Patent Application
20120064465
1. Field of the Invention
The present invention relates generally to a fuel combustion method and an apparatus for performing same. More particularly, the invention relates to an apparatus and/or method for providing a generally uniformly volume distributed combustion, and further, an improved apparatus and/or method of mixing for uniformly volume distributed combustion.
2. Description of Related Art
It was arguably not until the late 1970s and early 1980s, as a result of the first and the second energy crisis, that research and development activities began to seriously focus on improving energy efficiency. Similarly, in the same time period, industry began to truly recognize the need for eliminating noxious pollutants such as nitrogen oxides, mostly due to concerns over human health and concern for the environment.
To achieve these goals, the combustion temperature must be less than that at which nitrogen oxidizes. On the other hand, the combustion temperature must be high enough for complete combustion with carbon monoxide totally burnt. Therefore, the optimal combustion temperature must be around 1100° C. For combustion to occur at the optimal temperature, fuel and an oxidizer must be finely mixed and preheated throughout the entire combustor volume. Although uniformly distributed (flameless) combustion was discovered circa 1911, it was not until recently that uniformly distributed combustion (flameless oxidation) has become a focus of industrial research.
In flameless combustion, ignition occurs and progresses with generally no visible or audible signs of a flame that is usually associated with burning. As early as 1989, it was found that combustion in a furnace could be sustained even with an extremely low concentration of oxygen, if the combustion air was sufficiently preheated. Particularly, during experiments with a self-recuperative burner, it was observed that at furnace combustion temperatures of about 1000° C. and an air preheat temperature of about 650° C., no flame was visible and no ultraviolet signal was detected. Nevertheless, the fuel was totally burnt, and carbon monoxide as well as nitric oxide content of the exhaust was found to be extremely low.
Conventionally, to initiate flameless combustion, preheated oxidizing air and gas fuel is fed into a combustion chamber at relatively high injection speeds. The geometry of the combustion chamber and the high injection speed of the fuel-air mixture create large internal recirculation of the combustion mixture. Once the recirculation is sufficient, the combustion becomes distributed throughout the volume of the combustion chamber and the flame is no longer visible. Further, as an application of such a principle, nitric oxide emission can be reduced through the dilution of the combustion air with the circulated burned gas in the furnace. Dilution of the combustion air can reduce the oxygen content of the oxidizer, which decreases temperature fluctuations in the combustion chamber as well as the mean temperature, resulting in low amounts of nitric oxide emission.
Recognizing the potential benefits of flameless combustion, the industry has attempted to develop various types of combustion chambers which support flameless combustion. For example, U.S. Pat. No. 6,796,789 by Gibson et al., entitled “Method to Facilitate Flameless Combustion Absent Catalyst or High-Temperature Oxidant” describes an oval-shaped combustion chamber configured to circulate gas fuel with flue gas and combustible air. U.S. Pat. No. 5,340,020 by Manus et al., titled “Method and Apparatus for Generating Heat by Flameless Combustion of a Fuel in a Gas Flow” describes a combustion apparatus, which utilizes a catalyst for producing the flameless combustion. U.S. Pat. No. 6,826,912 B2, issued on Dec. 7, 2004 by Y. Levy et al., entitled “Design of Adiabatic Combustors” describes a gas turbine combustion chamber, to produce high-pressure gases for the turbine. The combustion chamber has a primary combustion zone containing a substantially vitiated-air zone into which the fuel is injected. The primary air inlet is positioned and directed to produce an internal recirculation that generates a ring-like vortex within the primary zone, thereby providing the vitiated-air zone and maintaining therein a state of flameless oxidation.
U.S. Pat. No. 5,839,270 by Jirnov et al., entitled “Sliding-Blade Rotary Air-Heat Engine with Isothermal Compression of Air” describes a particularly efficient combustion chamber originally configured for use with the sliding-blade rotary air-heat engine. The Jirnov “vortex” combustion combined with a straight-flow pre-combustion chamber successfully solved problems associated with multi-fuel operation with a high completeness of combustion over the wide range of the coefficient of air concentration, while producing a substantial drop in toxicity of the exhaust gases. The combustor was also characterized by providing a simplified combustor design and ease of fabrication, high thermal as well as volumetric efficiency, while being able to employ various types of combustible hydrocarbon gas or liquid fuel.
Yet another combustion apparatus suitable for flameless combustion is described in U.S. patent application Ser. No. 12/774,576, filed May 5, 2010, and entitled “Apparatus and Methods for Providing Uniformly Distributed Combustion of Fuel”, (which application is assigned to a common assignee of the present application and includes at least one common applicant/inventor). The disclosure of U.S. patent application Ser. No. 12/774,576 is incorporated herein by reference for all purposes and made a part of the present disclosure. In this previously filed application, a combustion chamber is described as including a precombustion chamber in addition to a main combustion chamber. The pre-combustion chamber provides delivery of a super-rich fuel and air mixture, ignition, and/or partial combustion and decomposition of heavy and low grade fuels. In operation with the Jirnov engine, prior to entering the pre-combustion chamber, the combustion air is preheated by exhaust gases and then, upon entry, heating coils in the pre-combustion chamber further heat the air. Heated fuel is also injected into the pre-combustion chamber prior to entry into the main vortex combustion chamber.
To further facilitate uniformly volume distributed combustion of fuel, the pre-combustion chamber in this previous application provides at least one air injection inlet port positioned to induce a first stage vortex in the pre-combustion chamber. Further, the pre-combustion chamber is interfaced with the main combustion chamber to induce a second stage vortex in the mian combustion chamber. Specifically, the entry of the fuel-air mixture into the main vortex combustion chamber is such that a very large swirl is created which helps ensure proper mixture and a substantially uniform combustion within the combustion chamber. The main vortex Combustion chamber may also be equipped with an elongated combustion exhaust conduit. The conduit extends from the exhaust of the combustion chamber to the opposite end of the chamber. The combustion exhaust conduit provided therefore is a physical or structural barrier between the inlet to the main vortex combustion chamber and its exhaust.
In recent years, due to the cost of fuel and due to concern for the environment, there has been a high interest in the use of bio-fuels. Bio-fuels can include solid, liquid or gas fuel derived from recently expired biological material. Theoretically, bio-fuel can be produced from any biological carbon source, the most common of which includes plants as well as plant-derived materials. The bio-fuel industry is expanding in Europe, Asia and the Americas. The most common use for bio-fuels is as liquid fuels for automotive transport. However, there is also a desire within the industry to use bio-fuels to generate steam and/or electricity. Bio-diesel is the most common bio-fuel in Europe, and is becoming more popular in Asia and America. Biodiesel can be produced from oils or fats and forms into a liquid similar in composition to petroleum diesel.
For example, bio-diesel production can result in glycerol (glycerin) as a by-product at one part glycerol for every 10 parts biodiesel. This has resulted in saturation in the market for glycerol. Accordingly, rather than being able to sell the glycerol, many companies have to pay for its disposal. Sources indicate that the 2006 levels of glycerol production were at about 350,000 tons per annum in the USA, and 600,000 tons per annum in Europe. Sources further indicate that such levels will only increase as biodiesel will become more popular as a homegrown energy source and as Europe implements EU directive 2003/30/EC, which requires replacement of 5.75% of petroleum fuels with bio-fuel, across all member states by 2010. Therefore, inventors recognized the need for an apparatus as well as methods of economically disposing of glycerin or other byproducts in an environmentally friendly and energy efficient manner.
The applicants also recognize that, although considered a waste product of biodiesel fuel production, byproducts, such as glycerin, have significant energy delivery potential. Glycerin, however, along with some other forms of waste/bio-fuels, has characteristics which must be overcome in order to employ them as a fuel source. Conditions required for efficient combustion of glycerin and other waste/bio-fuels include preheating, fuel fine atomization, fast and fine mixing with oxidizer as well as sufficient residence time in a combustion chamber. Therefore, recognized by the applicants is the need for an apparatus and methods for economically and efficiently burning such heavily viscous waste/bio-fuels in a combustion chamber to produce an exhaust which can be utilized as an energy source.
Further recognized by the applicants is the need for such an apparatus and methods which can provide uniform volume-distributed oxidation to thereby decrease harmful emissions and increase energy efficiency. To this end, it is also desirable to provide improved means and apparatus for uniform volume distributed oxidation and uniform flameless combustion.
In view of the foregoing, embodiments of the present invention advantageously provide an apparatus and methods for economically and efficiently burning gaseous and liquid fuels, as well as viscous low-grade bio-fuels. Embodiments of the present invention also advantageously provide an apparatus a combustion chamber configured to provide a uniform volume distributed fuel-oxidizer mixture to thereby decrease nitric oxide emissions and increase energy efficiency. Embodiments of the invention also include related methods of operating same, and more particularly, combustion methods including advantageously organizing flows within a chamber to enhance mixing and/or heat transfer. Embodiments of the present invention provide an apparatus and methods which improve upon the Jirnov vortex combustion chamber and precombustion chamber and methods described in U.S. Pat. No. 5,839,270 by Jirnov et al., entitled “Sliding-Blade Rotary Air-Heat Engine with Isothermal Compression of Air” and the U.S. patent application Ser. No. 12/774,576, filed May 5, 2010, titled “Apparatus and Methods for Providing Uniformly Distributed Combustion of Fuel.”
As used herein, the term “fine mixing” is a term known by those skilled in the art, and means that the distance between an oxidizer molecule and a fuel molecule become close or substantially close to the free path of molecules. The term “fast mixing” is also a term in the art and means that the time of mixing is significantly shorter than the residence time (axial length dimension/axial velocity). The mixing time is generally understood to be equal to a dimension scale of eddies divided by the turbulence velocity (difference in two magnitude of velocities). It is desirable for the mixing time to be substantially smaller small than the combustion time (which is a function of temperature, pressure etc.). In other, more specific descriptions of aspects of the invention provided here, the term mixing may refer also to facilitating and enhancing the heat transfer between “mixed’ or distributed constituents of the combustion chamber.
In the pursuit of desirable combustion properties, including stable and substantially complete fuel burning with low levels of harmful emissions, it is desirable to generate high speed counter flows, and fine scale Karman eddies so as to promote fast and fine mixing of combustion constituents. As further understood by applicants, fast and fine mixing, including preheating, facilitates uniformly volume distributed oxidation and uniform flameless combustion. To achieve these specific conditions, applicants sought to provide a combustor and method that entail the specific organization of advantageous flows preceding or simultaneous with combustion.
In one aspect, a combustion apparatus is disclosed having a generally elongated combustion container. The container has a longitudinal axis, a proximal end, an exhaust end spaced axially forward from the proximal end, a proximate end wall, an exhaust end wall, and an all-around sidewall extending between the end walls and about the longitudinal axis, the end walls and sidewall substantially defining a combustion chamber. The apparatus further includes a combustion chamber exhaust positioned on the exhaust end, a delivery system positioned to direct fuel into the combustion chamber for combustion, and an air inlet located generally tangentially on the sidewall to direct air flow generally tangentially into the chamber and induce swirl about the longitudinal axis. In a preferred embodiment, an outside casing is provided about the combustion container and spaced circumferentially outward from the container to define an air annulus therebetween. The casing is equipped with an outer air inlet that communicates an external air supply with both the annulus and the air inlet into the combustor chamber. Accordingly, the air annulus can direct air flow toward the proximate end and along the outside of the container thereby exchanging heat with the side walls of the container and more preferably, directing hot air to the proximate end and in the vicinity of a fuel-air delivery system associated with the combustion chamber. In this way, the annulus serves to cool the side walls and recirculate the heat loss back into the combustion chamber.
In another aspect, a method of combustion is provided. The method entails providing an elongated combustion container having a longitudinal axis, a pair of axially spaced apart end walls generally defining a proximate end and a distal end, a sidewall extending between the end walls, and an exhaust opening in the distal end. Fuel is delivered into the chamber at the proximal end and tangential air flow is introduced into the combustion chamber to induce swirl flow about the longitudinal axis. The swirl flow further induces meridional circulation in the combustion chamber, including circulatory regions and flow through regions exiting the exhaust opening. Furthermore, combustion is initiated in the combustion chamber, which includes exhausting hot gases through the exhaust opening.
In yet another aspect, a fuel and air delivery system is disclosed having a radial air swirler and a fuel nozzle. The air swirler includes a swirl chamber positioned about a swirl axis, a radial inlet for introducing rotational air flow into the swirl chamber, and a central opening positioned to receive swirling flow from the chamber. The fuel nozzle is directed axially through the central opening of the swirler, and wherein the air swirler further includes a nozzle outlet in fluid communication with the central opening and having an all around forwardly diverging sidewall for directing a diverging annular swirl flow outward.
So that the manner in which the features and advantages of the present invention may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only various exemplary embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.
The present invention will now be described more fully with reference to the accompanying drawings, which illustrate the various exemplary embodiments of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited by the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough as well as complete and will fully convey the scope of the invention to those skilled in the art and the best and preferred modes of practicing the invention.
Referring first to
Referring to
In preferred embodiments, the combustion apparatus 7 exhausts hot flue gases at the distal end and through a centrally located exhaust opening 25. An exhaust pipe 23 extends though the distal end wall 19 and engages the exhaust opening 25 to receive the high pressure, hot flue gases. The exhaust pipe 23 communicates the gases to a transition piece, turbine, nozzle, or other component, as required by the specific application. In some of the descriptions provided herein, components, fluids, or processes described at or about the distal end wall 19 may be referred to as being forward or downstream of components or fluids described as near the proximal end wall 17. The distal side or end of the combustion apparatus 7 may also be referred to as the exhaust or exhaust end.
The combustion apparatus 7 also includes an elongated, preferably cylindrical combustor liner (or combustion container) 31 having a diameter less than that of the outer housing 13. The combustor liner 31 is positioned centrally within the outer housing 13 about the longitudinal axis YY, thereby defining an elongated cavity or combustion chamber 33. The preferably cylindrical combustor liner 31 is further described as including all around sidewalls 35 that extend axially between a substantially enclosed proximal end wall 37 and a partially open distal end wall 39. The distal end wall 37 is located substantially adjacent the distal end wall 19 of the housing 13, such that the centrally located exhaust opening 25 goes through both end walls 19, 39. The proximal end wall 37 is preferably spaced axially forward of the proximal end wall 17 of the outer housing 13 to define a cylindrical space 9 therebetween. In preferred embodiments, the proximal end wall 37 and the area thereabout are utilized for receiving primary air, liquid or gaseous fuel, and delivering the desired fuel-air mixture for combustion. The cylindrical space 9 accommodates some of the components and facilitates some of the processes involved, as further described below.
The combustor liner 31 is also sized such that when the combustor liner 31 is centered within the housing 13, an annulus 41 of desired gap width is provided between the outer housing 3 and the combustor liner 31. As shown in
Pressurized air is also delivered to the combustion chamber 33. In the embodiment depicted by
The configuration in
Referring specifically to
The primary components of the swirler 47 include a pair of open-centered circular discs or plates 53 that are attached to the proximal end wall 37 and about a circular opening in the end wall 37 and a swirl axis ZZ (which is preferably coincidental with axis YY). Independent of the end wall 37, the circular plates 53 are spaced apart in mutually parallel relation to define a swirl chamber and a converging air path therebetween. A plurality of radially arranged guide vanes are supported between the plates 53 just inside of the periphery of the plates 53. The radial guide vanes 55 are spaced apart and similarly angled to draw primary air into the swirl chamber along generally the same tangential direction (relative to swirl axis ZZ). Because the swirler 47 draws air from inlets that are on a plane generally parallel to the swirl axis ZZ, the swirler 47 is sometimes described as being a radial swirler or having radial inlets (as opposed to as axial swirlers or axial inlets).
The swirler 47 further includes a forwardly extending swirler nozzle or a diverging outlet 51, which for convenience of description may be referred to simply as cone 51 (although, the configuration may be more cone-like than a true geometrical cone). In an aspect of the invention, the cone 51 defines a divergent sidewall 61 positioned about swirl axis ZZ, but which diverges from the axis YY along the forward axial direction. The divergent sidewall 61 is shaped in a specific advantageous manner, as further described below. The open center of the swirler 47 preferably corresponds with the opening in the end wall 37 so that the cone 51 extends forwardly and outwardly in the combustion chamber 33 (see e.g.,
In respect to Figures of specific embodiments provided herein, the cone 51 or divergent sidewall 61 may be described as having or defining an internal region or zone Zi radially inward of the cone 51 (also referred to as the fuel and air delivery zone Zi). Just forward of the end wall 37, the diameter of the divergent sidewall 61 is reduced to define a throat area or throat 57 of minimum diameter. The fuel nozzle 49 extends through the center opening of the swirler plates 53 and into the throat 57. The fuel nozzle 49 is centered on the swirl axis ZZ to establish an annular gap 59 between it and the swirler plates 53. The nozzle 49 is, therefore, positioned to deliver an atomized fuel spray into the internal zone Zi of the cone 51.
In accordance with the invention, a pathway of rotating air flow A1 commences at the inlets between successive guide vanes 55 and rotates about the axis ZZ. While advancing radially inward, the air flow A1 intensifies as the rotational path shortens and converges on the annular gap 59 and the swirl axis ZZ. This creates a low pressure area at the center of the swirler 47. Upon entry into the annular gap 49, the now swirling flow presses against the center rim of the forward plate 55 and then the base of the sidewall 61. The annular swirl flow A3 moves axially forward, moving past the throat 57 and then, into the zone Zi defined internally (i.e., surrounded) by the cone 51. Centrifugal force presses the diverging, rotating flow to the sidewall where it forms an annular jet-like outflow A3.
As illustrated in
The profile of the sidewall 61 has the shape of the streamline indicated by the bold curve SW. In preferred embodiments, the sidewall profile is described by the relation, r/rmin=xs{x[2xs−(1+xs)x](1+xs)}−½, x=cos θ, and xs=cos θs. In this equation, r is the length of a line connecting the axis-bottom intersection and a point on the sidewall, rmin is the minimum value of r, θ is the angle between the line and the axis, and θs is the θ value for a point located at the sidewall upper edge. The parameters, rmin and θs, can be conveniently selected depending on the air flow rate and the fuel spray angle δ (see the angle between the swirl axis ZZ and the dotted line). Thus, a fuel spray angle δ 5 may be achieved that is sufficiently less than the sidewall angle θs to ensure that the thin air flow A3 passes by the hot flue gas counterflow CF.
In accordance with the present invention, several operational features arise from the design of the swirler 47 and the sidewall profile. First, the surface of sidewall 61 exhibits relatively little or low drag due to its design as a stream surface. Secondly, the swirler 47 generates a low pressure area, which can be largely attributed to a rarefaction near the throat 57 generated by focused air rotation about axis ZZ. A strong suction is generated at the throat 57 which draws hot flue gases passing in front of the swirler 47 and the local circulation zone LCR. This suction creates a hot counter flow-CF toward the throat 57. As
Furthermore, because the swirling jet outflow A3 is pressed to the diverging part of the sidewall 61 by centrifugal force, there is little swirl in the center and in the hot flue gas counter flows CF. With reference again to the diagram of
In operation, the combustion apparatus 7 according to the invention initiates a combustion process with multiple advantageous features. In one aspect of the invention, such a combustion method is achieved utilizing a single combustion chamber for flameless combustion.
In a further aspect, a method of combustion according to the invention involves the advantageous high-speed circulation of combustion fluids (air, fuel, and/or fuel-air mixture) inside the combustion chamber. More specifically, preferable operation of the combustion apparatus 7, according to the invention, establishes dual modes of circulation or fluid flow: a first mode entailing the revolution of fluid particles around the longitudinal axis YY (swirl) and a second mode entailing circulatory meridional motion of the combustion fluids. As described below, this dual mode of circulation enhances the mixing of air and fuel in the combustion chamber and helps achieve desired combustion characteristics and temperature profiles.
The simplified schematic of
Additionally, the applicants utilize the contribution of swirl-decay mechanisms in generating counter-flows (i.e., both the circulation and the U-shape flow-through, in the combustion chamber). Generally, air-sidewall friction causes a pressure drop in the air flow in the axial direction. Thus, the pressure at air inlet 43 is significantly higher than the pressure at the end of axial flow travel, near the proximal end wall 37. Pressure is also lower at the swirl vortex. Thus, pressure near the sidewall 35 at the proximal end is significantly greater than the pressure at the axis YY (the swirl axis) near the proximal end wall 37. Finally, the pressure at the axis YY near the distal end wall 39 is greater than the pressure at the axis YY at the proximal end wall 37. This is primarily due to the swirl rotational speed having decreased along the axial length of the sidewall 35 friction and effecting less of a pressure drop at the proximal end. The above-described pressure gradients help drive the meridional motion and in particular, the advantageous turns and reverse flows made by fluid flow in the combustion chamber 33. These pressure gradients and swirl decay effects are also utilized in the embodiments of the present invention through strategic arrangement of the tangential and axial air inlets, as described below.
Referring first to the schematic of
The fresh air inflow A0 has, of course, a temperature that is significantly less than that of the gases already inside the chamber 33, especially the hot flue gases. Thus, the constituents of this fresh air inflow A0 generally are of a higher density than the hot gases and other combustion particulates. In the combustion chamber 33 of the invention, centrifugal buoyancy and centrifugal force act to push the higher-density air radially outward. The effect of centrifugal acceleration on the air particles may be larger than that of gravitational acceleration by four to five orders of magnitude. As a result, even a small difference in temperature (and therefore in density) causes stratification (until mixing and combustion together heat the incoming flow up to the flue gas temperature in the circulation regions CR). Since most of the incoming air initially flows in a thin, annular layer close to the sidewall 35, its axial velocity is low compared with that of the existing circulatory flows and the central flow-through. The maximum axial velocity of the near-sidewall flow is estimated to be around one third of that of the near-axis flow. The relatively low axial velocity of the near-sidewall air flow increases its residence time, however, and thus, provides sufficient time for the preheating, mixing and combustion of air. In preferred embodiments, the residence time of the near sidewall air flow may be higher than the mixing time by orders of magnitude, and its combustion time smaller than the mixing time.
Returning to
As shown in
The high-speed circulatory flows generally consist of hot flue gases moving in the circumferential, axial, and radial directions. Notably, the circulatory flows are located downstream of the swirler 47 and the nozzle 49. The nozzle and swirler arrangement and orientation provide for the injection of atomized fuel into the circulatory region CR. Droplets of liquid fuel introduced into the region CR will evaporate quickly upon contact with the hot flow. Gaseous fuel introduced into the region CR, on the other hand, will be quickly preheated and mixed by the hot, high-speed and turbulent flow.
In one aspect of the present invention, the circular flow described above and illustrated in
The direction of cooler incoming air flows along the sidewalls 35 provide yet another benefit. The cooler air flow provides a buffer between the combustion region and the sidewalls and end walls of the liner 31, and helps to maintain the sidewalls 35 at cooler temperatures. Such thermal protection allows for the use of lower-cost material for the sidewall 35 and typically results in a more double and longer lasting sidewall 35.
Double Spiral Swirl Promotes Fast and Fine Mixing throughout
In a further aspect of the invention, swirl generated in the combustion chamber 33 is characterized by an advantageous double-spiral geometric pattern.
For each of the trajectories in
Comparison of trajectories Td and Te also reveals that a particle moving close to the sidewall, (e), makes more revolutions around the axis YY than the particle remote from the sidewall, (d). The particle close to the sidewall 35 has, therefore, a lower axial velocity than that the one remote from the sidewall 35. Furthermore, the particle close to the sidewall 35 has a longer residence time in the combustion chamber 33 than the particle remote from the sidewall 35. As centrifugal stratification provides that the colder particles will be closer to the sidewall 35 than the hotter particles, the cold particles are provided sufficient time to heat up. Moving slowly along the sidewall 35, the cold particles are continually heated by the hot sidewall 35, by the hotter flue gases with which it mixes, and finally due to heat from combustion. Trajectory (e) in
An important feature revealed in
The volume dominance and high-speed motion of the circulatory flows provide intense and fine mixing of incoming air with flue gases. The circulatory flows quickly heat up the incoming air up to the self-ignition temperature. The volume dominance and high temperature of the circulatory flows also provide intense preheating and evaporation (for liquids) of fuel injected by the nozzle 49 into the circulatory flow regions CR. The fast and fine mixing results in uniform distribution of both fuel and air in the entire combustion chamber volume. Therefore the fuel and air meet and combust everywhere in the chamber 33, i.e., volume-distributed oxidizing occurs.
The volume dominance, high speed and high temperature of the circulatory flows also help to establish the circulatory regions CR as safe and efficient flame holders. Because the flow-through regions FT is pressed proximate the combustor sidewall 35 by centrifugal force and centrifugal buoyancy, the flow-through streams cannot readily cause blow-out and/or cool down the circulatory flows. Furthermore, combustion uniformly heats all of the constituents throughout the chamber 33 due to intense mixing and, in particular, maintains the circulatory flow at high temperature. Combustion also causes the through-flow and circulation flows to accelerate and thus, maintain the circulatory flows at high-speed.
As compared with operation of the earlier-described combustion apparatus 7, operation of this combustor 107 features a shorter passage length (the flow-through flow line from the air inlet 171 to the exhaust 25). Accordingly, the residence time of the particle in the flow-through line is shorter. Seemingly, this feature would present a significant performance disadvantage, especially considering the benefits provided by longer residence times as explained above in respect to the combustion apparatus 7 of
The provision of a second inlet 243b near the proximal end wall 237 advantageously provides for a higher speed, cooler flow-through at the “hot” proximal end. The local circulation region LCR and combustion zone are present at the proximal end. In the previous configuration, the sidewall 235 at the proximal end experiences higher temperatures due to its proximity to the combustion zone and also, because the inlet air flow A0 gets hotter and slows as it travels axially along the sidewall 35 before arriving at the proximal end. The higher speed, cooler air inflow A2 provides a more effective cooling fluid flow. Additionally, the addition of higher speed swirl flow near and in contact with the local circulation zone LCR and near the fuel spray from the nozzle 149 enhances mixing and heating of combustion constituents. More particularly, the addition of higher speed swirl flow at the proximal end helps to generate counter-flows (flows in opposite directions), thereby promoting the occurrence of swirling vortices and Karman eddies. These eddies facilitate the desired fast and fine mixing of combustion constituents.
The simplified illustration of
As before, the fuel-air delivery system 345 includes a fuel nozzle 349, a radial air swirler 347, and a swirler nozzle or cone 351 extending forwardly along a swirler axis ZZ. The cone 351 further includes a divergent sidewall 361 having an advantageous profile as described previously. In this alternate configuration, the air swirler 347 and fuel nozzle 349 are supported within a casing 381. More specifically, the swirler 347 is mounted on the inside wall of a flange or backplate 383, such that the cone 351 extends outward through a central opening of the backplate 383. As second backplate 385 encloses the casing 381 to define an air chamber 385. As shown in
During operation, an air inflow A1 is drawn by radial guide vanes 355 of the swirler 347. The guide vanes 355 generate a high speed rotational internal flow that converges on the center of the swirler 347 and advances forwardly therefrom into a throat 357 of the swirler 347 and along the divergent sidewall 361 of the cone 351 (as discussed previously). Additional air flow A2 is drawn through an annular gap 359 around the nozzle 349 and passed into the throat 385 to engage any counter flowing fuel droplets drawn back into the swirler 347 or throat 385. As also described earlier, a jet-like air swirl flow A3 generated by the swirler 347 is pressed thinly and annularly against the sidewall 361, while and fuel spray is directed outwardly by the nozzle 349 from the area of the throat 385. Advantageously, the angle of the fuel spray is designed to be less than that of the sidewall 361 so that the thin jet-like layer of air swirl A3 near the sidewall 361 is clear from the extent of the fuel spray.
As illustrated in
The simplified schematic of
In this embodiment, the combustor liner 431 is equipped with two pressurized air inlets 443. A tangential air inlet 443a is located near the exhaust 425 as before and a second tangential or radial air inlet 443b is located in the cylindrical air space 409. This second air inlet 443b supplies primary air A1 to the fuel-air delivery system 445. Independent of the first air inlet 443a, this dedicated inlet 443a may be equipped with the required valves and controls to allow independent regulation of the primary air A1 feed to the delivery system 445. Specifically, the primary air fed to the swirler 447 may be controlled directly and independently of the air inflow A0 utilized in the combustion chamber 433.
During operation, the combustion apparatus 407 generates, in addition to swirl about the longitudinal axis YY, global meridional circulation similar to that described in respect to combustion apparatus 407. An additional or local meridional circulation is also generated, however, local to the pre-chamber 433b. As illustrated in
The diaphragm 477 also helps to minimize the effect of increased air inflow A0 on the local circulation regions LCR. In particular, the baffles 479 help to mitigate the effects of higher inflows and prevent blow out in the local circulation region LCR. Accordingly, modes of operation requiring higher rate of air inflows may be achieved by the combustor 407 without compromising the performance of the fuel-air delivery systems 445 and local circulation regions LCR.
The combustion apparatus 507 further includes a cylindrical combustor liner 531 and a slightly conical transition piece 587 attached to the combustor liner 531. As shown in
As shown in the Figures, the two air inlets 543a, 543b may have substantially the same configuration. Each air inlet 543a, 543b provides a set of radial guide vanes 593 arranged about the periphery, with each vane being positioned angularly to direct swirling air flow tangentially (not radially) into the combustion chamber 533. The configurations of the two air inlets 543a, 543b differ, however, in that the direction of the guide vanes 593 for one inlet is generally clockwise while those of the other inlet are counter-clockwise. Thus, the directions of tangential air flows downstream of the air inlets 543a, 543b and the swirl flows about axis YY generated thereby, are also in opposite rotational directions (clockwise or counter clockwise) and will collide and mix midway across the sidewall 535.
In this embodiment, two igniters 597 are provided and positioned on either side of the center fuel-air delivery systems 545. The igniters 597 extend into the combustion chamber 533 at an axial position proximate the rim of the cones 551. As discussed previously in respect to the fuel-air delivery system 145, each of the systems 545 generates a local circulation region LCR in front of and within each cone 551 (see e.g.,
The simplified flow representations (and their discussion) in
During operation of the combustion apparatus, the combustion chamber 533 features two annular regions of high speed axial flow. The first is an annular region near the liner sidewall 535 and the other is located near the axis YY. These two regions of high speed flow is separated by an annular region of counterflow (in the portion of the chamber 533 near the fuel-air delivery system 545) or by lower-speed co-flow (near the middle of the chamber 533). In addition, the similar counterflow and the low-speed co-flow are located near the axis YY. The instability of this complex flow, having multiple shear layers, generates turbulent Karmantype eddies densely packed throughout entire combustion chamber 533. The presence of largescale eddies and small-scale turbulence result yet again in fast and fine mixing of air, fuel, and flue gases, thereby promoting stable and complete combustion with low level of harmful emission.
Now turning to the side or profile view of
As further shown in
Thus, in a preferred combustion apparatus and method of combustion according to the invention, a combustion liner is provided having at least one air injection inlet tangentially positioned to induce high-speed swirl about the chamber axis. The combustion liner is further configured, and the inlet port(s) is properly positioned, so as to induce a desired high-speed meridional motion inside the chamber. Relatively large circular flow regions are generated and interact with flow-through regions, which include regions along the sidewalls. More preferably, at least one air-fuel swirler is provided for generating a narrow annular jet and a wide suction flow. The resulting multiple shear layers, densely packed Karman-type eddies, fine-scale turbulence, and particle trajectories of double-spiral geometry cause fast and fine mixing of air, fuel and flue gases as well as extremely uniform temperature distribution. The large circulation/flow-through volume ratio and high-speed circulation provide stable combustion, rapid preheating and mixing of injected fuel, and uniformly occurring oxidation in the entire combustion chamber or combustion liner volume at optimal temperature with minimum harmful emission.
The transition piece 687 is provided for engagement with a turbine or other suitable mechanism. The transition piece 687 has a diameter that increases gradually from the end at which it engages a combustion liner 631 and receives exhaust gases, to an exhaust opening 605 downstream. As shown in
In this embodiment, the hollow end wall 699 is configured with an interior hollow or cavity 675. At about the axis YY, an axially extending port 677 is provided from the cavity 675 to the outside of the end wall 699 (inside of the transition piece 687). The cap 673 is attached to the end wall 699 by a short rod 685 (near the port 677) and is centered on the axis YY.
Furthermore, the end wall 699 is supported in place by four short tubes 695 that extend from the housing 613. The tubes 695, which are open to the annulus 641 on one end and the cavity 675 on the other end, communicate relatively cool air from the annulus 641 to the end wall 699. Air flow directed into the cavity 675 converge on the axis YY and then exit through the port 677. The pressurized air spills into the annular gap between the cap 673 and the end wall 699, and then deflected by the cap 673. From there, the deflected air flow moves outward to the exhaust opening 671 along the inside surface of the end wall 699. In this way, air flow convectively cools the outside, as well as the inside, of the end wall 699.
In one aspect of an invention provided in the present disclosure, a combustor features a single combustion chamber that receives fuel and air (or other oxidizer) and initiates combustion. More specifically, the combustor employs a combustion container having an elongated combustion chamber and a tangential air inlet into the chamber that induces swirl about the chamber axis and meridional circulation, thereby effecting advantageous mixing and preheating. Furthermore, the combustion container is preferably configured such that the tangential air inlet is located proximate the chamber's exhaust (without any structural barriers directly between the inlet and the exhaust).
An important additional element of a preferred combustor's design is the inclusion or incorporation of a casing that substantially encloses the container but is spaced outwardly from the combustion container to create a gap or annulus. This annulus serves to divert and direct air flow about the outside of the combustion container and\or to a fuel-air delivery system of the chamber. In this way, the annulus airflow serves to cool the combustion container and re-direct heat and energy back to the combustion process. This preferred embodiment of the combustor with a “Casing and Annulus for Air Flow Cooling and Energy Recapture” is also illustrated in the combustors of FIGS. 1 and 13-16, but may also be incorporated and adapted with the combustors described in respect to
To elaborate,
In the drawings and specification, there have been disclosed a typical preferred embodiments of the present invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The present invention has been described in considerable detail with specific reference to the illustrated embodiments. It will become apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing applications. For example, various components and systems described herein may be utilized in different combustion applications or in different combinations and configurations.
The present application claims the benefit of U.S. Provisional Application Ser. No. 61/403,290, filed on Sep. 12, 2010 (pending). The disclosure of the previously filed provisional application is hereby incorporated by reference for all purposes and made a part of the present disclosure.
This invention was made with government support under Contract Nos. ONR N00014-10-C-0334 and ONR N00014-09-C-0121 awarded by the Office of Naval Research. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61403290 | Sep 2010 | US |
