CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application No. 60/874,921, filed on Dec. 14, 2006, which is hereby incorporated by reference.
The present disclosure relates to exhaust after-treatment devices. More particularly, the disclosure pertains to regeneration, oxidation or reduction of emissions by such devices.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Exhaust after-treatment systems for on-highway Diesel engines will typically include Diesel particulate filters (DPF), NO, adsorbers (LNT) and selective catalytic reduction (SCR) systems in upcoming model years. A regenerative oxidizing or reducing fluid (a secondary fluid) is needed for proper functioning and/or maintenance of the substrates used in each of these devices. In most applications, DPFs will require injection of hydrocarbons (HC), for example, Diesel fuel, for periodic regeneration or oxidation of the trapped soot in the filter. SCR systems rely on injection of a reductant (typically urea) upstream of a catalyst for reduction of oxides of nitrogen emissions. LNTs require periodic regeneration using exhaust gas rich in hydrocarbon or carbon monoxide, typically provided by injecting excess Diesel fuel into the exhaust stream. Currently, common practice for injection of these hydrocarbon fuels and urea is to inject them into the exhaust pipe upstream of the after-treatment device. This injection must be done at a location far enough upstream of the device to insure adequate mixing, evaporation and/or hydrolysis of the injected fluid, typically a linear distance of ten or more pipe diameters upstream.
Disadvantages of the conventional method arise when SCR, LNT, and/or DPF systems must be either packaged into a restricted space or coupled together in a common housing. There may be insufficient exhaust pipe length available for adequate mixing, evaporation, and/or hydrolysis of the injected fluid, or the use of sufficient exhaust pipe length will result in unacceptable total back pressure for the after-treatment system. Due to packaging constraints, there may also be after-treatment components positioned in the exhaust pipe path needed for injection, mixing, evaporation, and/or hydrolysis, which would interfere with the proper functioning of the after-treatment devices.
Therefore there is seen to be a need in the art for an arrangement to facilitate adequate mixing, evaporation and/or hydrolysis of the injected secondary fluid where a suitable length of exhaust pipe is not available.
The present teachings are directed to auxiliary piping, alternative pipe routing and auxiliary devices needed to facilitate injection, mixing, evaporation and/or hydrolysis of the secondary fluids needed for vehicular exhaust after-treatment systems. Such secondary fluids are, for example and without limitation, regenerating fluids or oxidizing fluids or reducing fluids.
In one aspect of the invention, a pipe along the after-treatment device runs parallel to the exhaust flow. This pipe enters the after-treatment device from the side, upstream from the device substrate needing the secondary fluid. Prior to and during injection, this pipe is fed with compressed air to achieve pressure higher than that at the point where it enters the exhaust flow and to achieve flow rate sufficient for adequate mixing, evaporation and/or hydrolysis of the secondary fluid. At the point where the mixing pipe enters the exhaust flow, a valve maintains this positive pressure in the pipe. The secondary fluid is injected into this pipe and the valve is opened as needed.
In a second aspect of the present teachings, one or more pipes parallel to the main exhaust pipe between the engine and the after-treatment device run from a location off the exhaust manifold or turbocharger upstream of a turbine inlet to the point in the after-treatment system just upstream of the component requiring the injected secondary fluid.
In a third aspect of the instant teachings, the exhaust after-treatment device is provided with a center channel or conduit extending through the device substrate which comprises the mixing chamber for the exhaust/secondary fluid.
BRIEF DESCRIPTION OF THE DRAWING
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The objects and features of the present teachings will become apparent from a reading of a detailed description, taken in conjunction with the drawing, in which:
FIG. 1 is a cross-sectional view of an exhaust after-treatment system including a variety of after-treatment devices within a single housing, the system including a parallel path secondary fluid mixture system arranged in accordance with the instant teachings;
FIG. 2 is a side partial cross-sectional view of a first alternative embodiment of an exhaust after-treatment system arranged in accordance with the principles of the instant disclosure;
FIG. 3 is a partial cross-sectional view of a second alternative embodiment of an exhaust after-treatment system arranged in accordance with the principles of the instant disclosure,
FIGS. 4A and 4B are respective side and end cross-sectional views of the after-treatment device of FIG. 3 depicting a regenerative fluid distribution element arranged in accordance with the principles of the instant disclosure;
FIG. 5 is a cross-sectional view of a third embodiment of an exhaust after-treatment system arranged in accordance with the principles of the instant disclosure; and
FIG. 6 is a perspective view of an alternative exhaust after-treatment device with an internal mixing chamber with its outer shell removed and arranged in accordance with the principles of the instant disclosure.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
With reference to FIG. 1, exhaust after-treatment system 100 includes a multi-purpose exhaust after-treatment device containing several elements. Input exhaust to the device is shown at arrow 130, while output exhaust from the device is shown at arrow 132. The multi-purpose after-treatment device comprises a first Diesel oxidation catalyst or NOx adsorber substrate 102 a, a selective catalytic reduction substrate 104, a second Diesel oxidation catalyst or NOx adsorber substrate 102 b, a Diesel particulate filter substrate 106 and a third Diesel oxidation catalyst or NOx adsorber substrate 102 c. Each of these substrates are separated by an inter-substrate gap for purposes of receiving a secondary fluid distribution element to be discussed below.
A urea mixing tube 106 runs substantially parallel to exhaust flow alongside the exhaust after-treatment device and receives a combination of urea and compressed air at an input 108 for mixing within a chamber 116 of conduit 106. A valve 120 a introduces the compressed air/urea mixture into a first regenerative fluid distribution element 122 a placed between substrates 102 a and 104 and carrying a plurality of radially oriented perforations or orifices 123 for directing the secondary fluid coming from conduit 106 to the input face of substrate 104.
A hydrocarbon mixing tube 110 also extends substantially parallel to the exhaust flow and receives a mixture of hydrocarbons, such as Diesel fuel, and compressed air at an input 112 for mixing in chamber 118 of conduit 110. Optionally, a glow plug or other auxiliary heat component 114 may extend into the mixing chamber 118. A valve 120 b is used to meter the mixture of exhaust and secondary fluid into a distribution element 122 b. Conduits 106 and 110 enter the after-treatment device from the side, upstream from the particular substrate requiring the secondary fluid. Prior to and during injection, these pipes are fed additionally with compressed air to achieve a pressure higher than that at the point where the fluid/exhaust mixture enters the exhaust flow through the device and at a flow sufficient for proper mixing, evaporation and/or hydrolysis of the secondary fluid. At the point where the secondary fluid enters the exhaust flow, a valve maintains this positive pressure in the pipe. The secondary fluid is injected and the valve is opened as needed.
These parallel pipes expel the mixture of air and injected secondary fluid into the exhaust after-treatment device inter-substrate chamber just upstream of that substrate to a series of orifices tuned to provide the flow pattern needed across the face of the substrate being treated.
Other auxiliary devices might also be incorporated into this parallel piping system, including heating devices to aid in evaporation of secondary fluids, burners to assist in regeneration of LNTs and/or DPFs, and/or devices to create laminar or turbulent flow profiles or to aid in mixing of the exhaust gas and secondary fluids. Alternatively, the conduits such as 106 and 110 may be physically attached to the shell of the after-treatment device housing in such a way that heat transfer from the after-treatment device occurs thereby aiding the heating of the air/secondary fluid mixture.
In the embodiment of FIG. 2, exhaust after-treatment system 200 utilizes auxiliary piping for establishing a parallel exhaust flow stream into which is injected the secondary fluid. Diesel engine 202 has an exhaust manifold 204 which empties into a turbocharger 206. Exhaust is then carried via exhaust pipe 208 to an input 222 of an exhaust after-treatment device 220. Substantially parallel to the flow of exhaust through conduit 208 is a conduit 210 for carrying exhaust likewise directly from the exhaust manifold 204 or, optionally, from turbocharger 206 to a secondary input 224 of after-treatment device 220. Injector 212 injects the secondary fluid required into the exhaust stream flowing through conduit 210 for introduction to device 220 at input 224. This mixture then flows through the substrate 226 of after-treatment device 220 and exits at output 228 thereof for receipt by tailpipe or further exhaust pipe 230. Hence, it is seen that conduit 210 runs from a location on the exhaust manifold 204 or from a turbocharger 206 upstream of the turbine inlet to a point in the after-treatment system just upstream of the substrate component requiring the injected secondary fluid. Because conduit 210 originates at a location having pressure much higher than that just upstream of the substrate 226, flow of exhaust through conduit 210, past the injector 212 and through the mixing length of conduit 210 would be insured.
In another possible configuration such as set forth in FIG. 3, a pipe or pipes carry exhaust gas on a path parallel to the flow through an after-treatment substrate, bypass it and allow a diameter-to-length ratio sufficient for injection and proper mixing, evaporation, and/or hydrolysis of the secondary fluid. Exhaust after-treatment system 300 includes an after-treatment device 306 situated between an exhaust pipe 304 and a tailpipe 332. Exhaust flow is shown by arrows 302.
Exhaust enters device 306 at inlet 308 to an input chamber 310. From chamber 310 exhaust flows both through substrate 326 and through substantially parallel conduit 312 past an injector 316 for injecting secondary fluid into the exhaust flow as shown by arrow 322. This mixture then flows into chamber 311 of device 306 and there flows both through substrate 328 and back through a second parallel pipe 314 past a second injector 318. The mixture flows as shown in arrow 324 back to chamber 310 for treatment of substrate 326. Since this configuration may not necessarily carry gas from an area of higher pressure to one of lower pressure, an auxiliary pumping device 320 could be made part of system 300 to facilitate proper flow and adequate mixing, evaporation and/or hydrolysis of the secondary fluid.
With reference to FIGS. 4A and 4B, both of the embodiments of FIGS. 2 and 3 would expel the mixture of exhaust gas and injected secondary fluid into a chamber just upstream of the after-treatment substrate component being treated through a series of orifices 404 in a toroidal or helical ring 402 adjacent to the chamber's outer skin. In cases where injection is required on only a periodic basis (e.g., LNT or DPF regeneration), one or more valves may be positioned in the system to initiate and halt exhaust flow through the parallel pipe or pipes.
A third embodiment of an exhaust after-treatment system arranged in accordance with the principles of these teachings is set forth in FIG. 5. Exhaust after-treatment system 500 includes an input exhaust pipe 502 having an injector 504 for injecting secondary fluid into the exhaust stream entering input 518 of after-treatment device 510. In this embodiment, the mixing chamber is contained inside after-treatment device 510 by forming a channel for receipt of a mixing conduit 508 which extends through the substrate 512. In the particular device shown in FIG. 5, the exhaust outlet 520 of the device 510 is located at the same end as the exhaust inlet. A turnaround chamber 516 takes the mixture of exhaust gas and secondary fluid and forces it to turn in a reverse direction and flow through the substrate orifices itself thence to an output chamber 514 for expulsion from output 520.
An alternative to the after-treatment device 510 shown in FIG. 5 is set forth in FIG. 6. In the arrangement of FIG. 6, two pipes running from a chamber at the front face of the after-treatment device substrate pass through the after-treatment device substrate to its rear face. One of these pipes carries exhaust gas through the catalyst substrate to its rear face where flow would reverse and pass back through the substrate itself. The second pipe would carry the gas after its emerges from the front face of the substrate and reverses direction again back through the internal channel of the substrate to the chamber in front of a second downstream substrate. An example would be an SCR system followed by a DPF, where secondary fluids must be injected and mixed prior to each after-treatment device. By carrying exhaust gas on a path parallel to the flow through an after-treatment component, bypassing it and allowing a diameter-to-length ratio sufficient for injection and proper mixing, evaporation, and/or hydrolysis, the arrangement of FIG. 6 enables proper introduction of the secondary fluid in situations where such might be otherwise impracticable. Again, where injection of the secondary fluid is required only on a periodic basis, one or more valves may be positioned in the system to close off the injectors from the exhaust flow.
Device 600 of FIG. 6 receives exhaust gas flow from exhaust pipe 602, the flow being depicted by arrows 604 a. Exhaust input conduit 606 forms a first mixing chamber for the exhaust gas and the secondary fluid injected via injector 610 into the input volume defined by a first partition 608 on one side thereof. The exhaust/secondary fluid mixture then proceeds as shown by arrows 604 b down the conduit 606 to a turnaround chamber at a downstream face of the substrate 616 defined by a second partition 618. The exhaust/secondary fluid mixture then proceeds via arrows 604 c back through the structure of the substrate 616 itself to a second injection area defined between the substrate 616 and partition 608 where a second injector 612 injects a further secondary fluid into the exhaust stream for carrying back through substrate 616 through a second internal conduit 614 for use downstream by a further after-treatment device which is located to the left of partition 618 as shown in FIG. 6. This output flow of exhaust/secondary fluid is shown by arrows 604 d.
Systems arranged in accordance with the principles of the disclosure herein provide packaging advantages where the envelope for the after-treatment system is small and a combination of after-treatment devices must be coupled together in a common housing shell. Systems in accordance with the disclosure likewise provide ease of configuration in situations where there is insufficient length in the main exhaust pipe to support proper mixing, evaporation, and/or hydrolysis of the secondary fluid. Additionally, such systems provide more effective mixing and uniformity of the mixture in cases where the mixing conduits can be made with a better length-to-diameter ratio and/or a straighter path than the main exhaust pipe. Furthermore, a tunable entry path for the secondary fluid-rich mixture into a region upstream of the after-treatment component being treated is provided. Finally, the systems of the instant disclosure enable use of larger diameter catalyst substrates (for better flow uniformity and lower system back pressure), which will in many cases require positioning of the substrates close together, thereby eliminating lengths of pipe, end cones, etc., between the substrates that would otherwise be suitable for injection, and proper mixing of the exhaust stream with the secondary fluid in use.
The invention has been described with reference to embodiments which have been set forth for the sake of example only. The invention is to be described with reference to the appropriately construed claims.