DE4021033A1 - Exhaust cleaner for IC engine of motor vehicle - has porous silicon-carbide filter in thermally insulating mounting for burning off carbon deposits - Google Patents

Abstract

The exhaust gases are ducted through a special filter composed of porous silicon carbide (5) to remove carbon particles and unburnt fuel. The filter is surrounded by a shell of thermal insulation, with openings fore and aft for the flow and mounted inside a housing. The good thermal conductivity of the silicon carbide ensures rapid burn of the carbon when the integral electric heating element is powered. The heating can be by direct electric element, microwave heating or hot gas heating. The filter element has a pore size 20 to 30 microns and a density of 1.7 to 1.9 gm/sq.cm. The filter size has a diameter to length ratio of 5 to 70, and a surface area to volume ratio of 0.2 to 0.5. ADVANTAGE - Rapid carbon reduction, minimal thermal losses.

Description

The invention relates to an exhaust gas purification device, the Exhaust gases from an internal combustion engine, such as. B. a diesel engine, cleans.

For cleaning an exhaust gas, e.g. B. from a diesel engine according to the prior art, a filter made of a cordierite to a honeycomb structure filter and one on the filter component with the exhaust gas Connected to the exhaust side of the diesel engine, and the carbon, NOx and HC, etc. in the exhaust gas are oxidized by means of the Filters decomposed.

Because the filter of the above filter device Cordierite with a low melting point (1200 to 1300 ° C) is formed, and during the regeneration treatment for Removal of carbon present in the filter if the Carbon is ignited at one end of the filter and then air through the filter from the inflamed side is fed, a non-uniform combustion of the Exhaust gas occurs, causing a local temperature increase causes the problem that arises with a repeated filter regeneration treatment Decomposition is damaged, causing its reuse becomes impossible.  

It is already to solve the above problem been proposed as a sintered filter material Use silicon carbide, which is excellent Has heat resistance and thermal conductivity. Because the Thermal conductivity of the material is too high in this Trap with sintered silicon carbide filters Heat sources used in the prior art, and the z. B. hot air from the exhaust gas of the engine or a electric heater, not sufficient on one high temperature, causing the Regeneration treatment becomes impossible or incomplete. In short, effective regeneration is one Heat source with larger capacity required, and in the case an electric heater becomes a heater with large Dimensions are used, or there is a current flow for a long time Time required. In this case, problems occurred like shortening the battery life for that Heater and causing higher costs.

If the regeneration treatment using a Large capacity heat source is carried out Temperature distribution also within the above mentioned filter caused, whereby cracks formed when the regeneration treatment is repeated is performed, and the filter as a whole is replaced by the Cracks destroyed, resulting in no solution to the above Problem leads.

There have been experiments on the heat balance of the sintered Silicon carbide produced filters at the Regeneration treatment performed, and found that the heat content required to heat the filter itself and the exhaust gas flowing through the filter lost heat content is relatively low, but one considerable heat content in the direction of the filter diameter  is transmitted, namely to that on the outer periphery of the filter located housing, which shows that the Heat loss through the use of an insulating layer between the filter and the housing can be prevented extremely effectively can.

The present invention has been made in view of the above the situation described, and their task is to provide an exhaust gas purification device that the one with the during the regeneration treatment with the Prevent heat conduction associated with filter loss can, is stable and complete regeneration enables, and one by the formation of cracks as a result the temperature difference between certain parts of the filter prevents destruction of the filter, and which has improved durability.

To solve the above task According to the invention, a housing is provided which with a Exhaust outlet side of an internal combustion engine connected passage is equipped, a filter that is in a honeycomb-like Sintered porous silicon carbide structure is formed, and with an insulating layer between the filter and the inner wall of the above Passage is arranged. By taking advantage of the effective A filter can use heat resistance of silicon carbide excellent heat resistance. It can also heat transfer between the outside Peripheral part of the filter and the housing through the Insulation layer can be prevented from the outset To prevent heat radiation from the filter, while heating to a temperature that is satisfactory Regeneration treatment using conventional ones Heat sources enables, can be effected, and yet the Heat transfer within the filter can be effected quickly  can to complete regeneration within a to allow extremely short time. Furthermore, the Temperature difference between the two end parts of the filter can be made smaller, whereby one by thermal Damage caused to the filter is prevented and also damage (defects, Jumping off, chipping and abrasion) by mechanical Shocks, etc. can be prevented.

The subject of the present invention is therefore a Exhaust gas purification device according to claim 1.

Appropriate embodiments of an inventive Exhaust gas cleaning device are the subject of claims 2 to 12.

Brief description of the drawings

Fig. 1 illustrates, in a partial sectional view of an exhaust gas purifying device of the invention. Figs. 2 is a sectional view of a filter. FIG. 3 is a plan view of the filter. FIG. 4 is a partially sectional view showing a part of the exhaust gas purifying apparatus according to the modified Example 1. The Fig. 5 is a partial sectional view according to the modified example 2. Fig. 6 and Fig. 7 are other embodiments of the invention.

The above-mentioned insulating layer should be more desirable Way of an inorganic or organic insulating material be formed, or from an air layer. As inorganic Insulating materials can e.g. B. can be used: Alumina silicate ceramic fibers, alumina fibers, Zirconium oxide fibers, silicon dioxide fibers, mineral wool, asbestos etc., and as organic insulating materials such. B.  Moldings made of fibers, such as. B. nylon, kevlar, etc., or foams, such as. B. urethanes, etc., or combinations from that. Preferably, in part or in total inorganic fibers used.

The thickness of the above insulating layer should be desirably 3/14 to 5/7 of the outer diameter of the Filters amount. If the thickness of the insulating layer is less than 3/14, the insulating effect is lowered, whereby the Temperature difference between certain parts of the filter is increased. If the thickness is greater than 5/7, the Device enlarged as a whole and is thus in the Difficult to handle.

If an air layer is provided as an insulating layer, it is desirable to use different insulating materials like them are mentioned above, or necessary connecting parts as Use support elements that attach both ends of the filter to the Support the housing. For such support elements, especially for Maintaining the tightness of the insulating air layer, are insulating materials that expand when heated, e.g. B. from vermiculite, inorganic fibers, organic fibers and inorganic binders layer materials in terms of excellent elasticity, Heat resistance, etc. more effective. If an air layer than Insulation layer is used, it is also effective Air convection by dividing the air layer with some Partitions to prevent heat conduction through Convection heat transfer within the air layer too prevent.

The present invention will now be described in more detail with reference to the drawings. As shown in Fig. 1, the exhaust gas purification device 1 is equipped with a housing 2 of a metal funnel tube, and the passage 2 a of the housing 2 is connected to the exhaust gas outlet pipe Ea of an internal combustion engine E. Within the housing 2, a filter 5 is disposed for cleaning the exhaust gas, and between the filter 5 and the inner wall of the passage 2a of the casing 2 is formed an insulating layer. 4

The porous sintered used in the present invention Silicon dioxide carbide material preferably has a density of 1.7 to 1.9. The average pore size of the sintered material is preferably within the range of 20 to 30 µm (measured with a porosimeter). If the average pore size is smaller than 20 µm, the pressure loss becomes larger, while if it exceeds 30 µm, the strength and the Interception properties of the sintered material reduced will. The porosity of the sintered material lies preferably at 40 to 60%. A porosity of less than 40% gives an increase in pressure loss, while one Porosity greater than 60% decrease in strength results.

The value of the outer wall surface (cm ² ) / volume (cm ³ ) of the filter according to the invention is preferably within the range from 0.2 to 0.5. If this value is less than 0.2, the outer diameter of the filter becomes too large to be used as a device. If the value exceeds 0.5, the outer diameter becomes smaller and the longitudinal expansion of the filter becomes longer, which can lead to breakage when heated.

The value of the cross section / length of the filter according to the invention is preferably within the range of 5 to 70. If the value is less than 5, the longitudinal extension becomes longer, whereby the filter tends to break when heated. If if the value exceeds 70, the diameter of the filter becomes great to be used as a device.  

As shown in Fig. 2 and Fig. 3, the filter 5 is formed with a porous sintered silicon carbide material with a high melting point (less than 3000 ° C) in a honeycomb structure and has an overall columnar shape. A large number of gas passage pores 6 are formed in the filter 5 , which extend parallel to the longitudinal axis, and are alternately closed with small strips 7 of silicon carbide material at one end of the feed side and the exhaust gas outlet side of the corresponding gas passage pores 6 . Silica films can also be formed on the inner wall surfaces of the corresponding gas passage pores 6 of the filter 5 , and an oxidation catalyst comprising a platinum group element or other metal elements and oxides thereof, etc. can be supported by the silicon dioxide films. As the shape of the filter according to the invention, the shape of a column, an ellipsoidal column and a polygonal column are preferred.

The thickness of the above-mentioned insulating layer 4 is set at 3/14 to 5/7 of the outer diameter of the filter 5 . More specifically, when the filter 5 has a diameter of 144 mm, the thickness of the insulating layer 4 is about 3 to 10 cm. On the exhaust gas outlet side of the filter 5 , a ceramic heater 8 for regeneration is also mounted in the housing 2 . In another embodiment, the thickness of the insulating layer is preferably not less than 15 mm.

When the exhaust gas from the internal combustion engine E is introduced into the filter 5 from the feed side of the housing 2 , as shown by the arrow in Fig. 1 and Fig. 2, carbon (soot), hydrocarbons, etc. in the exhaust gas are caused by a Filtered wall part of the gas passage pores 6 , and also oxidized with the oxidation catalyst. The cleaned exhaust gas is then discharged from the filter 5 .

When the regeneration treatment of the filter 5 is carried out in the manner described above, when a certain amount of carbon is left in the filter 5 , the heating of the filter 5 with the ceramic heater 8 is started. When the temperature of the filter 5 in the vicinity of the heating device has reached a certain temperature (300 to 800 ° C.), the feeding of additional air into the housing 2 is started to promote combustion. By continuing this treatment, the carbon in the filter 5 is burned to regenerate the filter 5 .

Because the insulating layer 4 is formed between the filter 5 and the inner wall part of the housing 2 , the heat radiation from the peripheral part of the filter 5 can be prevented according to the invention, whereby the temperature suitable for regeneration can be reached within a short time, and also the total Temperature becomes more uniform, which allows the regeneration treatment to proceed in a short time. In addition, thermal energy can be saved to increase the temperature for regeneration. In addition, the temperature between the two end parts of the filter 5 can be kept low. The proportion of the cracks formed in the filter 5 caused by a partial temperature difference can be kept lower, as a result of which the number of regeneration treatments can be increased and the durability can be improved.

According to the heating device for regeneration on End part of the filter may be provided. In such a case the heater should preferably cover the entire area of the Cover and heat the end part of the filter to make it sufficient  heat, and should preferably be at a distance of 1 up to 2 mm, so that the heating device is not in comes in direct contact with the filter. In this case, the Heater on either the upstream or the provided downstream side of the exhaust passage be. However, if the heater is on one more upstream point than the filter is provided soot will easily stick to the heater, causing too Damage to the heating device. Therefore, the Heating device preferably on the downstream Page may be provided.

Heating devices in the device according to the invention are applicable, in addition to the above called ceramic heater a microwave heater, a high temperature gas heating above 650 ° C, a direct one electrical heating, etc. The microwave heating can uniform heating, and in this way it can Occurrence of cracks due to a thermal Stress can be prevented. The high temperature gas heater can cause a uniform heating and also to a Perform regeneration in a short time. The High temperature gas heating can be done using exhaust gas be performed.

In one embodiment according to the invention, the Heater for regeneration around the filter be provided. For example, a linear ceramic Heating device for regeneration treatment around the filter be wound, and preferably the distance between the Turns compared to the inlet side of the filter are smaller closer to the gas outlet side of the filter, d. H. the Then turns become denser. In this case it is Heating device embedded in the insulating material to a Training heater in which the  Heat transfer loss is reduced and the thermal Efficiency is improved. In making the above Device are on the two peripheral ends of the filter Sealing or buffer materials with a width of 5 to 10 mm and a thickness of 2 mm, and the insulating material, in where the heater is embedded is around the filter attached by means of sealing or buffer materials.

Examples and comparative examples relating to the regeneration treatment of the filter 5 are described below.

example 1

Filter 5 was one with a diameter of 140 mm, a length of 50 mm and a thermal conductivity of 40 to 70 Kcal / m. hr. ° C and a specific heat of 0.23 Kcal / kg. ° C is used. The thickness of the partition between the corresponding gas passage pores 6 in the filter 5 was 0.43 mm, and the corresponding gas passage pores 6 were formed in a number of 170 per square inch (170/6452 cm ² ). A ceramic fiber with a thickness of 60 mm and a thermal conductivity of 0.2 Kcal / m was used as the material for the insulating layer 4 . hr. ° C used. For the ceramic heater for regeneration treatment, a heater with 12 V - 2.5 KW was used.

After connecting the exhaust gas purification device 1 as described above to the internal combustion engine E, as shown in FIG. 1, the internal combustion engine E was operated and the carbon was collected in the exhaust gas. During the collecting process, the pressure inside the exhaust gas outlet pipe Ea was monitored by a control device C via a pressure sensor Ps and a piezoelectric element Pe, and the collecting process was continued until the pressure reached a constant value (0.17 kg / cm ² ). At this time, the flow rate of the exhaust gas was 50 l / sec, and the time to reach the above constant pressure was about 40 minutes. To calculate the amount of carbon collected during this period, the volume of the filter 5 was made equal to the total amount of the gas permeable pores, and the amount of carbon retained was determined based on the change in weight before and after the collection treatment. As a result, the amount of carbon collected was 15 g / l.

Thereafter, the switch S was closed by the above-mentioned control device C to start the passage of current through the heater 8 . 3 minutes later, the compressor Co was then put into operation and additional air from the air inlet pipe Ca was fed into the filter 5 at a speed of 50 l / min. Using a thermocouple, the temperatures T 1 , T 2 and T 3 at the positions P 1 , which was 1 mm away from the heater 8 toward the gas outlet side (right side of FIG. 1), were at the central position P 2 in FIG Monitored longitudinal axis or at position P 3 on the central axis of the filter 5 on the gas intake side.

At the start of the feed of the additional air, the temperature T 1 at position P 1 was approximately 750 ° C. Since the temperature T 3 at the position P 3 of the gas receiving end dropped abruptly when the carbon combustion ended, the time from the start of the current passage through the heater 8 to the time of the temperature drop was equated with the regeneration time. As a result, the regeneration time was 15 minutes.

The regeneration treatment described above was repeated until the filter 5 broke . The results are shown in Table 1. In addition, the maximum temperature differences at the positions P 1 and P 3 at both ends of the filter 5 are given together.

Comparative Example 1

The same test as in Example 1 above was carried out carried out with the exception that the Flow rate of the air was set so that the temperature of the filter in an exhaust gas purification device of the conventional type with a cordierite filter with a size of 196 mm diameter and 196 mm length and a pair of ceramic heaters for the Regeneration treatment (12 V-3 KW × 2) without any Insulating layer was equipped, did not exceed 1000 ° C. The Results are shown in Table 1.

From the results of Table 1, it can be seen that in the filter of Comparative Example 1, approximately 3 times the regeneration time of Example 1 was required to burn the carbon, and the amount collected was also less than that of filter 5 of Example 1 (1st / 3 of example 1). Therefore, the time to burn the carbon after collecting the same amount of carbon as in Example 1 can be estimated to be 9 times that of the example, and it is clear that the carbon in the filter 5 of Example 1 is burned efficiently. On the other hand, the number of regenerations until breakage is lower in comparison to example 1, and it can be seen from this that the filter 5 according to the invention has excellent durability.

Comparative Example 2

In an exhaust gas purification device of the conventional type, which with a filter made of porous silicon carbide with the same size as in example 1 and a ceramic Heating device for regeneration treatment (12 V-2.5 KW) and was equipped with no insulation layer, the same Regeneration treatment as carried out in Example 1. The Results are shown in Table 1.

Because the exhaust gas purification device of Comparative Example 2 is not provided with an insulating layer, and also the Thermal conductivity of the filter is excellent No heat radiation from the peripheral parts of the filter can be prevented, thereby not only collecting the Carbon and the time required Regeneration treatment time can be increased, but also the maximum temperature difference in the filter becomes larger. Furthermore is also the number of regeneration treatments compared for example much lower, from which it can be seen that the Filters the example of excellent durability owns.  

Table 1

Modified example 1

As shown in FIG. 4, the filter 5 is supported in the housing 2 by the insulating material 14 when the insulating layer is an air layer 4 , using a filter 5 with the same structure as in Example 1 and applying the same insulating material 14 as in the previous example between both ends thereof and the case 2 . Even with such a construction, the same results of the regeneration treatment as in Example 1 are obtained.

Modified example 2

As shown in Fig. 5, partitions were made within the air layer between the housing and the filter 5 using a thermally expandable insulating material with 0.1 Kcal / m. hr. ° C arranged. As a result of the regeneration treatment of this example, the regeneration treatment time was 13 minutes to obtain an air insulation layer effect comparable to that of Comparative Example 2.

FIGS. 6 and 7 are other embodiments of the invention. In Fig. 6, 15 denotes a heater for regeneration, and 16 is a fabric for shielding radiant heat. In Fig. 7, 17 is a material reflecting the radiant heat.

As described in detail above, it is possible, according to the invention, the temperature difference between certain parts of the filter during the Regeneration treatment compared to the prior art to make extraordinarily small, reducing the scale of jumps caused by such a temperature difference less and the durability of the filter is improved. In addition, heat radiation from the filter can be prevented the time required for regeneration is shortened, and thus the degree of heat utilization is increased.

Claims (12)

1. An exhaust gas purification device comprising:
a housing ( 2 ) which is provided with a passage ( 2 a) which communicates with the exhaust gas outlet side of an internal combustion engine (E);
a filter ( 5 ) which is formed from a porous sintered silicon carbide in a honeycomb structure and is arranged within the passage ( 2 a); and
an insulating layer ( 4 ) which is arranged between the filter ( 5 ) and the inner wall of the passage ( 2 a). 2. Emission control device according to claim 1, characterized in that the insulating layer ( 4 ) is formed from at least one of an inorganic insulating material and an organic insulating material. 3. Exhaust gas purification device according to claim 2, characterized in that the thickness of the insulating layer ( 4 ) is 3/14 to 5/7 of the outer diameter of the filter ( 5 ). 4. Exhaust gas purification device according to claim 1, characterized in that the insulating layer 4 is formed as an air layer. 5. An exhaust gas purification device comprising a filter that a porous sintered silicon carbide product in the form of a Column, ellipsoidal column or polygonal column, and the course of an insulating layer within the housing an exhaust pipe is attached. 6. Exhaust gas purification device according to claim 5, characterized characterized in that the filter is in a honeycomb structure is trained.   7. Exhaust gas purification device according to claim 5, characterized in that the porous silicon carbide has a density of 1.7 to 1.9 g / cm ³ and an average pore size of 20 to 30 µm. 8. Exhaust gas purification device according to claim 5, characterized characterized in that the value of outer wall area / volume of the Filters is 0.2 to 0.5. 9. Exhaust gas purification device according to claim 5, characterized characterized that the filter has a value Has cross-sectional area / length from 5 to 70. 10. Emission control device according to claim 5, characterized characterized in that the filter comprises a heating device, which are provided on a peripheral part thereof. 11. Emission control device according to claim 5, characterized characterized in that the filter comprises a heating device, which is provided on its gas supply side. 12. Exhaust gas purification device according to claim 5, characterized characterized in that the device further comprises at least one Heater comprises selected from the group consisting from a ceramic heating device, a microwave Heating, a high temperature gas heating above 650 ° C, one direct electric heating.