference number as <FIG>, whereas features in <FIG> that are similar to features in <FIG> are given the suffix "c".

As shown in <FIG>, the compressor <NUM> and the turbine <NUM> are positioned within the housing <NUM> on opposing sides of the combustors 240c. The combustors 240c are preferably axially aligned with one another and are radially spaced about the axis <NUM> of the jet engine 200c (<FIG>). Although five combustors 240c are illustrated in <FIG>, it will be appreciated that more or fewer combustors can be provided in accordance with the present invention. Furthermore, the combustors 240c can be symmetrically or asymmetrically spaced about the central axis <NUM>. The combustors 240c can extend substantially parallel to one another and the axis <NUM> or can extend at an angle relative to one another and/or the axis. A wall <NUM> is provided between the wall <NUM> of the housing <NUM> and the combustors 240c and between the combustors to ensure that fluid only flows into the combustors, i.e., not around or between the combustors and the wall of the housing. Another wall <NUM> is also preferably provided to prevent air or fuel/air from bypassing the combustors. The walls <NUM>, <NUM> can also serve as mounting plates or supports for the combustors 240c.

The combustors 240c are different from the combustors <NUM>, 240a, 240b in that no inner tube is used. The outer tube <NUM>' of the combustor has fluid directing structure <NUM> such that the mixture of air and fuel is directed from a fluid passage <NUM>' radially inward through the fluid directing structure into the interior <NUM>'. In this configuration, each combustor 240c includes a solid outer wall <NUM> that has a continuous surface such that no fluid passes radially through it. A cap 251c is provided on each combustor 240c to fluidly seal the upstream end of the tube <NUM> closer to the turbine <NUM> such that air and/or the fuel/air mixture cannot axially enter the passage <NUM>' of the combustor 240c, i.e., the air and/or fuel mixture must pass radially inward through the fluid directing structure <NUM>' and into the interior passage <NUM>'. The downstream end of the annular passage <NUM>' is sealed by a cap 257a which ensures that all the air (or fuel-air mixture) travels into the combustion passage <NUM>'.

Air exiting the compressor <NUM> is distributed amongst the combustors 240c. The air is mixed with fuel delivered by the fuel pipe 254c and is ultimately swirled and burned in the inner combustion chamber <NUM>'. Several methods and apparatus for injecting fuel into the burner 240c are illustrated in <FIG>. A fuel pipe 254c is shown in solid and, in the solid configuration, fuel is injected upstream of the combustor 240c where it is fully mixed with air delivered by the compressor <NUM> as described in connection with <FIG>, <FIG> and <FIG>. This fully mixed fuel/air charge then enters the region <NUM>' and travels into the combustion passage <NUM>' via ports <NUM> formed in the tubular member <NUM>'. As explained earlier, the ports are arranged to cause rotation of the fuel/air mixture in the combustion passage <NUM>'.

In an alternate embodiment, each combustor 240c utilizes the fuel/air delivery system described in connection with <FIG> and <FIG>. A fuel pipe 254c' includes a pre-mix chamber <NUM>". In this configuration, the fuel being delivered by the fuel pipe 254c' is partially mixed with air received by the pre-mix chamber <NUM>" from the compressor <NUM>. This partial fuel mixture is injected into the chamber <NUM>' through the cap 251c where it fully mixed with compressor air D6 that enters the chamber <NUM>' via the passage <NUM>' and then the ports <NUM> formed in the tubular member <NUM>'.

In still another embodiment, the combustors 240c utilize the fuel/air delivery system described in connection with <FIG> and <FIG>. In this configuration, the fuel is injected directly into the combustion passage <NUM>' via the fuel pipe 254c, the downstream end of which extends thought the cap 251c. The injected fuel is mixed with the swirling air delivered through the tubular members <NUM>' and <NUM>.

In all of these embodiments, an igniter (not shown) within the interior <NUM>' of the tube member <NUM>' of each combustor 240c ignites the swirling air/fuel mixtures. The swirling combustion products collectively exit the combustors 240c and pass through the turbine <NUM>, causing rotation of the turbine and expulsion of the combustion products from the jet engine 200c.

<FIG> illustrate a combustor or fuel burner <NUM> in accordance with the present invention. The combustor <NUM> can be used in industrial, household, and commercial heating appliances such as, for example, a water heater, boiler, furnace, etc. The combustor <NUM> includes outer and inner tubes <NUM>, <NUM> that are concentric with one another about a central axis <NUM>. Referring to <FIG>, the outer tube <NUM> extends from a first end <NUM> to a second end <NUM> and defines an interior or central passage <NUM>. The inner tube <NUM> extends from a first end <NUM> to a second end <NUM> and defines an interior or central passage <NUM> for receiving a pre-mixed mixture of combustible fuel and air. The combustible fuel can be a liquid, e.g., atomized or vaporized, or gas.

The space between the outer and inner tubes <NUM>, <NUM> defines a fluid passage <NUM>. The periphery of the inner tube <NUM> includes fluid directing structure <NUM> for directing fluid radially outward from the central passage <NUM> to the fluid passage <NUM>. The periphery of the outer tube <NUM> includes fluid directing structure <NUM> for directing fluid radially inward to the fluid passage <NUM>. The fluid directing structures <NUM>, <NUM> can constitute any of the aforementioned fluid directing structures or combinations thereof (see <FIG>).

A ring-shaped wall <NUM> is secured to the first ends <NUM>, <NUM> of the outer and inner tubes <NUM>, <NUM>. The wall <NUM> includes a ring-shaped base <NUM> and a pair of annular flanges <NUM>, <NUM> extending from the base. The flange <NUM> is secured to the first end <NUM> of the inner tube <NUM> in a fluid-tight manner. The flange <NUM> is secured to the first end <NUM> of the outer tube <NUM> in a fluid-tight manner. Consequently, the wall <NUM> seals one end of the fluid passage <NUM> in a fluid-tight manner. Another wall <NUM> is secured to the second end <NUM> of the inner tube <NUM> and seals the second end of the inner tube in a fluid-tight manner.

The outer and inner tubes <NUM>, <NUM> are positioned in a housing <NUM> extending from a first end <NUM> to a second end <NUM>. The housing <NUM> is centered on the axis <NUM> and defines an interior <NUM> for receiving the outer and inner tubes <NUM>, <NUM>. An end wall or plate <NUM> is secured to the second end <NUM> of the housing <NUM> and the second end <NUM> of the outer tube <NUM> to secure the housing to the outer tube. The wall <NUM> is secured to the outer tube <NUM> in a fluid-tight manner and is sized such that the housing <NUM>, outer tube <NUM>, and inner tube <NUM> are concentric.

Referring further to <FIG>, one or more supply members <NUM> carrying a fully pre-mixed mixture of combustible fuel and air, indicated by reference character F5, are positioned upstream of the outer and inner tubes <NUM>, <NUM>. The supply member <NUM> is generally aligned with and extend towards the central passage <NUM> to establish a direct fluid path between the supply member and the central passage. The supply member <NUM> can extend axially towards into the housing <NUM> (as shown) or radially inward through the housing, e.g., have an L-shaped configuration similar to the fuel supply members <NUM> in <FIG> (not shown). In any case, the supply member <NUM> delivers the pre-mixed mixture F5 to the interior <NUM> of the housing <NUM>.

Due to the configuration of the fuel burner <NUM> the pre-mixed mixture F5 is divided into two pre-mixed portions F6, F7 that take different flow paths from the interior <NUM> of the housing <NUM> to the fluid passage <NUM>. The pre-mixed portion F6 flows into the central passage <NUM> at the first end <NUM> of the inner tube <NUM>. The end wall <NUM> prevents the pre-mixed portion F6 from exiting the second end <NUM> of the inner tube <NUM> except through the fluid directing structure <NUM>. Consequently, the pre-mixed portion F6 is directed radially outward through the fluid directing structure <NUM> into the fluid passage <NUM>. When this occurs, the fluid directing structure <NUM> imparts a centrifugal force upon the pre-mixed portion F6 such that the pre-mixed portion swirls about the axis <NUM> of the combustor <NUM> while flowing through the fluid passage <NUM>.

At the same time, the pre-mixed portion F7 flows to the radial space between the housing <NUM> and the outer tube <NUM>. At this point, the fluid directing structure <NUM> directs the pre-mixed portion F7 radially inward into the fluid passage <NUM>. The end wall <NUM> prevents the pre-mixed portion F7 from exiting the second end <NUM> of the housing <NUM> except through the fluid directing structure <NUM>. Due to the configuration of the fluid directing structure <NUM>, the pre-mixed portion F7 is imparted with a centrifugal force about the axis <NUM> of the combustor <NUM> as it passes radially inward into the fluid passage <NUM>.

It is therefore clear that the pre-mixed mixture F5 flows along multiple flow paths - a portion F6 flowing radially outward through the fluid directing structure <NUM> and a portion F7 flowing radially inward through the fluid directing structure <NUM> - to reach the fluid passage <NUM>. The pre-mixed portions F6, F7 of the pre-mixed mixture F5 are recombined within the fluid passage <NUM> and collectively swirl around the axis <NUM> of the combustor <NUM> and between the inner and outer tubes <NUM>, <NUM>.

The combustor <NUM> is specifically configured to restrict fluid flow therethrough to what has been described. In addition to the aforementioned walls <NUM>, <NUM>, the end wall <NUM> prevents the pre-mixed portions F6, F7 and any flame produced therefrom from exiting the fluid passage <NUM> through the first ends <NUM>, <NUM> of the inner and outer tubes <NUM>, <NUM>. Consequently, the pre-mixed mixture F5 can only enter the fluid passage <NUM> by passing through the respective fluid directing structures <NUM> and <NUM>.

That said, the combustion products from the ignited air/fuel mixture exit the combustor <NUM> rotating within the fluid passage <NUM> and about the central axis <NUM> of the combustor <NUM> as indicated generally by arrows R3 in <FIG>. The rotating, spiraling air/fuel mixture R3 is ignited by an ignition device (not shown) of any number of types well known in the art and positioned in any number of suitable locations to light the combustor <NUM>. For example, the wall <NUM> can be provided with an opening (not shown) through which an igniter extends. Flame proving means (not shown) can be positioned in any number of suitable locations to detect the presence of flame.

It will be appreciated that the combustor <NUM> of <FIG> can be used in the same manner as the combustors <NUM>, 240a, 240b are used and can therefore receive a fully pre-mixed mixture or partially pre-mixed mixture and additional air in accordance with the present invention.

<FIG> illustrate a combustor or fuel burner <NUM>.

The combustor <NUM> constitutes an external swirl burner that can be used in industrial, household, and commercial heating appliances such as, for example, a water heater, boiler, furnace, etc. More specifically, the combustor <NUM> produces a swirling, spiraling and/or rotating flame about and along its exterior in a simple, inexpensive, and efficient manner.

The combustor <NUM> includes a tube <NUM> extending along a central axis <NUM> from a first end <NUM> to a second end <NUM>. The tube <NUM> includes an inner surface <NUM> defining an interior or central passage <NUM> and an outer surface <NUM>. The first end <NUM> of the tube <NUM> includes a flange <NUM> for securing the combustor <NUM> to, for example, a portion of the appliance. A wall <NUM> is secured to the second end <NUM> of the tube <NUM> to seal one end of the central passage <NUM> in a fluid-tight manner. In this example, the combustor <NUM> does not include an outer tube or housing and, thus, the tube <NUM> defines both the exterior and interior of the combustor <NUM>.

The periphery of the tube <NUM> includes fluid directing structure <NUM> for directing fluid radially outward from the central passage <NUM> to a position adjacent to and radially outward of the outer surface <NUM> and fluid directing structure <NUM>, i.e., exterior to or outside of the tube. The fluid directing structure <NUM> can constitute any of the aforementioned fluid directing structures or combinations thereof (see <FIG>).

As shown in <FIG>, the central passage <NUM> is configured to receive a pre-mixed mixture of combustible fuel and air. The combustible fuel can be a liquid, e.g., atomized or vaporized, or gas. To this end, one or more supply members <NUM> carrying a fully pre-mixed mixture of combustible fuel and air, indicated by reference character F8, are positioned upstream of the tube <NUM>. The supply member480 is generally aligned with and extends towards the central passage <NUM> to establish a direct fluid path between the supply member and the central passage. The supply members <NUM> extend axially towards and/or into the tube <NUM> and deliver the pre-mixed mixture F8 to the central passage <NUM>.

The pre-mixed mixture F8 flows into the central passage <NUM> at the first end <NUM> of the tube <NUM>. The end wall <NUM> prevents the pre-mixed mixture F8 from exiting the second end <NUM> of the tube <NUM> except through the fluid directing structure <NUM>. Consequently, the pre-mixed mixture F8 is directed radially outward through the fluid directing structure <NUM> to the tube exterior. When this occurs, the fluid directing structure <NUM> imparts a centrifugal force upon the pre-mixed mixture F8 such that the pre-mixed portion swirls about the axis <NUM> of the combustor <NUM> while flowing about the tube exterior.

The combustion products from the ignited air/fuel mixture exit the combustor <NUM> rotating about the central axis <NUM> of the combustor <NUM> around the exterior of the tube <NUM> as indicated generally by arrows R4 in <FIG>. To this end, the rotating, spiraling air/fuel mixture R4 is ignited by an ignition device (not shown) of any number of types well known in the art and positioned in any number of suitable locations to light the combustor <NUM>. Flame proving means (not shown) can be positioned in any number of suitable locations to detect the presence of flame. The ignited air/fuel mixture R4 is directed into, for example, the heat exchange tube of the heating appliance.

The combustor of the present invention is advantageous over conventional combustors or burners for several reasons. Unlike conventional combustors in which the flame is propagated primarily by molecular conduction of heat and molecular diffusion of radicals from the flame into the approaching stream of reactants, i.e., the air/fuel mixture, the combustor of the present invention forces additional heat transfer by convection and radiation from the high velocity flame envelope overlaying and intermixing with the incoming air/fuel mixture. The incoming air/fuel mixture is preheated while the flame zone is being cooled, which advantageously helps to reduce NOx. The flame envelope is advantageously spaced entirely from the inner surface of the inner tube when the air/fuel mixture is ignited within the inner tube and spaced entirely from the outer surface of the inner tube when the air/fuel mixture is ignited within the fluid passage.

Radicals are also forced into the incoming reactant stream by the overlaying and intermixing flame envelope. The presence of radicals in a mixture of reactants lowers the ignition temperature and allows the fuel to burn at lower than normal temperature. It also helps to significantly increase flame speed, which shortens the reaction time, thereby additionally reducing NOx formation while significantly improving flame stability/flame retention. The improved stability and flame retention reduces the chances of flame out.

Due to the exceptional flame retention/stability of the combustor of the present invention, it is capable of running at very high combustion loadings. High loadings allow the burner to run in a stable "lifted flame" mode i.e., the flame is spaced from the combustor surfaces. Lifting of the flame in this manner is desirable in that the combustor surfaces are not directly heated, thereby maintaining the surfaces at a lower temperature and lengthening the usable life of the combustor. A high combustion loading also allows the use of a smaller, space saving, and less costly combustor for a given application. Furthermore, the combustor of the present invention, due to the exceptional flame retention as discussed above, is also capable of operating cleanly (low CO) at very high levels of excess air, which produces NOx levels well below those achievable with conventional combustors.

The preferred embodiments of the invention have been illustrated and described in detail. However, the present invention is not to be considered limited to the precise construction disclosed. For example, it will be understood that any of the combustors described above can incorporate a "variable volume" combustion chamber, e.g., fluid passage, by configuring the wall 251c (shown in <FIG>) secured to the inner and outer tubes to be movable along the axis of the jet engine. Such a construction would allow for optimized combustion performance by matching the combustion chamber volume to the power output required.

The invention has been described in detail in connection with a jet engine application. Those skilled in the art will recognize that the principles of this invention can be applied to burners used in heating appliances such as hot water tanks, furnaces and boilers. Those skilled in the art will recognize that the disclosed burner configurations can be adapted for use in the identified heating applications. For some applications, the burner would be configured as a power burner in which a blower or the suitable device would force air into the burner where it would be mixed with the suitable liquid fuel such as fuel oil or a gaseous fuel such as natural gas or propane.

Claim 1:
A fuel burner (<NUM>) comprising:
an outer tube (<NUM>) extending along a central axis (<NUM>) from a first end (<NUM>) to a second end (<NUM>), the outer tube (<NUM>) including an outer surface and an inner surface defining a passage (<NUM>), the outer tube (<NUM>) including fluid directing structure (<NUM>) having a plurality of openings and a guide associated with each opening;
an inner tube (<NUM>) extending from a first end (<NUM>) to a second end (<NUM>) and being positioned within the passage (<NUM>) of the outer tube (<NUM>), the inner tube (<NUM>) including an outer surface and an inner surface defining a central passage (<NUM>), wherein a fluid passage is defined between the outer surface of the inner tube and the inner surface of the outer tube, the central passage (<NUM>) being supplied with a mixture of air and combustible fuel pre-mixed upstream of the inner tube (<NUM>), the inner tube (<NUM>) having fluid directing structure (<NUM>) for directing the pre-mixed mixture radially outward from the central passage (<NUM>) to the fluid passage such that the pre-mixed mixture rotates radially about the central axis (<NUM>) between the inner tube (<NUM>) and the outer tube (<NUM>), the fluid directing structure (<NUM>) on the outer tube (<NUM>) being supplied with the pre-mixed mixture and directing the pre-mixed mixture radially inward to the fluid passage to mix with the pre-mixed mixture from the fluid directing structure (<NUM>) on the inner tube (<NUM>);
a first end wall (<NUM>) closing the second end (<NUM>) of the inner tube (<NUM>) in a fluid-tight manner;
and
a second end wall (<NUM>) securing the first end (<NUM>) of the inner tube (<NUM>) to the outer tube (<NUM>) in a fluid-tight manner such that the fluid directing structure (<NUM>) on the inner tube (<NUM>) provides the only fluid path from the central passage (<NUM>) to the fluid passage,
characterized in that
the first end wall (<NUM>) intersects the central axis (<NUM>).