Claims:We Claim:
1. A selective catalytic reduction (SCR) system (10) in a vehicle (11), said SCR system (10) comprising:
- a first SCR unit (12) positioned in an exhaust path (13);
- a second SCR unit (14) placed in parallel to said first SCR unit (12);
- a temperature sensor (16) positioned upstream said first SCR unit (12) in said exhaust path (13);
characterized in that:
- at least one valve (15) placed upstream said first SCR unit (12) and said second SCR unit (14), such that, said at least one valve (15) is operated based on an input from said temperature sensor (16).

2. The SCR system (10) as claimed in claim 1, a control unit (20) adapted to operated said at least one valve (15) and any one of the SCR units comprising said first SCR unit (12) and said second SCR unit (14), based on a comparison result between said input received from said temperature sensor (16) and a predefined temperature.

3. The SCR system (10) as claimed in claim 3, wherein said control unit (20) operates said at least one valve (15) and said second SCR unit (14) ,when said input from temperature sensor is more than said predefined temperature.

4. The SCR system (10) as claimed in claim 1, wherein said first SCR unit (12) comprises vanadium compounds and said second SCR unit (14) comprises zeolite compounds.

5. The SCR system (10) as claimed in claim 1, wherein said second SCR unit (12) is a cylindrical structure with iron zeolite coating.

6. The SCR system (10) as claimed in claim 1, wherein said first SCR unit (12) and the second SCR unit (14) comprises a catalyst each, arranged in the form of a coating on an inert support.

7. The SCR system (10) as claimed in claim 1, wherein at least one dosing module (18) is placed in proximity to said temperature sensor (16) in said exhaust path (13).

8. The SCR system (10) as claimed in claim 1, wherein said predefined temperature is a temperature range calibrated, when said vehicle (11) is operating in at least one vehicle conditions comprising a low-load condition and a high-load condition.

9. The SCR system (10) as claimed in claim 1, wherein said at least one valve (15), said temperature sensor (16) and said at least one dosing module (18) are electronically controlled.
, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001] This invention relates to the field of selective catalytic reduction (SCR) system in a vehicle.

Background of the invention
[0002] vanadium SCR technology offers a low cost, robust and promising solution to meet legislative targets for non-road emission legislation like CEV stage IV and CPCB4+. We have a defined SCR system, which will use predominantly Vanadium SCR for meeting NOx conversion targets. When the temperature is a temperature range of 250-500 degrees. Unfortunately, high performance of vanadium catalyst is limited at temperature less than 250 0C.Due to low power density engines in India, engine out temperatures are on the lower side and it becomes difficult to meet performance targets with vanadium catalyst.

[0003] A Prior art document US7998423 discloses a selective catalytic reduction (SCR) filters that effectively provide simultaneous treatment of particulate matter and NOx. The SCR filter can include a fiber matrix wall flow filter comprising a plurality of non-woven inorganic fibers and a chabazite molecular sieve SCR catalyst on the fiber matrix wall flow filter. By combining a fiber matrix wall flow filter with a chabazite molecular sieve SCR catalyst, high catalyst loading can be achieved without causing excessive back pressure across the filter when implemented in emission treatment systems.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0005] Fig.1 illustrates a selective catalytic reduction (SCR) system in a vehicle in accordance with one embodiment of the invention;
[0006] Fig.2 illustrates a selective catalytic reduction (SCR) system in a vehicle in accordance with one embodiment of the invention; and
[0007] Fig. 3 illustrates a selective catalytic reduction (SCR) system in a vehicle in accordance with one embodiment of the invention.

Detailed description of the embodiments
[0008] Fig.1 illustrates a selective catalytic reduction (SCR) system in a vehicle, in accordance with one embodiment of the invention. The SCR system 10 comprises a first SCR unit 12 positioned in an exhaust path 13 and a second SCR unit 14 placed in parallel to the first SCR unit 12. The SCR system 10 comprises a temperature sensor 16 positioned upstream to the first SCR unit 12 in the exhaust path 13. Characterized in that, at least one valve 15 placed upstream to the first SCR unit 12 and the second SCR unit 14 , such that, at least one valve 15 is operated based on an input from the temperature sensor 16.

[0009] Further, the construction of the SCR system 10 and the components of the SCR system 10 and their working are explained below. The vehicle 11 comprises an engine 22 connected to a diesel oxidation catalyst (DOC) 24 positioned in the exhaust path 13 in the vehicle 11. The DOC 24 is used to convert the exhaust gas emitting from the engine 22 during the working of the vehicle 11. The working of the DOC 24 and the engine 22 is well known in the state of the art, so hereby, the working and the construction of the engine 22 and the DOC 24 is not explained in the present document. The first SCR unit 12 and the second SCR unit 14 comprises a catalyst each, arranged in the form of a coating on an inert support (not shown). The first SCR unit 12 comprises vanadium compounds and the second SCR unit 14 comprises zeolite compounds. The catalyst composition is selected from the group consisting of the oxides of vanadium, iron and copper. At least one valve 15 is a two way valve operated electronically. A person skilled in the art knows the working of the two-way valve.

[0010] The first SCR unit 14 catalyst has a coating of vanadium compounds. According to one embodiment of the invention, the second SCR unit 12 is a cylindrical structure with iron zeolite coating. For instance, on an inert ceramic honeycomb, the coating containing the second SCR unit 12 catalyst is applied up along the length of the inert support by a conventional dipping process as known to a person skilled in the art.

[0011] The SCR system 10 comprises a control unit 20 adapted to operate the at least one valve 15 and any one of the SCR units comprising the first SCR unit 12 and the second SCR unit 14, based on a comparison result between the input received from the temperature sensor 16 and a predefined temperature. The predefined temperature is a temperature range calibrated, when the vehicle 11 is operating in at least one-vehicle conditions comprising a low-load condition, a normal load and a high-load condition. During, the low-load condition, the temperature of the exhaust gas in the exhaust path 13 ranges from 180degrees-250 degrees and in the normal load conditions, the temperature of the exhaust gas ranges from 250 degrees-500 degrees. During the later temperature range (250degrees-500 degrees), the first SCR unit 12 is operated.

[0012] During the high load conditions, where the temperatures in the exhaust path 13 exceeds beyond 500 degrees, then the second SCR unit 14 is operated. The different temperature ranges are stored in the control unit 20 of the system 10. According to one embodiment of the present invention, the predefined temperature is 500 degrees. If the input from the temperature sensor 16 is less than 500 degrees, the first SCR unit 12 is operated and if the input from the temperature sensor 16 is more than 500 degrees, the second SCR unit 14 is operated.

[0013]A bypass path 26 is made to the existing exhaust path 13, where the second SCR unit 14 is placed in parallel to the first SCR unit. At the junction of the existing exhaust path 13 and the bypass path 26, at least one valve 15 is placed, such that, either one of the SCR units (12, 14) is operated by opening or closing the at least one valve 15.

[0014] Fig.2 illustrates a selective catalytic reduction (SCR) system in a vehicle in accordance with one embodiment of the invention. According to one embodiment of the invention, two valves (a first valve 15 and a second valve 15) are used each on the existing exhaust path 13 and on the bypass path 26 to control the flow of the exhaust gas reaching the first SCR unit 12 and the second SCR unit 14 respectively. The control unit 20 upon receiving the detected temperature input from the temperature sensor less than the predefined value, operates the first valve 15 (that is located on the existing exhaust path 13) to direct the flow of the exhaust gas through the first SCR unit 12. When the detected temperature in the exhaust path is more than the predefined temperature, then the control unit 20 operates the second valve 15 (that is located on the bypass path 26) to direct the exhaust gas through the second SCR unit 14.

[0015]The SCR system 10 further comprises at least one dosing module 18 positioned in proximity to the temperature sensor 16. The at least one dosing module 18 is electronically controlled by the control unit 20. During the normal operating conditions of the vehicle 11, the temperature sensor 16 detects the temperature of the exhaust gas and transmits a signal to the control unit 20. The control unit 20 upon detecting the temperature received, activates the at least one dosing module 18 in the system 10.

[0016]If the system is using a double dosing technique with two dosing modules, a first dosing module 18 (a) and a second dosing module 18(b), the first dosing module 18 (a) is placed in the existing exhaust path 13 and the second dosing module 18(b) is placed in the bypass exhaust path 26. When the control unit 20 detects a temperature less than 500 degrees (predefined temperature), activates the first dosing module 18(a). The ammonia mixed in the exhaust gas passes through the first SCR unit 12 and the exhaust gas undergoes the conversion process. The exhaust gas having the temperature less than the 500 degrees is efficiently converted into the non-harmful gases in the first SCR unit 12 due to the vanadium coating on the honeycomb like structure.

[0017]Wherein, when the temperature of the exhaust gas is more than the predefined temperature i.e., more than 500 degrees, the control unit 20 activates the second dosing module 18(b) and the dosed exhaust gas is directed into the bypass exhaust path 26 by opening the at least one valve 15.

[0018]Fig.3 illustrates a selective catalytic reduction (SCR) system in a vehicle in accordance with one embodiment of the invention. The first SCR unit 12 and the second SCR unit 14 are placed in series in the exhaust path 13. The first SCR unit 12 is designed to operate in one predefined temperature range and the second SCR unit 14 is designed to operate in another predefined temperature range. For instance, the first SCR unit 12 is operated in temperature range from 250degrees- 500 degrees, wherein the second SCR unit 14 is operated in the temperature range above 500 degrees. If the temperature of the exhaust gas is more than the predefined temperature, the first SCR unit 12 cannot convert the exhaust gas into non-harmful gases. When the exhaust gas enters the second SCR unit 14 from the first SCR unit 12, the conversion process is improved due to the iron zeolite coating present in the second SCR unit 14.

[0019]With the above system and the method, the conversion process of the exhaust gas into the non-harmful gases will be efficient. The system 10 provides a simple, cost-effective solution as the use of exclusively zeolite-based SCR catalyst systems is very expensive, because of the high raw material prices for zeolites. The usage of the iron zeolite not only helps in oxidizing the nitrogen oxides during the conversion process, but also helps in storing the ammonia during the cold-start.

[0020]The dosing of the ammonia upstream first SCR unit 12 at lower quantities of Diesel effluent fluid (DEF) (as it is expected to operate at low load conditions), and the dosing of the ammonia upstream second SCR unit 14 during higher DEF quantities helps in increasing field robustness of exhaust path as double dosing would reduce the risk of crystallization/deposits. The emission compliance is efficiently achieved for low temperature and for high temperature operating conditions by the above-disclosed system 10.

[0018] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.