JP2005256626A - Exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of solving a pipe jamming problem by raising the temperature of an inside wall surface of pressure takeoff piping to obtain a dry soot state not sticking to the inside wall surface of the pressure takeoff piping while preventing unflammable fuel of exhaust gas from becoming like tar. <P>SOLUTION: In the exhaust emission control system 1, an exhaust gas passage 12 of an internal combustion engine 10 is provided with a diesel particulate filter 13, and and the pressure takeoff piping 2 is provided with a differential pressure sensor to measure the pressure of exhaust gas of the diesel particulate filter 13. An inlet part 2a of the pressure takeoff piping 2 is provided projecting to a passing part of exhaust gas G inside the exhaust gas passage, and the projecting inlet part 2a can be heated by the exhaust gas G passing through the exhaust gas passage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification system for measuring the pressure in an exhaust gas passage.

  The amount of particulate matter (PM: particulate matter: hereinafter referred to as PM) emitted from diesel internal combustion engines is being regulated more and more year by year with NOx, CO and HC. A technique for reducing the amount of PM collected by a filter called a filter (DPF: Diesel Particulate Filter: hereinafter referred to as DPF) and discharged to the outside has been developed.

  DPFs that collect PM include ceramic monolith honeycomb wall flow type filters, fiber type filters made of ceramic or metal fibers, and exhaust gas purification systems using these DPFs. Like other exhaust gas purification systems, the exhaust gas is installed in the middle of the exhaust passage of the internal combustion engine, and exhaust gas generated in the internal combustion engine is purified and discharged.

  The combustion temperature of PM is lowered by the action of a continuous regeneration type DPF device in which an oxidation catalyst is provided on the upstream side of the DPF, or the catalyst carried on the filter with the catalyst, and PM is incinerated with exhaust gas. There is a continuous regeneration type DPF device and the like.

This upstream regeneration catalyst continuous regeneration type DPF device utilizes the fact that oxidation of PM by NO ₂ (nitrogen dioxide) is performed at a low temperature by oxidizing PM with oxygen in exhaust gas. The catalyst is composed of a catalyst and a filter, and the upstream side of the oxidation catalyst carrying platinum or the like oxidizes NO (nitrogen monoxide) in the exhaust gas to NO ₂ , and with this NO ₂ , the downstream filter The collected PM is oxidized to CO ₂ (carbon dioxide) to remove the PM.

Moreover, the continuous regeneration type DPF device for a filter with a catalyst is constituted by a filter with a catalyst having a catalyst such as cerium oxide (CeO ₂ ), and in the exhaust gas in the filter with a catalyst in a low temperature range (about 300 ° C. to 600 ° C.). oxidizing the PM by the O ₂ reaction using _{(oxygen) (4CeO 2 + C → 2Ce} 2 O 3 + CO 2, 2Ce 2 O 3 + O 2 → 4CeO 2 , etc.), PM is burned with O ₂ in the exhaust gas In a high temperature range (about 600 ° C. or higher) higher than the temperature, PM is oxidized by O ₂ in the exhaust gas.

  And even in the continuous regeneration type DPF device of this filter with catalyst, etc., an oxidation catalyst is provided on the upstream side, and the exhaust gas is prevented from being released into the atmosphere by oxidizing unburned HC and CO in the exhaust gas. It has been practiced to increase the gas temperature to promote PM oxidation removal.

  However, even in these continuous regeneration type DPFs, when the exhaust gas temperature is 350 ° C. or higher, PM trapped in the DPF is continuously burned and purified, and the DPF self-regenerates, but the exhaust temperature is low. When the exhaust gas temperature is low or the operating state of the internal combustion engine with low NO emission, for example, when the low exhaust temperature state such as the idling operation or low load / low speed operation of the internal combustion engine continues, the exhaust gas temperature is low and the catalyst temperature decreases. Therefore, since the oxidation reaction is not promoted and NO is insufficient, the above reaction does not occur and the filter cannot be regenerated by oxidizing the PM. Therefore, the PM is continuously deposited on the filter. The filter is clogged. Therefore, the problem of an increase in exhaust pressure due to the clogging of the filter occurs. For this clogging of the filter, when the clogging exceeds a predetermined clogging amount, it is considered that the exhaust temperature is forcibly raised to forcibly remove the collected PM. Yes.

  As a means for detecting clogging of this filter, a method of detecting by the differential pressure across the filter is often used, and a pressure introduction pipe is connected to the exhaust pipe upstream and downstream of the DPF, respectively, and one end side of this pressure introduction pipe A pressure sensor is provided to measure the pressure (for example, see Patent Document 1), or a differential pressure detector (differential pressure sensor) is provided between the upstream side and the downstream side of the collection filter to detect the differential pressure. (For example, refer to Patent Document 2).

  Further, as means for forcibly raising the exhaust temperature, there are a method by injection control in in-cylinder (in-cylinder) injection and a method by fuel control in direct fuel injection into the exhaust pipe. This in-cylinder injection control increases the exhaust gas by performing multi-injection (multi-stage injection) when the exhaust temperature is lower than the activation temperature of the oxidation catalyst provided upstream of the DPF or the oxidation catalyst supported on the DPF filter. When the temperature rises above the activation temperature, post-injection (post-injection) is performed, and the fuel in the exhaust gas is burned with an oxidation catalyst, and the exhaust gas is heated to a temperature higher than the temperature at which PM collected in the DPF burns. Then, the PM collected in the DPF is burned and removed to regenerate the DPF.

Normally, in these continuous regeneration type DPFs, when the amount of accumulated PM reaches a preset accumulation limit value of PM, the operating state of the internal combustion engine is automatically changed to forced regeneration mode operation to set the exhaust temperature. The regeneration process is performed by forcibly increasing or increasing the amount of NO or NO ₂ to oxidize and remove the PM collected by the filter.

  However, in the conventional pressure measurement pipe, the hole from the opening in the DPF case to the pressure sensor is connected by a pipe of a certain thickness and a rubber hose. However, as shown in FIG. Exhaust gas G containing unburned fuel enters the pressure extraction pipe 2X, and the unburned fuel in the invaded exhaust gas G becomes tar-like and has a low temperature disposed outside the exhaust gas passage. In the worst case, it adheres to the inner wall surface of the pipe 2X, and there is a problem that the inlet portion of the pressure take-out pipe 2X is blocked by the tar-like unburned fuel F and the pressure cannot be measured.

The intrusion of the exhaust gas into the pressure extraction pipe is caused by the pressure in the pressure extraction pipe compressed by the pressure when the pressure in the DPF case increases due to the operation of the engine. It enters the inlet part of the extraction pipe and occurs.
JP-A-6-50130 (FIG. 1) JP-A-5-125927 (FIGS. 1 and 2)

  The object of the present invention was made to solve the above-mentioned problem, while increasing the temperature of the inner wall surface of the pressure extraction pipe while preventing the unburned fuel of the exhaust gas from becoming tar-like. It is an object of the present invention to provide an exhaust gas purification system that can solve a pipe blockage problem by making a dry soot that does not adhere to the inner wall surface of a pressure extraction pipe.

  In order to achieve the above object, an exhaust gas purification system of the present invention is provided with a diesel particulate filter in an exhaust gas passage of an internal combustion engine, and the pressure of the exhaust gas of the diesel particulate filter is provided in a pressure extraction pipe for measurement. In the exhaust gas purification system, the inlet portion of the pressure extraction pipe is provided so as to protrude to a portion where the exhaust gas inside the exhaust gas passage passes, and the protruding inlet portion can be heated by the exhaust gas passing through the exhaust gas passage. Configured.

  According to the exhaust gas purification system of the present invention, the pressure extraction pipe projects to the inside of the exhaust gas passage, and the inlet wall portion of the projected pipe is heated by the exhaust gas, whereby the inner wall surface temperature of the inlet section can be increased. Therefore, even if exhaust gas containing unburned fuel such as post injection enters the inlet part, the unburned fuel in the exhaust gas does not become tar-like and becomes dry soot and sticks to the pipe inner wall surface of the inlet part. It is possible to prevent the pressure take-out piping from being blocked.

  In particular, in the exhaust gas purification system using this pressure measurement pipe, it is very important to measure the pressure of the exhaust gas of the DPF in determining the start of the DPF regeneration, and further, by post injection or the like during the control for the DPF regeneration. Since a situation in which a lot of unburned fuel is contained in the exhaust gas frequently occurs, the effect is remarkably increased when this pressure measurement pipe configuration is adopted.

  Hereinafter, an exhaust gas purification system according to an embodiment of the present invention will be described with reference to the drawings, taking as an example an exhaust gas purification system including a continuous regeneration type DPF device configured by a combination of an oxidation catalyst and a filter with a catalyst. explain.

  FIG. 1 shows the configuration of an exhaust gas purification system 1 for an internal combustion engine according to this embodiment. The exhaust gas purification system 1 is configured by providing a continuous regeneration type DPF 13 in an exhaust passage 12 connected to an exhaust manifold 11 of a diesel engine 10. The continuous regeneration type DPF 13 includes an oxidation catalyst 13a on the upstream side and a filter 13b with a catalyst on the downstream side in the case 13c.

  This oxidation catalyst 13a is formed by carrying an oxidation catalyst such as platinum (Pt) on a carrier such as a porous ceramic honeycomb structure, and the filter with catalyst 13b is formed at the inlet of the channel of the porous ceramic honeycomb. And a monolith honeycomb wall flow type filter in which the outlets are alternately sealed, or a felt-like filter in which inorganic fibers such as alumina are laminated at random. A catalyst such as platinum or cerium oxide is supported on the filter.

  When a monolith honeycomb wall flow type filter is adopted as the filter with catalyst 13b, PM (particulate matter) in the exhaust gas G is collected (trapped) by the porous ceramic wall, and the fibers When the mold filter type is adopted, PM is collected by the inorganic fibers of the filter.

  In order to estimate the amount of PM accumulated on the filter with catalyst 13b, a differential pressure sensor 21 is provided in the pressure extraction pipe 2 connected before and after the continuous regeneration type DPF 13. For regeneration control of the filter with catalyst 13b, an oxidation catalyst inlet exhaust temperature sensor 22 and a filter inlet exhaust temperature sensor are provided on the upstream side, the middle, and the downstream side of the oxidation catalyst 13a and the filter with catalyst 13b, respectively.

  Output values of these sensors are input to a control device (ECU: engine control unit) 30 that performs overall control of the operation of the engine 10 and also controls regeneration of the continuous regeneration type DPF 13, and is output from the control device 30. The control signal is used to adjust the fuel injection device (injection nozzle) 14 of the engine 10, the intake throttle valve 16 that adjusts the intake air amount to the intake manifold 15, and the EGR amount that is provided with the EGR cooler in the EGR passage (not shown). The EGR valve and the like to be controlled are controlled.

  The fuel injection device 14 is connected to a common rail injection system (not shown) that temporarily stores high-pressure fuel boosted by a fuel pump (not shown). In addition to information such as the accelerator opening from the accelerator position sensor (APS) 31 and the engine rotational speed from the rotational speed sensor 32, information such as the vehicle speed and the coolant temperature is also input.

  In the present invention, the structure of the pressure measurement pipe provided with the differential pressure sensor 21 for estimating the PM accumulation amount of the filter with catalyst 13b is configured as follows.

  As shown in FIG. 2, a pressure extracting pipe 2 connected before and after the continuous regeneration type DPF 13 is provided and connected to the differential pressure sensor 21 to measure the pressure of the exhaust gas passage in the case 13 c of the continuous regeneration type DPF 13. However, the inlet portion 2a of the pressure extraction pipe 2 is provided so as to protrude to a portion through which the exhaust gas G inside the exhaust gas passage passes. The opening on the exhaust gas side of the protruding inlet portion 2a is formed so as not to pick up the dynamic pressure of the exhaust gas G. That is, the inlet portion 2a is formed so as to be substantially perpendicular to the flow direction of the exhaust gas G. With this configuration, the protruding inlet portion 2a is heated by the exhaust gas G passing through the exhaust gas passage.

  In other words, the pressure extraction pipe 2 is provided so as to protrude to the inside of the case 13c of the continuous regeneration type DPF 13, and the temperature of the pipe is increased by using the protruding inlet portion 2a as a heat spot heated by the exhaust gas G. In order to improve the heating effect on the piping by the exhaust gas G, at least the inlet portion 2a of the pressure extraction piping 2 is formed of a material having high thermal conductivity. Moreover, you may add the fin for increasing a heat-transfer area to the inlet part 2a as needed.

  With this configuration, the air in the pressure extraction pipe 2 is compressed by an amount corresponding to the pressure increase in the case 13 c of the continuous regeneration type DPF 13, so that the exhaust gas G including unburned fuel due to post injection or the like is within the pressure extraction pipe 2. Even if it enters, the inlet portion 2a is warmed by the exhaust gas G, and the temperature inside the pipe 2 is higher than the temperature at which the unburned fuel in the exhaust gas G does not become tar-like and becomes completely dry soot. As a result, the unburned fuel becomes tar and does not adhere to the inside of the pipe 2, and the pipe 2 can be prevented from being blocked.

  The pressure take-out pipe 2 is provided with a differential pressure sensor 21 on one end side, and the exhaust gas G does not pass through the pressure take-out pipe 2. Since it is limited to the part 2a, if only this part is heated, adhesion of unburned fuel can be prevented.

  In many cases, the unburned fuel is contained in the exhaust gas G in front of the continuous regeneration type DPF 13, but the unburned fuel in the exhaust gas G is consumed by the oxidation catalyst 13a behind the continuous regeneration type DPF 13. Since there are few situations where unburned fuel is contained in the exhaust gas G, only the front side of the continuous regeneration type DPF 13 as shown in FIG. An inlet portion 2a of the extraction pipe 2 is provided so as to protrude to a portion through which the exhaust gas G inside the case 13c passes. As shown in FIG. 4, the inlet portion 2a of the pressure extraction pipe 2 is provided at the rear of the continuous regeneration type DPF 13. You may form without protruding from the inner wall of 13c.

  In the above description, the continuous regeneration type DPF device in the exhaust gas purification system is described as an example of the continuous regeneration type DPF device in which the catalyst is supported on the filter and the oxidation catalyst is provided on the upstream side of the filter. Is not limited to this, but other types such as a filter-only DPF device, a continuous regeneration type DPF device in which an oxidation catalyst is supported on the filter, and a continuous regeneration type DPF device in which an oxidation catalyst is provided on the upstream side of the filter The present invention can also be applied to other DPF devices and continuous regeneration type DPF devices.

1 is a system configuration diagram of an exhaust gas purification system according to an embodiment of the present invention. It is a figure which shows the structure of piping for pressure measurement of embodiment which concerns on this invention. It is a figure which shows the structure of piping for pressure measurement of a prior art.

Explanation of symbols

1 Exhaust gas purification system
2 Pressure relief piping
2a Inlet part of the pressure relief pipe
10 Diesel engine
13 Continuous regeneration type DPF device
13a Oxidation catalyst
13b Filter with catalyst
21 Differential pressure sensor
30 control unit (ECU)

Claims (1)

In an exhaust gas purification system in which a diesel particulate filter is provided in an exhaust gas passage of an internal combustion engine, and an exhaust gas pressure of the diesel particulate filter is provided in a pressure extraction pipe and measured, an inlet portion of the pressure extraction pipe is connected to the exhaust gas passage The exhaust gas purification system is characterized in that it is provided so as to protrude to a portion through which the exhaust gas passes inside, and the protruding inlet portion can be heated by the exhaust gas passing through the exhaust gas passage.

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