JP2014206123A - Gas conversion rate determination method of reductant in exhaust gas after treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas conversion rate determination method of a reductant in an exhaust gas after treatment device which can exactly estimate temperatures of fuel and urea water immediately before catalyst when injecting fuel and urea water and can exactly determine the conversion rate of fuel and urea water.SOLUTION: An exhaust pipe injector 23 is disposed on an exhaust pipe 20 of an engine E, DOC 25 and NOx occlusion reduction type catalyst 26 are connected to the exhaust pipe 20 of the downstream side, NOx in exhaust gas is occluded by an NOx occlusion reduction type catalyst 26 and, thereafter, fuel is injected from the exhaust pipe injector 23 through the exhaust pipe to produce reduction gas. When occluded NOx is reduced and purified by using the reduction gas, an HC conversion rate map 36 of fuel with respect to exhaust gas temperature and distance after fuel injection is prepared beforehand, exhaust gas temperature until just before the DOC 25 from fuel injection position is detected and, based on the detection temperature and the distance after fuel injection to the DOC 25, HC conversion rate of fuel is determined from the HC conversion rate map 36.

Description

  The present invention relates to an exhaust gas aftertreatment device using a NOx storage reduction catalyst or an SCR catalyst, and in particular, when fuel used for rich reduction of a NOx storage reduction catalyst or urea water used for an SCR catalyst is injected as a reducing agent. The present invention relates to a method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device capable of accurately determining the gas conversion rate of the reducing agent.

  As exhaust gas aftertreatment devices for diesel engines, DOC (Diesel Oxidation Catalyst), DPF (Diesel Particulate Filter), NOx occlusion reduction catalyst (LNT: Lean NOx Trap or NSR: NOx Storage Reduction), Urea SCR (Selective Crate) ) System etc. are put into practical use.

  DOC and DPF systems are powerful tools for reducing PM. The DOC provided in the front stage of the exhaust gas flow cannot oxidize the solid soot itself, but oxidizes most of the soluble organic component (SOF) that occupies 30 to 70% of the total PM, and simultaneously removes HC and CO. The DPF provided in is formed of a porous ceramic or the like having a pore diameter and captures most of the PM in the exhaust gas.

The NOx occlusion reduction type catalyst includes a catalyst carrier such as alumina (Al ₂ O ₃ ), a noble metal catalyst such as Pt and Pd, an alkali metal such as Na, K and Cs, an alkaline earth metal such as Ca and Ba, Y , La and other rare earths and other storage materials having NOx storage function are supported, and exhibit two functions of NOx storage and NOx release / purification depending on the oxygen concentration in the exhaust gas.

In this purification system using NOx occlusion reduction type catalyst, NO in exhaust gas is converted to NO ₂ by a noble metal catalyst such as Pt and Pd under conditions of high oxygen concentration in the exhaust gas (lean air-fuel ratio) as in the normal operation state. Oxidized and the occlusion material occludes it as nitrate (Ba (NO ₃ ) ₂ ) to purify NOx. Moreover, if NOx occlusion continues, nitrate will be saturated and the occlusion function of the occlusion material will be lost. Therefore, EGR (Exhaust Gas Recirculation) and fuel post-injection will be performed under conditions of low oxygen concentration by changing the operating conditions. In addition, exhaust pipe injection is performed to form a rich state, and fuel is reduced on the noble metal catalyst, so that CO, HC, H ₂ is generated in the exhaust gas, and NOx is released and purified by rich reduction. To do.

  The urea SCR system injects urea water upstream of the SCR catalyst, hydrolyzes the urea water with the heat of exhaust gas, generates ammonia, and reacts the NOx in the exhaust gas with NOx on the SCR catalyst to generate NOx. Denitration.

  Fuel (light oil) injection into the exhaust pipe is used for the rich reduction of the NOx storage reduction catalyst and the temperature rise of the catalyst during the forced regeneration of DPF PM. Further, even in the urea SCR catalyst, urea water is injected into the exhaust pipe for NOx reduction.

  Exhaust fuel injection involves injecting into the cylinder during the expansion stroke of combustion (so-called post-injection), and there is no oil dilution with fuel. There are advantages such as reduction in fuel consumption.

JP 2004-092497 A JP 2011-247135 A JP 2012-127301 A JP 2009-085172 A

  However, conversely, the exhaust pipe has a disadvantage that the gas temperature is lower than the in-cylinder temperature during the expansion stroke, and it takes time until the fuel (light oil) is gasified into HC. If the fuel reaches the catalyst without being completely gasified, the fuel partially oxidizes on the front surface of the catalyst to generate soot, which may cause coking on the front surface and increase pressure loss. Also, HC slips after the catalyst, HC poisons the catalyst to reduce its activity, or conversely, HC is ignited when the exhaust gas temperature rises after poisoning, causing abnormal combustion, and in the worst case the catalyst It is also conceivable that the material melts.

  Even in the case of a urea SCR catalyst, if the exhaust gas temperature is low, the distance from the urea water injection valve to the SCR catalyst is short, and when urea water droplets reach the catalyst without being gasified, it is converted to ammonia. Becomes uneven, the utilization efficiency of urea decreases, and locally concentrated ammonia causes ammonia slip.

  In view of this, conventionally, a temperature threshold that enables exhaust fuel injection and urea water injection is provided, and the fuel is injected at a higher temperature (Patent Documents 1 to 3).

  However, since the temperature is measured immediately before the catalyst, the temperature distribution from the previous engine outlet and the length of the exhaust pipe are not taken into consideration, and a difference occurs in the conversion rate at that portion. In addition, the exhaust pipe does not take into account the effects of heat radiation due to differences in atmospheric temperature and vehicle speed wind. That is, even if the temperature just before the catalyst is appropriate, the amount of heat release becomes large during the winter season or when the vehicle speed wind is fast, and the problem of falling below the temperature threshold is not taken into consideration while reaching the catalyst immediately before the injection position.

  Therefore, the object of the present invention is to solve the above-mentioned problems and accurately predict the temperature immediately before the catalyst and inject the fuel and urea water and accurately determine the conversion rate of these fuel and urea water. An object of the present invention is to provide a method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device.

  In order to achieve the above object, the present invention provides an exhaust pipe injector in an exhaust pipe of an engine, and a DOC, NOx occlusion reduction type catalyst, and DPF are connected to an exhaust pipe downstream of the exhaust pipe injector. Constituting a processing device, storing NOx in the exhaust gas with a lean air-fuel ratio with a NOx storage-reduction catalyst, generating a reducing gas by injecting fuel from the exhaust pipe injector under a rich air-fuel ratio condition, When reducing and purifying the stored NOx with the reducing gas, a fuel HC conversion rate map is prepared in advance for the exhaust gas temperature and the distance after fuel injection, and the exhaust gas temperature from the fuel injection position to just before the DOC is detected. An exhaust gas aftertreatment device characterized in that the HC conversion rate of fuel is obtained from the HC conversion rate map based on the detected temperature and the distance after fuel injection to the DOC. Of a gas conversion determining method of the reducing agent.

  Fuel is injected into the exhaust pipe when the calculated HC conversion rate is above a certain value, and when the HC conversion rate is below a certain value, post-injection is performed to increase the exhaust gas temperature so that the HC conversion rate is above a certain value. After this, it is preferable that the exhaust pipe is injected.

  The distance after fuel injection in the HC conversion rate map is obtained from the spatial distance from the fuel injection position to immediately before the DOC, and the HC conversion rate is obtained from the exhaust gas flow rate and the exhaust gas temperature when the engine is at a normal load. The HC conversion rate at the full load is preferably obtained by idling or using the space velocity of the exhaust gas at the full load as a coefficient, and correcting the spatial distance of the normal load with the coefficient.

  In the present invention, an exhaust pipe injector is provided in an exhaust pipe of an engine, a DPF is connected to an exhaust pipe downstream of the exhaust pipe injector, and an SCR and a DOC are connected to an exhaust pipe downstream of the DPF, A urea water injection nozzle is provided in the upstream exhaust pipe of the SCR to constitute an exhaust gas aftertreatment device, and urea water is injected from the urea water injection nozzle to generate a reducing gas composed of ammonia, and the SCR When NOx is denitrated above, an ammonia conversion rate map of urea water relative to the exhaust gas temperature and the distance after urea water injection is prepared in advance, the exhaust gas temperature from the urea water injection position to the SCR is detected, and the detected temperature and An exhaust gas aftertreatment device characterized in that an ammonia conversion rate of urea water is obtained from the ammonia conversion rate map based on a distance after urea water injection to the SCR. It takes a gas conversion determining method of the reducing agent.

  When the calculated ammonia conversion rate is above a certain value, urea water is injected from the urea water injection nozzle, and when the ammonia conversion rate is less than a certain value, post injection is performed so that the ammonia conversion rate is above a certain value. It is preferable to inject urea water after raising the exhaust gas temperature.

  Further, according to the present invention, an exhaust pipe injector is provided in an exhaust pipe of an engine, and an exhaust gas aftertreatment device is configured by connecting a DOC and a DPF to an exhaust pipe downstream of the exhaust pipe injector, and PM is deposited on the DPF. When this occurs, fuel is injected from the exhaust pipe injector into the exhaust pipe to generate a reducing gas, the reducing gas is burned in the DOC, the exhaust gas temperature is raised, and the PM deposited on the DPF is burned to regenerate the DPF. In this case, a fuel HC conversion rate map with respect to the exhaust gas temperature and the distance after fuel injection is prepared in advance, the exhaust gas temperature from the fuel injection position to immediately before the DOC is detected, and the detected temperature and the fuel injection distance to the DOC are detected. Based on the HC conversion rate map, the HC conversion rate of the fuel is obtained from the HC conversion rate map. That.

  When the calculated HC conversion rate is equal to or higher than a certain value, fuel is injected from the exhaust pipe injector to generate reducing gas composed of HC and the like, and the reducing gas is burned in the DOC to raise the exhaust gas temperature to the DPF regeneration temperature. When the HC conversion rate is less than a certain value, it is preferable to perform post injection so that the HC conversion rate is equal to or greater than a certain value, raise the exhaust gas temperature reaching the DOC, and then perform exhaust pipe injection.

  In the present invention, when fuel or urea water is injected, the temperature immediately before the catalyst can be accurately predicted, the conversion rate of these fuel and urea water can be accurately determined, and the injection of these reducing agents is accurately controlled. As a result, it is possible to avoid problems such as soot coking on the front surface of the DOC, HC poisoning of the catalyst, and abnormal temperature rise after HC poisoning.

It is a figure which shows the apparatus structure of the gas conversion rate determination method of the reducing agent of the exhaust gas aftertreatment apparatus using the NOx storage reduction catalyst of this invention. In this invention, it is a figure explaining the exhaust gas temperature distribution from the upstream of a fuel injection position to a catalyst inlet. In this invention, it is a figure which shows the HC conversion rate map which calculated | required the HC conversion rate of the fuel with respect to the distance after fuel injection, and exhaust gas temperature. It is a figure which shows the apparatus structure of the gas conversion rate determination method of the reducing agent of the exhaust gas aftertreatment apparatus using the SCR catalyst of this invention.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows an exhaust gas aftertreatment device 10 using a NOx occlusion reduction type catalyst.

  A turbocharger 11 and an EGR pipe 12 are connected to the intake / exhaust system of the engine E, and the air sucked from the air cleaner 13 is compressed by the compressor 14 of the turbocharger 11 and is pumped to the intake passage 15. E is supplied into the engine E from the intake manifold 16 of E. An intake valve 17 for adjusting the amount of air to the engine E is provided in the intake passage 15.

  The exhaust gas discharged from the engine E is discharged from the exhaust manifold 18 to the turbine 19 of the turbocharger 11, drives the turbine 19, and is discharged to the exhaust pipe 20.

  An EGR pipe 12 is connected to the intake manifold 16 and the exhaust manifold 18, and an EGR cooler 21 for cooling exhaust gas from the exhaust manifold 18 to the intake manifold 16 is connected to the EGR pipe 12, and the EGR amount is adjusted. An EGR valve 22 is connected.

  In the exhaust gas aftertreatment device 10, an exhaust pipe injector 23 is provided in an exhaust pipe 20 on the downstream side of the turbine 19, and a DOC 25, NOx is placed in a canning container 24 formed in the exhaust pipe 20 on the downstream side of the exhaust pipe injector 23. The storage reduction catalyst 26 and the DPF 27 are sequentially canned.

  An exhaust pipe 20 on the upstream side of the exhaust pipe injector 23 is provided with an engine outlet side temperature sensor 28 for detecting the exhaust gas temperature on the engine outlet side. A DOC inlet side temperature sensor 29 and a NOx occlusion reduction type catalyst 26 are provided on the upstream side of the DOC 25. A catalyst inlet side temperature sensor 30 is provided on the inlet side, and a catalyst outlet side temperature sensor 31 is provided on the outlet side.

  The engine E is generally controlled by the ECU 32. The ECU 32 includes a temperature detection unit 33, an air-fuel ratio control unit 34, and an injection control unit 35, and stores an HC conversion rate map 36.

  The detected values of the temperature sensors 28 to 31 from the engine outlet side to the catalyst outlet side are input to the temperature detection means 33 of the ECU 32 that controls the operation of the engine E.

  The air-fuel ratio control means 34 controls the EGR valve 22 and the intake valve 17, and the injection control means 35 controls the combustion injection amount of the engine E, controls multi-injection such as post-injection by the injector, and further exhaust pipe injector The fuel injected from 23 is controlled.

  The exhaust gas aftertreatment device 10 using the NOx occlusion reduction catalyst normally stores NOx by the NOx occlusion reduction catalyst 26 in an air-fuel ratio lean state, and in the meantime, the exhaust gas injector 23 pulsates the fuel HC in a pulsed manner. NOx reduction purification is performed in the fuel-rich state.

  PM in the exhaust gas is captured by the DPF 27. If a predetermined amount of PM accumulated on the DPF 27 accumulates, for example, when the differential pressure before and after the DPF 27 reaches a constant value, or travels a predetermined travel distance. At this time, the ECU 32 performs automatic regeneration control of PM. At the time of this PM regeneration, post-injection or fuel injection by the exhaust pipe injector 23 is performed to raise the exhaust gas temperature to 600 ° C., thereby burning the PM deposited on the DPF 27.

  When injecting the fuel HC during the rich reduction or PM regeneration, the ECU 32 determines the HC when the fuel HC is injected from the HC conversion rate map 36 based on the exhaust gas temperature of the temperature sensors 28 to 31 input to the temperature detection means 33. A conversion rate is obtained, and it is determined whether or not the HC conversion rate is equal to or greater than an injectable threshold value K, and it is estimated whether the fuel can be decomposed into HC before the catalyst, and fuel injection into the exhaust pipe 20 is performed only when possible. To perform rich or DPM 27 PM regeneration. Otherwise, post-injection in the expansion stroke of combustion is performed to supply HC.

  A gas conversion rate determination method for obtaining the HC conversion rate of the fuel injected from the HC conversion rate map 36 based on the exhaust gas temperature will be described with reference to FIGS.

  FIG. 2 shows an example of the temperature distribution of exhaust gas from the engine outlet upstream of the exhaust pipe injector to the catalyst (DOC) inlet.

  In FIG. 2, assuming that the temperature distribution Tab in which the exhaust gas at the engine outlet falls to the temperature Yb due to heat dissipation while flowing in the exhaust pipe at the temperature Ya is the standard state, the winter and vehicle speed are fast and the heat radiation is large. Even if the exhaust gas at the engine outlet is at the temperature Ya, the temperature distribution Tac indicated by the broken line is obtained, and the exhaust gas at the catalyst inlet falls to the temperature Yc. In this case, even if the exhaust gas at the engine outlet is high (temperature Ya), the exhaust gas at the engine outlet is as low as the temperature Yd, and the exhaust gas temperature Yc is the same as the exhaust gas temperature Yc at the catalyst inlet of the temperature distribution Tdc with a small amount of heat release. . Further, when measured at an intermediate point between the engine outlet and the catalyst inlet, the temperature Yf decreases when heat dissipation is large with respect to the standard temperature Ye, and the temperature Yg decreases when the engine outlet temperature decreases.

  As described above, in the measurement of the exhaust gas temperature at the catalyst inlet, the temperature history before that is unknown even at the same temperature, and even if measured at the midpoint between the engine outlet and the catalyst inlet, there is a difference in the temperature at the catalyst inlet. Therefore, obtaining the HC conversion rate of the fuel HC from the temperature measurement values at the catalyst inlet and the intermediate point causes an error.

  Therefore, in the present invention, based on the temperature difference between the exhaust gas temperature at the engine outlet at the engine outlet side temperature sensor 28 and the catalyst inlet temperature at the DOC inlet side temperature sensor 29, from the injection position to the catalyst inlet at the exhaust pipe injector position. The average temperature of the exhaust gas temperature is obtained, and the HC conversion rate is obtained based on this average temperature.

  FIG. 3 shows the HC conversion rate map stored in the HC conversion rate map 36 of the ECU 32.

  This HC conversion rate map shows the HC conversion rate by changing the exhaust gas temperature and the distance after fuel injection experimentally by taking the exhaust gas temperature on the horizontal axis and the exhaust gas temperature on the vertical axis. A three-dimensional map is created by creating a curve of the relationship between the distance after fuel injection and the exhaust gas temperature at which the conversion rate is 100%, 80%, 60%, 40%, 20%, 0%.

This HC conversion rate map is based on the exhaust gas space velocity (SV = 3 × 10 ⁴ (h ⁻¹ )) at the exhaust gas flow rate when the engine is operated at a normal load. During operation, the space velocity (SV = 1 × 10 ⁴ (h ⁻¹ )) and at full load the space velocity (SV = 1 × 10 ⁵ (h ⁻¹ )). The distance after fuel injection shown in FIG. 3 is corrected to obtain an HC conversion rate described later.

  In order to obtain the HC conversion rate from this HC conversion rate map, the distance X (constant) from the fuel injection position of the exhaust pipe injector to the catalyst, the exhaust gas temperature detected by the engine outlet side temperature sensor 28 and the DOC inlet side temperature sensor 29. Based on this, the average temperature from the fuel injection position of the exhaust pipe injector to the catalyst inlet is defined as the exhaust gas temperature Y (sensor value), and the conversion rate Z to HC can be obtained from these.

  Here, if the obtained conversion rate Z is equal to or greater than the threshold value K (a constant value: 70%, for example) of the HC conversion rate that can be injected, the exhaust pipe injection in the exhaust pipe injector is permitted to perform rich reduction or PM regeneration. I do.

  When the obtained conversion rate Z is less than the threshold value K and the exhaust pipe cannot be injected, the exhaust pipe is injected after the exhaust gas temperature is raised to a state where the exhaust pipe can be injected by post injection in the cylinder.

  In addition, even if the exhaust gas amount changes and the exhaust gas temperature Y is the same during idle operation or full load operation, the fuel residence time from the exhaust pipe injector to the catalyst is different. Therefore, the fuel injection of the exhaust pipe injector is performed using the space velocity as a coefficient. The HC conversion rate is obtained by correcting the distance X from the position to the catalyst.

  In the case of DPF regeneration, if the exhaust gas temperature is the same as that for rich reduction, the post-injection amount is slightly increased (about + 5%). However, during DPF regeneration, feedback control is performed on the exhaust gas temperature. Therefore, it is not particularly necessary to correct the HC conversion rate map. Even in the case of rich injection that performs both post injection and exhaust pipe injection, if the gas conversion efficiency by exhaust pipe injection is low and cannot be used, the amount is added to post injection.

  Although the exhaust gas temperature is detected by the engine outlet side temperature sensor 28 and the DOC inlet side temperature sensor 29, the exhaust gas temperature may be measured anywhere between the engine outlet and the catalyst inlet. Any position may be used as long as the temperature distribution up to is obtained. The temperature distribution is obtained by both the temperature sensors 28 and 29, and the average temperature from the fuel injection position to the catalyst is obtained, so that the heat radiation amount changes due to the traveling wind and the air temperature to the exhaust pipe 20, and the catalyst inlet temperature drop changes. Since an accurate exhaust gas temperature can be obtained, an accurate exhaust gas temperature can be obtained even under the influence of heat radiation, and an accurate HC conversion rate can be obtained.

  FIG. 4 shows an exhaust gas aftertreatment device 10 using an SCR catalyst. Except for the exhaust gas aftertreatment device 10, the basic configuration of the engine E is the same as that in FIG. 1, and this will be described again.

  The turbocharger 11 and the EGR pipe 12 are connected to the intake / exhaust system of the engine E, and the air from the air cleaner 13 is compressed by the compressor 14 of the turbocharger 11 and is pumped to the intake passage 15, and passes through the intake valve 17 to the engine. E is supplied into the engine E from the intake manifold 16 of E. The exhaust gas discharged from the engine E is discharged from the exhaust manifold 18 to the turbine 19 of the turbocharger 11, drives the turbine 19, and is discharged to the exhaust pipe 20.

  An EGR pipe 12 is connected to the intake manifold 16 and the exhaust manifold 18, and an EGR cooler 21 and an EGR valve 22 are connected to the EGR pipe 12.

  In the exhaust gas aftertreatment device 10, an exhaust pipe injector 23 is provided in the exhaust pipe 20 on the downstream side of the turbine 19, and a DPF device 41 and an SCR device 42 are provided in the exhaust pipe 20 on the downstream side of the exhaust pipe injector 23. The DPF device 41 is configured by canning a DOC 44 and a DPF 45 in a DPF canning container 43 formed in the exhaust pipe 20. The SCR device 42 is provided with a SCR catalyst 47 and a DOC 48 for preventing ammonia slip in an SCR canning container 46 formed in the exhaust pipe 20, and a urea water injection nozzle in the exhaust pipe 20 upstream of the SCR canning container 46. 49 is provided.

  The exhaust pipe 20 on the upstream side of the exhaust pipe injector 23 has an engine outlet side temperature sensor 28 for detecting the exhaust gas temperature on the engine outlet side, and the DOC inlet side temperature sensor 50 and the DPF 45 on the upstream side of the DOC 44 of the DPF device 41. A DPF temperature sensor 51 is provided on the inlet side, an SCR catalyst inlet side temperature sensor 52 is provided on the inlet side of the SCR catalyst 47 of the SCR device 42, and an SCR catalyst outlet side temperature sensor 53 is provided on the outlet side.

  The engine E is generally controlled by the ECU 32. The ECU 32 includes a temperature detection unit 33, an air-fuel ratio control unit 34, and an injection control unit 35, and stores a conversion rate map 37 of HC and urea water.

  The detection values of the temperature sensors 28, 50, 51, 52, 53 of the exhaust gas aftertreatment device 10 are input to the temperature detection means 33 of the ECU 32 that controls the operation of the engine E.

  The air-fuel ratio control means 34 controls the EGR valve 22 and the intake valve 17, and the injection control means 35 controls the combustion injection amount of the engine E, controls multi-injection such as post-injection by the injector, and further exhaust pipe injector The fuel injected from 23 is controlled.

  The urea water injection nozzle 49 is controlled by a DCU (Dosing Control Unit) 55 connected to the ECU 32. Although the urea water injection by the urea water injection nozzle 49 is omitted in the drawing, the supply module controlled by the DCU 55 sucks the urea water in the urea water tank and raises it to a predetermined pressure, thereby injecting the urea water. The DCU 55 controls the on-off valve in the nozzle 49 so that a predetermined amount of urea water corresponding to the NOx concentration in the exhaust gas is injected from the urea water injection nozzle 49.

  While the injected urea water flows into the SCR device 42 from the exhaust pipe 20, ammonia is generated by hydrolysis, and the generated ammonia and NOx in the exhaust gas are reacted by the SCR catalyst 47 to denitrate. Excess ammonia is adsorbed on the DOC 48 to prevent ammonia slip.

  In the exhaust gas aftertreatment device 10 using the SCR catalyst 47, PM in the exhaust gas is captured by the front DPF device 41, and NOx in the exhaust gas is denitrated by the rear SCR device 42.

  At the time of the denitration, the ECU 32 receives urea water from the conversion rate map 37 based on the temperature sensors 28 to 31 input to the temperature detection means 33, particularly the exhaust gas temperature Y of the DPF temperature sensor 51 and the SCR catalyst inlet side temperature sensor 52. When the ammonia conversion rate at the time of injection is obtained, it is determined whether the ammonia conversion rate is equal to or higher than a threshold K for injection, and it is estimated whether urea water can be decomposed into ammonia at the inlet side of the SCR catalyst 47. Only urea water is injected from the urea water injection nozzle 49 to the exhaust pipe 20.

  The ammonia conversion rate map 37 obtains the exhaust gas temperature distribution from the urea water injection nozzle 49 to the inlet of the SCR catalyst 47 by the DPF temperature sensor 51 and the SCR catalyst inlet side temperature sensor 52 as described in FIG. The post-injection distance from the urea water injection nozzle 49 to the inlet of the SCR catalyst 47 is obtained to obtain the average temperature, and the ammonia conversion from the ammonia conversion rate map prepared in advance in the same manner as described in FIG. 3 based on this average temperature. The rate Z is obtained, and it is estimated whether or not the ammonia conversion rate Z is equal to or greater than the threshold value K. If it is equal to or greater than the threshold value K (K = approximately 100%), the urea water injection is permitted. If it is not possible, urea injection is prohibited.

  Further, in the case of DPF regeneration, the fuel HC injection from the exhaust pipe injector 23 is obtained by using the HC conversion rate map of the conversion rate map 37 to obtain the HC conversion rate as described with reference to FIGS. Based on this, jetting is permitted or not permitted.

  As described above, in the case of the urea SCR catalyst, it is estimated whether the urea water can be converted to ammonia immediately before the SCR catalyst 47, and only when possible, the urea water is injected to improve the use efficiency of the urea water or to reduce the ammonia slip. There is merit such as prevention.

20 Exhaust pipe 23 Exhaust pipe injector 25 DOC
26 NOx storage reduction catalyst 36 HC conversion map E Engine

Claims (7)

  An exhaust pipe injector is provided in the exhaust pipe of the engine, and an exhaust gas aftertreatment device is configured by connecting a DOC, NOx occlusion reduction type catalyst, and DPF to the exhaust pipe downstream of the exhaust pipe injector, and the air-fuel ratio is lean The NOx in the exhaust gas is occluded by the NOx occlusion reduction type catalyst, the fuel is injected into the exhaust pipe from the exhaust pipe injector under the rich air-fuel ratio condition to generate the reducing gas, and the reduced NOx is reduced / reduced by the reducing gas. At the time of purification, a fuel HC conversion rate map with respect to the exhaust gas temperature and the distance after fuel injection is prepared in advance, the exhaust gas temperature from the fuel injection position to immediately before the DOC is detected, and the detected temperature and the fuel injection to the DOC are detected. A method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device, wherein an HC conversion rate of fuel is obtained from the HC conversion rate map based on a rear distance.   Fuel is injected into the exhaust pipe when the calculated HC conversion rate is above a certain value, and when the HC conversion rate is below a certain value, post-injection is performed to increase the exhaust gas temperature so that the HC conversion rate is above a certain value. The method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device according to claim 1, wherein the exhaust pipe injection is performed after the exhaust pipe is injected.   The distance after fuel injection in the HC conversion rate map is obtained from the spatial distance from the fuel injection position to immediately before the DOC, and the HC conversion rate is obtained from the exhaust gas flow rate and the exhaust gas temperature when the engine is at a normal load. The HC conversion rate at the full load is obtained by using the space velocity of the exhaust gas at idling or full load as a coefficient, and correcting the spatial distance of the normal load by the coefficient. Gas conversion rate judgment method.   An exhaust pipe injector is provided in an exhaust pipe of the engine, a DPF is connected to an exhaust pipe downstream of the exhaust pipe injector, an SCR and a DOC are connected to an exhaust pipe downstream of the DPF, and an upstream side of the SCR A urea water injection nozzle is provided in the exhaust pipe to constitute an exhaust gas after-treatment device, and urea water is injected from the urea water injection nozzle to generate a reducing gas composed of ammonia, and NOx is denitrated on the SCR with the reducing gas. In this case, an ammonia conversion rate map of urea water with respect to the exhaust gas temperature and the distance after urea water injection is prepared in advance, the exhaust gas temperature from the urea water injection position to the SCR is detected, and the detected temperature and urea to the SCR are detected. Based on the distance after water injection, the ammonia conversion rate of urea water is obtained from the ammonia conversion rate map. Scan conversion rate determination method.   When the calculated ammonia conversion rate is above a certain value, urea water is injected from the urea water injection nozzle, and when the ammonia conversion rate is less than a certain value, post injection is performed so that the ammonia conversion rate is above a certain value. The method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device according to claim 4, wherein urea water is injected after raising the exhaust gas temperature.   An exhaust pipe injector is provided in the exhaust pipe of the engine, and an exhaust gas aftertreatment device is configured by connecting DOC and DPF to the exhaust pipe downstream of the exhaust pipe injector. When PM is deposited on the DPF, When exhaust gas is injected from the pipe injector into the exhaust pipe to generate reducing gas, the reducing gas is burned in the DOC to raise the exhaust gas temperature, and the PM deposited on the DPF is burned to regenerate the DPF. An HC conversion rate map of the fuel with respect to the distance after fuel injection is prepared in advance, the exhaust gas temperature from the fuel injection position to immediately before the DOC is detected, and based on the detected temperature and the distance after fuel injection to the DOC, A method for determining a gas conversion rate of a reducing agent in an exhaust gas aftertreatment device, wherein an HC conversion rate of fuel is obtained from the HC conversion rate map.   When the calculated HC conversion rate is equal to or higher than a certain value, fuel is injected from the exhaust pipe injector to generate reducing gas composed of HC and the like, and the reducing gas is burned in the DOC to raise the exhaust gas temperature to the DPF regeneration temperature. The exhaust gas aftertreatment according to claim 6, wherein when the HC conversion rate is less than a certain value, post-injection is performed so that the HC conversion rate becomes a certain value or more, the exhaust gas temperature reaching the DOC is increased, and then exhaust pipe injection is performed. A method for determining a gas conversion rate of a reducing agent in an apparatus.

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