JP4986877B2 - Exhaust purification device and exhaust purification method - Google Patents

Description

  The present invention relates to an exhaust purification device and an exhaust purification method for purifying exhaust gas discharged from an internal combustion engine.

  Conventionally, exhaust gas purification is performed by providing a NOx purification catalyst such as a three-way catalyst (TWC), a NOx storage reduction catalyst (LNT), or a NOx adsorption reduction catalyst (LNC) in the exhaust passage of an internal combustion engine. . However, while the NOx purification catalyst (particularly LNT) is not activated as immediately after the start of the internal combustion engine, NOx is not sufficiently removed and discharged to the atmosphere.

  Therefore, in Patent Document 1, immediately after the internal combustion engine is started, reducing gas produced from fuel by a fuel reformer is supplied upstream of the NOx purification catalyst, and exhaust gas introduced into the NOx purification catalyst is set to a rich condition. Techniques to do this are disclosed. Thereby, since the purification performance of the NOx purification catalyst is improved, it is expected that the exhaust gas can be sufficiently purified immediately after the start of the internal combustion engine.

  However, the reforming reaction of fuel (especially light oil) requires high temperature conditions of about 800 to 1000 ° C. For this reason, in the technique disclosed in Patent Document 1, hydrocarbons vaporized from the fuel are released from the fuel reformer and discharged to the atmosphere until the reforming catalyst in the fuel reformer reaches such a high temperature condition. Will be.

Therefore, Patent Document 2 discloses a technique for raising the temperature of the fuel supplied to the reforming catalyst in the fuel reformer in advance using an oxidation catalyst provided with a heater or a burner. According to this technique, since the fuel whose temperature has been raised is supplied to the reforming catalyst, the time until the reforming catalyst in the fuel reformer reaches the high temperature condition can be shortened.
JP 2001-234737 A JP 2006-242020 A

  However, in the technique disclosed in Patent Document 2, a large amount of white smoke mainly composed of organic soluble components (SOF) and hydrocarbons (HC) is generated until the temperature of the oxidation catalyst or burner is sufficiently increased. Then, it is discharged from the fuel reformer and discharged to the atmosphere. In addition, it is conceivable to increase the output of the heater or burner in order to increase the temperature raising rate, but a significant reduction in fuel consumption is unavoidable.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust purification device and an exhaust purification method capable of improving exhaust gas purification performance under low temperature conditions while maintaining fuel efficiency.

  The inventors have found that white smoke is returned to the intake passage and burned in the internal combustion engine, thereby suppressing white smoke and hydrocarbons from being mixed into the gas supplied to the NOx purification catalyst. The invention has been completed. Specifically, the present invention provides the following.

(1) An exhaust purification device that purifies exhaust discharged from an internal combustion engine,
A throttle valve provided in the intake passage of the internal combustion engine and capable of adjusting the intake pressure;
A NOx purification catalyst that is provided in an exhaust passage of the internal combustion engine and that adsorbs and stores NOx in the exhaust;
A fuel reformer provided separately from the exhaust passage and having a reforming catalyst for reforming fuel;
A supply means for supplying the internal combustion engine with a discharge gas discharged from the fuel reformer,
The supply means includes a supply path communicating the fuel reformer to a position upstream of the NOx purification catalyst in the exhaust passage, and the fuel reformer downstream of the throttle valve in the intake passage. And an exhaust purification device in which the exhaust gas is supplied to the internal combustion engine through the supply path and / or the recovery path.

According to the invention of (1), since the supply path is provided, the release gas is supplied upstream of the NOx purification catalyst, and the removal of NOx by the NOx purification catalyst using the reducing gas in the release gas is promoted. The
In addition, since the recovery path is provided, the released gas is also supplied to the intake passage and is eventually introduced into the internal combustion engine. For this reason, even if a white smoke component is included in the emitted gas in order not to raise the temperature of the reforming catalyst at a high output under low temperature conditions, at least a part of the white smoke component is burned in the internal combustion engine. For this reason, the amount mixed into the exhaust gas is reduced.
Accordingly, it is possible to improve the exhaust gas purification performance under low temperature conditions while maintaining fuel efficiency.

  Further, since the fuel reformer communicates with the downstream of the throttle valve, when the throttle valve opening is decreased, the differential pressure between the downstream of the throttle valve and the fuel reformer increases. As a result, a sufficient differential pressure can be obtained without excessive pressure increase on the fuel reformer side, and the exhaust gas containing the white smoke component is supplied to the intake passage. Therefore, the boosting means (for example, compressor, pump) on the fuel reformer side can be reduced in size, and the degree of design freedom can be improved.

  Note that “upstream side of the NOx purification catalyst” means that it is upstream side of at least one NOx purification catalyst. When a plurality of NOx purification catalysts are installed, all the NOx purification catalysts are not necessarily present. It does not mean that it is upstream.

  In addition, “white smoke” in the present specification refers to a gas in which an organic soluble component (SOF) derived from fuel or hydrocarbon (HC) is excessively present. Depending on the concentration of organic soluble component (SOF) and hydrocarbon (HC), white smoke may not be visible, but such gas is also included in “white smoke”.

  (2) The exhaust emission control device according to (1), wherein the supply unit further includes a flow rate ratio adjusting unit that adjusts a flow rate ratio of the emitted gas flowing through each of the supply path and the recovery path.

  According to the invention of (2), since the flow rate ratio of the released gas flowing through each of the supply path and the recovery path can be adjusted, the NOx removal by the NOx purification catalyst and the combustion in the internal combustion engine can be controlled according to various conditions. You can change the priority. For example, when the amount of white smoke component contained in the released gas is large as in low temperature conditions, increase the flow rate of the recovery path to burn the white smoke component, and supply when the amount of white smoke component is small The flow rate of the path may be increased to remove NOx.

(3) further comprising a flow rate ratio control means for controlling the flow rate ratio adjusting means;
The flow rate ratio control means is configured so that, under a non-permissible condition in which the amount of white smoke component in the emitted gas exceeds an allowable amount, the amount of white smoke component in the emitted gas is less than an allowable amount, and in the recovery path. The exhaust emission control device according to (2), wherein the flow rate ratio is increased.

According to the invention of (3), under a non-permissive condition such as a low temperature condition, the flow rate ratio of the recovery path increases as compared with the permissible condition, and the tendency that the white smoke component is burned in the internal combustion engine is increased. Thereby, it is suppressed more that the amount of white smoke components exceeding an allowable amount is discharged to the atmosphere.
In addition, when the permissible condition is reached, the flow rate of the recovery path is reduced as compared with the non-permissible condition, and the release gas rich in reducing gas is supplied to the NOx purification catalyst, and the tendency to promote the removal of NOx increases.
Thus, since the location where the release gas is supplied is appropriately selected according to the state of the release gas, the exhaust gas purification performance can be further improved.

(4) It further comprises detection means for detecting at least one selected from the group consisting of the temperature of the reforming catalyst, the air-fuel ratio of the released gas, and the composition of the released gas,
The exhaust gas purification apparatus according to (3), wherein the flow rate ratio control unit includes a condition selection unit that selects either the non-permissible condition or the permissible condition based on a value detected by the detection unit.

It is technically difficult to directly detect the degree of white smoke generation in the emitted gas. It is also conceivable to estimate the degree of white smoke generation in the emitted gas based on the elapsed time after the start of the internal combustion engine, but in the case of a cryogenic start, determination of allowable conditions and non-permissible conditions The accuracy is extremely poor.
Therefore, according to the invention of (4), since easily detectable parameters such as the temperature of the reforming catalyst, the air-fuel ratio of the released gas, and the composition of the released gas are adopted, allowable conditions and non-allowable conditions can be easily and accurately set. Determined. Thereby, since the location to which the released gas is supplied is selected with high accuracy and appropriateness, the exhaust gas purification performance can be further improved.

  (5) The system further comprises intake air / fuel ratio control means for controlling the air / fuel ratio (intake air / fuel ratio) of the intake air flowing through the intake passage to a predetermined value or more, and self-ignition of the intake air is suppressed (1) to (4) Any one of the exhaust gas purification apparatuses.

If the amount of white smoke component supplied to the intake passage is excessive, that is, if the intake air-fuel ratio is too low, intake air self-ignition may occur and NVH and drivability may deteriorate.
Therefore, according to the invention of (5), since the intake air-fuel ratio is controlled to a predetermined value or higher, the self-ignition of intake air is suppressed, and NVH and drivability can be improved.

  (6) The exhaust emission control device according to (5), wherein the predetermined value is a preset value.

  According to the invention of (6), taking into account variations in various environmental conditions such as temperature, pressure, humidity, presence / absence of a glow heater, and variations in each component, the value of the self-ignition probability of intake air is sufficiently low. By setting the predetermined value, it is possible to prevent the occurrence of self-ignition of intake air with a high probability.

  Thereby, the necessity for providing a means for detecting self-ignition is reduced, and the cost can be reduced when such means is not provided.

(7) It further comprises self-ignition detecting means for detecting self-ignition of the intake air,
The exhaust air purification apparatus according to (5) or (6), wherein the intake air / fuel ratio control means includes intake air / fuel ratio correction means for increasing the intake air / fuel ratio when self-ignition is detected by the self-ignition detection means.

Due to fluctuations in various environmental conditions such as temperature, pressure, humidity, presence / absence of glow heater, and variations in each component, the intake air-fuel ratio when intake air self-ignites is not constant, and self-ignition is completely prevented It is difficult.
According to the invention of (7), even when the self-ignition of the intake air occurs, the self-ignition detection means detects the self-ignition, and the intake air-fuel ratio is increased in response to the detection, and the self-ignition is eliminated. The Therefore, NVH and drivability can be further improved.

  In this way, even if self-ignition occurs, it can be eliminated, so considering various factors such as the above environmental conditions and variations in each component, it is necessary to consider the complicated work of adapting the intake air-fuel ratio to prevent self-ignition. The need is reduced.

(8) The intake air-fuel ratio control means includes an opening degree adjusting means for adjusting the opening degree of the throttle valve,
The exhaust emission control device according to any one of (5) to (7), wherein the opening degree adjusting means increases or decreases the intake air-fuel ratio through increase or decrease of the opening degree of the throttle valve.

  According to the invention of (8), just by adjusting the opening of the throttle valve, the differential pressure between the downstream of the throttle valve and the fuel reformer increases and decreases, and the supply amount of the released gas to the intake passage varies. The intake air fuel ratio increases or decreases. Therefore, while improving NVH and drivability, the burden of the pressure | voltage rise means (for example, a compressor, a pump) by the side of a fuel reformer can be reduced, and the freedom degree of design can be improved.

(9) a throttle valve provided in the intake passage and capable of adjusting the intake pressure;
A NOx purification catalyst provided in the exhaust passage for adsorbing and storing NOx in the exhaust;
An exhaust purification method for purifying exhaust discharged from an internal combustion engine, comprising a fuel reformer provided separately from the exhaust passage and having a reforming catalyst for reforming fuel,
An exhaust purification method for supplying a white smoke component contained in an exhaust gas discharged from the fuel reformer to a position downstream of the throttle valve in the intake passage.

According to the present invention, since the supply path is provided, the release gas is supplied upstream of the NOx purification catalyst, and the removal of NOx by the NOx purification catalyst using the reducing gas in the release gas is promoted.
In addition, since the recovery path is provided, the released gas is also supplied to the intake passage and is eventually introduced into the internal combustion engine. For this reason, even if a white smoke component is included in the emitted gas in order not to raise the temperature of the reforming catalyst at a high output under low temperature conditions, at least a part of the white smoke component is burned in the internal combustion engine. For this reason, the amount mixed into the exhaust gas is reduced.
Accordingly, it is possible to improve the exhaust gas purification performance under low temperature conditions while maintaining fuel efficiency.

  Further, since the fuel reformer communicates with the downstream of the throttle valve, when the throttle valve opening is decreased, the differential pressure between the downstream of the throttle valve and the fuel reformer increases. As a result, a sufficient differential pressure can be obtained without excessive pressure increase on the fuel reformer side, and the exhaust gas containing the white smoke component is supplied to the intake passage. Therefore, the boosting means (for example, compressor, pump) on the fuel reformer side can be reduced in size, and the degree of design freedom can be improved.

  FIG. 1 is a diagram showing a configuration of an internal combustion engine and an exhaust purification device according to an embodiment of the present invention. An internal combustion engine (hereinafter referred to as “engine”) 1 in the present embodiment is a diesel engine that directly injects fuel into a combustion chamber and burns the fuel by compression ignition, and uses light oil as the fuel. A fuel injection valve (not shown) is provided in the combustion chamber of each cylinder 7. These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as “ECU”) 40, and the valve opening time and valve closing time of the fuel injection valve, that is, the fuel injection amount and the fuel injection timing are determined by the ECU 40. Controlled by

<Internal combustion engine>
The engine 1 includes an intake pipe 2 as an intake passage through which intake air flows, an exhaust pipe 4 as an exhaust passage through which exhaust flows, and an exhaust recirculation passage that recirculates part of the exhaust gas in the exhaust pipe 4 to the intake pipe 2. 6 and a supercharger 8 that pumps intake air into the intake pipe 2.

  The intake pipe 2 is connected to the intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of the intake manifold 3. The exhaust pipe 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5. The exhaust gas recirculation passage 6 branches from the exhaust manifold 5 and reaches the intake manifold 3.

  The supercharger 8 includes a turbine (not shown) provided in the exhaust pipe 4 and a compressor (not shown) provided in the intake pipe 2. The turbine is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 4. The compressor is rotationally driven by the turbine, pressurizes the intake air, and pumps it into the intake pipe 2. The turbine includes a plurality of variable vanes (not shown), and is configured to change the turbine rotation speed (rotational speed) by changing the opening of the variable vanes. The vane opening degree of the turbine is electromagnetically controlled by the ECU 40.

  An air cleaner case (not shown) is provided on the upstream side of the supercharger 8 in the intake pipe 2, and outside air that has passed through the air cleaner case is sucked into the supercharger 8. Further, on the downstream side of the supercharger 8 in the intake pipe 2, an intercooler 11 for cooling the intake air pressurized by the supercharger 8, and the intake pipe 2 on the downstream side of the supercharger 8. A throttle valve 26 for adjusting the internal pressure is provided. The throttle valve 26 is connected to the ECU 40 via an actuator, and its opening degree is electromagnetically controlled by the ECU 40. Thus, EGU40 comprises an opening degree adjustment means.

  The exhaust gas recirculation passage 6 connects the exhaust manifold 5 and the intake manifold 3 and recirculates part of the exhaust discharged from the engine 1. The exhaust gas recirculation passage 6 is provided with an EGR cooler 12 that cools the exhaust gas that is recirculated, and an EGR valve 13 that controls the flow rate of the recirculated exhaust gas. The EGR valve 13 is connected to the ECU 40 via an actuator (not shown), and the opening degree is electromagnetically controlled by the ECU 40.

<NOx purification catalyst>
The exhaust pipe 4 is provided with a first catalytic converter 31, a DPF 32, and a second catalytic converter 33 in this order from the upstream side. The number and order of these members may be set as appropriate. For example, a catalyst having a similar oxidation function may be supported on the DPF without providing the catalytic converter separately from the DPF. Thereby, in addition to the effect similar to the said embodiment, an exhaust gas purification apparatus can be reduced in size.

The first catalytic converter 31 in this embodiment includes a three-way catalyst (TWC), which is rhodium (Rh) as a noble metal active species in a catalytic combustion reaction such as light hydrocarbons contained in the exhaust, and oxygen storage. And ceria (CeO ₂ ) having the ability. When exhaust gas is supplied to such a first catalytic converter 31, the temperature can be quickly increased even when the exhaust gas temperature is low. In addition, by including ceria, a stable catalytic action can be exhibited even in a sudden change in oxygen concentration.

In the present embodiment, as the first catalytic converter 31, platinum (Pt) is 2.4 (g / L), rhodium is 1.2 (g / L), and palladium (Pd) is 6.0 (g / L). L), ceria 50 (g / L), alumina (Al ₂ O ₃ ) 150 (g / L), and binder 10 together with an aqueous medium and mixed with a ball mill to produce a slurry. Then, after coating this slurry on a support made of Fe—Cr—Al alloy, the slurry prepared by drying and firing at 600 ° C. for 2 hours is used.

  When the exhaust gas passes through fine holes in the filter wall, the DPF 32 collects PM mainly composed of carbon in the exhaust gas by depositing it on the surface of the filter wall and the holes in the filter wall. As a constituent material of the filter wall, for example, ceramics such as silicon carbide (SiC) or a porous metal body is used.

The second catalytic converter 33 in the present embodiment is a NOx adsorption reduction catalyst (LNC), specifically, alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), and a complex oxide of cerium and rare earth (hereinafter referred to as “the following oxides”). Platinum (Pt) acting as a catalyst, supported on a carrier of “ceria-based complex oxide”, ceria or ceria-based complex oxide having NOx adsorption capability, and ammonia (NH ₃ ) generated in the catalyst And zeolite having a function of holding as ammonium ions (NH ₄ ⁺ ).

  In the present embodiment, the second catalytic converter 33 is formed by supporting a NOx reduction catalyst composed of two layers on a catalyst carrier.

  The lower layer of the NOx reduction catalyst is platinum (4.5 g / L), ceria 60 (g / L), alumina 30 (g / L), and Ce—Pr—La—Ox 60 (g). / L) and 20 (g / L) of Zr-Ox together with an aqueous medium are put into a ball mill and stirred and mixed to produce a slurry, and this slurry is coated on a catalyst carrier. Formed.

  Moreover, the upper layer of the NOx reduction catalyst is 75 (g / L) obtained by ion-exchange of β-type zeolite with iron (Fe) and cerium (Ce), 7 (g / L) alumina, and 8 binders. (G / L) is mixed with an aqueous medium into a ball mill and stirred and mixed to produce a slurry, and this slurry is coated on the lower layer.

  When the amount of adsorbed ammonia in the second catalytic converter 33 decreases, the NOx purification capacity decreases. Therefore, in order to reduce NOx, the reducing agent is supplied to the second catalytic converter 33 (hereinafter referred to as “reduction”) as appropriate. In this reduction, the reducing agent is supplied to the second catalytic converter 33 by making the air-fuel ratio (engine air-fuel ratio) of the air-fuel mixture in the combustion chamber of the engine 1 richer than the stoichiometric ratio. That is, by enriching the exhaust air-fuel ratio discharged from the engine 1, the concentration of the reducing agent in the exhaust flowing into the second catalytic converter 33 becomes higher than the oxygen concentration, and reduction is performed.

The purification of NOx in the second catalytic converter 33 will be described.
First, when the engine air-fuel ratio is set leaner than the stoichiometric ratio and so-called lean burn operation is performed, the reducing agent concentration in the exhaust gas flowing into the second catalytic converter 33 becomes lower than the oxygen concentration. As a result, nitrogen monoxide (NO) and oxygen (O ₂ ) in the exhaust gas react with each other by the action of the catalyst, and are adsorbed as NO ₂ on ceria or ceria-based complex oxide. In addition, carbon monoxide (CO) that has not reacted with oxygen is also adsorbed to ceria or ceria-based composite oxide.

Next, so-called rich operation is performed in which the engine air-fuel ratio is set to be richer than the stoichiometric ratio, and the exhaust air-fuel ratio is enriched. That is, when reduction is performed to make the reducing agent concentration in the exhaust gas higher than the oxygen concentration, carbon monoxide (CO) in the exhaust gas reacts with water (H ₂ O), and carbon dioxide (CO ₂ ) and hydrogen ( H ₂ ) is generated, and hydrocarbons (HC) in the exhaust gas react with water to generate hydrogen together with carbon monoxide (CO) and carbon dioxide (CO ₂ ). Furthermore, NOx contained in the exhaust gas, NOx (NO, NO ₂ ) adsorbed on ceria or ceria-based complex oxide (and platinum), and the generated hydrogen react with each other by the action of the catalyst, and ammonia (NH ₃ ) and water are produced. Further, the ammonia generated here is adsorbed on the zeolite in the form of ammonium ions (NH ₄ ⁺ ).

Next, when lean burn operation is performed in which the engine air-fuel ratio is set leaner than the stoichiometric ratio, and the reducing agent concentration in the exhaust gas flowing into the second catalytic converter 33 is set lower than the oxygen concentration, ceria or NOx is adsorbed on the ceria-based composite oxide. Further, in a state where ammonium ions are adsorbed on the zeolite, NOx and oxygen in the exhaust gas and ammonia react to generate nitrogen (N ₂ ) and water.

  As described above, according to the second catalytic converter 33, the ammonia generated during the supply of the reducing agent is adsorbed by the zeolite, and the ammonia adsorbed during the lean burn operation reacts with NOx, so that the NOx is efficiently purified. be able to.

  When SOx in the exhaust is absorbed by the second catalytic converter 33, the NOx purification performance of the second catalytic converter 33 is degraded. For this reason, it is necessary to perform an SOx regeneration process for purifying the SOx absorbed by the second catalytic converter 33. Specifically, the exhaust gas flowing into the second catalytic converter 33 may be reduced and the temperature of the second catalytic converter 33 may be raised.

<Fuel reformer>
A supply pipe 54 as a supply path is provided upstream of the second catalytic converter 33 in the exhaust pipe 4, and a fuel reformer 50 is connected to the supply pipe 54. Accordingly, the fuel reformer 50 is provided separately from the exhaust pipe 4, in other words, the fuel gas supply device 52 and the reforming catalyst 531 described later are not provided in the exhaust pipe 4. In the present embodiment, the supply pipe 54 is connected between the DPF 32 and the second catalytic converter 33. However, the present invention is not limited to this, and the supply pipe 54 is connected between the first catalytic converter 31 and the DPF 32 or upstream of the first catalytic converter 31. It may be.

The fuel reformer 50 reforms the fuel gas to produce a reformed gas containing hydrogen (H ₂ ) and carbon monoxide (CO), and releases it as a release gas. The fuel reformer 50 is provided in the gas passage 51, a gas passage 51 whose one end is connected to the exhaust pipe 4, a fuel gas supply device 52 that supplies fuel gas from the other end of the gas passage 51, and the gas passage 51. Catalyst casing 53.

  A fuel valve 521 is provided between the catalyst casing 53 and the fuel tank, and an air valve 525 is provided between the catalyst casing 53 and the air compressor 523 that pumps external air. Since the opening degree of the fuel valve 521 and the air valve 525 is adjusted by the ECU 40, fuel gas in which fuel and air are mixed at a desired ratio is supplied to the catalyst casing 53. When the fuel gas is in a lean atmosphere, the temperature of the reforming catalyst 531 described later is accelerated, but the temperature control of the reforming catalyst 531 becomes difficult. On the other hand, when the fuel gas is rich, the temperature of the reforming catalyst 531 described later is delayed, but the temperature control of the reforming catalyst 531 is facilitated. Although not particularly limited, in this embodiment, the fuel gas is made rich.

  Further, the fuel gas supply amount is controlled by the ECU 40 to control the discharge gas supply amount GRG (the amount of discharge gas supplied into the exhaust pipe 4 per unit time) supplied to the exhaust pipe 4. It is possible to do.

  Here, the electric heater 533 and the reforming catalyst 531 are stored in the fuel reformer 50 in order from the upstream. The electric heater 533 operates at the same time as or immediately after the start of the engine 1 and can heat the reforming catalyst 531. Note that an ignition device and a burner may be provided instead of or together with the electric heater 533. As a result, since the fuel and air are burned and heated to be introduced into the reforming catalyst 531, the catalytic function of the reforming catalyst 531 is rapidly improved.

The reforming catalyst 531 contains rhodium and ceria. In this embodiment, as a reforming catalyst 531, 1 mass% of Rh with respect to CeO ₂ powder is put into a ball mill together with an aqueous medium, and a slurry produced by stirring and mixing is coated on an Fe alloy carrier. , Dried at 600 ° C. for 2 hours, and prepared by firing.

  The reforming catalyst 531 is a catalyst that reforms the fuel gas supplied from the fuel gas supply device 52 to produce a reformed gas containing hydrogen and carbon monoxide. More specifically, the reforming catalyst 531 has a pressure higher than the atmospheric pressure and contains more carbon monoxide than hydrogen in a volume ratio due to a partial oxidation reaction between the hydrocarbon fuel constituting the fuel gas and air. Produces reformed gas. Further, as described above, the partial oxidation reaction is an exothermic reaction. Thus, the fuel reformer 50 can supply reducing gas having a temperature higher than that of the exhaust gas in the vicinity of the inlet 14 in the exhaust pipe 4 into the exhaust pipe 4.

  However, under a low temperature condition such as immediately after the engine 1 is started, the reforming catalyst 531 is not activated, so that the reforming reaction does not occur, and organic soluble components (SOF) and hydrocarbons (HC) are the main components. Tend to generate a large amount of white smoke. If such white smoke is supplied to the exhaust pipe 4, there is a risk that it will be released to the atmosphere as it is.

  Therefore, the gas passage 51 in this embodiment is provided with a recovery pipe 55 as a recovery path in addition to the supply pipe 54, and the recovery pipe 55 communicates the fuel reformer 50 with the intake pipe 2. Thereby, even if a white smoke component is included in the emitted gas, at least a part of the white smoke component is combusted in the engine 1, so that the amount mixed into the exhaust gas is reduced. The supply pipe 54 and the recovery pipe 55 described above constitute supply means.

  In particular, the recovery pipe 55 is connected to a position downstream of the throttle valve 26 in the intake pipe 2. Depending on the opening of the throttle valve 26, the internal pressure of the intake pipe 2 on the downstream side of the throttle valve 26 increases and decreases, and the differential pressure with the fuel reformer 50 expands and contracts. Easy to control.

  Further, the supply pipe 54 and the recovery pipe 55 are connected downstream of the gas passage 51 with a switching valve 513 serving as a flow rate ratio adjusting unit. The switching valve 513 adjusts the flow rate of the released gas flowing through each of the supply pipe 54 and the recovery pipe 55 by changing the opening degree to the supply pipe 54 and the recovery pipe 55. The amount of exhaust gas supplied to the intake pipe 2 varies according to the flow rate ratio of the recovery pipe 55, and as a result, the air-fuel ratio of the intake air introduced into the engine 1 also varies. If this intake air-fuel ratio becomes excessive, self-ignition occurs, which may cause deterioration of NVH and drivability.

<Electronic control unit>
The ECU 40 detects an air flow meter 21 that detects the intake air amount GA of the engine 1 (the amount of air that is newly sucked into the engine 1 per unit time), and a temperature T _afcat of the exhaust gas that circulates in the gas passage 51. The temperature of the discharge gas temperature sensor 23, the in-cylinder pressure sensor 25 for detecting the internal pressure of each cylinder 7, the pressure sensor 27 for detecting the pressure in the intake pipe 2 on the downstream side of the throttle valve 26, and the temperature of the second catalytic converter 33 are detected. The catalyst temperature sensor 29 is connected, and detection signals from these sensors are supplied to the ECU 40.

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, “ CPU ”). In addition, the ECU 40 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, a throttle valve 26, a switching valve 513, an EGR valve 13, a supercharger 8, a fuel injection valve of the engine 1, and the like. And an output circuit for outputting a control signal.

  The engine 1 is normally operated with the engine air-fuel ratio set to a leaner side than the stoichiometric ratio, and when the PM accumulated on the DPF 32 is burned or when the SOx adsorbed on the second catalytic converter 33 is purified. The reproduction process is performed.

  Next, the reproduction processing of this embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a procedure for supplying the released gas by the ECU 40.

  First, based on the detection value of the catalyst temperature sensor 29, it is determined whether or not the temperature of the second catalytic converter 33 is equal to or lower than a predetermined temperature (ST1). The “predetermined temperature” refers to a temperature necessary for the second catalytic converter 33 to reach an active state that can sufficiently remove NOx even if the reducing gas in the discharged gas is not supplied. It may be set as appropriate according to the performance of 33, the exhaust composition, and the like. When the determination in ST1 is “NO”, it is not necessary to supply the emission gas, so the supply of the emission gas is not performed (ST2). If “YES”, the process proceeds to ST3.

In ST3, it is determined whether or not the situation is in an unacceptable condition in which the amount of white smoke component in the emitted gas exceeds the allowable amount. In this embodiment, based on the detection value of the emission gas temperature sensor 23, the temperature T _afcat of the emission gas from the reforming catalyst 531 is a temperature T _at which the amount of white smoke component in the emission gas is assumed to exceed the allowable amount. _It is determined whether or not it is equal to or less than _smoke . The temperature T _{afcat of the} released gas corresponds to the temperature of the reforming catalyst 531. This determination is made by determining the air-fuel ratio of the released gas, the composition of the released gas (for example, at least one of hydrogen concentration, carbon monoxide concentration, oxygen concentration, and hydrocarbon concentration), after the start of operation of the fuel reformer 50. You may carry out based on elapsed time etc.

  When the determination in ST3 is “YES”, the non-permissible condition is selected, and the flow rate ratio of the recovery pipe 55 is increased in the switching valve 513 (ST4). Under a low temperature condition such as immediately after the engine 1 is started, the determination in ST3 is normally “YES”, so the routine proceeds to ST4. Subsequently, the opening degree of the throttle valve 26 is adjusted to acquire the target differential pressure (ST5). The “target differential pressure” is a differential pressure ΔP necessary for easily supplying the released gas to the intake pipe 2 and is set as appropriate.

  Next, in ST6, the presence / absence of intake self-ignition is determined. Specifically, the presence / absence of a phenomenon (for example, pressure fluctuation (dp / dΘ), heat generation pattern) that estimates self-ignition is determined based on the detection value of the in-cylinder pressure sensor 25. In addition, the determination may be performed based on detection of a knock signal, angular velocity fluctuation, ion current, and the like.

  If the determination in ST6 is “YES”, the opening of the throttle valve 26 is increased (ST7). As a result, the intake air-fuel ratio rises and self-ignition is easily eliminated. However, since the differential pressure decreases as the opening of the throttle valve 26 increases, the decrease in the differential pressure is compensated by increasing the pressure of the air compressor 523 (ST8), and then the process proceeds to ST11 described later.

  The “predetermined value” refers to an intake air-fuel ratio in a range where the self-ignition of intake air is suppressed to a desired level, and in the present embodiment, the predetermined value is set afterwards. However, the “predetermined value” may be set in advance. In this case, the following adjustment operation of the opening degree of the throttle valve 26 is performed so that the intake air-fuel ratio of the “predetermined value” is obtained.

  The upper diagram in FIG. 3 is a graph showing the relationship between the opening degree of the throttle valve 26 and the intake air-fuel ratio, and the lower diagram is the opening degree of the throttle valve 26, the inside of the intake pipe 2 on the downstream side of the throttle valve 26, and the fuel modification. It is a graph which shows the relationship with the differential pressure | voltage of the mass device. These graphs are created based on the precondition that the fuel supplied to the reforming catalyst 531 is constant and the air-fuel ratio of the fuel gas supplied to the reforming catalyst 531 is also constant.

  First, as a lower limit of the predetermined value, a critical value (self-ignition line) of the intake air-fuel ratio at which intake self-ignition is assumed under the above preconditions is obtained. The opening of the throttle valve 26 giving this critical value is set as the minimum value of the opening (see the upper diagram in FIG. 3). The predetermined value is preferably set in a range that is excessively separated from the lower limit in consideration of variations in various environmental conditions such as temperature, pressure, and humidity, and variations in each component. Thereby, the occurrence of self-ignition of intake air can be prevented with high probability.

  Further, the upper limit of the opening degree of the throttle valve 26 is the difference in pressure (target differential pressure) required for easily supplying the released gas to the intake pipe 2 if the air compressor 523 exhibits the maximum pressure under the above-mentioned preconditions. ) Is the maximum value of the opening that can be secured (see the lower diagram of FIG. 3). The differential pressure ΔP is calculated based on the output of the air compressor 523 and the detected value of the pressure sensor 27.

  The opening of the throttle valve 26 in the present embodiment provides a required differential pressure even when the pressure of the air compressor 523 is close to the atmospheric pressure (that is, in a substantially open state) in order to realize a reduction in the size of the air compressor 523. The opening (target opening) that can be secured is set (see the lower diagram of FIG. 3).

  If the opening degree of the throttle valve 26 is set within such a range, the intake air-fuel ratio becomes a predetermined value, and the self-ignition of intake air should not theoretically occur. For this reason, the necessity to install the in-cylinder pressure sensor 25 is reduced, and the cost can be reduced when the in-cylinder pressure sensor 25 is not provided. However, there are cases where the self-ignition of the intake air occurs due to various factors, and leaving the self-ignition in such a case leads to deterioration of NVH and drivability. Therefore, an in-cylinder pressure sensor 25 may be provided and ST8 may be performed.

  Returning to FIG. 2, when the reforming catalyst 531 is sufficiently warmed up with the passage of time, the determination in ST3 is “NO”. In this case, an allowable condition is selected, and the flow rate ratio of the supply pipe 54 is increased in the switching valve 513 (ST9). Subsequently, the opening degree of the throttle valve 26 is increased, normally opened fully, and the output of the engine 1 is maximized (ST10). Thereafter, the process proceeds to ST11.

  In ST11, the released gas is supplied. When moving to ST11 through ST4 to ST8, since the flow rate ratio of the recovery pipe 55 is increased, the emission gas containing the white smoke component exceeding the allowable amount is preferentially introduced into the engine 1 and used as fuel. . Further, when moving to ST11 through ST9 to ST10, since the flow rate ratio of the recovery pipe 55 is reduced, the amount of the white smoke component amount is less than the allowable amount and the release gas rich in reducing gas is preferentially second. It is introduced into the catalytic converter 33 and used to remove NOx.

[Function and effect]
According to this embodiment, the following effects can be obtained.

Since the supply pipe 54 is provided, the released gas is supplied upstream of the second catalytic converter 33, and the removal of NOx using the reducing gas in the released gas is promoted.
Moreover, since the recovery pipe 55 is provided, the released gas is also supplied to the intake pipe 2 and is introduced into the engine 1 in due course. For this reason, even if a white smoke component is contained in the emitted gas because the output of the electric heater 533 is small under low temperature conditions, at least a part of the white smoke component is burned in the engine 1, The amount of gas mixed is reduced.
Accordingly, it is possible to improve the exhaust gas purification performance under low temperature conditions while maintaining fuel efficiency.

  Since the fuel reformer 50 communicates with the downstream of the throttle valve 26, the differential pressure between the downstream of the throttle valve 26 and the fuel reformer 50 increases when the opening of the throttle valve 26 is decreased. As a result, a sufficient differential pressure can be obtained without excessively increasing the pressure by the air compressor 523, and the discharge gas containing the white smoke component is supplied to the intake pipe 2. Therefore, the air compressor 523 can be reduced in size and the degree of design freedom can be improved.

  Since the switching valve 513 is provided, the flow rate ratio of the released gas flowing through each of the supply pipe 54 and the recovery pipe 55 can be adjusted. Thereby, the priority of the NOx removal in the second catalytic converter 33 and the combustion in the engine 1 can be changed according to various conditions.

Under a non-permissive condition such as a low temperature condition, control is performed such that the flow rate ratio of the recovery pipe 55 is increased as compared with the permissible condition, so that the tendency of the white smoke component to burn in the engine 1 increases. Thereby, it is suppressed more that the amount of white smoke components exceeding an allowable amount is discharged to the atmosphere.
Further, when the permissible condition is reached, the flow rate of the recovery pipe 55 is reduced as compared with the non-permissible condition, and the release gas rich in reducing gas is supplied to the second catalytic converter 33 and the removal of NOx tends to be promoted. Becomes stronger.
Thus, since the location where the release gas is supplied is appropriately selected according to the state of the release gas, the exhaust gas purification performance can be further improved.

  Since the easily detectable parameter of the temperature of the reforming catalyst 531 is employed, the allowable condition and the non-permissible condition are determined easily and accurately. Thereby, since the location to which the released gas is supplied is selected with high accuracy and appropriateness, the exhaust gas purification performance can be further improved.

  Since the intake air-fuel ratio is controlled to a predetermined value or higher, intake air self-ignition is suppressed, and NVH and drivability can be improved.

  Even when the self-ignition of the intake air occurs, the self-ignition is detected by the in-cylinder pressure sensor 25, and the intake air-fuel ratio is increased in response to this detection, and the self-ignition is eliminated. Therefore, NVH and drivability can be further improved.

  By simply adjusting the opening of the throttle valve 26, the differential pressure ΔP downstream of the throttle valve 26 and the fuel reformer 50 increases and decreases, the supply amount of the released gas to the intake pipe 2 fluctuates, and the intake air-fuel ratio becomes smaller. Increase or decrease. Therefore, while improving NVH and drivability, the burden of the air compressor 523 can be reduced, and the design freedom can be improved.

<Modification>
The present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention. For example, in the above-described embodiment, a diesel engine is employed as the internal combustion engine. However, the present invention is not limited thereto, and may be a gas turbine engine, a jet engine, a direct injection gasoline engine, or the like. The target differential pressure and T _smoke may be set as appropriate according to the type of internal combustion engine and fuel.

1 is a diagram illustrating a configuration of an internal combustion engine and an exhaust purification device according to an embodiment of the present invention. It is a flowchart which shows the procedure of the discharge gas supply by ECU which concerns on the said embodiment. A graph (upper side) showing the relationship between the opening degree of the throttle valve 26 and the intake air-fuel ratio, and the opening degree of the throttle valve 26 and the pressure difference between the inside of the intake pipe 2 and the fuel reformer 50 on the downstream side of the throttle valve 26 It is a graph (lower side) which shows the relationship.

Explanation of symbols

1 engine (internal combustion engine)
2 Intake pipe (intake passage)
4 Exhaust pipe (exhaust passage)
23 Emission gas temperature sensor (detection means)
25 In-cylinder pressure sensor (self-ignition detection means)
26 Throttle valve
31 catalytic converter 32 DPF (particulate filter)
33 NOx purification catalyst 40 Electronic control unit (flow rate ratio control means, intake air-fuel ratio control means, intake air-fuel ratio correction means, opening degree adjustment means)
50 Fuel reformer 54 Supply pipe (supply path, supply means)
55 Recovery pipe (recovery path, supply means)
513 switching valve (flow rate ratio adjusting means)
531 Reforming Catalyst

Claims (7)

An exhaust purification device for purifying exhaust discharged from an internal combustion engine,
A throttle valve provided in the intake passage of the internal combustion engine and capable of adjusting the intake pressure;
A NOx purification catalyst that is provided in an exhaust passage of the internal combustion engine and that adsorbs and stores NOx in the exhaust;
A fuel reformer provided separately from the exhaust passage and having a reforming catalyst for reforming fuel;
A supply means for supplying the internal combustion engine with a discharge gas discharged from the fuel reformer,
The supply means includes a supply path communicating the fuel reformer to a position upstream of the NOx purification catalyst in the exhaust passage, and the fuel reformer downstream of the throttle valve in the intake passage. A recovery path communicating with a position, and the exhaust gas is supplied to the internal combustion engine through the supply path and / or the recovery path ,
The supply means further includes a flow rate ratio adjusting means for adjusting a flow rate ratio of the released gas flowing through each of the supply path and the recovery path,
A flow rate control unit for controlling the flow rate control unit;
The flow rate ratio control means is configured so that, under a non-permissible condition in which the amount of white smoke component in the emitted gas exceeds an allowable amount, the amount of white smoke component in the emitted gas is less than an allowable amount, and in the recovery path. An exhaust purification device that increases the flow rate . A detector for detecting at least one selected from the group consisting of the temperature of the reforming catalyst, the air-fuel ratio of the released gas, and the composition of the released gas;
The flow rate control means, on the basis of the value detected by the detection means, the exhaust gas purifier according to claim 1, further comprising a condition selection means for selecting one of the non-permissive or the allowable conditions. The exhaust emission control device according to claim 1 or 2 , further comprising an intake air / fuel ratio control means for controlling an air / fuel ratio (intake air / fuel ratio) of intake air flowing through the intake passage to a predetermined value or more, wherein self-ignition of the intake air is suppressed. . The exhaust emission control device according to claim 3 , wherein the predetermined value is a preset value. A self-ignition detecting means for detecting the self-ignition of the intake air;
The exhaust purification apparatus according to claim 3 or 4, wherein the intake air-fuel ratio control means includes intake air-fuel ratio correction means for increasing the intake air-fuel ratio when self-ignition is detected by the self-ignition detection means. The intake air-fuel ratio control means has an opening degree adjusting means for adjusting the opening degree of the throttle valve,
The exhaust emission control device according to any one of claims 3 to 5 , wherein the opening degree adjusting means increases or decreases the intake air-fuel ratio by increasing or decreasing the opening degree of the throttle valve. A throttle valve provided in the intake passage and capable of adjusting the intake pressure;
A NOx purification catalyst provided in the exhaust passage for adsorbing and storing NOx in the exhaust;
An exhaust purification method for purifying exhaust discharged from an internal combustion engine, comprising a fuel reformer provided separately from the exhaust passage and having a reforming catalyst for reforming fuel,
Supplying the white smoke component contained in the exhaust gas discharged from the fuel reformer to a position downstream of the throttle valve in the intake passage ;
A supply path communicating the fuel reformer with a position upstream of the NOx purification catalyst in the exhaust passage and / or a position of the fuel reformer downstream of the throttle valve in the intake passage. The exhaust gas is supplied to the internal combustion engine through a recovery path communicating with the internal combustion engine;
The flow rate ratio of the released gas flowing through each of the supply path and the recovery path can be adjusted,
Exhaust purification that increases the flow rate of the recovery path under non-permissive conditions in which the amount of white smoke component in the emitted gas exceeds an allowable amount, compared to the allowable condition in which the amount of white smoke component in the emitted gas is less than or equal to the allowable amount Method.

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