After-treatment system and method

Abstract

According to the present disclosure, there is provided an after-treatment system. The after-treatment system may be for use with an engine. The engine may have an exhaust conduit. The exhaust conduit may be arranged to route exhaust from the engine during operation of the engine. The after-treatment system may be arranged to connect to the exhaust conduit and to receive and treat the flow of exhaust from the engine. The after-treatment system may comprise an after-treatment device for treating received exhaust. The after-treatment system may further comprise a conduit for connecting an outlet of the after-treatment device to a point ahead of an inlet of the after-treatment device along the exhaust conduit. The after-treatment device may further comprise a pump to pump at least part of the emissions from the outlet of the after-treatment device to the point ahead of the inlet of the after-treatment device. There is further provided an after-treatment method.

Description

[0001] 24-0542W001

[0002] 1

[0003] After-Treatment System and Method

[0004] TECHNICAL FIELD

[0005] The present disclosure relates to improvements in exhaust after-treatment systems and methods. In particular, the present disclosure relates to improvements in after-treatment systems and methods through use of a feedback loop.

[0006] BACKGROUND

[0007] Power units, such as engines, and in particular internal combustion engines, may produce a complex mixture of exhaust emissions including air pollutants and condensate. In order to reduce unwanted emissions and sometimes improve performance of the engine a combustion exhaust gas after-treatment (or after treatment) assembly may be provided, connected to exhaust ports of the engine, for treating the exhaust. Exhaust may include gases, liquids and solids, such as particulate matter and soot.

[0008] With increased awareness of and attention to environmental considerations, exhaust emission standards are becoming ever more stringent. Moreover, due to increase of fuel costs, engine performance and economics have become more important. In order to meet these standards, engine manufacturers may employ a combustion exhaust after-treatment assembly or system which may be tailored to specific engines, depending on e.g. engine type, size, class and intended use of the engines, fuel types and engine loads.

[0009] Recent emission regulations driving the transition into Ultra Low Emissions may include up to a 90% reduction of NOXlevels in vehicle exhaust emissions, when compared with previous regulations. To achieve an Ultra Low Emissions engine, after-treatment may require complex technologies. One example of complex after-treatment technologies is a dual dosing system.

[0010] A solution is proposed to improve exhaust processing, while avoiding overly complex technologies, by recycling treated exhaust from an after-treatment device. This may allow 24-0542W001

[0011] 2 part or all of the exhaust to be treated two or more times, which may improve the input composition of the exhaust, as some undesirable components will have already been processed / removed, and may allow the after-treatment device more time to reach a desired operating conditions.

[0012] SUMMARY

[0013] According to the present disclosure, there is provided an after-treatment system. The after- treatment system may be for use with an engine. The engine may have an exhaust conduit. The exhaust conduit may be arranged to route exhaust from the engine during operation of the engine. The after-treatment system may be arranged to connect to the exhaust conduit and to receive and treat the flow of exhaust from the engine. The after-treatment system may comprise an after-treatment device for treating received exhaust. The after-treatment system may further comprise a conduit for connecting an outlet of the after-treatment device to a point ahead of an inlet of the after-treatment device along the exhaust conduit. The after-treatment system may further comprise a pump to pump at least part of the emissions from the outlet of the after-treatment device to the point ahead of the inlet of the after- treatment device.

[0014] According to the present disclosure, there is further provided a method for treating emissions from an internal combustion engine. The method may comprise passing exhaust from the internal combustion engine through an after-treatment device. The method may further comprise recirculating at least part of the emissions from an outlet of the after-treatment device to a point ahead of an inlet of the after-treatment device. The method may further comprise passing the recirculated emissions through the after-treatment device.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures. 24-0542W001

[0017] 3

[0018] Examples will now be described, by way of example only, with reference to the following figures, in which:

[0019] Figure 1 shows a simplified schematic of an after-treatment system;

[0020] Figure 2 shows a simplified schematic of an after-treatment system including a diesel exhaust fluid (DEF) Mixer;

[0021] Figure 3 shows a further simplified schematic of an after-treatment system including a DEF Mixer;

[0022] Figure 4 shows a simplified schematic of an after-treatment system including an SCR device;

[0023] Figure 5 shows a simplified schematic of an after-treatment system including an AMOX device;

[0024] Figure 6 shows a simplified schematic of an after-treatment system with a variation on the positioning of the recirculation conduit;

[0025] Figure 7 shows a simplified schematic of an after-treatment system including a control device;

[0026] Figure 8 shows a flowchart of a method for exhaust after-treatment;

[0027] Figure 9 shows a flowchart of a further method for exhaust after-treatment; and

[0028] Figure 10 shows a flowchart of a further method for exhaust after-treatment;

[0029] DETAILED DESCRIPTION

[0030] The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the words “exemplary” and “example” mean “serving as an example, instance, or illustration.” Any implementation described herein as exemplary, or an example is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description. 24-0542W001

[0031] 4

[0032] In some examples, there is provided an after-treatment system 10 as shown in figure 1. The after-treatment system 10 may be for use with an engine 1. The engine 1 may have an exhaust conduit 2. The exhaust conduit 2 may be arranged to route exhaust from the engine 1 during operation of the engine 1. The after-treatment system 10 may be arranged to connect to the exhaust conduit 2 and to receive and treat the flow of exhaust from the engine 1. The after-treatment system 10 may comprise an after-treatment device 100 for treating received exhaust. The after-treatment system 10 may further comprise a conduit 110 for connecting an outlet 102 of the after-treatment device 100 to a point, along the exhaust conduit 2, ahead of an inlet 101 of the after-treatment device 100. The after-treatment device

[0033] 100 may further comprise a pump 120 to pump at least part of the emissions from the outlet 102 of the after-treatment device 100 to the point ahead of the inlet 101 of the after- treatment device 100.

[0034] The exhaust conduit 2 may connect the engine 1 to the after-treatment device 100 and the after-treatment device 100 to an outlet such as an exhaust pipe / tailpipe. The conduit 110 may be referred to as an emissions conduit, a feedback conduit or a feedback loop. The conduit 110 may include a conduit inlet 111 and a conduit outlet 112. The conduit inlet 111 may connect to the exhaust conduit 2 to provide a fluid connection to the outlet 102 of the after-treatment device 100. The conduit outlet 112 may be collocated with the point ahead of the inlet 101 of the after-treatment device 100 to which the emissions are pumped. The conduit outlet 112 may connect to the exhaust conduit 2 to provide a fluid connection to the inlet 101 of the after-treatment device 100. In some examples, there may be further components of the after-treatment system 10 positioned between the conduit outlet 112 and the inlet 101 of the after-treatment device 100.

[0035] In an example, the flow may pass from the engine 1, along the exhaust conduit 2, to the inlet

[0036] 101 of the after-treatment device 100, through the after-treatment device 100 to the outlet

[0037] 102 thereof. Part of the treated exhaust (also referred to as emissions from the after- treatment device 100) may then be expelled from the system 10, via an exhaust pipe or tailpipe of the system 10 which may simply be the end of the exhaust conduit 2, and part may enter the conduit 110 via the conduit inlet 111 , pass along the conduit 110 to the conduit outlet 112 at which point the treated exhaust rejoins untreated exhaust from the engine 1 and travels along the exhaust conduit 2 and through the after-treatment device 100 again. 24-0542W001

[0038] 5

[0039] The point “ahead” of the inlet 101 of the after-treatment device 100, refers to a point upstream of the inlet 101 such that emissions passing through the point then flow on to the inlet 101. The flow may be caused by exhaust from the engine 1 having a relatively high pressure.

[0040] The after-treatment device 100 may include one or more than one of a low temperature selective catalytic reduction, Lo-SCR, device (sometimes referred to as a low temperature selective catalytic reduction catalyst or a light off SCR), a selective catalytic reduction, SCR, device, a diesel oxidation / oxidising catalyst, DOC, an ammonia oxidation, AMOX, device, and a diesel particulate filter, DPF or any other device associated with exhaust after- treatment. That is to say the after-treatment device 100 may include one of any or all of the above features or any combination of one or more of each thereof.

[0041] In some examples, the after-treatment device 100 may be a Lo-SCR. In such an example, recirculation of treated exhaust may be useful to achieve a desired input NCh / NOx ratio by combining some of the already treated exhaust, which will have a lower amount of NOXpresent, with the engine exhaust, which, when running in a cold-start scenario, may have a higher than usual amount of NOXpresent. In a specific example, the NCh / NOx ratio at the Lo- SCR input, on the first pass, may be around 0.05 to 0.1. With the recirculation as described above, this ratio may be brought closer to the desired 0.5 ratio level.

[0042] In some examples, where the after-treatment device 100 is a Lo-SCR device, recirculation may be used to assist with desulphation of the Lo-SCR device, which forms part of the maintenance of the Lo-SCR device. Desulphation may be required when sulphur oxides (SOX), which are produced as by-products, begin to interfere with the catalytic function of the Lo-SCR. Desulphation may be achieved by increasing the temperature of the Lo-SCR device beyond its normal operating temperature. Using recirculation to assist with increasing temperature may be of particular benefit when there is a downstream oxidation catalyst performing oxidation of hydrocarbons, which will result in an elevated downstream temperature, which may then be fed back upstream, thus avoiding the need to elevate the temperature by other means.

[0043] In some examples, an AMOX device may be positioned after a Lo-SCR to convert any excess ammonia into nitrogen and water. Alternatively, or in combination with such a configuration, recirculation may be used to allow the ammonia to pass through the Lo-SCR 24-0542W001

[0044] 6 again and assist in converting further NOXpresent in either the recirculated treated exhaust or the exhaust from the engine 1 .

[0045] In some examples, the after-treatment device 100 may include a diesel exhaust fluid (DEF) Mixer. In such an example, the recirculation of treated exhaust may be useful to aid deposit removal in the DEF Mixer. Deposit removal may be achieved by increasing pressure and / or temperature ahead of the DEF Mixer through recirculation of the treated exhaust through the conduit 110. This may also improve nitrogen oxide conversion. Recirculation may further be used to control / increase velocity of the exhaust passing through the DEF Mixer. DEF Mixer performance may be improved with higher flow rates / velocities.

[0046] In some examples, the after-treatment device 100 may include a diesel oxidising catalyst (DOC). In such an example, the recirculation of treated exhaust may be useful to provide a thermal regulation function, such as a cooling or heating function, as desired. The temperature of a DOC may be regulated to improve conversion of carbon monoxide and hydrocarbons into carbon dioxide and water vapour. For example, an after-treatment device 100 may include a DEF Mixer and a DOC in series, wherein treated exhaust from the DOC, which may have an elevated temperature, may be fed back to the DEF Mixer to heat the DEF Mixer and achieve the above-described benefits. In some examples, the downstream temperature may be lower than the desired temperature of the DEF Mixer, in which case the treated exhaust may be fed back to have a cooling function.

[0047] The functioning of a number of different after-treatment devices 100 may be improved by operating within a desired temperature range and wherein input emissions are within desired processing limits for specific substances.

[0048] In some examples, the after-treatment system 10 may comprise a diesel exhaust fluid (DEF) input point which may be along the exhaust conduit 2 after an output from the engine 1 , from where the combustion exhaust is output. Next, the after-treatment system 10 may comprise a DEF Mixer configured to decompose diesel exhaust fluid (DEF) into ammonia which may be output to an SCR for NOXreduction. Then, the after-treatment system 10 may comprise a Lo-SCR device, as the after-treatment device 100, configured to receive the ammonia and carry out selective catalytic reduction to lower the concentration of NOXin the exhaust. Then, the after-treatment system 10 may comprise an AMOX device to convert any excess ammonia into nitrogen and water. Next, the after-treatment system 10 may comprise a DOC. A DOC may for example be used to reduce the amount of carbon monoxide (CO) and 24-0542W001

[0049] 7 particulate matter present in the exhaust. A DOC typically produces heat as well. Then, the after-treatment system 10 may comprise a DPF. A DPF may be used to reduce or filter out particulate matter present in the exhaust. A DPF typically operates at elevated temperatures and so the heat produced by a DOC, or other heat source, may be used to achieve these conditions. In some examples, the after-treatment system 10 may further comprise a further DEF input point followed by a further DEF Mixer. Then, the after-treatment system 10 may comprise one or more further SCR devices. Finally, the after-treatment system 10 may comprise a further AMOX device. In such a system, the recirculation conduit may recirculate treated or partially treated exhaust from a point along the after-treatment system 10 at any of: after the Lo-SCR or the SCR, after either AMOX device, after the DOC or after the DPF. The treated or partially treated exhaust may be pumped to a point either after the engine outlet (for example before the first DEF input point) or between the first DEF Mixer and the Lo-SCR device. Each of these configurations may be used to achieve one or more of advantages / benefits detailed above.

[0050] Turning to further examples, the after-treatment system 10 may further comprise, as shown in figure 2, a first diesel exhaust fluid, DEF, mixer 130 positioned between the engine 1 and the after-treatment device 100. In such an example, the after-treatment device 100 may be an SCR or Lo-SCR, which serves to reduce NOXpresent in the exhaust and benefits from ammonia output by the DEF Mixer 130. Further, an AMOX catalyst may be positioned after such an SCR or Lo-SCR, to convert any excess ammonia into nitrogen and water. The conduit 110 may connect to the exhaust conduit 2 at a point after the DEF Mixer 130, for example between the DEF Mixer 130 and the after-treatment device 100.

[0051] The after-treatment system 10 may further comprise, as shown in figure 3, a second diesel exhaust fluid, DEF, mixer 140 positioned after the outlet 102 of the after-treatment device 100 in the direction of flow. While the DEF mixer 140 is referred to as a “second” DEF mixer to aid distinction from the first DEF mixer 130, the DEF mixer 140 may be the only DEF mixer included in the system 10. Therefore, the first DEF mixer 130 may alternatively be referred to as an upstream DEF mixer 130 (referring to its position relative to the after- treatment device 100) and the second DEF mixer 140 may be referred to as a downstream DEF mixer 140 (referring again to its position relative to the after-treatment device 100). An SCR or Lo-SCR may additionally be positioned after the DEF Mixer 140, to benefit from the ammonia output by the DEF Mixer 140 and further reduce NOXlevels in the exhaust. 24-0542W001

[0052] 8

[0053] Further, an AMOX catalyst may be positioned after such an SCR or Lo-SCR, to convert any excess ammonia into nitrogen and water.

[0054] The after-treatment system 10 may further comprise, as shown in figure 4, a selective catalytic reduction, SCR, device 150 positioned after the outlet 102 of the after-treatment device 100. In some examples, the after-treatment system 10 may include more than one SCR device, each positioned sequentially downstream of the after-treatment device 100 to further catalyse unwanted compounds in the treated exhaust. In such an example, the after- treatment device 100 may for example be a DEF Mixer. An AMOX catalyst may be positioned after such an SCR 150 to convert any excess ammonia into nitrogen and water.

[0055] The after-treatment system 10 may further comprise, as shown in figure 5, an outlet ammonia oxidation, AMOX, device 160. In such an example, the after-treatment device 100 may for example be an SCR or Lo-SCR.

[0056] In an example, as shown in figure 6, the point to which the conduit 110 connects may be ahead of an inlet of a diesel exhaust fluid, DEF, mixer 130. In such an example, the recirculation of treated exhaust may be useful to aid deposit removal in the DEF Mixer. Deposit removal may be achieved by increasing pressure and / or temperature ahead of the DEF Mixer through recirculation of the treated exhaust through the conduit 110. Recirculation may further be used to control / increase velocity of the exhaust passing through the DEF Mixer. DEF Mixer performance may be improved with higher flow rates / velocities.

[0057] The after-treatment system 10 may further comprise, as shown in figure 7, a control device 170 to control the pump 120. The control device 170 may control the pump 120, based on a temperature of the emissions and / or a temperature of the after-treatment device. The control device 170 may be referred to as a pump control device. The temperature of the emissions may be detected by a thermometer located at or near the outlet 102 or at any point along the recirculation path, such as at or near the pump 120 or the conduit outlet 112 or at or near the after-treatment device inlet 101. The control device 170 may control the pump 120, based on a performance characteristic of the after-treatment device 100, such as a detected amount of NCh / NOx in the engine exhaust, treated exhaust or both, a mass flow and / or pressure.

[0058] The control device 170 may control the pump 120 based on a pressure at the point ahead of the inlet 101 of the after-treatment device 100, for example at or near conduit outlet 112. In an example, the after-treatment device 100 comprises a DEF Mixer and the control device 170 may control the pump 120, based on a pressure at the point ahead of the inlet 101 of 24-0542W001

[0059] 9 the after-treatment device 100. This may be used to improve the pressure and flow rate through the DEF Mixer to improve efficiency.

[0060] In one example, the after-treatment device 100 may comprise a Lo-SCR device, and the control device 170 may control the pump 120, based on a detected level of NO2 and / or NOXand / or ammonia present in the emissions from the after-treatment device 100 and / or in the exhaust from the engine 1.

[0061] In one example, the after-treatment device 100 may comprise a DOC device and the control device 170 may control the pump 120, based on a temperature of the emissions and / or the after-treatment device 100 for example relative to the desired operating temperature of the DOC device. This may help to reduce the risk of hydrothermal aging and / or platinum volatilisation.

[0062] In some examples, there is provided a method for treating emissions from an internal combustion engine, as shown in figure 8. The method may comprise passing S101 exhaust from the internal combustion engine through an after-treatment device. The method may further comprise recirculating S102 at least part of the emissions from an outlet of the after- treatment device to a point ahead of an inlet of the after-treatment device. The method may further comprise passing S103 the recirculated emissions through the after-treatment device.

[0063] The method may further comprise, as shown in figure 9, controlling S104 an amount of the emissions being recirculated based on at least one of temperature, pressure and composition of the emissions.

[0064] The method may further comprise, as shown in figure 10, controlling S105 a temperature of the after-treatment device by adjusting an amount of the emissions which are recirculated.

[0065] Any functional features described in connection with the systems or devices above may be carried out as part of the methods for treating emissions.

[0066] In some examples, a method for abating certain engine exhaust constituents, for use in a diesel engine for example, is by use of an exhaust after-treatment system that may utilize, among other things, selective catalytic reduction (SCR) of nitrogen oxides. In a typical SCR system, urea or a urea-based water solution is mixed with exhaust gas. In some applications, a urea solution is injected directly into an exhaust passage through a specialized injector device. The injected urea solution, which is sometimes referred to as diesel exhaust fluid (DEF), mixes with exhaust gas and breaks down to provide ammonia 24-0542W001

[0067] 10

[0068] (NH3) in the exhaust stream. The ammonia then reacts with nitrogen oxides (NOX) in the exhaust at a catalyst to provide nitrogen gas (N2) and water (H2O).

[0069] In typical applications, especially for large engines, high efficiency diesel particulate filters (DPF) may be used in conjunction with NOXreduction systems, such as systems using SCR. Such systems are generally quite effective in filtering soot while also converting nitrous oxide emissions from diesel exhaust. Such systems however may be improved during cold-start scenarios in which components of the engine and / or after-treatment system are not yet operating within a desired temperature range.

[0070] In some examples, in a cold-start scenario, an after-treatment system may include a low- temperature selective catalytic reduction (Lo-SCR) device. The outlet of the Lo-SCR device may be attached to a feedback channel to divert some or all of the exhaust from the Lo-SCR device back upstream of the Lo-SCR device to be processed again by the Lo-SCR device. The Lo-SCR device may be positioned on a channel, with the Lo-SCR inlet fluidly connected either directly or indirectly to the exhaust outlet of, for example, a diesel engine. The area between the engine and the Lo-SCR inlet may have a relatively high pressure and the area downstream of the Lo-SCR outlet may have a relatively low pressure. Therefore, the feedback channel may include a pump to compensate for this pressure difference and allow for the feedback of Lo-SCR exhaust to the high pressure area, and combine with the exhaust from the engine outlet.

[0071] This feedback of Lo-SCR exhaust means that the exhaust from the engine may be processed, at least partly, two or more times. This means that unconverted NOXmay be passed through the Lo-SCR again leading to an overall higher conversion rate.

[0072] Further, by feeding back the Lo-SCR exhaust, which typically has a relatively high temperature, components of the after-treatment system 10 may be brought up to a desired operating temperature range more quickly.

[0073] Lo-SCR based after-treatment system can warm up quickly and reduce cold-start emissions. However, NOXreduction capability can be limited by the Lo-SCR inlet NCh / NOx ratio (In the range of 5 to 10% average, which is same as engine out NCh / NOx). Therefore, recycling part of the Lo-SCR emissions may help to bring the NC>2 / NOXratio closer to the desired level of 0.5. 24-0542W001

[0074] 11

[0075] In one specific example, the after-treatment system 10 may be used in connection with a diesel internal combustion engine (ICE). As part of the conversion of exhaust from the ICE, the after-treatment system 10 may comprise an after-treatment device 100, such as a low temperature selective catalytic reduction (Lo-SCR) device. A low temperature selective catalytic reduction device may be used to reduce the amount of NOXpresent in the exhaust from the ICE. Lo-SCR devices operate more efficiently when the NO2 to NOXratio is approximately 0.5.

[0076] In particular, during so-called cold-starts of the ICE, i.e. where the ICE is started and all of the respective components are not yet operating at their desired temperature, ICEs may have a higher amount of NOXpresent in the exhaust than desired.

[0077] Lo-SCRs tend to reach operating temperature faster than other SCRs and so are useful for cold-start applications.

[0078] An example operating temperature for an SCR device may be around 530°C. An example operating temperature for a DEF Mixer may be 450°C.

[0079] 600°C and above may be an example of a temperature range that is too high and, as such, temperature regulation as described above may be implemented to bring the temperature back to desired levels.

[0080] In some circumstances, such as when an engine is first started, a so-called cold-start, many of the components of the engine and the after-treatment system may not be operating at their optimal temperature or within a desired operating temperature range. Therefore, recirculating treated exhaust may offer the benefit that the exhaust can be passed through the after-treatment device more than once, and indeed multiple times, to improve the quality of the emissions, emitted from the after-treatment system, which would then be emitted into the open environment. Improvement of the quality of the emissions may include removal of undesired compounds, such as NOXwhich can be harmful to respiratory health in humans and animals, filtering of larger particulate matter, such as soot, or conversion of uncombusted hydrocarbons into CO2 and water. Further actions may be included in the improvement of the quality of the emissions.

[0081] Further, recirculation may be used to achieve a warming or cooling effect / temperature regulation of the after-treatment device, to maintain the temperature of the after-treatment device within a desired operating range. 24-0542W001

[0082] 12

[0083] In some examples, improvements in the functioning of the Lo-SCR may have knock-on improvements in the functioning of downstream DOC and / or DPF devices. This is achieved because DOC and DPF devices may operate more efficiently and effectively when the input composition is improved, for example that the ratio of matter to be removed / processed / filtered lies within a desired range, that the temperature of the input allows the DOC / DPF to operate within a desired temperature range and / or that the flowrate of exhaust is at a level allowing more complete processing of the exhaust.

[0084] In an example, this may be achieved without the pump. However, many ICE exhaust systems will have a higher pressure at the conduit outlet (the point upstream of the inlet of the after-treatment device) than at the conduit inlet (the after-treatment device outlet), so a pump will usually be beneficial.

[0085] The disclosed embodiments in this description are directed to addressing at least one of the issues as set out above or to providing an alternative system or method for exhaust gas after treatment.

[0086] While the preceding text sets forth a detailed description of the embodiments of the present disclosure, it should be understood that the scope of protection is defined by the words of the appended claims. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented which would still fall within the scope of the claims defining the scope of protection. Any features of any claim may be combined with any features of any other claim.

Claims

24-0542W00113CLAIMS1. An after-treatment system for use with an engine, the engine having an exhaust conduit, the exhaust conduit being configured to route exhaust from the engine during operation of the engine, the after-treatment system being configured to connect to the exhaust conduit and to receive and treat a flow of exhaust from the engine, the after- treatment system comprising: an after-treatment device for treating received exhaust; a conduit for connecting an outlet of the after-treatment device to a point ahead of an inlet of the after-treatment device along the exhaust conduit; and a pump to pump at least part of the emissions from the outlet of the after-treatment device to the point ahead of the inlet of the after-treatment device.

2. The after-treatment system of claim 1, wherein the after-treatment device includes at least one of a low temperature selective catalytic reduction, Lo-SCR, device, a selective catalytic reduction, SCR, device, a diesel oxidation catalyst, DOC, and a diesel particulate filter, DPF.

3. The after-treatment system of any preceding claim, wherein the system further comprises a first diesel exhaust fluid, DEF, mixer positioned between the engine and the after-treatment device.

4. The after-treatment system of claim 3, wherein the point to which the conduit connects is ahead of an inlet of a diesel exhaust fluid, DEF, mixer.

5. The after-treatment system of any preceding claim, wherein the system further comprises a second DEF mixer positioned after the outlet of the after-treatment device.24-0542W001146. The after-treatment system of any preceding claim, wherein the system further comprises a selective catalytic reduction, SCR, device positioned after the outlet of the after-treatment device.

7. The after-treatment system of any preceding claim, wherein the system further comprises an outlet ammonia oxidation, AMOX, device.

8. The after-treatment system of any preceding claim, further comprising a control device to control the pump.

9. The after-treatment system of claim 8, wherein the control device is configured to control the pump, based on a temperature of the emissions and / or the after- treatment device.

10. The after-treatment system of claim 8 or 9, wherein the after-treatment device comprises a DEF Mixer and the control device is configured to control the pump, based on a pressure at the point ahead of the inlet of the after-treatment device.

11. The after-treatment system of and of claims 8 to 10, wherein the after- treatment device comprises a Lo-SCR device and the control device is configured to control the pump, based on a detected level of one or more of NO2, NOXand ammonia in the emissions from the after-treatment device and / or in the exhaust from the engine.

12. The after-treatment system of any of claims 8 to 11, wherein the after- treatment device is a DOC device and the control device is configured to control the pump, based on a temperature of the emissions and / or the after-treatment device.

13. A method for treating emissions from an internal combustion engine comprising:24-0542W00115 passing exhaust from the internal combustion engine through an after-treatment device; recirculating at least part of the emissions from an outlet of the after-treatment device to a point ahead of an inlet of the after-treatment device; and passing the recirculated emissions through the after-treatment device.

14. The method for treating emissions from an internal combustion engine of claim 13, further comprising: controlling an amount of the emissions being recirculated based on at least one of temperature, pressure and composition of the emissions.

15. The method for treating emissions from an internal combustion engine of claim 13 or claim 14, further comprising: controlling a temperature of the after-treatment device by adjusting an amount of the emissions which are recirculated.

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