Patent Application
20140366514
The present disclosure relates generally to exhaust aftertreatment systems. More specifically, the present disclosure relates to a premixer conduit for exhaust aftertreatment system.
Exhaust gases from internal combustion engines may contain substances, such as nitrogen oxides (NOx), particulate matter, and/or the like. Some exhaust gas substances may be unfavorable to the environment. Over the years, efforts have been made within the automotive industry to reduce unfavorable substances present in exhaust gases before the gases are discharged into the atmosphere. This has been accomplished by improvement of the combustion process or/and by treatment of the exhaust gases. One strategy of exhaust treatment of NOx emissions is the use of the selective catalytic reduction (SCR) system. Typically, the SCR system may include an exhaust pipe, a reductant injector, and an SCR catalyst. In SCR systems, a reductant, such as liquid urea, is injected through the reductant injector into the exhaust pipe, where it mixes with an exhaust gas flow. The reductant droplets undergo vaporization and hydrolysis reactions to form ammonia gas. The ammonia is absorbed by the SCR catalyst and reacts with NOx in the exhaust gas flow. The end result of the reaction between ammonia and NOx at the SCR catalyst is water and nitrogen. In general, the reductant injection site may be located at various positions, such as at a pipe elbow or in the center of a straight segment of an exhaust conduit.
Those skilled in the art will appreciate the elements of a successful mixing strategy in which the reductant droplets interact with the exhaust gas flow. In most cases, the strategy may be evaluated based on the uniformity of the ammonia gas distribution at the SCR catalyst combined with minimal or no reductant deposits in a portion of the exhaust conduit upstream from the SCR catalyst. One of the key issues associated with reductant injection, especially in pipe elbow entry configurations, is urea deposit formation. The occurrence of deposit in the flow path may create severe issues related to performance, such as an increase in back pressure, reductions in ammonia distribution uniformity, and even structural damage if a deposit build-up separates from a wall of the mixer and damages a key component. The problem is further complicated by the fact that reductant spray distribution may be dependent upon exhaust conditions, for example, low flow associated with machine idle versus high exhaust flow conditions associated with the engine being operated at a rated condition. The issue faced with reductant injection may include spray distribution variation with different exhaust flow conditions and deposit risk at the injector tip. However, in addition to above mentioned concerns, an additional issue may be the flow conditions caused by the bend in elbow pipes.
U.S. Pat. No. 8,091,341 describes an exhaust passage with a step, beyond which the exhaust passage expands in order to generate swirls in the exhaust gas flow. The purification agent is introduced at the step, or in the vicinity, thus accelerating atomization of the purification agent. However, favorable exhaust gas flow at the injection location depends on inflow condition of the exhaust gas, which may vary over the duration of engine operation. Because of the varying exhaust inflow conditions, an exhaust aftertreatment system that can operate with optimum performance is desired.
In the present disclosure, an exhaust aftertreatment system is disclosed. The exhaust aftertreatment system includes a premixer conduit, a baffle, and a reductant injector. The premixer conduit includes an internal surface that defines an exhaust flow path. The premixer conduit includes a premixer inlet in fluid communication with the engine. The premixer conduit further includes a premixer outlet opposite the premixer inlet, along a flow direction of the exhaust gases. The premixer outlet of the premixer conduit is in fluid communication with a selective catalytic reduction (SCR) catalyst. Further, the exhaust aftertreatment system includes the baffle in the exhaust flow path. Between the baffle and the internal surface of the premixer conduit, an annular flow path is defined. The reductant injector is disposed in the premixer conduit, downstream from the baffle and upstream from the premixer outlet, along a flow direction of the exhaust gases. The reductant injector is in fluid communication with the exhaust flow path and a reductant source. The baffle has an upstream radial dimension and a downstream radial dimension, each defined transverse to a respective local flow direction of the exhaust gases. The upstream radial dimension is smaller than the downstream radial dimension. A ratio of a radial dimension of the exhaust flow path at the premixer inlet and a radial dimension of the exhaust flow path at the premixer outlet of the premixer conduit may not attain a value less than 0.5 or greater than 1.0.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Referring to
The exhaust aftertreatment system 102 may include a first exhaust conduit 104, a diesel particulate filter 106, a second exhaust conduit 108, a premixer conduit 110, a reductant supply system 112, a third exhaust conduit 114, and a catalytic chamber 116. The first exhaust conduit 104 defines an exhaust flow path and is disposed along a flow direction 118 (shown by arrow) of the exhaust gases. The first exhaust conduit 104 includes a first inlet 120 and a first outlet 122. The first inlet 120 of the first exhaust conduit 104 is in fluid communication with the cylinder, such that, the exhaust gases that exit the cylinders are directed into the first exhaust conduit 104. The first outlet 122 is in fluid communication with the diesel particulate filter 106. The diesel particulate filter 106 is positioned downstream of the first exhaust conduit 104.
The premixer conduit 110 is positioned downstream of the diesel particulate filter 106. The premixer conduit 110 is in fluid communication with the diesel particulate filter 106, via the second exhaust conduit 108. The premixer conduit 110 is positioned upstream of the catalytic chamber 116 and is in fluid communication with the catalytic chamber 116. The catalytic chamber 116 houses an SCR catalyst 124, via the third exhaust conduit 114. The premixer conduit 110 is connected to the reductant supply system 112. The reductant supply system 112 includes a reductant source 126, which is fluidly connected to a reductant injector 128, via a supply line 130. The reductant injector 128 is provided for injection into the premixer conduit 110.
Referring to
The transition section 206 connects the first inlet section 202, the second inlet section 204, and to the outlet section 210. In other words, the transition section 206 is disposed between the first inlet section 202 and the outlet section 210. Similarly, the transition section 206 is disposed between the second inlet section 204 and the outlet section 210. The transition section 206 has an upstream radial dimension (D2) and a downstream radial dimension (D3). The transition section 206 is a frustoconical surface which extends from the upstream radial dimension (D2) to the downstream radial dimension (D3). In an embodiment, the transition section 206 is nozzle cone type. Those skilled in the art will understand that the upstream radial dimension (D2) is larger than the downstream radial dimension (D3).
The outlet section 210 is positioned downstream of the transition section 206. At an end of the outlet section 210, there is provided the premixer outlet 212, which allows navigation of the exhaust gases to the third exhaust conduit 114. The outlet section 210 includes the reductant injector 128 attached on a wall of the outlet section 210. The reductant injector 128 is in fluid communication with the exhaust flow path. The reductant injector 128 has a longitudinal axis (X-X), which is substantially perpendicular to the flow direction 118 of the exhaust gases.
The baffle 208 is positioned in the premixer conduit 110 along the exhaust flow path. The baffle 208 includes an upstream face 216 with an upstream radial dimension and a downstream face 218 with a downstream radial dimension. Each of the upstream radial dimension and the downstream radial dimension is transverse to a respective local flow direction 118 of the exhaust gases. The upstream radial dimension of the baffle 208 is smaller than a downstream radial dimension of the baffle 208. In an embodiment, the baffle 208 is positioned in the outlet section 210, immediately downstream from the transition section 206.
Referring to
The outlet section 210 is positioned downstream of the transition section 206 and is in fluid communication with the premixer outlet 212. The outlet section 210 has a radial dimension (D4). The outlet section 210 includes the reductant injector 128, which is in fluid communication with the exhaust flow path. The outlet section 210 includes the baffle 208 positioned along the exhaust flow path and at a position which is immediate downstream of the transition section 206.
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For each of the first configuration, the second configuration, the third configuration, the fourth configuration, and the fifth configuration, at least one of the first inlet section 202 and the second inlet section 204 has the radial dimension (D1). Thus, a ratio of the radial dimension (D1) of the first inlet section 202 and the radial dimension (D4) of the outlet section 210 is between a range of 0.5-1.0. At least one of the first inlet section 202 and the second inlet section 204 is connected to the transition section 206 having a linear dimension (L1), the upstream radial dimension (D3), and the downstream radial dimension (D3). A ratio of the linear dimension (L1) of to the transition section 206 to the radial dimension (D4) of the outlet section 210 is between a range of 0.27-1.0.
The premixer conduit 110 includes the baffle 208. The baffle 208, along with the internal surface 214 of the premixer conduit 110, defines an annular flow path for the exhaust gases. The baffle 208 is positioned upstream of the reductant injector 128, with an injector plane along the longitudinal axis (X-X). At the injector plane, the ratio between flow area of the annular flow path and the flow area of the exhaust flow path is between the range 0.3-1.0. The reductant injector 128 is positioned at a first distance (D5) from the downstream face 218 of the baffle 208. The ratio of the first distance (D5) to the downstream radial dimension (D3) of the transition section 206 is between a range of 0.2-0.7.
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Similarly, the inner conical ring 706 has an inner ring cone angle (θ2) within a range of 15-45 degrees. The inner conical ring 706 has an inner radial dimension (R2) and an inner length (L3). A ratio of the inner radial dimension (R2) to the radial dimension (D4) of the outlet section 210 is within a range of 0.08-0.15. Further, a ratio of the inner length (L3) to the radial dimension (D4) of the outlet section 210 is within a range of 0.02-0.18.
In operation, the cylinders located in the engine 100 receive a combination of air and fuel. The air/fuel mixture is combusted in the plurality of cylinders. The combustion of the air/fuel mixture produces exhaust gases in the cylinder. The exhaust gases from the engine 100 may contain substances, such as nitrogen oxides (NOx), particulate matter, and/or the like. Some exhaust gas substances are unfavorable to the environment. The exhaust gases are directed from the cylinder into the exhaust aftertreatment system 102. The exhaust aftertreatment system 102 may be operated by movement of the exhaust gases from an engine end towards a tailpipe end. The exhaust gases that enter the first exhaust conduit 104, flow to the diesel particulate filter 106. The diesel particulate filter 106 removes diesel particulate matter or soot from the exhaust gases. The exhaust gases are then directed to the premixer conduit 110, via the second exhaust conduit 108. In the premixer conduit 110, the exhaust gases that enter through the premixer inlet 200 are premixed with the reductant injected by the reductant injector 128. Further, the exhaust gases, are directed to pass through the baffle 208. As the exhaust gases pass through the baffle 208, the exhaust gases are diffused and evenly spread, thereby altering the flow of exhaust gases, downstream to the baffle 208. The altered flow of the exhaust gases is directed towards the reductant injector 128. The reductant may be urea, ammonia, diesel fuel, or some other hydrocarbon. The uniform flow of exhaust gases reacts with the reductant, to remove NOx emissions from the exhaust gases. The exhaust gases are then directed to the catalytic chamber 116, via the third exhaust conduit 114. The catalytic chamber 116 facilitates continuous passage of the exhaust gases across the catalytic chamber 116. The SCR catalyst 124 in the catalytic chamber 116 reduces the NOx emissions in the exhaust gases. Reduction of the NOx gasses occurs by conversion of the NOx emissions into diatomic nitrogen (N2) and water (H2O).
The disclosed premixer conduit 110 facilitates a uniform and even flow of the exhaust gases to premix with the reductant, prior to flow of the exhaust gases to the catalytic chamber 116. Hence, the arrangement of the components in the premixer conduit 110 controls the flow conditions of the exhaust gases that enter the premixer conduit 110 via the first inlet section 202 and the second inlet section 204. The objective achieved by the disclosed premixer conduit 110 arrangements is production of a desirable and favorable flow condition of the exhaust gases inside of the outlet section 210. The created flow conditions aid in the avoidance of deposit formation caused by uneven flow and varying backpressure.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
