(19)
(11)EP 3 333 387 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
24.03.2021 Bulletin 2021/12

(21)Application number: 16203475.5

(22)Date of filing:  12.12.2016
(51)International Patent Classification (IPC): 
F01N 3/20(2006.01)
F01N 11/00(2006.01)
F01N 9/00(2006.01)

(54)

INJECTOR DEPOSIT DETECTION FOR SCR INJECTION SYSTEM

ERKENNUNG VON INJEKTORABLAGERUNGEN FÜR SCR-EINSPRITZSYSTEM

DÉTECTION DE DÉPÔTS D'INJECTEUR POUR UN SYSTÈME DE RÉDUCTION CATALYTIQUE SÉLECTIVE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
13.06.2018 Bulletin 2018/24

(73)Proprietor: Perkins Engines Company Limited
Cambridgeshire PE1 5FQ (GB)

(72)Inventors:
  • Gharpure, Siddharth Subhash
    Peterborough, PE7 8DG (GB)
  • Smith, Stuart
    Stamford, Lincolnshire PE9 1HB (GB)
  • McCloskey, James K.
    Stamford, Lincolnshire PE9 1AS (GB)
  • Carlill, Tom
    Stamford, Lincolnshire PE9 3UF (GB)

(74)Representative: BRP Renaud & Partner mbB Rechtsanwälte Patentanwälte Steuerberater 
Königstraße 28
70173 Stuttgart
70173 Stuttgart (DE)


(56)References cited: : 
EP-A1- 2 578 834
WO-A1-2011/161175
US-A1- 2011 099 983
EP-A1- 2 787 185
JP-A- 2002 242 663
US-A1- 2011 107 742
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The present disclosure relates to a method for monitoring an SCR injection system, and a related SCR injection system.

    Background



    [0002] Engine systems for vehicles and the like may comprise an aftertreatment module for removing unwanted gaseous emissions or pollutants from the exhaust gases of an internal combustion engine. In particular, a selective catalytic reduction system (SCR) may be provided in the exhaust gas system for removing nitrogen oxides (NOx). Typically, an SCR system comprises a reductant injector reaching into a mixing pipe located upstream of a catalyst. The reductant injector may inject a liquid reductant into the exhaust gases before they contact the catalyst. Suitable liquid reductants may include anhydrous ammonia, aqueous ammonia and urea. The high temperature of the exhaust gases may evaporate the liquid reductant and upon contact with the catalyst, the gaseous reductant may react with the NOx in the exhaust gas to form nitrogen and water.

    [0003] However, if the exhaust gas temperature is too low, such as during low engine load conditions and in low duty cycles, the reductant may be deposited as solid compounds on components of the SCR system. In particular, the reductant may be deposited on or around an outlet nozzle of the reductant injector when eddy currents in the exhaust gas flow redirect injected reductant back onto the outlet nozzle. In addition, the reductant injector may undesirably leak small volumes of reductant, particularly when it is fully pressurized, onto the outlet nozzle. Since the outlet nozzle of the reductant injector may have a relatively low surface temperature due to low exhaust gas temperature, the redirected and leaked reductant may condense on it and the liquid components of the reductant may evaporate. Solid reductant deposits may subsequently be left on the outlet nozzle, which may therefore become partially or fully blocked. This may lead to increased reductant deposit growth and cause poor SCR system conversion efficiency. Additionally, for example, re-circulation zones in the exhaust mass flow caused by the design of the exhaust lines may cause deposits at or near a nozzle outlet of the reductant injector.

    [0004] For example, US 2016/0298515 A1 of Perkins Engines Company Limited discloses a method of controlling an engine system having an aftertreatment module within which a reductant injector is located. The reductant injector may be controlled to inject reductant fluid to expel solid reductant deposits formed on the reductant injector.

    [0005] US 2011/099983 A1 discloses a method for detecting abnormality of a reductant injection valve caused by clogging comprising comparison of pressure values detected by a pressure sensor after the start of supply path depressurisation by sucking gas from the exhaust pipe into the supply path via the injection hole with threshold values.

    [0006] The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.

    Summary of the Disclosure



    [0007] In one aspect, a method for monitoring an SCR injection system is disclosed, as described in Claim 1.

    [0008] In another aspect, an SCR injection system for an internal combustion engine is disclosed, as described in claim 5. The SCR injection system comprises a reductant tank, a reductant injector, and a pump fluidly connecting the reductant tank and the reductant injector. A pressure sensor measures a pressure in the SCR injection system. A control unit performs a method as disclosed herein.

    [0009] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

    Brief Description of the Drawings



    [0010] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. In the drawings:

    Fig. 1 is a schematic of an engine system suitable for implementing a method and SCR injection system according to the present disclosure;

    Fig. 2 is a schematic of an exhaust aftertreatment module of the engine of Fig. 1;

    Fig. 3 is a schematic of a reductant injector of the exhaust aftertreatment module of Fig. 2;

    Fig. 4 is a graph showing different pressure developments during a priming operation of an SCR injection system, and associated states of an outlet of a reductant injector;

    Fig. 5 is a graph showing different pressure developments during a purging operation of an SCR injection system; and

    Fig. 6 is an enlarged view of a section of Fig. 5 showing different pressure drop developments during the purging operation of the SCR injection system, and associated states of an outlet of a reductant injector.


    Detailed Description



    [0011] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described therein and illustrated in the drawings are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of patent protection. Rather, the scope of patent protection shall be defined by the appended claims.

    [0012] The present disclosure is based in part on the realization that deposits at an outlet of a nozzle of a reductant injector reduce a flow cross-section through the reductant injector. Accordingly, the deposits can be detected by monitoring pressure drop developments during actuation of the reductant injector. Particularly, it was found that the pressure developments during purging operations of an SCR injection system are suitable for detecting deposits at the outlet of the nozzle of the reductant injector, because they show particularly characteristic pressure developments.

    [0013] The present disclosure is further based in part on the realization that a determination to perform a deposit mitigation strategy is based on two subsequently measured pressure drop values. Particularly, a comparison between two or more measured pressure drop values measured during subsequent key cycles increases the detection resolution compared to a comparison between one measured pressure drop value and a predetermined threshold. The comparison between two subsequently measured pressure drop values allows to detect also small relative changes in the system behavior.

    [0014] FIG. 1 illustrates an exemplary embodiment of an engine system 10 suitable for implementing the method and SCR injection system of the present disclosure. The engine system 10 comprises an engine 19, and an aftertreatment module 25. Additionally, as shown in Fig. 1, the engine system 10 may comprise a turbocharger 12, a supercharger 16, and a cooler 21.

    [0015] Particularly, the engine system 10 comprises a first conduit 11 for directing intake gas, such as atmospheric air, to the turbocharger 12. The turbocharger 12 comprises a turbocharger compressor 13. The turbocharger compressor 13 is connected to the first conduit 11 and arranged to be driven by a turbine 14 via a shaft 15. The engine system 10 further comprises the supercharger 16 for receiving intake gas from the turbocharger compressor 13 via a second conduit 17. A supercharger drive arrangement 18 may be provided for selectively driving the supercharger 16. The engine 19 is arranged to provide power to the supercharger 16 mechanically via the supercharger drive arrangement 18.

    [0016] In the shown embodiment, the engine system 10 further comprises a third conduit 20 for directing the intake gas from the supercharger 16 to the cooler 21. The engine system 10 further comprises a supercharger bypass arrangement 22 for selectively allowing intake gas to bypass the supercharger 16.

    [0017] The engine 19 may be an internal combustion engine, such as a compression-ignition or spark-ignition engine. Fuel, such as diesel, gasoline or natural gas, may be selectively provided to engine cylinders in the engine 19 to combust with the intake gas and drive the pistons, thereby rotating a crankshaft and providing an engine output torque and power. The by-product of the combustion process is exhaust gas, which is directed from the engine cylinders along a fifth conduit 23 of the engine system 10 for example, via an exhaust manifold. The exhaust gas may comprise unwanted gaseous emissions or pollutants, such as nitrogen oxides (NOx), particulate matter (such as soot), sulphur oxides, carbon monoxide, unburnt hydrocarbons and/or other organic compounds. The fifth conduit 23 directs exhaust gas from the engine 19 to the turbine 14 of the turbocharger 12. The engine system 10 further comprises a sixth conduit 24 for directing exhaust gas from the turbine 14 to the exhaust aftertreatment module 25. A turbine bypass arrangement 26 may be provided for selectively allowing exhaust gas to bypass the turbine 14.

    [0018] The exhaust aftertreatment module 25 receives and treats the exhaust gas to remove pollutants prior to directing the exhaust gas to atmosphere via a seventh conduit 27.

    [0019] As illustrated in further detail in FIG. 2, the exhaust aftertreatment module 25 may comprise a selective catalytic reduction (SCR) system 28 and may comprise a diesel oxidation catalyst (DOC) 29. The DOC 29 may be arranged to receive exhaust gases from the sixth conduit 24 and located upstream of the SCR system 28. The SCR system 28 comprises an SCR conduit 30 leading from the DOC 29 to an SCR catalyst arrangement 31. The SCR system 28 further comprises an SCR injection system 50.

    [0020] The SCR injection system 50 comprises a reductant injector 32, a reductant tank 52, and a pump 54. The reductant injector 32 reaches into the SCR conduit 30 for selectively injecting reductant fluid 33 into the SCR conduit 30 upstream of the SCR catalyst arrangement 31. The reductant tank 52 is configured to store the reductant fluid 33, which may comprise aqueous urea, aqueous ammonia or the like In particular, the reductant fluid 33 may be diesel exhaust fluid (DEF) and the DEF may meet the IS022241 standard and comprise from 31.8% to 33.2% urea by weight. The pump 54 is configured to pump the reductant fluid 33 from the reductant tank 52 to the reductant injector 32 during priming and normal operations. The pump 54 is further configured to pump a fluid from the reductant injector 32 to the reductant tank 52 during a purging operation. For example, the pump 54 may be a diaphragm pump. Additionally, a fluid pressure sensor 56 is arranged and configured to measure a fluid pressure of the reductant fluid 33 in and/or downstream of the pump 54. In the shown embodiment, the fluid pressure sensor 56 is connected to a fluid connection between the pump 54 and the reductant injector 32. Alternatively, for example, the fluid pressure sensor 56 may be integrated in the pump 54 and/or in the reductant injector 32

    [0021] Furthermore, a control unit 58 is communicatively connected to the pump 54, the pressure sensor 56 and the reductant injector 32. The control unit 58 is configured to receive pressure data from the pressure sensor 56, to control the pump 54, and to control (actuate) the reductant injector 32.

    [0022] In the shown embodiment, the SCR catalyst arrangement 31 comprises, in the direction of exhaust gas flow, a mixer 34, a catalyst substrate 35 and a further oxidation catalyst or AMOx 36. The reductant injector 32 may selectively inject the reductant fluid 33, preferably as a liquid, into the stream of exhaust gas to provide a dose of reductant fluid 33 to the SCR catalyst arrangement 31. The high exhaust gas temperature may cause the reductant fluid 33 to evaporate and the resulting combination of gases may contact the catalyst substrate 35. The reductant fluid 33 may react with the NOx in the exhaust gas to reduce it to nitrogen and water, which may pass out of the engine system 10 via the seventh conduit 27. The catalyst substrate 35 may comprise zeolites, vanadium or the like.

    [0023] The engine system 10 may further comprise at least one sensor arranged to sense one or more parameters relating to one or more of the components of the engine system 10 and send signals relating thereto to the control unit 58. In particular, the engine system 10 may comprise a temperature sensor in communication with the control unit 58 for determining the exhaust gas temperature at the outlet of the engine 19 and/or in the exhaust aftertreatment module 25. In some embodiments, the control unit 58 may also be in communication with one or more actuators for controlling the operation of the engine 19. In particular, the control unit 58 may be operable to control the turbocharger 12, the supercharger 16, the rate of fuel injection to the engine 19 and the injection of the reductant fluid 33 by the reductant injector 32. The control unit 58 may be a computer and may be operable to store and implement one or more computer programs and may comprise at least one memory, at least one processing unit and at least one communication means. The control unit 58 may be an engine control unit (ECU).

    [0024] An exemplary reductant injector 32 suitable for such an engine system 10 is illustrated in FIG. 3. The reductant injector 32 comprises a housing 37 for mounting in the SCR system 28, particularly in the wall of the SCR conduit 30, upstream of the SCR catalyst arrangement 31. Inside the housing 37 a passageway 38 leads from a reductant fluid inlet 39 to a nozzle 40 and injector or nozzle outlet 41. The reductant fluid inlet 39 is in fluid communication with the pump 54 (see Fig. 2). A valve member 42, for example including a needle element 42A, is located within the passageway 38. The valve member 42 is moveable by an actuator 43 between an open position and a closed position. The actuator 43 may be an electrically activated solenoid or the like. The actuator 43 is communicatively connected to the control unit 58 such that the control unit 58 controls the movement of the valve member 42 (the needle element 42A) between the open and closed positions. The closed position is illustrated in FIG. 3.

    [0025] During operation of the engine system 10, the control unit 58 controls the injection of reductant fluid 33 in order to control the reduction of NOx by the SCR system 28. During injection, the reductant fluid 33 may be directed back onto the nozzle 40 after injection by eddy currents or gas recirculation in exhaust gases passing through the SCR conduit 30. Additionally, when the reductant injector 32 is in the closed position reductant fluid 33 may leak through the injector outlet 41 due to the high pressure of the reductant fluid 33 in the passageway 38. Leakage of reductant fluid 33 may be particularly likely in aged and worn reductant injectors 32. The leaked reductant fluid 33 may cause reductant fluid 33 to deposit on the nozzle 40. The amount leaked and deposited may be increased if the reductant injector 32 is not opened for a prolonged period of time. The nozzle 40 may typically have a relatively low surface temperature, such as around 100°C, such that the reductant fluid 33 on the nozzle 40 may condense. The liquid components of the reductant fluid 33 may subsequently evaporate and solid reductant deposits 44 may remain on the nozzle 40. FIG. 3 illustrates the reductant injector 32 in the closed position with solid reductant deposits 44 formed on the nozzle 40 partially blocking the injector outlet 41. The interruption of flow of the reductant fluid 33 from the reductant injector 32 may reduce the conversion efficiency of the SCR system 28. If these solid reductant deposits 44 build up further they may fully block the injector outlet 41.

    [0026] The present disclosure suggests to detect formation of deposits at or near the nozzle 40 by comparing pressure drop values of the SCR injection system 50. The pressure drop values are measured by the pressure sensor 56 during actuation of the reductant injector 32 at different times. The comparison between two subsequently measured pressure drop values increases the detection resolution compared to a comparison between one measured pressure drop value and a predetermined threshold. One reason may be that the predetermined threshold is always set as a compromise considering that systems do not behave identical behaviors, and system behaviors change over time, etc.. In contrast, the comparison between two or more subsequently measured pressure drop values allows to detect also small relative changes in the system behavior, and to determine suitable countermeasures if required.

    [0027] Particularly, herein it is suggested to compare pressure drop values measured during consecutive purging operations of the SCR injection system 50. It was found that those operation modes are particularly suitable, because deviations in the pressure drop due to formation of deposits are particularly quantifiable during those operation modes. Additionally, typically, the engine 10, and thus the SCR injection system 50, are operated over a prolonged period of time between consecutive purging operations. A shutdown and restart, or a stop-start of the SCR injection system 50) separates consecutive purging operations. More particularly, each shutdown of the SCR injection system 50 triggers one purging operation. The internal combustion engine 10 may be idle or may be shutdown and restarted when the SCR injection system 50 performs a stop-start or a shutdown and a restart.

    [0028] As used herein, the term "priming operation" refers to an operation mode of the SCR injection system 50, in which the SCR injection system 50 is made ready for operation. The priming operation includes activating the pump 54 to pump reductant from the reductant tank 52 to the reductant injector 32. The priming operation further includes actuating the reductant injector 32 to move into the open position. Simultaneously to the actuation of the reductant injector 32, a pressure drop occurs in the SCR injection system 50.

    [0029] As used herein, the term "purging operation" refers to an operation mode of the SCR injection system 50, in which the SCR injection system 50 removes remaining reductant in the SCR injection system 50. The purging operation includes activating and operating the pump 54 to pump remaining reductant from the reductant injector 32 back to the reductant tank 52. The purging operation further includes actuating the reductant injector 32 to move into the open position. An end of the purging operation is indicated by a negative pressure building up in the SCR injection system 50, particularly between the pump 54 and the reductant injector 32, because no fluid is left in the reductant injector 32 and the fluid connection to the pump 54. During purging operation, a pressure drop occurs in the SCR injection system.

    [0030] The following exemplary methods include a comparison of two measured pressured drop values. However, it should be noted that in other embodiments more than two pressure drop values may be compared.

    [0031] Referring to Fig. 4, a first exemplary method, not according to the invention, performed during consecutive priming operations of the SCR injection system 50 is described in the following.

    [0032] Fig. 4 shows three exemplary pressure developments of different priming operations measured by the pressure sensor 56 of the SCR injection system 50.

    [0033] A first pressure development is indicated by a solid line and referred to by reference numeral 100. A second pressure development is indicated by a dashed-dotted line and referred to by reference numeral 102. Lastly, a third pressure development is indicated by a dotted line and referred to by reference numeral 104.

    [0034] As can be seen in Fig. 4, during priming operation, the pressure in the SCR injection system 50 increases due to operation of the pump 54. At about point in time t1, the reductant injector 32 is actuated (opened). As a result, the pressure drops. Specifically, the first pressure development 100 drops to a first pressure drop value p1, the second pressure development 102 drops to a second pressure drop value p2, and the third pressure drop development 104 drops to a third pressure drop value p3. After closing the reductant injector 32 at about point in time t2, pressure developments 100 - 104 increase again.

    [0035] Assuming a first situation, in which during a first priming operation of the SCR injection system 50, the first pressure drop value p1 has been measured, and during a second, consecutive priming operation of the SCR injection system 50, the second pressure drop value p2 has been measured. A first deviation Δp1 is calculated. The first deviation Δp1 is compared to a first deviation pressure drop threshold. In case of the first deviation Δp1 exceeding the first deviation pressure drop threshold, it is determined that a deposit mitigation strategy is required for cleaning the nozzle 40. In case of the first deviation Δp1 not exceeding the first deviation pressure drop threshold, it is determined that no deposit mitigation strategy is required. In the example shown in Fig. 4, the first deviation Δp1 indicates that operation of the reductant injector 32 is already deteriorated due to deposits 44 at the nozzle 40, although the reductant injector 32 is still operable.

    [0036] Assuming a second situation, in which during a first priming operation of the SCR injection system 50, the pressure drop value p1 has been measured, and during a second, consecutive priming operation of the SCR injection system 50, the third pressure drop value p3 has been measured. A second deviation Δp2 is calculated. The second deviation Δp2 is compared to the first deviation pressure drop threshold. In the example shown in Fig. 4, the second deviation Δp2 indicates that operation of the reductant injector 32 is considerably deteriorated due to deposits at the nozzle 40, although the reductant injector 32 is still operable.

    [0037] Since the second deviation Δp2 is greater than the first deviation Δp1, a more effective deposit mitigation strategy may be chosen in the second situation compared to the first situation. In other words, the method further allows to select a suitable deposit mitigation strategy based on the first and second pressure drop values p1 and p2, particularly an amount of the calculated deviation. The method step of performing a deposit mitigation strategy for reducing deposits at an outlet of the injector further comprises selecting one deposit mitigation strategy from a plurality of deposit mitigation strategies based on the deviation pressure value.

    [0038] Examples of deposit mitigation strategies include increasing the exhaust gas temperature, increasing an exhaust gas mass flow, pumping a reductant to the reductant injector to dissolve deposits, and/or increasing a dosing rate for the SCR injection. For example, a "enhanced" deposit mitigation strategy may include increasing the exhaust gas temperature to a higher temperature than a standard" deposit mitigation strategy.

    [0039] For example, the first deviation pressure drop threshold may be within a range between about 0.1 bar and about 1.9 bar, particularly up to about 1 bar, more particularly up to about 0.5 bar.

    [0040] In some embodiments, the method may further comprise, for each measured pressure drop value p1 to p3, determining whether the respective pressure drop value p1, p2 or p3 is within a predetermined acceptable range for operation. The predetermined acceptable range extends between an upper limit pu and a lower limit pL as indicated in Fig. 4. For example, for an SCR injection system having an operation pressure of about 9 bar, the upper pressure limit pu may be about 8 bar, and the lower pressure limit pL may be about 6 bar. The predetermined acceptable range may be set to determine if the reductant injector 32 is inoperable, for example due to a failure of the valve member 42, the actuator 43, and/or considerable deposits in the SCR injection system 50.

    [0041] Referring to Figs. 5 and 6, a second exemplary method of the invention performed during consecutive purging operations of the SCR injection system 50 is described in the following. Fig. 6 shows a detail of Fig. 5 showing different pressure drop developments during the purging operation of the SCR injection system, and associated states the outlet 41 of the reductant injector 32.

    [0042] A fourth pressure development is indicated by a solid line and referred to by reference numeral 200. A fifth pressure development is indicated by a dashed-dotted line and referred to by reference numeral 202. Lastly, a sixth pressure development is indicated by a dotted line and referred to by reference numeral 204.

    [0043] As can be seen in Fig. 5, during purging operation, the pressure in the SCR injection system 50, particularly in a passage between a pump impeller of the pump 54 and the nozzle outlet 41 of the reductant injector 32, decreases. The pressure decreases, because the pump 54 is operated to pump fluid from the reductant injector 32 to the reductant tank 52 for cleaning the piping of the SCR injection system 50 from residues of the reductant 33. During the purging operation, the reductant injector 32 is opened. The pump 54 creates a vacuum to remove fluid from the piping of the SCR injections system 50 during purging operation. The fluid carries residue drops of the reductant 33. The nozzle outlet 41 acts as an orifice so that after a period of time, a pressure within the SCR injection system 50 drops below atmosphere pressure pa (about 1 bar). The amount of the pressure drop below atmosphere pressure indicates a flow cross-section through the nozzle outlet 41. The more the nozzle outlet 41 is clogged, less will be the flow through the outlet 41.

    [0044] Specifically, the fourth pressure development 200 drops to a fourth pressure drop value p4, the fifth pressure development 202 drops to a second pressure drop value p5, and the sixth pressure drop development 204 drops to a sixth pressure drop value p6.

    [0045] Assuming a third situation, in which during a first purging operation of the SCR injection system 50, the fourth pressure drop value p4 has been measured by the pressure sensor 56. During a second, consecutive purging operation of the SCR injection system 50, the fifth pressure drop value p5 has been measured. A third deviation Δp3 is calculated form the fourth pressure drop value p4 and the fifth pressure drop value p5. The third deviation Δp3 is compared to a second deviation pressure drop threshold (other than the first deviation pressure drop threshold for the priming operation). In case of the third deviation Δp3 exceeding the second deviation pressure drop threshold, it is determined that a deposit mitigation strategy is required for cleaning the nozzle 40. In case of the third deviation Δp3 not exceeding the deviation pressure drop threshold, it is determined that no deposit mitigation strategy is required. In the example shown in Fig. 5, the deviation Δp3 indicates that operation of the reductant injector 32 is already deteriorated due to deposits 44 at the nozzle 40, although the reductant injector 32 is still operable. The deposit mitigation strategy may be performed during a subsequent restart of the SCR injection system 50.

    [0046] Assuming a fourth situation, in which during a first purging operation of the SCR injection system 50, the fourth pressure drop value p4 has been measured. During a second, consecutive priming operation of the SCR injection system 50, the sixth pressure drop value p6 has been measured. A fourth deviation Δp4 is calculated. The fourth deviation Δp4 is compared to the respective deviation pressure drop threshold. In the example shown in Fig. 5, the deviation Δp4 indicates that operation of the reductant injector 32 is considerably deteriorated due to deposits 44 at the nozzle 40, although the reductant injector 32 is still operable. Additionally, a more effective deposit mitigation strategy may be chosen in the fourth situation than in the third situation, because the fourth deviation Δp4 is greater than the third deviation Δp3 (the fifth pressure drop value p5 is greater than the sixth pressure drop value p6).

    [0047] For the exemplary method described with reference to Figs. 5 and 6 the deposit mitigation strategy, if any, may be implemented after the SCR injections system 50 has started again at a later time.

    [0048] For example, the second deviation pressure drop threshold may be within a range between about 0.1 bar and about 0.9 bar. A pressure drop value indicating a clean nozzle outlet 41 may be about 0.9 mbar, and a pressure drop value indicating a clogged nozzle outlet 41 may be lower than 0.9 mbar, for example between about 0.4 mbar and 0.7 mbar.

    [0049] As one skilled in the art will appreciate, the above described first and second exemplary methods may be combined so that the method includes comparing pressure drop values of consecutive priming operations of the SCR injection system 50, and comparing pressure drop values of consecutive purging operations of the SCR injection system 50. The method may then perform a deposit mitigation strategy if a deviation of the pressure drop values measured during consecutive priming operations exceeds a first threshold and/or if a deviation of the pressure drop values measured during consecutive purging operation exceeds a second threshold.

    Industrial Applicability



    [0050] The method for monitoring an SCR injection system, and the SCR injection system as disclosed herein are applicable in internal combustion engines equipped with an SCR system.

    [0051] Terms such as "about", "around", "approximately", or "substantially" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ± 10% or less, preferably ±5% or less, more preferably ±1% or less, and still more preferably ±0.1% or less of and from the specified value, insofar as such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" refers is itself also specifically, and preferably, disclosed.

    [0052] Although the preferred embodiments of this invention have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.


    Claims

    1. A method for monitoring an SCR injection system (50) including a pump (54) and a reductant injector (32), the method including:

    operating the pump (54);

    measuring a first pressure drop value in the SCR injection system (50) during actuation of the reductant injector (32) during a purging operation of the SCR injection system (50), in which the SCR injection system (50) is purged wherein the pump (54) is operated to pump a fluid from the reductant injector (32) to a reductant tank (52);

    measuring a second pressure drop value in the SCR injection system (50) during a further actuation of the reductant injector (32) during a second purging operation later than the first purging operation;

    determining to perform a deposit mitigation strategy for reducing deposits at the outlet (41) of the reductant injector (32) based on the first pressure drop value and the second pressure drop value;

    determining that the first pressure drop value is within a preset acceptable pressure range; and/or

    determining that the second pressure drop value is within a present acceptable pressure range, wherein

    the first purging operation and the second purging operation are separated by a shutdown and restart, or a stop-start of the SCR injection system (50), particularly a shutdown and a restart of the internal combustion engine (10).


     
    2. The method of claim 1, wherein the method step of determining to perform a deposit mitigation strategy includes:

    calculating a first deviation between the first pressure drop value and the second pressure drop value; and

    if the first deviation exceeds a predetermined threshold, performing the deposit mitigation strategy.


     
    3. The method of claim 1 or claim 2, wherein the step of determining to perform a deposit mitigation strategy for reducing deposits at an outlet (41) of the reductant injector (32) further comprises selecting one deposit mitigation strategy of a plurality of deposit mitigation strategies based on the first pressure drop value and the second pressure drop value.
     
    4. The method of any one of the preceding claims, wherein the deposit mitigation strategy includes at least one of increasing the exhaust gas temperature, increasing an exhaust gas mass flow, and pumping a reductant to the reductant injector (32).
     
    5. An SCR injection system (50) for an internal combustion engine (10), comprising
    a reductant tank (52);
    a reductant injector (32);
    a pump (54) fluidly connecting the reductant tank (52) and the reductant injector (32);
    a pressure sensor (56) configured to measure a pressure in the SCR injection system (50); and
    a control unit (58) configured to perform a method according to any one the preceding claims.
     
    6. The SCR injection system (50) of claim 5, wherein:

    the control unit (58) is further configured to store the first pressure drop value, and optionally also the second pressure drop value; and/or

    the pressure sensor (56) is integrated in the pump (54).


     


    Ansprüche

    1. Verfahren zum Überwachen eines SCR-Einspritzsystems (50), das eine Pumpe (54) und einen Reduktionsmittelinjektor (32) einschließt, wobei das Verfahren einschließt:

    Betreiben der Pumpe (54);

    Messen eines ersten Druckabfallwerts im SCR-Einspritzsystem (50) während der Betätigung des Reduktionsmittelinjektors (32) während eines Spülvorgangs des SCR-Einspritzsystems (50), in dem das SCR-Einspritzsystem (50) gespült wird, wobei die Pumpe (54) betrieben wird, um ein Fluid vom Reduktionsmittelinjektor (32) zu einem Reduktionsmitteltank (52) zu pumpen;

    Messen eines zweiten Druckabfallwerts im SCR-Einspritzsystem (50) während einer weiteren Betätigung des Reduktionsmittelinjektors (32) während eines zweiten Spülvorgangs, der später als der erste Spülvorgang stattfindet;

    Bestimmen, eine Ablagerungsminderungsstrategie zum Reduzieren von Ablagerungen am Auslass (41) des Reduktionsmittelinjektors (32) basierend auf dem ersten Druckabfallwert und dem zweiten Druckabfallwert durchzuführen;

    Bestimmen, dass der erste Druckabfallwert innerhalb eines voreingestellten zulässigen Druckbereichs liegt; und/oder

    Bestimmen, dass der zweite Druckabfallwert innerhalb eines gegenwärtigen zulässigen Druckbereichs liegt, wobei

    der erste Spülvorgang und der zweite Spülvorgang durch eine Abschaltung und einen Neustart oder einen Stopp-Start des SCR-Einspritzsystems (50), insbesondere eine Abschaltung und einen Neustart des Verbrennungsmotors (10), getrennt sind.


     
    2. Verfahren nach Anspruch 1, wobei der Verfahrensschritt des Bestimmens, eine Ablagerungsminderungsstrategie durchzuführen, Folgendes einschließt:

    Berechnen einer ersten Abweichung zwischen dem ersten Druckabfallwert und dem zweiten Druckabfallwert; und

    wenn die erste Abweichung einen vorgegebenen Schwellenwert überschreitet, Durchführen der Ablagerungsminderungsstrategie.


     
    3. Verfahren nach Anspruch 1 oder Anspruch 2, wobei der Schritt des Bestimmens, eine Ablagerungsminderungsstrategie zum Reduzieren von Ablagerungen an einem Auslass (41) des Reduktionsmittelinjektors (32) durchzuführen, ferner ein Auswählen einer Ablagerungsminderungsstrategie aus einer Vielzahl von Ablagerungsminderungsstrategien basierend auf dem ersten Druckabfallwert und dem zweiten Druckabfallwert umfasst.
     
    4. Verfahren nach einem der vorstehenden Ansprüche, wobei die Ablagerungsminderungsstrategie mindestens eines aus Erhöhen der Abgastemperatur, Erhöhen eines Abgasmassenstroms und Pumpen eines Reduktionsmittels zum Reduktionsmittelinjektor (32) einschließt.
     
    5. SCR-Einspritzsystem (50) für einen Verbrennungsmotor (10), umfassend
    einen Reduktionsmitteltank (52);
    einen Reduktionsmittelinjektor (32);
    eine Pumpe (54), die den Reduktionsmitteltank (52) und den Reduktionsmittelinjektor (32) fluidisch verbindet;
    einen Drucksensor (56), der konfiguriert ist, einen Druck im SCR-Einspritzsystem (50) zu messen; und
    eine Steuereinheit (58), die konfiguriert ist, ein Verfahren gemäß einem der vorstehenden Ansprüche durchzuführen.
     
    6. SCR-Einspritzsystem (50) nach Anspruch 5, wobei:

    die Steuereinheit (58) ferner konfiguriert ist, den ersten Druckabfallwert und wahlweise auch den zweiten Druckabfallwert zu speichern; und/oder

    der Drucksensor (56) in die Pumpe (54) integriert ist.


     


    Revendications

    1. Procédé de surveillance d'un système d'injection SCR (réduction catalytique sélective) (50) incluant une pompe (54) et un injecteur de réducteur (32), le procédé incluant :

    le fonctionnement de la pompe (54) ;

    la mesure d'une première valeur de chute de pression dans le système d'injection SCR (50) pendant l'actionnement de l'injecteur de réducteur (32) pendant une opération de purge du système d'injection SCR (50), dans laquelle le système d'injection SCR (50) est purgé dans lequel la pompe (54) est exploitée pour pomper un fluide à partir de l'injecteur de réducteur (32) vers un réservoir de réducteur (52) ;

    la mesure d'une deuxième valeur de chute de pression dans le système d'injection SCR (50) pendant un actionnement supplémentaire de l'injecteur de réducteur (32) pendant une deuxième opération de purge postérieure à la première opération de purge ;

    la détermination de mise en œuvre d'une stratégie d'atténuation de dépôts pour réduire des dépôts au niveau de la sortie (41) de l'injecteur de réducteur (32) sur la base de la première valeur de chute de pression et de la deuxième valeur de chute de pression ;

    la détermination que la première valeur de chute de pression se situe dans une plage de pression acceptable prédéfinie ; et/ou

    la détermination que la deuxième valeur de chute de pression se situe dans une plage de pression acceptable actuelle, dans lequel

    la première opération de purge et la deuxième opération de purge sont séparées par une mise à l'arrêt et un redémarrage, ou un arrêt-démarrage du système d'injection SCR (50), particulièrement une mise à l'arrêt et un redémarrage du moteur à combustion interne (10).


     
    2. Procédé selon la revendication 1, dans lequel l'étape de procédé de détermination de mise en œuvre d'une stratégie d'atténuation de dépôts inclut :

    le calcul d'une première déviation entre la première valeur de chute de pression et la deuxième valeur de chute de pression ; et

    si la première déviation dépasse un seuil prédéterminé, la mise en œuvre de la stratégie d'atténuation de dépôts.


     
    3. Procédé selon la revendication 1 ou la revendication 2, dans lequel l'étape de détermination de mise en œuvre d'une stratégie d'atténuation de dépôts pour réduire des dépôts au niveau d'une sortie (41) de l'injecteur de réducteur (32) comprend en outre la sélection d'une stratégie d'atténuation de dépôts d'une pluralité de stratégies d'atténuation de dépôts sur la base de la première valeur de chute de pression et de la deuxième valeur de chute de pression.
     
    4. Procédé selon l'une quelconque des revendications précédentes, dans lequel la stratégie d'atténuation de dépôts inclut au moins l'un parmi l'augmentation de la température de gaz d'échappement, l'augmentation d'un débit massique de gaz d'échappement, et le pompage d'un réducteur vers l'injecteur de réducteur (32).
     
    5. Système d'injection SCR (50) pour un moteur à combustion interne (10), comprenant
    un réservoir de réducteur (52) ;
    un injecteur de réducteur (32) ;
    une pompe (54) reliant fluidiquement le réservoir de réducteur (52) et l'injecteur de réducteur (32) ;
    un capteur de pression (56) configuré pour mesurer une pression dans le système d'injection SCR (50) ; et
    une unité de commande (58) configurée pour mettre en œuvre un procédé selon l'une quelconque des revendications précédentes.
     
    6. Système d'injection SCR (50) selon la revendication 5, dans lequel :

    l'unité de commande (58) est en outre configurée pour stocker la première valeur de chute de pression, ainsi que facultativement la deuxième valeur de chute de pression ; et/ou

    le capteur de pression (56) est intégré dans la pompe (54).


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description