JP2006057614A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve low pressure loss an high reducing rate by avoiding a clogging phenomenon which is possibly caused by particulate materials containing solid substances, although hydrocarbon and carbon monoxide out of harmful substances in exhaust gas from an internal combustion engine, particularly, a diesel engine, are relatively easily reduced by an effective oxidation catalyst. <P>SOLUTION: A ceramic balloon filled part supporting the oxidation catalyst is provided for combining the oxidation promoting operation of the oxidation catalyst and the burning operation of infrared rays. Ceramic balloons are well responsive to the temperature of exhaust gas to improve the effectiveness of the infrared rays. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

Detailed Description of the Invention

  The present invention relates to an exhaust gas purifying apparatus for reducing particulate matter contained in exhaust gas discharged from an internal combustion engine such as a diesel engine by oxidation.

  In order to purify particulate matter contained in exhaust gas from diesel engines etc. by oxidation, the particulate matter is burned by passing it through a porous ceramic honeycomb, metal honeycomb or wire mesh carrying an oxidation catalyst. Or a method of trapping particulate matter with a filter having fine pores and incineration at a high temperature later, or without using any oxidation catalyst, filling the filling part in the container with a ceramic sphere or short tube and exhausting the exhaust gas There is a method of spontaneously combusting the particulate matter passing by using a high temperature.

  When using a honeycomb or wire mesh carrying an oxidation catalyst, or a filter with fine pores for trapping, the exhaust gas passage is narrowed to several to several tens of microns. In many cases, clogging gradually expands due to ash containing a lot of minerals and minerals, resulting in a decrease in purification rate and an increase in pressure loss, leading to a decrease in function. Cleaning work or replacement was necessary.

  In the method of filling ceramic spheres or short tubes, the internal voids are relatively large compared to the particulate matter, so they are not easily clogged. However, in order to improve the purification rate, it is necessary to increase the filling amount. However, when the filling amount is increased, the flow path of the exhaust gas becomes longer, the fluid resistance increases and the pressure loss increases, and the purification rate and the pressure loss are in a trade-off relationship.

  In the case of a diesel engine, the flow rate of the exhaust gas flowing in the exhaust pipe is approximately square of the exhaust gas temperature in the low to middle range of the exhaust gas temperature, and is almost linearly related to the exhaust gas temperature in the middle to high range. It is a general trend to increase. On the other hand, in the case of a compressible gas, the pressure loss has a relationship that increases at about 1.7th power of the flow rate, and the flow rate of the exhaust gas has a relationship that is substantially proportional to the engine output. Further, the pressure loss generated in the exhaust gas purifying apparatus having the filling portion is more dominant due to fluid friction in the filling portion than due to the change in the shape of the flow path or the change in the direction of the exhaust gas. As a result, it can be said that the pressure loss is proportional to the approximately 3.4th power of the exhaust gas temperature in the low to mid range of the exhaust gas, and approximately 1.7th power in the mid to high range. This means that increasing the filling amount for the purpose of improving the exhaust gas purification rate or increasing the exhaust gas temperature always increases the pressure loss, which increases the combustion efficiency and engine output. Will result in a decline.

Problems to be solved by the invention

  The present invention has been made in view of the above circumstances, and the problem to be solved is an exhaust gas purifying apparatus such as a diesel engine, which does not cause clogging of the apparatus due to particulate matter and has a relatively low pressure. An object of the present invention is to provide an exhaust gas purification device that enables a high purification rate with loss.

Means for solving the problem

  The exhaust gas purification apparatus of the present invention employs the following means.

  Ceramic balloons, which are a kind of ceramic spheres, are used, and they are small and have a substantially uniform diameter. A structure in which an oxidation catalyst for particulate matter is supported on the surface of the ceramic balloon and a large number of ceramic balloons are filled in a filling portion in the container, and the particulate matter in the passing exhaust gas is oxidized and burned with residual oxygen. To do.

  The exhaust gas flowing into this container through the exhaust pipe of a diesel engine is usually at a high temperature, and the temperature changes due to load fluctuations and the like.

  The components of particulate matter contained in the exhaust gas of diesel engines vary depending on the fuel properties, engine type, operating conditions, etc., but soot is the majority and soluble organic components consisting of unburned fuel and unburned lubricating oil And a sulfate obtained by oxidizing sulfur in the fuel, and an ash derived from a mineral added to the lubricating oil in a small amount.

  In order to exert the function of the oxidation catalyst for the particulate matter, the particulate matter must first come into contact with the catalyst, and the particulate matter passing away from the ceramic balloon carrying the catalyst has no oxidizing effect. . In addition, when the exhaust gas flow rate is high, the chance of contact is reduced, so that a slower flow rate is more desirable than rectification.

  It has been reported that even in an apparatus in which only an oxidation catalyst is not used, for example, filled only with a ceramic balloon, the particulate matter is reduced by 60 to 90% depending on the running mode. Oxidation reaction in low-power running areas, such as urban driving, is caused by the fact that soluble organic components with an ignition temperature of 200 to 300 ° C. are first ignited, and the effects of high-temperature infrared rays and OH, H, O, etc. associated with combustion of hydrocarbon fuels It is believed that soot begins to ignite and burn under the action of radicals.

  In this case, the space formed by the ceramic balloons in contact with each other plays the role of an ultra-fine combustion furnace, and part of the infrared rays generated by the combustion is absorbed directly by the particulate matter, and once in the surrounding ceramic balloon Part of the infrared rays that have been absorbed and re-emitted are also absorbed by the particulate matter, which further raises the temperature rising effect. However, since the minimum ignition energy of the material that has been irradiated with infrared rays is reduced, it becomes more easily burnable. On the other hand, nitrogen and oxygen present as main components in the exhaust gas are inactive without being involved in the absorption and emission of infrared rays, so that the rise in exhaust gas temperature due to infrared rays generated by combustion is limited.

  When comparing solid ceramic spheres and ceramic balloons, if the material, shape, and dimensions are the same, the ceramic balloon is hollow and the overall specific heat is small and responsive to changes in exhaust gas temperature. Is good. Therefore, the effect is exhibited particularly in the boundary temperature region on the low temperature side of the combustion by the oxidation catalyst.

  When the driving state of a diesel engine car is about the level of urban driving, the exhaust gas temperature in the muffler section fluctuates roughly in the range of about 100 to 400 ° C, but the oxidation catalyst activity is relatively high, around 300 ° C or higher. When exhaust gas of about 300 ° C. or higher is generated, utilizing the heat without losing the machine leads to an improvement in the exhaust gas purification rate. Therefore, it can be said that a ceramic balloon with good temperature responsiveness is superior to a solid ceramic sphere.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 schematically shows the overall structure of the exhaust gas purification device.

  The high-temperature exhaust gas discharged from the engine passes through the exhaust gas inlet 2 in front of the cylindrical container 1 and passes through a number of holes opened in the rectifying plate 3, so that the flow velocity becomes substantially uniform with respect to the traveling direction. To be adjusted.

  The HC / CO oxidation catalyst 4 has an oxidation catalyst supported on a ceramic honeycomb and oxidizes hydrocarbon HC and carbon monoxide CO in the exhaust gas to form water and carbon dioxide gas. The gas temperature will rise somewhat.

  Next, the exhaust gas is directed to the balloon filling portion 7 filled with the ceramic balloon 6, and the flow is adjusted by the rectifying plate 5 with an electric heater so that the flow is equal to the balloon partition plate 8.

  The balloon filling portion 7 is filled with a ceramic balloon 6 and has a structure surrounded by a balloon partition plate 8 made of a punching plate having a number of minute holes through which exhaust gas can easily pass. In order to reduce the fluid resistance by increasing the passage area of the exhaust gas, the balloon partition plate 8 is installed in an inclined manner in the cylindrical container 1, but the present invention is limited to the installation in an inclined manner. It is not a thing.

  In the balloon filling portion 7, the particulate matter is oxidized, and the purified exhaust gas is discharged to the outside through the exhaust gas outlet 9.

  If for some reason the accumulation of particulate matter in the balloon filling section 7 causes a problem in exhaust gas discharge, electricity is supplied from an external power source to the electric heater of the rectifying plate 5 with electric heater. The accumulated particulate matter can be combusted by raising the temperature of the exhaust gas in operation in the idling state.

  FIG. 2 shows the space 11 between the balloons by enlarging the state of the filled ceramic balloon 6.

  The surface of the ceramic balloon 6 is covered with a particulate matter oxidation catalyst support layer 10, and the particulate matter contained in the exhaust gas first remains in the exhaust gas by the action of the oxidation catalyst activated by the high temperature of the exhaust gas. Combines with oxygen and burns.

  The filled ceramic balloon 6 has a spherical shape having a substantially uniform diameter. However, an inter-balloon space 11 exists between the ceramic balloons 6a, 6b, and 6c adjacent to each other, and the balloon filling portion 7 is formed. The exhaust gas flowing into the air passes through the space 11 between the balloons.

  The particle size of the particulate matter contained in the exhaust gas of diesel engines is distributed within the range of 1 to 2 microns to 10 microns, which is within the range of coarse particles, in addition to those of 1 micron or less, which are called fine particles. Not like that.

  When an exhaust gas purification device that reduces particulate matter by combustion is evaluated as a device, the evaluation items include purification rate, effective exhaust gas temperature range, pressure loss and maintainability, as well as device dimensions, noise reduction performance, and price. The removal performance of fine particles, which are said to be greatly involved in health hazards, can also be evaluated.

  The material of the ceramic balloon 6 is mainly alumina, but is not limited to this. The size is suitably 2 to 4 mm in diameter. The thickness of the shell is suitably around 0.3 mm from the viewpoints of workability, infrared characteristics, thermal shock resistance and the like. The wall thickness of the oxidation catalyst is usually 5 to 20 microns at the processing level.

  When the ceramic balloon 6 having a diameter of 3 mm is adopted, the approximate aperture ratio is 7% and the surface area is 1.4 m 2 / L. When the balloons are clogged with no gaps, the space 11 between the balloons has a shape close to an equilateral triangle having a side of about 0.85 mm, and forms a three-dimensional mesh-like flow path interconnected in the balloon filling portion 7.

  The thickness of the balloon filling portion 7 is suitably 100 to 200 mm from the balance between the purification rate and the pressure loss.

  Comparing solid ceramic spheres and ceramic balloons of the same diameter and the same material, the solid ceramic spheres have a large heat capacity, and therefore have a large tendency to level the surface temperature against fluctuations in exhaust gas temperature. That is, considering the case where the exhaust gas temperature suddenly rises, the internal temperature of the solid ceramic sphere is low, so that the action to prevent the surface temperature from rising works. It will take more time.

  In the cylindrical container 1, the space from the exhaust gas inlet 2 to the balloon filling part 7 has a function of temporarily accumulating exhaust gas pulsating the diesel engine and equalizing the pressure. Since the exhaust gas loses kinetic energy in the process of passing through the space 11 between the balloons several times, a silencing effect is obtained.

  In the case of a ceramic balloon having a diameter of 3 mm in the balloon filling portion 7, an exhaust gas flow path having a branch shape and a shape close to an equilateral triangle having a side of about 0.85 mm, that is, 850 microns is continued. It can be said that particulate matter having a diameter of about 10 microns can easily pass through and is not in a state of accumulation. As a result, it is possible to realize an exhaust gas purifying apparatus which is free from clogging at a fine portion seen in a honeycomb wall penetration type or wire mesh type particulate matter filter and has excellent maintainability.

  Although pressure loss due to fluid resistance generated in the balloon filling portion 7 is inevitable, the oxidation reaction is promoted by supporting the oxidation catalyst on the ceramic balloon 6, and the flow of the balloon filling portion 7 is less than that when the oxidation catalyst is not used. The thickness in the road direction can be reduced, and the pressure loss can be reduced. As a result, the output reduction in the high output range of the diesel engine can be minimized, and the deterioration of the fuel consumption in the entire operation range can be suppressed to the minimum.

  In addition to the method of filling the whole amount with a ceramic balloon carrying an oxidation catalyst having a substantially uniform diameter in the balloon filling portion 7, the surface area per volume of the ceramic balloon is increased and the space 11 between the balloons is narrowed to reduce the amount of particulate matter. A method of partially using ceramic balloons with a smaller diameter of an oxidation catalyst supported for the purpose of increasing combustion efficiency, etc., and further supporting the oxidation catalyst partially due to processing restrictions on the ceramic balloon. The method of using a type ceramic sphere is also within the scope of the present invention.

  It is one method to attach a heat insulating material to the inner surface of the cylindrical container 1 for the main purpose of minimizing heat dissipation from the surface of the cylindrical container 1 and maintaining the internal temperature as much as possible.

The invention's effect

  As described above, the exhaust gas purifying apparatus of the present invention can remove hydrocarbons, carbon monoxide and particulate matter discharged from a diesel engine, and at the same time have a silencing function.

  By supporting the oxidation catalyst for particulate matter on the ceramic balloon, it becomes possible to react sensitively and exhibit the oxidation function when the exhaust gas temperature rises from a low temperature and reaches the active region of the catalyst. Thus, it can be a maintenance-free and relatively low pressure loss purification device.

  Furthermore, the exhaust gas purifying apparatus according to the present invention has the potential as an apparatus that can efficiently remove fine particles having a particle size of 2.5 microns or less, which are the main cause of human health damage, by combustion. is doing.

  That is, the smaller the particle size passing through the space between the ceramic balloons without contacting the oxidation catalyst, the smaller the particle size, the more receiving the radicals and the infrared rays emitted from the surrounding ceramic balloons or other particulate matter during combustion. This is because it can be easily burned.

Cross-sectional view of the structure of an exhaust gas purifying apparatus according to the present invention Sectional view showing the space between balloons

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical container 2 Exhaust gas inlet 3 Rectifier plate 4 HC / CO oxidation catalyst 5 Rectifier plates 6, 6a, 6b, 6c with electric heater Ceramic balloon 7 Balloon filling part 8 Balloon partition plate 9 Exhaust gas outlet 10 Particulate matter oxidation Catalyst support layer 11 Space between balloons

Claims (1)

An internal combustion engine such as a diesel engine having a space partitioned by a punching plate or a metal mesh in a cylindrical container, and the total amount of the filler in the space or a part thereof is a ceramic balloon carrying an oxidation catalyst Exhaust gas purification device for engines.

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