Abstract:
An exhaust fluid treatment apparatus used to treat exhaust fluid emitted by a combustion engine includes a check of its functionality. A method of monitoring operation of an exhaust fluid treatment apparatus includes comparing a calculated temperature difference with an expected temperature difference associated with combustion of fuel. If the calculated temperature difference is within an acceptable margin of the expected temperature difference, further fuel injection may be permitted. If the calculated temperature difference is outside the acceptable margin of the expected temperature difference, a temperature of the exhaust gas upstream of the exhaust fluid treatment apparatus may be increased.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure relates to the field of exhaust fluid treatment and, in particular, to monitoring operation of an exhaust fluid treatment apparatus having a diesel oxidation catalyst. 
       BACKGROUND 
       [0002]    An exhaust fluid treatment apparatus may comprise a plurality of modules, wherein each module is intended to treat one or more constituents of an exhaust fluid. The modules may be arranged in series such that exhaust fluid flows through each module in sequence. 
         [0003]    An exhaust fluid treatment apparatus may comprise a diesel oxidation catalyst module, a diesel particulate filter module downstream of the diesel oxidation catalyst module and/or a selective catalytic reduction module, downstream of the diesel particulate filter module. 
         [0004]    It may be appropriate to perform periodic checks on individual modules of the exhaust fluid treatment apparatus to ensure that the individual modules are performing as expected. This may be particularly important if unexpected performance of a module earlier in the fluid flow path may have an effect on performance of modules which are located later in the fluid flow path. 
         [0005]    For example, unexpected performance in the diesel oxidation catalyst can result in reduced oxidation of hydrocarbons in the diesel oxidation catalyst. This, in turn, may mean that the fluid output from the diesel oxidation catalyst has a lower temperature than expected and/or desired. Such unexpected performance may also result in emission of unburnt fuel to atmosphere. Unexpected performance in the diesel oxidation catalyst may arise as a consequence of deposits, such as sulphurous deposits, collecting on the catalytic surfaces of the diesel oxidation catalyst. A reduced temperature of fluid output from the diesel oxidation catalyst can result in unexpected performance of a diesel particulate filter located downstream of the diesel oxidation catalyst since, at lower temperatures, carbon entering the diesel particulate filter in the form of soot is less likely to oxidise in the diesel particulate filter. Lower temperatures can also effect performance in a selective catalytic reduction module located downstream of the diesel particulate filter. 
         [0006]    It is known to inject fuel into the diesel oxidation catalyst for combustion therein, for example to increase temperature in the diesel oxidation catalyst or to cause particular constituents within the diesel oxidation catalyst to be combusted. For example, it may be desirable to desulphate the exhaust fluid treatment apparatus or to remove deposits therefrom. It may be undesirable, however, to inject fuel into the diesel oxidation catalyst where the fuel may pass through the diesel oxidation catalyst without combusting. It may, therefore, be appropriate to check performance of a diesel oxidation catalyst in order to ensure that injected fuel combusts as expected. 
         [0007]    Against this background, there is provided a method for checking operation of the diesel oxidation catalyst module. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    A method of monitoring operation of an exhaust fluid treatment apparatus, the apparatus comprising a diesel oxidation catalyst comprising an inlet and an outlet, the method comprising:
       receiving an input temperature data value being indicative of temperature of fluid at the inlet;   injecting a first quantity of fuel upstream of the diesel oxidation catalyst for combustion in the diesel oxidation catalyst;   receiving an output temperature data value being indicative of temperature of fluid at the outlet;   calculating a calculated temperature difference between the input temperature data value and the output temperature data value and comparing the calculated temperature difference with an expected temperature difference associated with the quantity of fuel injected; and:   if the calculated temperature difference is within an acceptable margin of the expected temperature difference, injecting a second quantity of fuel into the exhaust fluid for combustion in the diesel oxidation catalyst; and   if the calculated temperature difference is outside the acceptable margin of the expected temperature difference, raising a temperature of exhaust gas upstream of the inlet to the diesel oxidation catalyst.       
 
         [0015]    Specific embodiments of the disclosure will now be described, by way of example only, with reference in the accompanying drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a schematic drawing of an embodiment of an exhaust fluid treatment apparatus to which the method may be applied; 
           [0017]      FIG. 2  shows a more detailed schematic drawing of an embodiment of an exhaust fluid treatment apparatus to which the method may be applied; 
           [0018]      FIG. 3  shows a schematic drawing of an external appearance of the embodiment of  FIG. 2 ; and 
           [0019]      FIG. 4  shows a flow chart which illustrates an embodiment of the method of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Before describing the specifics of an embodiment of the method of the disclosure, the following is an explanation of the features and broad operation of an exhaust fluid treatment apparatus to which the method of the disclosure might be applied. 
         [0021]    Referring first to  FIGS. 1 to 3 , there is illustrated an embodiment of an exhaust fluid treatment apparatus  1 . The apparatus  1  may comprise a fluid flow path through which fluid may flow sequentially through various conduits, such as a first conduit  10 , a first end coupling  15 , a second conduit  20 , a second end coupling  25 , and a third conduit  30 . The first, second and third conduits  10 ,  20 ,  30  may be substantially mutually parallel. 
         [0022]    The fluid flow path may comprise, in series, a diesel oxidation catalyst (DOC) module  110 , a diesel particulate filter (DPF) module  120 , a mixer module  130 , a selective catalytic reduction (SCR) module  140  and/or an ammonia oxidation catalyst (AMOX) module  150 . 
         [0023]    In use, fluid may be supplied to the exhaust fluid treatment apparatus  1  via the inlet  4 . Fluid may pass into the DOC module  110  in the first portion of the first conduit  10 . Prior to receipt at the inlet  4 , the pressure of the exhaust fluid may be controlled by a back pressure valve (not shown). 
         [0024]    The DOC module  110  may comprise one or more catalysts, such as palladium or platinum. These materials serve as catalysts to cause oxidation of hydrocarbons ([HC]) and carbon monoxide (CO) present in the fluid flow in order to produce carbon dioxide (CO 2 ) and water (H 2 O). The DOC may also serve to convert NO to NO 2  so as to achieve a NO:NO 2  ratio of 1:1. The catalysts may be distributed in a manner so as to maximise the surface area of catalyst material in order to increase effectiveness of the catalyst in catalysing reactions. 
         [0025]    Fluid may flow from the DOC module  110  to the DPF module  120  which comprises features which are intended to restrict onward passage of carbon (C) in the form of soot. Carbon particles in the fluid may thus be trapped in the DPF. The DPF module  120  may be regenerated through known regeneration techniques. These techniques may involve controlling one or more of the temperature of the fluid, the pressure of the fluid and the proportion of unburnt fuel in the fluid at this point in the apparatus. 
         [0026]    Exhaust fluid may pass from the DPF module  120  into the first end coupling  15  where it flows past the injector module  16 . The injector module  16  may be associated with or attachable to a pump electronic tank unit (PETU). The pump electronic tank unit may comprise a tank for providing a reservoir for emissions fluid to be injected by the injector. Such emissions fluids may include urea or ammonia. 
         [0027]    The PETU may further comprise a controller configured to control a volume of emissions fluid to be injected from the tank by the injector. The controller may have as inputs, for example, temperature information and quantity of NO x  information which may be derived from sensors in the SCR module  140 . 
         [0028]    Emissions fluid may pass from the injector module  16  into the mixer module (not shown) located in the second conduit  20 . The mixer module may comprise features for ensuring that the exhaust fluid originating from the first conduit  10  is well mixed with the emissions fluid originating from the injector  16 , to create a mixed fluid. 
         [0029]    The mixed fluid may pass from the second conduit  20  and into the SCR module located in the first portion of the third conduit via the second end coupling  25 . The SCR module  140  may comprise one or more catalysts through which the mixed fluid may flow. As the mixed fluid passes over the surfaces of the catalyst a reaction may occur which converts the ammonia and NO x  to diatomic nitrogen (N 2 ) and water (H 2 O). 
         [0030]    Fluid may pass from the SCR module  140  to the AMOX module  150  located in the second portion of the third conduit  30 . The AMOX module  150  may comprise an oxidation catalyst which may cause residual ammonia present in the fluid exiting the SCR module to react to produce nitrogen (N 2 ) and water (H 2 O). 
         [0031]    Fluid may pass from the AMOX module  150  to the exhaust fluid treatment apparatus outlet located at the second end  32  of the third conduit  30 . 
         [0032]    As shown in  FIG. 2 , the exhaust fluid treatment apparatus  1  may comprise sensors for detecting characteristics of the fluids at particular stages in their flow through the exhaust fluid treatment apparatus  1 . There may be a first temperature sensor (not shown) upstream of the DOC module  110 , a second temperature sensor  190  between the DOC module  110  and the DPF  120  and/or a third temperature sensor  191  between the mixer module  130  and the SCR  140 . There may be a first NO x  sensor  192  between the DPF module  120  and the injector  16  and there may be a second NO x  sensor  193  downstream of the AMOX module  150 . There may also be a first soot sensor  194  immediately upstream of the DPF  120  and possibly a second soot sensor  195  immediately downstream of the DPF  120 . 
         [0033]    Having described the features and broad operation of the exhaust fluid treatment apparatus, the method of the present disclosure will now be described. 
         [0034]    Referring to  FIG. 4 , there is illustrated a flow chart  300  showing an embodiment of the method of the disclosure. 
         [0035]    In use, exhaust fluid from an engine is received into an inlet  4  of the exhaust fluid treatment apparatus  1  for onward travel to the DOC module  110 . The exhaust fluid has a temperature at the point where it is received into the DOC module  110 . The method may involve receiving a first data value  310  relating to the temperature of fluid flowing into the DOC module  110 . The temperature of the gas at the point where it is received into the DOC module  110  may not be directly measurable due to location of temperature sensors. That is, there may not be a temperature sensor immediately prior to the inlet of the DOC module  110 . The method may therefore involve receiving temperature information at a point upstream of the DOC module  110  and accounting, perhaps by predictive models or similar, for likely changes in temperature between the upstream point and the inlet to the DOC module  110 . Whether directly measured or not, the first data value  310  is indicative of a temperature of gas flowing into the DOC module  110 . 
         [0036]    The method may involve injecting a first quantity of unburnt fuel upstream of the DOC module  110  for oxidation in the DOC module  110 . This fuel may be injected at any point upstream of the DOC module  110  such as, for example, into a combustion cylinder of an engine to which the exhaust fluid treatment apparatus may be attached (at a time in the combustion cycle when it is unlikely to combust in the cylinder). Alternatively, it may be injected directly into a conduit upstream of the DOC module  110 . 
         [0037]    The method may also involve receiving a second data value  320  relating to the temperature of fluid flowing out of the DOC module  110 . This might be measured using the temperature sensor  190  located immediately downstream of the DOC. 
         [0038]    The method may involve checking a data library to determine the expected temperature rise associated with oxidation in the DOC module  110  of the first quantity of fuel injected. The expected temperature rise may be compared with the difference between the second data value  320  and the first data value  310 . 
         [0039]    Since the temperature may be varying as a consequence of other factors (i.e. changing speed and load on the engine with which the exhaust fluid treatment apparatus is in use), the expected temperature rise may take into account the influence of such other factors in addition to the temperature difference expected from the combustion of the first quantity of fuel in the DOC module  110 . This may be achieved by superimposing an expected temperature difference deemed to be attributable to the combustion of the first quantity of fuel in the DOC module  110  onto an expected temperature difference deemed to be attributable to other factors, so as to arrive at a net expected temperature difference. Alternatively, it may be achieved by seeking effectively to subtract from the total expected temperature difference a temperature difference deemed to be attributable to other factors in order to isolate a temperature difference deemed to be attributable to the combustion of the first quantity of fuel in the DOC module  110 . Alternatively, the data library may comprise a plurality of different data sets each of which take into account different conditions likely to influence the temperature of gas in the DOC module  110  in order to provide an expected temperature difference for a wide range of different conditions. 
         [0040]    The method may involve determining if the temperature difference is within an expected margin of the expected temperature difference. The expected margin of the expected temperature difference may be, for example, within 30% of the expected temperature difference. Alternatively, the expected margin of the expected temperature difference may be, for example, within 20% of the expected temperature difference. 
         [0041]    Any change in temperature resulting from oxidation of fluid in the DOC (or resulting from changing input conditions) may occur after a delay. Moreover, the speed with which an expected temperature rise may be expected to occur may vary depending on a wide range of parameters. As such, there may be a delay between the step of receiving an input temperature data value being indicative of temperature of exhaust fluid at the inlet and the step of receiving an output temperature data value being indicative of temperature of exhaust fluid at the outlet. The duration of any delay may depend on a range of operating parameters. 
         [0042]    It may be that a continuous flow of input temperature data values is received, each input temperature data value being indicative of temperature of fluid at the inlet. It may also be that a continuous flow of output temperature data values is received, each output temperature data value being indicative of temperature of fluid at the outlet. It may also be that the method involves comparing an input temperature data value received at a first time with an output temperature data value received at a second time, wherein the second time is after the first time, in order to allow for the expected period for the temperature to change. 
         [0043]    In the event that the difference between the first and second data values is within the expected margin of the expected temperature rise, the method may assume that the DOC is operating within required margins. Consequently, the method may involve injecting a second quantity of fuel for combustion in the DOC module  110  since the check assumes that the second quantity of fuel will combust in the DOC module  110 , thus reducing a risk that fuel will pass out of the DOC module  110  unburnt. 
         [0044]    In the event that the difference between the first and second data values is outside the expected margin of the expected temperature rise, the method may involve increasing a temperature of the gas entering the DOC module  110 . This might be achieved, for example, by moving the back pressure valve more towards the closed position therefore requiring the engine to do more work and thereby produce more heat. The backpressure valve may be located upstream of the diesel oxidation catalyst. By this method, the temperature of fluid in the DOC may increase. Alternatively, if the engine comprises exhaust gas recirculation, in may be achieved by altering the proportion of exhaust fluid being recirculated. There are a number of options for increasing the temperature of the gas entering the DOC module  110 , and the method of the disclosure is not limited to any particular option. However, the number of options and extent of their possible application may be limited by a desire that the change be unnoticeable to a user. 
         [0045]    The step of increasing a temperature of the gas entering the DOC module  110  may involve seeking to increase the temperature in the DOC from, for example, approximately 240° C. to, for example, approximately 270° C. 
         [0046]    With age (i.e., hundreds or thousands of hours of use) DOC module  110  performance may be expected to deteriorate. When this is the case it may be appropriate, in the event that the calculated temperature difference is outside the acceptable margin of the expected temperature difference, to increase the temperature by a greater amount than when the DOC module  110  is new (or freshly refurbished or regenerated). Consequently, the method may allow for an increased temperature rise with increased age of the DOC module  110 . For example, the method may involve seeking to increase the temperature in the DOC to at least, approximately 240° C. and possibly, up to approximately 290° C. 
         [0047]    As an additional or alternative approach to possible deterioration of the DOC module  110  with age, it may be that the expected margin of the expected temperature change adjusts according to the method with age of the DOC module  110 . 
         [0048]    The method of the present disclosure may be performed periodically while the engine and exhaust fluid treatment apparatus are in normal use. Consequently, there may be a limit on the parameters which can be changed in order to increase the temperature so as to prevent the change in parameters being evident to the user of the apparatus. 
         [0049]    As stated above, there may be a variety of reasons why and circumstances in which it may be desirable to inject into engine cylinders fuel which is intended to pass through the cylinders unburnt. One further example may be a desire to achieve desulphation of an SCR module located downstream of the DOC as part of a SCR desulphation procedure. Such a desulphation procedure may require an increased temperature in the SCR in order that sulphur combusts. The increased temperature in the SCR may be achieved by injecting unburnt fuel into the DOC (upstream of the SCR) for burning in the DOC and thereby increasing a temperature of the fluid arriving at the SCR. Such a procedure may take place intermittently and might occur only when a need for such a procedure has been identified as part of overall engine control. The method of the present invention may be used as part of this procedure. 
         [0050]    The terms exhaust gas and exhaust fluid may be used interchangeably. The exhaust gas/fluid may include solid particles such as particles of soot which, while in the solid phase, may be understood to be a constituent of exhaust gas/fluid. 
         [0051]    While the term data library is used in this disclosure, the data may be stored in any suitable facility for the storage of data such as a look up table.