Patent Application
20140260198
The present disclosure relates to an exhaust system, and particularly to an exhaust aftertreatment system for large engine applications.
Growing concern for environment pollution has created new challenges for manufacturers. Improvement in exhaust systems are required in order to comply with the current pollution regulatory norms. More specifically, exhaust aftertreatment systems are utilized to treat exhaust containing relatively harmful pollutants, such as nitrogen oxides (NOx). The exhaust aftertreatment systems are known to employ selective catalytic reduction (SCR) for such treatment. In the SCR process, a reductant, for example urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust and adsorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOx in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). Hence, the SCR process effectuates a reduction in harmful emissions.
A variety of designs for the exhaust aftertreatment system exist. These designs may vary based on the type of application. Known exhaust aftertreatment system designs typically occupy space. However, there may be space constraints in certain large engine applications to accommodate the exhaust aftertreatment system. Therefore, there is a need to provide an improved design for the exhaust aftertreatment system.
For example, U.S. Published Application No. 2011/0146253 relates to an aftertreatment module for use with an engine. The aftertreatment module includes a plurality of inlets configured to direct exhaust in a first flow direction into the aftertreatment module. The aftertreatment module also has a mixing duct configured to receive exhaust from the plurality of inlets, and a branching passage in fluid communication with the mixing duct. The branching passage may be configured to redirect exhaust from the mixing duct into separate flows that exit the aftertreatment module in a second flow direction opposite the first flow direction. However, the disclosed aftertreatment system has a relatively large design.
In one aspect of the present disclosure an exhaust aftertreatment module is provided. The exhaust aftertreatment module includes a housing having a first end and a second end. At least one inlet is disposed between the first end and the second end. The at least one inlet is configured to introduce exhaust into the housing. Further, a mixing tube is disposed downstream of the at least one inlet. The mixing tube is configured to direct the exhaust towards the second end of the housing. The exhaust aftertreatment module further includes a single bank of Selective Catalytic Reduction (SCR) catalysts disposed at an oblique angle to a longitudinal axis of the mixing tube. The single bank of SCR catalyst is configured to receive the exhaust redirected from the second end of the housing. In one embodiment, a sound attenuation chamber is provided in the aftertreatment module. The sound attenuation chamber is disposed downstream of the at least one inlet and proximate to the mixing tube. The sound attenuation chamber is configured to receive the exhaust from the at least one inlet.
In another aspect, a method is provided. The method introduces exhaust into at least one inlet disposed between a first end and a second end of a housing. The method receives the exhaust into a mixing tube disposed downstream of the at least one inlet. Further, the method directs the exhaust towards the second end of the housing. Thereafter, the method receives the exhaust redirected from the second end of the housing into a single bank of Selective Catalytic Reduction (SCR) catalysts disposed at an oblique angle to a longitudinal axis of the mixing tube.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Multiple separate sub-systems may be included within the power system 100 to promote power production. For example, the power system 100 may include, among other things, an air induction system 108 and an exhaust system 110. The air induction system 108 may be configured to direct air or an air/fuel mixture into the power system 100 for subsequent combustion. The exhaust system 110 may treat and discharge byproducts of the combustion process to the atmosphere. The exhaust system 110 may include components that condition and direct exhaust from cylinders of the engine 104 to the atmosphere. For example, the exhaust system 110 may include an aftertreatment module 112 connected to receive and treat exhaust from the engine 104. The aftertreatment module 112 may treat, condition, and/or otherwise reduce constituents of the exhaust before the exhaust is discharged to the atmosphere.
The aftertreatment module 112 includes a housing 114.
Referring to
Further, the aftertreatment module 112 may include at least one oxidation catalyst, for example a diesel oxidation catalyst (DOC) 216 within the housing 114. The illustrated embodiment depicts two DOCs 216 located downstream of the inlet 214. The DOC 216 is configured to receive the exhaust from the inlet 214. It should be understood that the DOC 216 may include a porous ceramic honeycomb structure, a metal mesh, a metal or ceramic foam, or another suitable substrate coated with or otherwise containing a catalyzing material, in order to catalyze a chemical reaction. The chemical reaction may alter a composition of the exhaust passing through the DOC 216. Exemplary materials used to make the DOC 216 may include palladium, platinum, vanadium, or a mixture thereof that may facilitate a conversion of NO present in the exhaust into NO2. In one embodiment, the DOC 216 may alternatively or additionally perform particulate trapping functions, hydro-carbon reduction functions, carbon-monoxide reduction functions, and/or other functions known in the art for the treatment of the exhaust.
In one embodiment, a sound attenuation chamber 218 may be disposed downstream of the DOC 216. The sound attenuation chamber 218 may receive the exhaust from the DOC 216. It should be noted that parameters related to the sound attenuation chamber 218 such as, shape, size and dimension may vary as per requirement. The sound attenuation chamber 218 may include one or more compartments. In one exemplary embodiment, as shown in
Referring closely to
Further, the sound attenuation chamber 218 may fluidly connect an outlet of the DOC 216 with an upstream open end of the mixing tube 228. As shown, the mixing tube 228 may have a hollow tubular structure. A longitudinal axis X-X of the mixing tube 228 may be substantially parallel to the bottom surface of the housing 114. The mixing tube 228 may be supported within the housing 114 using suitable supporting structures. In an exemplary case, a diameter of the mixing tube 228 is approximately about 216 mm.
A reductant injector (not shown) may be located at or near the upstream open end of the mixing tube 228. The reductant injector is configured to inject a reductant into the exhaust flowing through the mixing tube 228. A gaseous or liquid reductant, most commonly a water/urea solution, ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, an ammine salt, or a hydrocarbon such as diesel fuel, may be sprayed or otherwise advanced into the exhaust passing through the mixing tube 228. In an embodiment, a mixer (not shown) may be located within mixing tube 228 in order to enhance incorporation of the reductant with the exhaust flowing through the mixing tube 228. The mixer may be located downstream of reductant injector.
Referring to
The single bank of SCR catalysts 238 may include a number of SCR catalysts. Each of the SCR catalysts 238 may have similar dimensions and properties. In the illustrated embodiment, the single bank of SCR catalysts 238 includes four cylindrical shaped SCR catalysts. A person of ordinary skill in the art will appreciate that the number of SCR catalysts 238 may vary based on the application. Moreover, each of the of SCR catalysts 238 has a corresponding SCR inlet 240 and an SCR outlet 242. As shown in accompanying figures, each of the SCR catalysts 238 is arranged side by side with the respective SCR inlets 240 oriented proximate to the sidewall 242.
The single bank of SCR catalysts 238 is configured to receive the redirected exhaust from the second end of the housing 214. It should be noted that the orientation of the single bank of SCR catalyst 238 relative to the sidewalls 206, 208 of the housing may cause a restriction in the exhaust flow entering the single bank of SCR catalysts. To this end, each of the SCR catalysts 238 may receive an equal distribution of the exhaust flow. More specifically, each of the plurality of SCR catalysts 238 may include a generally cylindrical substrate fabricated from or otherwise coated with a ceramic material such as titanium oxide, a base metal oxide such as vanadium and tungsten, zeolites, and/or a precious metal. With this composition, decomposed reductant entrained within the exhaust redirected into the single bank of SCR catalysts 238 may be adsorbed onto the surface and/or absorbed within the single bank of the SCR catalysts 238. The reductant may react with NOx (NO and NO2) present in the exhaust to form water (H2O) and diatomic nitrogen (N2).
The exhaust may exit the single bank of SCR catalysts 238 via the SCR outlet 242. Further, the housing 114 may include at least one outlet 244 proximate to the first end 202 of the housing 114. As shown, the outlet 244 may be provided on the sidewall 202 of the housing 114. The exhaust leaving the single bank of SCR catalysts 238 may exit the exhaust aftertreatment module 112 via the outlet 244. In one case, the outlet 244 has a diameter of approximately about 254 mm. It should be noted that the housing 114 may additionally include a number of compartments or divisions in order to assist in directing the exhaust flow within the housing. These compartments may be created using any suitable material.
In one embodiment, a NOx sensor may be provided in order to detect a NOx concentration in the exhaust exiting the bank of SCR catalysts 238 through the SCR outlet 242. The location of the NOx sensor within the housing 114 may vary. For example, the NOx sensor may be located on an outer surface of mixing tube 228. Alternatively the NOx sensor may be located upstream of the single bank of SCR catalysts 238 on an inner surface of mixing tube 228.
The NOx sensor may generate a signal indicative of the concentration of NOx present in the exhaust flowing through a given region or area within the housing 114. In one embodiment, the signal may be received by an exhaust or power system controller (not shown). The controller may then responsively adjust parameters of the engine 104 and/or aftertreatment operation, such as, for example, adjusting the amount of the reductant being injected in order to maintain a concentration of NOx below regulated limits.
The exhaust may then pass through the DOC 216. In one embodiment, NO present in the exhaust may be converted to NO2 within the DOC 216. Alternatively or additionally, particulate matter, hydrocarbons, and/or carbon monoxide present in the exhaust may be trapped, converted, and/or reduced within the DOC 216.
In one embodiment, the exhaust may be received by the sound attenuation chamber 218. As the exhaust passes through the plurality of compartments of the sound attenuation chamber 218, sound associated with the flow may reverberate therein and dissipate. As shown by the arrowheads, the exhaust may flow into the trapezoidal shaped compartment 220. In one exemplary embodiment, the exhaust may flow in and out of the triangular shaped compartment 230 provided adjacent to the trapezoidal shaped compartment 220 via the at least one opening 232. In another exemplary embodiment, the exhaust may further flow in and out of the rectangular shaped compartment 224 via the opening (not shown). It should be noted that an extension of the mixing tube 228 into the sound attenuation chamber 218 may enhance the attenuation effects of the sound attenuation chamber 218.
Further, the exhaust may enter into the mixing tube 228. In one embodiment, turbulence of the exhaust flowing through the mixing tube 228 may be promoted by the mixer. Also, the reductant may be injected into the exhaust upstream of the mixer located in the mixing tube 228. As the turbulent flow of the exhaust mixed with the reductant passes along a length of the mixing tube 228, the mixture may continue to homogenize and the reductant may begin to decompose. It should be noted that a bulk of the reductant may be decomposed in this process.
Subsequently, the exhaust may flow out of the mixing tube 228 and collide against the sidewalls 206, 208 of the housing 114. The construction of the housing 114 and more particularly the arrangement of the sidewalls 206, 208 relative to the mixing tube 228 and the single bank of SCR catalysts 238 may cause a reversal in the flow of the exhaust, causing the exhaust to be redirected towards the SCR inlet 240. Moreover, in one embodiment, a decreasing flow area defined between the mixing tube 228, the sidewalls and the bank of SCR catalysts may cause the a uniform distribution of the exhaust entering the SCR inlets 240.
Within the single bank of SCR catalysts 238, the NOx present in the exhaust may be reduced to water and diatomic nitrogen. The exhaust may then flow out of the single bank of the SCR catalysts 238 via the SCR outlet 242. The treated exhaust may then flow towards the outlet 244 and exit the exhaust aftertreatment module 112 therefrom.
Typically in known exhaust systems, the use of a catalytic convertor may cause problems in some situations. In particular, the catalytic convertor may restrict the exhaust flow to some extent and thereby cause an increase in a back pressure of the exhaust. If the exhaust back pressure is too high, breathing ability and subsequent performance of the engine could be negatively impacted. As a general rule, increased back pressure results in lower fuel efficiency, decreased performance and a more limited altitude range for any given engine.
Further, the exhaust systems of many internal combustion engines may also be equipped with noise attenuation devices, such as mufflers. The mufflers are typically located downstream of the catalytic converter to dissipate noise in the exhaust gases. Although these mufflers assist in reduction of noise, the inclusion of these serially located devices often increases the size of the exhaust system.
The present disclosure provides the aftertreatment module 112 having a compactly designed housing 114. The housing 114 may contain the sound attenuation chamber 218 for reduction in noise associated with the exhaust. The sound attenuation chamber 218 may function similar to the known muffler. The incorporation of the sound attenuation chamber within the aftertreatment module 112 to form a single unit may further enhance design compactness. Also, the single bank of SCR catalysts 224 located proximate to the mixing tube 220 may provide an improved flow path for the exhaust, causing uniform redirection of the exhaust flow towards the single bank of SCR catalysts 224. The aftertreatment module 112 may also provide the necessary backpressure required for large engine applications. Additionally, the DOC 216 and/or the bank of SCR catalysts may be replaced as per requirement.
Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to a person skilled in the art that various modifications and variations to the above disclosure may be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
