Patent Application
20140255261
This application relates to the field of motor-vehicle engineering, and more particularly, to emissions-control catalyst bricks and methods for making the same.
An emissions-control device of a motor vehicle typically includes a core, or ‘brick’, made from a ceramic material. The brick may be coated with a catalytic washcoat, which may include a precious-metal catalyst. The catalyst encourages the breakdown of undesirable engine emissions—nitrogen oxides (NOx), hydrocarbons, carbon monoxide (CO), and particulates, for example. In the current state-of-the-art, the brick is an assembly of many narrow tubes, or honeycombs, open at one or both ends, with the catalyst coating the inside of each tube.
In some kinetic domains, heterogeneous catalysis of a gas-phase chemical reaction—such as the breakdown of NOx or oxidation of CO—is overall faster when the gas flows turbulently over the catalyst. However, the long, thin tubes of a state-of-the-art catalyst brick transport the exhaust gas with relatively little turbulence. Typically, turbulent exhaust flow at the ends of each tube transitions to a laminar flow regime as it travels through the tube. Smooth, laminar flow limits mass transport of the exhaust gasses and reaction products at the catalytic reaction surface.
Furthermore, the individual tubes of the state-of-the-art brick may become clogged over time, due to particulate build-up. This effect not only increases the exhaust back pressure on the engine, but also reduces the catalytically active surface area available to the exhaust, eroding both engine efficiency and emissions-control performance. Finally, the ceramic material from which a state-of-the-art brick is made is invariably brittle and subject to stress-induced fracture. Such fracture may lead to additional clogging.
Accordingly, one embodiment of this disclosure provides an emissions-control catalyst brick comprising a plurality of formed metal ribbons that together define a repeating pattern of open cells. The ribbons are joined together in layers with the open cells of each layer offset from those of the adjacent layer. A catalyst wash coat is then applied to the plurality of metal ribbons. With this structure, exhaust gas flows turbulently throughout the brick, for faster mass transport to and from the catalytic surface of the cells. In addition, overall flow through the brick is less affected by clogging of the individual cells, which do not extend the whole length of the brick. Here, the exhaust flow merely seeks a path around clogged cells. Furthermore, the flexible metallic structure of the brick is much less susceptible to fracture, relative to a ceramic substrate.
The summary above is provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content of this summary nor to implementations that address the problems or disadvantages noted herein.
Aspects of this disclosure will now be described by example and with reference to the illustrated embodiments listed above. Components, process steps, and other elements that may be substantially the same in one or more embodiments are identified coordinately and are described with minimal repetition. It will be noted, however, that elements identified coordinately may also differ to some degree. It will be further noted that the drawing figures included in this disclosure are schematic and generally not drawn to scale. Rather, the various drawing scales, aspect ratios, and numbers of components shown in the figures may be purposely distorted to make certain features or relationships easier to see.
Compressor 14 is coupled fluidically to intake manifold 22 via charge-air cooler (CAC) 24 and throttle valve 26. Pressurized air from the compressor flows through the CAC and the throttle valve en route to the intake manifold. In the illustrated embodiment, compressor by-pass valve 28 is coupled between the inlet and the outlet of the compressor. The compressor by-pass valve may be a normally closed valve configured to open to relieve excess boost pressure under selected operating conditions.
Exhaust manifold 20 and intake manifold 22 are coupled to a series of cylinders 30 through a series of exhaust valves 32 and intake valves 34, respectively. In one embodiment, the exhaust and/or intake valves may be electronically actuated. In another embodiment, the exhaust and/or intake valves may be cam actuated. Whether electronically actuated or cam actuated, the timing of exhaust and intake valve opening and closure may be adjusted as needed for desired combustion and emissions-control performance.
Cylinders 30 may be supplied any of a variety of fuels, depending on the embodiment: gasoline, alcohols, or mixtures thereof. In the illustrated embodiment, fuel from fuel system 36 is supplied to the cylinders via direct injection through fuel injectors 38. In the various embodiments considered herein, the fuel may be supplied via direct injection, port injection, throttle-body injection, or any combination thereof. In engine system 10, combustion is initiated via spark ignition at spark plugs 40. The spark plugs are driven by timed high-voltage pulses from an electronic ignition unit (not shown in the drawings).
Engine system 10 includes high-pressure (HP) exhaust-gas recirculation (EGR) valve 42 and HP EGR cooler 44. When the HP EGR valve is opened, some high-pressure exhaust from exhaust manifold 20 is drawn through the HP EGR cooler to intake manifold 22. In the intake manifold, the high pressure exhaust dilutes the intake-air charge for cooler combustion temperatures, decreased emissions, and other benefits. The remaining exhaust flows to turbine 16 to drive the turbine. When reduced turbine torque is desired, some or all of the exhaust may be directed instead through wastegate 46, by-passing the turbine. The combined flow from the turbine and the wastegate then flows through the various exhaust-aftertreatment devices of the engine system, as further described below.
In engine system 10, three-way catalyst (TWC) device 48 is coupled downstream of turbine 16. The TWC device includes an internal catalyst-support structure to which a catalytic washcoat is applied. The washcoat is configured to oxidize residual CO, hydrogen, and hydrocarbons and to reduce nitrogen oxides (NOx) present in the engine exhaust. Lean NOx trap (LNT) 50 is coupled downstream of TWC device 48. The LNT is configured to trap NOx from the exhaust flow when the exhaust flow is lean, and to reduce the trapped NOx when the exhaust flow is rich.
It will be noted that the nature, number, and arrangement of exhaust-aftertreatment devices in the engine system may differ for the different embodiments of this disclosure. For instance, some configurations may include an additional soot filter or a multi-purpose exhaust-aftertreatment device that combines soot filtering with other emissions-control functions, such as NOx trapping.
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Engine system 10 includes electronic control system 60 configured to control various engine-system functions. The electronic control system includes memory and one or more processors configured for appropriate decision making responsive to sensor input and directed to intelligent control of engine-system componentry. Such decision-making may be enacted according to various strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. In this manner, the electronic control system may be configured to enact any or all aspects of the methods disclosed hereinafter. Accordingly, the method steps disclosed hereinafter—e.g., operations, functions, and/or acts—may be embodied as code programmed into machine-readable storage media in the electronic control system. In this manner, the ECS may be configured to enact any or all aspects of the methods disclosed herein, wherein the various method steps—e.g., operations, functions, and acts—may be embodied as code programmed into machine-readable storage media in the ECS.
Electronic control system 60 includes sensor interface 62, engine-control interface 64, and on-board diagnostic (OBD) unit 66. To assess operating conditions of engine system 10 and of the vehicle in which the engine system is installed, sensor interface 62 receives input from various sensors arranged in the vehicle—flow sensors, temperature sensors, pedal-position sensors, pressure sensors, etc. Some example sensors are shown in FIG. 1—manifold air-pressure (MAP) sensor 68, manifold air-temperature sensor (MAT) 70, mass air-flow (MAF) sensor 72, NOx sensor 74, and exhaust-system temperature sensor 76. Various other sensors may be provided as well.
Electronic control system 60 also includes engine-control interface 64. The engine-control interface is configured to actuate electronically controllable valves, actuators, and other componentry of the vehicle—throttle valve 26, compressor by-pass valve 28, wastegate 46, and EGR valves 42 and 56, for example. The engine-control interface is operatively coupled to each electronically controlled valve and actuator and is configured to command its opening, closure, and/or adjustment as needed to enact the control functions described herein.
Electronic control system 60 also includes on-board diagnostic (OBD) unit 66. The OBD unit is a portion of the electronic control system configured to diagnose degradation of various components of engine system 10. Such components may include oxygen sensors, fuel injectors, and emissions-control components, as examples.
Diesel particulate filter (DPF) 82 is coupled downstream of DOC device 80. The DPF is a regenerable soot filter configured to trap soot entrained in the engine exhaust flow; it comprises a soot-filtering substrate. Applied to the substrate is a washcoat that promotes oxidation of the accumulated soot and recovery of filter capacity under certain conditions. In one embodiment, the accumulated soot may be subject to intermittent oxidizing conditions in which engine function is adjusted to temporarily provide higher-temperature exhaust. In another embodiment, the accumulated soot may be oxidized continuously or quasi-continuously during normal operating conditions.
Reductant injector 84, reductant mixer 86, and SCR device 88 are coupled downstream of DPF 82 in engine system 78. The reductant injector is configured to receive a reductant (e.g., a urea solution) from reductant reservoir 90 and to controllably inject the reductant into the exhaust flow. The reductant injector may include a nozzle that disperses the reductant solution in the form of an aerosol. Arranged downstream of the reductant injector, the reductant mixer is configured to increase the extent and/or homogeneity of the dispersion of the injected reductant in the exhaust flow. The reductant mixer may include one or more vanes configured to swirl the exhaust flow and entrained reductant to improve the dispersion. Upon being dispersed in the hot engine exhaust, at least some of the injected reductant may decompose. In embodiments where the reductant is a urea solution, the reductant will decompose into water, ammonia, and carbon dioxide. The remaining urea decomposes on impact with the SCR catalyst (vide infra).
SCR device 88 is coupled downstream of reductant mixer 86. The SCR device may be configured to facilitate one or more chemical reactions between ammonia formed by the decomposition of the injected reductant and NOx from the engine exhaust, thereby reducing the amount of NOx released into the ambient. The SCR device comprises an internal catalyst-support structure to which an SCR washcoat is applied. The SCR washcoat is configured to sorb the NOx and the ammonia, and to catalyze the redox reaction of the same to form dinitrogen (N2) and water.
The engine systems described above include various emissions-control devices—TWC device 48, LNT 50, DOC device 80, DPF 82 and SCR device 88, for example. Any, some, or all of these devices may include an emissions-control catalyst brick 92 inside an enclosure 94, as shown for generic emissions-control device 96 of
Catalyst brick 92A is configured to conduct exhaust from inlet end 108 to outlet end 110 of each open cell 106. In the embodiment as illustrated, the wall portions are parallel to each other and to the direction of exhaust flow through the brick. In other embodiments, the wall portions may be oblique to the direction of exhaust flow through the brick, to enhance flow separation and turbulence.
In the embodiment of
Returning now to
No aspect of the above drawings or description should be understood in a limiting sense, for numerous other embodiments are within the spirit and scope of this disclosure. For instance, instead of the various layers of the catalyst brick being flat and parallel to each other, as shown in the drawings, the layers may be concentric like those of a jelly roll. This structure may be used in a cylindrical brick, which is supported in a cylindrical enclosure, for example.
The configurations described herein enable various methods for making an emissions-control catalyst brick. Accordingly, some such methods are now described, by way of example, with continued reference to the above configurations. It will be understood, however, that the methods here described, and others within the scope of this disclosure, may be enabled by different configurations as well. Further, some of the process steps described and/or illustrated herein may, in some embodiments, be omitted without departing from the scope of this disclosure. Likewise, the indicated sequence of the process steps may not always be required to achieve the intended results, but is provided for ease of illustration and description. One or more of the illustrated actions, functions, or operations may be performed repeatedly, depending on the particular strategy being used.
In certain other methods, the layers of folded metal ribbons may be rolled into a jellyroll configuration (c.f., 134 of method 124) instead of being stacked. In that embodiment, the rolled layers of folded metal ribbons may be enclosed in a cylindrical enclosure. In another stacked configuration, a long sheet of a structure and thickness corresponding to one layer 104 of the catalyst brick may be formed via a continuous process. That sheet may be folded in a zig-zag pattern to form parallel layers, which are subsequently joined together to form a rectangular prismatic brick.
It will be understood that the articles, systems, and methods described hereinabove are embodiments of this disclosure—non-limiting examples for which numerous variations and extensions are contemplated as well. This disclosure also includes all novel and non-obvious combinations and sub-combinations of the above articles, systems, and methods, and any and all equivalents thereof.
