JPH0160652B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an exhaust gas filter that removes particulates and harmful gas components contained in exhaust gas from a diesel engine. In connection with air pollution prevention, it is essential to remove or reduce fine particles, mainly black smoke particles, and harmful gas components HC, CO, and NO _x emitted from diesel engines. Diesel engines inject fuel into compressed high-temperature air in the cylinder and combust it. Due to its nature, the air-fuel ratio is large and there is an excess of air, so the HC and CO contents in the exhaust gas are relatively low and NO _x The content is slightly higher.
However, because the fuel is injected before the combustion starts, the fuel is not vaporized sufficiently and burns as oil droplets in a lack of air, producing black smoke or intermediate products, which are emitted as so-called fine particles containing soot. This has become one of the major problems with diesel engines. Among these harmful components, NO _x has a large air-fuel ratio, so the three-way catalyst that is effectively used to purify exhaust gas from gasoline engines cannot be used.
In addition, the EGR (exhaust gas recirculation system) also contains a large amount of particulates, making it difficult to use as easily as in a gasoline engine, and countermeasures are being considered, mainly by delaying the timing of fuel injection. However, if the fuel injection timing is delayed, NO _x will decrease;
This results in an increase in particulates mainly consisting of HC, CO and black smoke particles. Regarding HC and CO, the oxidation catalyst used to treat the exhaust gas of gasoline engines is severely deteriorated due to the deposition of large amounts of fine particles in the exhaust gas, making it impossible to use them effectively. Improvements to the air intake system and combustion chamber are being considered, but they are still insufficient.In particular, there is a need to significantly reduce the current concentration of fine particles from the perspective of air pollution, but there are still no effective methods. No method of reduction has been established. The present invention was invented in order to significantly remove and reduce fine particles in the exhaust gas from diesel engines that contain such problems, along with the HC and CO contained at the same time. The end faces of the entrances of adjacent through-holes of a honeycomb-shaped ceramic body consisting of a large number of mutually parallel through-holes with polygonal cross sections are alternately closed in a checker flag pattern, and the end faces of the other exit part are closed alternately in a checker flag pattern. In this case, the end faces of the through holes other than those closed at the inlet portion are closed, and the diesel engine exhaust gas introduced from the inlet side of the honeycomb-shaped ceramic body is contained when passing through the porous thin wall. The ceramic body is configured such that fine particles are filtered out and discharged from the outlet side of the ceramic body, and an oxidation catalyst for exhaust gas purification is supported on the outlet side portion of the hole wall of the through hole of the ceramic body. This is an exhaust gas filter for diesel engines. A first example showing a more detailed configuration of the present invention.
To explain based on the figures and FIG. 2, a ceramic body 3 has a plurality of mutually parallel through holes 2 which are partitioned on all sides by a porous ceramic thin wall 1 and have a rectangular cross section. The inlet part 4 and the outlet part 4' of the ceramic body 3 are alternately substantially closed with a ceramic material 5 that is the same as the ceramic thin wall 1 or has a smaller porosity than that of the ceramic thin wall 1, and the diesel inlet introduced from the inlet side 6 of the ceramic body 3 is When the engine exhaust gas passes through the porous ceramic thin wall 1, the fine particles 7 contained in the exhaust gas are filtered and removed, and the fine particles in the diesel engine exhaust gas are now discharged from the outlet side 8 of the ceramic body. In the filter body,
This is an exhaust gas filter for a diesel engine, in which an oxidation catalyst 10 for exhaust gas purification is supported on the outlet portion of the through-hole wall of a ceramic body, and at the same time, harmful components such as HC and CO in the exhaust gas are oxidized and purified. . Next, to explain in more detail the structure and operation of the exhaust gas filter for a diesel engine of the present invention, the ceramic body 3 is made of ceramic materials such as silica, alumina, titania, zirconia, mullite, cordierite, or a mixture or composite oxide thereof. These raw material powders or raw material powders that are fired to produce these oxides are kneaded, extruded, dried, and fired using normal ceramic techniques, and the porosity of the thin wall is determined by the amount of gas passing through it. In terms of pressure loss and the strength of ceramics, it is 10 to 60% by volume, and the average pore diameter of the thin wall is 0.1 to 0.2 μ, which is the average diameter of the fine particles to be filtered.When actually filtering, crosslinking occurs, so it is efficient. A material with a diameter of 1 to 20 μm that can be filtered and does not increase pressure loss due to clogging of pores can be used. The average diameter and porosity of the pores can be adjusted by selecting the particle size distribution of the raw material powder and by adding carbon, wood chips, or other organic combustible powder to the raw material powder. The larger the number of parallel through-holes partitioned by thin walls, the larger the filtration area for exhaust gas, which is advantageous, but conversely, the cross-section of the through-hole becomes smaller, and the gas passage becomes blocked by the accumulation of particulates. Although it is dangerous, the range that can be used effectively is 1.5 to 150 pieces/cm ² in the cross section of the ceramic body. In addition, the thickness of the thin wall must be reduced as the number of through holes per cross-sectional area of the ceramic body increases, but from the viewpoint of manufacturing, the lower limit is 0.05 mm, and 1.5 mm is required to keep pressure loss below a certain level. mm is the upper limit. There is no particular restriction on the external cross-sectional shape of the ceramic body, but a circular or oval shape can usually be used from the standpoint of mounting to the engine. The ceramic that closes the through holes must have a porosity equal to or lower than the porosity of the thin wall because the thin wall is used as a filter, and it is preferable to extrude the ceramic body and then plasticize it after drying. The kneaded material is injected into the inlet or outlet of the ceramic body to a length of, for example, 2 to 10 mm, enough to substantially close the through hole, dried, and fired simultaneously with the ceramic body. As the oxidation catalyst supported on the outlet portion of the pore walls of the present filter, base metal oxides such as copper, manganese, and cobalt can be used, but noble metal catalysts can be used more efficiently. In other words, as is used in the treatment of exhaust gas from gasoline engine vehicles, the surface of the ceramic thin wall should first be coated with an active substance such as activated alumina, and then precious metals such as platinum, palladium, and platinum-palladium should be purified.
Supports depending on the amount of HC and CO can be used. If there are relatively few particulates in the exhaust gas from a diesel engine, the oxidation catalyst function can be achieved even if they are supported at the inlet of the ceramic body, but if there are many particulates, they will settle on the oxidation catalyst layer and the catalytic function will be impaired. In this case, it is better to support the catalyst on the exit part of the pore wall of the ceramic body, since the exhaust gas passes through the filter and most of the fine particles are filtered out, and then passes through the catalyst layer. It is possible to effectively purify HC and CO with little deterioration. The filter body 17 of the present invention is housed in a metal case as shown in FIG. and are connected as shown in Figure 3B. Exhaust gas from the diesel engine 15 enters the filter body through the filter inlet 6, and the fine particles are mainly filtered as they pass through the pores in the thin wall portion where no catalyst is supported, and remain on the inlet side of the thin wall. Most of the filtered and removed exhaust gas is discharged from the outlet side of the filter body. At this time, if an oxidation catalyst is supported on the outlet part of the filter body pore wall, HC and CO are each oxidized as they pass through this catalyst layer. harmless _H2O ,
It becomes CO ₂ and is emitted. It should be noted that fine particles, mainly black smoke particles, filtered and accumulated on the thin wall on the inlet side block the pores of the thin wall, causing an increase in pressure loss over time. However, the black smoke particles that make up the majority of these particles are 400 to 450.
It is known that combustion occurs in an oxygen-excess state when exposed to temperatures above ℃, and the filter body of the present invention can easily reduce the exhaust gas temperature to 400℃ by increasing the engine speed and engine load appropriately.
In this case, the black smoke particles accumulate substantially on the thin wall and can be burned off continuously without clogging the pores. In the present invention, the effect of combining an oxidation catalyst with a filter body is that it is possible to filter out particulates and oxidize and purify HC and CO in the same filter body. The oxidation catalyst, which was previously unusable due to deterioration due to the deposition of fine particles, can now be used in combination with a filter, and when there are relatively few black smoke particles, the filtration By supporting the oxidation catalyst at the body entrance,
The heat of reaction from the combustion of HC and CO can increase the temperature of the exhaust gas, and therefore the combustion of black smoke particles on thin walls can be promoted. Next, examples of the present invention will be described. 15 through holes per cross section made by extrusion method
^cm2 thin wall thickness 0.4mm, porosity 42%, average pore diameter
Every other cordierite ceramic through-hole with a diameter of 118 mm and a length of 200 mm is made of 10μ, and the porosity is 10 mm at the inlet and outlet.
28% cordierite ceramics was used to coat the thin wall of the outlet part of the filter block in the checker flag pattern as shown in the figure, and γ-alumina was coated to a thickness of about 30 μm at a distance of 50 mm from the outlet, and a platinum catalyst was coated in total. A filter body of the present invention was obtained by supporting 1 g of the filter. This filter body was placed in a metal case in the same manner as shown in Fig. 2A, and connected to the exhaust manifold of a 4-cylinder diesel engine vehicle with a displacement of 2 in the same manner as shown in Fig. 2B.
An exhaust gas test in three modes and an exhaust smoke test in three bench modes were conducted, and the results were compared with those before the filter of the present invention was installed, and the following results were obtained.

[Table] That is, when the filter device of the present invention is used, according to this example, it is not effective in purifying NO _x , but
It had a significant purifying effect on HC and CO, and about 50% of fine particles could be removed when measured by the opacity of the main black smoke. As described above, in the exhaust gas filter for a diesel engine according to the present invention, the end surfaces of the inlet portions of adjacent through holes of the honeycomb-shaped ceramic body are alternately closed in a checker flag pattern, and the end surfaces of the inlet portions of the adjacent through holes of the honeycomb-shaped ceramic body are closed in a checker flag pattern, and the outlet portions of the other through holes are closed alternately. On the end face, the end face of the through hole other than the through hole closed at the inlet part is closed, and the diesel engine exhaust gas is always contained in the exhaust gas while passing through the thin wall of the through hole from the inlet side to the outlet side. After the graphite particles are filtered out, they pass through the catalyst layer, so there is little deterioration of the catalyst, and the graphite particles collected on the wall of the inlet side through-hole are burned and removed, resulting in effective purification of HC and CO. There are great industrial advantages that can be achieved.

[Brief explanation of drawings]

Figure 1A is a perspective view schematically showing the outer shape of the filter of the present invention, Figure 1B is a side view showing the inlet and outlet sides of the filter, and Figure 1C is the same. A vertical cross-sectional view, FIG. 2A is an enlarged vertical cross-section for explaining the filtration action of the filter, FIG. 2B is an enlarged side view showing the inlet side or outlet side, and FIG. FIG. 3B is a sectional view showing an example of the assembled device, and FIG. DESCRIPTION OF SYMBOLS 1... Thin wall, 2... Through hole, 3... Ceramic body, 4... Inlet part, 4'... Outlet part, 5... Ceramic material for closing, 6... Inlet side, 7... Fine particles,
8...exit side, 9...inlet part, 9'...exit part,
10... Oxidation catalyst, 11... Filter body, 12... Metal case, 13... Metal wire mesh, 14... Metal holding material, 15... Diesel engine, 16... Exhaust manifold, 17... Filter in metal case body,
18...Exhaust pipe.

Claims (1)

[Claims] 1. A checker flag pattern is formed alternately on the end faces of the entrances of adjacent through holes of a honeycomb-shaped ceramic body consisting of a large number of mutually parallel through holes with polygonal cross sections partitioned by thin porous walls. On the other outlet end face, the through holes other than those closed at the inlet part are closed, and the diesel engine exhaust gas introduced from the inlet side of the honeycomb-shaped ceramic body is passed through the porous ceramic body. The fine particles contained in the ceramic body are filtered and removed when passing through the thin wall of the ceramic body, and are discharged from the outlet side of the ceramic body. An exhaust gas filter for a diesel engine characterized by supporting a catalyst.