Exhaust gas aftertreatment system

Abstract

The present invention shows an exhaust gas aftertreatment system comprising at least a first route and a second route arranged in parallel in an exhaust gas stream, wherein the first route and the second route are provided with exhaust gas aftertreatment subsystems. The exhaust gas aftertreatment subsystems of the first route and the second route use different exhaust gas aftertreatment technologies.

Claims

1. An exhaust gas aftertreatment system comprising at least a first route and a second route arranged in parallel in an exhaust gas stream, wherein the first route and the second route are provided with exhaust gas aftertreatment subsystems, wherein a piping of the first route has a larger sectional area than a piping of the second route, the exhaust gas aftertreatment subsystems of the first route and the second route use different exhaust gas aftertreatment technologies, the first route is provided with a SCR catalyst and the second route is provided with a diesel oxidation catalyst, and the first route is not provided with a diesel oxidation catalyst and the second route is not provided with a SCR catalyst, and further wherein the exhaust gas aftertreatment system further comprises a first valve or flap for controlling the exhaust gas stream through the first route, wherein the first valve or flap is arranged downstream of the exhaust gas aftertreatment subsystem of the first route, and the exhaust gas aftertreatment system further comprises a second valve or flap for controlling the exhaust gas stream through the second route, wherein the second valve or flap is arranged downstream of the exhaust gas aftertreatment subsystem of the second route.

2. The exhaust gas aftertreatment system according to claim 1, wherein a volume of the exhaust gas aftertreatment subsystem of the first route is bigger than a volume of the exhaust gas aftertreatment subsystem of the second route.

3. The exhaust gas aftertreatment system according to claim 2, wherein the volume of the exhaust gas aftertreatment subsystem of the second route is between 5% to 15% of the volume of the exhaust gas aftertreatment subsystem of the first route.

4. The exhaust gas aftertreatment system of claim 1, wherein the first route is provided with at least one out of a first valve and a first flap and the second route is provided with at least one out of a second valve and a second flap, wherein the at least one out of the first valve and the first flap and the at least one out of the second valve and the second flap are each operable to selectively open and close a respective route.

5. The exhaust gas aftertreatment system according to claim 4, wherein the at least one out of the first valve and the first flap is naturally open and wherein the at least one out of the second valve and the second flap is naturally closed.

6. The exhaust gas aftertreatment system according to claim 1, wherein the second route bypasses a turbocharger arranged in the exhaust gas stream.

7. The exhaust gas aftertreatment system according to claim 6, wherein the second route is mounted upstream of the turbocharger.

8. The exhaust gas aftertreatment system according to claim 1, further comprising a plurality of first routes, each provided with an exhaust gas aftertreatment subsystem and arranged in parallel in the exhaust gas stream.

9. The exhaust gas aftertreatment system according to claim 8, wherein the plurality of first routes is combined with a single second route.

10. The exhaust gas aftertreatment system according to claim 1, further comprising a controller to selectively control exhaust gas flow through the first and/or second route, wherein the controller is configured to direct the exhaust gas flow through the first route during a first engine operation condition and to direct the exhaust gas flow through the second route during a second engine operation condition.

11. The exhaust gas aftertreatment system according to claim 10, wherein in the first engine operation condition, at least one out of a load and an exhaust gas temperature of the engine is higher than in the second engine operation condition.

12. The exhaust gas aftertreatment system according to claim 10, wherein the second route is configured to bypass the first route when the controller is configured to direct the exhaust gas flow through the second route during the second engine operation condition.

13. The exhaust gas aftertreatment system according to claim 12, wherein the second engine operation condition includes the engine running at idle.

14. The exhaust gas aftertreatment system according to claim 12, wherein HC emissions are reduced as a result of the bypass.

15. The exhaust gas aftertreatment system according to claim 12, wherein the bypass is used during motoring time to avoid the SCR catalyst cooling.

16. An engine comprising an exhaust gas aftertreatment system according to claim 1.

17. A machine comprising the engine according to claim 16.

18. The machine of claim 17, wherein the machine is a mobile working machine configured to be operated electrically during at least one operation phase, wherein the engine is running in idle mode during the at least one operation phase.

19. The exhaust gas aftertreatment system according to claim 1, wherein the SCR catalyst uses urea injection and wherein the diesel oxidation catalyst is electrically heated.

20. The exhaust gas aftertreatment system according to claim 1, wherein a sectional area of the piping of the second route is between 10% to 30% of a sectional area of the piping of the first route.

21. The exhaust gas aftertreatment system according to claim 1, wherein a volume of the SCR catalyst is bigger than a volume of the diesel oxidation catalyst.

22. The exhaust gas aftertreatment system according to claim 1, wherein a volume of the diesel oxidation catalyst is between 5% to 15% of a volume of the SCR catalyst.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In the drawings:

(2) FIG. 1 shows a first embodiment according to the present invention,

(3) FIG. 2 shows a second embodiment according to the present invention using a plurality of first routes,

(4) FIG. 3 shows a third embodiment according to the present invention using a plurality of first routes connected upstream to a common exhaust gas manifold,

(5) FIG. 4 shows a first operation state of the first embodiment according to the present invention,

(6) FIG. 5 shows a second operation state of the first embodiment according to the present invention, and

(7) FIG. 6 shows a prior art exhaust gas aftertreatment system.

DETAILED DESCRIPTION

(8) The embodiment of the present invention shown in FIG. 1 shows an exhaust gas aftertreatment system (2) comprising at least a first route (2a) and a second route (2b) arranged in parallel in the exhaust gas stream.

(9) The first route (2a) is provided with a first aftertreatment subsystem (3) and the second route (2b) with a second exhaust gas aftertreatment subsystem (4). The first exhaust gas aftertreatment subsystem (3) of the first route (2a) and the second exhaust gas aftertreatment subsystem (4) of the second route (2b) use different exhaust gas aftertreatment technologies.

(10) Further, flaps and/or valves (5, 6) are provided to selectively direct the exhaust gas stream through the first route (2a) and the second route (2b). The flaps and/or valves (5, 6) are controlled by a controller (10). The controller may comprise a microprocessor and code stored in memory for controlling the flaps and/or valves (5, 6). The controller may further be connected to sensors or receive inputs from an engine controller.

(11) In the embodiment, the first aftertreatment subsystem (3) is an SCR catalyst, and the second aftertreatment subsystem (4) is a Diesel oxidation catalyst. The SCR catalyst may in particular be a Vanadium based SCR. The details described with respect to the embodiments can however also be used with other types of catalysts.

(12) The present invention aims at diverting the exhaust gas away from the SCR catalyst (3) when the engine is running at idle by closing one or several valves and opening one valve. The goal is to avoid having hydrocarbons (HC) emitted from the engine to be adsorbed on the SCR catalyst (3) and damaged it by either coking or thermal decomposition leading to the substrate damage. Further, in the embodiment, a heater or a heated catalyst (4) is used when the main aftertreatment subsystem comprising a SCR catalyst (3) is bypassed.

(13) In standard exhaust systems such as shown in FIG. 6 the diesel oxidation catalyst (DOC) is mounted upstream of the SCR system. In such a configuration, the DOC has to be large enough to avoid having high pressure drop at engine full load. In such a layout, the large DOC is very expensive because of the material and the precious metal needed to manufacture it.

(14) The invention represented on the FIG. 1 is designed to treat the exhaust gases (1) from an internal combustion engine using a modular exhaust gas aftertreatment system (2). The modular exhaust gas aftertreatment system (2) comprises two exhaust routes:

(15) A main route (2a) with large diameter piping which is optimized to have a low exhaust pressure drop for all the engine operating conditions. This exhaust piping is composed of an SCR system (3) which aims at reducing the NOx emissions using an ammonia precursor injecting in front of a SCR catalyst and/or filter. It may further have an ammonia clean up catalyst. Further, an exhaust valve/flap (5) is provided;

(16) A secondary route (2b) with lower pipe diameter than the main route (2b) piping. The exhaust piping is designed for low engine load operation, hence low exhaust volume flow. On this piping is fitted an electrically heated diesel oxidation catalyst (4) and an exhaust valve/flap (6). The electrical heater can be either part of the diesel oxidation substrate or mounted in front of the diesel oxidation catalyst.

(17) The exhaust valves/flaps can be either mounted downstream or upstream of the SCR catalyst (3) and the diesel oxidation catalyst (4). However, due to possible exhaust leakage and/or high temperature, the preferred location is downstream of the SCR catalyst (3) and the diesel oxidation catalyst (4).

(18) The valve/flap (5) located downstream the SCR system (3) would be preferably a naturally open valve/flap and the valve/flap (6) located downstream the DOC (4) would be preferably a naturally closed valve/flap in order to still be able to use the engine if the control function of the valve is damaged.

(19) In this invention, the diesel oxidation catalyst (4) internal volume is preferably only of 5 to 15% of the SCR catalyst internal volume of the SCR system (3) located on the main route (2a). The exhaust pipe section of the secondary route (2b) is preferably 10 to 30% of the one of the main route (2a).

(20) The invention can be applied to a single exhaust piping as shown on FIG. 1 or on multiple exhaust pipings where the pipings are independent (FIG. 2) or attached to an exhaust collector (FIG. 3).

(21) In FIGS. 2 and 3, the main route (2a) is divided into a plurality of parallel exhaust gas pipings (21a) to (23a) each being provided with a separate SCR catalyst (31) to (33) and a separate valve/flap (51) to (53).

(22) In contrast, there is only a single secondary route (2b) provided with a DOC (4) and a valve/flap (6).

(23) In FIG. 2, the single secondary route (2b) provided with a DOC (4) and a valve/flap (6) is connected via separate pipings (21b) to (23b) to the parallel exhaust gas pipings (21a) to (23a) of the main route (2a).

(24) In FIG. 3, the secondary route (2b) and the parallel exhaust gas pipings (21a) to (23a) of the main route (2a) are connected on a downstream side to an exhaust collector (7).

(25) In FIG. 1, the exhaust bypass, secondary route (2b) can be mounted upstream of a turbocharger 15 and thus the turbocharger 15 may be bypassed when the SCR system (3) is bypassed.

(26) The way the exhaust gas aftertreament system (2) is operated by the controller (10) is described by the FIGS. 4 and 5:

(27) At normal operation, described by the FIG. 4, where the temperature allows DEF to be injected in front of the SCR catalyst and the NOx to be reduced, the valve/flap (5) on the main route (2a) is open and the valve/flap (6) on the secondary route (2b) is closed. Here the electrical heater of the diesel oxidation (4) is switched OFF.

(28) At low load and particularly at engine idle, described by the FIG. 5, where the temperature is too low to allow DEF to be injected in front of the SCR catalyst, the valve/flap (5) on the main route (2a) is closed and the valve/flap (6) on the secondary route (2b) is open. Here the electrical heater of the diesel oxidation catalyst (4) is switched ON to reduce the engine emissions such as CO, HC and the particulate matter.

(29) A third possibility would be to use the invention during motoring phases. The valves would be set in the same position than the ones during idle as described by the FIG. 5 but the heater would be switched OFF.

(30) The exhaust has aftertreatment system of the present invention could be used on mobile working machines such as mining trucks.

(31) The mobile working machine may in particular have a trolley system and/or not have a grid box that could be used to increase the engine load at idle. More and more mining trucks are equipped with trolley system and for those trucks, the engine stays at idle when going uphill.

(32) Other applications, especially those using vanadium SCR systems and emitting a large quantity of HC at idle, may equally use the exhaust has aftertreatment system of the invention, especially if they do not have the possibility to increase the exhaust temperature at idle.

(33) Possible applications are mining/construction vehicles, electric generators, ships, etc.