JP4131783B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for improving the purification efficiency of nitrogen oxides, particularly in an exhaust gas purification apparatus for an internal combustion engine.
[0002]
[Prior art]
In the exhaust discharged from the internal combustion engine, harmful carbon dioxide (CO ₂ ), water (H ₂ O), nitrogen (N ₂ ), harmful carbon monoxide (CO), hydrocarbon (HC) It is known that nitrogen oxides (NOx) are contained. For this reason, for the purpose of purifying NOx, which is a harmful substance, for example, an exhaust purification device as disclosed in JP-A-6-137136 has been proposed. In such an exhaust purification device, a NOx reduction catalyst is interposed in the exhaust passage of the internal combustion engine in order to convert NOx into harmless N ₂ , oxygen (O ₂ ), etc. in an oxygen-excess atmosphere. Further, in order to increase the NOx purification efficiency in the NOx reduction catalyst, a configuration is adopted in which fuel such as light oil containing HC as a reducing agent is added to the upstream exhaust passage.
[0003]
[Problems to be solved by the invention]
However, if a reducing agent having a temperature lower than that of the exhaust gas is added to the exhaust passage as it is, the exhaust gas temperature is lowered, and the NOx purification efficiency by the NOx reduction catalyst may be lowered. In addition, when liquid fuel such as light oil is used as the reducing agent, the reducing agent in a droplet state is added to the exhaust passage, so that the diffusion of the reducing agent becomes insufficient, and the reducing agent is supplied to the NOx reduction catalyst. There was also a problem that unevenness was likely to occur. Furthermore, since the liquid fuel is composed of polymer HC having a low NOx reduction activity, there has been a problem that it is difficult to improve the NOx purification efficiency.
[0004]
Therefore, in view of the conventional problems as described above, the present invention improves the NOx purification efficiency by the NOx reduction catalyst by suppressing the decrease in the exhaust temperature due to the addition of the reducing agent and enhancing the diffusibility and activity of the reducing agent. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine.
[0005]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, a nitrogen oxide reduction catalyst that is interposed in the exhaust passage of the internal combustion engine and converts the nitrogen oxide in the exhaust gas into a harmless substance by a reduction reaction, and a reducing agent containing hydrocarbons Mixture generating means for generating an air-fuel mixture in which air and air are mixed at a predetermined ratio, and a reducing agent added to the upstream side of the nitrogen oxide reduction catalyst while heating the air-fuel mixture generated by the air-fuel mixture generation means In the exhaust gas purification apparatus for an internal combustion engine including an injection valve, the reducing agent injection valve has an air-fuel mixture channel formed between two heating elements that extend in the axial direction and are arranged substantially concentrically. In addition, the air-fuel mixture inlet is open at a position offset with respect to the axial center in the cross section of the air-fuel mixture flow path .
[0006]
According to this configuration, since the air-fuel mixture in which the reducing agent and air are mixed at a predetermined ratio is heated and added to the upstream side of the nitrogen oxide reduction catalyst, even if the air-fuel mixture and the exhaust gas are mixed. And the fall of exhaust temperature is suppressed. Further, since the gas mixture is heated, vaporization of the reducing agent is promoted, so that the supply distribution of the reducing agent with respect to the nitrogen oxide reduction catalyst is made uniform and the diffusibility is improved.
Further, the reducing agent injection valve has an air-fuel mixture flow path formed between two heating elements that extend in the axial direction and are substantially concentric, and the air-fuel mixture inlet is the axial center in the cross section of the air-fuel mixture flow path. Therefore, a swirling flow is generated in the mixture flow path. For this reason, the air-fuel mixture is effectively heated.
[0007]
The invention according to claim 2 is characterized in that a reforming catalyst for reforming the reducing agent by partially oxidizing the reducing agent is applied to the inner wall surface of the mixture flow path of the reducing agent injection valve .
According to this configuration, when the air-fuel mixture of the reducing agent and air passes through the air-fuel mixture flow path, the hydrocarbon that is the main component of the reducing agent is modified to a lower molecular weight hydrocarbon, aldehyde, carbon monoxide, hydrogen, or the like. Quality. For this reason, the nitrogen oxide reduction activity by a reducing agent is increased, and the purification efficiency of nitrogen oxide is further improved.
[0008]
The invention according to claim 3 is characterized in that the reforming catalyst is made of a noble metal.
According to such a configuration, the reducing agent is effectively reformed by using the noble metal as the reforming catalyst .
[0010]
In the fourth aspect of the invention, the operating state detecting means for detecting the engine operating state, the reducing agent temperature detecting means for detecting the temperature of the reducing agent, the operating state detecting means and the reducing agent temperature detecting means are respectively detected. And a heating amount control means for controlling the heating amount of the air-fuel mixture by the reducing agent injection valve based on the engine operating state and the reducing agent temperature.
[0011]
According to such a configuration, since the amount of heating of the air-fuel mixture is controlled based on the engine operating state and the reducing agent temperature, the amount of heating can be minimized, and power consumption and heat generation required for heating the air-fuel mixture can be achieved. Thermal deterioration of the body is suppressed as much as possible.
The invention according to claim 5 is characterized in that air supply means for supplying only air to the reducing agent injection valve after the addition of the air-fuel mixture is provided.
[0012]
According to this configuration, after the addition of the air-fuel mixture is completed, only air is supplied to the reducing agent injection valve . For example, only air is injected from the injection hole, and clogging of the injection hole is prevented.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an overall configuration of a diesel engine equipped with an exhaust gas purification device for an internal combustion engine (hereinafter referred to as “exhaust gas purification device”) according to the present invention.
A diesel particulate filter (DPF) 14 that collects and removes particulate matter (PM) and a NOx reduction catalyst 16 that reduces and purifies NOx are disposed in the exhaust passage 12 of the diesel engine 10 along the exhaust flow direction. Intervened.
[0014]
The DPF 14 has a structure in which a large number of cells substantially parallel to the exhaust flow are formed by partition walls made of a porous member such as ceramic, and the inlets and outlets of each cell are alternately sealed in a staggered pattern by a plugging material. Eggplant. When the exhaust gas in the cell whose outlet is blocked flows into the adjacent cell whose inlet is blocked via the partition wall, PM in the exhaust gas is collected and removed by the porous member forming the partition wall. The
[0015]
On the other hand, the NOx reduction catalyst 16 has a configuration in which, for example, a zeolite-based active component is supported on a monolith type catalyst carrier having a honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel. Make. Then, the active component supported on the catalyst carrier is activated by receiving supply of HC as an additive, and effectively converts NOx into a harmless substance.
[0016]
A reducing agent injection valve 18 for injecting and adding an air-fuel mixture in which a reducing agent such as light oil containing HC and air are mixed at a predetermined ratio is interposed in the exhaust passage 12 upstream of the NOx reduction catalyst 16. An air reservoir 22 is connected to the reducing agent injection valve 18 via an air introduction path 20. A reducing agent storage tank 28 such as a fuel tank is connected to the air introduction path 20 via a reducing agent introduction path 26 in which a constant pressure pump 24 is interposed. The reducing agent introduction path 26 is desirably connected to the air introduction path 20 so that, for example, a spraying action is exerted so that the reducing agent is refined by the air flow flowing through the air introduction path 20. Further, in the air introduction path 20 and the reducing agent introduction path 26, the air flow rate control valve 32 and the reducing agent flow rate, which are duty-controlled by a control unit 30 incorporating a microcomputer, in order to control the air flow rate and the reducing agent flow rate, respectively. A control valve 34 is interposed.
[0017]
The air introduction path 20, the air reservoir 22, the constant pressure pump 24, the reducing agent introduction path 26, the reducing agent storage tank 28, the control unit 30, the air flow rate control valve 32 and the reducing agent flow rate control valve 34, An air supply means is configured.
As shown in FIG. 2, the reducing agent injection valve 18 extends in the axial direction and is substantially concentrically arranged to increase the temperature of the mixture of reducing agent added to the exhaust passage 12 and air. Between the bodies 18A and 18B, a reducing agent channel 18C as an air-fuel mixture channel is formed. Here, it is desirable that the heating elements 18A and 18B are constituted by low-heat capacity electric heaters capable of heating the reducing agent in a short time. A heat shield 18D is disposed on the outer periphery of the heating element 18B in order to suppress heat from being dissipated to the outside. Note that the reducing agent inlet 18E as the air-fuel mixture inlet preferably opens at a position offset with respect to the axial center of the reducing agent injection valve 18 so that a swirling flow is generated in the reducing agent flow path 18C ( (See FIG. 2B). Further, both of the heating elements 18A and 18B are not necessarily arranged, and at least one of them may be arranged.
[0018]
The inner wall surface of the reducing agent channel 18C, that is, the outer peripheral surface of the heating element 18A disposed in the center and the inner peripheral surface of the heating element 18B disposed in the periphery thereof, should increase NOx reduction activity by the reducing agent. It is desirable to apply a reforming catalyst made of a noble metal such as platinum (Pt) that modifies HC as a reducing agent to lower molecular weight HC, aldehyde, CO, hydrogen (H ₂ ) or the like. Here, “aldehyde” refers to an oxo compound having at least one hydrogen atom in the carbonyl group (that is, aldehyde group —CHO), such as formaldehyde (HCHO) and acetaldehyde (CH ₃ CHO).
[0019]
In order to control the exhaust emission control device, various sensors for detecting the engine operating state, the reducing agent state, and the like are provided. In other words, the NOx sensor 36 for detecting the NOx concentration C _NOx in the exhaust and the exhaust temperature sensor 38 for detecting the exhaust temperature Te are interposed in the exhaust passage 12 on the downstream side of the DPF 14, respectively. The diesel engine 10 is provided with an intake flow sensor 40 that detects the intake flow rate Q, a rotational speed sensor 42 that detects the engine rotational speed N, and a load sensor 44 that detects the engine load L. The NOx sensor 36, the exhaust temperature sensor 38, the intake flow rate sensor 40, the rotation speed sensor 42, and the load sensor 44 constitute an operating state detection means. A reducing agent temperature sensor 46 (reducing agent temperature detecting means) for detecting the reducing agent temperature Tr is interposed in the reducing agent introduction path 26 on the downstream side of the constant pressure pump 24.
[0020]
Then, in the control unit 30, the processing shown in FIG. 3 is repeatedly executed at predetermined time intervals, and the heating elements 18A and 18B, the air flow rate control valve 32, and the reducing agent flow rate control valve 34 of the reducing agent injection valve 18 are controlled. . The power supply control for the heating elements 18A and 18B corresponds to the heating amount control means.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the NOx concentration from the NOx sensor 36, the exhaust temperature sensor 38, the intake flow rate sensor 40, the rotational speed sensor 42, and the load sensor 44 is set as the engine operating state. C _NOx , exhaust temperature Te, intake air flow rate Q, rotational speed N and engine load L are detected. Further, the reducing agent temperature Tr is detected from the reducing agent temperature sensor 46.
[0021]
In step 2, for example, the reducing agent addition amount map and the reducing agent addition flow rate map are referred to, and the reducing agent addition amount and the reducing agent addition flow rate (reducing agent addition amount per unit time) corresponding to the engine operating state are respectively calculated. The
In step 3, the air flow rate corresponding to the calculated reducing agent addition flow rate is calculated so that the mixing ratio of the reducing agent and air becomes substantially constant. The mixing ratio of the reducing agent and air may be changed according to the engine operating state.
[0022]
In step 4, the power supplied to the heating elements 18A and 18B of the reducing agent injection valve 18 is calculated based on the reducing agent addition flow rate, the exhaust gas temperature Te, and the reducing agent temperature Tr. That is, as shown in FIG. 4, the power supplied to the heating elements 18A and 18B is proportional to the reducing agent addition flow rate and depends on the exhaust gas temperature Te and the reducing agent temperature Tr. Therefore, for example, the slope of the straight line shown in FIG. 4 can be obtained from the map based on the exhaust temperature Te and the reducing agent temperature Tr, and the power supplied to the heating elements 18A and 18B can be obtained by a simple calculation.
[0023]
In step 5, heating of the reducing agent and injection of a mixture of the reducing agent and air are started. That is, based on the calculated supply power, for example, the voltage or / and current applied to the heating elements 18A, 18B is controlled, and the mixture of the reducing agent and air supplied to the reducing agent injection valve 18 is heated. The Further, based on the calculated reducing agent addition flow rate and air flow rate, the opening degrees of the reducing agent flow rate control valve 34 and the air flow rate control valve 32 are duty controlled, respectively, and the reducing agent injection valve 18 enters the exhaust passage 12. An air-fuel mixture heated and heated is injected.
[0024]
In step 6, it is determined whether or not the injection of the air-fuel mixture has ended, that is, whether or not the calculated reducing agent addition amount has been injected into the exhaust passage 12. Whether or not the injection of the air-fuel mixture has ended can be determined, for example, by whether or not the injection time determined by dividing the reducing agent addition amount by the reducing agent addition flow rate has elapsed since the start of the injection of the air-fuel mixture. . If the mixture injection is completed, the process proceeds to step 7 (Yes). If the mixture injection is not completed, the determination in step 6 is repeated (No).
[0025]
In step 7, the energization of the heating elements 18A and 18B is interrupted to stop the heating of the air-fuel mixture, and the reducing agent flow rate control valve 34 is controlled to close to stop the injection of the reducing agent.
In step 8, it is determined whether or not a predetermined time has elapsed after the air injection is completed, that is, after the injection of the reducing agent is stopped. And if air injection is complete | finished, it will progress to step 9 (Yes), and if air injection is not complete | finished, the determination in step 8 will be repeated (No).
[0026]
In step 9, the air flow control valve 32 is controlled to be closed in order to stop air injection.
According to such a configuration, since the air-fuel mixture in which the reducing agent and air are mixed at a predetermined ratio is heated and added to the upstream side of the NOx reduction catalyst 16, even if the air-fuel mixture is mixed with the exhaust gas, the exhaust gas is exhausted. A decrease in temperature can be suppressed. Further, since the gas mixture is heated to promote the vaporization of the reducing agent, the supply distribution of the reducing agent to the NOx reduction catalyst 16 is made uniform, and the diffusibility can be improved. The NOx purification efficiency by the NOx reduction catalyst 16 can be improved by using the minimum reducing agent by the synergistic effect of suppressing the decrease in the exhaust temperature and improving the diffusibility of the reducing agent.
[0027]
Further, when a reforming catalyst is applied to the inner wall surface of the reducing agent flow path 18C of the reducing agent injection valve 18, HC, which is the main component of the reducing agent, is HC, aldehyde, CO, H having lower molecular weight. Modified to ₂ mag. For this reason, the NOx reduction activity by the reducing agent is increased, and the NOx purification efficiency can be further improved. Here, since a noble metal such as platinum is used as the reforming catalyst, the reducing agent can be effectively reformed.
[0028]
Furthermore, since the reducing agent flow path 18C extends in the axial direction and the reducing agent introduction path 18E is opened at a position offset with respect to the axial center in the cross section of the reducing agent injection valve 18, the reducing agent flow A swirling flow is generated in the path 18C. For this reason, heating of a reducing agent comes to be performed effectively and the NOx purification efficiency by a NOx purification catalyst can be improved further. When the reforming catalyst is applied to the inner wall surface of the reducing agent channel 18C, the reducing agent can be effectively reformed by the swirling flow.
[0029]
In addition, since the heating amount of the air-fuel mixture in the reducing agent injection valve 18 is controlled based on the reducing agent injection amount, the exhaust temperature Te, and the reducing agent temperature Tr, the heating amount can be minimized and heating is performed. Power consumption and heat deterioration of the heating elements 18A and 18B can be suppressed as much as possible.
In addition, since only air is supplied to the reducing agent injection valve 18 after the addition of the air-fuel mixture, for example, only air is injected from the injection hole, and clogging of the injection hole can be prevented.
[0030]
The heating elements 18A and 18B of the reducing agent injection valve 18 may be controlled by the control unit 30 or may be of a self-temperature adjusting type. Needless to say, the exhaust emission control device of the present invention is not limited to a diesel engine, but can also be applied to an internal combustion engine such as a gasoline engine or a compressed natural gas (CNG) engine.
[0031]
【The invention's effect】
As described above, according to the first aspect of the present invention, by the synergistic effect of suppressing the decrease in the exhaust temperature and improving the diffusibility of the reducing agent, the minimum amount of liquid reducing agent is used and the nitrogen oxide reduction catalyst is used. The purification efficiency of nitrogen oxides can be improved. Further, the mixture can be effectively heated by the swirling flow generated in the mixture flow path.
According to invention of Claim 2, the nitrogen oxide reduction activity by a reducing agent is heightened, and the purification efficiency of nitrogen oxide can be improved further.
[0032]
According to the invention described in claim 3, the reducing agent can be effectively reformed by using the noble metal as the reforming catalyst .
[0033]
According to the fourth aspect of the present invention, since the amount of heating of the air-fuel mixture is minimized, it is possible to suppress power consumption required for heating the air-fuel mixture and thermal deterioration of the heating element as much as possible.
According to the fifth aspect of the present invention, for example, clogging of the air-fuel mixture injection hole in the reducing agent injection valve can be prevented.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a diesel engine equipped with an exhaust purification device according to the present invention. FIG. 2 shows details of a reducing agent injection valve, (A) is a longitudinal sectional view, and (B) is a transverse sectional view. 3] Flow chart showing the control contents of the exhaust purification device [FIG. 4] Explanatory diagram of the principle for calculating the power supplied to the heating element
10 diesel engine 12 exhaust passage 16 NOx reduction catalyst 18 reducing agent injection valve 18A heating element 18B heating element 18C reducing agent passage 18E reducing agent introduction port 20 air introduction path 22 air reservoir 24 constant pressure pump 26 reducing agent introduction path 28 reducing agent storage Tank 30 Control unit 32 Air flow rate control valve 34 Reductant flow rate control valve 36 NOx sensor 38 Exhaust temperature sensor 40 Intake flow rate sensor 42 Rotational speed sensor 44 Load sensor 46 Reductant temperature sensor

Claims (5)

A nitrogen oxide reduction catalyst that is interposed in the exhaust passage of the internal combustion engine and converts the nitrogen oxide in the exhaust gas into a harmless substance by a reduction reaction;
An air-fuel mixture generating means for generating an air-fuel mixture in which a reducing agent containing hydrocarbon and air are mixed at a predetermined ratio;
A reducing agent injection valve that is added to the upstream side of the nitrogen oxide reduction catalyst while heating the mixture generated by the mixture generation means;
It is configured to include a,
In the reducing agent injection valve, an air-fuel mixture flow path is formed between two heating elements that extend in the axial direction and are substantially concentrically arranged, and the air-fuel mixture inlet is the axial center in the cross section of the air-fuel mixture flow path An exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification apparatus is opened at a position offset with respect to the engine. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a reforming catalyst for reforming the reducing agent by partially oxidizing the reducing agent is applied to an inner wall surface of the mixture flow path of the reducing agent injection valve .   The exhaust purification device of an internal combustion engine according to claim 2, wherein the reforming catalyst is made of a noble metal. An operating state detecting means for detecting an engine operating state;
Reducing agent temperature detecting means for detecting the temperature of the reducing agent;
A heating amount control means for controlling the heating amount of the air-fuel mixture by the reducing agent injection valve based on the engine operating state and the reducing agent temperature detected by the operating state detection means and the reducing agent temperature detection means, respectively;
It is inclusive constitute an exhaust purification system of an internal combustion engine according to any one of claims 1 to 3, characterized in. The exhaust of the internal combustion engine according to any one of claims 1 to 4 , further comprising air supply means for supplying only air to the reducing agent injection valve after the addition of the air-fuel mixture. Purification equipment.

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