JP2004346800A - Particulate trap for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particulate trap which is further improved in particulate collecting efficiency , in the particulate trap with extremely low initial pressure loss at the time of collecting and small increase in pressure loss. <P>SOLUTION: In this particulate trap, two or more honeycomb bodies 7 are arranged in the axial direction. The two or more honeycomb bodies are formed of many gas passing cells by alternately superposing and winding, or laminating plain plates 1 made of nonwoven fabric of metal fiber and corrugated plates 2 made by corrugating nonwoven fabric of metal fiber. A space 19 is provided between the honeycomb bodies 7 adjacent to each other. Cell density of the honeycomb body 7 in an exhaust gas downstream side is higher than that of the honeycomb body 7 in an upstream side. Direction of a locus 17 of corrugation tops of the corrugated plates 2 made of the nonwoven fabric of metal fiber is inclined to an axial direction 14 of the honeycomb bodies 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a particulate trap for collecting and removing fine particles (particulates) such as carbon in exhaust gas of a diesel engine.
[0002]
[Prior art]
It is extremely important for environmental measures to remove particulates mainly composed of carbon contained in exhaust gas of a diesel engine. Various techniques have been proposed for disposing a particulate trap in an exhaust gas system of a diesel engine, collecting the particulate, and removing the particulate by post-processing. As a filter for collecting particulates, a honeycomb-like porous body of cordierite ceramics and a ceramic fiber trap in which ceramic fibers are made into a candle shape are known.
[0003]
Patent Literature 1 proposes a particulate trap having a small trap structure having a large filter surface area through which exhaust gas passes by combining a plurality of flat filters or different-diameter cylindrical filters made of a metal fiber nonwoven fabric. The use of a metal fiber non-woven fabric as a filter improves durability and reliability during reproduction, and the surface area of the non-woven fabric is increased to reduce clogging and pressure loss.
[0004]
Patent Document 2 proposes a particulate trap in which a laminated material obtained by alternately laminating an even number of two or more flat filters and two or more corrugated sheets made of metal is also rolled. I have. A flat plate made of a metal fiber nonwoven fabric functions as a particulate filter.
[0005]
In Patent Literature 3, a large number of gas flow cells are formed by alternately overlapping and winding a flat plate of a metal fiber nonwoven fabric and a corrugated corrugated corrugated sheet of a metal fiber nonwoven fabric, or by laminating. A particulate filter using a honeycomb body as a feature is described. In this honeycomb body, the exhaust gas flow passing through the cell repeatedly collides with the metal fiber nonwoven fabric constituting the cell. In the course of the collision, the particulates contained in the exhaust gas are captured by the metal fibers of the non-woven fabric, and thus function as a particulate trap. On the other hand, the exhaust gas passes through not only the cell but also the inside of the non-woven fabric and flows into an adjacent cell, and at that time, repeatedly collides with the metal fibers inside the non-woven fabric violently. This flow traps the particulates inside the nonwoven fabric. Further, the exhaust gas that travels straight through the cell is only affected by the turbulent flow, so that the pressure loss can be significantly reduced as compared with the related art, and the increase in the pressure loss when the collection proceeds can be suppressed. As a result, a particulate trap having an extremely low initial pressure loss at the time of collection and a small increase in pressure loss can be obtained.
[0006]
[Patent Document 1]
JP-A-8-243333
[Patent Document 2]
JP-A-9-262414
[Patent Document 3]
JP-A-2002-113798
[0007]
[Problems to be solved by the invention]
In the particulate trap described in Patent Document 3, it is important that the exhaust gas flow passing through the cells of the honeycomb body becomes turbulent, and that the particulates in the exhaust gas repeatedly collide with the metal fiber nonwoven fabric on the cell walls. is there. By the way, the Reynolds number of the gas passing through the cells of the honeycomb body is about 150 to 600. The exhaust gas before flowing into the honeycomb body is in a turbulent state, and the turbulent state can be maintained immediately after flowing into the cell, but when the Reynolds number inside the cell is a value of this degree, the inside of the cell The flow shifts to laminar flow. Therefore, it is preferable that the flow in the cell can be maintained in a turbulent state as much as possible, because the collection efficiency of particulates can be further improved.
[0008]
An object of the present invention is to provide a particulate trap in which the initial pressure loss at the time of collection is extremely low and the rise in pressure loss is small, and in which the particulate collection efficiency is further improved.
[0009]
[Means for Solving the Problems]
That is, the gist of the present invention is as follows.
(1) A particulate trap in which two or more honeycomb bodies 7 are arranged in the axial direction. For two or more of the honeycomb bodies 7, a flat plate of metal fiber nonwoven fabric and a single metal fiber nonwoven fabric are corrugated. A particulate trap characterized by being a honeycomb body formed by forming a large number of gas flow cells by alternately superposing and winding or laminating corrugated sheets.
(2) The particulate trap according to (1), wherein a space 19 is provided between adjacent honeycomb bodies 7.
(3) The particulate trap according to (1) or (2), wherein the cell density of the honeycomb body 7 on the downstream side of the exhaust gas is higher than the cell density of the honeycomb body 7 on the upstream side.
(4) The paste according to any one of (1) to (3), wherein the porosity of the honeycomb body 7 on the downstream side of the exhaust gas is lower than the porosity of the honeycomb body 7 on the upstream side. Cured trap.
(5) The particulate trap according to any one of (1) to (4), wherein a catalyst is supported on the metal fibers 4 of the metal fiber nonwoven fabric.
(6) Any of the above (1) to (5), wherein the direction of the locus 17 of the crest of the corrugated sheet 2 of the metal fiber nonwoven fabric is inclined with respect to the axial direction 14 of the honeycomb body. The particulate trap described in Crab.
(7) The particulate trap according to the above (6), wherein the direction of inclination of the trajectory 17 of the crest is opposite between the adjacent honeycomb bodies.
(8) The particulate trap according to (6), wherein the inclination angle of the locus 18 of the crest with respect to the axial direction 14 of the honeycomb body changes in the axial direction of the honeycomb body.
(9) The particulate trap according to (8), wherein the center of curvature of the locus of the crest portion drawn by the honeycomb body axial direction is in the opposite direction between the adjacent honeycomb bodies.
(10) The particulate trap according to any one of the above (1) to (9), wherein at least one of the honeycomb bodies has a heating section 10 by electric heating.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The particulate trap of the present invention is formed by forming a large number of gas flow cells by alternately stacking and winding a flat plate of a metal fiber nonwoven fabric and a corrugated corrugated corrugated metal fiber nonwoven fabric, or by laminating. Two or more honeycomb bodies are prepared, and as shown in FIG. 1, two or more honeycomb bodies including this honeycomb body are arranged in the axial direction of the filter. FIG. 2A shows a honeycomb body in which a large number of gas flow cells are formed by alternately overlapping and winding a flat plate of a metal fiber nonwoven fabric and a corrugated corrugated corrugated sheet of a metal fiber nonwoven fabric, and FIG. b) represents a honeycomb body in which a number of gas flow cells are formed by laminating a flat plate of a metal fiber nonwoven fabric and a corrugated corrugated sheet of the metal fiber nonwoven fabric.
[0011]
In the particulate trap of the present invention, the basics for collecting diesel particulates in exhaust gas are the same as those described in Patent Document 3. That is, as shown in FIG. 3, the exhaust gas flow passing through the inside of the cell 3 repeatedly collides with the metal fiber non-woven fabric constituting the cell, and in the course of this collision, the particulates contained in the exhaust gas become the metal of the non-woven fabric. Captured by fiber. On the other hand, the exhaust gas passes not only through the cells but also through the non-woven fabric as a gas flow 24 through the non-woven fabric, flows into the adjacent cells, and also repeatedly violently collides with the metal fibers inside the non-woven fabric. The particulates are captured inside the nonwoven fabric by these flows. The pressure loss can be significantly reduced as compared with the related art, and an increase in the pressure loss when the collection proceeds can be suppressed.
[0012]
In the particulate trap having the above configuration using a single honeycomb body, the particulates are trapped mainly on the cell walls near the exhaust gas inlet and outlet of the honeycomb body. As shown in FIG. 4C, since the gas is in the turbulent flow 15 near the exhaust gas inlet of the honeycomb body 7, the collision with the cell wall is repeated so that the particulates in the gas are captured by the cell wall. On the other hand, it is considered that the gas flow changes from the turbulent flow 15 to the laminar flow 16 in the interior away from the inlet, and the trapping efficiency of particulates decreases. It is considered that the reason why the trapping efficiency is improved again near the exit is that turbulence occurs due to a pipe expansion effect or the like.
[0013]
A feature of the present invention is that a plurality of honeycomb bodies 7 whose cell walls are formed of a metal fiber nonwoven fabric are arranged in the axial direction of the trap. Most basically, a plurality of honeycomb bodies are arranged close to each other as shown in FIG. Since the upstream honeycomb body 7a and the downstream honeycomb body 7b arranged close to each other in the axial direction of the trap coincide with the axial direction of the cell and the axial direction of the trap, as shown in FIG. The exhaust gas passing through the cells of the upstream honeycomb body 7a and discharged from the cell outlet immediately flows into the cells from the cell inlet of the downstream honeycomb body 7b. At this time, since the cell center axes of the cells 3 of the upstream honeycomb body 7a and the cells 3 of the downstream honeycomb body 7b do not basically coincide with each other, the gas flow is disturbed near the honeycomb body contact surface, The gas flow flowing into the cells of the honeycomb body on the downstream side becomes a turbulent flow 15. As a result, the particulate capture efficiency can be increased near the exhaust gas inlet of the downstream honeycomb body. Further, similarly to the case of the single honeycomb body, there is a portion having a high particulate capture efficiency in the vicinity of the outlet in addition to the vicinity of the exhaust gas inlet for each honeycomb body. Therefore, if a plurality of honeycomb bodies are arranged and the entire length of the honeycomb body in the axial direction of the particulate trap is kept constant, the abundance ratio of a portion having a high particulate capture efficiency is increased, and the overall particulate capture efficiency is improved. can do.
[0014]
If the number of honeycomb bodies arranged in the axial direction of the particulate trap 9 is two or more, the greater the number, the more the particulate capture efficiency can be improved. When arranging three or more honeycomb bodies, it is not necessary to use all the honeycomb bodies as honeycomb bodies using a nonwoven fabric made of metal fiber. Some of the honeycomb bodies are formed using, for example, metal foil, A catalyst carrier having a catalyst supported on the surface may be used.
[0015]
The metal fiber nonwoven fabric forming the honeycomb body has a predetermined thickness. Therefore, when two honeycomb bodies are brought into contact in the axial direction of the filter as shown in FIG. 1 (a), the gas-flowable aperture ratio at the contact portion is reduced, and a high pressure loss occurs here. Become. FIG. 5 is a schematic diagram showing a state in which two honeycomb bodies overlap each other when viewed in the axial direction of the honeycomb body. The gas flow passage is greatly reduced due to the overlap between the upstream honeycomb body 31 and the downstream honeycomb body 32. The situation is clear. In the present invention, as shown in FIG. 1 (b), it is preferable that the space 19 is provided between the adjacent honeycomb bodies, because it is possible to prevent a decrease in the gas flow opening ratio at the contact portion. As shown in FIG. 4B, the exhaust gas flowing in the space 19 between the honeycomb bodies maintains a turbulent state, and when the exhaust gas flows into the downstream honeycomb body, the gas maintains the turbulent state. If the distance provided between the two honeycomb bodies is 5 mm or more, the effect can be surely exhibited. More preferably, it is 10 mm or more. On the other hand, if the distance exceeds 45 mm, the effect is saturated, and the entire length of the particulate trap is unnecessarily increased, which is not preferable. More preferably, the distance is 20 mm or less.
[0016]
The cell size of the honeycomb body formed of the metal fiber nonwoven fabric can be expressed by the cell density which is the number of cells per unit cross-sectional area of the honeycomb body. The higher the cell density, the smaller the cross-sectional area of each cell, and the larger or smaller the particulate diameter can be captured. However, there is a disadvantage that the cell cross-sectional area is reduced by capturing a large amount of particulates, and the passage resistance of the exhaust gas is rapidly increased. Conversely, when the cell density increases, large-diameter particulates can be captured, but the capture ratio of the small-diameter particulates decreases, and the disadvantage that the passage resistance of the exhaust gas increases instead hardly occurs.
[0017]
In the present invention, as shown in FIG. 6A, the cell density of the honeycomb body 7b on the downstream side of the exhaust gas is higher than the cell density of the honeycomb body 7a on the upstream side. The problem can be solved. That is, a honeycomb body 7a having a low cell density is arranged on the upstream side, and particulates having a large diameter are selectively captured by the honeycomb body 7a on the upstream side. A honeycomb body 7b having a high cell density is arranged on the downstream side, and the exhaust gas after the already trapped particulates having a large diameter is passed therethrough so as to intensively capture the remaining particulates having a small diameter. With such a configuration, both large-diameter particulates and small-diameter particulates can be captured, and the cell cross-sectional area of the honeycomb body does not decrease due to excessive capture of the particulates, and is stable. Particulates can be captured. As a result, pressure loss when the exhaust gas passes through the particulate trap can be minimized, so that the load on the engine can be suppressed.
[0018]
In a particulate trap in which two honeycomb bodies are arranged as shown in FIG. 6A, the cell density of the upstream honeycomb body 7a is set to 100 to 400 CPSI (Cell / inch).²), And the cell density of the downstream-side honeycomb body 7b is preferably about 300 to 1200 CPSI. When three honeycomb bodies are arranged as shown in FIG. 6B, the cell density of the honeycomb body 2b disposed in the middle is 200 to 600 CPSI, and the cell densities of the honeycomb bodies before and after the honeycomb body 2b are the two cell densities. It is good to be similar to the case of the honeycomb body.
[0019]
With respect to the metal fiber nonwoven fabric constituting the honeycomb body, the porosity of the nonwoven fabric can be adjusted to various values by adjusting the density of the metal fibers and the like. In a nonwoven fabric in which the porosity is small, that is, the metal fibers are densely arranged, it is possible to capture both large-diameter particulates and small-diameter particulates. On the other hand, in a nonwoven fabric having a large porosity, that is, a metal fiber is sparsely arranged, a particulate having a large diameter can be captured, but the capturing efficiency of a particulate having a small diameter is reduced.
[0020]
In the present invention, the porosity of the honeycomb body on the downstream side of the exhaust gas is set to a value lower than the porosity of the honeycomb body on the upstream side, so that a particulate having a large diameter can be selectively used in the honeycomb body on the upstream side. The exhaust gas after the large-diameter particulates have already been captured is passed through the downstream honeycomb body, and the remaining small-diameter particulates are intensively captured. With such a configuration, both large-diameter particulates and small-diameter particulates can be captured, and the cell cross-sectional area of the honeycomb body does not decrease due to excessive capture of the particulates, and is stable. Particulates can be captured. As a result, pressure loss when the exhaust gas passes through the particulate trap can be minimized, so that the load on the engine can be suppressed.
[0021]
In the particulate trap in which two honeycomb bodies are arranged, it is preferable that the porosity of the honeycomb nonwoven fabric on the upstream side is 95 to 80% and the porosity of the honeycomb nonwoven fabric on the downstream side is about 85 to 65%. When three honeycombs are arranged, the porosity of the honeycomb arranged in the middle is set to 85 to 75%, and the porosity of the honeycombs before and after the honeycomb is preferably the same as that of the two honeycombs. .
[0022]
In the particulate trap of the present invention, the catalyst can be supported on the metal fibers of the metal fiber nonwoven fabric constituting the honeycomb body. As shown in FIG. 7B, the catalyst supported on the metal fibers is coated on the surface of each metal fiber 4 as a catalyst supporting layer 5, so that the gas can pass through this nonwoven fabric. Therefore, not only can it function as a catalyst, but it can also trap particulates. The total surface area of the catalyst-carrying layer in the cell is greatly increased in the present invention as compared with the conventional case where the flat plate and the corrugated plate constituting the cell are formed of a metal plate and coated with a catalyst. As a result, the size of the catalyst carrier can be significantly reduced.
[0023]
When the particulate trap of the present invention in which a catalyst is supported on metal fibers is used for an exhaust gas system of a diesel engine, the particulates contained in the exhaust gas are trapped in irregularities between the metal fibers, so that the particulates having a small pressure loss are used. At the same time as functioning as a curate trap, a catalytic reaction is caused by a catalyst on the surface of the metal fiber, and harmful components in exhaust gas can be removed at the same time.
[0024]
When the particulate trap of the present invention in which a catalyst is supported on metal fibers is used in an exhaust gas system of a gasoline engine, it functions as a catalyst carrier for purifying exhaust gas. Compared to a conventional catalyst carrier in which a flat metal foil and a corrugated foil are wound or laminated, the total surface area of the catalyst supporting layer on the inner surface of the cell is greatly increased, so that the catalytic reaction efficiency is remarkably improved. Further, turbulence is generated over the entire surface by the unevenness of the metal fiber nonwoven fabric constituting the cell wall surface, and the catalytic reaction is promoted. It is also good as a methanol reformer.
[0025]
In a catalyst carrier used for purifying exhaust gas of an automobile, it is necessary to raise the temperature of the catalyst to a temperature equal to or higher than the ignition temperature as soon as possible at the start of the engine, ignite the catalyst, and allow the catalytic reaction to proceed. On the other hand, when the engine is started, the catalyst carrier is cold and the temperature of the exhaust gas flowing in is also low. It is valid. In the present invention, when a catalyst is supported by supporting a catalyst on a metal fiber nonwoven fabric, the cell density of the honeycomb body on the downstream side of the exhaust gas is higher than the cell density of the honeycomb body on the upstream side as described above. With this configuration, the heat capacity of the honeycomb body on the exhaust gas entry side can be reduced. As a result, since the heat capacity is small on the exhaust gas inlet side, the temperature of the honeycomb body rises early when the engine is started, and the catalyst is ignited.
[0026]
In the present invention, it is preferable that the direction of the trajectory 18 of the crest of the corrugated sheet made of metal fiber nonwoven fabric is inclined with respect to the axial direction 14 of the honeycomb body as shown in FIG. When a honeycomb body is formed by alternately stacking and winding a flat plate and a corrugated sheet using such a corrugated sheet 2, as shown in FIG. 8B, the direction of the cells 3 formed in the honeycomb body is changed. The cells 3 are not straight but slightly curved, while being inclined from the axial direction 14 of the honeycomb body. It is known that the flow is destabilized by the action of centrifugal force inside the boundary layer of the flow along the curved surface having a concave curvature in the flow direction, and a vertical vortex line is formed in the flow direction. This vortex is called Göller vortex, and due to this vortex, the collision between the exhaust gas passing through the cell and the inner surface of the cell becomes violent, increasing the particulate collection efficiency and reducing the catalytic reaction efficiency. An increase can be obtained. A preferable range of the inclination angle of the crest is 5 ° to 30 °. If it is less than 5 °, the effect of setting the inclination angle cannot be sufficiently exerted. If it exceeds 30 °, the pressure loss increases, and the possibility of insufficient particulate collection or catalytic reaction increases.
[0027]
When the direction of the trajectory 18 of the crest of the corrugated sheet is inclined with respect to the axial direction 14 of the honeycomb body, the direction of the inclination of the trajectory 18 of the crest is, as shown in FIG. It is preferable that the directions be opposite. This is because the flow direction in the upstream honeycomb body changes abruptly when entering the downstream honeycomb body, and the effect of improving the particulate collection efficiency due to the change in the flow direction is obtained.
[0028]
When the direction of the locus 18 of the crest of the corrugated sheet is inclined with respect to the axial direction 14 of the honeycomb body, the inclination angle of the crest with respect to the axial direction of the honeycomb body is, as shown in FIG. Preferably, it changes in the axial direction. This means that the locus 18 drawn by the crest before the corrugated sheet is wound around the honeycomb body is a curve. This makes it possible to obtain a curved shape as a synergistic effect between the curved shape that the corrugated plate has before winding and the curved shape that results from winding the corrugated plate. Further, even when the honeycomb body is formed by stacking the flat plate and the corrugated plate instead of winding them alternately, the cells of the honeycomb body can have a curved shape.
[0029]
As shown in FIG. 10, the curved shape drawn by the crest locus 18 of the corrugated plate has the centers of curvature alternately located on both sides of the crest in the axial direction from the exhaust gas inlet side to the outlet side of one honeycomb body. Alternatively, the center of curvature may be located only on one side of the crest as shown in FIG. 9A. In any case, it is preferable that the inclination angle between the locus 18 of the crest and the axial direction 14 of the honeycomb body be smaller on the exhaust gas inlet side. This allows the exhaust gas to flow smoothly into the cell. In the form in which the centers of curvature are alternately located on both sides of the crest, the inclination angle between the crest locus 18 and the honeycomb body axial direction 14 can be reduced also on the exhaust gas exit side.
[0030]
In the embodiment in which the center of curvature is located only on one side of the crest as shown in FIG. 9A, it is inevitable to reduce the inclination angle between the crest and the honeycomb body axial direction on the exhaust gas entry side. On the exhaust gas outlet side, the inclination angle between the crest and the honeycomb body axial direction increases. In such a case, it is preferable that the center of curvature drawn by the locus of the crest portion in the honeycomb body axial direction is in the opposite direction between the adjacent honeycomb bodies as shown in FIG. 9B. Thereby, the exhaust gas flowing in the cell is subjected to a large centrifugal force, and the generation of the Gertler vortex is promoted, so that the particulate capture efficiency can be improved.
[0031]
In a particulate trap of a diesel engine, the particulates trapped in the trap react with the oxidizing gas in the exhaust gas due to the high temperature of the exhaust gas and are burnt and removed. Therefore, when the temperature of the exhaust gas is low, the trapped particulates are not sufficiently burned and removed, and the particulates are deposited on the particulate trap. When the engine is started or idling, the temperature of the exhaust gas is low, and the combustion of the captured particulates becomes insufficient.
[0032]
The particulate trap of the present invention can solve this problem by having the heating section 10 by electric heating. The temperature of the exhaust gas passing through the particulate trap rises due to the heat generated by the electric heating, and the burning of the particulate trapped in the trap starts. When the combustion starts, the temperature of the exhaust gas further increases due to the heat of combustion, so that the temperature of the exhaust gas is maintained at a high temperature from upstream to downstream in the honeycomb body of the particulate trap, and the combustion of the captured particulates can be sufficiently performed. it can.
[0033]
In the case where the particulate trap having a heat generating portion by electric heating according to the present invention also has a portion carrying a catalyst at the same time, the catalytic reaction for burning unburned components in the exhaust gas is performed at a high temperature equal to or higher than a predetermined temperature. appear. Immediately after the start of the engine or at the time of idling, the temperature of the exhaust gas is low, and ignition for starting the catalytic reaction does not occur. In such a case, if the catalyst carrier has a heat-generating portion by electric heating, the exhaust gas heated by the heat-generating portion rises to a temperature equal to or higher than the ignition temperature, and even if the exhaust gas has a low temperature, the catalytic reaction occurs. Can be caused.
[0034]
As for the heat generating portion by electric heating, for example, a method described in JP-A-9-88561 can be used. That is, as shown in FIG. 11, a combination foil obtained by combining a flat foil and a corrugated foil having at least one surface insulated is spirally wound around the center electrode 11 to form a cylindrical shape. The honeycomb body 7b is housed in the casing 8 to which the external electrode 12 is connected, and a voltage is applied to both ends in the circumferential direction of the combined foil. This honeycomb body 7b is provided with a plurality of local heat generating portions 10 that locally break insulation and electrically connect adjacent combination foils in the radial direction. When a voltage is applied between the two electrodes, heat is generated when the current passes through the local heating portion, and the temperature of the exhaust gas passing around the heating portion can be increased.
[0035]
【Example】
The present invention was applied to a particulate trap in which a flat plate of a metal fiber nonwoven fabric and a corrugated corrugated corrugated metal fiber nonwoven fabric were alternately overlapped and wound to form a large number of gas flow cells.
[0036]
The outer diameter of the particulate trap is 100 mm. As shown in FIG. 1B, two honeycomb bodies having a length of 50 mm are arranged in series at intervals of 25 mm as a honeycomb body forming a particulate trap, and the comparative example is a 110 mm long honeycomb body. One thing is arranged. In both the present invention example and the comparative example, a metal nonwoven fabric having a thickness of 0.3 mm and a porosity of 70% was used, and the cell density of the honeycomb body was 300 CPSI.
[0037]
The particulate traps of the present invention and comparative examples were connected to the exhaust system of a 4-cycle water-cooled diesel engine (displacement 764 cc), and the collection rate of particulates in exhaust gas was evaluated.
[0038]
The fuel used for the engine was commercial light oil, the engine was operated at 3600 rpm, and the load was 10 kW. Before each measurement, the system was sufficiently warmed up without a particulate trap, and a particulate trap was attached. After confirming that there was no gas leakage, the measurement was started when the test conditions were reached. In addition, when the particulate trap was not attached, the measurement was performed after the exhaust temperature was stabilized. The test temperature was normal temperature during normal operation. The CVS flow rate was 10 m during the measurement throughout the entire test.³/ Min.
[0039]
As the measurement items, the amount of discharged particulate matter and the amount of collected particulate matter were measured, and the trapping rate was calculated from the measurement results. In addition, pressure loss was measured.
One measurement was performed for 700 seconds, and the measurement was repeated three times.
[0040]
The particulate matter was introduced into a dilution tunnel at a constant flow rate of 110 liter / min at a flow rate of 110 liter / min, and then using a 70 mmφ Teflon (registered trademark) coating filter (Pallflex TX40HI-20-ww, pore 0.3 μm). Collected. The amount of particulate matter discharged was determined from the difference in filter mass before and after the collection of particles.
[0041]
The particulate matter emission was determined by the following equation.
PMmass = (Vmix + Vs) × {PMs / Vs−PMb / Vb (1-1 / DF)} × 10^-5
Here, PMmass: amount of particulate matter emitted (g), Vmix: amount of diluted exhaust gas per test (liter), PMs: mass of particulate matter collected from diluted exhaust gas (μg), Vs: collection of diluted exhaust gas Collection flow rate (liter), PMb: mass of particulate matter collected from dilution air (μg), Vb: collection flow rate of dilution air (liter). DF is a dilution ratio obtained from the following equation.
DF = 13.3 / ｛CO_2e  + (HC_e+ CO_e) × 10^-4｝
Where CO_2e: CO in diluted exhaust gas₂Concentration (%), HC_e: HC concentration (ppmc) in diluted exhaust gas, CO_e: CO concentration (ppm) in diluted exhaust gas.
[0042]
FIG. 12 shows the measurement results of the collection rates of the present invention example and the comparative example. As is clear from FIG. 12, in the example of the present invention in which two honeycomb bodies are arranged in the axial direction, the collection rate is improved by 20 to 25% as compared with the comparative example using one honeycomb body.
[0043]
Regarding the pressure loss, there was no difference between the present invention example and the comparative example at about 3 KPa.
[0044]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, in the particulate trap which the initial pressure loss at the time of collection is extremely low, and the rise of a pressure loss is small, the particulate trap which further improved the particulate collection efficiency can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective sectional view showing a particulate trap of the present invention, wherein (a) shows a case where adjacent honeycomb bodies are densely arranged, and (b) shows a case where a space is provided between adjacent honeycomb bodies. .
FIGS. 2A and 2B are views showing a honeycomb body of the present invention, wherein FIG. 2A is a perspective view of a flat plate and a corrugated plate which are alternately overlapped and wound, and FIG. It is a front view of a thing.
FIG. 3 is a perspective sectional view showing a state of an exhaust gas flow flowing through a honeycomb body of the present invention.
FIG. 4 is a cross-sectional view showing a state of an exhaust gas flow flowing through the honeycomb body of the present invention.
FIG. 5 is a schematic view showing an overlapping state of an upstream honeycomb body and a downstream honeycomb body.
FIG. 6 is a perspective sectional view showing a particulate trap of the present invention.
FIG. 7 (a) is a partially enlarged perspective view showing a metal fiber nonwoven fabric, and FIG. 7 (b) is a partially enlarged perspective view showing a metal fiber nonwoven fabric carrying a catalyst on the surface of a metal fiber.
8A and 8B are diagrams showing a particulate trap of the present invention, wherein FIG. 8A is a diagram showing a locus of a crest, FIG. 8B is a perspective view of a honeycomb body, and FIG. 8C is a perspective sectional view of the particulate trap. is there.
9A and 9B are diagrams showing a particulate trap of the present invention, wherein FIG. 9A is a diagram showing a locus of a crest, and FIG. 9B is a perspective sectional view of the particulate trap.
FIG. 10 is a diagram showing a locus of a crest in the particulate trap of the present invention.
FIG. 11 is a view showing a particulate trap of the present invention having a heat generating portion by electric heating.
FIG. 12 is a diagram comparing the particulate matter collection rates of the present invention example and the comparative example.
[Explanation of symbols]
1 Flat plate of nonwoven fabric made of metal fiber
2 Corrugated sheet of metal fiber non-woven fabric
3 cells
4 Metal fiber
5 Catalyst support layer
6 outer cylinder
7. Honeycomb body
8 Casing
9 Particulate trap
10 Heating part
11 center electrode
12 External electrodes
13 Exhaust gas flow
14 Honeycomb body axial direction
15 Exhaust gas flow (turbulent flow)
16 Exhaust gas flow (laminar flow)
17 Crest
18 Crest trajectory
19 Space
21 Inlet gas flow
22 Outlet gas flow
23 Gas flow inside the cell
24 Gas flow through nonwovens
31 upstream honeycomb body
32 Downstream honeycomb body

Claims (10)

A particulate trap in which two or more honeycomb bodies are arranged in the axial direction, wherein two or more of the honeycomb bodies alternate between a flat plate of metal fiber nonwoven fabric and a corrugated corrugated metal fiber nonwoven fabric. A particulate trap, which is a honeycomb body formed by forming a large number of gas flow cells by superposing and winding or laminating the same. The particulate trap according to claim 1, wherein a space is provided between adjacent honeycomb bodies. 3. The particulate trap according to claim 1, wherein the cell density of the honeycomb body on the downstream side of the exhaust gas is higher than the cell density of the honeycomb body on the upstream side. 4. The particulate trap according to claim 1, wherein the porosity of the honeycomb body on the downstream side of the exhaust gas is lower than the porosity of the honeycomb body on the upstream side. The particulate trap according to any one of claims 1 to 4, wherein a catalyst is supported on the metal fibers of the metal fiber nonwoven fabric. The particulate trap according to any one of claims 1 to 5, wherein a direction of a locus of a crest of the corrugated sheet of the metal fiber nonwoven fabric is inclined with respect to an axial direction of the honeycomb body. 7. The particulate trap according to claim 6, wherein the direction of the inclination of the locus of the crest is opposite between adjacent honeycomb bodies. The particulate trap according to claim 6, wherein the inclination angle of the trajectory of the crest with respect to the axial direction of the honeycomb body changes in the axial direction of the honeycomb body. 9. The particulate trap according to claim 8, wherein the center of curvature drawn by the locus of the crest portion in the honeycomb body axial direction is in the opposite direction between adjacent honeycomb bodies. The particulate trap according to any one of claims 1 to 9, wherein at least one of the honeycomb bodies has a heat-generating portion by electric heating.

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