Burner for heating exhaust gas

Abstract: A burner for heating an exhaust gas stream includes a combustor head (38) with a fuel/air charge preparator (52) comprising a fuel nozzle (60) and dual vortex atomiser (56). The charge preparator is mounted on one side of a partition (46) including an outlet (48) through which the atomised fuel and air pass to a combustion chamber (34) formed by a combustor tube (36) fixed to the partition (46). The combustor tube (36) has igniting means (42) and outlets (44) for the burning fuel/air mixture. The outlets (44) have flow directing louvres (110) directing the combusted mixture in a predetermined direction to optimise mixing of the combusted mixture with the exhaust gas stream. The combustor head (38) is mounted through an opening (78) in a housing which positions the combustor tube outlets (44) in the exhaust stream.

Description: This invention relates to a burner for heating an exhaust gas stream of, for example, an internal combustion engine. Advancement in emission technologies for internal combustion engines has resulted in significantly lowered total engine emissions. In general, automotive emissions applications employ an exhaust mounted catalytic treatment device for reducing regulated exhaust constituents such as Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NO x ) in the engine exhaust prior to their release to the atmosphere. The catalyst treatment devices, or catalytic converters, rely on the heat of the exhaust gas to become catalytically active following a cold start. Initiation of catalyst activity occurs at the light-off temperature (operating temperature) and is typically in the area of 400 degrees C. A vehicle may require 75-100 seconds or more of engine operation before the exhaust supplies sufficient heat to reach catalyst light-off. In order to reduce cold-start emissions, attempts have been made to provide an additional heat source at or shortly after engine start-up to promote faster heating of the converter and, therefore, a shorter time to optimal catalyst efficiency. Several technologies have been considered for the preheating of catalytic converters. Electrically heated converters, which use an engine driven electrical system to heat elements in the converter or the catalyst support itself, in the case of metal supports, have been proposed. The heat output of the electrically heated units is directly related to the electrical input. In order to achieve the desired rapid heating of the catalyst support, significant power must be supplied by the electrical system. Burner systems have also been considered for achieving rapid heating. Although not suffering from the drawbacks of electrically heated units, such systems require a burner, a fuel system and an ignition system along with the related complexity and packaging problems associated with such systems. In addition, rapid, reliable ignition of the burner, burner control and adequate mixing of the burner output with the engine exhaust have been problematic. The present invention seeks to provide an improved burner. According to an aspect of the present invention, there is provided a burner for heating an exhaust gas stream as specified in claim 1. It is possible with the present invention to provide a simplified burner design which is capable of integration into a vehicle fuel and powertrain system to reduce cost and complexity and to increase reliability. It is also possible to provide a burner having unique fuel charge preparation which can assure complete fuel atomisation and efficient combustion. The preferred embodiment of burner has a combustor design capable of reliable and efficient operation substantially regardless of location in the exhaust gas stream and under a wide range of fuel and air supply conditions. In an embodiment, the burner comprises a combustor head assembly having means for mixing fuel and air, a source of ignition for the fuel/air mixture and a charge preparation assembly within the combustor head assembly preferably comprising a two-stage vortex which cooperates with a fuel nozzle to atomise the fuel and combine it with combustion air to produce a fuel/air mist. The fuel/air mist is subsequently injected into a combustor which may comprise an elongated tubular combustor chamber having the combustor head at a first end and a series of outlets at a second end. The outlets of the combustor may be placed circumferentially about the outer periphery of the tubular combustor with louvres at the openings to direct burner output in a predetermined direction to optimise mixing with exhaust gas passing through the burner. In a preferred embodiment, the combustor is mounted within a burner housing. An interlocking flange assembly may be provided to retain the combustor and the burner housing together as one unit. Exhaust gas may enter the housing through an inlet adjacent to the combustor outlets such that exhaust gas entering the burner housing can pass over the exterior of the combustor and past the louvred outlets to maximise heat retrieval. Dilution air, which may be required to complete combustion of the burner fuel and to assure maximum conversion efficiencies in the catalytic converter during the initial phase of engine operation, may be added to the exhaust gas stream at a location upstream of the combustor so as to encourage mixing of the dilution air with the exhaust gas prior to heating by the burner. The burner assembly is preferably operably connected to a catalytic converter with the exit from the burner preferably lying in close or adjacent proximity to the inlet of the converter. Such a configuration can reduce the size of the assembly and can limit the loss of heat between the burner and the converter. In the preferred embodiment, it is possible to provide reliable ignition and through mixing of the burner output with the engine exhaust upstream of the converter, in a compact package. Advantageously, there is provided a combustor having a simplified flange arrangement for mounting coaxially within the burner housing. In addition, fuel/air charge preparation in the combustor is preferably handled by a two-stage vortex which can produces a highly atomised fuel mist for efficient combustion in the combustor chamber. In an embodiment, the burner utilises burner outlet louvers to direct the output in a desired direction, assuring optimal mixing of the output with the engine exhaust. According to another aspect of the present invention, there is provided a burner as specified in claim 8. The present invention is described below with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an internal combustion engine system including the preheater; Figure 2 is a side elevational view in cross-section of the embodiment of exhaust burner catalyst preheater of Figure 1; Figure 3 is a sectional view of the exhaust burner catalyst preheater of Figure 2, taken along line 3-3 of Figure 2; Figure 4 is a perspective view, partially in section, of a two-stage vortex element of the preheater of Figure 2; Figure 5 is a perspective view, partially in cross-section, of a combustor tube of the preheater of Figure 2; and Figure 6 is a sectional side view of another embodiment of combustor tube for the preheater of Figure 2. Referring to Figure 1, an internal combustion engine system comprises an engine 10 having a fuel system which includes fuel injectors 12, a fuel line 14 for delivery of fuel to the injectors 12 and a source such as a fuel tank 16 from which pressurised fuel is obtained. Fuel and air are combusted in the engine 10 and are exhausted through manifold 18 to an exhaust system 20. The exhaust system 20 comprises a burner assembly 22 and a catalytic converter 24, see Figure 2. The converter 24, which operates to reduce the level of undesirable exhaust constituents which exit the exhaust system, must be operated above a particular temperature, referred to as the light-off temperature, to achieve optimal performance. In order to reduce the time required for the converter 24 to reach the light-off temperature, the burner 22 is located so that its output is mixed with the exhaust gas upstream thereof. The burner 22 is operated for a short time following engine start-up to heat the exhaust gas, thereby contributing to the heat available in the exhaust gas which is available to heat the converter 24. An electronic controller 26 controls fuel and air supplied to the burner by fuel metering assembly 28 and blower or air pump 30, respectively. Fuel meter 28 regulates fuel from supply 16 to a desired pressure and flow rate which is consistent with the goals of the burner control strategy. The fuel meter 28 may be a pulse-width modulated injector or electronic fuel regulator capable of continually modulating fuel supply to a predetermined input duty cycle. An example of such a metering device is described in our co-pending European application ............ (MJD/3830) and in our co-pending United States application 07/909488 filed July 6, 1992. Similarly, combustion air is supplied to the burner 22 via an engine driven or electrical air pump 30. The air supply is regulated to a predetermined pressure, also consistent with the chosen burner control strategy. A check valve 32, disposed between the burner 22 and the blower 30, provides protection to the blower from exhaust gas during periods in which it is not in operation. Referring to Figures 2 to 4, burner assembly 22 comprises a primary combustor assembly 34. A principle component of the primary combustor assembly 34 is combustor tube 36, an axially extending tube having a combustor head 38 located at a first end, a combustion chamber 40 with spark plug 42 and a series of burner outlets 44 located at the second end thereof. The combustor head 38 includes a base member 46 fixed to and closing the first end of combustor tube 36. The base member 46 has a through bore 48 which opens into the combustion chamber 40 and a flange member 50 extending outwardly from the primary combustor tube 36 about the perimeter of the base member 46. A charge preparation assembly 52 is mounted to one side of the base member 46 and comprises a fuel nozzle 54 which receives fuel from supply 16 and a two-stage vortex 56 (shown separately in Figure 4) which mixes fuel from nozzle 54 with pressurised air from air pump 30 to create a fuel/air mist which is subsequently supplied to the primary combustor tube 36, by way of through bore 48, for ignition and burning therein. The fuel nozzle 54 may have any known form, such as a fuel filming nozzle which utilises fuel system pressure to aid in fuel atomisation. Such a nozzle configuration is desirable for its robust design which allows reliable burner operation under a wide range of fuel and air flows and combustor back pressure. The nozzle 54 has a connector, such as banjo fitting 58, in communication with fuel line 60 from fuel meter 28 and is mounted to vortex 56 so that its discharge end injects pressurised fuel into the first stage 62 of the two-stage vortex 56. As illustrated in Figure 4, the two-stage vortex has first and second stages 62, 64, respectively. Each stage comprises a set of vanes or directors 66 which form orifices 68 therebetween. Pressurised air is supplied at the outer perimeter of the vortex 46 and passes between vanes 66 to exit orifices 68 at the centre of the vortex, where it mixes with and atomises fuel from the nozzle 54 in a vortex chamber 69 formed by orifices 68, with a high degree of tangential velocity and swirling effect. The vortex shape, area and number of vanes define the pressure drop across orifices 68, the velocity of the exiting air swirl and the flow rate of air through the primary combustor assembly 34. The second vortex stage 64 may differ from the first, principally in the flow area and direction of the vanes and therefore the direction and velocity of the air entering the combustor. In operation, the first stage 62 of vortex 56 atomises the fuel particles from the nozzle 54 and sends the fuel/air mixture through the opening 70 and into vortex chamber 71 of second stage 64 with a high degree of tangential velocity. The second stage 64 further atomises the fuel/air mixture to produce a mist of high tangential velocity which spreads rapidly into the combustor chamber 40 following the contour of the base member 46. The base member 46 may have an integral, angled director 72 to impart an axial direction to the radially outwardly moving fuel/air mist. An ignitor such as spark plug 42 initiates combustion of the fuel/air mist moving axially through the combustor tube 36. Upon reaching the end of the combustor tube 36 opposite the base member 46, the burning fuel/air mixture, or burner output exits the combustor tube through a series of outlets 44 spaced circumferentially about the side of the tube 36. The primary combustor assembly 34 is mounted within an outer shell, or burner housing 74, to form a burner assembly 22 which can be mounted integrally within the exhaust system 20 of engine 10. The burner housing 74 is of a suitable configuration for support of the primary combustor assembly 34 in a substantially coaxial orientation therein. In the preferred embodiment illustrated in Figures 1 to 3, the housing is configured with an inlet conduit 76 for conducting exhaust gas from engine 10 into the assembly, an opening 78 for the mounting of the combustor assembly 34 located at the base, or exit end of the inlet conduit 76 and an outlet configured to be mounted in operable communication with a catalytic converter 24. The opening 78 has a mounting flange 80 extending about the perimeter thereof which is configured to co-operate with the flange 50 of base member 46 to support the combustor assembly 34 within burner housing 74. An air distribution housing 82 has a mating surface or retaining flange 84 which is configured sealingly to engage burner housing flange 80 and combustor base flange 50 to support rigidly the individual components relative to one another. Fastening means such as bolts 86 may be used to assemble the components and sealing means such as gasket 88 assure a leak proof seal at the component interfaces. The supply of combustion air to the two-stage vortex 56 and the supply of reaction air to the exhaust gas is through the air supply housing 82. Once in place, the air supply housing 82 forms an air chamber 90 which receives a supply of pressurised air through inlet 92 which is connected to air pump 30 through air conduit 94 (best seen in Figure 1). From chamber 90, combustion air enters vortex 56 through the vortex openings 96, as described above. Reaction air passes through an opening 98 in the base member 46 and into a distribution tube or manifold 100 which is fixedly attached to the base member and extends into the exhaust gas flow in inlet tube 76. A series of reaction air outlets 102 ensures distribution of the air in the exhaust gas stream. An opening 104 in the air distribution housing facilitates the attachment of the fuel supply to the fuel nozzle 54. In order to minimise the likelihood of air leakage out of the housing through the opening, the housing is configured to rest against a shoulder 108 on the nozzle body 54. A sealing member, such as copper crush washer 106, may be placed between the air housing 82 and the shoulder 108 to assure a sealing interface. Exhaust from the engine 10 is conducted into the burner housing 74 through inlet 76 where it is combined with reaction air as it passes reaction air manifold 100 and mixes with the burner output as it passes the outlets 44 of combustor tube 36. To optimise the benefits of the burner 22 relative to converter light-off time, effective mixing of the burner output with the exhaust gas should be provided. The outlets 44 of the combustor tube 36 utilise louvres 110 (best seen in Figure 5) to direct the burner output to promote thorough mixing of the two components. The louvres 110 are individually adjustable, if required, to allow for flow optimisation when the combustor assembly 34 is utilised in burner housings of varying configuration. In certain instances, it may be desirable to remove heat from the combustor tube 36 at a higher rate than is possible by the flow of exhaust gas over the exterior thereof. In Figure 6, a second embodiment of the combustor tube which has a single outlet 113, is illustrated. A cooling sleeve 112 has a cylindrical configuration with a diameter slightly larger than that of the combustor tube 36, although cooling sleeve 112 could be used for any combustor tube configuration requiring additional cooling. The sleeve 112 attaches to the base member 46 and extends around the combustor tube forming a space 114 therebetween. Air inlets 116, comprising through-bores in the combustor base 46, dispense a portion of the combustion/reaction air to the space 114 to cool the outer surface of the combustor tube 36. A small outlet gap 118 between the inwardly turned end of the sleeve 112 and the combustor tube 36 allows the cooling air to escape from the space 114 to mix with the exhaust gas stream, carrying heat removed from the combustor to mix with the exhaust gas. Should it be desirable to add a portion of the combustion air to the fuel/air mixture within the combustor tube 36 following initiation of combustion, additional combustion air inlets 120 may extend through the combustor tube 36 to direct a portion of the cooling air from the space 114 to the combustor tube 36.

Claims: A burner for heating an exhaust gas stream comprising a combustor head (38) including a fuel and air charge preparator (52) and a combustion chamber (40) operably coupled to the combustor head; the charge preparator including fuel and air supply means and a dual vortex mixer (56) comprising a first vortex chamber (62) adjacent to and in communication with the fuel and air supply means and including a series of vanes (66) forming a plurality of orifices (68) through which pressurised air can enter the first vortex chamber to atomise the fuel and air mixture, and a second vortex chamber (71) communicating with the first vortex chamber through an opening (70) therebetween and including a series of vanes (66) forming a plurality of orifices (68) through which pressurised air can enter the second vortex chamber to impart additional atomising action to the fuel and air mixture entering from the first vortex chamber; the second vortex chamber opening into the combustion chamber for the passage of the atomised fuel and air mixture into the combustion chamber; and ignition means (42) operable to ignite the atomised fuel and air mixture in the combustion chamber; the combustion chamber including outlets (44) in communication with the exhaust stream for directing the burning fuel and air mixture to mix with the exhaust gas stream. A burner according to claim 1, wherein the series of vanes (66) of the first and second vortex chambers (62,71) extend from an outer perimeter of the vortex mixer. A burner according to claim 1 or 2, wherein the second vortex chamber (71) is located substantially in a centre of the vortex mixer. A burner according to claim 1, 2 or 3, comprising a burner housing (74) including an exhaust gas inlet and outlet (20,24), an opening (78) and a first mounting flange (80) extending around the perimeter of the opening; a second mounting flange (50) extending around a portion of the burner housing and engageable with the first mounting flange to support the combustor head within the housing; and a burner air supply housing (82) sealingly covering the fuel and air charge preparator for supplying air to the first and second vortex chambers; the air supply housing including a sealing flange (84) engaging the first and second mounting flanges to fix the combustor head and the burner housing relative to one another. A burner according to claim 4, comprising a dilution air manifold (100) extending into the exhaust gas stream and including a series of openings (102) for release of dilution air into the exhaust gas stream and an inlet end in communication with a through-hole (98) in the second mounting flange to facilitate flow of air from the air supply housing to the dilution air manifold. A burner according to any preceding claim, wherein the combustion chamber (40) is formed from an elongate tubular member (36) including a first end in communication with the fuel and air supply means and a second end including a series of outlets (44) for release of the combusted fuel and air mixture from the elongate tubular member and including one or more flow directing louvres (110) for imparting a predetermined flow direction to the combusted fuel and air mixture. A burner according to any preceding claim, comprising a cooling sleeve (112) disposed around the combustion chamber (40) for the passage of cooling air around the combustion chamber (40). A burner according to claim 7, comprising a housing including an exhaust gas inlet and outlet (20,24) and an opening located intermediate the inlet and outlet and including mounting means for mounting the combustor head within the housing.

Inventors: PETTIT WILLIAM HENRY, PETTIT, WILLIAM HENRY
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: F23G7
IPC codes: F23G7, F01N9, F01N3