JP2010261328A - Method for detecting abnormality in reducing agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detecting method for a reducing agent for detecting a case of incorrectly supplying fuel to a reducing agent tank. <P>SOLUTION: There is disclosed the method for detecting abnormality in the reducing agent 17 supplied to a reducing agent tank 14, in an exhaust purification device wherein the reducing agent 17 is added from the reducing agent tank 14 to a selective reduction type catalyst 10 on the way of an exhaust pipe 9 to thereby reduce and purify NOx, and the method detects an oxygen concentration by a NOx sensor 23 positioned on the downstream side of the selective reduction type catalyst 10, and determines that the fuel is supplied into the reducing agent tank 14 when the oxygen concentration decreases. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for detecting abnormality of a reducing agent used in an exhaust purification device.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst The required amount of reducing agent is added from the reducing agent tank to the upstream side of the catalyst, and the reducing agent is subjected to a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective reduction catalyst, thereby reducing the NOx emission concentration. There is something that can be done.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a technique 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, non-toxic urea water is used as a reducing agent.

  In addition, as prior art document information relevant to the present invention, for example, the following Patent Document 1 already exists.

JP 2003-314258 A

  However, in such an exhaust purification device, when a fuel such as light oil, heavy oil, or kerosene is accidentally supplied to a reducing agent tank that stores the reducing agent, a driver or the like indicates that the fuel has been supplied accidentally. There was a problem that could not be easily informed.

  Specifically, when the selective catalytic reduction catalyst is deteriorated, the NOx purification rate is lowered, so that it is not possible to distinguish between when the fuel is accidentally replenished and when the selective catalytic reduction catalyst is deteriorated. There was a problem.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a reducing agent abnormality detection method that easily and suitably detects a case where fuel is accidentally replenished to a reducing agent tank.

  The present invention detects an abnormality of the reducing agent replenished in the reducing agent tank with respect to the exhaust purification device that reduces and purifies NOx by adding the reducing agent from the reducing agent tank to the selective reduction catalyst in the middle of the exhaust pipe. An abnormality detection method for a reducing agent for detecting an oxygen concentration with a NOx sensor located downstream of the selective catalytic reduction catalyst, and when a decrease in the oxygen concentration is detected, fuel is contained in the reducing agent tank. It is characterized by determining that it has been replenished.

  In the present invention, it is preferable to determine that the selective catalytic reduction catalyst has deteriorated when a decrease in the NOx purification rate is detected and a decrease in the oxygen concentration is not detected.

  In the present invention, the comparison oxygen concentration is detected by the NOx sensor located upstream of the selective catalytic reduction catalyst, and the comparative oxygen concentration and the oxygen detected by the NOx sensor located downstream of the selective catalytic reduction catalyst. It is preferable to determine a decrease in oxygen concentration by comparing the concentration.

  In the present invention, when the selective catalytic reduction catalyst is poisoned with hydrocarbon and recovery control of the selective catalytic reduction catalyst is being carried out, it is preferable to stop detecting the oxygen concentration by the NOx sensor.

  In the present invention, it is preferable that a particulate filter is provided on the upstream side of the selective catalytic reduction catalyst, and detection of the oxygen concentration by the NOx sensor is stopped when the particulate filter is being regenerated.

  According to the reducing agent abnormality detection method of the present invention, when fuel is accidentally replenished to the reducing agent tank, the NOx purification rate is reduced, and the oxygen concentration in the exhaust gas is reduced as the fuel is oxidized. Therefore, by detecting the decrease in the oxygen concentration with the downstream NOx sensor, it can be determined that the reductant tank has been replenished with fuel, and the driver or the like can be notified. Further, when the selective catalytic reduction catalyst is deteriorated, the NOx purification rate is lowered, but the oxygen concentration is not lowered. Therefore, the downstream NOx sensor does not detect the oxygen concentration drop, and therefore the selective reduction catalyst is selectively reduced. It is possible to determine that there is a possibility that the type catalyst has deteriorated and inform the driver or the like. In addition, since the reduction of oxygen concentration is a judgment requirement, there is a clear distinction between when fuel is accidentally replenished and when the selective catalytic reduction catalyst is deteriorated, and when fuel is accidentally replenished to the reductant tank It is possible to achieve various excellent effects that can be detected easily and suitably.

It is the schematic which shows the embodiment which implements this invention. It is a conceptual diagram which shows the position of a downstream NOx sensor in an example of embodiment of this invention. It is a conceptual diagram which shows the position of the downstream NOx sensor in the other example of embodiment of this invention. It is a conceptual diagram which shows the case where a particulate filter is provided. It is a graph which shows the fall of the oxygen concentration at the time of mixing fuel.

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

  1 to 5 show an example of an embodiment for carrying out the present invention, and show an exhaust purification device and a reducing agent abnormality detection method. Reference numeral 1 in FIG. 1 denotes an engine that is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided, and air 4 guided from an air cleaner 3 is passed through an intake pipe 5 to the turbocharger. 2 is sent to the compressor 2a, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the air 4 is guided from the intercooler 6 to an intake manifold (not shown). 1 is introduced into each cylinder.

  The exhaust gas 7 discharged from each cylinder of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 that has driven the turbine 2b goes out of the vehicle through the exhaust pipe 9. It is supposed to be discharged.

In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, a selective catalytic reduction catalyst 10 is mounted by being held by a casing 11, and the selective catalytic reduction catalyst 10 is a flow-through type honeycomb structure. It is formed and has the property that NOx can be selectively reacted with ammonia (NH ₃ ) even in the presence of oxygen. Here, immediately after the selective catalytic reduction catalyst 10 in the casing 11, an ammonia reduction catalyst 10 a that oxidizes ammonia slipped from the selective catalytic reduction catalyst 10 as shown in FIGS. 2 and 3 may be provided.

  A urea water injection valve 13 with an injection nozzle 12 is installed on the upstream side of the casing 11, and a urea water supply line is provided between the urea water injection valve 13 and a urea water tank (reducing agent tank) 14 provided at a required place. 15, the urea water (reducing agent) 17 in the urea water tank 14 is driven through the urea water injection valve 13 by the drive of the supply pump 16 provided in the middle of the urea water supply line 15. Can be added to the upstream side. The urea water tank 14 is provided with a liquid level detecting means 18 such as a liquid level sensor for detecting the liquid level of the urea water 17 inside. Here, the liquid level detection means 18 may use a float, an ultrasonic wave, or the like, and may have another configuration as long as it can detect the liquid level of the urea aqueous solution 17 inside. The configuration of the urea water tank 14 is not limited to the configuration of the injection nozzle 12, the urea water injection valve 13, the urea water supply line 15, and the supply pump 16, and the urea water 17 is disposed upstream of the selective reduction catalyst 10. Other configurations may be used as long as they can be added.

  Further, the engine 1 is equipped with a rotation sensor 19 for detecting the engine rotation speed, and a rotation speed signal 19a from the rotation sensor 19 and an accelerator sensor 20 (a sensor for detecting an accelerator pedal depression angle). The load signal 20a is input to an ECU (Electronic Control Unit) control device 21 constituting an engine control computer.

  On the other hand, in this control device 21, the amount of NOx generated is estimated based on the current operating state determined from the rotation speed signal 19 a from the rotation sensor 19 and the load signal 20 a from the accelerator sensor 20, and is estimated. Further, the amount of urea water 17 added corresponding to the amount of NOx generated is calculated and the required amount of urea water 17 is added. More specifically, the urea water injection valve 13 is opened. A valve command signal 13 a is output, and a drive command signal (not shown) is output to the supply pump 16. The urea water injection valve 13 opens the urea water 17. The addition amount is appropriately controlled, and the injection pressure required at the time of addition is appropriately obtained by driving the supply pump 16. Further, in the control device 21, the amount of the urea water 17 in the urea water tank 14 is estimated from the liquid level signal 18 a from the liquid level detecting means 18, and the remaining amount of the urea water 17 and the replenishment timing of the urea water 17 are determined. I am doing so.

  Furthermore, on the inlet side and the outlet side of the casing 11 that holds the selective catalytic reduction catalyst 10, an upstream NOx sensor 22 that detects the NOx concentration and a downstream NOx sensor 23, and an exhaust temperature are detected. Temperature sensors 24 and 25 are respectively provided, and these detection signals 22a and 23a and detection signals 24a and 25a are also input to the control device 21, and these detection signals 22a and 23a and The NOx purification rate is detected based on the detection signals 24a and 25a. Here, the NOx purification rate may be detected based on one of the detection signals 22a and 23a and the detection signals 24a and 25a, or other signals may be used, and the actually measured NOx purification rate can be detected. Then, means and methods are not particularly limited. 2 and 3, when the ammonia reduction catalyst 10a is provided downstream of the selective reduction catalyst 10, a downstream NOx sensor 23 may be provided downstream of the ammonia reduction catalyst 10a. Alternatively, a downstream NOx sensor 23 (see FIG. 3) may be disposed between the selective catalytic reduction catalyst 10 and the ammonia reduction catalyst 10a. Further, a particulate filter 29 may be provided on the upstream side of the selective catalytic reduction catalyst 10 by a casing 28 as shown in FIG.

  Further, the control device 21 includes a display means 26 such as a display monitor or a display lamp which shows an abnormality by a display signal 26a under a predetermined condition, and a display means such as a display monitor or a display lamp which shows an abnormality by a display signal 27a under other conditions. 27 is connected. Furthermore, a predetermined function is built in the control device 21 in advance.

  Hereinafter, the operation of an example of an embodiment of the present invention will be described.

  When reducing the exhaust concentration of NOx in the exhaust gas by the exhaust purification device, urea water 17 is added from the urea water tank 14 to the upstream side of the selective reduction catalyst 10, and the urea water 17 is added to the selective reduction catalyst 10. A reduction reaction with NOx in the exhaust gas 7 is performed to reduce the NOx emission concentration. Thereafter, when the urea water 17 in the urea water tank 14 decreases due to the addition of the urea water 17, the urea water 17 is appropriately replenished to the urea water tank 14.

  Further, when fuel such as light oil, heavy oil, kerosene, etc. is accidentally replenished to the urea water tank 14, the fuel is oxidized by the ammonia reduction catalyst 10a having an oxidation function, and oxygen in the exhaust gas 7 is consumed. The downstream NOx sensor 23 detects a decrease in oxygen concentration as shown in FIG. When detecting a decrease in oxygen concentration, the upstream NOx sensor 22 detects the oxygen concentration for comparison, and compares the oxygen concentration for comparison with the oxygen concentration detected by the downstream NOx sensor 23. Thus, the decrease in oxygen concentration may be appropriately determined.

  At the same time, NOx purification rate reduction is detected by the NOx sensors 22 and 23 and the temperature sensors 24 and 35. At this time, the decrease in the NOx purification rate is compared with a reference NOx purification rate (threshold) recorded in advance, and a decrease in the NOx purification rate is detected based on whether or not the NOx purification rate is lower than the reference NOx purification rate. When the rate is lower than the reference NOx purification rate, it is determined that there is a decrease in the NOx purification rate, and when the NOx purification rate is not lower than the reference NOx purification rate, it is determined that there is no decrease in the NOx purification rate.

  Thereafter, the control device 21 sends a display signal 26a to the display means 26, which gives a warning to the driver that the urea water tank 14 has been replenished by mistake with the display means 26.

  Here, the selective catalytic reduction catalyst 10 may be poisoned with hydrocarbon (HC). When the selective catalytic reduction catalyst 10 is poisoned with hydrocarbon (HC), the temperature of the selective catalytic reduction catalyst 10 is increased. It is necessary to recover the reduction performance. At the time of recovery, the adsorbed hydrocarbon (HC) is released and oxidized by the downstream ammonia reduction catalyst 10a. Therefore, during the recovery control, the NOx sensor 23 on the downstream side is used. Stop detection of oxygen concentration. Here, the poisoning of hydrocarbon (HC) may be determined by integrating under various conditions, or may be determined based on other conditions.

  Further, when the particulate filter 29 is provided on the upstream side of the selective catalytic reduction catalyst 10, it is necessary to regenerate the particulate filter 29 as soot accumulates on the particulate filter 29. During the regeneration of 29, the detection of the oxygen concentration by the downstream NOx sensor 23 is stopped. Here, during regeneration of the particulate filter 29, it may be determined by the operation of the heating means or the like, or may be determined under other conditions.

  On the other hand, when the selective catalytic reduction catalyst 10 is deteriorated, the controller 21 detects a decrease in the NOx purification rate without detecting a decrease in oxygen concentration, and the control device 21 sends a display signal 27a to the display means 27 to display the display means. At 27, a warning that the selective catalytic reduction catalyst 10 is deteriorated is issued to notify the driver or the like.

  Thus, according to an example of the embodiment, when fuel is accidentally replenished to the urea water tank 14, the NOx purification rate is lowered and the exhaust gas is discharged along with the oxidation of the fuel. Therefore, by detecting the decrease in the oxygen concentration with the downstream NOx sensor 23, it can be determined that the fuel has been replenished in the urea water tank 14, and the driver or the like can be notified. Further, when the selective catalytic reduction catalyst 10 is deteriorated, the NOx purification rate is lowered, but the oxygen concentration is not lowered. Therefore, the downstream NOx sensor 23 does not detect the oxygen concentration drop. It is possible to determine that the selective catalytic reduction catalyst 10 is likely to be deteriorated and notify the driver or the like.

  In addition, since a reduction in oxygen concentration is used as a determination requirement, a distinction is made between when fuel is accidentally replenished and when the selective catalytic reduction catalyst 10 is deteriorated, and fuel is erroneously replenished to the urea water tank 14. Can be detected easily and suitably.

  In one example of the present embodiment, the comparison oxygen concentration is detected by the NOx sensor 22 located upstream of the selective catalytic reduction catalyst 10, and the comparative oxygen concentration is located downstream of the selective catalytic reduction catalyst 10. When a decrease in oxygen concentration is determined by comparing with the oxygen concentration detected by the NOx sensor 23, the case where the urea water tank 14 is erroneously replenished with fuel can be easily and suitably detected.

  In an example of the present embodiment, when the selective catalytic reduction catalyst 10 is poisoned with hydrocarbon (HC) and recovery control of the selective catalytic reduction catalyst 10 is performed, the oxygen concentration by the downstream NOx sensor 23 is used. When the detection is stopped, the decrease in the oxygen concentration is determined under appropriate conditions, so that it is possible to easily and suitably detect the case where the urea water tank 14 is replenished with fuel by mistake.

  In one example of this embodiment, the particulate filter 29 is provided on the upstream side of the selective catalytic reduction catalyst 10, and when the particulate filter 29 is being regenerated, the detection of the oxygen concentration by the downstream NOx sensor 23 is stopped. Since the decrease in the oxygen concentration is determined under appropriate conditions, it is possible to easily and suitably detect the case where the urea water tank 14 is erroneously replenished with fuel.

  The method for detecting an abnormality of the reducing agent of the present invention is not limited to the above-described embodiment. The fuel that is replenished by mistake may be other than light oil, heavy oil, and kerosene, and the reducing agent may be urea. Of course, other than water may be adopted, and various modifications can be made without departing from the scope of the present invention.

9 Exhaust pipe 10 Selective reduction catalyst 14 Urea water tank (reducing agent tank)
17 Urea water (reducing agent)
22 NOx sensor on the upstream side 23 NOx sensor on the downstream side 29 Particulate filter

Claims (5)

  A reducing agent for detecting an abnormality of the reducing agent replenished in the reducing agent tank for an exhaust gas purification device that reduces and purifies NOx by adding the reducing agent from the reducing agent tank to the selective reduction catalyst in the middle of the exhaust pipe. In this abnormality detection method, an oxygen concentration is detected by a NOx sensor located downstream of the selective catalytic reduction catalyst, and when a decrease in the oxygen concentration is detected, it is determined that fuel is supplied into the reducing agent tank. A method for detecting an abnormality of a reducing agent, comprising:   2. The reducing agent abnormality detection method according to claim 1, wherein when the decrease in the NOx purification rate is detected and the decrease in the oxygen concentration is not detected, it is determined that the selective catalytic reduction catalyst has deteriorated.   The comparison oxygen concentration is detected by the NOx sensor located upstream of the selective reduction catalyst, and the comparison oxygen concentration is compared with the oxygen concentration detected by the NOx sensor located downstream of the selective reduction catalyst. The method for detecting an abnormality of the reducing agent according to claim 1, wherein a decrease in the oxygen concentration is determined.   2. The reduction according to claim 1, wherein when the selective catalytic reduction catalyst is poisoned with hydrocarbon and recovery control of the selective catalytic reduction catalyst is performed, detection of the oxygen concentration by the NOx sensor is stopped. Abnormal detection method of the agent.   The abnormality of the reducing agent according to claim 1, further comprising a particulate filter upstream of the selective catalytic reduction catalyst, and stopping the detection of the oxygen concentration by the NOx sensor when the particulate filter is being regenerated. Detection method.

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