JP2015105633A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of making a selective reduction type catalyst recover from an HC poisoning state before a function of the selective reduction type catalyst is significantly degraded.SOLUTION: In an exhaust emission control device in which a selective reduction type catalyst 5 and a particulate filter 10 are combined, a control device 13 is constituted to estimate an accumulation amount of particulate on the particulate filter 10 and an accumulation amount of HC on the selective reduction type catalyst 5 according to an operating state of a diesel engine 1, forcibly regenerate the particulate filter 10 when any of the accumulation amounts reaches a predetermined specified amount or more, and reset both of the accumulation amounts when the forcible regeneration is completed.

Description

  The present invention relates to an exhaust emission control device.

  Conventionally, a diesel engine is equipped with a selective catalytic reduction catalyst having a property of selectively reacting NOx (nitrogen oxide) with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows. A required amount of reducing agent was added upstream of the selective catalytic reduction catalyst, and the reducing agent was allowed to undergo a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is something.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied.

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is hydrolyzed into ammonia and carbon dioxide gas by the following equation by the heat of the exhaust gas, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The NOx contained therein is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

  On the other hand, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas, and particulates contained in the exhaust gas are also collected through the particulate filter. However, when this type of particulate filter is employed, it is necessary to regenerate the particulate filter by appropriately burning and removing the particulate before the exhaust resistance increases due to clogging.

  For this reason, a flow-through type oxidation catalyst is attached to the preceding stage of the particulate filter, and fuel is added to the exhaust gas upstream from the oxidation catalyst when the amount of particulate accumulation increases. It is considered to force playback.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter immediately after that is raised, the particulates are burned out, and the particulate filter is regenerated.

  In general, as a specific means for performing the fuel addition as described above, the post-injection is executed at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is considered to add fuel to the exhaust gas, but in order to efficiently use the added fuel for forced regeneration and to oxidize the added fuel before the exhaust gas temperature drops as much as possible, It is considered preferable to arrange the curate filter and the preceding oxidation catalyst upstream of the selective reduction catalyst.

  In such an exhaust purification device, there is a risk that the selective catalytic reduction catalyst is poisoned by HC in the exhaust gas and the catalytic function is lowered. It is known that HC is desorbed and oxidized by high temperature exhaust gas flowing into the selective catalytic reduction catalyst during high load operation. So far, measures to recover HC poisoning of the selective catalytic reduction catalyst The fact is that there is no special treatment.

  The prior art document information related to the exhaust gas purification apparatus using the selective reduction catalyst and the particulate filter in combination as described above includes the following Patent Document 1.

JP 2008-75620 A

  However, a vehicle or the like that travels only in a crowded urban area may continue to operate at a medium load or lower for a long period of time without reaching a high load operation. There is a possibility that the required NOx reduction performance cannot be exhibited by not recovering while the function is deteriorated due to poison.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust purification device that can recover a selective catalytic reduction catalyst from a state of HC poisoning before causing a significant functional deterioration.

  The present invention relates to a selective reduction catalyst that is arranged in the middle of an exhaust pipe and can selectively react NOx with ammonia even in the presence of oxygen, and urea water as a reducing agent in the exhaust gas upstream of the selective reduction catalyst. A urea water addition means for adding a particulate filter, a particulate filter disposed in the middle of the exhaust pipe upstream of the urea water addition position of the urea water addition means and provided with an oxidation catalyst in the preceding stage, and upstream of the oxidation catalyst Fuel addition means for forcibly regenerating the particulate filter by increasing the exhaust temperature by adding fuel to the exhaust gas and causing an oxidation reaction on the oxidation catalyst, fuel addition by the fuel addition means, and addition of the urea water And a control device for controlling the addition of urea water, and the amount of particulates deposited in the particulate filter and the amount of HC deposited in the selective catalytic reduction catalyst are determined. The particulate filter is forcibly regenerated when estimated according to the operating condition of the engine and any one of the accumulated amounts exceeds a predetermined amount set for each, and when the forced regeneration is completed, The present invention relates to an exhaust emission control device characterized in that the control device is configured to reset both accumulation amounts.

  Thus, in this way, not only when it is estimated that the particulate accumulation amount in the particulate filter has exceeded the prescribed amount, but also the HC accumulation amount in the selective reduction catalyst exceeds the prescribed amount. Even when it is estimated that the particulate filter has become, forced regeneration of the particulate filter is started, the fuel adding means is controlled by the control device, and the fuel is added by the fuel adding means, and the added fuel becomes the oxidation catalyst. The exhaust gas rises in temperature due to the reaction heat generated during the oxidation reaction above, and the inflow of the exhaust gas raises the catalyst bed temperature of the particulate filter immediately after that, so that the particulates are burned out and the particulate filter is regenerated. It will be illustrated.

  At this time, the selective reduction type catalyst located downstream of the particulate filter is supplied with exhaust gas that has been heated by burning of the particulates that have been collected in the particulate filter, and corresponds to a catalyst corresponding to high load operation. As a result of the heating up to the bed temperature and the desorption and oxidation of HC proceed, the amount of HC deposited becomes zero and the selective catalytic reduction catalyst recovers from the HC poisoning state.

  In addition, while the forced regeneration time required for burning and removing the particulates collected by the particulate filter is relatively long, the recovery required for oxidization by desorbing the HC of the selective catalytic reduction catalyst. Since the time can be significantly reduced, even if it is estimated that the amount of HC deposited on the selective catalytic reduction catalyst exceeds the specified amount, even if the amount of particulate deposited on the particulate filter is not so large, Once the forced regeneration of the curate filter is started, the selective catalytic reduction catalyst recovers in a short time.

  In carrying out the present invention more specifically, the particulate generation amount based on the current engine operating state is read out from the particulate generation map based on the engine speed and the fuel injection amount from time to time, and accumulated. The controller can be configured to estimate the amount of accumulated particulates by interrupting the accumulation of particulates only when the inlet side exhaust temperature of the particulate filter is equal to or higher than a predetermined temperature. .

  Also, the HC generation amount based on the current engine operating state is read from the HC generation amount map based on the engine speed and the fuel injection amount from time to time, and the read-out value is converted to the inlet side exhaust temperature of the selective catalytic reduction catalyst. Accordingly, it is also possible to configure the control device so as to estimate the amount of HC deposition by multiplying and correcting the coefficient in consideration of the amount of oxidation treatment at the temperature, and then accumulating.

  Further, the particulate regeneration amount corresponding to the inlet filter temperature of the particulate filter is accumulated from the start of the forced regeneration of the particulate filter, and the forced regeneration is performed when the accumulated regeneration amount catches up with the particulate accumulation amount. The controller can be configured to determine completion.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) Forced regeneration of the particulate filter is started even when it is estimated that the amount of accumulated HC in the selective catalytic reduction catalyst has exceeded a specified amount, and the particulate filter is regenerated while attempting to regenerate the particulate filter. Since the selective catalytic reduction catalyst on the side can be recovered from the HC poisoning state, the selective catalytic reduction catalyst can be recovered from the HC poisoning state before causing a significant deterioration in function, leading to high-load operation. Even if the vehicle has an operation mode in which the operation at a medium load or lower continues for a long period of time, it can be maintained so that the required NOx reduction performance can be surely exhibited.

  (II) Since the selective reduction catalyst can be recovered from the HC poisoning state by effectively utilizing the system for forcibly regenerating the existing particulate filter, the cost can be reduced without adding new equipment. Can be implemented.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the specific control procedure in the control apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention. In the exhaust purification apparatus of this embodiment, an exhaust pipe through which exhaust gas 3 discharged from a diesel engine 1 (engine) through an exhaust manifold 2 flows. 4 is equipped with a selective catalytic reduction catalyst 5 having the property of selectively reacting NOx with ammonia even in the presence of oxygen.

A urea water addition injector 7 (urea water addition means) for injecting urea water 6 as a reducing agent is installed in the exhaust pipe 4 upstream of the selective reduction catalyst 5 and the selective reduction catalyst. Immediately after 5, an NH ₃ slip catalyst 8 that oxidizes surplus ammonia as a countermeasure against leaked ammonia is provided, and the exhaust pipe 4 is disposed upstream of the urea water 6 addition position by the urea water addition injector 7. The particulate filter 10 provided with the oxidation catalyst 9 is disposed in the previous stage.

  Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 11 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and the rotational speed is set at an appropriate position of the diesel engine 1. The rotation sensor 12 to detect is equipped, The accelerator opening signal 11a and the rotation speed signal 12a from these accelerator sensor 11 and the rotation sensor 12 are input into the control apparatus 13 which comprises an engine control computer (ECU: Electronic Control Unit). It has come to be.

  On the other hand, in the control device 13, the fuel injection timing and the injection toward the fuel injection device 14 for injecting the fuel into each cylinder according to the current operation state determined from the accelerator opening signal 11a and the rotation speed signal 12a. A fuel injection signal 14a for commanding the amount is output.

  Here, the fuel injection device 14 is constituted by a plurality of injectors (not shown) provided for each cylinder, and the electromagnetic valves of these injectors are appropriately opened by a fuel injection signal 14a from the control device 13. Thus, the fuel injection timing and the injection amount (valve opening time) are appropriately controlled.

  However, in the present embodiment, the control device 13 determines the fuel injection signal 14a in the normal mode based on the accelerator opening signal 11a and the rotation speed signal 12a. When execution of forced regeneration of the filter 10 is decided, the normal mode is switched to the forced regeneration mode, and the non-ignition which is later than the compression top dead center following the main injection of fuel performed near the compression top dead center (crank angle 0 °). The fuel injection signal 14a is determined so as to perform post injection at the timing (start time is in the range of crank angle 90 ° to 130 °).

  That is, the fuel injection device 14 in this embodiment functions as a fuel addition means for adding fuel into the exhaust gas 3 upstream of the oxidation catalyst 9, and follows the main injection as described above. If post-injection is performed at a non-ignition timing later than the compression top dead center, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3 by this post-injection, and this unburned fuel The fuel is oxidized on the oxidation catalyst 9, and the catalyst bed temperature of the particulate filter 10 is raised immediately by the inflow of the exhaust gas 3 heated by the reaction heat, and the particulates are burned out. Can be regenerated.

  In the example shown here, the case where fuel is added by post injection by the fuel injection device 14 is illustrated, but instead of such post injection, the exhaust pipe 4 upstream of the oxidation catalyst 9 is used. Of course, an injector may be separately provided as a fuel addition means, and fuel may be directly injected into the exhaust gas 3 in the exhaust pipe 4 by this injector.

  Further, the control device 13 extracts the fuel injection amount determined from the rotational speed of the diesel engine 1 and the output value of the fuel injection signal 14a, and from the NOx generation amount map based on the rotational speed and the fuel injection amount, The amount of NOx generated based on the operating state of the diesel engine 1 is estimated, and the addition of a necessary amount of urea water 6 commensurate with the amount of NOx generated is directed to the urea water addition injector 7 as a urea water injection signal 7a. It has become.

  When the selective reduction catalyst 5 decides to perform the forced regeneration of the particulate filter 10, it is performed according to the flowchart of FIG. 2 as described in detail below.

  That is, in step S1, the number of revolutions of the diesel engine 1 and the fuel injection amount determined from the output value of the fuel injection signal 14a are extracted, and the current diesel engine is calculated from the particulate generation map based on the number of revolutions and the fuel injection amount. The amount of particulate generation based on the operating state of 1 is read out every moment and integrated.

  However, the accumulation of the amount of generated particulates is interrupted only when the inlet side exhaust temperature of the particulate filter 10 detected as the detection signal 15a by the temperature sensor 15 is equal to or higher than a predetermined temperature. Only the amount of particulates generated when the inlet side exhaust temperature of the curative filter 10 is lower than the predetermined temperature is integrated, and the amount of particulates accumulated is estimated as if all of the particulates were accumulated on the particulate filter 10. It has become.

  Here, the accumulation of the amount of particulate generation is interrupted only when the inlet side exhaust temperature of the particulate filter 10 is equal to or higher than a predetermined temperature. This is because it can be considered that the combustion (oxidation reaction) of the catalyst proceeds efficiently and the amount of deposition does not increase.

  In addition, if the combustion (oxidation reaction) of the particulates proceeds efficiently, the amount of deposition may rather decrease, but it is difficult to accurately calculate the amount of decrease, and errors will occur as the integration is repeated. Therefore, from the viewpoint of reliably avoiding the risk of the particulate filter 10 falling into an over trapped state, the accumulation of the amount of generated particulates is only interrupted.

  In the next step S2, the determination as to whether or not the accumulation amount estimated in the previous step S1 is equal to or greater than the prescribed amount A required for the particulate filter 1 is repeated until it reaches the prescribed amount A or more. When the prescribed amount A is exceeded, the process proceeds to step S3.

  On the other hand, in parallel with the flow of Steps S1 and S2, in Step S4, the generation of HC based on the current operation state of the diesel engine 1 from the HC generation amount map based on the rotational speed of the diesel engine 1 and the fuel injection amount. The amount (the amount of HC emitted from the diesel engine 1) is read out every moment and the read value is detected as a detection signal 16a by the temperature sensor 16 according to the inlet side exhaust temperature of the selective catalytic reduction catalyst 5 at that temperature. After the correction is made by multiplying the coefficient by taking into account the amount of treatment (the ratio of oxidation treatment in the exhaust gas 3 or the oxidation catalyst 9), the accumulation is performed.

  In the next step S5, the determination as to whether or not the accumulation amount estimated in the previous step S4 is equal to or greater than the prescribed amount B that requires recovery of the selective catalytic reduction catalyst 5 is repeated until it reaches the prescribed amount B or more. When the amount exceeds the specified amount B, the process proceeds to step S3.

  In this step S3, when it is determined in any one of step S2 and step S4 that the deposition amount is equal to or greater than the specified amount A or B, the forced regeneration of the particulate filter 10 is determined, The forced regeneration of the particulate filter 10 is started.

  In the next step S6, the particulate regeneration amount corresponding to the inlet side exhaust temperature of the particulate filter 10 is accumulated from the start of the forced regeneration of the particulate filter 10, and the accumulated regeneration amount is used as the particulate amount. Completion of forced regeneration is determined when catching up the accumulation amount (particulate accumulation amount accumulated in step S1) (when it becomes the same).

  At this time, in calculating the particulate regeneration amount, the particulate regeneration speed corresponding to the inlet exhaust temperature of the particulate filter 10 is obtained by a preliminary experiment or the like, and the inlet exhaust temperature of the particulate filter 10 is calculated. What is necessary is just to obtain | regenerate the amount of reproduction | regeneration based on time transition.

  When it is determined that the compulsory regeneration of the particulate filter 10 has been completed in this way, the process proceeds to step S7, where the particulate accumulation amount in the particulate filter 10 (the particulate accumulation amount accumulated in step S1), and The amount of HC accumulated in the selective catalytic reduction catalyst 5 (the amount of HC accumulated in step S4) is reset.

  Thus, in this way, not only is it estimated that the particulate accumulation amount in the particulate filter 10 has become equal to or greater than the prescribed amount A, but also the HC accumulation amount in the selective catalytic reduction catalyst 5 is prescribed. Even when it is estimated that the amount has exceeded the amount B, the forced regeneration of the particulate filter 10 is started, and the fuel injection device 14 is controlled by the control device 13 and the fuel injection device 14 performs post injection. Fuel is added, and the exhaust gas 3 is heated by reaction heat when the added fuel undergoes an oxidation reaction on the oxidation catalyst 9, and the catalyst bed temperature of the particulate filter 10 immediately after the exhaust gas 3 flows in is increased. The particulate filter is burned out and the particulate filter 10 is regenerated.

  At this time, the exhaust gas 3 heated to a high temperature as a result of burning of the particulates collected in the particulate filter 10 flows into the selective catalytic reduction catalyst 5 located on the downstream side of the particulate filter 10, thereby operating at a high load. As a result of heating to the catalyst bed temperature corresponding to the occasion and the HC desorption and oxidation proceed, the amount of HC deposited becomes zero and the selective catalytic reduction catalyst 5 recovers from the HC poisoning state.

  The forced regeneration time required for burning and removing the particulates collected by the particulate filter 10 is relatively long. On the other hand, the HC of the selective catalytic reduction catalyst 5 is desorbed and oxidized. Since the required recovery time is much shorter, when it is estimated that the amount of HC deposited on the selective catalytic reduction catalyst 5 has exceeded the specified amount B, the amount of particulate deposited on the particulate filter 10 is not so large. Even if the forced regeneration of the particulate filter 10 is once started, the selective catalytic reduction catalyst 5 is recovered in a short time.

  Therefore, according to the embodiment described above, the forced regeneration of the particulate filter 10 is started even when it is estimated that the amount of HC accumulated in the selective catalytic reduction catalyst 5 is equal to or greater than the prescribed amount B. Since the downstream selective catalytic reduction catalyst 5 can be recovered from the HC poisoning state while the particulate filter 10 is being regenerated, the selective catalytic reduction catalyst 5 is brought into the HC poisoning state before causing significant functional deterioration. Even if the vehicle is in a driving mode where it can continue to drive under medium load for a long period of time without reaching high load operation, it will be maintained to ensure that the required NOx reduction performance can be exhibited. can do.

  Moreover, in the exhaust emission control device provided with the particulate filter 10, the oxidation catalyst 9 provided in the preceding stage of the particulate filter 10, or the fuel that adds fuel to the exhaust gas 3 upstream of the oxidation catalyst 9. Since the fuel injection device 14 that can perform post-injection is originally provided as the addition means, the selective reduction type catalyst 5 is made to be HC by effectively utilizing such a system for forcibly regenerating the existing particulate filter 10. If it is possible to recover from the poisoned state, it is possible to carry out at a low cost without adding new equipment.

  The exhaust purification device of the present invention is not limited to the above-described embodiment. In the drawing, the control device is shown as a single unit for convenience of explanation, but the control device for engine control and urea water addition control are shown. In this case, it is sufficient that information can be shared among the control devices, and the scope of the present invention is not deviated. Of course, various changes can be made.

1 Diesel engine (engine)
3 Exhaust gas 4 Exhaust pipe 5 Selective reduction catalyst 6 Urea water 7 Injector for urea water addition (urea water addition means)
9 Oxidation catalyst 10 Particulate filter 13 Control device 14 Fuel injection device (fuel addition means)

Claims (4)

  A selective reduction catalyst that is arranged in the middle of the exhaust pipe and can selectively react NOx with ammonia even in the presence of oxygen, and urea that adds urea water as a reducing agent in the exhaust gas upstream of the selective reduction catalyst Water addition means, a particulate filter disposed in the middle of the exhaust pipe upstream of the urea water addition position of the urea water addition means and provided with an oxidation catalyst in the previous stage, and in the exhaust gas upstream of the oxidation catalyst A fuel addition means for forcibly regenerating the particulate filter by increasing the exhaust temperature by adding a fuel and causing an oxidation reaction on the oxidation catalyst; a fuel addition of the fuel addition means; and a urea water of the urea water addition means And a control device for controlling the addition, and the amount of particulates accumulated in the particulate filter and the amount of HC deposited in the selective reduction catalyst are determined by the engine. The particulate filter is forcibly regenerated when each of the accumulation amounts is estimated according to the operation status and any of the accumulation amounts exceeds a predetermined amount set for each of the accumulation amounts. An exhaust emission control device, wherein the control device is configured to reset both amounts.   From the particulate generation map based on the engine speed and fuel injection amount, the particulate generation amount based on the current engine operating state is read and integrated momentarily, and the inlet side exhaust temperature of the particulate filter exceeds the specified temperature. 2. The exhaust emission control device according to claim 1, wherein the control device is configured to estimate the particulate accumulation amount by interrupting the accumulation of the particulate generation amount only when   The HC generation amount based on the current engine operating state is read from time to time from the HC generation amount map based on the engine speed and the fuel injection amount, and the read value corresponds to the inlet side exhaust temperature of the selective catalytic reduction catalyst. 3. The control device according to claim 1, wherein the control device is configured to estimate an accumulation amount of HC by multiplying and correcting after multiplying by a coefficient considering an oxidation treatment amount at temperature. Exhaust purification equipment.   From the start of forced regeneration of the particulate filter, the regeneration amount of the particulate according to the inlet side exhaust temperature of the particulate filter is accumulated, and when the accumulated regeneration amount catches up with the accumulated amount of particulate, the forced regeneration is completed. The exhaust emission control device according to claim 1, wherein the control device is configured to make a determination.

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