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 a controller to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of 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, on 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.

[0003] The prior art IN201941043085, a method of removing diesel exhaust fluid (DEF) deposits in exhaust path of a vehicle is described. In the first step S1 of the method, at least one vehicle operating condition is detected for a predefined amount of time. In the second step S2, a regeneration interval of a diesel particulate filter (DPF) 14 is determined based on the detected at least one vehicle operating condition. In third step S3, formation of the DEF deposits 12 in a mixing zone 16 of the exhaust path 13 is determined, based on the detected at least one vehicle operating condition for the predefined amount of time. In fourth step S4, at least one de-crystallization process to remove the DEF deposits 12 is activated, when the DPF 14 regeneration interval is not scheduled for operation. The conversion process of the exhaust gas into the non-harmful gases is efficient. The method provides a simple, cost-effective solution of removing the DEF deposits 12 formed in the exhaust path 13.

[0004] Available prior arts suggest that there are no direct methods to predict crystal growth. SOx and HC (hydrocarbon) based models are used to predict load collectives (Engine speed, Injection Quantity, exhaust temperature, exhaust gas mass flow) in order to trigger regeneration. The same increases the rate of aging of the catalyst due to higher number of regenerations.

[0005] The present disclosure proposes to predict crystal growth based an operation capacity of the mixer (Load Index). This load index is determined based on a set of vehicle operating conditions including (but not limited to) a DEF dosage amount, exhaust mass flow rate and the exhaust temperature. Based on a modelled threshold, the regeneration of the SCR system can be activated. The known DPF(diesel particulate filter) regeneration process may be activated where the temperature in the exhaust path reaches approximately 600 degrees, by which the soot particles are oxidized. With the increased temperature in the exhaust path, along with the soot particles oxidization in the DPF, the DEF deposits in the mixing zone can also be removed.

Brief description of the accompanying drawings
An embodiment of the invention is described with reference to the following accompanying drawings:
[0006] Figure 1 depicts a controller to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle.
[0007] Figure 2 depicts a flow chart for a method to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle.

[0008] Detailed description of the drawings

[0009] 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.

[0010] An exhaust gas treatment system comprises a diesel oxidation catalyst (DOC) , the Diesel particulate filter and a selective catalytic reduction system arranged in an exhaust path to convert the harmful exhaust gas emitted from an engine into non-harmful gas before releasing the same into the atmosphere. The dosing of the DEF (urea) by a dosing module/doser into the exhaust path to reduce the NOx emissions is positioned upstream to the SCR system. The portion where the DEF/urea is mixed with the exhaust gas with a mixer is called a mixing zone. According to one embodiment, the mixing zone is located between the DPF and the SCR unit. According to another embodiment, the mixing zone is located between the DOC and the SCR unit. Due to the vehicle operating conditions, the DEF deposits are formed in the mixing zone, which reduces the efficiency of the vehicle.

[0011] Referring to figure 1, the same depicts a controller (1) to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle. The SCR system (10) comprises a mixer (3) to mix the DEF injected with an exhaust air flowing into the SCR system (10). The SCR system (10) includes a doser and an SCR catalyst component. The doser 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. 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 into the exhaust stream at a position upstream of a SCR catalyst. 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.

[0012] The SCR includes at least one engine-out NOx sensor 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 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. 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.

[0013] The SCR system (10) may also include at least one system-out NOx sensor that is positioned downstream of the SCR catalyst component. The system-out NOx sensor 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.
[0014] The SCR system (10) may also include at least one temperature sensor that is in communication with the controller (1). According to certain embodiments, the temperature sensor can be used to determine a temperature of the SCR catalyst. According to certain embodiments, the temperature sensor is positioned within the SCR catalyst component. Alternatively, the temperature sensor 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.

[0015] Said controller (1) is adapted to detect a set of vehicle operating conditions (4) for a pre-defined amount of time. Said set of operating conditions (4) comprises an engine speed, a volume of exhaust air flowing into the SCR system (10), a temperature of the SCR system (10), a distance travelled by said vehicle, the mass of the exhaust air flowing into the SCR system (10), and a volume of nitrous oxides (NOx) in the exhaust air. It is to be understood that any of the said set of operating conditions (4) or all of the set of operating conditions (4) may be detected by the controller (1). It is further to be understood that the described set of operating conditions (4) are not limited nor are to be construed as an exhaustive list.

[0016] Said controller (1) is adapted to obtain an operating capacity (5) of the mixer (3) and determine formation of said deposits in the exhaust path of the SCR system (10) based on the said set of vehicle operating conditions (4) and said operating capacity (5) of the mixer. The controller (1) is adapted to activate a regeneration (9) process to remove said determined DEF deposits in the exhaust path.

[0017] The operating capacity (5) of the mixer (3) is obtained based on said set of vehicle operating conditions (4). According to the present invention, the dosage limiter obtains a Load Index which represents a maximum dosing amount of the DEF that is digestible by the mixer. 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)
[0018]

[0019] The determined operating capacity (5) (load index) may be compared to a reference load index map to determine formation of DEF deposits (crystals). In an example, a possibility of DEF deposit may be predicted when for an DEF injection quantity X, exhaust mass flow Y and exhaust temperature Z, the reference load index map suggest deposit formation.

[0020] The controller determines formation of said deposits in the exhaust path of the SCR system (10) based on the said set of vehicle operating conditions (4) and said operating capacity (5)of the mixer.

[0021] The controller (1) is adapted to activate a regeneration (9) process to remove said determined DEF deposits in the exhaust path. A known DPF(diesel particulate filter) regeneration (9) process may be activated where the temperature in the exhaust path reaches approximately 600 degrees, by which the soot particles are oxidized. With the increased temperature in the exhaust path, along with the soot particles oxidization in the DPF, the DEF deposits in the mixing zone can also be removed.

[0022] A threshold quantity (6)representing a maximum operating capacity (5) for a specific set of operating conditions (4) maybe obtained through modelling and optimizing experimental data. When the obtained operating capacity (5) of the mixer (3) (load index) as obtained from set of vehicle operating conditions (4) reaches the threshold, the regeneration (9) process may be activated. It is to be understood that the threshold quantity (6)may vary from situation to situation. A weightage to one of the vehicle operating conditions may be given more to determine the said threshold quantity (6)in a particular situation. In an example, for an engine speed S and a DEF injection quantity Q, the threshold quantity (6)may be different than for an engine speed S0 and a DEF injection quantity Q1 .

[0023] Further, the threshold quantity (6)may be determined by the controller (1) based on a catalyst condition (7), said catalyst condition (7) may be determined based on a NOx conversion capacity of the catalyst. The same may be determined based on a comparison between a predicted downstream NOx value and the determined downstream NOx value. The weightage to one of the vehicle operation condition may also be given based on the said catalyst condition (7).

[0024] The controller (1) is further adapted to determine formation of said deposits in the exhaust path of the SCR system (10) based on a comparison between a predicted volume of DEF reacting with the exhaust air and an actual volume of DEF reacting with the exhaust air flowing into the SCR and an actual volume of DEF reacting with the exhaust air. The controller (1) determines formation of said deposits based on a comparison between the predicted volume (12) of DEF reacting with the exhaust air and the actual volume (11) of DEF reacting with the exhaust air flowing into the SCR when the operating capacity (5)of mixer (3) is not known. The predicted volume can be modelled based on experimental data and the actual volume may be determined by the system out NOx sensor. In a situation when the operating capacity (5 )of the mixer (3) cannot obtained, a feedback based SCR control loop may be used to predict the formation of DEF deposits. Based on a conversion efficiency (8) (proportion of NOx reacting with ammonia), the formation of DEF deposits may be predicted. A reference conversion efficiency map may be used to predict DEF deposit formation. The threshold quantity (6)for a specific conversion efficiency may be determined and regeneration (9) may be activated when said threshold quantity (6)is reached.

[0025] Referring to Figure 2, the same depicts a flowchart for a method (100) to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle. The method (100) may be implemented by the system as described in Figure 1. The method step (100) includes the first step (101) of detecting a set of vehicle operating conditions (4), by a controller (1) for a pre-defined amount of time. This is followed by the step (102) of obtaining an operating capacity (5) of the mixer, by the controller (1) . The next step (103) is determining by the controller (1), formation of said deposits in the exhaust path of the SCR system (10) based on the said set of vehicle operating conditions (4) and said operating capacity (5)of the mixer, followed by step (104) of activating, by the controller (1), a regeneration (9) process to remove said determined DEF deposits in the exhaust path.

, Claims:We Claim:

1. A controller (1) to determine a quantity of Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle, said SCR system (10) comprising a mixer (3) to mix the DEF injected with an exhaust air flowing into the SCR system (10),

said controller (1) adapted to:
- detect a set of vehicle operating conditions (4) for a pre-defined amount of time;

characterized in that, the controller (1) adapted to:
- determine formation of said deposits in the exhaust path of the SCR system (10) based on the said set of vehicle operating conditions (4) and an operating capacity (5)of the mixer; and
-activate a regeneration (9) process to remove said determined DEF deposits in the exhaust path.

2. The controller (1) as claimed in claim 1, wherein, the controller (1) obtains the operation capacity of mixer (3) based on a mass of the exhaust air flowing into the system, a temperature of the SCR system (10) and a volume of the DEF injected into the SCR system (10).

3. The controller (1) as claimed in Claim 1, wherein, said set of operating conditions (4) comprises:

-an engine speed,

-the volume of exhaust air flowing into the SCR system (10),
- the temperature of the SCR system (10),
-a distance travelled by said vehicle,
-the mass of the exhaust air flowing into the SCR system (10), and
- a volume of nitrous oxides (NOx) in the exhaust air .

4. The controller (1) as claimed in Claim 1, wherein, activating the regeneration (9) process when said determined DEF deposits are greater than a threshold quantity (6) of DEF deposits.

5. The controller (1) as claimed in Claim 1, wherein, the controller (1) is further adapted to determine formation of said deposits in the exhaust path of the SCR system (10) based on a comparison between a predicted volume of DEF reacting with the exhaust air and an actual volume of DEF reacting with the exhaust air flowing into the SCR.

6. The controller (1) as claimed in Claim 6, wherein, the controller (1) determines formation of said deposits based on a comparison between the predicted volume of DEF reacting with the exhaust air and the actual volume of DEF reacting with the exhaust air flowing into the SCR when the operating capacity (5) of mixer (3) is not known.

7. The controller (1) as claimed in Claim 1, wherein, the controller (1) determines a catalyst condition (7) based on a comparison between the predicted volume (12) of DEF reacting with the exhaust air and the actual volume (11) of DEF reacting with the exhaust air flowing into the SCR.
8. The controller (1) as claimed in Claim 8, wherein, the threshold quantity (6) of DEF deposits is determined based on the catalyst condition (7).

9. A method(100) to determine Diesel Exhaust Fluid (DEF) deposits in an exhaust path of a selective catalytic reduction (SCR) system of a vehicle, said SCR system (10) comprising a mixer (3)to mix the DEF injected with an exhaust air flowing into the SCR system (10), the method comprising the steps of:
- detecting a set of vehicle operating conditions (4), by a controller (1) for a pre-defined amount of time (101);

characterized in that,
-obtaining an operating capacity (5)of the mixer, by the controller (102);
– determining by the controller (1), formation of said deposits in the exhaust path of the SCR system (10) based on the said set of vehicle operating conditions (4) and said operating capacity (5)of the mixer (103); and
-activating, by the controller (1), a regeneration (9) process to remove said determined DEF deposits in the exhaust path (104).