Patent Application
20180347426
During a combustion cycle of an internal combustion engine (ICE), air/fuel mixtures are provided to cylinders of the ICE. The air/fuel mixtures are compressed and/or ignited and combusted to provide output torque. After combustion, pistons of the ICE force exhaust gases in the cylinders out through exhaust valve openings and into an exhaust system. The exhaust gas emitted from an ICE, particularly a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (CO), unburned hydrocarbons (HC), and oxides of nitrogen (NOx), and oxides of sulfur (SOx) as well as condensed phase materials (liquids and solids) that constitute particulate matter.
Exhaust gas treatment systems may employ catalysts in one or more components configured for accomplishing an after-treatment process such as reducing NOx to produce more tolerable exhaust constituents of nitrogen (e.g., N2) and water. One type of exhaust treatment technology for reducing NOx emissions is a selective catalytic reduction device (SCR), which generally includes a catalytic composition capable of reducing NOx species. A reductant, such as urea, is typically sprayed into hot exhaust gases upstream of the SCR, decomposed into ammonia, and absorbed by the SCR device. The ammonia then reduces the NOx to nitrogen and water in the presence of the SCR catalyst. Another type of exhaust treatment device is an oxidation catalyst (OC) device, which is commonly positioned upstream from a SCR to serve several catalytic functions, including oxidizing HC and CO species. Further, OCs can convert NO into NO2 to alter the NO:NOx ratio of exhaust gas in order to increase the NOx reduction efficiency of the downstream SCR.
According to an aspect of an exemplary embodiment, an exhaust gas system is provided. The system can include a hydrolysis catalyst device (HCD) in fluid communication with an exhaust gas conduit, a turbocharger turbine disposed downstream from the HCD and in fluid communication therewith via the exhaust gas conduit, a selective catalytic reduction device (SCR) disposed downstream from the turbocharger turbine and in fluid communication therewith via the exhaust gas conduit, and a reductant injector configured to inject reductant into the exhaust gas conduit upstream from the HCD. The HCD can include one or more of TiO2 and V2O5. The HCD can include one or more of TiO2, V2O5, A12O3, and SiO2. Reductant can include urea and/or a nitrogen-rich substance capable of decomposing into ammonia. A decomposition temperature threshold of the reductant can be higher than a light-off temperature of the SCR. The SCR can be close-coupled to the turbocharger turbine.
According to another aspect of an exemplary embodiment, an internal combustion engine (ICE) exhaust gas system is provided. The system can include an ICE configured to emit exhaust gas to an exhaust gas conduit, a turbocharger turbine disposed downstream from the ICE and in fluid communication therewith via the exhaust gas conduit, a selective catalytic reduction device (SCR) disposed downstream from the turbocharger turbine and in fluid communication therewith via the exhaust gas conduit, and a first reductant injector configured to inject reductant into the exhaust gas conduit at a first injection location upstream from the turbocharger turbine. A decomposition temperature threshold of the reductant can be higher than a light-off temperature of the SCR. The system can further include a hydrolysis catalyst device (HCD) in fluid communication with the exhaust gas conduit and disposed between the reductant injection location and the turbocharger turbine. The HCD can include one or more of TiO2, V2O5, A12O3, and SiO2. The system can further include a second reductant injector configured to inject reductant into the exhaust gas conduit at a second injection location downstream from the turbocharger turbine and upstream from the SCR. The ICE can be a diesel ICE. The reductant can include urea and/or a nitrogen-rich substance capable of decomposing into ammonia. The system can further include an oxidation catalyst device in fluid communication with the exhaust gas conduit and disposed downstream from the SCR.
According to another aspect of an exemplary embodiment, a method for controlling an internal combustion engine (ICE) exhaust gas system is provided. The system can include an ICE configured to emit exhaust gas to an exhaust gas conduit, a turbocharger turbine disposed downstream from the ICE and in fluid communication therewith via the exhaust gas conduit, a selective catalytic reduction device (SCR) disposed downstream from the turbocharger turbine and in fluid communication therewith via the exhaust gas conduit, and a first reductant injector configured to inject reductant into the exhaust gas conduit at a first injection location upstream from the turbocharger turbine. A decomposition temperature threshold of the reductant can be higher than a light-off temperature of the SCR. Reductant can include urea and/or a nitrogen-rich substance capable of decomposing into ammonia. The method can include injecting reductant upstream from turbocharger turbine. Injecting reductant upstream from the turbocharger turbine can occur while the SCR is below a NOx light-off temperature and/or a reductant decomposition temperature threshold. The method can further include subsequently ceasing injection of reductant upstream from the turbocharger turbine after the SCR achieves a NOx light-off temperature and/or a reductant decomposition temperature threshold. The system can further include a second reductant injector configured to inject reductant into the exhaust gas conduit at a second injection location downstream from the turbocharger turbine and upstream from the SCR, and the method further can further include injecting reductant via the second injector after the SCR achieves a NOx light-off temperature and/or a reductant decomposition temperature threshold.
Although many of the embodiments herein are describe in relation to ICE exhaust gas systems, the embodiments herein are generally suitable for all systems capable of accepting and treating NOx species using selective oxidation/reduction catalysts.
Other objects, advantages and novel features of the exemplary embodiments will become more apparent from the following detailed description of exemplary embodiments and the accompanying drawings.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Generally, this disclosure pertains to exhaust gas treatment systems utilizing turbochargers, selective catalytic reduction devices (SCR), and reductant injectors configured to inject reductant upstream from the turbocharger. Injecting reductant upstream from turbochargers provides better reductant decomposition and increases SCR performance, particularly at low temperatures. The exhaust gas treatment systems described herein can be implemented in various ICE systems that can include, but are not limited to, diesel engine systems, gasoline direct injection systems, and homogeneous charge compression ignition engine systems. The ICEs will be described herein for use in generating torque for vehicles, yet other non-vehicular applications are within the scope of this disclosure. Therefore when reference is made to a vehicle, such disclosure should be interpreted as applicable to any application of an ICE. Moreover, exhaust gas treatment systems are described in combination with an optional ICE for the purposes of illustration only, and the disclosure herein is not to be limited to gas sources provided by ICEs. It should be further understood that the embodiments disclosed herein may be applicable to treatment of any exhaust streams including oxides of nitrogen (NOx) or other chemical species which are desirably reduced by SCRs.
ICE 1 can include one or more cylinders 2 capable of each accepting a piston (not shown) which can reciprocate therein. Air and fuel are combusted in the one or more cylinders thereby reciprocating the appurtenant pistons therein. Air 4 can be supplied to one or more cylinders 2 via an air intake manifold 3, for example. The pistons can be attached to a crankshaft (not shown) operably attached to a vehicle driveline (not shown) in order to deliver tractive torque thereto, for example. ICE 1 can be of a spark ignition or a compression ignition design and can generally include any number of cylinder arrangements and a variety of reciprocating engine configurations including, but not limited to, V-engines, inline engines, and horizontally opposed engines, as well as both overhead cam and cam-in-block configurations. ICE I can comprise any engine configuration or application, including various vehicular applications (e.g., automotive, marine and the like), as well as various non-vehicular applications (e.g., pumps, generators and the like),
Exhaust gas 8 can generally include carbon monoxide (CO), unburned hydrocarbons (HC), water, NOx species, and optionally oxides of sulfur (SOx). Constituents of exhaust gas, as used herein, are not limited to gaseous species. As used herein, “NOx” refers to one or more nitrogen oxides. NOx species can include NyOx species, wherein y>0 and x>0. Non-limiting examples of nitrogen oxides can include NO, NO2, N2O, N2O2, N2O3, N2O4, and N2O5. HC refers to combustable chemical species comprising hydrogen and carbon, and generally includes one or more chemical species of gasoline, diesel fuel, or the like.
Turbocharger 10 includes a turbine 11, for example disposed within a turbine housing (not shown), and a compressor 12, for example disposed within a compressor housing (not shown). Turbine 11 and compressor 12 are mechanically coupled via a common rotatable shaft 13. Turbine 11 is configured in fluid communication with ICE 1 in order to receive exhaust gas 8 therefrom. In operation, the turbine 11 receives exhaust gas 8 from ICE 1, for example via a turbine exhaust intake (not shown). The intake can communicate exhaust gas to a circumferential volute, or scroll, which receives the exhaust gas 8 and directs the same to turbine 11, whereafter exhaust gas 8 is expelled from the turbine housing. Turbine 11 captures kinetic energy from the exhaust gases and spins the compressor 12 via common shaft 13. Volumetric restrictions of the exhaust gas within the turbine housing further convert thermal energy into additional kinetic energy which is similarly captured by the turbine 11. Such a conversion results in a temperature differential (ΔT) across turbine 11. For example, under normal ICE 1 operating conditions, the temperature of exhaust gas 8 may be 400° C. upstream from turbine 11 and 200° C. upstream from turbine 11 (i.e., a ΔT of 200° C.). The rotation of compressor 12 via the common shaft 30 draws in air 4 through a compressor intake (not shown) which is compressed and delivered to the intake manifold 3 of ICE 1. Turbochargers are commonly used to enhance the efficiency and/or performance of ICEs, and are ideally close-coupled to an appurtenant ICE such that exhaust gas 8 kinetic energy and/or thermal energy is maximized prior to contacting turbine 11. As used herein, “close-coupled” refers to a close orientation of a device (e.g., turbine 11) relative to another (e.g., ICE 1), such as within 1 meter of linear exhaust gas conduit 9, or within the engine compartment of a vehicle.
In general, the SCR 20 includes all devices which utilize a reductant 36 and a catalyst to reduce NOx species to desired chemical species, including diatomic nitrogen, nitrogen-containing inert species, or species which are considered acceptable emissions, for example. The reductant 36 can be ammonia (NH3), such as anhydrous ammonia or aqueous ammonia, or generated from a nitrogen and hydrogen rich substance such as urea (CO(NH2)2). For example, the reductant 36 can comprise urea and/or a nitrogen-rich substance capable of decomposing into ammonia. Additionally or alternatively, the reductant 36 can be any compound capable of decomposing or reacting in the presence of exhaust gas 8 and/or heat to form ammonia. The reductant 36 can be diluted with water in various implementations. In implementations where the reductant 36 is diluted with water, heat (e.g., from the exhaust) evaporates the water, and ammonia is supplied to the SCR 20. Non-ammonia reductants can be used as a full or partial alternative to ammonia as desired. In implementations where the reductant 36 includes urea, the urea reacts with the exhaust to produce ammonia, and ammonia is supplied to the SCR 20. Equation (1) below provides an exemplary chemical reaction of ammonia production via urea decomposition.
CO(NH2)2+H2O→2NH3+CO2 (1)
It should be appreciated that Equation (1) is merely illustrative, and is not meant to confine the urea or other reductant 36 decomposition to a particular single mechanism, nor preclude the operation of other mechanisms. Efficient decomposition urea to NH3 typically requires temperatures in excess of about 200° C., and, depending on the amount of urea injected, for example relative to a flow rate of exhaust gas 8, urea can crystalize in temperatures less than about 200° C. Accordingly, reductant 36 injection events and/or dosing quantities are typically determined based upon system temperature and exhaust gas 8 flow rate, among others, such that urea decomposition yield is maximized and urea crystallization is minimized. A reductant 36 decomposition threshold can accordingly refer to a temperature threshold below which reductant 36 crystalizes and/or does not suitably decompose.
Equations (2)-(6) provide exemplary chemical reactions for NOx reduction involving ammonia.
6NO+4NH3→5N2+6H2O (2)
4NO+4NH3+O2→4N2+6H2O (3)
6NO2+8NH3→7N2+12H2O (4)
2NO2+4NH3+O2→3N2+6H2O (5)
NO+NO2+2NH3→2N2+3H2O (6)
It should be appreciated that Equations (2)-(6) are merely illustrative, and are not meant to confine SCR 20 to a particular NOx reduction mechanism or mechanisms, nor preclude the operation of other mechanisms. SCR 20 can be configured to perform any one of the above NOx reduction reactions, combinations of the above NOx reduction reactions, and other NOx reduction reactions. In some instances, SCR 20 comprises a NOx oxidizing temperature threshold above which SCR 20 can oxidize reductant 36 and/or its decomposition products (e.g., urea, NH3) into NOx. A NOx oxidizing temperature threshold can be 500° C., for example.
SCR 20 includes a catalytic composition (CC) and can be packaged in a shell or canister in fluid communication with exhaust gas conduit 9 and configured to receive exhaust gas 8 and reductant 36 at upstream side. The shell or canister can comprise a substantially inert material, relative to the exhaust gas constituents, such as stainless steel. CC can comprise, be disposed on, or impregnated into a porous and high surface area material which can operate efficiently to convert NOx constituents in the exhaust gas 8 in the presence of a reductant 36, such as ammonia. For example, the catalyst composition can contain a zeolite impregnated with one or more base metal components such as iron (Fe), cobalt (Co), copper (Cu), vanadium (V), sodium (Na), barium (Ba), titanium (Ti), tungsten (W), and combinations thereof. In a particular embodiment, the catalyst composition can contain a zeolite impregnated with one or more of copper, iron, or vanadium. In some embodiments the zeolite can be a β-type zeolite, a Y-type zeolite, a ZM5 zeolite, or any other crystalline zeolite structure such as a Chabazite or a USY (ultra-stable Y-type) zeolite. In a particular embodiment, the zeolite comprises Chabazite. In a particular embodiment, the zeolite comprises SSZ. Suitable CCs can have high thermal structural stability, particularly when used in tandem with particulate filter (PF) devices or when incorporated into selective catalytic reduction filter devices (SCRF), which are regenerated via high temperature exhaust soot burning techniques. CC can optionally further comprise one or more base metal oxides as promoters to further decrease the SO3 formation and to extend catalyst life. The one or more base metal oxides can include WO3, Al2O3, and MoO3, in some embodiments. In one embodiment, WO3, Al2O3, and MoO3 can be used in combination with V2O5.
SCR 20 can have a light-off temperature above which CC exhibits desired or suitable catalytic activity or yield (e.g., reduction of NOx species). The light-off temperature can be dependent upon the type of catalytic materials of which CC is comprised, and the amount of catalytic materials present in SCR 20, among other factors. For example, a CC comprising V2O5 can have a light off temperature of about 300° C. In another example, a CC comprising Fe-impregnated zeolite can have a light off temperature of about 350° C. In another example, a CC comprising Cu-impregnated zeolite can have a light off temperature of about 150° C. When SCR 20 operates at a temperature below its light-off temperature, undesired NOx breakthrough and NH3 slip can occur wherein NOx and/or NH3 pass through SCR 20 unreacted or unstored. NOx breakthrough and NH3 slip can be particularly problematic immediately after engine startup and in cold conditions. NOx breakthrough can also be exacerbated by lean burn strategies commonly implemented in diesel engines, for example. Lean burn strategies coordinate combustion at higher than stoichiometric air to fuel mass ratios to improve fuel economy, and produce hot exhaust with a relatively high content of O2 and NOx species. The high O2 content can further inhibit or prevent the reduction of NOx species in some scenarios. While SCRs 20 with low NOx light-off temperatures can reduce or prevent NOx breakthrough, reductant 36 decomposition thresholds ultimately limit SCR 20 performance.
Exhaust gas treatment devices which reduce the pressure and/or temperature of exhaust gas 8, such as SCR 20, are commonly positioned downstream from turbine 11 in order to maximize turbocharger 10 performance. In some instances, SCR 20 is preferably positioned downstream from turbine 11 because, under some ICE 1 operation conditions, exhaust gas 8 upstream from turbine 11 can exceed SCR 20 NOx oxidizing thresholds. Reductant 36 can be supplied from a reductant reservoir (not shown) and is commonly injected into the exhaust gas conduit 9 at a location upstream from SCR 20 via an injector 30, or other suitable delivery means. Specifically, system 100 includes injector 30 configured to inject reductant 36 into exhaust gas conduit 9 at an injection location upstream from turbine 11 where exhaust gas 8 temperatures are higher. Reductant 36 injection upstream from turbine 11 better facilitates reductant 36 heating and/or decomposition and utilizes turbine 11 as a mixer/vaporizor, thereby allowing reductant 36 to be injected sooner in an ICE 1 operating cycle and eliminating or reducing reductant 36 crystallization, for example. In order to maximize the benefits of upstream turbine 11 reductant 36 injection, in some embodiments SCR 20 is close-coupled to turbine 11.
The position of injector 30 is particularly advantageous during vehicle cold starts and in operating conditions wherein the temperature of system 100 and/or the ambient is below the reductant 36 decomposition threshold. Specifically, injection of reductant 36 upstream from turbine 11 allows reductant 36 to contact higher-temperature exhaust gas 8 and effect greater decomposition and mixing/vaporization, and the disposition of SCR 20 downstream from turbine 11 does not deprive turbine 11 of thermal energy. As used herein, a cold start refers to an ICE 1 start or operating period that occurs while the temperature of one or more exhaust gas 8 treatment devices (e.g., SCR 20) is lower than the ideal or suitable operating temperature of the device. Particularly, the temperature of SCR 20 can refer to the average temperature of the CC. Additionally or alternatively a cold start can be identified by an ambient temperature threshold (e.g., below 40° C.), or an ambient temperature less than an ideal or suitable operating temperature of SCR 20 CC.
In some embodiments, in order to increase turbocharger 10 performance, increase SCR 20 performance, optimize reductant 36 decomposition, and/or reduce wear to the turbine 11 caused by upstream reductant injection 36, system 100 can further comprise a second injector 30′ configured to inject reductant 36 at a second injection location downstream from turbine 11 and upstream from SCR 20. Accordingly, reductant 36 can be supplied by injector 30 under certain conditions, and reductant 36 can be supplied by injector 30′ the same certain conditions and/or other conditions. For example, reductant 36 can be supplied by injector 30 during a vehicle cold start, and reductant 36 can subsequently be supplied by 30′ after system 100 has achieved a desired temperature. Reductant 36 can be supplied to injectors 30 and 30′ from a common reservoir (not shown) in some embodiments.
Optional HCD 40 is configured to accept exhaust gas 8, for example via exhaust gas conduit 9, and facilitate and/or encourage the decomposition of reductant 36 into desired chemical species. In particular, HCD 40 is configured to decompose urea into NH3. HCD 40 comprises a CC which can be packaged in a shell or canister configured to receive exhaust gas 8 at upstream side. The shell or canister can comprise a substantially inert material, relative to the exhaust gas constituents, such as stainless steel. CC can comprise, be disposed on, or impregnated into a porous and high surface area material, and can comprise one or more of TiO2, V2O5, Al2O3, and SiO2. In one embodiment, the CC comprises TiO2 and/or V2O5. For example the CC can be disposed on a porous monolith substrate, such as those discussed above. The HCD 40, and in particular the CC substrate, can be configured to exhibit a low pressure differential (AP) across the device. The volume of HCD 40 and the amount of CC can depend on many factors including the type of ICE 1, the volumetric flow of exhaust gas 8, and the amount of reductant 36 normally injected, for example. While the HCD 40 may exacerbate pre-turbine 11 heat lost and turbocharger 10 lag, its disposition upstream from turbine 11 serves to effect enhanced decomposition of reductant 36 and enhance SRC 20 performance, particularly in cold conditions. In some embodiments, as an alternative to HCD 40, turbine 11 can comprise HCD 40 CC on one or more outer surfaces such that the CC contacts reductant 36. An HCD, such as HCD 40, can have a similar NOx light-off temperature to an SCR, such as SCR 20.
Optional OC 50 is a flow-through device comprising a CC and configured to accept exhaust gas 8. OC 50 is generally utilized to oxidize various exhaust gas 8 species, including HC, CO and NOx species. CC can he housed within a housing, such as a metal housing, having an inlet (i.e., upstream) opening and outlet (i.e., downstream) opening, or be otherwise configured to provide structural support and facilitate fluid (e.g., exhaust gas) flow through OC 50. CC can comprise many various catalytically active materials and physical configurations thereof, and can optionally comprise a substrate such as a porous ceramic matrix or the like. Catalytically active materials can comprise platinum group metal catalysts, metal oxide catalysts, and combinations thereof. Suitable platinum group metals can include Pt, Pd, Rh, Ru, Os or Ir, or combinations thereof, including alloys thereof. In one embodiment, suitable metals include Pt, Pd, and combinations thereof, including alloys thereof. Suitable metal oxide catalyst can include iron oxides, zinc oxides, aluminum oxides, perovksites, and combination thereof, for example. In one embodiment, CC can comprise Pt and Al2O3. In many embodiments, CC comprises zeolite impregnated with one or more catalytically active base metal components. The zeolite can comprise a β-type zeolite, a Y-type zeolite, a ZM5 zeolite, or any other crystalline zeolite structure such as a Chabazite or a USY (ultra-stable Y-type) zeolite. In a particular embodiment, the zeolite comprises Chabazite. In a particular embodiment, the zeolite comprises SSZ. It is to be understood that the CC is not limited to the particular examples provided, and can include any catalytically active device capable of oxidizing HC, CO, and NOx species. OC 50 can store and/or oxidize NOx species in exhaust gas 8, which, for example, may form during the combustion of fuel. For example, in some embodiments, OC 50 can be utilized to convert NO into NO2 in order to optimize the exhaust gas NO:NO2 ratio for downstream SCRs and/or SCRFs which generally operate more efficiently with exhaust gas feed streams having a NO:NO2 ratio of about 1:1. As shown in
System 100 can further include a control module 60 operably connected to monitor and/or control ICE 1, turbocharger 10, SCR 20, injector 30, HCD 40, DOC 50, and combinations thereof. As used herein, the term module refers to 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. Module 60 can control reductant 36 injection, for example.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
