JP2013142363A - Exhaust emission control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of a diesel engine for reducing a size by effectively using the heat of exhaust gas by devising the arrangement of respective postprocessing units.SOLUTION: An exhaust emission control device 10 of a diesel engine 11 includes a DOC 29 arranged in an exhaust passage 16 of the diesel engine 11, a DPF 30 arranged in the exhaust passage 16 downstream of the DOC 29, a urea injection nozzle 32 arranged in the exhaust passage 16 downstream of the DPF 30, a turbine 19 of a turbocharger 18 arranged in the exhaust passage 16 downstream of the urea injection nozzle 32, an SCR 33 arranged in the exhaust passage 16 downstream of the turbine 19, and a control means 36 for performing control for adsorbing and oxidizing HC to the DOC 29 when the longitudinal differential pressure of the DPF 30 falls within a predetermined differential pressure range and an inlet temperature of the DPF 30 is a predetermined temperature or lower.

Description

  The present invention relates to an exhaust gas purification device for a diesel engine.

  From the viewpoint of global environmental conservation, automobile exhaust gas regulations are being further promoted. In particular, diesel engines are required to reduce PM (Particulate Matter) and NOx (nitrogen oxide). To reduce PM, post-processing units such as DPF (Diesel Particulate Filter) are required. Used to reduce NOx, urea SCR (Urea-Selective Catalytic Reduction), HC-SCR (HydroCarbon-Selective Catalytic Reduction), LNT (Lean NOx Trap: NOx storage catalyst) A post-processing unit is used.

  An exhaust gas purification apparatus having such an aftertreatment unit is described in Patent Document 1, for example. Patent Document 1 describes disposing a DPF between two-stage turbo turbines.

JP 2009-299499 A

  By the way, in recent years, combustion improvement of diesel engines has been promoted, and the total emission amount of PM and NOx has been reduced along with the improvement of fuel efficiency. However, contrary to the reduction of PM and NOx, the temperature of the exhaust gas is low. Furthermore, when switching from JE05 (transitional driving mode based on actual driving conditions in the city), NEDC (New European Driving Cycle), etc. to WHDC (Worldwide Harmonized Heavy Duty Certification) Further, a technique for reducing exhaust gas at a high temperature and a high flow rate is required. As countermeasures, approaching the engine of the aftertreatment device composed of the aftertreatment unit (arranged directly under the turbine), reducing the heat capacity of the aftertreatment device (such as downsizing), heat insulation and heat insulation of the aftertreatment device are being studied. In the present situation, it is inevitable to increase the size of the post-processing apparatus. For this reason, there are problems such as securing the location of the post-processing device, the effect on fuel consumption due to weight increase, and cost increase.

  An object of the present invention, which was created in view of the above circumstances, is to exhaust a diesel engine that can effectively use the heat of exhaust gas and can be downsized by devising the arrangement of each post-processing unit. The object is to provide a gas purification device.

  In order to achieve the above object, an exhaust gas purification apparatus for a diesel engine according to the present invention is provided in an exhaust path of the diesel engine, and an oxidation catalyst for purifying CO and HC in the exhaust gas, and downstream of the oxidation catalyst. A diesel particulate filter that collects particulate matter in the exhaust gas, and is disposed in the exhaust passage downstream of the diesel particulate filter, and urea water is contained in the exhaust gas. A urea injection nozzle for generating ammonia by spraying, and a turbocharger turbine disposed in the exhaust path downstream of the urea injection nozzle and stirring the sprayed urea water to promote decomposition of urea And disposed in the exhaust path downstream of the turbine, and detoxifies NOx in the exhaust gas by a reduction reaction with ammonia. The selective reduction catalyst and the diesel particulate filter adsorb and oxidize HC when the pressure difference between the front and rear of the diesel particulate filter is within a predetermined differential pressure range and the inlet temperature of the diesel particulate filter is equal to or lower than a predetermined temperature. Control means for performing control.

  The control means includes a differential pressure sensor for detecting a differential pressure across the diesel particulate filter, a temperature sensor for detecting an inlet temperature of the diesel particulate filter, and an injector for adsorbing and oxidizing HC on the oxidation catalyst. And a controller that performs exhaust injection by an exhaust pipe injector.

  The exhaust gas purification device may further include a rear-stage oxidation catalyst that is disposed in the exhaust path downstream of the selective reduction catalyst and oxidizes ammonia that has flowed out of the selective reduction catalyst to render it harmless.

  The oxidation catalyst has a first oxidation catalyst disposed in each cylinder portion of the exhaust manifold of the diesel engine and a second oxidation catalyst disposed in an exhaust pipe connected to a downstream end of the exhaust manifold. The first oxidation catalyst may be superior to the second oxidation catalyst for CO purification, and the second oxidation catalyst may be superior to the first oxidation catalyst for HC purification. .

  The first oxidation catalyst may be a catalyst including an oxide having an oxygen storage material and an oxide semiconductor, and the second oxidation catalyst may be a metal catalyst.

The oxide having the oxygen storage material may be an oxide containing Ce, and the oxide semiconductor may be TiO ₂ , ZnO, or Y ₂ O ₃ .

  A noble metal may be supported on the oxide having the oxygen storage material.

  The exhaust gas purification device includes a high-pressure EGR pipe connected to the exhaust path downstream of the diesel particulate filter and upstream of the urea injection nozzle, and a high-pressure EGR valve disposed in the high-pressure EGR pipe. May be further provided.

  The exhaust gas purification device may further include a low pressure EGR pipe connected to the exhaust path downstream of the selective reduction catalyst, and a low pressure EGR valve disposed in the low pressure EGR pipe.

  According to the exhaust gas purification apparatus for a diesel engine according to the present invention, the heat of the exhaust gas can be effectively used and the size can be reduced by devising the arrangement of each aftertreatment unit.

It is a schematic block diagram of the exhaust-gas purification apparatus of the diesel engine which concerns on one Embodiment of this invention. It is a schematic block diagram of a control means. It is a control flowchart of the continuous reproduction | regeneration control performed by ECU. (A) is explanatory drawing which shows the relationship between the decreasing rate of DPF diameter when DPF length is made the same, and DPF pressure loss, (b) is DPF diameter when DPF length is made the same. It is explanatory drawing which shows the relationship between a decreasing rate and an exhaust manifold pressure (exhaust manifold pressure), (c) is explanatory drawing which shows the relationship between the decreasing rate of a DPF diameter when the length of DPF is made the same, and a torque. . It is explanatory drawing which shows the relationship between the elapsed time in JE05 mode, and DPF inlet_port | entrance temperature. It is explanatory drawing which shows the relationship between the temperature rising time at the time of DPF reproduction | regeneration, and DPF inlet_port | entrance temperature. It is explanatory drawing which compared the automatic reproduction | regeneration interval in a comparative example, and the automatic reproduction | regeneration interval in this embodiment. Comparison is an explanatory diagram comparing the CO ₂ emissions during DPF regeneration in CO ₂ emissions and the present embodiment at the time of DPF regeneration in the example. Is an explanatory view showing the relationship between SCR inlet temperature and NH ₃ production rate. It is explanatory drawing which compared the NOx purification rate in a comparative example, and the NOx purification rate in this embodiment. It is a schematic block diagram of the exhaust-gas purification apparatus of the diesel engine which concerns on other embodiment of this invention. It is a schematic block diagram of the exhaust-gas purification apparatus of the diesel engine which concerns on a comparative example.

  An embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a basic layout of an exhaust gas purification apparatus according to an embodiment of the present invention, and FIG. 12 shows a basic layout of an exhaust gas purification apparatus according to a comparative example.

<Comparative example>
First, an exhaust gas purification apparatus 10a according to a comparative example will be described with reference to FIG.

  As shown in FIG. 12, an exhaust pipe 13 is connected to an exhaust manifold (exhaust manifold) 12 of the diesel engine 11, and an intake pipe 15 is connected to an intake manifold (intake manifold) 14 of the diesel engine 11. The exhaust manifold 12 and the exhaust pipe 13 constitute an exhaust path 16, and the intake manifold 14 and the intake pipe 15 constitute an intake path 17. A turbocharger 18 is connected to the exhaust pipe 13 and the intake pipe 15. That is, the turbine 19 of the turbocharger 18 is disposed in the exhaust pipe 13, and the compressor 20 of the turbocharger 18 is disposed in the intake pipe 15.

  An intercooler 21 is disposed in the intake pipe 15 downstream of the compressor 20. The exhaust pipe 13 upstream of the turbine 19 and the intake pipe 15 downstream of the compressor 20 and upstream of the intercooler 21 are high-pressure EGR pipes 22 a that guide part of the exhaust gas directed to the turbine 19 to the intake pipe 15. It is connected. A high pressure EGR valve 23a and a high pressure EGR cooler 24a are arranged in this order from the exhaust pipe 13 side in the high pressure EGR pipe 22a. Note that the high-pressure EGR cooler 24a may be disposed in the high-pressure EGR pipe 22a closer to the exhaust pipe 13 than the high-pressure EGR valve 23a.

  An exhaust pipe 13 downstream of the turbine 19 is provided with a post-processing device 25a that purifies harmful substances (PM, NOx, CO, HC, etc.) in the exhaust gas. The post-processing device 25a will be described later. The exhaust pipe 13 downstream of the post-processing device 25a and the intake pipe 15 upstream of the compressor 20 are connected by a low-pressure EGR pipe 26a that guides a part of exhaust gas directed to the muffler (not shown) to the intake pipe 15. A low pressure EGR valve 27a and a low pressure EGR cooler 28a are disposed in the low pressure EGR pipe 26a in this order from the exhaust pipe 13 side. Note that the low-pressure EGR cooler 28a may be disposed in the low-pressure EGR pipe 26a closer to the exhaust pipe 13 than the low-pressure EGR valve 27a.

  The post-processing device 25a is disposed downstream of the first casing 31a and a first casing 31a in which an oxidation catalyst (hereinafter referred to as DOC) 29a and a diesel particulate filter (hereinafter referred to as DPF) 30a are accommodated. A urea injection nozzle 32a for spraying urea water in the exhaust pipe 13 and a second casing 34a disposed downstream of the urea injection nozzle 32a and containing a urea selective reduction catalyst (hereinafter referred to as SCR) 33a. Have.

The DOC 29a has a function of oxidizing and purifying CO and HC in the exhaust gas and oxidizing NO, and the DPF 30a has a function of collecting PM in the exhaust gas. The urea injection nozzle 32a has a function of generating ammonia (NH ₃ ) by hydrolysis or thermal decomposition of urea water sprayed in the exhaust pipe 13. The SCR 33a has a function of detoxifying water and nitrogen by reducing the NOx in the exhaust gas with ammonia.

  In the exhaust gas purifying apparatus 10a according to the comparative example, since all of the post-processing units (DOC 29a, DPF 30a, urea injection nozzle 32a, SCR 33a) constituting the post-processing device 25a are arranged on the downstream side of the turbine 19, the diesel engine The distance from the 11 exhaust ports to the post-processing device 25a is long. Therefore, the exhaust gas flowing out from the exhaust port of the diesel engine 11 is dissipated when passing through the exhaust pipe 13, expands in the turbine 19, and then reaches the post-processing device 25 a. For this reason, depending on the operating state of the diesel engine 11, the temperatures of the DOC 29a, DPF 30a, and SCR 33a may not rise to the catalyst activation temperature (about 250 ° C.).

<Embodiment>
Next, an exhaust gas purification apparatus 10 according to an embodiment of the present invention will be described with reference to FIG.

  Since this embodiment has the same constituent elements as the comparative example described above, the common constituent elements are denoted by the same reference numerals and description thereof is omitted. As for the exhaust gas purification device 10 and the post-treatment device 25, those with the suffix “a” represent comparative examples, and those without the suffix “a” represent this embodiment.

  As shown in FIG. 1, an exhaust gas purification device 10 for a diesel engine 11 according to this embodiment is disposed in an exhaust path 16 of the diesel engine 11 to purify NO and CO while purifying CO and HC in the exhaust gas. A DOC (oxidation catalyst) 29 at the front stage, a DPF (diesel particulate filter) 30 that is disposed in the exhaust passage 16 downstream of the DOC 29 and collects PM in the exhaust gas, and an exhaust passage 16 downstream of the DPF 30 The urea injection nozzle 32 for generating ammonia by spraying urea water in the exhaust gas, and the exhaust passage 16 downstream of the urea injection nozzle 32 and sprayed urea water The turbine 19 of the turbocharger 18 that promotes the decomposition of urea by stirring and the exhaust path 16 downstream of the turbine 19 is disposed in the exhaust gas N. SCR (selective reduction catalyst: urea SCR) 33 detoxified by reducing x with ammonia, and when the differential pressure across the DPF 30 is within a predetermined differential pressure range and the inlet temperature of the DPF 30 is below a predetermined temperature, The control means 36 (refer FIG. 2) which performs control (it is called continuous regeneration control in this embodiment) which adsorb | sucks and oxidizes HC in DOC29 is provided. Further, a downstream oxidation catalyst (R-DOC) 35 for oxidizing and detoxifying the ammonia flowing out from the SCR 33 is disposed in the exhaust passage 16 downstream of the SCR 33. In FIG. 2, only a part of the exhaust path 16 of the diesel engine 11 is illustrated, and the intake path 17 and the like are not illustrated.

  Each post-processing unit (DOC29, DPF30, urea injection nozzle 32, SCR33, R-DOC35) will be described in detail later.

  Further, in the exhaust gas purification apparatus 10 according to the present embodiment, the exhaust pipe 13 upstream of the DPF 30, the downstream of the DPF 30, and the upstream of the urea injection nozzle 32 and the downstream of the intercooler 21. The intake pipe 15 is connected by a high-pressure EGR pipe 22 that guides a part of the exhaust gas directed to the turbine 19 to the intake pipe 15. The high pressure EGR pipe 22 is provided with a high pressure EGR valve 23 and a high pressure EGR cooler 24 in order from the exhaust pipe 13 side. Note that the high-pressure EGR cooler 24 may be disposed in the high-pressure EGR pipe 22 closer to the exhaust pipe 13 than the high-pressure EGR valve 23.

  In the exhaust gas purification apparatus 10 according to the present embodiment, the high-pressure EGR pipe 22 includes a downstream EGR pipe 22x connected to the exhaust passage 16 downstream of the DPF 30 and upstream of the urea injection nozzle 32, and will be described later. Connected to the upstream EGR pipe 22y connected to the exhaust passage 16 downstream of the M / F-DOC 29x and upstream of the P / T-DOC 29y described later, and to the intake passage 17 downstream of the intercooler 21, and downstream The high-pressure EGR valve 23 includes a downstream EGR valve 23x disposed on the downstream EGR pipe 22x and an upstream EGR pipe. The intake EGR pipe 22z joins the side EGR pipe 22x and the upstream EGR pipe 22y. And an upstream EGR valve 23y disposed at 22y. Further, the high pressure EGR cooler 24 is disposed in the intake side EGR pipe 22z.

  Note that one of the downstream EGR pipe 22x and the downstream EGR valve 23x, and the upstream EGR pipe 22y and the upstream EGR valve 23y can be omitted. That is, the high-pressure EGR pipe 22 may be configured with only the downstream EGR pipe 22x and the intake-side EGR pipe 22z, and the high-pressure EGR pipe 22 may be configured with only the upstream EGR pipe 22y and the intake-side EGR pipe 22z.

  Further, in the exhaust gas purification apparatus 10 according to the present embodiment, the exhaust pipe 13 downstream of the SCR 33 and the intake pipe 15 upstream of the compressor 20 allow a part of the exhaust gas directed to the muffler (not shown) to the intake pipe 15. They are connected by a low pressure EGR pipe 26 that guides them. A low pressure EGR valve 27 and a low pressure EGR cooler 28 are disposed in the low pressure EGR pipe 26 in order from the exhaust pipe 13 side. Note that the low pressure EGR cooler 28 may be disposed in the low pressure EGR pipe 26 closer to the exhaust pipe 13 than the low pressure EGR valve 27.

  As shown in FIG. 2, the control means 36 includes a differential pressure sensor 37 that detects the differential pressure across the DPF 30, a temperature sensor 38 that detects the inlet temperature of the DPF 30, a detected value of the differential pressure sensor 37, and the temperature sensor 38. In accordance with the detected value, an injector 39 provided in the diesel engine 11 and a controller (ECU) 41 that drives and controls the exhaust pipe injector 40 provided in the exhaust pipe 13 are provided. More specifically, the ECU 41 performs post injection by the injector 39 or exhaust pipe injection by the exhaust pipe injector 40 in order to adsorb and oxidize HC in the DOC 29 (M / F-DOC 29x, P / T-DOC 29y). Note that the exhaust pipe injector 40 can be omitted when exhaust pipe injection is not performed.

  The ECU 41 performs HC adsorption and oxidation control (continuous regeneration control) of the DOC 29 according to a control flow as shown in FIG.

Specifically, ECU 41 is a differential pressure detection value of the sensor 37 is not less and less automatic regeneration determination differential pressure [Delta] P _H in the continuous regeneration determination differential pressure [Delta] P _L or higher (DPF 30 the differential pressure P of) the detection of the temperature sensor 38 When the value (inlet temperature T of the DPF 30) is equal to or lower than the continuous regeneration control start temperature _TL , post injection by the injector 39 or exhaust pipe injection by the exhaust pipe injector 40 is executed. That is, in the exhaust gas purification apparatus 10 according to the present embodiment, the desorption and oxidation of HC adsorbed on the DOC 29 is used for auxiliary heat for DPF regeneration.

  A control flow of the continuous regeneration control executed by the ECU 41 will be described with reference to FIG.

In step S1, the inlet temperature T of the DPF 30 and the front-rear differential pressure ΔP of the DPF 30 are measured. In step S2, whether the front-rear differential pressure ΔP of the DPF 30 is equal to or higher than the continuous regeneration determination differential pressure ΔP _L (ΔP ≧ ΔP _L ). to decide. When the differential pressure [Delta] P in step S2 DPF 30 is smaller than [Delta] P _L, the process returns to step S1.

When the front-rear differential pressure ΔP of the DPF 30 is greater than or equal to ΔP _{L in} step S2, it is determined in step S3 whether the front-rear differential pressure ΔP of the DPF 30 is equal to or less than the automatic regeneration determination differential pressure ΔP _H (ΔP ≦ ΔP _H ). When in step S3 the differential pressure [Delta] P of the DPF30 is larger than the automatic regeneration determination differential pressure [Delta] P _H, the process proceeds to the control flow 50 of the automatic regeneration control terminates the control flow. The automatic regeneration determination differential pressure ΔP _H is a set value for determining the automatic regeneration timing (forced regeneration timing), and is set to a value larger than the continuous regeneration determination differential pressure ΔP _L.

When in step S3 the differential pressure [Delta] P of the DPF30 is less automatic regeneration determination differential pressure [Delta] P _H, at step S4, whether the inlet temperature T of the DPF30 is a continuous regeneration control start temperature T _L or less (T ≦ T _L) Judging. When in step S4 the inlet temperature T of the DPF30 is greater than T _L, the flow advances to step S9. The continuous regeneration control start temperature _TL is set to 200 ° C. to 250 ° C., for example.

When the inlet temperature T in step S4 DPF 30 is equal to or less than the continuous regeneration control start temperature T _L, in step S5, whether the inlet temperature T of the DPF 30 is continuous regeneration control end temperature T _H below (T ≦ T _H) to decide. When the inlet temperature T of the DPF 30 is higher than T _{H in} step S5, the process proceeds to step S9. The continuous regeneration control end temperature T _H is set to a value higher than the continuous regeneration control start temperature T _L , and is set to, for example, 300 ° C. to 350 ° C.

When the inlet temperature T in step S5 DPF 30 is equal to or less than the continuous regeneration control end temperature T _H in step S6, performing exhaust pipe injection by post injection or exhaust pipe injector 40 by the injector 39.

Next, in step S7, the inlet temperature T of the DPF 30 and the differential pressure ΔP before and after the DPF 30 are measured. In step S8, whether the inlet temperature T of the DPF 30 is equal to or lower than the continuous regeneration control start temperature T _L (T ≦ T _L ). Judging. When the inlet temperature T in step S8 DPF 30 is greater than T _L, the flow returns to step S5.

When the inlet temperature T in step S8 DPF 30 is equal to or less than the continuous regeneration control start temperature T _L, in step S9, whether the differential pressure [Delta] P of the DPF 30 is continuous regeneration determination differential pressure [Delta] P _L or less (ΔP ≦ ΔP _L) Judging. When the differential pressure [Delta] P at the step S9 DPF 30 is larger than [Delta] P _L, the process returns to step S5, at the time the differential pressure [Delta] P of the DPF 30 is less than [Delta] P _L step S9, the control is terminated flow (return) .

  Further, the ECU 41 performs control called automatic regeneration control (forced regeneration control) according to a control flow (not shown).

Specifically, ECU 41 is the value detected by the differential pressure sensor 37 (the differential pressure [Delta] P of the DPF 30) is larger than the automatic regeneration determination differential pressure [Delta] P _H, the detection value of the temperature sensor 38 (the inlet temperature T of the DPF 30) is when: the automatic regeneration control start temperature T _a, executes the exhaust pipe injection by post injection or exhaust pipe injector 40 by the injector 39. That, ECU 41 basically performs automatic regeneration control until the detection value of the differential pressure sensor 37 (the differential pressure [Delta] P of the DPF 30) is equal to or less than the automatic regeneration determination differential pressure [Delta] P _H. Automatic regeneration control start temperature T _A is set to a value higher than the continuous regeneration control start temperature T _L and the continuous regeneration control end temperature T _H, for example, it is set to 450 ° C. to 500 ° C..

  Next, the effect of this embodiment will be described.

  By disposing the DPF 30 in the exhaust path 16 on the upstream side of the turbine 19, there is no influence of the expansion ratio of the turbine 19, and in this embodiment, the DPF pressure loss increases compared to the comparative example, and the exhaust manifold pressure and torque are increased. The effect on the is relatively small. As a result, as shown in FIG. 4, when the influence on the engine performance such as the torque and the exhaust manifold pressure is made the same, this embodiment can reduce the diameter of the DPF 30 by about 40% with the same length as the comparative example. . By increasing the size of the DPF 30 (reducing the heat capacity), it is possible to shorten the temperature increase time during regeneration of the DPF.

  Further, by disposing the DPF 30 in the exhaust path 16 on the upstream side of the turbine 19, in the present embodiment, the DPF 30 can be closer to the exhaust port of the diesel engine 11 than the comparative example. Therefore, as shown in FIG. 5, the present embodiment can keep the inlet temperature of the DPF 30 at 100 ° C. or higher than the comparative example. Therefore, the frequency at which the continuous regeneration of the DPF 30 (the inlet temperature of the DPF 30 is 250 ° C. to 500 ° C.) can be increased. Furthermore, as shown in FIG. 6, this embodiment can shorten the temperature rising time until the inlet temperature of DPF30 reaches predetermined temperature compared with a comparative example. Therefore, the heat of the exhaust gas can be used effectively, and the temperature of each aftertreatment unit (DOC29, DPF30, SCR33, R-DOC35) can be easily secured at the catalyst activation temperature (about 250 ° C.).

Based on these advantages, the exhaust gas purification apparatus 10 according to the present embodiment performs HC adsorption and oxidation control (continuous regeneration control) of the DOC 29 as shown in FIG. 3 to continuously regenerate the DPF 30 (inlet temperature of the DPF 30). The frequency at which 250 ° C. to 500 ° C.) can be further increased. That is, by adding continuous regeneration control, the frequency with which the DPF 30 can be continuously regenerated can be increased. As a result, it is possible to prevent clogging of the DPF 30 and prevent automatic regeneration control (forced regeneration control) as much as possible. As shown in FIG. 7, in this embodiment, the automatic regeneration of the DPF 30 (the inlet temperature of the DPF 30 is The interval of 500 ° C. or higher) could be greatly extended compared to the comparative example. As a result, as shown in FIG. 8, the present embodiment was able to significantly reduce the CO ₂ emission during DPF regeneration. In addition, by using a CO adsorbent (carbon monoxide adsorbent) that can adsorb a large amount of CO such as CeO ₂ (cerium oxide) and ZrO ₂ (zirconium oxide) to the DOC 29, the calorific value of the DOC 29 can be further increased. It is.

  In addition, by disposing the DPF 30 in the exhaust path 16 on the upstream side of the turbine 19, it is possible to reduce the size of the DPF 30 and increase the degree of freedom in layout. Furthermore, since the DPF 30 is not affected by the ash content derived from the oil of the turbine 19, it is advantageous for suppressing clogging of the DPF 30. In addition, exhaust gas from the exhaust path 16 directly under the DPF 30 upstream of the turbine 19 (downstream EGR pipe 22x of the high-pressure EGR pipe 22) or directly under the SCR 33 close to the exhaust port of the diesel engine 11 (low-pressure EGR pipe 26). Therefore, the EGR path (the high pressure EGR pipe 22 or the low pressure EGR pipe 26) can be shortened. Furthermore, it is effective for antifouling measures of the EGR device (high pressure EGR pipe 22, high pressure EGR valve 23, high pressure EGR cooler 24, low pressure EGR pipe 26, low pressure EGR valve 27, low pressure EGR cooler 28).

  Each post-processing unit will be described in detail.

[DOC]
The DOC 29 includes a first oxidation catalyst (M / F-DOC: manifold oxidation catalyst) 29x disposed in each cylinder portion of the exhaust manifold 12 of the diesel engine 11, and an exhaust pipe 13 connected to the downstream end of the exhaust manifold 12. And a second oxidation catalyst (P / T-DOC: pre-turbine oxidation catalyst) 29y. The upstream M / F-DOC 29x is used for CO purification better than the downstream P / T-DOC 29y, and the downstream P / T-DOC 29y is more than the upstream M / F-DOC 29x. Those excellent in HC purification are used. DOC generally has better HC adsorption and purification when no CO is present in the exhaust gas, and CO adsorption and purification does not deteriorate even if HC is present in the exhaust gas. This is because it has properties. Note that, depending on the exhaust temperature, the HC / CO concentration, and the like, the DOC 29 can be configured with only the M / F-DOC 29x (see FIG. 11).

  M / F-DOC29x consists of a catalyst containing an oxide and an oxide semiconductor having an oxygen storage material (OSC: Oxygen Storage Capacity) excellent in CO purification (CO adsorption), and P / T-DOC29y is an HC purification ( It consists of a metal catalyst (Pt catalyst etc.) excellent in HC adsorption). By configuring the DOC 29 in this way, a catalyst configuration excellent in low-temperature activity can be obtained, the entire DOC 29 can be reduced in size, and can be disposed without difficulty on the upstream side of the turbine 19.

The M / F-DOC 29x may be a catalyst layer including a catalyst in which an OSC-containing oxide and an oxide semiconductor are mixed. The P / T-DOC 29y includes a noble metal catalyst (such as a Pt catalyst) and an HC adsorbent. A catalyst in which is mixed may be used. An oxide containing cerium (Ce) (cerium oxide or the like) may be used as the oxide having OSC, and a noble metal (Pt or the like) may be supported on the oxide. As the oxide semiconductor, TiO ₂ , ZnO, or Y ₂ O ₃ is used.

  By the way, the exhaust gas recirculated to the intake path 17 via the high pressure EGR pipe 22 branches from the exhaust pipe 13 downstream of the M / F-DOC 29x and upstream of the urea injection nozzle 32 (downstream EGR pipe 22x, upstream side). EGR piping 22y). Further, the exhaust gas recirculated to the intake path 17 via the low pressure EGR pipe 26 branches from the exhaust pipe 13 downstream of the SCR 33. As a result, the exhaust gas after passing through DOC29 (M / F-DOC29x, P / T-DOC29y), DPF30, and SCR33 becomes high-pressure EGR pipe 22 (downstream EGR pipe 22x, upstream EGR pipe 22y, intake side EGR). It is returned to the intake pipe 15 through the pipe 22z) or the low pressure EGR pipe 26. Therefore, unburned substances (SOF component: Soluble Organic Fraction Element) in the recirculated exhaust gas are reduced, and an EGR valve (high pressure EGR valve 23, low pressure EGR valve 27) or EGR cooler (high pressure EGR cooler 24, low pressure) by SOF. The adverse effects such as clogging and corrosion of the EGR cooler 28) can be suppressed.

[Urea injection nozzle]
In the comparative example, the urea injection nozzle 32 a is disposed in the exhaust pipe 13 downstream of the turbine 19. In order to inject urea water substantially uniformly by the arrangement of the comparative example, a certain distance (for example, a distance of 25 cm or more) from the urea injection position to the inlet of the SCR 33a is required.

On the other hand, in the present embodiment, the urea injection nozzle 32 is disposed in the exhaust pipe 13 downstream of the DPF 30 and upstream of the turbine 19. For this reason, the urea water sprayed from the urea injection nozzle 32 is agitated by the turbine 19 and diffused substantially uniformly on the downstream side of the turbine 19 to promote hydrolysis and thermal decomposition of urea. For this reason, the distance from the urea injection position of the urea injection nozzle 32 to the inlet of the SCR 33 can be made closer than in the comparative example, and further, the spray diffusion of urea into the exhaust pipe 13 after passing through the turbine 19 is made uniform. The In addition, since the temperature of the urea injection position (DPF outlet temperature) can be kept higher by 100 ° C. or more than the comparative example (see FIG. 4), as shown in FIG. 9 and FIG. The production rate to NH ₃ ) can be improved as compared with the comparative example, and the present embodiment can improve the NOx purification rate of the SCR 33 on the JE05 mode average as compared with the comparative example.

  By the way, when high EGR combustion is performed, sulfur oxide (SOx) is generated in the exhaust gas. Corrosion of the exhaust pipe 13 and the turbine 19 due to the SOx is suppressed by using the following reaction.

First, ammonia (NH ₃ ) generated by hydrolysis and thermal decomposition of urea water sprayed from the urea injection nozzle 32 reacts with SO ₄ in the exhaust gas, and 2NH ₃ + SO ₄ → (NH ₄ ) 2SO ₄ is produced. Since the produced (NH ₄ ) 2 SO ₄ is a neutralized product, the problem of corrosion of the exhaust pipe 13 and the turbine 19 does not occur.

Thereafter, the (NH ₄ ) 2 SO ₄ is captured by the SCR 33 downstream of the turbine 19 and thermally decomposed to produce ammonia (NH ₃ ). This ammonia (NH ₃ ) is used for the NOx reduction reaction in the SCR 33. The

[DPF]
The filter body of the DPF 30 has a structure in which the purification characteristic (PM collection characteristic) is the same as that of the conventional product and the pressure loss is small by optimizing the porosity, the pore diameter, and the wall thickness. Due to this improvement, a small DPF 30 having a volume 50% or more smaller than that of the conventional product was used.

  In FIG. 1, the P / T-DOC 29y and the DPF 30 are accommodated in the same first casing 31, but the first casing 31 is separated into the P / T-DOC 29y and the DPF 30, and the space between them is separated. You may connect with short piping.

[SCR]
As the SCR 33, a small SCR 33 in which the catalyst amount per specific volume was increased by using a catalyst carrier (monolith catalyst) or the like and the volume was reduced by 50% or more compared with the conventional SCR 33 was used.

[R-DOC]
If the spray amount of urea water is controlled according to the operating state of the diesel engine 11 so that all ammonia (NH ₃ ) generated by the urea water sprayed from the urea injection nozzle 32 is consumed by the SCR 33, R− The DOC 35 can be omitted (see FIG. 11). That is, the R-DOC 35 may be disposed as necessary.

  In FIG. 1, the SCR 33 and the R-DOC 35 are accommodated in the same second casing 34, but the second casing 34 is separated from the SCR 33 and the R-DOC 35, and they are connected by a short pipe. May be.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various other embodiments can be adopted.

  For example, the present invention can be applied to a diesel engine having a multi-stage turbo. In that case, DOC and DPF are arranged in the exhaust path upstream of the turbine located in the uppermost stage (diesel engine exhaust port side), and SCR and R-DOC are arranged in the exhaust path downstream of the turbine located in the lowermost stage. Will be disposed.

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification apparatus 11 Diesel engine 16 Exhaust path 18 Turbocharger 19 Turbine 22 High pressure EGR piping 23 High pressure EGR valve 26 Low pressure EGR piping 27 Low pressure EGR valve 29 Oxidation catalyst (DOC)
29x 1st oxidation catalyst (M / F-DOC)
29y Second oxidation catalyst (P / T-DOC)
30 Diesel particulate filter (DPF)
32 Urea injection nozzle 33 Urea selective reduction catalyst (SCR)
35 Back-stage oxidation catalyst (R-DOC)
36 Control means 37 Differential pressure sensor 38 Temperature sensor 39 Injector 40 Exhaust pipe injector 41 ECU (controller)

Claims (9)

An oxidation catalyst disposed in the exhaust path of the diesel engine to purify CO and HC in the exhaust gas;
A diesel particulate filter disposed in the exhaust path downstream of the oxidation catalyst and collecting particulate matter in the exhaust gas;
A urea injection nozzle that is disposed in the exhaust path downstream of the diesel particulate filter and generates ammonia by spraying urea water into the exhaust gas;
A turbocharger turbine disposed in the exhaust path downstream of the urea injection nozzle and agitating the sprayed urea water to promote decomposition of urea;
A selective reduction catalyst that is disposed in the exhaust path downstream of the turbine and detoxifies by reducing the NOx in the exhaust gas with ammonia;
Control means for performing control to adsorb and oxidize HC on the oxidation catalyst when the differential pressure across the diesel particulate filter is within a predetermined differential pressure range and the inlet temperature of the diesel particulate filter is equal to or lower than a predetermined temperature; An exhaust gas purifying device for a diesel engine characterized by comprising:   The control means includes a differential pressure sensor for detecting a differential pressure across the diesel particulate filter, a temperature sensor for detecting an inlet temperature of the diesel particulate filter, and an injector for adsorbing and oxidizing HC on the oxidation catalyst. The exhaust gas purification apparatus for a diesel engine according to claim 1, further comprising a controller that executes post-injection by means of exhaust gas or exhaust pipe injection by means of an exhaust pipe injector.   3. The diesel engine according to claim 1, further comprising a rear-stage oxidation catalyst that is disposed in the exhaust path downstream of the selective reduction catalyst and oxidizes and detoxifies ammonia flowing out of the selective reduction catalyst. Exhaust gas purification device. The oxidation catalyst has a first oxidation catalyst disposed in each cylinder portion of the exhaust manifold of the diesel engine and a second oxidation catalyst disposed in an exhaust pipe connected to a downstream end of the exhaust manifold. And
The first oxidation catalyst is more excellent in CO purification than the second oxidation catalyst;
The exhaust gas purification apparatus for a diesel engine according to any one of claims 1 to 3, wherein the second oxidation catalyst is more excellent in HC purification than the first oxidation catalyst. The first oxidation catalyst is a catalyst containing an oxide having an oxygen storage material and an oxide semiconductor;
The exhaust gas purification apparatus for a diesel engine according to claim 4, wherein the second oxidation catalyst is a metal catalyst. The oxide having the oxygen storage material is an oxide containing Ce,
Wherein the oxide semiconductor is, the exhaust gas purifying device for a diesel engine according to claim 5 which is a TiO _2, ZnO or Y ₂ O _3. The exhaust gas purification device for a diesel engine according to claim 5 or 6, wherein a noble metal is supported on the oxide having the oxygen storage material.   The apparatus further comprises a high pressure EGR pipe connected to the exhaust path downstream of the diesel particulate filter and upstream of the urea injection nozzle, and a high pressure EGR valve disposed in the high pressure EGR pipe. 8. An exhaust gas purifying device for a diesel engine according to any one of 7 above.   The diesel engine according to any one of claims 1 to 8, further comprising: a low pressure EGR pipe connected to the exhaust path downstream of the selective reduction catalyst; and a low pressure EGR valve arranged in the low pressure EGR pipe. Exhaust gas purification device.

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