US20140041370A1

US20140041370A1 - Exhaust Treatment System for Internal Combustion Engine

Info

Publication number: US20140041370A1
Application number: US13/959,042
Authority: US
Inventors: Charles E. Solbrig; Ognyan N. Yanakiev; Peter Hubl; Erik W. Dennis
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-08-08
Filing date: 2013-08-05
Publication date: 2014-02-13

Abstract

An exhaust treatment system for an internal combustion engine comprises an exhaust gas conduit configured to receive an exhaust gas from the internal combustion engine and to deliver the exhaust gas to an exhaust treatment device. A fluid delivery system is located upstream of the exhaust treatment device and is configured to deliver a fluid thereto. It comprises a fluid injector, a fluid tube in fluid communication with the fluid injector and extending radially into the exhaust gas conduit for receipt of fluid from a spray tip of the fluid injector, a controller configured to energize the fluid injector to deliver fluid to the fluid tube, and opening(s) in the tube, disposed beyond the boundary layer of exhaust gas flow in the exhaust gas conduit, for release of the fluid into the exhaust gas flow.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to U.S. Patent Application Ser. No. 61/680,826 filed Aug. 8, 2012 which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Exemplary embodiments of the invention relate to exhaust treatment systems for internal combustion engines and, more particularly, to exhaust treatment systems capable of fully mixing and vaporizing injected fluids into the exhaust gas flow for improved performance thereof.

BACKGROUND

Manufacturers of internal combustion engines must satisfy customer demands while meeting various government regulations for reduced emissions and improved fuel economy. One example of a way to improve fuel economy is to operate an engine at an air/fuel ratio that is lean (an excess of oxygen) of stoichiometry. Examples of such lean-burn engines include compression ignition engines (diesel) and lean-burn spark-ignition engines. However, while lean burn engines may have improved fuel economy, the exhaust gas emitted from such an engine, particularly a diesel engine, may be a heterogeneous mixture that includes gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in various exhaust system devices to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
An exhaust treatment technology in use for high levels of particulate matter reduction, particularly in diesel engines, is the Diesel Particulate Filter (“DPF”) device. There are several known filter structures used in DPF devices that have displayed effectiveness in removing the particulate matter from engine exhaust gas such as ceramic honeycomb wall flow filters, wound or packed fiber filters, open cell foam filters, sintered metal foams, etc. Ceramic wall flow filters have experienced significant acceptance in automotive applications.
The filter is a structure for removing particulates from the exhaust gas and, as a result, the accumulation of filtered particulate matter will eventually have the effect of increasing the exhaust system backpressure experienced by the engine. Such increase in backpressure will eventually have a negative impact on engine performance and fuel economy. To address exhaust system backpressure increases caused by the accumulation of particulate matter, the DPF device is periodically cleaned, or regenerated. Regeneration of a DPF device in vehicular applications is typically automatic and is carried out by an engine or other controller based on signals received by engine and exhaust system sensors. The regeneration event typically involves raising the temperature of the DPF device to levels that are often above 600 C in order to burn the accumulated particulates thereby cleaning the DPF device.
One method of generating the temperatures required in the exhaust system for regeneration of the DPF device is to deliver unburned HC, often in the form of raw fuel to an oxidation catalyst (“OC”) device that is disposed upstream of the DPF device. The OC device typically carries an oxidation catalyst compound which aides in oxidizing HC in an exothermic event which raises the temperature of the exhaust gas. The heated exhaust gas travels downstream to the DPF device where it burns the particulates trapped therein. Injection of the fuel into the exhaust treatment system is often carried out using injection devices similar to fuel injectors used in engines. A common challenge for exhaust system designers is to inject the HC upstream of the OC device in a manner that allows for the HC to fully disperse in order to utilize the entire OC for oxidation and to fully vaporize so as to completely combust as it passes through the OC device.
Accordingly it is desirable to provide an HC delivery system that achieves substantially uniform mixing, distribution and vaporization of a fluid injected into the exhaust gas of an exhaust gas treatment system.

SUMMARY

In an exemplary embodiment, an exhaust treatment system for an internal combustion engine comprises an exhaust gas conduit configured to receive an exhaust gas from the internal combustion engine and to deliver the exhaust gas to an exhaust treatment device. A fluid delivery system is located upstream of the exhaust treatment device and is configured to deliver a fluid thereto. The fluid delivery system comprises a fluid injector, a fluid tube in fluid communication with the fluid injector and extending radially into the exhaust gas conduit for receipt of fluid from a spray tip of the fluid injector, a controller configured to energize the fluid injector to deliver fluid to the fluid tube, and an opening in the tube, disposed beyond the boundary layer of exhaust gas flow in the exhaust gas conduit, for release of the fluid into the exhaust gas flow.
The above feature and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS AND APPENDIX

FIG. 1 is a schematic view of an engine and exhaust treatment system embodying features of the invention;

FIG. 2, including FIGS. 2A-2H, are an enlarged portion of the exhaust system of FIG. 1 including examples of fluid tubes embodying features of the invention;

FIG. 3 is a flow diagram illustrating flow characteristics and other features of the invention;

FIG. 4 is another example of a fluid tube embodying features of the invention;

FIG. 5 is another example of a fluid tube embodying features of the invention;

FIG. 6 is another example of a fluid tube embodying features of the invention;

FIG. 7 is another example of a fluid tube embodying features of the invention;

FIG. 8 is a flow diagram illustrating further flow characteristics and other features of the invention; and

FIG. 9 is an illustration, partially in section, of an injector and fluid tube embodying features of the invention.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
Referring to FIG. 1, an exemplary embodiment of the invention is directed to an exhaust gas treatment system 10, for the reduction of regulated exhaust gas constituents emitted from an internal combustion engine, such as diesel engine 12. It is appreciated that the diesel engine 12 is merely exemplary and that the invention described can be implemented in various engine systems requiring an exhaust gas particulate filter. For ease of description, the disclosure will be discussed in the context of diesel engine 12.
The exhaust gas treatment system 10 includes an exhaust gas conduit 14, which may comprise several segments, that functions to transport exhaust gas 16 from the diesel engine 12 to the various exhaust gas treatment devices of the exhaust gas treatment system. In an exemplary embodiment, the exhaust treatment devices may include a first oxidation catalyst device (“OC1”) 18. The OC1 18 may include a flow-through metal or ceramic monolith substrate 20 that is wrapped in an intumescent mat (not shown) that expands when heated, securing and insulating the substrate 20. The substrate 20 is packaged in a rigid shell or canister having an inlet and an outlet in fluid communication with exhaust gas conduit 14. The substrate 20 has an oxidation catalyst compound (not shown) disposed thereon. The oxidation catalyst compound may be applied as a washcoat and may contain platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh) or other suitable oxidizing catalyst, or combination thereof. The OC1 18 is useful in treating unburned gaseous and non-volatile HC and CO, which are oxidized to form carbon dioxide and water.
A selective catalytic reduction device (“SCR”) 22 may be disposed downstream of the OC1 18. In a manner similar to the OC1, the SCR 22 may also include a flow-through ceramic or metal monolith substrate 24 that is wrapped in an intumescent mat (not shown) that expands when heated, securing and insulating the substrate 24. The substrate 24 is packaged in a rigid shell or canister having an inlet and an outlet in fluid communication with exhaust gas conduit 14. The substrate 24 has an SCR catalyst composition (not shown) applied thereto. The SCR catalyst composition preferably contains a zeolite and one or more base metal components such as iron (“Fe”), cobalt (“Co”), copper (“Cu”) or vanadium (“V”) which can operate efficiently to convert NO_xconstituents in the exhaust gas 16 in the presence of an injected exhaust fluid such as an ammonia (“NH₃”) reductant 26. The NH₃ reductant 26, supplied from reductant supply tank 28 through conduit 30, may be injected into the exhaust gas conduit 14 at a location upstream of the SCR 22 using a fluid delivery system 32 to be described below. The reductant may be in the form of a liquid or an aqueous urea solution when it is delivered to the exhaust gas 16 by the fluid delivery system 32. A mixer or turbulator 50 may also be disposed within the exhaust conduit 14 in close downstream proximity to the fluid delivery system to further assist in thorough mixing of the reductant 26 with the exhaust gas 16.
In one exemplary embodiment, an exhaust gas filter assembly, in this case a diesel particulate filter device (“DPF”) 34 is located within the exhaust gas treatment system 10, downstream of the SCR 22 and operates to filter the exhaust gas 16 of carbon and other particulates. The DPF 34 may be constructed using a ceramic wall-flow monolith filter 36 that is wrapped in an insulating mat that secures and insulates the filter 36. The filter 36 may be packaged in a rigid shell or canister having an inlet and an outlet in fluid communication with exhaust gas conduit 14. Exhaust gas 16 entering the filter 36 is directed to migrate through adjacent longitudinally extending walls (not shown) and, it is through this wall-flow mechanism that the exhaust gas 16 is filtered of carbon and other particulates. The filtered particulates are deposited in the filter 36 and, over time, will have the effect of increasing the exhaust gas backpressure experienced by the diesel engine 12. It is appreciated that a ceramic wall-flow monolith filter 36 is merely exemplary in nature and that the DPF 34 may include other filter devices such as wound or packed fiber filters, open cell foams, sintered metal fibers, etc.
In an exemplary embodiment, the increase in exhaust backpressure caused by the accumulation of particulate matter requires that the DPF 34 be periodically cleaned, or regenerated. Regeneration involves the oxidation or burning of the accumulated carbon and other particulates in what is typically a high temperature (>600° C.) and excess oxygen environment. For regeneration purposes a second oxidation catalyst device (“OC2”) 38 may be located upstream of the filter 36, proximate to its upstream end. In the embodiment illustrated in FIG. 1, the OC2 38 is a flow-through metal or ceramic monolith substrate 40 that is wrapped in an intumescent mat (not shown) that expands when heated, securing and insulating the substrate 40. The substrate 40 is packaged in the canister of the DPF 34. The substrate 40 has an oxidation catalyst compound (not shown) disposed thereon. The oxidation catalyst compound may be applied as a wash coat and may contain platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh) or other suitable oxidizing catalysts, or combination thereof. While the embodiment described includes the OC2 38 disposed in the canister of the DPF 34, it is contemplated that, depending on packaging and other system constraints, the OC2 38 may also be disposed within a separate canister (not shown) that is located upstream of the DPF 34. In an other embodiment, the OC2 38 and the DPF 36 may also be in a common or separate canisters(s) and be located in a close coupled position relative to the engine turbocharger or exhaust conduit 14, with the SCR catalyst 24 being located downstream of the OC2/DPF.
Disposed upstream of the DPF 34, in fluid communication with the exhaust gas 16 in the exhaust gas conduit 14, is a fluid delivery system 42 to be described below. The fluid delivery system 42, in fluid communication with HC fluid 44 in fuel supply tank 46 through fuel conduit 48, is configured to introduce unburned HC fluid 44 (raw fuel) into the exhaust gas stream for delivery to the OC2 38 associated with the DPF 34. A mixer or turbulator 50 may also be disposed within the exhaust conduit 14, in close, downstream proximity to the fluid delivery system 42, to further assist in thorough mixing, breakup, vaporization and distribution of the HC with the exhaust gas 16.
A controller such as vehicle controller 52, for example, is operably connected to, and monitors, the exhaust gas treatment system 10 through signal communication with a number of sensors. As used herein the term controller may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. In an exemplary embodiment, a backpressure sensor 54, located upstream of DPF 34 or between OC 38 and turbulator 50, generates a signal indicative of the carbon and particulate loading in the ceramic wall flow monolith filter 36. This pressure sensor 54 may also be of a delta pressure type with the downstream part located after the DPF 36. Upon a determination that the particulate loading in the DPF (which may be determined by a signal that the backpressure has reached a predetermined level indicative of the need to regenerate the DPF 34), the controller 52 activates the fluid delivery system 42 to deliver HC fluid 44 into the exhaust gas conduit 14 for mixing with the exhaust gas 16. The fuel/exhaust gas mixture enters the OC2 38 inducing oxidation of the HC fluid 44 in the exhaust gas 16 and raising the exhaust gas temperature to a level (e.g. >600° C.) suitable for regeneration of the carbon and particulate matter in the filter 36. The controller 52 may monitor the temperature of the exothermic oxidation reaction in the OC2 38 and the ceramic wall-flow monolith filter 36 through temperature sensor 56 and adjust the HC delivery rate of fluid delivery system 42 to maintain a predetermined temperature depending on many factors such as temperature upstream of the OC 38, the exhaust mass flow rate 16, etc.
Referring now to FIGS. 2 and 3, with continuing reference to FIG. 1, the fluid deliver systems 32 and 42 will now be described in detail. For ease of description, the following discussion will focus on the HC fluid delivery system 42, however it should be understood the description applies equally to the delivery of NH3 reductant to the exhaust gas treatment system 10 by fluid delivery system 32. In an exemplary embodiment, an enlarged portion of the exhaust treatment system 10 illustrates exhaust gas conduit 14 adjacent to the inlet end 60 of the DPF device 34 which, in the exemplary embodiment described above houses the OC2 38 directly upstream of the ceramic wall-flow monolith filter 36. In the embodiment shown, the fluid delivery system 42 comprises at least one HC atomizer 62 that is mounted in an opening in the exhaust gas conduit 14. The HC atomizer 62, which may be an injector, vaporizer, or pump, is in fluid communication with a fluid tube 64, extending radially into the exhaust gas conduit 14, and receives atomized HC fluid 44 through the spray tip 66 of the HC atomizer 62. In exemplary embodiments, there may be more than 1 spray tip. When the HC atomizer 62 is energized by the controller 52 upon determination that the ceramic wall flow monolith filter 36 of the DPF device 34 requires regeneration. HC fluid 44 enters the fluid tube 64 and is heated due to the placement of the tube in the exhaust gas flow, which assists in the vaporization of the HC fluid 44. Additionally the fuel passes through the fluid tube and past the slower moving boundary layer of exhaust gas 16 near the outer circumference 68 of the exhaust gas conduit 14 and is placed in a location of exhaust gas 16 which is favorable for good mixing and a variety of exhaust flow conditions. In one embodiment, the HC fluid 44 enters the exhaust gas 16 from a position centrally located within the conduit 14.
HC fluid openings 70A, 70B are located in the fluid tube 64 at various locations along the length of the fluid tube 64. These openings 70A, 70B may face upstream, into the oncoming flow of the exhaust gas 16, downstream, away from the flow of the exhaust gas or they may be placed in a tangential orientation to the flow of the exhaust gas. The number and placement of the HC fluid openings 70A, 70B may be determined by the exhaust flow rate (i.e. velocity, flow volume) of the particular engine 12 and exhaust treatment system 10 as well as the configuration (i.e. diameter, etc.) of the exhaust gas conduit 14 at the location at which the fluid tube 64 is placed. Upstream facing openings 70A allow the exhaust gas 16 to enter the fluid tube 64 and entrain the HC fluid 44 for flow out of downstream facing openings 70B for example FIGS. 2A,B,C,D,F,G,H. Downstream only openings 70B, FIG. 2E, utilize a vacuum created by flow around the fluid tube 64 to pull or extract the HC fluid 44 vapor into the exhaust gas 16 flowing around the fluid tube 64 but the HC fluid 44 vapor is mainly motivated for flow into the exhaust conduit 14 by the fuel flow from the atomizer and temperature in the exhaust causing the HC fluid 44 to vaporize and greatly expand. As illustrated in FIGS. 2A, B, F, G, H, and FIG. 3 a series of HC fluid openings 70A, 70B distributed along the length of the fluid tube 64 will allow HC fluid 44 vapor to be substantially evenly distributed across the diameter of the exhaust gas conduit 14 and, thus the exhaust gas flow 16. In one embodiment, HC fluid 44 vapor is distributed across a central portion of the exhaust gas flow 16. It should be appreciated that, HC fluid openings 70A, 70B that are more centrally concentrated near the centerline of the exhaust gas conduit 14 will disperse the HC fluid 44 into the highest velocity portion of the exhaust gas flow 16. The determination of which design of tube to use may also be determined by the type, number and location of the mixer(s) 50 chosen for any particular application as well as the diameter (area) of gas conduit 14 (which may be variable along its length) and the distance of the fluid tube 64 from the OC 38.
Referring again to FIG. 2 the fuel tube 64 may extend across the entire diameter of the exhaust gas conduit 14 or only partially there across. In such instances in which the tube extends across the entire diameter of the exhaust gas conduit, an option exists to add a second HC atomizer 62 and spray tip 66, FIGS. 2A, B, C, D, E and F2 at the opposite or distal end from the first HC atomizer 62 and spray tip 66. In such instances, further fuel control or resolution is provided to the controller 52 during regeneration. However, there may be cost or design advantages to have the fuel tube 64 extend only partially across the diameter of the exhaust gas conduit as illustrated in FIGS. 2G and H. In such case one HC atomizer 62 and spray tip 66 is utilized to deliver fuel to the exhaust gas stream 16 flow through the exhaust gas conduit 14.
Referring now to FIGS. 4-7, with continuing reference to FIG. 1, another exemplary embodiment of the fluid delivery systems 32 and 42 will now be described in detail. Similarly, for ease of description, the following discussion will focus on the HC fluid delivery system 42, however it should be understood that the description applies equally to the delivery of NH₃reductant to the exhaust gas treatment system 10. In an exemplary embodiment, as shown in FIG. 2, the exhaust gas conduit 14 may be adjacent to the inlet end 60 of the DPF device 34 which houses the OC2 38 directly upstream of the ceramic wall-flow monolith filter 36. In the embodiment shown, the fluid delivery system 42 comprises at least one HC injector 80 that is mounted in an opening in the exhaust gas conduit 14 in a known manner. The HC injector 80 is in fluid communication with fuel passages 86, FIGS. 4-7, of fluid tube 64. The fuel passages 86 receive injected HC fluid 44 when the injector is energized by the controller 52 upon determination that the ceramic wall flow monolith filter 36 of the DPF device 34 requires regeneration. The fuel passages 86 may be drilled into a solid fluid tube 64 with intersecting outlet portions 87 also drilled at various locations along the length thereof. Once HC fluid 44 enters the fuel passages 86 in the fluid tube 64 it is heated due to the placement of the fluid tube 64 in the exhaust gas flow, which assists in the vaporization of the HC fluid 44. Additionally the fuel passes through the fuel passages in the fluid tube 64 and past the slower moving boundary layer of exhaust gas 16 near the outer circumference 68, FIG. 3, of the exhaust gas conduit 14. In exemplary embodiments, having multiple passages 86 (FIGS. 5, 6 and 7) provide advantages for better distribution the HC fluid 44 from spray tip 66.
Fuel passages 86 open at various locations along the length of the fluid tube 64, FIGS. 5-7. The fluid passages 86 may face upstream, into the oncoming flow of the exhaust gas 16, downstream, away from the flow of the exhaust gas 16 or they may be placed in a tangential orientation to the flow of the exhaust gas. The number and placement of the fluid passages 86 will be determined by the exhaust flow rate (i.e. velocity, flow volume) of the particular engine 12 and exhaust treatment system 10 as well as the configuration (i.e. diameter, etc.) of the exhaust gas conduit 14 at the location at which the fluid tube 64 is placed. The determination of which design tube to use will also be matched to the type, number and location of the mixer(s) 50 chosen for any particular application as well as the diameter (area) of gas conduit 14 (which may be variable down the length) and the distance of the fluid tube 64 from the OC 38.
As illustrated in FIGS. 5-7, a series of fluid passages 86 opening along the length of the fluid tube 64 will allow HC fluid 44 to be evenly distributed across the diameter of the exhaust gas conduit and, thus the exhaust gas flow 14. It should be appreciated that fuel openings that are more centrally concentrated near the centerline of the exhaust gas conduit 14 as in FIG. 4 will disperse the HC fluid 44 into the highest velocity portion of the exhaust gas flow 16.
Referring now to FIG. 8, the effect of the fluid tube 64 on the flow of exhaust gas 16 can be seen. As the exhaust gas passes the fluid tube 64 a turbulent wake region 88 is created. In cases in which the fuel tube 64 includes HC fluid openings or fluid passages that face in the downstream or tangential direction, additional fuel mixing is encouraged in the wake region 88 due to added turbulence as well as residence time of that gas as it slows momentarily. It is contemplated as is illustrated in FIG. 8, that different fluid tube cross sections 89A-89D may be used. The diameter of the tube 64 will be chosen to accentuate this effect in relation the exhaust conduit 14 area and the exhaust flow range for the application.
Referring now to FIG. 9, in an exemplary embodiment, an exhaust boss 90 is fixed externally to the exhaust conduit 14 and defines a through-hole 92 for fluid access to the exhaust gas flow 16. The fluid tube 64 is inserted through the exhaust boss 90 through hole 92 and is supported in the through hole 92 by a flared upper end 94. The flared upper end 94 receives the spray tip 66 of the HC atomizer 62 or the injector tip 82 of the HC injector 80 and is subsequently locked in place by a gland nut 96 which is threated into the exhaust boss 90.
In exemplary embodiments, the distance from the atomizer 62 and the fuel tube 64 to the OC 38, the design of the tube, and the design location and number of mixers 50 may be varied based on the type of the engine 12 and the desired performance characteristics of the exhaust gas treatment system 10.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed but that the invention will include all embodiments falling within the scope of the present application.

Claims

What is claimed is:

1. An exhaust treatment system for an internal combustion engine comprising:

an exhaust gas conduit configured to receive an exhaust gas from the internal combustion engine and to deliver the exhaust gas to an exhaust treatment device;

a fluid delivery system located upstream of the exhaust treatment device and configured to deliver a fluid thereto, the fluid delivery system comprising:

a fluid injector;

a fluid tube in fluid communication with the fluid injector and extending into the exhaust gas conduit for receipt of fluid from a spray tip of the fluid injector;

a controller configured to energize the fluid injector to deliver fluid to the fluid tube; and

an opening in the tube, centrally disposed within exhaust gas flow in the exhaust gas conduit, for release of the fluid into the exhaust gas flow.

2. The exhaust treatment system of claim 1, the exhaust treatment device comprising an oxidation catalyst and the fluid comprising unburned hydrocarbon.

3. The exhaust treatment system of claim 1, the exhaust treatment device comprising an selective catalytic reduction device and the fluid comprising an ammonia (“NH₃”) reductant.

4. The exhaust treatment system of claim 1, wherein the fluid tube extends diametrically across the diameter of the exhaust gas conduit having a second end in communication with the exhaust gas conduit.

5. The exhaust treatment system of claim 4, comprising a second fluid injector in communication with the second end of the fluid tube to deliver fluid to the fluid tube.

6. The exhaust treatment system of claim 1, wherein the fluid injector is a fluid vaporizer.

7. The exhaust treatment system of claim 1, further comprising multiple openings located at locations along the length of the tube.

8. The exhaust treatment system of claim 7, further comprising upstream facing openings configured to allow the exhaust gas to enter the fluid tube and entrain the fluid and downstream facing downstream facing openings configured for the flow of fuel and exhaust gas out of the fluid tube.

9. The exhaust treatment system of claim 1, wherein the fluid tube extends radially into the exhaust gas conduit.

10. The exhaust treatment system of claim 1, wherein the opening in the tube is centrally disposed beyond the boundary layer of exhaust gas flow in the exhaust gas conduit.

11. A fluid delivery system configured to deliver a fluid to an exhaust treatment device via an exhaust gas conduit, the fluid delivery system comprising:

a fluid injector;

an opening in the tube, centrally disposed within the exhaust gas conduit, for release of the fluid into the exhaust gas conduit.

12. The fluid delivery system of claim 11, wherein the fluid tube extends diametrically across the diameter of the exhaust gas conduit having a second end in communication with the exhaust gas conduit.

13. The fluid delivery system of claim 12, comprising a second fluid injector in communication with the second end of the fluid tube to deliver fluid to the fluid tube.

14. The fluid delivery system of claim 11, wherein the fluid injector is a fluid vaporizer.

15. The fluid delivery system of claim 11, further comprising multiple openings located at locations along the length of the tube.

16. The fluid delivery system of claim 15, further comprising upstream facing openings configured to allow the exhaust gas to enter the fluid tube and entrain the fluid and downstream facing downstream facing openings configured for the flow of fuel and exhaust gas out of the fluid tube.

17. The fluid delivery system of claim 11, wherein the fluid tube extends radially into the exhaust gas conduit.

18. The fluid delivery system of claim 11, wherein the opening in the tube is centrally disposed beyond the boundary layer of exhaust gas flow in the exhaust gas conduit.