EP1899587A2

EP1899587A2 - Swirl-stabilized burner for thermal management of exhaust system and associated method

Info

Publication number: EP1899587A2
Application number: EP06772742A
Authority: EP
Inventors: Wilbur H. Crawley; Adam Coker; John Philip Nohl; Thomas R. Hodnett
Original assignee: Emcon Technologies LLC
Current assignee: Faurecia Emissions Control Technologies USA LLC
Priority date: 2005-06-15
Filing date: 2006-06-09
Publication date: 2008-03-19
Also published as: CN101501308A; WO2006138174A3; WO2006138174A2; US20080087013A1; CN101501308B; EP1899587A4; US20060283181A1

Abstract

An apparatus (10) comprises a reciprocating or Wankel engine (16), an exhaust gas passageway (20) fluidly coupled to the engine, and a fuel-fired burner (12). The burner is positioned in the exhaust gas passageway (20) and comprises a swirler (22) configured to swirl exhaust gas of the engine (16) so as to stabilize in the exhaust gas passageway (20) a flame generated by the burner (12) without use of supplemental combustion air when the engine (16) is operating above idle. An associated method is disclosed.

Description

SWIRL-STABILIZED BURNER FOR THERMAL MANAGEMENT OF EXHAUST SYSTEM AND ASSOCIATED METHOD

This application claims priority to U.S. Patent Application Serial No. 11/152,869 filed June 15, 2005, the entirety of which is hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to apparatus and methods for thermally managing emission abatement devices.

BACKGROUND OF THE DISCLOSURE

There are a variety of ways to heat emission abatement devices. For example, fuel- fired burners and electric heaters have been used in connection with some types of emission abatement devices.

SUMMARY OF THE DISCLOSURE

According to an aspect of the present disclosure, there is provided an apparatus comprising a fuel-fired burner that is positioned in an exhaust gas passageway and comprises a swirler configured to swirl exhaust gas of a reciprocating or Wankel engine so as to stabilize in the exhaust gas passageway a flame generated by the burner without use of supplemental combustion air when the engine is operating at idle and above idle. The swirl-stabilized flame is useful for thermally managing an emission abatement device. An associated method is disclosed. Such flame stabilization has a number of benefits. For example, it promotes use of the burner during occurrences of relatively high exhaust gas flow rates which might otherwise blow out the flame. In addition, the diameter of the burner can be reduced since the burner can handle such relatively high flow rates. Further, flame stabilization promotes reduction of the flame length, thereby allowing the burner length to be reduced accordingly. A relatively compact burner package can thus be provided for applications where space economy may be a factor (e.g., onboard a vehicle). The burner may have a plurality of swirlers for swirling exhaust gas to promote flame stabilization. In an exemplary implementation, the burner has three swirlers, two in a pilot section of the burner and one in a main section of the burner. One of the swirlers of the pilot section is positioned about a pilot fuel nozzle for stabilizing a pilot flame generated by the pilot section. The other pilot section swirler is positioned about a perforated pilot tube to promote passage of oxygen present in exhaust gas through apertures defined in the pilot tube into the pilot flame. The swirler in the main section is used to stabilize a main flame initiated by the pilot flame.

Swirl stabilization of the pilot flame and/or the main flame is useful for thermally managing a variety of emission abatement devices. Such emission abatement devices include, but are not limited to, oxidation catalysts (e.g., diesel oxidation catalysts), particulate filters (e.g., catalyzed or uncatalyzed diesel particulate filters), selective catalytic reduction devices ("SCR devices"), and/or NOx traps. The above and other features of the present disclosure will become apparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram showing an apparatus for thermally managing an emission abatement device by use of a swirl-stabilized flame of a burner;

FIG. 2 is a fragmentary perspective view of the burner;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2; FIG. 3 a is a sectional view of a portion of a pilot tube showing a wall- cooling layer of exhaust gas formed on an inner surface of the pilot tube;

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 3;

FIG. 5 is a perspective view of an upstream side of a variable swirler; FIG. 6 is an elevation view of the upstream side of the variable swirler;

FIG. 7 is a perspective view of a downstream side of the variable swirler;

FIG. 8 is a perspective view of a twisted vane of a swirler;

FIG. 9 is a sectional view taken along lines 9-9 of FIG. 3 showing an alternative embodiment of components of the burner;

FIG. 10 is a perspective view of an embodiment of a swirler;

FIG. 11 is a rear elevation view of the swirler of FIG. 10;

FIG. 12 is an end elevation view of the swirler of FIGS. 10 and 11; and

FIG. 13 is a perspective view showing a swirler tube positioned about a fuel dispenser.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims. Referring to FIG. 1, there is shown an apparatus 10 comprising a burner 12 that generates a swirl-stabilized flame 14 in exhaust gas ("EG" in the drawings). The exhaust gas is from a reciprocating (e.g., piston) or Wankel (e.g., rotary) internal combustion engine 16 (e.g., diesel engine) for use in thermal management of an emission abatement device 18. The burner 12 generates the flame 14 without use of supplemental combustion air. In other words, it uses the oxygen present in the exhaust gas for the combustion reaction. The burner 12 is positioned in an exhaust gas passageway 20 and comprises a swirler 22 configured to swirl exhaust gas so as to stabilize in the exhaust gas passageway 18 the flame 14 generated by the burner 12. The burner 12 is thus able to stabilize the flame 14 when the engine 16 is at idle and above idle.

Illustratively, the swirler 22 swirls exhaust gas to generate an outer swirl zone 24 of swirling exhaust gas which induces generation of an inner recirculation zone 26 of recirculating exhaust gas within the swirl zone 24. In the swirl zone 24, exhaust gas swirls around an axis 28 of the burner 12 (e.g., in a clockwise direction or counter-clockwise direction) as the exhaust gas advances downstream along the axis 28. In the recirculation zone 26, exhaust gas recirculates back toward the swirler 22. The swirl zone 24 may have a relatively high velocity depending, for example, on the output of the engine 16. However, the recirculation zone 26 has a relatively low velocity conducive to flame stabilization. In other words, the velocities in the recirculation zone 26 are sufficiently low to allow the flame 14 to reside therein without being blown out by the potentially higher velocities in the outer swirling zone 24. The flame 14 is thus stabilized in and near the recirculation zone 26 by use of the swirler 22.

The swirler 22 may be configured to generate one or more secondary recirculation zones 29 as well. Illustratively, the swirler 22 provides a sudden change in the flow area (i.e., a "dump plane") at its periphery. Such a feature generates secondary recirculation zones 29 just downstream therefrom. The zones 29 may thus be used to promote flame stabilization in the zones 29 in addition to or in place of the recirculation zone 26. It is within the scope of this disclosure to configure the swirler 22 so as to swirl the exhaust gas to achieve any swirl number, the swirl number being indicative of the amount of swirl induced in the flow per unit length. For example, swirl numbers between about 0.5 and about 2.0 may be particularly useful to promote stabilization of the flame 14. Swirl numbers between about 0.76 and 1.1 may be most useful to promote stabilization of flame 14.

Swirl stabilization of the flame 14 has a number of benefits. For example, it promotes use of the burner 12 during occurrences of relatively high exhaust gas flow rates which might otherwise blow out the flame 14. This may be particularly useful with vehicles such as relatively large commercial vehicles (e.g., truck tractors, buses) that have a relatively large engine (e.g., 12.7 liter engine) capable of producing a relatively large amount of exhaust gas. In addition, flame stabilization promotes provision of a relatively compact burner package for applications where space economy may be a factor. In particular, the diameter of the burner 12 can be reduced since the burner 12 can handle relatively high exhaust gas flow rates. Further, the burner length can be reduced since flame stabilization results in a shorter flame length. The burner 12 with its swirler 22 is thus particularly useful in an exhaust system.

The emission abatement device 18 is thermally managed by use of the swirl-stabilized flame 14. In particular, exhaust gas passing through the burner 12 is heated thereby and advances to the emission abatement device 18 to heat the emission abatement device 18.

The device 18 may take a variety of forms. Exemplarily, the device 18 may include an oxidation catalyst (e.g., diesel oxidation catalyst), a particulate filter (e.g., catalyzed or uncatalyzed diesel particulate filter), an SCR device, and/or a NOx trap. According to one example, the device 18 includes an oxidation catalyst and a particulate filter. In such a case, the oxidation catalyst is positioned fluidly between the burner 12 and the particulate filter. The exhaust gas heated by the swirl- stabilized flame 14 heats the oxidation catalyst to its operational temperature (e.g., between about 250° C and about 300° C). The oxidation catalyst then oxidizes fuel that has been introduced into the exhaust gas at the burner 12 or at a location separate and from the burner 12. Heat generated by the exothermic reaction at the oxidation catalyst heats the particulate filter to burn off particulate matter trapped thereby so as to regenerate the particulate filter for further use. It is within the scope of this disclosure to use the swirl-stabilized flame to regenerate the particulate filter without the assistance of an oxidation catalyst.

In the case where the device 18 is an SCR device, the swirl-stabilized flame 14 is used to facilitate establishment of the SCR device within its operational temperature range. In the case of a NOx trap, the swirl-stabilized flame 14 may be used to elevate the temperature of the NOx trap to facilitate de-sulfurization of the NOx trap. Further, the burner 12 may be used with the exhaust systems of U. S. Patent No. 6,871,489, the disclosure of which is hereby incorporated by reference herein.

Referring to FIGS. 2 and 3, there is shown an exemplary implementation of the burner 12. In particular, there is shown a fuel-fired burner 112 for use as the burner 12 in the apparatus 10 to thermally manage the emission abatement device 18 in any of its forms. The burner 112 comprises a number of swirlers positioned in an exhaust gas passageway 120 defined in part by a housing 118 of the burner 112 to swirl exhaust gas flowing from the engine 16 to the emission abatement device 18 for flame stabilization in the passageway 120 even during occurrences of relatively high exhaust gas flow rates. The burner 112 comprises a pilot section 130 and amain section 132. The pilot section 130 generates a swirl-stabilized pilot flame 134 used to initiate a swirl-stabilized main flame 136 of the main section 132. Once the main flame 136 is initiated, the pilot section 130 can be shut down to extinguish the pilot flame 134 or can be continued to be operated.

The pilot section 130 comprises a swirl-stabilized pilot fuel dispenser 138 (see also FIG. 4). The dispenser 138 extends through an aperture formed in a first swirler 122a such that the swirler 122a circumferentially surrounds the dispenser 138. The swirler 122a is secured to an end of a perforated pilot tube 142 and is configured as a plate comprising a plurality of radially extending vanes 144 that are inclined to swirl exhaust gas in the pilot tube 142 either clockwise or counter-clockwise (depending on the orientation of the vanes 144) about a burner axis 145. As such, the swirler 122a generates an outer swirl zone 24 of swirling exhaust gas in the pilot tube 142 and an inner recirculation zone 26 of recirculating exhaust gas within the outer swirl zone 24.

The dispenser 138 dispenses fuel supplied by a pilot fuel line 148 into the recirculation zone 26 for ignition of the fuel by an igniter 146 that extends into the recirculation zone 26. In this way, the pilot flame 134 is initiated in the pilot tube 142. Moreover, the pilot flame 134 is stabilized in the pilot tube recirculation zone 26 due to the relatively low exhaust gas velocities in that zone 26. A flow-obstructing device 150 which may be used to hold the pilot flame 134 is mounted in the pilot tube 142 to further facilitate stabilization of the pilot flame 134.

A second swirler 122b of the pilot section 130 mates against the housing 118 and is secured thereto so as to be mounted in the passageway 120. The pilot tube 142 extends through an aperture defined in the swirler 122b such that the swirler 122b surrounds the pilot tube 142 and the pilot tube 142 is secured to the swirler 122b. The pilot tube 142, the swirler 122a, and the dispenser 138 secured to the pilot tube 142 are thus mounted in the passageway 120.

The swirler 122b is configured, for example, as a plate comprising inclined radially extending vanes 153 that swirl exhaust gas outside the pilot tube 142 in either a clockwise or counter-clockwise direction (depending on the orientation of the vanes 153) about the burner axis 145. in this way, the swirler 122b causes exhaust gas to pass through apertures 154 defined in the pilot tube 142 so as to "feed" oxygen present in the exhaust gas to the pilot flame 134 for combustion with the pilot fuel. In addition, exhaust gas which passes through the apertures 154 into the pilot tube 142 due to the swirler 122b forms a generally annular wall-cooling layer 155 of exhaust on the inner surface of the pilot tube 142. This wall-cooling layer 155 serves as a layer of thermal insulation between the pilot tube 142 and the pilot flame 134, thereby enhancing the durability of the pilot tube 142 and penrritting use of less costly materials for the pilot tube 142. The thickness of the wall-cooling layer 155 may be about 1/8 inch.

The main section 132 is positioned just downstream from the pilot section 130. A main fuel dispenser 156 secured to the housing 118 receives fuel from a main fuel line 122c and dispenses that fuel into the main section 132 for generation of the main flame 136. The main section 132 comprises a third swirler 122c for swirl- stabilization of the main flame 136. The swirler 122c is configured, for example, as a plate comprising inclined radially extending vanes 159 that swirl exhaust gas in either a clockwise or counter-clockwise direction (depending on the orientation of the vanes 159) about the burner axis 145 upon passage of the exhaust gas through the swirler 122c. This generates immediately downstream from the swirler 122c an outer swirl zone 24 of swirling exhaust gas in the housing 118 of the main section 132. This outer swirl zone 24 of the main section 132 induces an inner recirculation zone 26 of recirculating exhaust gas within the main section outer swirl zone 24. The main flame 136 is stabilized in this main section recirculation zone 26 due to the relatively low exhaust gas velocities present in this zone 26. A transition member 160 secured to an upstream side of the swirler 122c facilitates passage of exhaust gas through the swirler 122c.

The swirler 122c comprises a dump plane 162 along an outer periphery of the swirler 122c. The dump plane 162 is an imperforate annular wall that blocks flow of exhaust gas therethrough so as to generate a radially outer recirculation zone immediately downstream from the dump plane 162 for flame stabilization in that zone also. It is within the scope of this disclosure to omit the dump plane 162 and extend the vanes 159 to the outer periphery of the swirler 122c.

The burner 112 may include a fuel-dosing section 164 for dispensing fuel into the heated exhaust gas for use with a downstream oxidation catalyst or other component of the emission abatement device 18. hi such a case, the fuel-dosing section 164 has a fuel-dosing dispenser 166 secured to the housing 118. The dispenser 166 dispenses dosing fuel supplied by a dosing fuel line 168 into the passageway 120 at a location between the swirler 122c and a fourth swirler 122d. The swirler 122d is configured, for example, as a plate comprising inclined vanes 172 that swirl the dosing fuel and exhaust gas in either a clockwise or counter-clockwise direction (depending on the orientation of the vanes 172) about the burner axis 145 upon passage through the swirler 122d. hi this way, the dosing fuel is thoroughly mixed with the exhaust gas upon arrival at the emission abatement device 18. It is within the scope of this disclosure to omit the fuel-dosing section 164 altogether from the apparatus 10 or to include the fuel-dosing section 164 as a component separate from the burner 112 such that the fuel-dosing section is positioned downstream from the burner 112 at some location between the burner 112 and the emission abatement device 18. It is within the scope of this disclosure to configure the swirlers 122a, 122b, 122c, 122d so as to swirl the exhaust gas to achieve any swirl number. For example, swirl numbers between about 0.5 and about 2.0 may be particularly useful to promote flame stabilization of flames 134 and 136. Swirl numbers between about 0.76 and 1.1 may be most useful to promote such flame stabilization.

Referring to FIG. 3, there is a shown a control system 174 for controlling operation of the burner 112. In particular, the control system 174 is responsive to inputs from an upstream oxygen sensor 176, an upstream temperature sensor 178, and a downstream temperature sensor 180 to control operation of a fuel and ignition module 182 which controls supply of fuel to fuel lines 148, 122c, 168 and supply of electricity via an ignition cable 184 to the igniter 146.

The direction of inclination of the vanes 144, 153, 159, 172 of the swirlers 122a, 122b, 122c, 122d may take a variety of forms. For example, all the vanes of the swirlers 122a, 122b, 122c, 122d may be inclined to swirl exhaust gas in the same direction about the axis 145. In other examples, the vanes 144, 153, 159, 172 of one or more swirlers 122a, 122b, 122c, 122d may be inclined to swirl exhaust gas in clockwise direction whereas the vanes 144, 153, 159, 172 of the other swirler(s) 122a, 122b, 122c, 122d maybe inclined to swirl exhaust gas in a counterclockwise direction. The vanes 144, 153, 159, 172 of any swirler 122a, 122b, 122c, 122d may have different pitches (the "pitch" is the angle of inclination of a vane). For example, some of vanes of a given swirler may have one or more pitches to swirl exhaust gas in a clockwise direction and some of the vanes of that same swirler may have one or more pitch angles to swirl exhaust gas in a counter-clockwise direction. Use of such pitch angles promotes mixing of exhaust gas. An example of such a swirler is shown in FIG. 15 and discussed below in connection therewith. The vanes 144, 153, 159, 172 of any swirler 122a, 122b, 122c, 122d may be fixed against movement relative to the housing 11 S or may be movable relative to the housing 118. As such, the pitch of the vanes may be invariable or variable. Referring to FIGS. 5-7, there is shown a variable swirler 222 for use as any one or more of the swirlers 22, 122a, 122b, 122c, 122d. The swirler 222 has a plurality of variable-pitch, radially extending vanes 230. The pitch of the vanes 230 can be varied by a pitch adjuster 232 operable by the control system 174. hi this way, the swirl number associated with the flow of exhaust gas can be varied. For example, the vanes 230 can be adjusted so as not to be inclined when the burner is shut down in order to reduce back pressure on the engine 16 associated with vane inclination, hi other examples, the pitch of the vanes 230 can be adjusted in response to conditions associated with the exhaust gas (e.g., flow rate, temperature, pressure, and/or oxygen content) to control flame stabilization. The swirl number associated with the exhaust gas can thus be varied accordingly.

The vanes 230 are mounted within a stationary frame for pivotable movement relative thereto. Exemplarily, the vanes 230 are secured to a stationary outer mounting ring 234 surrounding the vanes 230 and a stationary inner mounting hub 236. The hub 236 is mounted within the mounting ring 234 by a plurality of stationary mounting rods 238 (e.g., five). A transition member 260 is secured to the upstream side of the hub 236 to facilitate passage of flow through the swirler 222.

The pitch adjuster 232 comprises a drive unit 240 and a connector 242 operable by the drive unit 240 to pivot the vanes 230 to adjust their pitch. The drive unit 240 may have a motor (e.g., electric motor) and associated reduction gearing for rotating a rotatable drive shaft 244. The connector 242 comprises a lever 246 secured to the shaft 244 to be pivoted thereby upon rotation of the shaft 244. Such pivoting movement of the lever 246 moves a link 248 back and forth to cause a rotatable ring 250 to rotate about a swirler axis 252 of the swirler 222. Rotation of the ring 250 causes a pivot 254 associated with each vane 230 and extending through the mounting ring 234 thereto to pivot about a vane axis 256 of the vane 230. Such pivotable movement of the pivots 254 causes each vane 230 to rotate about its vane axis 256 to adjust the pitch thereof. In this way, a desired swirl number associated with the exhaust gas can be achieved in order to promote flame stabilization of either or both of the pilot flame 134 and the main flame 136 in the case of a non-zero swirl number and to promote reduction of engine back pressure in the case of a zero or near-zero swirl number. Further, in the case of a burner having multiple swirlers as with the burner 112, such pitch adjustment can be used to swirl the flow in opposite directions, hi particular, the vanes of one or more swirlers may be configured by the adjuster 232 to swirl exhaust gas in one direction whereas the vanes of one or more other swirlers may be configured by the adjuster 232 to swirl exhaust gas in an opposite direction. It is within the scope of this disclosure to achieve any swirl number by use of the swirler 220 and pitch adjuster 232. For example, swirl numbers between about 0.5 and about 2.0 may be particularly useful to promote flame stabilization. Swirl numbers between about 0.76 and 1.1 may be most useful to promote flame stabilization. Referring to FIG. 8, there is shown a vane 320 for use with any of the swirlers 22, 122a, 122b, 122c, 122d, 222. The vane 320 has a pitch that varies along the length of the vane 320 between a radially inner root 321 of the vane 320 and a radially outer tip 323 of the vane 320. Exemplarily, the vane 320 twists about a longitudinal axis 356 of the vane 320. The pitch of the vane 320 is thus varied along the length of the vane 320 to balance the pressure drop across the vane 320, to tailor flame stabilization, and to enhance the capacity of the vane 320 to address thermal fatigue by balancing vane loading. Further, the flow across the vane 320 is about the same at the center of the vane 320 as at the tip 323, producing a relatively uniform flow across the swirler to enhance mixing and thermal distribution when each of the vanes of the swirler is configured like the vane 320.

Referring to FIG. 9, there shown a swirler 422b used in place of the swirler 122b. The swirler is configured to swirl portions of the exhaust gas and to direct other portions of the exhaust gas toward a pair of fuel dispensers 156.

Referring to FIGS. 10-12, there is shown the swirler 422b. Swirl vanes 423 of the swirler 422b are inclined at a pitch 424 of, for example, about 45° to swirl exhaust gas that passes swirl vanes 423. Guide vanes 425 of the swirler 422b are used to direct exhaust gas that passes the guide vanes 425 toward the fuel dispensers 156. There are two pairs of guide vanes 425, each pair being associated with one of the fuel dispensers 156. The guide vanes 425 of each pair are inclined toward one another at a pitch 427 of, for example, about 60° in order to direct exhaust gas axially toward the associated fuel dispenser 156.

Referring to FIG. 13, there is shown a swirler tube 451 surrounding a nozzle 452 of a fuel dispenser 156. Exhaust gas is directed by a pair of guide vanes 425 toward the fuel dispenser 156. Such exhaust gas flows through apertures 454 defined in an upstream side of the swirler tube 451. Vanes 456 of the upstream side of the tube 451 impart a swirl to the exhaust gas that flows through the apertures 454 so that the exhaust gas flows around a dispenser axis 458 of the fuel dispenser 156 and around fuel spray 460 discharged from the nozzle 452 as shown by an arrow 462. In this way, the fuel spray 460 is shielded from incoming exhaust gas, promoting advancement of the fuel spray 460 into the main flame 136 and promoting fuel vaporization. Impingement of the fuel spray 460 on the swirler 122c and the pilot tube 142 is also reduced. Further, the swirling exhaust gas in the tube 451 swirl- stabilizes the nozzle 452. A flow-obstructing device 450 is secured to and extends from a distal end of the tube 451. Exemplarily, the device 450 is shaped generally as half of a spoon. The device 450 serves, for example, as a flame holder for the pilot flame 134 and/or the main flame 136 to further assist in flame stabilization. Each of the swirlers 22, 122a, 122b, 122c, 222, 422b or combinations thereof provides means for swirling exhaust gas so as to stabilize in the exhaust gas passageway 20 or 120 a flame 14, 134, and/or 136 generated by the burner 12 or 112 for thermal management of the emission abatement device 18.

While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. It will be noted that alternative embodiments of each of the systems of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A method, comprising the steps of: generating a flame in exhaust gas of a reciprocating or Wankel engine without use of supplemental combustion air, swirling the exhaust gas while the engine is operating above idle, and stabilizing the flame in the exhaust gas as a result of the swirling step.

2. The method of claim 1 , wherein: the swirling step comprises (i) generating an outer swirl zone of swirling exhaust gas and (ii) generating within the outer swirl zone an inner recirculation zone of recirculating exhaust gas, and the stabilizing step comprises stabilizing the flame in the inner recirculation zone.

3. The method of claim 1 , wherein: the generating step comprises generating a pilot flame, and the stabilizing step comprises stabilizing the pilot flame as a result of the swirling step.

4. The method of claim 3, wherein: the generating step comprises generating a main flame initiated by the pilot flame, and the stabilizing step comprises stabilizing the main flame as a result of the swirling step.

5. The method of claim 1, wherein: the generating step comprises a generating a main flame initiated by a pilot flame, and the stabilizing step comprises stabilizing the main flame as a result of the swirling step.

6. The method of claim 1, wherein: the generating step comprises generating a pilot flame in a perforated pilot tube, and the swirling step comprises swirling exhaust gas with a swirler surrounding the pilot tube so as to cause exhaust gas to enter the pilot tube through apertures formed therein, further comprising the step of forming a wall-cooling layer of exhaust gas on an inner surface of the pilot tube with exhaust gas that has entered the pilot tube through the apertures formed therein.

7. The method of claim 1, wherein the swirling step comprises varying a swirl number of the exhaust gas.

8. The method of claim 1, wherein the swirling step comprises swirling exhaust gas in opposite directions around an axis.

9. The method of claim I₅ further comprising directing exhaust gas toward a fuel dispenser by use of vanes adjacent to and inclined toward one another and swirling the exhaust gas directed toward the fuel dispenser about fuel dispensed from the fuel dispenser, wherein the generating step comprises combusting the fuel dispensed from the fuel dispenser to generate a main flame.

10. The method of claim 1 , further comprising thermally managing an emission abatement device by use of the swirl-stabilized flame.

11. An apparatus, comprising: a reciprocating or Wankel engine, an exhaust gas passageway fluidly coupled to the engine, and a fuel- fired burner positioned in the exhaust gas passageway and comprising a first swirler configured to swirl exhaust gas of the engine so as to stabilize in the exhaust gas passageway a flame generated by the burner without use of supplemental combustion air when the engine is operating above idle.

12. The apparatus of claim 11, wherein: the burner comprises a pilot section configured to generate a pilot flame, and the pilot section comprises a pilot fuel dispenser and the first swirler which is positioned about the pilot fuel dispenser for stabilizing the pilot flame.

13. The apparatus of claim 11 , wherein: the burner comprises a pilot section and a main section, the pilot section is configured to generate a pilot flame and the main section is configured to generate a main flame initiated by the pilot flame, and the main section comprises the first swirler for stabilizing the main flame.

14. The apparatus of claim 11, wherein: the burner comprises a pilot section and a main section, 41

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the pilot section is configured to generate a pilot flame and the main section is configured to generate a main flame initiated by the pilot flame, the pilot section comprises (i) a pilot fuel dispenser, (ii) the first swirler which is positioned circumferentially about the pilot fuel dispenser for stabilizing the pilot flame, (iii) a perforated pilot tube that is configured to receive the pilot flame, and (iv) a second swirler positioned circumferentially about the perforated pilot tube for swirling exhaust gas to promote passage of exhaust gas through apertures defined in the perforated pilot tube, and the main section comprises (i) a main fuel dispenser for dispensing fuel to be ignited at least initially by the pilot flame to generate the main flame and (ii) a third swirler configured to swirl exhaust gas so as to stabilize the main flame in the exhaust gas passageway.

15. The apparatus of claim 14, further comprising a particulate filter and an oxidation catalyst for heating the particulate filter, wherein: there is a fuel-dosing section for introducing fuel into the exhaust gas passageway upstream from the oxidation catalyst to promote operation of the oxidation catalyst, the fuel-dosing section is included as part of the burner or is separate from the burner so as to be positioned downstream therefrom at a location between the burner and the oxidation catalyst, and the fuel-dosing section comprises a fuel-dosing dispenser and a fourth swirler configured to swirl exhaust gas so as to mix exhaust gas and fuel dispensed by the fuel-dosing dispenser.

16. The apparatus of claim 11 , wherein the first swirler comprises at least one vane. US2006/022541

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17. The apparatus of claim 16, further comprising a pitch adjuster secured to the first swirler to adjust the pitch of the at least one vane,

18. The apparatus of claim 16, wherein the at least one vane is formed such that the pitch of the at least one vane varies along the length of the at least one vane.

19. The apparatus of claim 11, further comprising an emission abatement device, wherein the burner is positioned for thermal management of the emission abatement device by use of the swirl-stabilized flame.

20. A method, comprising the steps of: generating both a pilot flame and a main flame in exhaust gas of a reciprocating or Wankel engine without use of supplemental combustion air, swirling the exhaust gas about an axis while the engine is operating above idle, and stabilizing both the pilot flame and the main flame in the exhaust gas as a result of the swirling step.