Combination exhaust gas post treatment/muffler device in the exhaust gas section of an internal combustion engine

[0001] The present invention relates to a combination exhaust gas post treatment/muffler device in the exhaust gas section of an internal combustion engine, especially a diesel engine of a commercial vehicle such as a truck or bus, and includes a muffler, which is spatially delimited by a front and rear end wall as well as a peripheral outer wall, and in the interior of which is built in at least one preliminary oxidation catalytic converter, which significantly increases the amount of NO₂ in the exhaust gas that is flowing through, and at least one, especially catalytic, particle separator, whereby exhaust gas that is to undergo post treatment can be introduced into the muffler via an inlet tube, and after flowing through the preliminary oxidation catalytic converter as well as the particle separator or separators can again be conveyed out of the muffler in a clean and indirectly muffled state.

[0002] In the following, the discussion concerns PM-KAT systems. PM-KAT® is a trademark of the applicant MAN Nutzfahrzeuge Aktiengesselschaft. PM-KAT systems refer to non-blocking means for reducing soot or carbon particles in the exhaust gas of diesel engines. Such PM-KAT systems comprise at least one preliminary oxidation catalytic converter, subsequently referred to as P-cat, the carrier of which is coated with platinum as the active component, and a downstream, especially catalytic, particle separator, subsequently abbreviated as PM separator. Such a PM separator, could, for example, have the configuration or structure disclosed in DE 100 20 120 C1. For trucks, an arrangement has been disclosed of a P-cat in a preliminary muffler that is disposed as close as possible to the internal combustion engine, and of one or more separators in the main muffler (see DE 101 23 358 A1).

[0003] In addition, the integration of the PM-KAT System in a commercial vehicle muffler was disclosed at the twenty-third International Viennese Motor Symposium on 25 and 26 Apr. 2002 and was documented in the Progress Reports, VDI Series 12 No. 490, Volume 2 Düsseldorf, VDI publication 2002, page 196–216. FIGS. 10 and 11 show this MP-KAT system of this literature citation. There it can be seen that disposed in the muffler 1 are four exhaust gas post treatment modules 2 for parallel flow therethrough, whereby each of the modules is encased in a casing 5 and is provided with a circular cylindrical P-cat 3 and following coaxially directly thereafter a circular cylindrical PM separator 4 having the same diameter. This integration of the PM-KAT system of the muffler 1 is provided when with a truck or bus there is no space for accommodating a preliminary muffler close to the engine. However, the drawback of this integration solution is a PM separator volume that is reduced by the volume of the P-cat, because the outer dimensions of the muffler 1 are dictated by the vehicle and can therefore not be increased. This leads to unsatisfactory separation rates of significantly less than 50%. Even an increase of the platinum concentration in the P-cat and an additional coating of the inner structures of the PM separator or separators would not lead to the goal of increasing the separation rate/conversion in the ETC (European Transient Cycle). Platinum is very expensive and therefore determines to a very considerable extent the cost of the overall system.

[0004] It is therefore an object of the present application, in a combination exhaust gas post treatment/muffler device of the aforementioned general type, to accommodate in the muffler a P-cat and PM separator having such a volume and such a shape and design that particle conversion rates of at least 50%, preferably, however, considerably greater than 50% in the ETC, can be achieved while using a minimum amount of platinum in the P-cat.

[0012] The combination exhaust gas post treatment/muffler device of the present application is characterized primarily in that the free exhaust gas inlet surface of the preliminary oxidation catalytic converter is considerably smaller than the free exhaust gas inlet surface of the particle separator or separators, in that the aspect ratio AR=I/Ø_eff of the preliminary oxidation catalytic converter is approximately between 0.4 and 0.6, in that the aspect ratio AR=I/Ø_eff of the particle separator or separators is approximately between 0.5 and 1.0, in that the volume of the preliminary oxidation catalytic converter is between approximately 2.5 and 4 liters, the volume of the particle separator or separators is between approximately 5.5 and 22 liters, and the ratio of the volume of the catalytic converter to the volume of the particle separator or separators is between approximately 0.15 and 0.55, in that the ratio of the aspect ratio of the particle separator to the aspect ratio of the catalytic converter is between approximately 1.05 and 2.2, and in that at maximum exhaust gas volume flow [Nm^3/h] the channel velocity, which results from exhaust gas volume flow/free exhaust gas inlet surface, in the preliminary oxidation catalytic converter is greater than 8 m/sec and in the particle separator or separators is greater than 5 m/sec, whereby the maximum exhaust gas volume flow is delimited by the maximum permissible pressure loss and the maximum permissible exhaust gas pressure with respect to the functionality of the internal combustion engine that supplies the exhaust gas.

[0013] In contrast to the known solution of FIGS. 10 and 11 having four P-cats, with the present invention, the volume of the single P-cat is smaller by a factor of 2.5–3.5, and in addition the use of platinum for the coating of the P-cat is reduced, depending upon the embodiment, by a factor of 3.3–11.7. This saves an enormous amount of costs. In addition, with this only relatively small P-cat, more space is provided for the PM separator or separators, and a significant increase of the particle conversion is achieved.

[0014] Further specific features of the present application will be described in detail subsequently.

[0015] Referring now to the drawings in detail, FIGS. 1–8 show a combination exhaust gas post treatment/muffler device that is disposed in the exhaust gas section of an internal combustion engine, especially a diesel engine of a commercial vehicle such as a truck or bus. This device has a muffler 10 that is spatially delimited by a front end wall 11, a rear end wall 12 and a peripheral outer wall 13, whereby the latter can have a round, oval, square or somewhat rectangular cross-section, and in a longitudinal direction can be cylindrical or can bulge in a barrel-shaped manner. Leading into the interior of the muffler 10 is an exhaust gas inlet tube 14 to which the exhaust gases of the pertaining internal combustion engine can be fed via a non-illustrated exhaust gas line. Built into the interior of the muffler 10 are additionally a preliminary oxidation catalytic converter 15 (subsequently called P-cat 15), which due to its platinum coating significantly increases the amount of NO₂ in the exhaust gas that flows through, and at least one in particular catalytic particle separator 16 (subsequently called PM-separator 16). The reference numeral 17 indicates a sound-dampening end tube via which clean exhaust gas is conducted out of the interior of the muffler 10 and into the atmosphere. Exhaust gas that is to be post treated is consequently supplied via the exhaust gas inlet tube 14 to the muffler 10, from there flows first through the P-cat 15 and subsequently through the PM separator or separators 16, and is subsequently again conveyed out of the muffler 10 in a cleaned and indirectly sound-dampened manner via the end tube 17. The end walls 11,12 and, to the extent necessary, also the peripheral outer wall 13 as well as the end tube 17, are coated with sound-dampening material. Also contributing to the sound dampening or muffling are special designs in the region of the introduction and discharge of the exhaust gas, as well as transverse walls within the muffler, as will be described in greater detail subsequently.

[0016] In the three examples of FIGS. 1,2 and 3,4 and 5,6, the P-cat has a circular cylindrical configuration, and is built into a housing 18 of austenitic or ferritic stainless steel, and in particular parallel to the longitudinal axis 19 of the muffler 10. Extending a certain amount into the entry chamber 20 of this housing 18, which initially widens in a funnel-shaped manner from the front end wall 11 and then continues cylindrically, is the exhaust gas inlet tube 14, which at that location is preferably provided with a perforation or holes 21 so that the supplied exhaust gas can exit the exhaust gas inlet tube 14 not only radially but also axially into the entry chamber 20, and can then flow through the P-cat 15, which is enclosed in the cylindrical portion of the housing 18.

[0017] Each of the PM separators 16 that is present in these three examples has a circular cylindrical configuration, is also built into a housing 22 of austenitic or ferritic stainless steel, and together with the housing is disposed parallel to the axis 19 of the muffler therein. In this connection, in the example of FIGS. 1 and 2 four, in the example of FIGS. 3 and 4 three, and in the examples of FIGS. 5 and 6 one such housing 22, with built-in PM separator 16, is disposed above and/or next to the housing 18 with the P-cat built therein. To fix the position of the housings 20 and 22, a transverse wall 23 is provided in the muffler; this transverse wall is preferably made gas-permeable via a perforation or holes, so that the exhaust gas that leaves the P-cat 15 after flowing therethrough can, prior to flowing through the PM separator or separators 16, separate on the outside about these separators and can therefore preheat or hold them at a favorable operating temperature. With all three examples of FIGS. 1 to 6, the PM separator or separators 16 open into a discharge chamber 24, that within the muffler 10 is, via walls 25 and 26, gas tight relative to the rest of the interior of the muffler 10. The end tube 17 also communicates with this chamber 24. The wall 25, which is parallel to the transverse wall 23, via openings or apertures, respectively spans the outlet side end regions of the PM separator housing or housings 22 and the inlet region of the end tube 17 in a gas tight manner and thus also contributes to the fixing of the position thereof in the muffler 10.

[0018] With the embodiment of FIGS. 7 and 8, the P-cat 15 and the PM separator 16 used here are each circular cylindrical but have different diameters and in a common housing 27 are disposed axially after one another, yet separated by a transfer chamber 28 that widens in a tunnel-shaped manner from the discharge surface or plane of the P-cat 15 to the entry surface or plane of the PM separator 16. Here, the exhaust gas inlet tube 14 is extended relatively far into the interior of the muffler 10 to shortly before the end tube 17, and is also provided with a perforation or holes 21. The housing 27, with built-in P-cat 15 and PM separator 16, is built into the muffler 10 above the exhaust gas inlet tube 14 and parallel to the axis 19 of the muffler, and is held within the muffler, as are the exhaust gas inlet tube 14 and the end tube 17 by two transverse walls 29,30. In this connection, the transverse wall 29 is made gas permeable by holes or a perforation, whereas the other transverse wall 30, which is parallel to the transverse wall 29, has a gas tight configuration and thus in conjunction with the front end wall 11 and the peripheral outer wall 13 delimits a discharge chamber 31. The PM separator 16 opens out into the discharge chamber 31 from which the end tube 17 starts. In this connection, the housing 27, the end tube 17 and the exhaust gas inlet tube 14 are accommodated in a gas tight manner in openings or apertures of the transverse wall 30. Between the transverse wall 30 and the rear end wall 12 the interior of the muffler can, due to the gas-permeability of the transverse wall 29, be filled with exhaust gas that exits the inlet tube 14 radially and axially, so that also with this embodiment the housing 27, with the P-cat 15 and PM separator 16, can be preheated or held to a favorable operating temperature.

[0019] In general, all of the embodiments fulfill the following inventive features:

• [0020] a) The free exhaust gas inlet surface or plane of the P-cat 15 is considerably smaller than the exhaust gas inlet surface or plane of the PM separator or separators 16.
• [0021] b) The aspect ratio AR=length (I)/diameter_eff(Ø_eff) is approximately between 0.4 and 0.6 for the P-cat 15.
• [0022] c) The aspect ratio AR=length (I)/diameter_eff (Ø_eff) of the PM separator or separators 16 is approximately between 0.5 and 1.0.
• [0023] d) The volume of the P-cat 15 is approximately between 2.5 and 4 liters, the volume of the or all of the PM separators 16 is approximately between 5.5 and 22 liters, and the ratio volume P-cat 15/volume of the or all of the PM separators 16 is approximately between 0.15 and 0.55.
• [0024] e) The relation aspect ratio for the or all of the PM separators 16/aspect ratio P-cat 15 is approximately between 1.05 and 2.2.
• [0025] f) At maximum exhaust gas volume flow [Nm³/h], the channel velocity KG (=exhaust gas volume flow/free exhaust gas inlet surface) in the P-cat 15 should be greater than 8 m/sec and in the PM separator or separators 16 greater than 5 m/sec, whereby the maximum exhaust gas volume flow is limited by the maximum permissible pressure loss and the maximum permissible exhaust gas counter pressure with regard to the functionality of the internal combustion engine that supplies the exhaust gas.

[0026] The term Ø_eff mentioned in b) and c) indicates the diameter that is effective at the inlet of the round inlet surface of the P-cat 15 and of the PM separator 16 (for the case where only one is used), or where a plurality of PM separators 16 are used, their effective overall inlet surface assuming a circular surface and the diameter resulting therefrom.

[0027] Listed in the table of FIG. 9 are ten tested examples of combinations of different P-cats 15 and a different number of different PM separators 16, and the conversion rates (particle separation rates) resulting herefrom pursuant to ESC (European Steady State Cycle) and ETC (European Transient Cycle). To avoid repetition, the table of FIG. 9, and the contents thereof, are made a part of this specification. The testing of the individual variants is effected with a diesel engine, which supplies exhaust gas having a raw particle emission of the order of magnitude of about 40 mg/KWh at ESC-Test, and of about 50 mg/KWh at ETC-Test, in each case at a maximum exhaust gas volume flow of 1200 Nm³/h. At this maximum exhaust gas volume flow, the channel velocities and conversion rates listed in the Table of FIG. 9 result.

[0028] In the examples of FIGS. 1 and 2, it was attempted to increase the conversion rate with 3 variants (1–3), in each case with the same P-cat 15 and with the use of PM separators 16 having the same diameter but different lengths. The best mode solution is represented by variant 3. This shows that the longer the PM separator or separators 16 are, despite a relatively small diameter, the greater is the conversion rate. The elongated embodiment of the PM separator 16 is therefore very expedient.

[0029] In the example of FIGS. 3 and 4, in conformity with the variants 4 and 5 in each case three identical PM separators 16 were associated with a respectively different P-cat 15.

[0030] In the examples of FIGS. 5 and 6, with the variant 6 a PM separator 16 having a similar total volume to the three PM separators 16 of the variants 4 and 5 was used in conjunction with the same P-cat 15. Comparably good conversion rates were established.

[0031] In the example of FIGS. 7 and 8, in the four variants 7–10 in each case a PM separator 16 having a different cellular structure was combined with a P-cat 15 that either had a different cellular structure or a different diameter.

[0032] All of the variants had ETC conversion rates of at least 50%, while in the peak with the variant 3, a phenomenal 79% was achieved. In the tested variants 1 to 10, PM separators 16 not having a platinum coating were used. However, there are also certainly applications where the use of platinum-coated PM separators 16 is necessary. Thus, the invention is applicable not only to uncoated but also to platinum-coated PM separators 16. In addition, it is possible to use P-cats 15 and PM separators 16 having a cellular structure other than that given. Furthermore, as a modification of the illustrated embodiment, it is, of course, also possible to combine a P-cat 15 with two, five or six PM separators 16 in the event that there is sufficient space in the muffler 10 and/or the amount of muffling to be achieved to permit this.

[0033] The specification incorporates by reference the disclosure of German priority document 103 16 802.8 filed Apr. 11, 2003.

[0034] The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.