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
The present disclosure relates to controller to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system and a method thereof

[0001] Background of the invention
[0002] Selective Catalyst Reduction (SCR) systems use a catalyst to treat the exhaust gas in exhaust gas treatment systems of vehicle. A diesel exhaust fluid (DEF) is used which acts a precursor to ammonia. Normally, NH3 is generated by the pyrolysis process of urea and urea is introduced into the exhaust system by the injection of urea-water-solution (herein referred to as Diesel exhaust fluid). When DEF (urea water solution) is injected into the SCR system, water evaporates and pure urea comes in contact with the hot exhaust gas, leading to the formation of Ammonia. This ammonia reacts with nitrous oxides (NOx) in the exhaust gas to reduce it into nitrogen and water. Fast evaporation of water and the high mixing quality of NH3 could contribute to the high conversion rate of NOx in an SCR system. However at low load conditions with low exhaust gas temperatures and low mass flow rates, increased amount of urea deposits(DEF deposits) are formed, reducing the active sites of the catalyst required for the reduction reaction to proceed. The deposits can form on the mixer (used to mix the DEF/urea with the incoming exhaust gas), urea injector tip, pipe walls and as well as on an inlet face of a selective catalytic reduction unit (SCR).This urea/DEF crystallization leads to a wrong learning of amount of DEF to be injected into the SCR system, reduced performance of SCR catalyst, incorrect dosing quantity calculation, choking of urea injector, increase in back pressure of the exhaust line, accelerated corrosion of exhaust line, mis detection of catalyst efficiency monitors and an event of ammonia slip where unreacted ammonia from the DEF slips through the SCR system and enters the atmosphere. The proposed solution improves the robustness of DEF injection to minimize the ammonia slippage and prevent crystallization by improving a dosage volume of DEF into the SCR.
[0003] The prior art CN112943420A proposes a strategy for correcting urea injection quantity to prevent urea crystallization, relates to the technical field of tail gas aftertreatment, and solves the technical problem that the existing scheme aggravates urea crystallization, and the strategy comprises the following steps: calibrating urea crystallization rates under different urea injection quantities according to the exhaust temperature and the exhaust flow to obtain a urea crystallization rate MAP; calculating to obtain the maximum urea injection amount under each working condition according to the urea crystallization rate MAP and the urea crystallization rate smaller than 0.5 g/h; calibrating the maximum urea injection quantity under each working condition to a urea injection limit MAP; calculating to obtain required urea injection quantity according to the actual exhaust flow, the actual exhaust temperature and the actual nitrogen oxide concentration when the engine actually runs; inquiring the urea injection limit MAP according to the actual exhaust flow and the actual exhaust temperature to obtain the urea injection limit quantity; and comparing the required urea injection quantity with the urea injection limiting quantity, taking a small value as an actual urea injection quantity, and controlling the SCR system to work according to the actual urea injection quantity.
[0004] In the prior arts, the SCR systems control the amount of DEF injected into the SCR system through open-loop control system and Closed loop feedback systems. However, the properties and operating capacity of the mixer is not taken into the account. The proposed logic limits the dosing amount independent from the current open loop and closed loop quantity. Hence the crystal formation is reduced to the greatest possible extent.

Brief description of the accompanying drawings
An embodiment of the invention is described with reference to the following accompanying drawings:
[0005] Figure 1 depicts a controller to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system.
[0006] Figure 2 depicts a flow chart for a method to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system.

[0007] Detailed description of the drawings

[0008] The present invention will now be described by way of example, with reference to accompanying drawings. Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations, and fragmentary views. In predetermined instances, details which are not necessary for an understanding of the present invention, or which render other details difficult to perceive may have been omitted. It is to be understood that interrelated properties may be interchangeable. For instance, use of the term ‘volume’ may be interchangeable with the term ‘mass’.

[0009] Referring to figure 1, the same depicts a controller (1) to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system. The SCR system (10) comprises a mixer (5) to mix the DEF injected with an exhaust air flowing into the SCR system (10). The SCR system (10) includes a doser (16) and an SCR catalyst component. The doser (16) is in fluid communication with a DEF source, and is controllable by the controller (1). The controller (1) may be a computer system with an associated memory and an embedded software programmed to receive signals from plurality of sensors and to provide control signals to flow control valves of the doser (16). The DEF may contain a reductant such as, for example, ammonia (NH3), urea, and/or a hydrocarbon, that is supplied for injection by the doser (16) into the exhaust stream at a position upstream of a SCR. The SCR catalyst at least assists in the reductant reacting with NOx in the exhaust gas to reduce the amount of NOx in the exhaust stream.

[0010] The SCR includes at least one engine-out NOx sensor (13) that is used in detecting a NOx level in an exhaust stream upstream of the SCR system (10). Further, according to the illustrated embodiment, the engine-out NOx sensor (13) may provide a signal for the controller (1) that indicates, and/or is used in determining, a level of NOx in the exhaust gas at a location upstream of the doser (16). Alternatively, the quantity of engine-out NOx may be modeled, calculated from an engine operation map, and/or measured from a location that is different than the location of the engine-out NOx sensors.

[0011] The SCR system (10) may also include at least one system-out NOx sensor (14) that is positioned downstream of the SCR catalyst component. The system-out NOx sensor (14) may be used in determining the quantity of NOx that is being released from the SCR system (10). Further, the SCR system (10) may include additional NOx sensors positioned at other locations throughout the SCR system (10) that provide information that indicates, or otherwise is used to determine, NOx levels in the exhaust air.

[0012] The SCR system (10) may also include at least one temperature sensor (15) that is in communication with the controller (1). According to certain embodiments, the temperature sensor (15) can be used to determine a temperature of the SCR catalyst. According to certain embodiments, the temperature sensor (15) is positioned within the SCR catalyst component. Alternatively, the temperature sensor (15) is positioned upstream and/or downstream of the SCR catalyst in the SCR system (10). Further, the temperature of the SCR catalyst component may be determined in a variety of different manners, including, for example, at least by utilizing a weighted average of temperature sensors that are positioned upstream and downstream of the SCR catalyst component, or modeling and/or estimating the temperature of the SCR catalyst component based upon other temperature measurements available in the engine system, and more specifically, within the SCR system (10). Further, the at least one temperature may also be used to determine the temperature of exhaust air flowing into the SCR system (10). Further an air flow sensor may be present in communication with the controller (1), in the SCR system (10) to measure a mass or a flow rate of the exhaust air in the SCR system (10) and a volume of the SCR catalyst.

[0013] Said controller (1) comprises a dosage governor (2) adapted to obtain a volume of the DEF to be injected into the SCR system (10) and a feed back unit (3) adapted to obtain a corrected volume (12) of the DEF to be injected into the SCR system (10).

[0014] Said controller (1) further comprises a dosage limiter (4) adapted to maintain the corrected volume (12) to be injected into the SCR system (10) within a threshold volume range (11), said threshold volume range (11) obtained based on an operating capacity of the mixer.

[0015] Said controller (1) comprising the dosage governor (2) is adapted to detect a set of operating conditions (6) of the SCR system (10) for a pre-defined time and obtain the volume of the DEF to be injected into the SCR based on said set of operating conditions (6). The set of operating conditions (6) comprises at least a temperature of the SCR system (10), a mass of an exhaust air flowing into the SCR system (10) and a volume of nitrous oxides (NOx) in the exhaust air. The volume of nitrous oxides (NOx) comprises the first volume of NOx in in the exhaust air flowing into the SCR system (10) and a second volume of NOx in the exhaust air flowing out of the SCR system (10). Said set of operating conditions (6) may be measured by the at least one temperature sensor (15), the air flow sensor and the at least one NOx sensor comprising the engine-out NOx sensor (13) and the system-out NOx sensor (14)as explained above. The present disclosure as explained above performs an open loop SCR control with the dosage governor (2) wherein the amount of urea to be injected is computed based on the set of operating conditions (6) using look up tables.

[0016] The controller (1) comprising the feed back unit (3) obtains the corrected volume (12) based on a deviation between the obtained volume of DEF injected into the SCR system (10) and an actual volume of DEF reacting with the exhaust air flowing into the SCR. The feed back unit (3) provides a closed-loop control of the SCR system (10) over an open-loop SCR control as explained above . The feed back unit (3) obtains a corrected volume (12) of the DEF to be injected into the SCR system (10). The feed back unit (3) obtains said corrected volume (12) based on the deviation between the volume of DEF injected into the SCR system (10) and the actual volume of DEF reacting with the exhaust air in real time. The feed back unit (3) obtains the actual volume of DEF reacting with the exhaust air based on the second volume of NOx in the exhaust air flowing out of the SCR system (10).

[0017] The feed back unit (3) obtains the corrected volume (12) to obtain an ideal conversion efficiency (proportion of NOx reacting with ammonia). The controller (1) further regulates the injection of DEF into the SCR system (10) based on said corrected volume (12). Assuming that the volume to be injected obtained by the dosage governor is X unit and that the corrected volume is Y units it is to be understood X may be less than Y or Y may be less than X.

[0018] The controller (1) comprises a dosage limiter (4) adapted to maintain the corrected volume (12) to be injected into the SCR system (10) within a threshold volume range (11), said threshold volume range (11) obtained based on an operating capacity of the mixer. The operating capacity of the mixer (5) is obtained by the dosage limiter (4) based on a mass of the exhaust air flowing into the SCR system (10) and a temperature of the SCR system (10). The dosage limiter (4) limits the dosing amount independent from the open loop and closed loop quantity as obtained by the dosage governor (2) and corrected by the feed back unit (3) respectively.
[0019] According to the present invention, the dosage limiter (4) obtains a Load Index which represents a maximum dosing amount of the DEF that is digestible by the mixer.
[0020] In an example, the load index determines how challenging an engine operating point is with respect to deposit formation. Assuming ? is a DEF dosing rate [kg/h] and ? is exhaust mass flow [kg/h]. Further assuming hvap is a vaporization enthalpy of DEF [the same is a standard value of ~ 2350 kJ/kg (including heat capacity for the liquid and gas phase)] , cp is heat capacity of exhaust gas (standard value of ~ 1.07 kJ/(kg·K)) and T is exhaust temperature [°C] and Tmin is lowest temperature for vaporization (at an experimental value of ~ 160°C), the load index L may be obtained using the following formula:

L= ?. hvap = ?. 2200 [°C ]
? .cp (T- Tmin ) ? . (T- 160°C)

[0021] In an example, for a mixer (5) type of MS GEN 3 EVO without bypass a limit of L = 4% has been determined through experiment. The highest AdBlue dosing rates ? are possible for high exhaust temperatures and high exhaust mass flows, whereas the maximum NOx concentration, that can be reduced, depends only on the exhaust temperature. Therefore, the Dosage limiter (4) can limit a maximum DEF loading rate based on this load index value (L). This limitation can be done over the open loop and closed loop values by the dosage governor (2) and feed back unit (3).

[0022] Referring to Figure 2, the same depicts a flowchart for a method to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system, said SCR system (10) comprises a mixer (5)to mix the DEF injected with an exhaust air flowing into the SCR system (10). The method comprises the first step (101) of obtaining a volume of the DEF to be injected into the SCR system (10) by a dosage governor (2) followed by the step (102) of obtaining a corrected volume (12) of the DEF to be injected into the SCR system (10) by a feed back unit (3). The next step (103) is maintaining, by a dosage limiter (4), the corrected volume (12) to be injected into the SCR system (10) within a threshold volume range (11), said threshold volume range (11) obtained based on an operating capacity of the mixer. The operating capacity of the mixer (5) by the dosage limiter (4) is obtained based on a mass of the exhaust air flowing into the SCR system (10) and a temperature of the SCR system (10).
[0023] The volume of the DEF to be injected into the SCR system (10) on a set of operating conditions (6) of the SCR system (10) comprising the temperature of the SCR system (10), the mass of an exhaust air flowing into the SCR system (10), a volume of nitrous oxides (NOx) in the exhaust air comprising a first volume of NOx in in the exhaust air flowing into the SCR system (10) and a second volume of NOx in the exhaust air flowing out of the SCR system (10). The feed back unit (3) obtains the corrected volume (12) based on a deviation between the obtained volume of DEF injected into the SCR system (10) and an actual volume of DEF reacting with the exhaust air flowing into the SCR.

, Claims:We Claim:

1. A controller (1) to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system, said SCR system (10) comprising a mixer (5)to mix the DEF injected with an exhaust air flowing into the SCR system (10), said controller (1) comprising:

-a dosage governor (2) adapted to obtain a volume of the DEF to be injected into the SCR system (10);
-a feed back unit (3) adapted to obtain a corrected volume (12) of the DEF to be injected into the SCR system (10);
characterized in that,
-a dosage limiter (4) adapted to maintain the corrected volume (12) to be injected into the SCR system (10) within a threshold volume range (11), said threshold volume range (11) obtained based on an operating capacity of the mixer.

2. The controller (1) as claimed in Claim 1, wherein, the operating capacity of the mixer (5) is obtained by the dosage limiter (4) based on a mass of the exhaust air flowing into the SCR system (10) and a temperature of the SCR system (10).

3. The controller (1) as claimed in Claim 1, wherein, the volume(X) of the DEF to be injected into the SCR system (10) is obtained based on a set of operating conditions (6) of the SCR system (10) comprising:
-the temperature of the SCR system (10),
- the mass of an exhaust air flowing into the SCR system (10), and
- a volume of nitrous oxides (NOx) in the exhaust air comprising a first volume of NOx in in the exhaust air flowing into the SCR system (10) and a second volume of NOx in the exhaust air flowing out of the SCR system (10).

4. The controller (1) as claimed in Claim 1, wherein the feed back unit (3) obtains the corrected volume (12) based on a deviation between the obtained volume of DEF injected into the SCR system (10) and an actual volume of DEF reacting with the exhaust air flowing into the SCR.

5. The controller (1) as claimed in Claim 4, wherein, the actual volume of DEF reacting with the exhaust air is obtained based on the second volume of NOx in the exhaust air flowing out of the SCR system (10).

6. A method (100) to maintain a volume of a diesel exhaust fluid (DEF) injected into a selective catalytic reduction (SCR) system, said SCR system (10) comprising a mixer (5)to mix the DEF injected with an exhaust air flowing into the SCR system (10),

method comprises the steps of:

- obtaining a volume of the DEF to be injected into the SCR system (10) by a dosage governor (101);
- obtaining a corrected volume (12) of the DEF to be injected into the SCR system (10) by a feed back unit (102);

characterized in that,
- maintaining, by a dosage limiter (4), the corrected volume (12) to be injected into the SCR system (10) within a threshold volume range (11), said threshold volume range (11) obtained based on an operating capacity of the mixer (103).

7. The method (100) as claimed in Claim 6, wherein, obtaining the operating capacity of the mixer (5) by the dosage limiter (4) based on a mass of the exhaust air flowing into the SCR system (10) and a temperature of the SCR system (10).

8. The method (100) as claimed in Claim 6, wherein, obtaining the volume of the DEF to be injected into the SCR system (10) on a set of operating conditions (6) of the SCR system (10) comprising:
-the temperature of the SCR system (10),
- the mass of an exhaust air flowing into the SCR system (10), and
- a volume of nitrous oxides (NOx) in the exhaust air comprising a first volume of NOx in in the exhaust air flowing into the SCR system (10) and a second volume of NOx in the exhaust air flowing out of the SCR system (10).

9. The method(100) as claimed in Claim 6, wherein, obtaining by the feed back unit (3), the corrected volume (12) based on a deviation between the obtained volume of DEF injected into the SCR system (10) and an actual volume of DEF reacting with the exhaust air flowing into the SCR.