JP2009243419A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent exhaust gas particulates from being discharged to the outside by processing the exhaust gas particulates included in exhaust gas of an internal combustion engine by utilizing corona discharge. <P>SOLUTION: The exhaust gas control device 1 is arranged with a corona discharge electrode 2 and a confronting electrode 3 in a cylindrical housing H connected with an exhaust gas flow passage 42 of the engine 41 and is provided with a corona discharge part for generating corona discharge by applying high voltage between both the electrodes 2, 3. The exhaust gas particulate is controlled by oxidation combustion by applying energy so large that the generation energy by the corona discharge excesses activation energy for oxidizing the exhaust particulate in the exhaust gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust particulate purification device that purifies exhaust particulates contained in exhaust gas of an internal combustion engine using corona discharge.

  Various devices have been proposed for treating exhaust particulate (PM) emitted from diesel engines and lean burn gasoline engines. As an example, a particulate filter made of porous ceramics is installed in the exhaust channel to collect exhaust particulates. However, small particulates (nanoparticulates) with a particle size of nanomicron are captured. There is a risk of passing without being. On the other hand, if the particulate filter is narrowed to prevent the fine particles from slipping through, there is a problem that the pressure loss of the exhaust passage increases.

Therefore, an apparatus that electrostatically aggregates fine particles using corona discharge has been studied. For example, in Patent Document 1, a high-voltage electrode is disposed at the center of an exhaust passage, and a low-voltage electrode is disposed on the outer periphery of the exhaust passage. An apparatus is disclosed in which fine particles are collected by diverting to a peripheral portion having a high spatial density distribution and a central portion having a low spatial density distribution, and disposing a filter suitable for each in the downstream.
JP 2005-76497 A

Further, Patent Document 2 discloses an apparatus in which a discharge electrode and a conductive mesh-shaped dust collecting electrode are disposed opposite to each other in an exhaust passage. This device is configured such that the electric charge discharged to the dust collection electrode is collected to the grounding part via the coil, and the charged state of the exhaust particulates is easily maintained. Coulomb force acts between them to promote the aggregation of charged fine particles.
JP 2006-37899 A

  However, electrostatically agglomerated fine particles have a problem of redispersion because the bonding force is weak. In the apparatus of Patent Document 1, a low voltage electrode arranged on the outer periphery of the high voltage electrode is provided with a transmission part, and electrostatically aggregated fine particles are collected by a filter outside the transmission part. Since there is an exhaust flow, the aggregated particles may collide in the filter and re-disperse or leave.

  Even in the configuration of Patent Document 2, a particulate filter (DPF) or the like is installed downstream to collect the fine particles aggregated by the dust collection electrode. As a result, the agglomerated fine particles are re-dispersed and pass through the cell walls. In that case, the separated fine particles may not be collected and discharged to the outside.

  Accordingly, an object of the present invention is to provide an exhaust particulate purification device capable of treating exhaust particulate contained in exhaust gas of an internal combustion engine using corona discharge and preventing the exhaust particulate from being discharged to the outside. There is.

  In the exhaust emission control device according to the first aspect of the present invention, a corona discharge electrode and a counter electrode are disposed in a cylindrical container constituting a part of an exhaust passage of an internal combustion engine, and a high voltage is applied between both electrodes. A corona discharge unit for generating corona discharge. The corona discharge part is characterized in that the energy generated by the corona discharge is greater than the activation energy for oxidizing the exhaust particulates in the exhaust, and the exhaust particulates are purified by oxidative combustion.

  When the energy generated by the corona discharge exceeds the activation energy necessary for the oxidation reaction of the exhaust particulates, the carbon constituting the exhaust particulates combines with the oxygen in the exhaust to become carbon dioxide. In other words, by applying sufficient energy, nanoparticles can be burned and purified, and high purification performance is achieved by suppressing the release of nanoparticles by passing through and the redispersion / detachment of aggregated particles. It becomes possible to do.

  In the invention of claim 2, the corona discharge part causes electrons to be emitted from the discharge part of the corona discharge electrode disposed at a substantially central part of the cylindrical container into the exhaust passage, and the emitted electrons are oxygenated. It adheres and becomes oxygen ions and collides with exhaust particulates to give oxidation energy.

  Specifically, it is preferable that the corona discharge electrode is disposed at a substantially central portion of the exhaust flow path so that electrons are efficiently emitted toward the exhaust fine particles to be introduced.

  According to a third aspect of the present invention, there is provided a control unit that controls energy input to the corona discharge unit, and the control unit applies to the corona discharge electrode according to the amount of exhaust particulates generated in the internal combustion engine. Determine the voltage.

  Specifically, it is preferable that the control unit calculates the energy required to oxidize the generated exhaust particulates and efficiently inputs the necessary energy.

  According to a fourth aspect of the present invention, an exhaust particulate collection unit is provided in the corona discharge part or downstream of the corona discharge part, and a part of the exhaust particulates are charged and charged by a part of energy input to the corona discharge part. Aggregate and collect in the collecting part.

  In addition to purification by exhaust gas oxidation, collection by charging / aggregation can be used in combination. At this time, preferably, the collection part is provided to collect the aggregated fine particles, thereby preventing discharge to the outside.

  In the invention of claim 5, the corona discharge part has a hollow mesh conductive cylindrical wall part arranged along the inner peripheral surface of the cylindrical container as the counter electrode, and the internal space is the collecting part. And

  Specifically, the collecting part can be a hollow mesh conductive cylindrical wall part, which also serves as a counter electrode.

  A first embodiment in which the present invention is applied to an exhaust emission control device for a diesel engine will be described below with reference to the drawings. FIG. 1A shows the overall configuration of the exhaust purification device 1, and FIG. 1B shows the connection structure of the exhaust purification device 1 to the exhaust pipe 41. In the figure, an exhaust purification device 1 includes a corona discharge electrode 2 and a ground electrode 3 that is a counter electrode disposed in a housing H as a cylindrical container connected to an exhaust pipe 42 of an engine 41 to provide a corona discharge portion. It is composed. In the present embodiment, the cylindrical portion of the housing H surrounding the corona discharge electrode 2 is configured as a ground potential, and the cylindrical inner wall is configured as the ground electrode 3. The housing H is a cylindrical tube having a diameter larger than that of the exhaust pipe 42, and the inside thereof becomes the exhaust passage 11 having a circular cross section, and is connected to the straight portion of the exhaust pipe at both end small diameter portions.

  In FIG. 1A, the corona discharge electrode 2 has an upper half protruding from the cylindrical wall of the housing H to the outside (upward in the drawing), and a lower half positioned in the exhaust flow path 11 in the housing H. The holding plate 12 is bolted to the housing H so as to close the opening provided in the upper cylindrical wall, and the corona discharge electrode 2 is provided with a male screw portion provided on the outer periphery of the lever portion 23 on the holding plate 12. It is screwed into the female thread portion and is fastened and fixed with a nut 13.

  The corona discharge electrode 2 includes a rod-shaped conductive portion 21 whose outer periphery is held by the insulator portion 23, and a discharge portion 22 provided at the tip (lower end side in the figure). The conductive portion 21 is located outside the housing H and has a base end (upper end side in the figure) protruding from the insulator portion 23 connected to a DC high-voltage power source (not shown), and a distal end side exposed from the insulator portion 23 in an L shape. It is bent. The L-shaped bent portion extends along the axis of the exhaust passage 11 and guides a high voltage to the most advanced discharge portion 22. The discharge part 22 has, for example, a substantially disk shape and a shape having a large number of protrusions provided radially on the outer periphery. In this way, by providing a large number of protrusions, the discharge rate can be increased, and the corona discharge can be evenly generated in the exhaust passage 11 to improve the purification performance.

  Next, the mechanism of exhaust particulate purification by the exhaust purification apparatus 1 of the present invention will be described. In FIG. 1 (b), the exhaust particulates generated by the engine 41 and discharged to the exhaust pipe 42 usually have a particle size of about 0.01 μm to several μm and cannot be captured by a normal particulate filter (DPF). Contains fine particles. The exhaust purification device 1 is provided with a control unit 5 that controls energization to the corona discharge electrode 2. When a negative DC high voltage is applied from the DC high voltage power source to the conductive unit 21 of the corona discharge electrode 2, discharge is performed. Corona discharge occurs near the protrusion at the tip of the portion 22. At this time, as shown as 1) to 3) in the figure, the electrons emitted by the corona discharge have high energy, adhere to oxygen and become oxygen ions, and exhaust particulates in the exhaust passage 11. It collides with (nano PM in the figure) and reacts.

When shown in this FIG. 1 (c), the reactants are as exhaust particles (C) and oxygen molecules (O _2), generating energy by corona discharge is applied, the activation state. That is, in order to exceed the activation energy required to cause the oxidation reaction, the exhaust particulates (C) and oxygen ions (O ₂ ⁻ ) can react to generate carbon dioxide (CO ₂ ). In the present invention, since the nanoparticle is directly changed to carbon dioxide (CO ₂ ) which is a gas molecule, the nanoparticle can be purified by effectively using the energy generated by corona discharge.

  The controller 5 controls energy input to the corona discharge electrode 2. The energy input to the corona discharge unit is determined according to the amount of exhaust particulate generated in the engine 41, and the energy necessary for oxidizing and combusting the exhaust particulate introduced into the exhaust purification device 1 is determined by corona discharge. generate. FIG. 2 is a graph showing the relationship between the amount of generated exhaust particulates (generated PM amount: g / hr) and the energy required for PM combustion (E: kJ / hr). For example, the graph is discharged to the exhaust pipe 42. Assuming that the amount of PM to be generated is M0, it is understood that the energy generated by corona discharge should be greater than the required energy E0 for activating and oxidizing the carbon corresponding to M0.

Here, the energy E required for PM combustion is calculated using the following equation (1).
E = (M / m) · Ea (1)
・ Necessary energy for collected PM combustion: E (kJ / hr)
-Collected PM weight: M (g / hr)
Carbon molecular weight: m (= 12)
Activation energy: Ea (= 236 kJ / mol)
On the other hand, the generated energy Ec in the corona discharge is calculated using the following formula (2).
Ec = Ev · Ia · t (2)
・ Supply voltage: Ev (kV)
-Current: Ia (A)
・ Time: t (s)

From equation (1), for example, if M0 = 1.2 (g / hr), the energy required for PM combustion is E = 24 (kJ / hr), so that the generated energy of E0 ≧ 24 (kJ / hr) is If so, exhaust particulates can be purified by oxidation combustion. In order to establish E0 = Ec ≧ 24 (kJ / hr) from the equation (2), for example, the supply voltage and current may be set as in the following equation (3).
Ec = Ev · Ia · t
= 13 × 0.5 × 10 ⁻³ × 60 ² = 24 (kJ / hr) (3)
That is, when the current Ia = 0.5 (mA), if the negative DC high voltage applied to the conductive portion 21 from the DC high voltage power supply is Ev = −13 (kV) or more, the activation energy or more is reached. .

  At this time, the corona discharge electrode 2 is arranged at the substantially central portion of the corona discharge portion where the concentration of exhaust particulates is high for efficient purification. However, in actuality, it is generated due to the exhaust particulate distribution in the corona discharge portion. Energy loss occurs. For this reason, it is preferable to input, for example, 1.5 times or more energy (E1 = 1.5 × E0) in consideration of the loss of generated energy. Therefore, from equations (1) and (2), for example, if M0 = 1.2 (g / hr) and current Ia = 0.5 (mA), if there is generated energy of E1 ≥36 (kJ / hr) If the applied voltage Ev for this is equal to or higher than −20 (kV), sufficient purification performance can be obtained.

  In this way, in the present invention, the input energy by the control unit 5 is changed according to the amount of exhaust particulates to be generated and the energy required for combustion is generated, so that the exhaust particulates can be purified more effectively. . An example of the specific control is shown in the flowchart of FIG. 3. First, in step 1, the load and rotation speed information of the engine 41 is fetched, and in step 2, the exhaust particulates generated in the engine 41 using these information. The amount (PM amount M: g / hr) is calculated. The PM amount M can be stored in the control unit 5 as a map, for example, by conducting an experiment in advance to obtain the relationship between the load and the rotational speed and the amount of exhaust particulate generation.

  In step 3, it is determined whether the PM amount M calculated in step 2 is 0 or more (PM amount M> 0). If a positive determination is made in step 2, the process proceeds to step 4. If a negative determination is made, the process returns to step 1. This is because, for example, when the combustion efficiency of the engine 41 is high and almost no exhaust particulates are generated, such as during a high load, or in an operating state in which the exhaust temperature is high and the generated exhaust particulates spontaneously combust, Since it is judged that it is not necessary to operate 1, energy loss can be avoided by not energizing the corona discharge part.

  In step 4, the necessary energy E1 for oxidizing the PM amount M (g / hr) calculated in step 2 is calculated by using the relations of the above equations (1), (2) and FIG. The supply voltage Ev to 2 is determined. In the subsequent step 5, a predetermined voltage Ev is applied from the DC high voltage power source to the corona discharge electrode 2, and the process returns to step 1. In this way, it is possible to purify the exhaust particulates by applying the supply voltage Ev according to the operating state of the engine and generating corona discharge.

FIG. 4 shows the results of an evaluation test conducted to confirm the effect of the exhaust emission control device 1 of the present invention. FIG. 4A is a diagram showing the configuration of the evaluation apparatus, in which exhaust particulates discharged from the PM generator 6 and air from the air cylinder 7 are introduced into the exhaust purification apparatus 1 to generate a corona discharge, and downstream thereof. A change in CO ₂ concentration was examined with the installed CO ₂ meter 8. The CO ₂ meter 8 measures low-concentration CO _{2 in the} order of ppm, and since it is necessary to set the evaluation condition to room temperature, equivalent exhaust particulates were generated using the PM generator 6 instead of the actual vehicle engine. . Exhaust particulate generation amount Qp = 3.9 g / min. , Air flow rate = 7.6 L / min. FIG. 4B shows the change in CO ₂ concentration in the exhaust discharged from the exhaust purification device 1 when the required energy calculated by the method shown in FIGS. It was.

As shown in FIG. 4 (b), the CO ₂ concentration in the exhaust gas has increased rapidly since the start of the operation of the exhaust gas purification device 1, and a corona discharge is generated by applying a voltage to the corona discharge electrode 2. It was confirmed that an oxidation reaction of exhaust particulates occurred and CO ₂ was generated. The exhaust gas purification device 1 was in a state where the CO ₂ concentration was high while continuing the operation, and gradually decreased from the time when the operation was stopped, and returned to the initial concentration.

  FIG. 5 shows a second embodiment of the present invention. The exhaust purification apparatus 1 of the present embodiment uses both purification by exhaust gas oxidation reaction using corona discharge energy and aggregation of exhaust fine particles by charging. The ground electrode 3 of the exhaust emission control device 1 also serves as a dust collection electrode and has a function of holding aggregated fine particles. Other apparatus configurations are the same as those in the first embodiment, and a description thereof will be omitted.

  In the control based on FIG. 3 described above, the energy required for oxidation increases as more exhaust particulates are generated. For this reason, for example, in a state where the battery voltage is low, sufficient energy corresponding to the amount of exhaust particulates cannot be input, and activation energy may be insufficient. Therefore, in the present embodiment, the energy that can be input is determined according to the amount of exhaust particulates and the battery voltage, and all of the generated exhaust particulates are not subjected to an oxidation reaction, but a part of them are charged and aggregated and collected. In this case, when corona discharge occurs and electrons are emitted, some of them negatively ionize gas molecules (oxygen) with high electron affinity and adhere to the nearby exhaust particles (nano PM in the figure). Is negatively charged (1) to 2)). The charged exhaust particulates (nano PM) are attracted to the ground electrode 3 also serving as a dust collecting electrode by the Coulomb force, gradually depart from the gas flow toward the downstream, and move to the outer peripheral side while aggregating. When the agglomerated exhaust particulates reach the ground electrode 3, they are discharged and agglomerated and held (in the figure, 3) to 5)).

As shown in FIG. 6, the exhaust particulate purification method is determined by the amount of exhaust particulate generated (PM weight) and the input energy. If the purification by exhaust gas oxidation reaction is the CO ₂ region, and the aggregation by exhaust gas charging is the charge collection region, the region where the PM weight is low and the input energy is high is the CO ₂ region, the PM weight is high and the input energy is low. The region becomes a charge collection region. These intermediate regions are CO ₂ region + charge collection region. In this manner, exhaust particulates can be purified by efficiently using energy by combining electrification collection with purification by oxidation reaction according to the energy that can be input.

  FIG. 7 shows the result of verifying the agglomeration phenomenon of exhaust particulates due to voltage application to the corona discharge electrode 2 in the exhaust purification device 1 of the present embodiment. FIG. 7A shows the particle size distribution of fine particles adhering to the vicinity of the ground electrode 3 that also serves as the dust collection electrode of the exhaust purification apparatus 1 in the state where the applied voltage is 0 V, ie, no corona discharge is generated. These show the particle size distribution of the fine particles adhering to the vicinity of the ground electrode 3 when the applied voltage is −10 V, respectively. FIG. 7A shows that the peak of the particle size distribution is 1 μm or less, and the standard particles that are discharged from the engine are mainly aggregates of ultrafine particles of 1 μm or less. On the other hand, in FIG. 7B, the peak of 1 μm or less disappeared, the weight of coarse particles of 5 to 10 μm increased, and it was confirmed that charging and aggregation of fine particles occurred due to the energy generated by corona discharge. It was.

  FIG. 8 shows an example of control by the control unit 5 of the present embodiment. First, in step 11, load and rotation speed information of the engine 41 is taken, and in step 12, the amount of exhaust particulates (PM amount M: g / hr) generated in the engine 41 is calculated using these information. The PM amount M can be stored in the control unit 5 as a map, for example, by conducting an experiment in advance to obtain the relationship between the load and the rotational speed and the amount of exhaust particulate generation.

  In step 13, it is determined whether the PM amount M calculated in step 12 is 0 or more (PM amount M> 0). If an affirmative determination is made in step 12, the process proceeds to step 14, and if a negative determination is made, the process returns to step 11. In step 14, the battery voltage information is taken in, and based on this information, the generated energy that can be input is calculated in step 15. This is because the necessary energy E1 for oxidizing the calculated PM amount M (g / hr) may not be supplied in a state where the battery voltage is low. Purifies exhaust particulates.

In step 16, the purification method is determined using the calculated PM amount M, the generated energy that can be input, and the relationship shown in FIG. The purification method is purification by exhaust gas oxidation reaction (CO ₂ region), aggregation by charging of exhaust particulates (charge collection region CO ₂ region), or a combination thereof. Next, in step 17, a voltage corresponding to the generated energy that can be input is applied, and corona discharge energy is input.

  Further, in step 18, the collection amount Mc (cumulative value) of the charged and agglomerated exhaust particulates is calculated, and in step 19, whether or not the collection amount Mc exceeds the collection allowable value (Mc> collection allowable value). ). If a negative determination is made in step 19, the process returns to step 17, and if an affirmative determination is made, the process proceeds to step 20 to activate an alarm (warning) means for the driver. Thus, in addition to the purification method of exhaust particulates by oxidative combustion, the exhaust particulates can be effectively purified by effectively using generated energy by appropriately combining the collection method by charge aggregation.

  FIG. 9 shows a third embodiment of the present invention. The exhaust emission control device 1 of the present embodiment is based on the configuration of the second embodiment of FIG. 5 described above, and is further provided in the collection unit so that the charged and aggregated exhaust particulates can be collected. As shown in FIG. 9, in the present embodiment, the housing H of the exhaust purification device 1 has a shape in which the diameter of the downstream side of the corona discharge electrode 2 is expanded, and along the inner periphery of the expanded portion that becomes the ground electrode 3. The collection part 31 which consists of a hollow mesh conductive cylinder is provided. The collection unit 31 has an exhaust passage 11 inside the cylinder, and has a large number of through holes that open into the exhaust passage 11. Other configurations are the same as those in the second embodiment, and a description thereof will be omitted.

  Also in the present embodiment, by combining exhaust particulate purification by oxidative combustion and collection by charge aggregation, charged particulate by corona discharge is generated in the exhaust purification apparatus 1 (1 to 2) in the figure). The charged fine particles are attracted by the Coulomb force to the ground electrode 3 that also serves as a dust collecting electrode, move to the outer peripheral side, and enter the collecting portion 31 from a large number of through holes that open in the exhaust passage 11. The charged fine particles are further moved to the back of the collection unit 31 and emitted and then aggregated and held (3) to 5)).

  As described above, by providing the collection unit 31 on the outer periphery of the exhaust gas purification apparatus 1 to have a filter function, an effect of preventing re-dispersion of the charged and aggregated exhaust particulates can be obtained.

  The hollow mesh conductive cylindrical body constituting the collecting part 31 usually has a size that does not hinder the inflow of coarse particles having a particle size of about 1 μm to 10 μm, and contains aggregated fine particles inside. It is desirable to have sufficient space to hold. It is preferable to adjust the size, shape, and depth of the through holes as appropriate so that a desired collection effect can be obtained.

  As described above, according to the present invention, exhaust particulate discharged from a diesel engine or gasoline lean burn engine is purified by oxidation combustion, and further, collection by agglomeration and filter function are combined to release to the outside. Can be suppressed. Therefore, by using corona discharge, it is possible to realize an exhaust purification device that has excellent purification performance, high efficiency, and low pressure loss.

(A) is the whole schematic block diagram of the exhaust emission control device in the first embodiment of the present invention, (b) is a diagram for explaining the operation of the first embodiment, (c) is the purification of exhaust particulates It is a figure for demonstrating the mechanism of. It is a figure which shows the relationship between the amount of generated PM and the required energy for PM combustion. It is a flowchart of the input energy control in 1st Embodiment. (A) is an evaluation apparatus block diagram for confirming the effect of 1st Embodiment, (b) is a figure which shows an evaluation result. It is a whole schematic block diagram of the exhaust gas purification device in the 2nd Embodiment of this invention. It is a figure for demonstrating the PM purification method in 2nd Embodiment. (A), (b) is a figure for demonstrating the effect of 2nd Embodiment. It is a flowchart of the input energy control in 2nd Embodiment. It is a whole schematic block diagram of the exhaust gas purification apparatus in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust purification device 11 Exhaust flow path 2 Corona discharge electrode 21 Conductive part 22 Discharge part 23 Insulator part 3 Ground electrode (counter electrode)
31 Collection part 4 Engine 41 Exhaust pipe 5 Control part

Claims (5)

  A corona discharge electrode and a counter electrode are disposed in a cylindrical vessel that constitutes a part of an exhaust flow path of an internal combustion engine, and a corona discharge unit that generates a corona discharge by applying a high voltage between the electrodes is provided. The corona discharge part is characterized in that the energy generated by the corona discharge is greater than the activation energy for oxidizing the exhaust particulates in the exhaust, and the exhaust particulates are purified by oxidative combustion. An exhaust purification device for an internal combustion engine.   The corona discharge part emits electrons into the exhaust flow path from the discharge part of the corona discharge electrode disposed at a substantially central part of the cylindrical container, and the emitted electrons collide with exhaust particulates to oxidize energy. The exhaust emission control device for an internal combustion engine according to claim 1, wherein   2. A control unit for controlling energy input to the corona discharge unit is provided, and the control unit determines an applied voltage to the corona discharge electrode according to an amount of exhaust particulates generated in an internal combustion engine. Or the exhaust gas purifying device for an internal combustion engine according to 2 above.   An exhaust particulate collection part is provided in the corona discharge part or downstream of the corona discharge part, and a part of the exhaust particulates is charged and aggregated by a part of the energy input to the corona discharge part. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, wherein the exhaust gas purification device is collected in a portion.   5. The corona discharge part has a hollow mesh conductive cylindrical wall part disposed along an inner peripheral surface of the cylindrical container as the counter electrode, and an internal space as the collecting part. An exhaust emission control device for an internal combustion engine according to any one of the above.

Images