JP2013142362A - 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 turbine 19 of a turbocharger 18 arranged in an exhaust passage 16 of the diesel engine 11, a DOC 29 arranged in the exhaust passage 16 upstream of the turbine 19 and purifying CO and HC in the exhaust gas, a DPF 30 arranged in the exhaust passage 16 downstream of the DOC 29 and upstream of the turbine 19 and collecting PMs in the exhaust gas, and a control means 32 for performing control for adsorbing and oxidizing the HC to the DOC 29 when the longitudinal differential pressure of the DPF 30 falls within a predetermined differential pressure range and the 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 a turbocharger turbine disposed in an exhaust path of a diesel engine, and in the exhaust path upstream of the turbine, An oxidation catalyst for purifying CO and HC in the exhaust gas, a diesel particulate filter disposed in the exhaust path downstream of the oxidation catalyst and upstream of the turbine, and for collecting PM in the exhaust gas; 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 It is equipped with.

  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 oxidation catalyst may be a catalyst including a carbon monoxide adsorbent that adsorbs CO.

The carbon monoxide adsorbent may be CeO ₂ or ZrO ₂ .

  The exhaust gas purification device further includes a high pressure EGR pipe connected to the exhaust path downstream of the diesel particulate filter and upstream of the turbine, and a high pressure EGR valve disposed in the high pressure EGR pipe. You may prepare.

  The exhaust gas purification device may further include a low pressure EGR pipe connected to the exhaust path downstream from the turbine 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. 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. 9 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. 9, 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 includes a 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. 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.

  In the exhaust gas purifying apparatus 10a according to the comparative example, all of the post-processing units (DOC 29a, DPF 30a) constituting the post-processing apparatus 25a are arranged on the downstream side of the turbine 19, so that the post-processing is performed from the exhaust port of the diesel engine 11. The distance to the 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 operation state of the diesel engine 11, the temperature of the DOC 29a and the DPF 30a 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 the present embodiment is disposed in an exhaust path 16 upstream of a turbine 19 to purify CO and HC in exhaust gas, and also NO. A DOC (oxidation catalyst) 29 to be purified, a DPF (diesel particulate filter) 30 that is disposed in the exhaust passage 16 downstream of the DOC 29 and upstream of the turbine 19 and collects PM in the exhaust gas, and a DPF 30 Control means for performing control (referred to as continuous regeneration control in this embodiment) for adsorbing and oxidizing HC on the DOC 29 when the differential pressure before and after the pressure is within a predetermined differential pressure range and the inlet temperature of the DPF 30 is equal to or lower than the predetermined temperature. 32 (see FIG. 2). 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.

  Further, in the exhaust gas purification apparatus 10 according to the present embodiment, the exhaust pipe 13 downstream of the DPF 30 and upstream of the turbine 19 and the intake pipe 15 downstream of the intercooler 21 are configured to transmit exhaust gas toward the turbine 19. A part is connected by a high pressure EGR pipe 22 that leads a part 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.

  Furthermore, in the exhaust gas purifying apparatus 10 according to the present embodiment, the exhaust pipe 13 downstream of the turbine 19 and the intake pipe 15 upstream of the compressor 20 remove a part of the exhaust gas directed to the muffler (not shown). Are connected by a low-pressure EGR pipe 26 leading to 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.

  Each post-processing unit (DOC29, DPF30) will be described in detail later.

  As shown in FIG. 2, the control means 32 includes a differential pressure sensor 33 that detects the differential pressure across the DPF 30, a temperature sensor 34 that detects the inlet temperature of the DPF 30, a detected value of the differential pressure sensor 33, and the temperature sensor 34. In accordance with the detected value, an injector 35 provided in the diesel engine 11 and a controller (ECU) 37 that drives and controls the exhaust pipe injector 36 provided in the exhaust pipe 13 are provided. More specifically, the ECU 37 performs post injection by the injector 35 or exhaust pipe injection by the exhaust pipe injector 36 in order to adsorb and oxidize HC in the DOC 29. In the case where exhaust pipe injection is not performed, the exhaust pipe injector 36 can be omitted.

  The ECU 37 performs HC adsorption and oxidation control (continuous regeneration control) of the DOC 29 according to a control flow as shown in FIG.

Specifically, the ECU 37 detects that the detected value of the differential pressure sensor 33 (the differential pressure P before and after the DPF 30) is equal to or greater than the continuous regeneration determination differential pressure ΔP _L and equal to or less than the automatic regeneration determination differential pressure ΔP _H. 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 35 or exhaust pipe injection by the exhaust pipe injector 36 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 37 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 36 by the injector 35.

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 37 performs control called automatic regeneration control (forced regeneration control) according to a control flow (not shown).

Specifically, ECU 37 is the value detected by the differential pressure sensor 33 (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 34 (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 36 by the injector 35. That, ECU 37 basically performs automatic regeneration control until the detection value of the differential pressure sensor 33 (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..

  Each post-processing unit will be described in detail.

[DOC]
DOC29 consists of a catalyst containing CO adsorption material (carbon monoxide adsorption material) which can adsorb | suck much CO. As the CO adsorbent, CeO ₂ (cerium oxide), ZrO ₂ (zirconium oxide), or the like can be used. By configuring the DOC 29 in this way, it is possible to further increase the amount of heat generated by the DOC 29.

[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 DOC 29 and the DPF 30 are accommodated in the same casing 31. However, the casing 31 may be separated from the DOC 29 and the DPF 30, and may be connected by a short pipe.

  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 post-processing unit (DOC29, DPF30) 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 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, since exhaust gas is taken out from the exhaust passage 16 via the high pressure EGR pipe 22 or the low pressure EGR pipe 26 downstream of the DPF 30, the EGR device (the high pressure EGR pipe 22, the high pressure EGR valve 23, the high pressure EGR cooler 24, the low pressure EGR 24). This is effective for antifouling measures for the pipe 26, the low pressure EGR valve 27, and the low pressure EGR cooler 28). Further, since exhaust gas can be taken out from the exhaust path 16 directly under the DPF 30 (high pressure EGR pipe 22) or directly under the turbine 19 (low pressure EGR pipe 26), the EGR path (high pressure EGR pipe 22 or low pressure EGR pipe 26) Shortening is possible.

  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, the DOC and the DPF are disposed in the exhaust path upstream of the turbine located on the uppermost stage (exhaust port side of the diesel engine).

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)
30 Diesel particulate filter (DPF)
32 Control means 33 Differential pressure sensor 34 Temperature sensor 35 Injector 36 Exhaust pipe injector 37 ECU (controller)

Claims (6)

A turbocharger turbine disposed in the exhaust path of the diesel engine;
An oxidation catalyst disposed in the exhaust path upstream of the turbine and purifying CO and HC in the exhaust gas;
A diesel particulate filter that is disposed in the exhaust path downstream of the oxidation catalyst and upstream of the turbine and collects PM in the exhaust gas;
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.   The exhaust gas purification apparatus for a diesel engine according to claim 1 or 2, wherein the oxidation catalyst is a catalyst containing a carbon monoxide adsorbent that adsorbs CO. The exhaust gas purification apparatus for a diesel engine according to claim 3, wherein the carbon monoxide adsorbent is CeO ₂ or ZrO ₂ .   The high-pressure EGR pipe connected to the exhaust path downstream from the diesel particulate filter and upstream from the turbine, and the high-pressure EGR valve disposed in the high-pressure EGR pipe are further provided. The exhaust gas purification apparatus of the diesel engine in any one.   The exhaust gas of a diesel engine according to any one of claims 1 to 5, further comprising a low-pressure EGR pipe connected to the exhaust path downstream of the turbine, and a low-pressure EGR valve arranged in the low-pressure EGR pipe. Purification equipment.

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