[0009] According to an aspect of the present invention there is provided an exhaust treatment apparatus for an internal combustion engine, the apparatus comprising:
[0010] a catalyst chamber containing a catalyst;
[0011] at least one exhaust gas inlet for supplying exhaust gases from the internal combustion engine to the catalyst chamber,
[0012] an exhaust gas outlet for supplying exhaust gases from the catalyst chamber to a turbocharger; and
[0013] an injection nozzle for introducing a reductant into the exhaust gases between the catalyst and the turbocharger.
[0014] At least in certain embodiments, the light-off time of the catalyst can be reduced since it is disposed upstream of the turbocharger. The reductant and exhaust gases flow through the turbocharger together and this can promote evaporation and mixing through the turbocharger. The reductant can be introduced at an earlier point in time from cold start or at lower vehicle speeds. The reductant can, for example, be urea which can operatively be introduced into the flow of exhaust gases in an aqueous liquid form.
[0015] The mixture of reductant and exhaust gases can subsequently be passed through a selective catalytic reduction (SCR) system or a selective catalytic reduction filter (SCRF) system. The apparatus can be configured to make use of existing packaging space within the vehicle to enable closer coupling of downstream after-treatment devices (e.g. cDPF, SCR, SCRF) with light-off and packaging benefits.
[0016] The catalyst can be carried on, or supported by, a substrate (or support structure). The substrate can define the three-dimensional open structure of the catalyst. The substrate can have a three-dimensional porous nature. By way of example, the Substrate can comprise a ceramic foam, a metallic foam or a fibrous structure. The substrate can be fully or partially coated with a catalytic coating (DOC or diesel oxidation and NOx absorption catalyst, DONAC).
[0069] The outlet port 21 is connected to a turbocharger 25 which is driven by the exhaust gases to provide forced induction for the engine 5 in conventional manner. The reductant 23 and exhaust gas are mixed further as they pass through the turbocharger 25. A combined selective catalytic reduction (SCR) and diesel particular filter (DPF) is provided down stream of the turbocharger 25 in the form of a selective catalytic reduction filter (SCRF)29. It will be appreciated that the SCR and the DPF could be provided as separate modules. A low pressure return line 31 is connected downstream of the SCRF 29 to provide low pressure exhaust gas recirculation (LPEGR). A conventional silencer or muffler (not shown) is typically provided downstream of the low pressure return line 31, for example disposed at the rear of the vehicle V. It will be appreciated that not all engines utilise LPEGR and the low pressure return line 31 can be omitted in certain embodimentS.
[0076] The operation of the DOC 3 will now be described with reference to the accompanying Figures. When the engine 5 is initially started, the DOC 3 achieves a light-off (operating) temperature more quickly than conventional catalysts as it is disposed closer to the engine 5. The DOC 3 can thereby begin to perform oxidation more quickly than conventional catalysts. The exhaust gases from the engine 5 are introduced into the exhaust manifold 13 from each cylinder 9A-D through the respective exhaust gas inlets 11A-D. The exhaust gases are introduced into the exhaust manifold 13 in a series of pulses dependent on the operating cycle of each cylinder within the engine 5. These pulses help to circulate the exhaust gases through the substrate 33. The substrate 33 can help to suppress noise radiation from the exhaust manifold 13 caused by the exhaust gas pulses.
[0077] The exhaust gases enter the apertures 41A-D formed in the substrate 33 and then travel through its open pore structure. By positioning the catalyst 35 within the exhaust manifold 13, the required light-off (operating) temperature can be achieved more quickly than conventional catalysts. The catalytic treatment of the exhaust gases can thereby occur over a wider range of operating conditions. The catalyst 35 uses oxygen to convert carbon monoxide (CO) and carbonaceous particulate matter in the exhaust gases to carbon dioxide (CO); and hydrocarbons (HC) in the exhaust gases to water (HO) and CO. The substrate 33 and/or the catalyst 35 can also function to clean exhaust gases prior to recirculation through the high-pressure return line 17. At least Some of the hydrocarbons and particulates in the exhaust gases can be removed within the exhaust manifold 13, thereby helping to reduce the build-up of contaminants in the engine 5, for example on valves, when the exhaust gas is recirculated to the engine 5 through the high-pressure return line 17.
[0078] As outlined above, the reductant 23 is introduced into the mixing chamber second region 39 as a liquid from the injection nozzle 19. For example, the reductant 23 can be an aqueous solution of urea. The reductant 23 is vaporised in the mixing chamber 43 and mixes with the exhaust gases. This arrangement ensures that the reductant 23 is not exposed to catalyst 35 which would potentially promote the formation of nitrogen oxides (NOx). In prior art systems, the reductant 23 is introduced downstream of the turbocharger 25. However, in the present embodiment, the reductant 23 is introduced upstream of the turbocharger 25 resulting in increased mixing with the exhaust gases as they travel through the turbocharger 25. The efficacy of the reductant 23 in removing nitrogen oxides (NOx) on the downstream SCR(F) catalyst from the exhaust gases can potentially be increased. At least in certain embodiments, it is not necessary to provide a separate urea mixer which might otherwise result in an unwanted backpressure increase. Furthermore, the SCRF 29 can be moved closer to the turbocharger 25 as it is not necessary to introduce the reductant 23 into the exhaust gases between these components and allow it to evaporate and mix with the exhaust gas prior to the SCR(F) catalyst.
[0079] The catalyst 35 within the catalyst chamber C may accumulate carbonaceous particulates over a period of time but can be regenerated periodically by employing a conventional regeneration strategy. The exhaust manifold 13 can be an assembly, for example consisting of first and second components, to enable the catalyst 35 to be replaced. Alternatively, the exhaust manifold 13 can have a sealed construction. The catalyst 35 could be formed inside the exhaust manifold 13.
[0080] The SCRF 29 disposed downstream of the turbo-charger 25 functions in conventional manner to convert nitrogen oxides (NOx) in the exhaust gases into nitrogen (N) and water (H2O). During this process, the reductant added upstream of the turbocharger 25 is absorbed onto a catalyst in the SCRF 29. Some of the exhaust gases downstream of the SCRF 29 are recirculated to the internal combustion engine 5 through the low pressure return line 31 in known manner.
[0081] FIGS. 1, 2 and 3 are intended merely to provide schematic representations of the apparatus 1. Notably, the positioning of the apparatus 1 within the vehicle V, as shown in FIG. 2, is not necessarily representative of a production arrangement. A possible arrangement would be to position the SCRF 29 within the engine bay, for example in front of the vehicle dashboard/pedals (not shown).