JP2005061246A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for appropriately eliminating PM (particulate matters) exhausted from an internal combustion engine such as a diesel engine. <P>SOLUTION: This exhaust emission control device has a plasma assist PM purifying reactor 10; PM accumulated amount detecting means 1, 2, 3 for detecting the accumulated amount of PM in the PM purifying reactor 10; a power supply means 7 for supplying electric power to the PM purifying reactor 10; and a power supply control means 5 for controlling the power supply means 7 based on signals from the PM accumulated amount detecting means 1, 2, 3. In the exhaust emission control device, when the PM accumulated amount detected by the PM accumulated amount detecting means 1, 2, 3 exceeds a prescribed amount, the power supply control means 5 controls the power supply means 7 to start the supply of electric power to the PM purifying reactor 10 or to increase the electric power supplied to the PM purifying reactor 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a purification device for exhaust gas from an internal combustion engine or the like, and more particularly to an exhaust gas purification device for removing particulate matter (particulate: hereinafter referred to as “PM”) discharged from a diesel engine.
[0002]
[Prior art]
Diesel engines are often installed in automobiles, particularly large vehicles, and it has been strongly desired to reduce PM emissions together with nitrogen oxides, carbon monoxide, hydrocarbons, and the like in the exhaust thereof. Therefore, not only technical development for fundamentally reducing PM by improving the engine or optimizing combustion conditions, but also establishment of technology for efficiently removing PM in exhaust gas is desired.
[0003]
However, in the method of collecting PM in exhaust gas simply with a diesel particulate filter (hereinafter referred to as “DPF”), as the usage time elapses, the filter is clogged by the collected PM and the ventilation resistance increases. This results in a burden on the engine.
[0004]
Therefore, conventionally, the DPF is heated by a heater or the like to forcibly burn the deposited PM.
[0005]
In recent years, as a more efficient method, it has been proposed to use plasma energy by discharge for the combustion removal of PM collected by the DPF. For example, Patent Literature 1 proposes that NO ₂ and active oxygen are generated by plasma in combination with a DPF and a plasma generator to promote oxidation of collected PM. Here, it is proposed that plasma is generated when the temperature of the DPF is low to promote the oxidation of PM.
[0006]
The Patent Document 2, HC is a harmful substance in the exhaust, CO, and combining the catalyst system and the plasma generating device with respect to the purification of NO _x, plasma minimum necessary power based engine speed, a catalyst temperature etc. It has been proposed to supply the generator.
[0007]
[Patent Document 1]
JP 2002-276333 A [Patent Document 2]
Japanese Patent Laid-Open No. 2002-129949
[Problems to be solved by the invention]
In these conventional techniques using plasma, the collected PM can be efficiently oxidized and removed even when the temperature of the DPF is low, such as when the engine is started. However, in addition to the case where the temperature of the DPF is low, a large amount of PM may accumulate on the DPF due to fluctuations in the combustion state in the engine.
[0009]
Once a large amount of PM is deposited as in this case, the formation of plasma becomes unstable, and the oxidation ability of PM is lowered, which causes a chain vicious cycle that leads to the deposition of the next PM.
[0010]
Further, if the accumulated large amount of PM is burned and removed at a time, a large amount of heat is generated. This large amount of heat shortens the life of the DPF and possibly damages the DPF.
[0011]
This problem is partially solved by performing control based not only on the DPF temperature but also on conditions such as the engine speed, as in Patent Document 2. However, fluctuations in the combustion state in the engine are not always predictable. Therefore, even if control based on conditions such as engine speed is added, it may still be insufficient for proper removal of accumulated PM.
[0012]
[Means for Solving the Problems]
The exhaust purification apparatus of the present invention supplies power to a plasma assisted PM purification reactor (or simply referred to as “PM purification reactor”), a PM deposition amount detection means for detecting the PM deposition amount in the PM purification reactor, and the PM purification reactor. An exhaust emission control device having a power supply control means for controlling the power supply means based on signals from the power supply means and the PM accumulation amount detection means. Here, in this exhaust purification apparatus, when the PM accumulation amount detected by the PM accumulation amount detection means exceeds a predetermined amount, the power supply control means controls the power supply means and starts supplying power to the PM purification reactor. Or the power supplied to the PM purification reactor is increased.
[0013]
According to a feature of the present invention, unexpectedly by controlling the power supply based on the “PM deposition amount” in the PM purification reactor rather than the “PM generation amount” associated with parameters such as engine speed. It is possible to prevent the disadvantages of unstable plasma generation and rapid combustion caused by a large amount of accumulated PM. Naturally, it is possible to remove PM with less electrical energy compared to the case where constant power is always supplied.
[0014]
In one aspect of the present invention, the PM accumulation amount detection means includes a differential pressure gauge that measures the differential pressure before and after the PM purification reactor.
[0015]
According to this aspect, the pressure loss in the PM purification reactor can be obtained from the differential pressure before and after the plasma-assisted PM purification reactor, and the PM deposition amount can be detected relatively accurately based on this. This is because the pressure loss in the PM purification reactor is an increasing function of the PM deposition amount.
[0016]
Further, when PM is burned and removed by heating the DPF with a heater or the like, PM is burned and removed mainly on the contact surface with the catalyst. Therefore, as shown in FIG. 4A, when PM11 is excessively deposited on the catalyst 13 on the base material 15, only PM near the contact surface with the catalyst 13 burns, and at a position away from the contact surface, SOF (soluble It is possible that only the organic component) burns and PM11 exists in a form floating from the catalyst 13 as shown in FIG. In the case of FIG. 4B, the relationship between the pressure loss and the PM accumulation amount is different from that in FIG. 4A, and it is difficult to determine the PM accumulation amount from the pressure loss of the PM purification reactor. There is also a possibility.
[0017]
On the other hand, when PM is burned and removed by the plasma-assisted PM purification reactor, PM is burned and removed by electrons emitted from the negative cell wall in the cell such as DPF and active NO ₂ generated by the plasma. And / or by active oxygen from the surface layer portion of the deposited PM. Also, the energization of the PM by applying a voltage promotes the energization combustion of the PM other than the catalyst / PM contact surface.
[0018]
Therefore, when PM is burned and removed by the plasma-assisted PM purification reactor, it is easier to detect the amount of accumulated PM based on the pressure loss than when the DPF is forcibly burned by heating the DPF with a heater or the like.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings are diagrams showing an outline of an exhaust emission control device constituting the present invention, and the present invention is limited to these embodiments. Is not to be done.
[0020]
FIG. 1 is a schematic configuration diagram showing the overall configuration of the exhaust emission control device of the present invention. In the exhaust gas purification apparatus shown in FIG. 1, exhaust gas from the engine (ENG) is supplied from a plasma-assisted PM purification reactor 10 and an optional other exhaust gas purification apparatus (not shown) such as NO downstream of the plasma-assisted PM purification reactor 10. It passes through the _x storage reduction catalyst in the direction indicated by arrow 9 and is released into the atmosphere.
[0021]
In this exhaust purification device, a PM purification reactor 10 is arranged downstream of the engine exhaust. The PM accumulation amount detection means including the differential pressure gauge 1 before and after the PM purification reactor 10, the signal line 2 and the calculation means 3 is connected to the power supply control means 5 by the signal line 4. Naturally, the calculating means 3 may be an ECU. The power supply control means 5 is connected to the power supply means 7 by the control line 6, and the power supply means 7 is connected to the PM purification reactor 10 by the power line 8.
[0022]
The power supply control means 5 controls the power supply means 7 based on the PM accumulation amount detected by the PM accumulation amount detection means 1, 2, 3 of the PM purification reactor 10. Here, when the PM accumulation amount detected by the PM accumulation amount detection means 1, 2, and 3 exceeds a predetermined amount, the power supply control means 5 controls the power supply means 7 through the control line 6, and the power supply means 7 The supply of power to the PM purification reactor 10 is started, or the power supplied from the power supply means 7 to the PM purification reactor 10 is increased.
[0023]
Here, the PM deposit amount detecting means including the differential pressure gauge 1, the signal line 2 and the calculating means 3 is used as the detection means for detecting the PM deposit amount of the plasma assisted PM purification reactor 10, but any other The amount of PM deposited in the PM purification reactor 10 can be measured by means. Thus, for example, PM deposition due to changes in electrical resistance, weight, blackening degree, or NO ₂ or O ₂ concentration (which is used for PM combustion, the concentration decreases as the PM deposition amount increases) in the PM purification reactor. The amount can also be detected.
[0024]
One mode of using the exhaust emission control device of the present invention shown in FIG. 1 will be described with reference to FIG. As shown in FIG. 2, the engine ENG is started, electric power is supplied to the PM purification reactor 10, and gas discharged from the engine is circulated to the plasma assist PM purification reactor 10 to collect PM. Thereafter, when the PM accumulation amount detection means 1, 2, and 3 detect that a predetermined amount of PM has accumulated in the PM purification reactor, the PM purification reactor is maintained for a predetermined period or until the detected PM accumulation amount becomes less than the predetermined amount. The power supply control means 5 controls the power supply means 7 so that the power supplied to 10 is increased. Further, when the PM accumulation amount detection means 1, 2, and 3 detect that a predetermined amount of PM is not accumulated in the PM purification reactor 10, the electric power supplied to the PM purification reactor 10 is not increased and the electric power as it is. After that, the PM accumulation amount is detected again by the PM accumulation amount detection means 1, 2, and 3.
[0025]
Here, the power supply is started at the start of the engine ENG. However, the power supply means 7 supplies power only when PM exceeding a predetermined amount is deposited without always supplying power. You may control by the power supply control means 5. FIG. Further, the control of power supply based on the engine operating state as shown in Patent Document 2, that is, the control of power supply based on the amount of PM that will be generated, is used in combination with the control based on the PM deposition amount according to the present invention. You can also According to this, while performing control based on the operating state of the engine at all times, the control according to the present invention is performed only when PM accumulation exceeding a predetermined amount is detected by the PM accumulation amount detection means. Can do.
[0026]
The plasma-assisted PM purification reactor used in the present invention generates plasma by applying a voltage, and this plasma promotes combustion removal of PM. For example, it may be as shown in Patent Documents 1 and 2.
[0027]
The plasma-assisted PM purification reactor used in the present invention may be as shown in FIG. In this plasma assisted PM purification reactor, a honeycomb structure 25 such as DPF is sandwiched between flat electrodes 20a to 20e such as mesh electrodes. Here, the exhaust gas containing PM flows through the flow path in the honeycomb structure 25 in the direction indicated by the arrow 9.
[0028]
Of the planar electrodes 20a to 20e, the planar electrodes 20b and 20d are connected to the power supply means 7, and the remaining planar electrodes 20a, 20c and 20e are grounded. These planar electrodes 20a to 20e are electrically insulated from adjacent planar electrodes by disposing the honeycomb structure 25 therebetween.
[0029]
In order to collect PM in a plasma assisted PM purification reactor, it is common to use DPF. However, if it is possible to collect PM, other components such as a straight flow type honeycomb structure may be used. The structure can also be used.
[0030]
In the use of the PM purification reactor shown in FIG. 1, electric power is supplied by the power supply means 7 between the planar electrodes 20a, 20c and 20e and the adjacent planar electrodes 20b and 20d, respectively. According to the use of the plasma assisted PM purification reactor having such a plurality of honeycomb structures and electrodes sandwiching them, not only the combustion removal of PM is promoted by the plasma but also the current combustion of the PM is promoted. You can also.
[0031]
The plasma-assisted PM purification reactor used in the present invention not only promotes PM combustion removal by plasma and energization, but also holds a NO _x purification catalyst such as a NO _x storage reduction catalyst for NO _x purification. Other functions can also be included.
[0032]
The applied voltage provided here is generally 5 kV or more, preferably 10 kV or more. The pulse period of the applied voltage is preferably 10 ms or less and 1 ms or less. A DC voltage, an AC voltage, a periodic waveform voltage, or the like can be applied between the electrodes of the PM purification reactor. In particular, a DC pulse voltage is preferable because corona discharge can be caused satisfactorily. When a DC pulse voltage is used, the applied voltage, pulse width, and pulse period can be arbitrarily selected as long as corona discharge can occur between both electrodes. The voltage of the applied voltage may be subject to certain restrictions due to device design, economy, etc., but a high voltage and a short pulse period voltage are desirable from the viewpoint of generating corona discharge satisfactorily. .
[0033]
【The invention's effect】
According to the present invention, PM in exhaust from an internal combustion engine such as a diesel engine can be appropriately removed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating one embodiment of the present invention.
FIG. 2 is a flowchart showing control of power supply in the exhaust emission control device of the present invention.
FIG. 3 is a front view showing one embodiment of a plasma-assisted PM purification reactor that can be used in an embodiment.
FIG. 4 is a conceptual diagram showing the shape of PM when accumulated PM is burned and removed by DPF heating.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Differential pressure gauge 2 ... Signal line 3 ... PM deposition amount detection means 4 ... Signal line 5 ... Power supply control means 6 ... Control line 7 ... Power supply means 8 ... Power line 9 ... Exhaust flow direction 10 ... Plasma assist PM purification reactor 11 ... Deposition PM
13 ... Catalyst layer 15 ... Base materials 20a to 20e ... Planar electrode 25 ... Honeycomb structure

Claims (2)

Plasma assisted PM purification reactor,
PM accumulation amount detection means for detecting the PM accumulation amount in the PM purification reactor,
Power supply means for supplying power to the PM purification reactor, and power supply control means for controlling the power supply means based on a signal from the PM accumulation amount detection means,
When the PM accumulation amount detected by the PM accumulation amount detection means exceeds a predetermined amount, the power supply control means controls the power supply means to supply the PM purification reactor to the PM purification reactor. An exhaust gas purification apparatus characterized by starting the supply of electric power or increasing the electric power supplied to the PM purification reactor. The exhaust gas purification apparatus according to claim 1, wherein the PM accumulation amount detection means includes a differential pressure gauge that measures a differential pressure before and after the PM purification reactor.

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