Method for controlling the operation of an exhaust gas treatment device

Abstract

A method of controlling an engine assembly comprising an internal combustion engine and an exhaust treatment device. The exhaust treatment device comprises a diesel oxidation catalyst (DOC) module and a selective catalytic reduction (SCR) module. The engine assembly provides a numerical indication of the efficiency of the SCR module. The method comprises comparing the numerical indication of the efficiency with a first threshold efficiency value. If the numerical indication remains above the first threshold efficiency value, waiting for a time interval t and then initiating a timed-initiated SCR cleaning event. If the numerical indication is below the first threshold efficiency value, initiating a threshold-initiated SCR cleaning event without waiting for the time interval t. Fuel is injected into the engine at a first injection rate, causing the fuel to burn in the diesel oxidation catalyst, thereby increasing the exhaust gas temperature in the diesel oxidation catalyst. A set of criteria is determined, including whether the SCR efficiency exceeds a second threshold efficiency after the threshold-initiated SCR cleaning event. If so, an error warning related to high sulfur fuel is triggered.

Description

Technical Field

[0001] The present invention relates to the field of exhaust gas treatment, and in particular to controlling the operation of an exhaust gas treatment device. Background Art

[0002] An exhaust treatment device may include multiple modules, wherein each module is designed to treat one or more components of the exhaust gas. The exhaust treatment device may include one or more of a diesel oxidation catalyst (DOC) module, a diesel particulate filter (DPF) module, and a selective catalytic reduction (SCR) module arranged in series, such that the exhaust gas flows through each module sequentially.

[0003] The diesel oxidation catalyst module can oxidize the components of the exhaust gas. The diesel particulate filter module can filter soot from the exhaust gas to prevent it from being released into the atmosphere. The SCR module can reduce the NO x Reacts chemically with ammonia to produce nitrogen and water.

[0004] The performance of each module may degrade with use. For example, the performance of an SCR module may be affected by the accumulation of deposits within the SCR module. Deposits within the SCR module may accumulate particularly rapidly if high-sulfur fuel is used. Deposits accumulated in the SCR module can be removed through an SCR cleaning process that involves increasing the temperature of the SCR module.

[0005] In order to increase the temperature of the exhaust gas before it reaches the SCR module, it is known to use a DOC module to increase the temperature of the exhaust gas passing through it. This can be achieved by introducing unburned fuel upstream of the DOC module for oxidation in the DOC, thereby increasing the temperature of the exhaust gas leaving the DOC module.

[0006] Therefore, in addition to injecting fuel for combustion, fuel can be injected into one or more cylinders of the engine as a post-combustion event, causing the fuel to flow out of one or more cylinders without oxidation. This fuel can be oxidized in the DOC module, thereby increasing the temperature of the exhaust gas therein. Injecting fuel in this manner is referred to as hydrocarbon (HC) dosing.

[0007] When using high sulfur fuel, the need to clean the SCR module may be much greater than when using conventional (low sulfur) fuel. Summary of the Invention

[0008] Against this background, a method of controlling an engine assembly comprising an internal combustion engine and an exhaust gas treatment device is provided.

[0009] An exhaust gas treatment device comprising: a diesel oxidation catalyst (DOC) module configured to convert carbon monoxide and hydrocarbons into carbon dioxide; and a selective catalytic reduction (SCR) module configured to promote NOx and ammonia, wherein the SCR module is downstream of the DOC module;

[0010] an engine assembly configured to provide a numerical indication of an efficiency of the SCR module;

[0011] The method includes:

[0012] comparing the numerical indication of efficiency to a first threshold efficiency value, and:

[0013] Where the numerical indication of the efficiency remains above a first threshold efficiency value, waiting until a time interval t has elapsed and then initiating a time-initiated SCR cleaning event;

[0014] In the event that the numerical indication of the efficiency is below a first threshold efficiency value, initiating a threshold-initiated SCR cleaning event without waiting until the time interval t has elapsed,

[0015] wherein each of the time-initiated SCR cleaning event and the threshold-initiated SCR cleaning event comprises: injecting fuel into the engine at a first injection rate after an engine combustion event such that the fuel passes through the engine without being combusted to cause the fuel to combust in the diesel oxidation catalyst, thereby targeting an increase in the temperature of the exhaust gas in the diesel oxidation catalyst;

[0016] determining whether a set of criteria is satisfied, wherein the set of criteria includes determining that the SCR efficiency exceeds a second threshold efficiency after a threshold initiated SCR cleaning event; and

[0017] Where this set of criteria is met:

[0018] Triggering false warnings related to high sulfur fuel.

[0019] Thus, advantageously, the use of high sulfur fuel may be detected and communicated to the operator of the machine and / or a party servicing the machine and / or a fleet owner of the machine and / or the manufacturer of the machine.

[0020] In another aspect, an engine assembly is provided, comprising an internal combustion engine and an exhaust treatment device,

[0021] The internal combustion engine assembly further includes an engine control module configured to:

[0022] comparing the numerical indication of efficiency to a first threshold efficiency value, and:

[0023] Where the numerical indication of the efficiency remains above a first threshold efficiency value, waiting until a time interval t has elapsed and then initiating a time-initiated SCR cleaning event;

[0024] In the event that the numerical indication of the efficiency is below a first threshold efficiency value, initiating a threshold-initiated SCR cleaning event without waiting until the time interval t has elapsed,

[0025] wherein each of the time-initiated SCR cleaning event and the threshold-initiated SCR cleaning event comprises: injecting fuel into the engine at a first injection rate after an engine combustion event such that the fuel passes through the engine without being combusted to cause the fuel to combust in the diesel oxidation catalyst, thereby targeting an increase in the temperature of the exhaust gas in the diesel oxidation catalyst;

[0026] determining whether a set of criteria is satisfied, wherein the set of criteria includes determining that the SCR efficiency exceeds a second threshold efficiency after a threshold initiated SCR cleaning event; and

[0027] Where this set of criteria is met:

[0028] Triggering false warnings related to high sulfur fuel.

[0029] Thus, advantageously, the use of high sulfur fuel may be detected and communicated to the operator of the machine and / or a party servicing the machine and / or a fleet owner of the machine and / or the manufacturer of the machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0031] Figure 1 shows a highly schematic representation of an engine assembly to which the method of the present invention may be applied;

[0032] Figure 2 A flow chart showing a first embodiment of a method for controlling an engine component according to the present invention;

[0033] Figure 3 shows a graph of SCR efficiency versus time for an example engine running on conventional (low sulfur) fuel when using the method of the present invention;

[0034] Figure 4 shows a graph of SCR efficiency versus time for an example engine running on conventional (low sulfur) fuel when using the method of the present invention;

[0035] Figure 5 a graph showing SCR efficiency versus time for an example engine operating on high sulfur fuel when using the method of the present invention; and

[0036] Figure 6 A graph showing SCR efficiency versus time for an example engine operating on high sulfur fuel when using the method of the present invention is shown. DETAILED DESCRIPTION

[0037] Engine and aftertreatment architecture

[0038] To understand the context of the method of the present invention, a possible exhaust treatment device 550 of an engine assembly 500 that can be controlled by the method is described below. As will be readily appreciated by those skilled in the art, the method of the present invention is applicable to a wide range of exhaust treatment devices and is not limited to the specific example described below, which is provided merely to help the reader understand the context of the method of the present invention.

[0039] Figure 1 The exhaust treatment device 550 includes an exhaust flow path comprising a plurality of modules 520 , 530 through which exhaust may flow sequentially via a plurality of conduits 515 , 525 , 535 before being released into the atmosphere.

[0040] The fluid flow path downstream of the engine 510 may include, in series, a first conduit 515 connecting the outlet of the engine 510 with the inlet of the DOC module 520, a second conduit 525 connecting the outlet of the DOC module 520 with the inlet of the SCR 530, and a third conduit 535 providing an outlet to the atmosphere from the SCR 530. The SCR module includes an ammonia injector 532 supplied by an ammonia tank 534.

[0041] The fluid flow path may also include a DPF module upstream of the SCR module ( Figure 1 Further modules (not shown) may be present downstream or upstream of other modules.

[0042] The engine 510 may include a combustion unit (not shown) having an exhaust conduit 515 and one or more combustion cylinders (not shown). Each of the one or more cylinders may include a piston, a fuel injector, an intake valve, and an exhaust valve leading to an exhaust conduit. Fuel may be injected into the combustion cylinder (or each combustion cylinder) via the fuel injector. The fuel injector may be configured to inject fuel according to a controlled timing pattern.

[0043] Post-processing cleaning

[0044] Aftertreatment cleaning may require increasing the temperature of the exhaust gas treatment device.

[0045] In order to increase the temperature of the exhaust gas in the exhaust treatment device, it is known to burn fuel in the DOC module 520 to increase the temperature of the exhaust gas. While it is possible to inject fuel directly into the DOC module 520 for this purpose, it is also possible to avoid the need for separate fuel injectors by utilizing fuel injectors already present in the combustion cylinders of the engine 510. This may involve injecting fuel for combustion in the DOC module 520 by injecting fuel into the combustion cylinders of the engine at a time in the combustion cycle (e.g., during the exhaust stroke of the cylinder) when conditions are such that the fuel will pass directly through the cylinder without being burned and is therefore available for combustion within the DOC module 520. Such injections may be referred to as auxiliary injections or post-combustion injections to distinguish them from main injections that are timed so as to combust in the cylinder and drive the piston in a conventional manner.

[0046] Processes designed to improve the efficiency of exhaust gas treatment devices can be described as aftertreatment system cleaning processes or regeneration processes.

[0047] The extent to which post-treatment cleaning is required may depend on the extent to which post-treatment efficiency has decreased.

[0048] In the case of a DPF module, the degree to which DPF cleaning is required can depend on the amount of soot sensed or inferred to be present in the DPF. The sensed or inferred amount of soot can be described as the soot loading. A moderate soot loading can prompt a cleaning strategy that differs from the cleaning strategy required if the soot loading is more significant. It is known to provide different DPF cleaning processes in response to soot loading. Furthermore, it is known to escalate a series of increasingly effective DPF cleaning processes in response to increasing soot loading.

[0049] In the case of an SCR module, the extent to which SCR cleaning is required may depend on the extent to which ammonia deposits have accumulated within the SCR module. In addition to sensing the deposits, it may be assumed that deposits may have accumulated after a predetermined time interval since a previous cleaning event, and thus the timing of cleaning the SCR may simply be based on the predetermined time interval since a previous cleaning event.

[0050] In one example particularly applicable to the present invention, improved efficiency of the aftertreatment device may involve a strategy for removing ammonia deposits from the SCR module, which may be referred to as an SCR cleaning event.

[0051] An indication of SCR efficiency can be obtained from a pair of NO x The sensors are located one upstream of the SCR module and the other downstream of the SCR module. In this way, the percent efficiency can be calculated based on the values obtained from the pair of sensors.

[0052] An SCR cleaning event can include injecting fuel into the engine's combustion cylinders with auxiliary injections so that the fuel does not burn in the engine's cylinders but instead reaches the DOC module 520, where it burns, thereby increasing the temperature of the exhaust gas in the DOC module 520. These auxiliary injections can be configured to target a temperature increase of ΔT1. By increasing the temperature of the exhaust gas in the DOC, the exhaust gas reaching the SCR module has an increased temperature. This increased temperature may cause combustion of ammonia deposits in the SCR.

[0053] Examples of methods according to the invention

[0054] Figure 2 A simplified flow chart of the method according to the invention is shown.

[0055] The method includes receiving SCR efficiency data (which may be sensed or inferred) at step 110 and determining at step 120 whether a decrease in SCR efficiency (e.g., caused by accumulation of ammonia deposits) has caused the SCR efficiency to drop below a first threshold. The first threshold may represent an absolute efficiency level, a percentage efficiency, or some other variable that is a function of efficiency. In other words, it is determined whether the efficiency shortfall is significant enough to cause the efficiency to drop below the first threshold level. Whether measured or inferred, the efficiency may be expressed numerically. The first threshold may, for example, be in the range of 20% to 30%.

[0056] Where the numerical indication of efficiency is determined to be not below the first efficiency threshold, the method includes determining whether a time interval t has elapsed since the previous SCR cleaning event at step 130. Where time interval t has not elapsed, the method returns to step 110.

[0057] In the event that the time interval t has elapsed, a time-initiated SCR cleaning event is performed at step 140. Once the SCR cleaning event is concluded, the method returns to step 110.

[0058] Therefore, if the SCR operates as intended in conventional operation using conventional (low sulfur) fuel, the method will remain within the limits of the flow chart defined by dashed line 105 .

[0059] In practice, SCR efficiency data is likely to be generated on a fairly continuous basis.

[0060] Figure 3 Shows that when the method Figure 2 An example of SCR efficiency versus time when operating within the dashed line 105. Figure 3 In the example shown, the first threshold is 25%, and it is clear that the SCR efficiency never falls below this threshold.

[0061] Figure 3Covers a period of time including two SCR cleaning events occurring at 60 hours intervals. Figure 3 In the example of , the time interval t is 60 hours.

[0062] exist Figure 3 , a particular operation period of the engine begins at time A, a first SCR cleaning event begins at time B (i.e., after 60 hours of operation), and the first SCR cleaning event ends at time C; a second SCR cleaning event begins at time D (i.e., after another 60 hours of operation), and the second SCR cleaning event ends at time E. After each SCR cleaning event, the SCR efficiency returns approximately to the efficiency seen after the previous SCR cleaning event.

[0063] Figure 3 Both SCR cleaning events are time-initiated SCR cleaning events. Figure 3 Both SCR cleaning events shown occur at the end of time interval t, which is Figure 3 In China, it is 60 hours.

[0064] It is known that the maximum SCR efficiency decreases with operation. The maximum SCR efficiency can be considered to be the SCR efficiency immediately after an SCR cleaning event. After hundreds or thousands of hours of operation, the maximum SCR efficiency will decrease.

[0065] Figure 4 A graph showing SCR efficiency versus time after hundreds of hours of operation is shown. Figure 3 , Figure 4 The SCR startup efficiency is low. This is because of the hundreds of hours of previous operation. Figure 3 Similarly, the first threshold is 25%. Obviously, Figure 4 Under these conditions, the SCR efficiency never falls below this threshold.

[0066] Figure 4 Covers a period of time including two SCR cleaning events occurring at 60 hours intervals. Figure 4 For example, the time interval t is 60 hours, as Figure 3 .

[0067] exist Figure 4 In Figure 1, a particular operating period of the engine begins at time A, the first SCR cleaning event begins at time B (i.e., after 60 hours of operation), and the first SCR cleaning event ends at time C; the second SCR cleaning event begins at time D (i.e., after another 60 hours of operation), and the second SCR cleaning event ends at time E. After each SCR cleaning event, the SCR efficiency returns approximately to the efficiency seen after the previous SCR cleaning event. However, the SCR efficiency is lower than Figure 3In other words, the entire SCR efficiency curve is simply shifted downward.

[0068] Figure 4 Both SCR cleaning events are time-initiated SCR cleaning events.

[0069] When using high sulfur fuel, it is expected that SCR efficiency will decrease rapidly, so that periodic SCR cleaning events at predetermined time intervals t may not be sufficient. When the SCR efficiency drops below a first efficiency threshold, additional SCR cleaning events may be required. Such cleaning events may be referred to as threshold-activated SCR cleaning events.

[0070] Reference again Figure 2 If the method determines at step 120 that the SCR efficiency is below the first threshold efficiency, a check is performed to determine if the ammonia is too lean or if the ammonia injector is clogged. If this check is positive, it cannot be concluded that the cause of the low SCR efficiency is due to the use of high sulfur fuel, and the method returns to step 110.

[0071] A threshold initiated SCR cleaning event is performed at step 160. This occurs regardless of the time interval since the previous SCR cleaning event.

[0072] Note that steps 150 and 160 may be relative to Figure 2 The order shown is reversed.

[0073] After the threshold-initiated SCR cleaning event of step 160, a check is performed at step 170 to determine whether the SCR efficiency has recovered to exceed a second efficiency threshold, wherein the second efficiency threshold is determined to be moderately less than the SCR efficiency after the previous SCR cleaning event. If the SCR efficiency does not exceed the second threshold, it cannot be concluded that the cause of the low SCR efficiency is due to the use of high sulfur fuel, and the method returns to step 110.

[0074] If the check performed at step 170 indicates that the SCR efficiency has recovered to exceed the second threshold, a high sulfur fuel warning is output at step 180. Also, optionally, a thermal management mode may be invoked at step 190 (discussed further below).

[0075] The high sulfur warning (step 180) may include one or more of: a visible warning to the operator of the engine assembly; a warning to a maintenance engineer; a warning to the fleet operator of the engine assembly; a warning to the owner of the engine assembly; or any other warning indicating that the fuel in use appears to have a high sulfur content.

[0076] Figure 5 Shown is a graph of SCR efficiency versus time using high sulfur fuel. Figure 5The second efficiency threshold for the example is 73%, although the figure is not an absolute percentage, but depends on the maximum SCR efficiency (in Figure 5 In the example, 75% is the percentage change. Figure 3 and Figure 4 In the example of FIG. 5 , the first efficiency threshold is 25%.

[0077] The operation of the engine begins at time A. The SCR efficiency decreases rapidly, such that the SCR efficiency drops below the first efficiency threshold before the time interval t (60 hours of operation) elapses. If the SCR efficiency drops below the first efficiency threshold, the method ( Figure 2 Step 160 in triggering an SCR cleaning event.

[0078] exist Figure 5 In the example of FIG, the SCR cleaning event (occurring between time B and time C) causes the SCR efficiency to return to the SCR efficiency seen at the beginning of the engine's operating period (75%), which exceeds the second efficiency threshold. (This is in Figure 2 The check performed in step 170.)

[0079] At time C, the method outputs a high sulfur fuel warning ( Figure 2 180 in step 180).

[0080] Between time C and time D, when the SCR cleaning event has ceased, the engine may be operated in a so-called thermal management mode ( Figure 2 190 in loop 100). This thermal management mode may involve taking steps to increase the temperature of the SCR module even between SCR cleaning events. The thermal management mode may thereby reduce the rate at which the SCR efficiency decreases. Thus, the gradient of the curve between times C and D is less than the gradient of the curve between times A and B. However, at time D, the SCR efficiency again drops below the first threshold efficiency, and thus another threshold-initiated SCR cleaning event is triggered (step 160 on a subsequent iteration of loop 100) to return the SCR efficiency to approximately the same as at the beginning of the engine's operating period (i.e., exceeding the second efficiency threshold). At time E, the method outputs (or continues to output) the SCR efficiency indicated by Figure 2 The second cycle of the logic shown generates a high sulfur fuel warning.

[0081] Thermal management mode may employ techniques other than auxiliary fuel injection to increase the temperature in the SCR. Examples include increasing engine speed, increasing the use of exhaust gas recirculation (EGR) (if present), deploying a back pressure valve (if present), or taking other appropriate steps.

[0082] Figure 6A graph of SCR efficiency versus time is shown, where high sulfur fuel is used initially, but periodically (low sulfur fuel) is supplied to the fuel tank to dilute the high sulfur fuel, perhaps as prompted by a high sulfur fuel warning at time C.

[0083] Since the proportion of sulfur in the fuel is reduced (on average) by this dilution, the gradient of the curve between time C and time D becomes shallower than the gradient between time A and time B. This means that Figure 6 In the example of FIG. 5 , the entire 60 hour time interval (between time C and time D) passes without the SCR efficiency falling below the first threshold.

[0084] In this case, a third efficiency threshold can be considered. Figure 6 In the example of , the third efficiency threshold is set to 50%. Since the SCR efficiency drops below the third efficiency threshold before the end of the 60 hour time interval, the thermal management mode can remain in place even after the next SCR cleaning event ends at time E.

[0085] It is possible that thermal management is only removed once the SCR efficiency has not dropped below the third efficiency threshold at any time during the 60 hour period.

[0086] Note that in Figure 2 Not shown is the logic associated with the third efficiency threshold.

[0087] The SCR efficiency value, the first efficiency threshold, the second efficiency threshold, the third efficiency threshold, and the time interval t may all be set to appropriate values for a particular implementation.

[0088] Note that none of the example values set forth herein are to be considered limiting.

[0089] The maximum SCR efficiency is not limited to the example of 75% used in the present invention. The first efficiency value is not limited to the example of 25% used in the present invention. The second efficiency value is not limited to the example of 73% used in the present invention. The third efficiency value is not limited to the example of 50% used in the present invention. The time interval t is not limited to the example of 60 hours used in the present invention.

[0090] The value of each of these may be set to any value appropriate for the particular implementation in question.

[0091] For example, the time interval t may be of the order of tens of hours, such as 50 hours, or 60 hours, or 70 hours, or 80 hours, or 90 hours, or 100 hours, or 110 hours, or 120 hours, or 130 hours, or 140 hours.

[0092] It should also be noted that the efficiency threshold may not remain constant and may be a function of temperature and space speed.

[0093] It is possible that each efficiency threshold is not defined as a fixed threshold, but rather as a fixed deficit of efficiency relative to a value indicated by, for example, the maximum efficiency immediately after the end of the preceding cleaning cycle.

[0094] Industrial Applicability

[0095] The strategy presented here can be applied to any internal combustion engine having an aftertreatment device including an SCR module whose efficiency can be improved through proper cleaning, thermal management, and warning of unsuitable fuels.

Claims

1. A method of controlling an engine assembly comprising an internal combustion engine and an exhaust gas treatment device, The exhaust gas treatment device comprises: a diesel oxidation catalyst (DOC) module configured to convert carbon monoxide and hydrocarbons into carbon dioxide; and a selective catalytic reduction (SCR) module configured to promote NO x and ammonia, wherein the SCR module is downstream of the DOC module; The engine assembly is configured to provide a numerical indication of the efficiency of the SCR module; The method comprises: comparing the numerical indication of efficiency to a first threshold efficiency value, and: Where said numerical indication of efficiency remains above a first threshold efficiency value, waiting until a time interval t has elapsed and then initiating a time-initiated SCR cleaning event; initiating a threshold-initiated SCR cleaning event without waiting until said time interval t has elapsed in case said numerical indication of efficiency is below said first threshold efficiency value, wherein each of the time-initiated SCR cleaning event and the threshold-initiated SCR cleaning event comprises: injecting fuel into the engine at a first injection rate after an engine combustion event such that the fuel passes through the engine without being combusted to cause the fuel to combust in the diesel oxidation catalyst, thereby targeting an increase in the temperature of the exhaust gas in the diesel oxidation catalyst; determining whether a set of criteria is satisfied, wherein the set of criteria includes determining that the SCR efficiency exceeds a second threshold efficiency after the threshold-initiated SCR cleaning event; and Where the stated set of criteria are met: Triggering false warnings related to high sulfur fuel.

2. The method of claim 1, wherein the set of criteria further comprises: It is determined that the ammonia concentration value of the ammonia supplied to the SCR is greater than an ammonia concentration threshold.

3. The method according to claim 2, further comprising: In a case where the ammonia concentration value of the ammonia supplied to the SCR is less than the ammonia concentration threshold value, an ammonia concentration warning is output.

4. The method according to any one of the preceding claims, wherein the set of criteria further comprises: It is determined that an injector for injecting ammonia into the exhaust treatment device exhibits injector behavior indicative of no clogging. 5 . The method of claim 4 , further comprising outputting an injector warning if injector behavior indicates a blockage. 6 . The method of claim 1 , further comprising confirming, after completion of the SCR cleaning event, that the numerical indication of efficiency exceeds a second threshold efficiency value. The method of claim 6 , wherein the second threshold efficiency value is between 70% and 80%.

8. The method of any one of claims 1-3, wherein the first threshold efficiency value is between 20% and 30%.

9. The method of any one of claims 1 to 3, wherein if the time interval is less than a threshold time interval, the method comprises, after the threshold-initiated SCR cleaning event: Take one or more of the following steps to increase the temperature of the exhaust gas in the SCR module: increasing an engine speed to a target increased temperature in the engine; increasing the use of exhaust gas recirculation; Deploy back pressure valves; Fuel is injected into the engine at a second injection rate after the engine combustion event, wherein the second injection rate is less than the first injection rate such that the fuel passes through the engine without being combusted to allow the fuel to combust in the diesel oxidation catalyst to maintain an increased temperature of the exhaust gas in the diesel oxidation catalyst between SCR cleaning events.

10. The method of claim 9, wherein said step of taking steps to increase the temperature of the exhaust gas in the SCR module continues until said numerical indication of efficiency remains above a third threshold efficiency value for a subsequent time period, wherein said subsequent time period has the same duration as said time interval t.

11. The method of any one of claims 1 to 3, wherein the numerical indication of efficiency is derived from a function of one or more of: SCR back pressure; From the NO located upstream of the SCR module x sensor-derived values; From the NO located downstream of the SCR module x The value derived by the sensor.

12. The method of claim 10, wherein the numerical indication of efficiency is derived from a function of the difference between: NO from the downstream of the SCR module x said sensor-derived value; and NO from the upstream of the SCR module x The value derived by the sensor.

13. An engine assembly comprising an internal combustion engine and an exhaust gas treatment device, The internal combustion engine assembly further includes an engine control module configured to: comparing the numerical indication of efficiency to a first threshold efficiency value, and: Where said numerical indication of efficiency remains above a first threshold efficiency value, waiting until a time interval t has elapsed and then initiating a time-initiated SCR cleaning event; initiating a threshold-initiated SCR cleaning event without waiting until said time interval t has elapsed in case said numerical indication of efficiency is below a first threshold efficiency value, Each of the time-initiated SCR cleaning event and the threshold-initiated SCR cleaning event comprises: injecting fuel into the engine at a first injection rate after an engine combustion event such that the fuel passes through the engine without being combusted to cause the fuel to combust in a diesel oxidation catalyst to target an increase in the temperature of the exhaust gas in the diesel oxidation catalyst; determining whether a set of criteria is satisfied, wherein the set of criteria includes determining that the SCR efficiency exceeds a second threshold efficiency after the threshold-initiated SCR cleaning event; and Where the stated set of criteria are met: Triggering false warnings related to high sulfur fuel.

14. The engine assembly of claim 13, further comprising an ammonia tank configured to supply ammonia to the SCR.

15. The engine assembly of claim 14, wherein the ammonia tank includes an ammonia concentration sensor.

16. The engine assembly of any one of claims 13-15, further comprising an injector configured to inject ammonia into the SCR module.

17. The engine assembly of claim 16, wherein the injector includes an injector sensor configured to detect a blockage in the injector.

18. The engine assembly of claim 17, wherein the injector sensor comprises a pressure sensor.

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