JP4735979B2 - Exhaust gas purification device and exhaust gas purification method - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus and an exhaust gas purification method.

In general, exhaust gas from a diesel engine contains particulate matter (hereinafter referred to as “PM (Particulate Matter)”) containing carbon as a main component, and is known to cause air pollution. Therefore, various apparatuses and methods for capturing and removing these particulate substances from exhaust gas have been proposed. For example, (i) a diesel particulate filter (hereinafter, “ (Ii) a method in which the collected PM is oxidized and burned by raising the temperature of the DPF, and (ii) a method in which NO ₂ is produced from NO in the exhaust gas and the PM is oxidized by NO ₂ No. 531762 (Patent Document 1), (iii) a method for oxidizing PM using a catalyzed DPF (for example, JP-A-6-272541 (Patent Document 2), JP-A-9-125931 ( Patent Document 3)) has been proposed.

However, in the method (i), the fuel is forcibly injected and fuel consumption is deteriorated, and PM burns rapidly, and the DPF is damaged due to a rapid temperature change derived from the reaction heat at that time. There was a problem that there was. Further, the method (ii) has a problem that it is difficult to completely oxidize and remove PM discharged from the engine because the oxidation rate of PM by NO ₂ is not sufficient. Furthermore, in the method (iii), since the catalyst and the PM are both solid, there is a problem that the two are not sufficiently in contact with each other and the PM oxidation reaction is insufficient.

Therefore, recently, a technique for oxidizing and treating PM using ozone (O ₃ ), which has stronger oxidizing power than NO ₂ , has been disclosed, for example, Japanese Patent Laid-Open No. 2002-129936 (Patent Document 4). Includes an ozone addition means for adding ozone to an intake passage or an exhaust passage of a diesel engine, an addition amount calculation means for calculating an ozone addition amount to be added to the intake passage or the exhaust passage based on an engine operating state, A diesel engine comprising: an addition amount control means for controlling the ozone addition means so that the ozone addition amount calculated by the addition amount calculation means is added to the intake passage or the exhaust passage. An exhaust purification device is disclosed.

However, in the exhaust gas purification apparatus for diesel engines as described in Patent Document 4, ozone is introduced from the upstream side of the exhaust gas to the PM collection unit, so the upstream PM is preferential in the PM collection unit. There was a tendency for PM to remain on the downstream side. For this reason, there is a problem that pressure loss increases due to the remaining PM, and the oxidation efficiency of PM decreases. Further, when the remaining PM is burned at a high temperature, there is a problem that the PM trapping portion is damaged due to a nonuniform temperature rise.
Special Table 2002-53762 JP-A-6-272541 JP-A-9-125931 JP 2002-129936 A

  The present invention has been made in view of the above-described problems of the prior art, and can uniformly perform ozone PM oxidation in the PM collection unit, and increase in pressure loss due to PM remaining in the PM collection unit. An object of the present invention is to provide an exhaust gas purifying apparatus and an exhaust gas purifying method capable of suppressing damage to the PM trapping part during high-temperature combustion and capable of efficiently oxidizing PM.

  As a result of intensive research to achieve the above object, the present inventors have collected PM in exhaust gas with a plurality of particulate matter collection devices, and used the ozone supplied from the ozone supply means to collect the PM. In the exhaust gas purifying apparatus to be oxidized, the exhaust gas flow path is configured so that ozone is supplied from the downstream side to some of the particulate matter collecting devices and the ozone is supplied from the upstream side to the remaining particulate matter collecting devices. And the ozone supply means can uniformly oxidize ozone in the PM trapping section, increase the pressure loss due to the PM remaining in the PM trapping section, and trap the PM during high-temperature combustion. It has been found that damage to the collecting portion can be suppressed and that PM can be efficiently oxidized, and the present invention has been completed.

That is, the exhaust gas purification apparatus of the present invention is connected to an internal combustion engine, and an exhaust gas passage branched into a plurality of passages;
A plurality of particulate matter collecting devices that are respectively disposed in the exhaust gas passages and collect particulate matter in the exhaust gas;
Ozone supply means connected to the exhaust gas passage on the downstream side of the particulate matter collection device and supplying ozone to the particulate matter collection device;
While supplying ozone from the downstream side to some of the particulate matter collectors, the ozone is supplied from the upstream side to the remaining particulate matter collectors, and
While the exhaust gas from the internal combustion engine is allowed to flow from the upstream side into the exhaust gas passage in which the remaining particulate matter collection device is disposed, the exhaust gas from the internal combustion engine is part of the particulate matter collection device. Control means for controlling the exhaust gas flow path and the ozone supply means so as not to flow into the exhaust gas passage arranged from the upstream side ;
Also the in which comprising: a.

  In the exhaust gas purifying apparatus of the present invention, it is preferable that the ozone supply means further supplies secondary air from the downstream side to the part of the particulate matter collecting apparatus.

  Further, in the exhaust gas purification apparatus of the present invention, a part of the exhaust gas flowing from the upstream side to the downstream side of the remaining particulate matter collection device is from the downstream side to the upstream side of the part of the particulate matter collection device. The exhaust gas flow path control means for controlling the exhaust gas flow path so as to be supplied to the exhaust gas flow path may be further provided.

An exhaust gas purification method of the present invention includes an exhaust gas passage connected to an internal combustion engine and branched into a plurality of passages,
A plurality of particulate matter collecting devices that are respectively disposed in the exhaust gas passages and collect particulate matter in the exhaust gas;
Ozone supply means connected to the exhaust gas passage for supplying ozone to the particulate matter collection device;
An exhaust gas purification method using an exhaust gas purification device comprising:
While supplying ozone from the downstream side to some of the particulate matter collectors, the ozone is supplied from the upstream side to the remaining particulate matter collectors, and
While the exhaust gas from the internal combustion engine is allowed to flow from the upstream side into the exhaust gas passage in which the remaining particulate matter collection device is disposed, the exhaust gas from the internal combustion engine is part of the particulate matter collection device. The exhaust gas flow path and the ozone supply means are controlled so as not to flow into the exhaust gas passage arranged from the upstream side .

  In addition, according to the exhaust gas purification apparatus and method of the present invention, ozone PM oxidation in the PM trapping part can be performed uniformly, and the pressure loss due to PM remaining in the PM trapping part is increased during high-temperature combustion. As a result, it is possible to efficiently oxidize PM. That is, when ozone is always supplied to the particulate matter collection device from a certain direction, for example, from the upstream side, the upstream PM is preferentially oxidized in the PM collection unit, and the PM remains on the downstream side. Tend to. On the other hand, in the present invention, while supplying ozone from the downstream side to some of the particulate matter collection devices, the ozone is supplied to the remaining particulate matter collection devices from the upstream side, The exhaust gas flow path and the ozone supply means are controlled. And according to the said exhaust gas flow path, since ozone will be supplied from the said ozone supply means to any one apparatus of several particulate matter collection apparatuses, ozone is each particulate matter. It will be supplied to the collection device from the upstream side and the downstream side. Therefore, in the present invention, ozone PM oxidation in the PM trapping part can be performed uniformly, and the PM remaining in the PM trapping part increases pressure loss and damages the PM trapping part during high-temperature combustion. It becomes possible to suppress.

  Further, in the present invention, ozone (unreacted ozone) that has passed through some of the particulate matter collection devices is used for PM oxidation of the remaining particulate matter collection devices, so that ozone can be used effectively. it can. Furthermore, in the present invention, since ozone is supplied from the downstream side where the temperature is relatively low, consumption of ozone due to thermal decomposition is suppressed, and ozone is effectively used. Therefore, in the present invention, it is possible to oxidize PM efficiently. Moreover, in this invention, since ozone is used effectively, a required ozone amount can be reduced and it becomes possible to suppress the deterioration of the fuel consumption resulting from the energy required for ozone generation.

  According to the present invention, ozone PM oxidation can be uniformly performed in the PM trapping part, and an increase in pressure loss due to PM remaining in the PM trapping part is suppressed, and damage to the PM trapping part during high-temperature combustion is suppressed. In addition, it is possible to provide an exhaust gas purification device and an exhaust gas purification method capable of efficiently oxidizing PM.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  FIG. 1 is a schematic diagram showing a preferred embodiment of an internal combustion engine equipped with the exhaust gas purifying apparatus of the present invention. The exhaust gas purification apparatus shown in FIG. 1 is connected to an internal combustion engine 1 and has an exhaust gas passage 2 branched into a plurality of passages (first passage 2a and second passage 2b), and the exhaust gas passage (first passage). 2a, a plurality of particulate matter collecting devices 3a and 3b respectively disposed in the second passage 2b), and the exhaust gas passage (first passage) downstream from the particulate matter collecting devices 3a and 3b. 2a, ozone supply means 4a, 4b connected to the second passage 2b) and an exhaust gas flow path switching valve 5 for controlling the exhaust gas flow path. The ozone supply means 4a and 4b and the exhaust gas flow path switching valve 5 are electrically connected to an engine control unit (ECU) 6, respectively.

  The exhaust gas purifying apparatus shown in FIG. 1 supplies ozone from a downstream side to a part of the particulate matter collection devices (for example, the particulate matter collection device 3b), while the ozone is collected from the remaining particulate matter. The exhaust gas flow path switching valve 5 and the ozone supply means 4a and 4b can be controlled so as to be supplied to the collector (for example, the particulate matter collector 3a) from the upstream side.

  The internal combustion engine 1 that can be used in the present invention is not particularly limited, and examples thereof include a lean combustion type internal combustion engine such as a diesel engine and a lean combustion gasoline engine.

The particulate matter collection devices 3a and 3b according to the present invention are respectively disposed in exhaust gas passages 2 (first passage 2a and second passage 2b) branched into a plurality of passages. Examples of the particulate matter collection devices 3a and 3b include a diesel particulate filter (hereinafter referred to as “DPF”). The form of such a DPF is not particularly limited, and may be a wall flow type or a foam type. The wall flow type DPF has a honeycomb structure in which a passage with a plug on the downstream side and a passage with a plug on the upstream side are alternately formed, and the exhaust gas is downstream. From the passage plugged on the side to the passage wall surface and into the passage plugged on the upstream side to flow downstream, at which time PM in the exhaust gas is collected by the flow wall surface Is done. Further, the material of such DPF is not particularly limited, but a base material made of ceramics such as cordierite, silicon carbide, silica, alumina, mullite, or a base material made of metal such as stainless steel containing chromium, nickel and aluminum. Is preferably employed. Note that if the DPF is coated with a catalyst such as a noble metal, it tends to be decomposed before O ₃ oxidizes PM, and therefore it is preferable that the DPF is not coated with a catalyst.

  The ozone supply means 4a and 4b according to the present invention are respectively connected to the exhaust gas passages (first passage 2a and second passage 2b) on the downstream side of the particulate matter collection devices 3a and 3b. Examples of such ozone supply means 4a and 4b include those equipped with an ozone generator as an ozone generation means and an ozone supply nozzle.

As such an ozone generator, a form in which ozone is generated while air or oxygen as a raw material is allowed to flow in a discharge tube to which a high voltage can be applied, or any other type can be used. If nitrogen is present in the gas supplied to the vessel, NO _x is generated, so it is preferable to supply only oxygen.

  Moreover, as such an ozone supply nozzle, the diameter of the downstream end face of the particulate matter collection device 3a, 3b is set to the full diameter so that ozone can be uniformly supplied to the entire downstream end face of the particulate matter collection device 3a, 3b. It is preferable to have a plurality of ozone supply ports. The ozone supply means 4a, 4b may have various forms other than those having such an ozone supply nozzle. For example, when only one ozone supply port is provided, the ozone supply port And the downstream end faces of the particulate matter collection devices 3a and 3b are preferably separated by a distance that allows ozone to spread evenly over the entire downstream end face.

  As such an exhaust gas flow path switching valve 5, a commercially available flow rate adjusting valve can be used as appropriate. In the exhaust gas purifying apparatus of the present invention, a device that can control the exhaust gas passage, for example, a flow rate adjusting valve or an on-off valve can be used instead of the exhaust gas passage switching valve 5.

  Such an engine control unit (ECU) 6 supplies ozone to a part of the particulate matter collection devices from the downstream side, and supplies the ozone to the remaining particulate matter collection devices from the upstream side. And a control means for controlling the exhaust gas flow path switching valve 5 and the ozone supply means 4a, 4b.

  Here, such control means will be described in more detail with reference to the timing chart shown in FIG. The timing chart shown in FIG. 2 shows the relationship between the exhaust gas flow path and the ozone supply means in a preferred embodiment of the control means according to the present invention. In such a control means, for example, as shown in the timing chart shown in FIG. 2, the exhaust gas flow path switching valve 5 and the ozone supply means 4a and 4b are controlled every predetermined time.

  In such a control means, when the exhaust gas flow path switching valve 5 is adjusted so that the exhaust gas from the internal combustion engine 1 flows into the particulate matter collecting device 3a, the particulate matter trapping in which the exhaust gas does not flow is performed. Ozone is supplied from the ozone supply means 4b to the collector 3b. Further, the ozone (unreacted ozone) flowing through the particulate matter collecting device 3b is supplied from the upstream side to the particulate matter collecting device 3a together with the exhaust gas from the internal combustion engine 1. On the other hand, when the exhaust gas flow path switching valve 5 is adjusted so that the exhaust gas from the internal combustion engine 1 flows into the particulate matter collection device 3b, the ozone supply means 4a is added to the particulate matter collection device 3a where the exhaust gas does not flow. Supply ozone from. In addition, ozone (unreacted ozone) flowing through the particulate matter collection device 3a is supplied from the upstream side to the particulate matter collection device 3b together with the exhaust gas from the internal combustion engine 1.

  With the control means as described above, ozone can be supplied to some of the particulate matter collection devices from the downstream side, and the ozone can be supplied to the remaining particulate matter collection devices from the upstream side. In addition, since such control means supplies ozone to each particulate matter collection device from the upstream side and the downstream side, ozone PM oxidation in the PM collection unit can be performed uniformly. Further, it is possible to suppress an increase in pressure loss due to PM remaining in the PM collection unit and damage of the PM collection unit during high-temperature combustion.

  Further, in the present invention, ozone (unreacted ozone) that has passed through some of the particulate matter collection devices is used for PM oxidation of the remaining particulate matter collection devices, so that ozone can be used effectively. it can. Furthermore, in the present invention, since ozone is supplied from the downstream side where the temperature is relatively low, consumption of ozone due to thermal decomposition is suppressed, and ozone is effectively used. Therefore, in the present invention, it is possible to oxidize PM efficiently.

The preferred embodiments of the exhaust gas purification device and the exhaust gas purification method of the present invention have been described above, but the exhaust gas purification device and the exhaust gas purification method of the present invention are not limited to the above embodiment. For example, in the exhaust gas purifying apparatus of the present invention, the ozone supply means (for example, the ozone supply means 4b) is connected to the part of the particulate matter collection device (for example, the particulate matter collection device 3b) from the downstream side. Secondary air may be further supplied. In this way, the ozone (unreacted ozone) flowing through the part of the particulate matter collection device 3b can be reliably supplied by the remaining particulate matter collection device 3a. The secondary air refers to a gas introduced from the outside other than the engine exhaust gas. Examples thereof include air, factory air, N ₂ , CO ₂ , and rare gases (He, Ne, Ar, etc.).

  Further, the exhaust gas purification apparatus of the present invention may include a flow rate adjusting valve 7 instead of the exhaust gas flow path switching valve 5 as in the exhaust gas purification apparatus shown in FIG. In the exhaust gas purifying apparatus shown in FIG. 3, a part of the exhaust gas circulated from the upstream side to the downstream side of the remaining particulate matter collection device (for example, the particulate matter collection device 3a) is part of the particulate matter. The exhaust gas flow path can be controlled so as to be supplied from the downstream side to the upstream side of the substance collection device (for example, the particulate matter collection device 3b) (see FIG. 3). In this way, the ozone (unreacted ozone) flowing through the part of the particulate matter collection device 3b can be reliably supplied by the remaining particulate matter collection device 3a.

  Furthermore, the exhaust gas purification apparatus of the present invention may further include a pressure sensor 8 as in the exhaust gas purification apparatus shown in FIG. In the exhaust gas purification apparatus shown in FIG. 4, the exhaust gas flow path switching valve 5 and the ozone supply means 4a and 4b are controlled based on the value of the pressure loss detected by the pressure sensor 8 so that the exhaust gas from the internal combustion engine 1 is The time for flowing into the particulate matter collection devices 3a and 3b can be adjusted. In this way, an increase in pressure loss due to PM remaining in the PM collection unit can be more reliably suppressed.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Example)
A test for purifying exhaust gas from the internal combustion engine 1 was performed using the exhaust gas purification apparatus shown in FIG. That is, as the internal combustion engine 1, a diesel engine (displacement 2L, direct injection, common rail, with turbo) was used. Further, as the particulate matter collection devices 3a and 3b, DPF (diameter 100 mm, length 150 mm, cell number 300 cpsi, manufactured by cordierite) was used. Further, as the ozone supply means 4a and 4b, those provided with an ozone generator (Esuhara Jitsugyo Co., Ltd.) (ozone supply amount: 2 mol / h) were used. As the exhaust gas flow path switching valve 5, an exhaust gas flow path switching valve (manufactured by Sakai Valve Co., Ltd.) was used. The gas flow rate of the exhaust gas discharged from the internal combustion engine 1 is 20 g / sec, and the exhaust gas composition is NO (100 ppm), NO ₂ (50 ppm), THC (100 ppm), CO (0 ppm), O ₂ ( 10%), CO (6.7%), H ₂ O (5%), N ₂ (balance). Moreover, the temperature of the exhaust gas at the inlets of the particulate matter collection devices 3a and 3b was 200 ° C.

  Then, using the exhaust gas purification apparatus shown in FIG. 1, the exhaust gas flow switching valve 5 and the ozone supply means 4a and 4b are controlled according to the timing chart shown in FIG. The test was conducted for 1 hour to purify the exhaust gas.

(Comparative example)
The ozone supply means 4a and 4b are connected upstream of the particulate matter collection devices 3a and 3b, and the exhaust gas flow path switching valve 5 and the ozone supply means 4a and 4b are controlled according to the timing chart shown in FIG. Similarly, a test for purifying exhaust gas from the internal combustion engine 1 was performed.

<Evaluation of PM oxidation performance>
The PM oxidation performance of the exhaust gas purifying apparatuses obtained in the examples and comparative examples was evaluated by the following method. That is, first, using a micro dilution tunnel (manufactured by F-Techno Co., MIT-2000), engine exhaust diluted with factory air is introduced into the filter for a predetermined time, PM is collected, and exhausted from the diesel engine due to change in filter weight. The amount of PM to be measured was measured. Next, a diesel engine with a DPF attached thereto was prepared, and the amount of PM passing through the DPF was measured by the same method as described above. Then, the PM amount accumulated in the DPF per hour was calculated from the value of the PM amount discharged from the diesel engine and the value of the PM amount passing through the DPF.

  Next, the weights of the DPFs obtained in Examples and Comparative Examples were measured, and the PM amount remaining in the DPF after 1 hour operation was calculated. Then, the amount of PM oxidized per hour in the exhaust gas purification apparatuses obtained in the examples and the comparative examples was calculated by subtracting the value of the PM amount remaining in the DPF from the value of the PM amount accumulated in the DPF. Moreover, the average PM oxidation rate (g / h) per hour was calculated from the value of the amount of PM oxidation. The obtained result is shown in FIG.

  As is clear from the results shown in FIG. 6, when the exhaust gas purification apparatus of the present invention was used (Example), the PM oxidation rate was high. Therefore, according to the present invention, it was confirmed that PM can be oxidized efficiently. Further, when the exhaust gas purifying apparatus of the present invention is used (Example), since the PM remaining in the DPF is small, according to the present invention, ozone PM oxidation in the PM trapping section can be performed uniformly. It was confirmed that increase in pressure loss due to PM remaining in the PM collection part and damage to the PM collection part during high-temperature combustion can be suppressed.

  As described above, according to the present invention, the ozone PM oxidation in the PM trapping part can be performed uniformly, the pressure loss due to the PM remaining in the PM trapping part, and the PM trapping during high-temperature combustion are increased. It is possible to provide an exhaust gas purification device and an exhaust gas purification method capable of suppressing damage to the collecting portion and efficiently oxidizing PM.

1 is a schematic diagram showing a preferred embodiment of an internal combustion engine equipped with an exhaust gas purification apparatus of the present invention. It is a timing chart which shows the relationship between the exhaust gas flow path and ozone supply means in suitable one Embodiment of the control means concerning this invention. It is a schematic diagram showing other suitable embodiments of an internal-combustion engine provided with an exhaust gas purification device of the present invention. It is a schematic diagram showing other suitable embodiments of an internal-combustion engine provided with an exhaust gas purification device of the present invention. It is a timing chart which shows the relationship between the exhaust gas flow path and ozone supply means in the exhaust gas purification apparatus obtained by the comparative example. It is a graph which shows PM oxidation rate in the exhaust gas purification apparatus obtained by the Example and the comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Exhaust gas passage, 2a ... First passage, 2b ... Second passage, 3a ... Particulate matter collection device, 3b ... Particulate matter collection device, 4a ... Ozone supply means, 4b ... Ozone supply means, 5 ... exhaust gas flow path switching valve, 6 ... engine control unit (ECU), 7 ... flow rate adjusting valve, 8 ... pressure sensor, A1 ... flow of exhaust gas from the internal combustion engine, A2 ... particulate matter collecting device Part of the exhaust gas flow that circulated.

Claims (4)

An exhaust gas passage connected to the internal combustion engine and branched into a plurality of passages;
A plurality of particulate matter collecting devices that are respectively disposed in the exhaust gas passages and collect particulate matter in the exhaust gas;
Ozone supply means connected to the exhaust gas passage on the downstream side of the particulate matter collection device and supplying ozone to the particulate matter collection device;
While supplying ozone from the downstream side to some of the particulate matter collectors, the ozone is supplied from the upstream side to the remaining particulate matter collectors, and
While the exhaust gas from the internal combustion engine is allowed to flow from the upstream side into the exhaust gas passage in which the remaining particulate matter collection device is disposed, the exhaust gas from the internal combustion engine is part of the particulate matter collection device. Control means for controlling the exhaust gas flow path and the ozone supply means so as not to flow into the exhaust gas passage arranged from the upstream side ;
An exhaust gas purification apparatus comprising:   The exhaust gas purifying apparatus according to claim 1, wherein the ozone supply means further supplies secondary air to the part of the particulate matter collecting apparatus from the downstream side.   The exhaust gas flow path is arranged such that a part of the exhaust gas flowing from the upstream side to the downstream side of the remaining particulate matter collection device is supplied from the downstream side to the upstream side of the partial particulate matter collection device. The exhaust gas purification apparatus according to claim 1 or 2, further comprising an exhaust gas flow path control means for controlling. An exhaust gas passage connected to the internal combustion engine and branched into a plurality of passages;
A plurality of particulate matter collecting devices that are respectively disposed in the exhaust gas passages and collect particulate matter in the exhaust gas;
Ozone supply means connected to the exhaust gas passage for supplying ozone to the particulate matter collection device;
An exhaust gas purification method using an exhaust gas purification device comprising:
While supplying ozone from the downstream side to some of the particulate matter collectors, the ozone is supplied from the upstream side to the remaining particulate matter collectors, and
While the exhaust gas from the internal combustion engine is allowed to flow from the upstream side into the exhaust gas passage in which the remaining particulate matter collection device is disposed, the exhaust gas from the internal combustion engine is part of the particulate matter collection device. An exhaust gas purification method comprising controlling an exhaust gas passage and the ozone supply means so as not to flow into the exhaust gas passage arranged from the upstream side .

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