GB2621882A - End can for an exhaust aftertreatment assembly with RF antennas - Google Patents

Abstract

An inlet end can 10 has a side wall 12 extending along an exhaust gas flowpath (F, fig 3) from an end wall 11. An inlet pipe 40 extends through an inlet aperture in the side wall. A baffle 20 includes a perforated centre plate 21 spaced apart from the end wall to define an exhaust gas receiving space (30, fig 3). The inlet pipe terminates inside the can at an open end 41 to direct exhaust gas across the flowpath into the receiving space. The open end is spaced apart from the baffle in the direction of an inlet pipe axis (Xi, fig 3) by a separation distance (Ds, fig 3). An antenna mount 50 supports a radio frequency (RF) antenna 51 that extends into the flowpath. An exhaust gas aftertreatment system (101, fig 8) includes the first end can, a treatment body (81, fig 8) and a second end can (90, fig 8) with a second RF antenna (53, fig 8) and a signal apparatus (102, fig 8) that transmits a radio frequency signal between the antennas and analyses the signal to determine particulate loading of the treatment body.

Description

End can for an exhaust aftertreatment assembly with RF antennas

Technical Field

[0001] This disclosure relates to exhaust gas aftertreatment assemblies equipped with RF antennas for monitoring the buildup of particulates in the filter or other exhaust gas treatment body, and particularly to the end can that closes the inlet end of the assembly.

Background

[0002] Exhaust gas aftertreatment assemblies include a filter or other treatment body through which the exhaust gas passes. The treatment body is arranged in a housing, referred to as the can, which directs the exhaust gas through the treatment body. The can is closed at each end by assemblies referred to as end cans, which generally include inlet and outlet pipes for connecting the can to the exhaust system of an internal combustion engine.

[0003] For efficient operation it is desirable for the exhaust gas flow to be as uniform as possible across the upstream face of the treatment body (and so, across the section area of the exhaust gas flowpath). Flow uniformity can be quantified using a standard algorithm as known in the art, yielding a uniformity index in which a value of I indicates a perfectly uniform velocity distribution. A uniformity index of 0.85 may be considered acceptable, and 0.9 is good.

[0004] Flow uniformity is usually achieved by distributing the exhaust gas through a structure having multiple openings into the exhaust gas flowpath. Such structure may be formed by the inlet pipe which extends into the can with a plurality of small perforations or larger openings through which the exhaust gas flows into the can; or, as a baffle, e.g. a perforated plate that receives and distributes the flow emanating from the exhaust inlet pipe; or as a combination of these.

[0005] It is also important that the connection between each of the inlet and outlet pipes and the body of the respective end can is adequate to react the mechanical forces that will be applied to the pipes in use.

100061 For this purpose, the inlet pipe may be arranged to extend through the tubular sidewall of the can, across the diameter of the can to the tubular sidewall on the opposite side of the can, or to a baffle plate on the opposite side of the can, so that it is supported at each end by these structures. It is also known to integrate the inlet pipe into the end wall of the can for extra support.

[0007] In use, the treatment body will accumulate particulates such as soot and ash. In order to maintain the efficiency of the engine, the treatment body may be regenerated periodically (e.g. by increasing its operating temperature) to clean it of particulates.

[0008] For maximum efficiency it is desirable to trigger the regeneration process responsive to determining that the particulate loading in the treatment body has reached a predefined limit. For this purpose it is known to determine the particulate loading by analysing a radio frequency (RF) signal transmitted between two antennas, which are arranged in spaced relation so that the signal passes through the treatment body between them. The amount and nature of particulate loading can be determined based on its known effect on the signal, for example, by determining the degree of attenuation of the received signal.

[0009] For example, W02007018658 (Al) teaches to distinguish between soot and ash accumulation based on the phase shift and attenuation of the received signal. This helps in managing the regeneration cycle to avoid generating excessive temperatures by decomposition of the accumulated soot.

[0010] It is convenient to mount the antennas in the end cans so that they are spaced apart along the exhaust gas flowpath, respectively upstream and downstream of the treatment body.

100111 W02012088016 (Al) teaches various computational algorithms for analysing the sensed signal data to compensate for the effects of temperature and resonant frequencies of the filter.

[0012] Even with the use of such algorithms, the antennas must be carefully positioned to obtain effective transmission of the signal.

100131 In use, the can will be mounted to the engine or other supporting structure, usually in a cradle that holds the can firmly and closely adjacent the supporting structure to suppress damaging vibrations. The available space for the internal combustion engine and its associated exhaust system is typically highly constrained, with multiple components located close together in the engine bay. The congested environment and the mounting arrangement for the can assembly dictate a limited number of possible locations for the antenna mounts, which in turn are constrained by the space required by the antenna.

[0014] In particular, it may be difficult to locate the antenna mount generally perpendicular to the inlet pipe (when considered in terms of its angular position about the flowpath axis), because the inlet pipe will generally be oriented close to the supporting structure. So, the generally perpendicular positions will extend respectively, outwardly away from the supporting structure (thus interfering with adjacent components in the engine bay) or towards the cradle and the supporting structure (where no space is available.) [0015] It can be difficult to reconcile all these competing design constraints.

Summary of the Disclosure

[0016] In accordance with the present disclosure there is provided a first end can for use in an exhaust aftertreatment can assembly.

[0017] The assembly defines an exhaust gas tlowpath and a flowpath axis extending centrally along the exhaust gas flowpath.

[0018] The first end can includes: a first end wall closing a first axial end of the exhaust gas flowpath; a first side wall extending from the first end wall along the exhaust gas flowpath; a baffle; an inlet pipe; and a first antenna mount.

[0019] The baffle includes a perforated centre plate which has a free edge spaced apart from the first end wall. The centre plate extends into the exhaust gas flowpath from the first side wall to its free edge. An exhaust gas receiving space is defined between the centre plate and the first end wall.

100201 The inlet pipe extends through an inlet aperture in the first side wall and terminates within the exhaust gas flowpath at an open end of the inlet pipe, and defines an inlet pipe axis which extends centrally through the inlet pipe at the open end. The inlet pipe is configured, in use, to discharge exhaust gas from the open end, along the inlet pipe axis, into the exhaust gas receiving space.

[0021] The first antenna mount defines a first antenna position and is configured, in use, to support a first radio frequency antenna to extend into the exhaust gas flowpath in the first antenna position.

[0022] When projected along the flowpath axis, the baffle and the open end of the inlet pipe are spaced apart by a separation distance Ds along the inlet pipe axis.

[0023] The first end can may be incorporated into an exhaust gas treatment apparatus which further includes: a first radio frequency antenna, a mid-portion, a treatment body, a second end can assembly, and a signal apparatus.

[0024] The first radio frequency antenna extends into the exhaust gas flowpath in the first antenna position. The mid-portion is arranged downstream of the first end can, and the treatment body is arranged in the mid-portion to extend across the exhaust gas flowpath.

[0025] The second end can assembly is arranged downstream of the mid-portion to close a second axial end of the exhaust gas flowpath, and includes: an outlet pipe for conducting the exhaust gas, in use, out of the exhaust gas flowpath; a second radio frequency antenna; and a second antenna mount which supports the second radio frequency antenna to extend into the exhaust gas flowpath in a second antenna position.

100261 The signal apparatus is arranged to transmit a radio frequency signal between the first and second antennas, and to analyse the signal to determine particulate loading of the treatment body.

[0027] In another aspect, the disclosure provides a method of treating exhaust gas, including: providing the exhaust gas treatment apparatus; transmitting the radio frequency signal between the first and second antennas and analysing the signal to determine particulate loading of the treatment body.

Brief Description of the Drawings

[0028] Further features and advantages will be appreciated from the illustrative embodiment which will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which: [0029] Fig. I is an axial end view of a first end can, seen from inside.

[0030] Fig. 2 is the same view as Fig. 1, illustrating some geometric parameters.

[0031] Fig. 3 is a longitudinal section at III -III of Fig. 1.

[0032] Fig. 4 is an outside view of the first end can.

[0033] Fig. 5 is another inside view of the first end can.

[0034] Fig. 6 is an outside view of the first end wall and first side wall forming the body of the first end can, before assembly of the other components.

[0035] Fig. 7 is an exploded view of the first end can.

[0036] Fig. 8 shows an exhaust gas treatment apparatus including the first end can.

[0037] Figs. 9 and 10 show the pattern of exhaust gas flow inside the can assembly of Fig. 8 generated by a CFD model.

[0038] Fig. 11 shows the exhaust gas flow velocity distribution over the upstream face of the treatment body inside the can assembly of Fig. 8 generated by a CFD model.

100391 Fig. 12 shows the signal attenuation obtained in tests of the can assembly of Fig. 8 with different levels of particulate contamination in the treatment body.

[0040] Fig. 13 shows the signal attenuation obtained when the tests were

repeated using a prior art end can.

100411 Reference numerals and characters appearing in more than one of the figures indicate the same or corresponding elements in each of them.

Detailed Description

[0042] Referring to Fig. 8, an exhaust gas aftertreatment apparatus 101 includes an exhaust gas can assembly 100, which defines a flowpath axis Xf extending centrally along an exhaust gas flowpath F, and a signal apparatus 102.

[0043] The can assembly 100 includes a first end can 10 having an inlet pipe for receiving a flow of exhaust gas (typically from an internal combustion engine); a second end can assembly 90 having an outlet pipe 91; and a mid-portion 80 arranged between the two end cans, downstream of the first end can 10 in the flow direction.

[0044] The mid-portion 80 may be cylindrical, and is generally referred to as a can. It contains a treatment body 81 which extends across the exhaust gas flowpath F, so that exhaust gas flowing into the inlet pipe 40 flows through the treatment body 81 along the exhaust gas tlowpath F, and then is conducted out of the exhaust gas flowpath via the outlet pipe 91, which is arranged downstream of the mid-portion 80 to close the second axial end of the exhaust gas flowpath F. [0045] The first and second end cans may be assembled, e.g. by welding from steel components, and then assembled together with the can 80 after sealingly installing the treatment body 81 inside the can 80, as well known in the art.

[0046] The treatment body 81 may include a block or an assembly of blocks, which are gas permeable and typically ceramic, and extends across the exhaust gas flowpath F so that all of the exhaust gas G flows through the treatment body. The treatment body 81 may be a particulate filter, for example, a diesel particulate filter (DPF) for removing particulates from the exhaust gas produced by a diesel engine. Alternatively or additionally, the treatment body 81 may include a catalyst for transforming combustion products of the engine.

[0047] The second end can assembly 90 may be generally of a similar configuration to the first end can 10, as further described below, except that a baffle may not be present. It has a second end wall 92 and a second side wall 93 extending from the second end wall 92 along the exhaust gas flowpath F. The outlet pipe 91 may extend through an outlet aperture 94 in the second side wall 93 in a similar arrangement to the inlet pipe 40 as further described below.

[0048] In use, the exhaust gas flows in through the inlet pipe 40 and then flows along the exhaust gas flowpath F and through the treatment body 81, before flowing out through the outlet pipe 91.

[0049] The first end can 10 includes a first antenna mount 50 which defines a first antenna position Al. The first antenna mount 50 is configured to support a first radio frequency antenna 51 to extend into the exhaust gas flowpath F in the first antenna position Al.

100501 The second end can assembly 90 includes a second radio frequency antenna 53 and a second antenna mount 52, which supports the second radio frequency antenna 53 to extend into the exhaust gas flowpath in a second antenna position A2, so that the signal is transmitted through the treatment body 81 between the antennas.

[0051] The first and second antennas 51, 53 may be monopole antennas, and may be arranged to transmit the radio frequency signal in a range, for example, of about 2.05 -2.25 GI-1z, as known in the art.

100521 As shown, the first and second antennas may be aligned at the same angular position about the flowpath axis Xf, which is defined as the angle al as further discussed below.

[0053] In a method of use, the signal apparatus 102 is arranged to transmit a radio frequency signal between the first and second antennas 51, 53, and to analyse the signal (for example, to measure the attenuation of the signal), as known in the art, to determine particulate loading of the treatment body 81 through which the signal passes.

[0054] It will be understood that as referred to herein, the signal may be merely a transmission of radio frequency energy, whether carrying any additional signal information or not; and analysing the signal, means comparing the received signal with the transmitted signal to determine how the signal has changed during transmission, e.g., by measuring attenuation of the signal or other signal characteristics.

[0055] The analysis may determine the degree of particulate buildup in the treatment body 81 based on the change in the signal (e.g. the measured signal attenuation) and on stored information, e.g. from a look-up table or embodied in an algorithm, that provides a known correlation between the range of measured signal characteristics and the levels of particulate contamination that correspond thereto [0056] By way of example, the values shown in Fig. 12 could be used to determine the degree of particulate buildup based on the measured signal attenuation at a given frequency if the signal is transmitted at that frequency, or over a given frequency range if the signal frequency varies through that range during transmission [0057] The degree of particulate buildup calculated by the signal apparatus 102 may be used to trigger regeneration of the treatment body 81, e.g. when the measured signal attenuation value or other signal characteristic reaches a threshold value.

[0058] Referring now to Figs. 1 -7, the first end can 10 includes a first end wall 11 closing a first axial end of the exhaust gas flow-path F, and a first side wall 12 extending from the first end wall 11 along the exhaust gas flowpath F. The first end wall and first side wall may be formed integrally, e.g by pressing from steel sheet, or may be assembled together, e.g. by welding.

[0059] As illustrated, the first end wall 11 may include an obtusely angled region 70, in which an internal surface 12' of the first side wall 12 defines an obtuse angle a2 with an adjacent internal surface 14' of an outer portion 14 of the first end wall 11, when considered in a plane Ph parallel with the flowpath axis Xf.

[0060] The first end wall may also define a pair of inner portions 15, and a channel 16 extending, as shown, between the inner portions 15, from the open end 41 of the inlet pipe 40 in a direction of the inlet pipe axis Xi. (It will be understood that the inner and outer portions 15, 14 are so described with respect to their position relative to the flowpath axis Xi) [0061] When considered in the plane Ph parallel with the flowpath axis Xf, an internal surface 15' of each of the inner portions 15 of the first end wall 11 may define an obtuse angle a3 with an adjacent, internal surface 14 of the outer portion 14 of the first end wall 11. (It will be understood that surfaces 14', 15' are internal in the sense that they are internal to the end can 10) [0062] As illustrated, the obtusely angled region 70 may extend through more than 180° around the flowpath axis Xf-which is to say, the obtuse angle a2 may be identified anywhere in that angular range, which as illustrated, may extend most of the way around the circumference of the end can 10 from one side of the inlet pipe 40 to the other.

[0063] The obtusely angled portions of the first end wall help to direct the RF radiation from the antennas along the flowpath through the treatment body 81 [0064] The first end can 10 also includes a baffle 20, which may be made from steel plate, and as illustrated, may have bent tabs around its periphery at which it may be welded to the side wall 12 and/or the end wall 11 during assembly.

[0065] The baffle 20 includes a perforated centre plate 21 which has a free edge 22 spaced apart from the first end wall 11. The centre plate 21 extends into the exhaust gas flowpath F from the first side wall 12 to its free edge 22, defining an exhaust gas receiving space 30 between the centre plate 21 and the first end wall 11.

100661 As illustrated, the centre plate 21 may be arranged generally perpendicular to the flowpath axis Xf, and so in parallel with the general orientation of the first end wall 11.

[0067] The inlet pipe 40 extends through an inlet aperture 13 in the first side wall 12 and terminates at an open end 41 within the exhaust gas flowpath F. A tongue 42 may extend from the open end 41 to form a part of the first end wall 11, as illustrated. In the illustrated arrangement, the inlet aperture 13 extends into the first end wall 11 to accommodate the depth of the tongue 42 (corresponding to the depth De of the channel 16) along the flowpath axis Xf. The tongue 42 is formed integrally with the inlet pipe 40 and welded to another part of the first end wall 11 (e.g. inner portions 15, as shown) to provide a strong connection between the inlet pipe 40 and the rest of the structure.

[0068] The inlet pipe 40 defines an inlet pipe axis Xi extending centrally through the inlet pipe 40 at its open end 41.

[0069] The inlet pipe 40 is configured to discharge exhaust gas G, from the open end 41, along the inlet pipe axis Xi, into the exhaust gas receiving space 30.

[0070] When considered as if projected along the flowpath axis Xf, the baffle and the open end 41 of the inlet pipe 40 are spaced apart by a separation distance Ds along the inlet pipe axis Xi. That is to say, the separation distance Ds can be observed when considering the first end can in axial end view, as shown in Fig. 1, even though the inlet path axis Xi is offset from the baffle 20 in the direction of the flowpath axis.

[0071] As illustrated, the inlet path axis Xi extends (or may be extended) from the open end 41, past the perforated centre plate 21 and through the exhaust gas receiving aperture 31 (further discussed below) into the exhaust gas receiving space 30, so that the stream of exhaust gas G flows out of the open end of the inlet pipe along that trajectory.

[0072] Preferably, as illustrated, when projected along the flowpath axis Xf, the baffle 20 and the open end 41 of the inlet pipe 40 are spaced apart on opposite sides of the flowpath axis Xf.

100731 The open space between the open end 41 and the free edge 22 of the baffle 20 thus extends for the distance Ds generally in the middle region of the end can, providing a large clear area in which the signal can travel without interference.

[0074] When considered in a transverse plane Pt perpendicular to the flowpath axis Xf, the first end can 10 has a mean internal transverse dimension D defined by a straight line passing through the flowpath axis Xf and bounded by opposite internal surfaces of the first side wall 12.

[0075] As illustrated, the first side wall 12 may be substantially cylindrical so that its internal diameter corresponds to the mean transverse dimension D. [0076] Preferably, Ds > 0.5 D. More preferably, Ds > 0.55 D. In the example illustrated, Ds = 0.58 D. That is to say, the clear space between the baffle 20 and the open end 41 of the inlet pipe 40 may extend at least halfway, and preferably more than halfway, across the internal diameter of the end can.

[0077] Preferably, the baffle 20 includes a pair of perforated shoulder plates 23 which extend axially with respect to the flowpath axis Xf, along the first side wall 12 between the centre plate 21 and the first end wall 11, respectively on opposite sides of a longitudinal centre plane Plc containing the flowpath axis Xf.

[0078] Each shoulder plate 23 has an outer edge 24 proximate the first side wall 12, and an inner, free edge 25 spaced apart from the first side wall 12.

[0079] Each shoulder plate 23 extends into the exhaust gas flowpath F from its outer edge 24 to its free edge 25, so that an exhaust gas receiving aperture 31 is defined between the first end wall 11, the free edge 22 of the centre plate 21, and the free edges 25 of the shoulder plates 23.

[0080] The exhaust gas receiving space 30 opens through the exhaust gas receiving aperture 31, which is arranged to receive the stream of exhaust gas G discharged from the open end 41 of the inlet pipe 40.

[0081] Preferably, the exhaust gas receiving aperture 31 extends over a relatively large part of the distance between the outer edges 24 of the shoulder plates 23, so that the RF signal can reflect out of the exhaust gas receiving space 30 and along the flowpath F with relatively little interference from the baffle.

[0082] As illustrated in Fig. 2, this dimensional parameter can be defined when the shoulder plates 23 are considered in a transverse plane Pt (Fig. 3) perpendicular to the flowpath axis Xf. (As shown in Fig. 2, the transverse plane Pt is the plane of the drawing.) 100831 The outer edges 24 of the shoulder plates 23 are spaced apart in the transverse plane Pt by a distance Dso, while the inner, free edges 25 of the shoulder plates 23 are spaced apart in the transverse plane Pt by a distance Dsi.

[0084] Preferably, Dsi > 0.65 Dso. More preferably, Dsi? 0.7 Dso. Most preferably, Dsi > 0.75 Dso. In the example illustrated, Dsi = 0.77 Dso.

[0085] That is to say, the exhaust gas receiving aperture 31 may be substantially more than half, preferably three quarters or more, of the overall distance across the can between the outer edges 24 of the shoulder plates 23.

[0086] The signal reflection may be assisted by forming the end wall 11 with a portion 17, which forms a wall of the exhaust gas receiving space 30 and is inclined towards and along the flowpath axis Xf. This may help to reflect the signal out of the exhaust gas receiving space 30 via the exhaust gas receiving aperture 31. As illustrated, the inclined portion 17 may form part of the obtusely angled region 70.

[0087] Preferably, as shown, the inlet pipe axis Xi lies in the longitudinal centre plane Plc and intersects the flowpath axis Xf. (That is to say, if extended, it would intersect.) Further preferably, as illustrated, the baffle 20 is mirror-symmetric about the longitudinal centre plane Plc.

[0088] Where the first side wall 12 is generally cylindrical, as shown, this provides a symmetric flow pattern in which the inflowing stream of exhaust gas G emanating from the open end 41 of the inlet pipe 40 is turned and divided by the diametrically opposite internal surface of the first side wall 12 to form two return flows which follow the side wall 12 and then are diffused through the perforations in the shoulder plates 23. Despite the abrupt termination of the inlet pipe 40 close to the side wall 12, this arrangement results in a remarkably even velocity distribution, as illustrated in Figs. 9 -11 and further discussed below.

[0089] Preferably, in order to further strengthen the connection between the inlet pipe 40 and the rest of the end can structure, a support plate 60 is fixed to at least one of the first end wall 11 and the first side wall 12, and fixed to the inlet pipe 40 at a location proximate the open end 41 and spaced apart from the inlet aperture 13.

[0090] The short, inwardly projecting portion of the inlet pipe helps to guide the flow which is projected across the open central portion of the exhaust gas flowpath F, into the exhaust gas receiving space 30. By also providing a support plate 60 proximate the open end 41 and in spaced relation to the first side wall 12, this short inward projection of the inlet pipe 40 also helps provide a strong moment connection between the inlet pipe 40 and the end and side walls 11, 12, so as to react applied forces without addition external supporting elements that would make the assembly more bulky.

[0091] Referring now to Fig. 2, when considered about the flowpath axis Xf, the first antenna position Al at the first side wall 12 is spaced apart by an angle al from the inlet pipe axis Xi at the first side wall 12. That is to say, the angle al can be observed when considered in axial end view, as shown in Fig. 2, and irrespective of the offset (if any) between the respective components in the direction of the flowpath axis Xf [0092] As previously discussed, it is often impractical to mount the antenna in a position that is generally perpendicular to the inlet pipe 40. However, in prior art arrangements with a perforated inlet pipe extending across the diameter of the end can, a position angularly close to the inlet pipe 40 is found to provide poor signal transmission due to reflection from the inlet pipe.

[0093] The novel assembly is found to provide good signal transmission when the first antenna is mounted angularly, substantially closer to the inlet pipe 40.

100941 Optionally therefore, as illustrated in Fig. 2, the first antenna position Al may be arranged such that al < 75°, or al < 65°, or even such that al < 55°.

[0095] In the example illustrated and tested to provide the signal attenuation readings presented in Fig. 12 and further discussed below, al = 54.35°.

Industrial Applicability

100961 An exhaust aftertreatment can assembly including the novel first end can may be used in the exhaust aftertreatment system of diesel engines and other internal combustion engines where it is required to monitor the buildup of particulates, e.g. soot, in the treatment body. The treatment body 81 may be for example a diesel particulate filter (DPF) for removing soot and other particulates in diesel exhaust, or any other block or assembly of blocks for filtering or otherwise treating exhaust gas flowing through the block.

[0097] In tests, it has been found that where conventional, perforated inlet pipe or inlet pipe and baffle structures extend all the way across the exhaust gas flowpath, these structures can cause undesirable reflection and resonance in the RE signal, particularly when the antenna position is located close to the inlet pipe (when considered about the flowpath axis).

[0098] By arranging the baffle 20 in spaced relation to the open end 41 of the inlet pipe 40 so that the exhaust gas flowpath F is generally unobstructed between these structures, it is found that the effect of these structures on the transmitted signal is substantially reduced, even when the first antenna position Al is angularly close to the inlet pipe axis Xi at the inlet aperture 13. This in turn makes it possible to locate the first antenna 51 close to the inlet pipe 40, which is more convenient since even in a congested engine layout there will usually be some space available adjacent the exhaust gas inlet pipework, which can accommodate the external portion of the antenna assembly. By increasing the separation distance Ds between the baffle 20 and the open end 41 of the inlet pipe 40, the signal interference is further reduced.

[0099] By way of example, Fig. 13 shows RF signal attenuation values obtained in tests on an exhaust gas treatment apparatus configured in the same way as the apparatus 101 of Fig. 8, but having a first end can of a conventional design, with a perforated inlet pipe extending across the diameter of the first end can. The perforations in the inlet pipe were round and numerous, similar in appearance to the central group of perforations that can be seen in the centre plate 21 of the novel apparatus. The first and second antennas 51, 53 were monopole antennas, similar to the antenna 51 as illustrated. The first antenna position Al defined an angle al = 54.35°, and the second antenna was at the same angular position when considered in the same direction of the flowpath axis XI', as shown in Fig. 8.

[00100] Each line on the graph shows the signal attenuation in dB (on the Y-axis) over the frequency range from 2.050 GHz to 2.250 GHz (on the X-axis), as obtained from a single test with a defined amount of soot in the treatment body. The tests were repeated with increasing amounts of soot, so that from top to bottom of the graph, the different lines represent progressively increasing amounts of soot in the treatment body 81.

[00101] It can be seen that the, at higher levels of soot loading, the variation in attenuation of the signal transmitted between the first and second antennas as a function of frequency departs markedly from that measured at lower levels of soot loading, so that the trace lines on the graph cross one another. This is believed to result from disruption of the RF field at the first antenna by the internal structure of the first end can, and makes it difficult to interpret the signal so at to obtain a reliable indication of the level of soot loading in the treatment body.

[00102] In an attempt to address this problem, the prior art inlet pipe was adapted so that, instead of numerous, round perforations, relatively few, larger, rectangular windows were formed in the cylindrical wall of the inlet pipe inside the end can, so that it resembled a rectilinear framework rather than a perforated cylinder. However, the signal interference was still observed.

[00103] Fig. 12 shows the corresponding signal attenuation values obtained in similar tests carried out on the novel apparatus 101 as illustrated in Fig. 8 including the first end can 10 as illustrated, using the same monopole antennas in the same positions @I = 54.35°) with the same signal frequency range from 2.050 GHz to 2.250 GHz. As discussed above, the dimensional relationships were: Ds = 0.58 D, and Dsi = 0.77 Dso.

1001041 Again, from top to bottom of the graph, the different lines represent progressively increasing levels of soot in the treatment body 81, corresponding to the levels used in the tests of Fig. 13.

1001051 It can be seen that the anomalous values obtained from the prior art apparatus as shown in Fig. 13 were no longer observed. Instead, attenuation was found to vary predictably as a function of frequency throughout the range of soot loading (from clean to very dirty), so that the individual lines obtained at different soot levels no longer cross one another; thus, it is possible to use the measured signal attenuation as a simple and reliable analogue of the level of soot loading in the treatment body 81.

1001061 Despite the separation between the baffle 20 and the open end 41 of the inlet pipe 40, it is found that a reasonably uniform flow can be obtained over the section area of the exhaust gas flowpath F by arranging the inlet pipe 40 to project the stream of exhaust gas G across the flowpath F into the exhaust gas receiving space 30, so that the kinetic energy of the exhaust gas G causes it to flow out through the perforations in the baffle 20.

[00107] In particular, by arranging for the flow to impinge on a surface (which, as illustrated, may be the internal surface of the first side wall 12 opposite the open end 41 of the inlet pipe 40 along the inlet pipe axis Xi) that causes it to turn and divide into two return streams which flow along the side wall and through further perforations in spaced shoulder plates 23 of the baffle 20, the remaining kinetic energy in the bifurcated stream can be dissipated to obtain a uniformity index up to 0.9 or even more over the section area of the exhaust gas flowpath F. 1001081 Figs. 9 and 10 show the flow velocity distribution obtained throughout the flowpath F in computational fluid dynamics (CFD) modelling carried out on the apparatus 101 as illustrated in Fig. 8 assuming typical use conditions, but without the treatment body 81. Fig. 11 was obtained by similar CFD modelling of the same apparatus including the treatment body 81, showing the flow velocity distribution over the upstream end face of the treatment body 81.

1001091 To assist in interpreting the indicated values in these figures (which were converted from colour to greyscale,) spot values from the velocity scale are indicated in square brackets (to distinguish from the reference numerals which don't have brackets.) 1001101 Figs. 9 and 10 show that the inlet and outlet pipes both carry a flow of about 90-100 m/s, which transitions to a lower velocity in the end cans 10, 90. The flow through the entire length of the mid-portion 80 has a velocity of about 7-9 m/s throughout the whole cross-sectional area of the flowpath F. [00111] The arrows superimposed on the flow lines in Fig. 10 show how the incoming flow of exhaust gas G is arranged to impinge on the cylindrical internal surface of the first side wall 12 so that it divides into two streams which turn back and flow along the inner surface of the first side wall 12 and then issue upwardly through the perforations in the shoulder plates 23, which are equally spaced on either side of the centre plane Plc containing the inlet pipe axis Xi.

1001121 This arrangement allows the shoulder plates 23 to be relatively narrow, and the exhaust gas receiving aperture 31 to be relatively wide; which is to say, the dimension Dsi occupies a relatively large proportion of the dimension Dso. This helps reduce signal interference caused by reflections within the exhaust gas receiving space 30.

1001131 Fig. 11 shows that the flow velocity distribution over the upstream face of the treatment body 81 is generally even, from about 8 -14 m/s over most of the block, with localised regions of slightly higher velocity (around 17 m/s), and two small regions of low velocity flow. Very small regions of high velocity flow are present near the bottom of the block (in the region of the baffle plate).

1001141 This velocity distribution was quantified based on a standard algorithm to provide a uniformity index of 0.886 (where 1 indicates a perfectly uniform distribution); this is a relatively high value and indicates a satisfactory flow regime.

1001151 Despite the separation between the inlet pipe 40 and the baffle 20, it is found that an adequately strong moment connection that reacts forces applied to the inlet pipe 40 against the rest of the structure of the first end can 10 can be obtained, even when the inwardly projecting portion of the inlet pipe 40 is relatively short so that the separation distance Ds is relatively large. For this purpose it is particularly effective to fix a support plate 60 to at least one of the first end wall 11 and the first side wall 12, and to the inlet pipe 40 at a location proximate its open end 41 and spaced apart from the inlet aperture 13. Since the support plate 60 is inside the end can 10, it does not add to the overall size of the can assembly, while the short inwardly projecting portion of the inlet pipe 40 serves to direct the exhaust gas flow towards the exhaust gas receiving space 30 and so enhances the bifurcated flow pattern as previously discussed. Additionally or alternatively, the first end wall 11 can incorporate a tongue 42 that is formed integrally with the inlet pipe 40, so that the welded connection between the inlet pipe 40 and the remaining structure of the first end wall 11 is extended along the edges of the tongue 42 to strengthen the assembly.

1001161 In order to further improve signal transmission, the first end can 10 preferably is shaped to define multiple internal, obtuse angles as previously discussed; these help to direct the RF radiation along the flowpath F between the transmitting and receiving antennas. The channel 16 helps to direct the flow into the exhaust gas receiving space, and also accommodates the tongue 42 which as shown may define a surface of rotation about the inlet pipe axis Xi so that it provides a stiff connection between the open end 41 of the inlet pipe and the rest of the end can structure.

1001171 In summary, an exhaust gas aftertreatment assembly 100 includes an inlet end can 10 having an inlet pipe 40, a baffle 20, and a mount 50 for an RF antenna 51. A side wall 12 extends along the exhaust gas flowpath F from the end wall 11 of the can. The baffle 20 includes a perforated centre plate 21 which is spaced apart from the end wall 11 of the can 10 to define an exhaust gas receiving space 30. The inlet pipe 40 terminates inside the can at an open end 41 to direct exhaust gas G across the flowpath F into the receiving space 30. The open end 41 is spaced apart from the baffle 20 in the direction of the inlet pipe axis Xi by a separation distance Ds. The baffle 20 may define an exhaust gas receiving aperture 31 in-between a pair of perforated shoulder plates 23. The exhaust gas G enters the receiving space 30 via the aperture 31 and then turns and divides into two return streams which flow along the side wall 12 and exit through the perforations in the shoulder plates 23. The shoulder plates 23 may be relatively narrow compared with the transverse width dimension Dsi of the receiving aperture 31. The open configuration defined by parameters Ds and Dsi provides improved RF signal transmission for monitoring particulate buildup in the treatment body 81.

[00118] The end cans 10, 90 and mid-portion 80 may include various additional features as known in the art. As illustrated, these may include enlarged axial end regions which engage together during assembly, brackets for mounting the assembly in its use position, mounts for probes that extend into the exhaust gas flowpath to monitor temperature, chemistry, or other parameters, and the like. [00119] Many further adaptations are possible within the scope of the claims. [00120] In the claims, reference numerals and characters are provided in parentheses, purely for ease of reference, and should not be construed as limiting features.

LIST OF ELEMENTS

TITLE: End can for an exhaust aftertreatment assembly with RF antennas FILE 22-0554GB01 First end can 11 First end wall 12 First side wall 12' Internal surface of the first side wall 13 Inlet aperture 14 Outer portion of the first end wall 14' Internal surface of outer portion 14 Inner portions of the first end wall 15' Internal surface of inner portion 15 16 Channel 17 Inclined portion of first end wall Baffle 21 Perforated centre plate 22 Free edge 23 Perforated shoulder plates 24 Outer edge of shoulder plate Inner, free edge of shoulder plate Exhaust gas receiving space 31 Exhaust gas receiving aperture Inlet pipe 41 Open end 42 Tongue First antenna mount 51 First radio frequency antenna 52 Second antenna mount 53 Second radio frequency antenna 60 Support plate Obtusely angled region NH-portion; can 81 Treatment body Second end can assembly 91 Outlet pipe 92 Second end wall 93 Second side wall 94 Outlet aperture Exhaust gas can assembly 101 Exhaust gas aftertreatment apparatus 102 Signal apparatus Al First antenna position A2 Second antenna position D Mean internal transverse dimension (diameter) Dc Depth of the channel Ds Separation distance Dsi Distance between inner, free edges of shoulder plates Dso Distance between outer edges of shoulder plates F Exhaust gas flowpath G Exhaust gas Ph Plane parallel with the flowpath axis Plc Longitudinal centre plane Pt Transverse plane Xf Flowpath axis Xi Inlet pipe axis al Angular position of the first antenna about the flowpath axis a2 Obtuse angle a3 Obtuse angle

Claims (3)

2. What is claimed is: 1. A first end can (10) for use in an exhaust afterh-eatment can assembly (100), the assembly (100) defining an exhaust gas flowpath (F) and a flowpath axis (Xf) extending centrally along the exhaust gas flowpath (F); the first end can (10) including: a first end wall (11) closing a first axial end of the exhaust gas flowpath (F), a first side wall (12) extending from the first end wall (11) along the exhaust gas flowpath (F), a baffle (20), the baffle (20) including a perforated centre plate (21), the centre plate (2 I) having a free edge (22) spaced apart from the first end wall (I I), the centre plate (21) extending into the exhaust gas flowpath (F) from the first side wall (12) to its free edge (22), an exhaust gas receiving space (30) being defined between the centre plate (21) and the first end wall (11); an inlet pipe (40) extending through an inlet aperture (13) in the first side wall (12) and terminating within the exhaust gas flowpath (F) at an open end (41) of the inlet pipe (40), the inlet pipe (40) defining an inlet pipe axis (Xi) extending centrally through the inlet pipe (40) at the open end (41), the inlet pipe (40) being configured, in use, to discharge exhaust gas (G), from the open end (41), along the inlet pipe axis (Xi), into the exhaust gas receiving space (30), and a first antenna mount (50) defining a first antenna position (Al), the first antenna mount (50) being configured, in use, to support a first radio frequency antenna (51) to extend into the exhaust gas flowpath (F) in the first antenna position (Al); wherein, when projected along the flowpath axis (Xf), the baffle (20) and the open end (41) of the inlet pipe (40) are spaced apart by a separation distance Ds along the inlet pipe axis (Xi) 2. A first end can according to claim 1, wherein, when projected along the flowpath axis (Xf), the baffle (20) and the open end (41) of the inlet pipe (40) are spaced apart on opposite sides of the flowpath axis (Xf).
3. 3. A first end can according to claim 1, wherein, when considered in a transverse plane (Pt) perpendicular to the flowpath axis (Xi), the first end can (10) has a mean internal transverse dimension D defined by a straight line passing through the flowpath axis (Xi) and bounded by opposite internal surfaces of the first side wall (12); wherein Ds? 0.5 D. A first end can according to claim 3, wherein Ds > 0.55 D. 5. A first end can according to claim 3, wherein the first side wall (12) is substantially cylindrical with an internal diameter corresponding to the mean transverse dimension D. 6. A first end can according to claim 1, wherein, when considered about the flowpath axis (Xi), the first antenna position (Al) at the first side wall (12) is spaced apart by an angle al from the inlet pipe axis (Xi) at the first side wall (12); wherein al < 750.A first end can according to claim 6, wherein al < 65°.A first end can according to claim 6, wherein al < 55°.9. A first end can according to claim 1, wherein the baffle (20) includes a pair of perforated shoulder plates (23) extending axially with respect to the flowpath axis (XI), along the first side wall (12) between the centre plate (21) and the first end wall (11), respectively on opposite sides of a longitudinal centre plane (Plc) containing the tlowpath axis (XI); each shoulder plate (23) having an outer edge (24) proximate the first side wall (12), and an inner, free edge (25) spaced apart from the first side wall (12), each shoulder plate (23) extending into the exhaust gas tlowpath (F) from its outer edge (24) to its free edge (25); wherein an exhaust gas receiving aperture (31) is defined between the first end wall (11), the free edge (22) of the centre plate (21), and the free edges (25) of the shoulder plates (23), the exhaust gas receiving aperture (31) being arranged to receive the exhaust gas (G) discharged, in use, from the open end (41) of the inlet pipe (40).10. A first end can according to claim 9, wherein, when considered in a transverse plane (Pt) perpendicular to the flowpath axis (XI): the outer edges (24) of the shoulder plates (23) are spaced apart in the transverse plane (Pt) by a distance Dso, and the inner, free edges (25) of the shoulder plates (23) are spaced apart in the transverse plane (Pt) by a distance Dsi; wherein Dsi > 0.65 Dso, 11. A first end can according to claim 10, wherein Dsi > 0.7 Dso.12. A first end can according to claim 9, wherein the inlet pipe axis (Xi) lies in the longitudinal centre plane (Plc) and intersects the flowpath axis (XI), 13. A first end can according to claim 12, wherein the baffle (20) is mirror-symmetric about the longitudinal centre plane (Plc).14. A first end can according to claim 1, further including a support plate (60) fixed to at least one of the first end wall (11) and the first side wall (12), and fixed to the inlet pipe (40) at a location proximate the open end (41) and spaced apart from the inlet aperture (13).15. A first end can according to claim 1, wherein a tongue (42) extends from the open end (41) of the inlet pipe (40) to form a part of the first end wall (11), the tongue (41) being formed integrally with the inlet pipe (40) and welded to another part of the first end wall (11).16. A first end can according to claim 1, including an obtusely angled region (70); wherein, in the obtusely angled region (70), an internal surface (12') of the first side wall (12) defines an obtuse angle (ct2) with an adjacent internal surface (14') of an outer portion (14) of the first end wall (11), when considered in a plane (Ph) parallel with the flowpath axis (Xi).17. A first end can according to claim 16, wherein the obtusely angled region (70) extends through more than 180° around the flowpath axis (XI).18. A first end can according to claim 16, wherein the first end wall (11) defines: a pair of inner portions (15), and a channel (16) extending, between said inner portions (15), from the open end (41) of the inlet pipe (40) in a direction of the inlet pipe axis (Xi); wherein, when considered in said plane (Ph) parallel with the flowpath axis (Xf), an internal surface (15') of each of said inner portions (15) of the first end wall (11) defines an obtuse angle (a3) with an adjacent, internal surface (14') of the outer portion (14) of the first end wall (11).19. An exhaust gas treatment apparatus (101) including: a first end can (10) as defined in any preceding claim; a first radio frequency antenna (51) extending into the exhaust gas flowpath (F) in the first antenna position (Al); a mid-portion (80) arranged downstream of the first end can (10); a treatment body (81) arranged in the mid-portion (80) and extending across the exhaust gas flowpath (F); a second end can assembly (90) arranged downstream of the mid-portion (80) to close a second axial end of the exhaust gas flowpath (F); and a signal apparatus (102); the second end can assembly (90) including: an outlet pipe (91) for conducting the exhaust gas (G), in use, out of the exhaust gas flowpath (F); a second radio frequency antenna (53); and a second antenna mount (52) supporting the second radio frequency antenna (53) to extend into the exhaust gas flowpath (F) in a second antenna position (A2); the signal apparatus (102) being arranged to transmit a radio frequency signal between the first and second antennas (51, 53) and to analyse the signal to determine particulate loading of the treatment body (81).20. A method of treating exhaust gas (G) including: providing an exhaust gas treatment apparatus (101) according to claim 19, transmitting the radio frequency signal between the first and second antennas (51, 53), and analysing the signal to determine particulate loading of the treatment body (81)