JP2006226149A - Intake element control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intake element control device of an internal combustion engine capable of reducing the occurrence of NOx by recovering steam only in exhaust gas to be mixed into intake air to lower the combustion temperature of fuel. <P>SOLUTION: A honeycomb structure H in which a zeolite film penetrates steam f in exhaust gas g to be separated is formed integrally with the base material surface is provided as an element separating means 18 which is interposed in an EGR pipe 16 and which separates a prescribed element in exhaust gas g. Cordierite is preferably used as the base material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an intake component control device for controlling a component of exhaust gas to be returned to intake air in an exhaust gas circulation device of an internal combustion engine such as a diesel engine.

  At present, nitrogen oxides (hereinafter referred to as NOx), dust, hydrocarbons, and the like emitted from automobiles and stationary internal combustion engines are problematic as environmental pollutants.

  NOx is generated when the combustion temperature exceeds 1800K due to rapid heat generation in the operating region where the local equivalence ratio is low in the fuel spray, which is a heterogeneous gas mixture. Therefore, NOx can be reduced by lowering the temperature of the combustion chamber.

  For this reason, in an exhaust gas recirculation (EGR) device that recirculates exhaust gas to the intake air of an internal combustion engine, an exhaust gas recirculation device that separates and circulates only useful components in the recirculated exhaust gas has been proposed (patent) Reference 1).

  The prior art disclosed in Patent Document 1 includes an EGR pipe that constitutes a flow path for circulating a part of exhaust gas to an intake pipe, a gas separation section that is provided in the EGR pipe and includes a gas separation membrane, and EGR And an exhaust gas recirculation device for an internal combustion engine, wherein the gas separation membrane is a carbon dioxide enriched membrane, a hydrogen enriched membrane, or an oxygen enriched membrane. The gas separation membrane enriches the water vapor, carbon dioxide, oxygen, etc. in the exhaust gas, and recirculates this enriched gas to suppress the decrease in oxygen concentration, and the complete combustion of the fuel prevents the generation of soot and hydrocarbons. It is said that NOx can be reduced by lowering the temperature of the combustion chamber by preventing discharge or absorbing heat generated by combustion with carbon dioxide or water vapor having a large specific heat, which is an enriched gas.

However, non-porous polymer membranes manufactured with materials such as silicone rubber, poly, polysulfone, and polyamide, which are exemplified as gas separation membranes, have problems with heat resistance because the exhaust gas temperature is high. Thus, stable component separation characteristics cannot be maintained over a long period of time.
JP-A-6-207560

  The present invention has been made in order to solve the above-described problems. Only the water vapor in the exhaust gas is recovered and mixed with the intake air, so that the combustion temperature of the fuel is lowered and NOx is generated. It is an object of the present invention to provide an intake component control device for an internal combustion engine that can be reduced.

  An intake component control apparatus according to the present invention includes an EGR pipe that is connected to an intake pipe and an exhaust pipe of an internal combustion engine and forms a flow path for circulating a part of the exhaust gas of the internal combustion engine to the intake pipe, and is interposed in the EGR pipe. Intake component control apparatus for controlling an intake component of an internal combustion engine, comprising component separation means for separating a predetermined component in the exhaust gas, and differential pressure generating means for introducing the exhaust gas to the component separation means interposed in the EGR pipe The component separation means includes a zeolite membrane that permeates and separates water vapor in the exhaust gas.

  The intake component control apparatus of the present invention includes a zeolite membrane as component separation means. Since the zeolite membrane has high heat resistance, water vapor in the exhaust gas can be stably separated even in high-temperature exhaust gas. And by mixing water vapor into the intake air of the internal combustion engine, the combustion temperature of the fuel in the combustion chamber can be lowered and the generation of NOx can be suppressed.

  In the intake component control apparatus of the present invention, the component separation means is preferably a honeycomb structure in which a zeolite membrane is integrally formed on the substrate surface.

  By separating the component into a honeycomb structure in which a zeolite membrane is integrally formed on the substrate surface, the water vapor separation area can be increased.

  In addition, in such a honeycomb structure, it is desirable that the opening portions of the cells having the sealing portion on one end side and the opening portion on the other end side and the sealing portions are arranged in parallel so as to be alternately adjacent. By adopting such a cell structure, the area of the separation membrane can be increased, and free circulation of the exhaust gas can be prevented to improve the separation efficiency of water vapor in the exhaust gas.

  The cell density of the honeycomb structure as described above is preferably 400 to 900 / inch 2 (62 to 140 / cm 2). By setting the cell density of the honeycomb structure within the above range, the component separating means can be made compact and highly efficient.

  In the intake component control apparatus of the present invention, it is desirable that the zeolite membrane of the component separation means has pores having a pore diameter of 0.26 to 0.5 nm. A zeolite membrane is a molecular sieve, and a molecular sieve having a pore size in this range allows only water vapor in the exhaust gas to permeate, but not oxygen molecules or nitrogen molecules. Therefore, only the water vapor in the exhaust can be separated efficiently.

  The base material of the honeycomb structure is preferably a porous body having through holes having a diameter of 0.1 to 50 μm. By setting the through-hole diameter of the base material within this range, the strength of the base material can be secured, and water vapor can be effectively separated without increasing the capacity of the differential pressure means.

  Here, the porous body is preferably a ceramic. Ceramics have high heat resistance and high strength, and can support the zeolite membrane stably even in high-temperature exhaust gas. Further, since it is porous, water vapor separated by the zeolite membrane can be easily permeated.

  The ceramic is preferably cordierite. Cordierite is suitable as a base material for zeolite membrane because it is excellent in moldability and strength, has good affinity with the zeolite membrane, and is inexpensive.

  In the intake component control apparatus of the present invention, the EGR pipe has a first flow path for exhaust gas to circulate to the intake pipe via the component separation means, and a second flow to circulate to the intake pipe by bypassing the component separation means. It is desirable to provide a road.

  In the intake component control apparatus of such an aspect, the exhaust gas component mixed in the intake air is adjusted by switching the exhaust gas flow path to the first flow path or the second flow path in accordance with the operating state of the internal combustion engine. Therefore, the combustion temperature of the fuel can be controlled more effectively, and the generation of NOx can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a system configuration of an intake component control device in a diesel engine according to a first embodiment of the present invention.

  The intake component control device 1 includes an EGR pipe 16 that communicates the exhaust pipe 14 and the intake pipe 12 of the engine E and circulates a part g of the exhaust gas G. The EGR pipe 16 has an upstream of the exhaust gas g. The component separation means 18 for separating predetermined components in the exhaust gas sequentially, the pump 20 as the differential pressure generating means for introducing the exhaust gas g into the component separation means 18 and circulating it, and the control for controlling the EGR amount to the intake air A And a valve 22.

  In the present embodiment, the component separation means 18 is a honeycomb structure H in which a zeolite membrane that permeates and separates water vapor in the exhaust gas is integrally formed on the surface of the substrate, and introduces exhaust gas into the EGR pipe 16. The honeycomb structure H, the pump 20, and the control valve 22 are arranged in this order from the section toward the downstream direction. In the figure, 11 is an intake valve, 13 is a fuel injector, 15 is an exhaust valve, 17 is a cylinder, and 19 is a piston.

  The honeycomb structure H is obtained by integrally forming an outer shell 24 and a large number of cells 26 as shown in FIG. FIG. 2 (b) schematically shows a partial cross section in the axial direction of the honeycomb structure H. Each cell 26 formed in a honeycomb shape is sealed at one end and opened at the other end. As it is, on the end face X of the honeycomb structure H (FIG. 2A), the sealing portions 28 (■) and the opening portions 30 (□) of the cells 26 are alternately arranged in a staggered manner. Yes. That is, the honeycomb structure H is formed so as to prevent free flow of exhaust gas from the one end X side to the other end X ′ side of the honeycomb structure H by the sealing portion 28 of each cell 26.

  As shown in FIG. 2 (c), the cells 26 of the honeycomb structure H can have an appropriate shape such as a square (A), a hexagon (A), and a triangle (U). The cell density is preferably 400 to 900 cells / inch 2 (62 to 140 cells / cm 2). If the cell density is less than 400 cells / inch2, the water vapor separation area is insufficient, and if it exceeds 900 cells / inch2, the pressure loss of the exhaust gas increases, which is not preferable. More preferably, it is 400-600 pieces / inch2 (62-93 pieces / cm2).

  In such a honeycomb structure H, it is desirable that the thickness of the cell partition wall 32 separating the cells 26 is 0.05 to 1.0 mm. If the thickness of the cell partition wall 32 is less than 0.05 mm, the strength is insufficient. If the thickness of the cell partition wall 32 exceeds 1.0 mm, the pump 20 having a large driving pressure is required, which is not appropriate. More preferably, it is 0.1-0.5 mm.

  As shown in FIG. 2B, a separation membrane 34 that selectively permeates and separates the water vapor H 2 O in the exhaust gas g is formed on the surface of the partition walls 32 of the honeycomb structure H (hereinafter referred to as partition walls). It may be formed integrally with 32. The separation membrane 34 is formed on the upstream side of the partition wall 32 with respect to the flow of the exhaust gas g, and the water vapor H2O that has permeated through the separation membrane 34 passes through the pores of the partition wall made of a porous base material. Enriched downstream.

  The separation membrane 34 is not particularly limited as long as it can separate water vapor from high-temperature exhaust gas, but a molecular sieve membrane made of a zeolitic material is suitable. Zeolite is a crystalline inorganic oxide having a pore size of molecular size, and gas components having different molecular sizes can be selected by selecting the pore size.

  FIG. 3 schematically shows how the water vapor H 2 O in the exhaust gas is separated by the molecular sieve membrane 34 of zeolite. In the exhaust gas, many gas components such as oxygen O 2, nitrogen N 2, carbon dioxide CO 2, water vapor H 2 O, or hydrocarbon CnHm are mixed. However, these gas components have different sizes at the molecular level, and as is well known, the molecular diameter is larger in the order of water vapor <carbon dioxide <oxygen <nitrogen <hydrocarbon. The molecular diameter of water vapor is about 0.26 nm and that of carbon dioxide is 0.33 nm. Therefore, by making the pore size of the molecular sieve film 34 larger than the molecular diameter of water vapor and smaller than the molecular diameter of carbon dioxide, only the water vapor can be transmitted and separated from other gas components. In consideration of the water vapor transmission efficiency and the like, specifically, the pore size (opening) of the molecular sieve film 34 is desirably 0.26 to 0.5 nm, more preferably 0.26 to 0.32 nm. is there.

  The thickness of the zeolite membrane 34 is desirably 0.1 to 100 μm. If the film thickness is less than 0.1 μm, defects such as insufficient strength and pinholes may occur, and if it exceeds 100 μm, the pressure difference for permeation increases and is not suitable. More preferably, it is 1-50 micrometers.

  As described above, only the water vapor in the exhaust gas can be separated and mixed into the intake air by the separation membrane 34 integrally formed on the surface of the porous substrate 32. Therefore, the base material 32 is desirably a porous body that does not inhibit the permeability of the separation membrane 34.

  The material of such a porous body is not particularly limited, and ceramics such as metals and metal oxides, carbon, and organic polymers can be used. However, from the viewpoint of strength and rigidity, ceramics such as metals and metal oxides, metal nitrides, and metal carbides are preferable. Furthermore, considering that the difference in coefficient of thermal expansion from the zeolite membrane is small or that the affinity is high, the sintered metal made of stainless steel as the metal, alumina, zirconia, silica, mullite, cordierite as the metal oxide , Titania, zeolite or zeolite analogues are preferred. Among these, cordierite, which is a porous ceramic, has good formability, and can easily obtain desired air permeability (pore diameter, hole density, etc.) and strength by blending raw materials and firing methods. Is preferred. The average through-hole diameter of such a porous body is preferably 100 μm or less, and more preferably 0.1 to 50 μm.

  In the present embodiment, the differential pressure generating means 20 is disposed on the downstream side of the honeycomb structure H, and introduces exhaust gas into the honeycomb structure H by reducing the pressure inside the EGR pipe. The differential pressure generating means is not particularly limited, and a normal vacuum pump or blower can be used. As shown in FIG. 4, the amount of water vapor V separated by the separation membrane increases in proportion to the pressure P of the pump that is the differential pressure generating means. Therefore, in the intake component control apparatus 10 having the honeycomb structure H of FIG. 1, the amount of water vapor mixed into the intake air can be changed by changing the exhaust pressure of the pump 20. That is, the intake component can be controlled by controlling the pump pressure.

  In the present embodiment, the control valve 22 is an on-off valve that selects the supply of water vapor to the intake air, and a known electromagnetic valve or the like can be used. That is, when the control device such as the ECU determines that the operation state of the internal combustion engine is in the NOx generation region, the control valve 22 is opened and water vapor is mixed into the intake air. Combustion temperature can be lowered by mixing water vapor into the intake air, and generation of NOx can be suppressed. When the operating state of the internal combustion engine is outside the NOx generation region, the control valve 22 is “closed” and exhaust gas recirculation (EGR) is stopped. By not performing EGR, the fuel efficiency of the internal combustion engine can be increased, and complete combustion can be promoted to suppress the generation of soot and hydrocarbons.

  In the second embodiment of the present invention, the EGR pipe that circulates a part of the exhaust gas from the exhaust pipe to the intake pipe bypasses the first flow path interposing the component separation means and the component separation means. 2 flow paths.

  FIG. 5 shows a system overview of the second embodiment. In addition, the same code | symbol is attached | subjected about the part similar to FIG. 1, and description is abbreviate | omitted.

  In the intake component control apparatus 2 of the present embodiment, the differential pressure generating means (pump) 20, the component separating means (honeycomb structure H) 18, and the first control are sequentially provided in the first flow path 16 a from the upstream side of the exhaust gas g. A valve 22a is disposed, and a second flow path 16b is provided in parallel with the first flow path 16a. The second flow path 16b is provided with a second control valve 22b, which can be opened and closed by a control device (not shown) in the same manner as the first control valve 22a.

  In the intake component control apparatus 2 configured as described above, the exhaust gas g is controlled by driving the pump 20 to introduce the exhaust gas g into the EGR pipe 16 and controlling the opening and closing of the control valve 22a and the control valve 22b. Can be selected to flow into the first flow path 16a or the second flow path 16b. For example, if the control valve 22b is “closed”, it functions as the intake component control device 1 similar to FIG. 1, and if the control valve 22a is “closed” and the control valve 22b is “open”, the exhaust gas g It can function as a normal EGR device that circulates as it is. Therefore, the generation of NOx can be more effectively suppressed by selecting the flow path of the exhaust gas g according to the operating state of the internal combustion engine by a control device such as an ECU.

  Next, an outline of control in the intake component control device 2 of the second embodiment will be described with reference to the flowchart of FIG.

  First, in step S1, the driver rotates the key to start the engine E. The control means (hereinafter referred to as ECU) measures the operating state of the engine using various sensors and instruments (step S2).

  The ECU determines whether the engine operating condition is a condition for generating NOx based on the obtained measurement value (step S3). If the ECU determines that the condition is a NOx generating condition (YES in step S3), the ECU proceeds to next step S4 move on. On the other hand, if it is determined that the condition is not NOx generation (NO in step S3), both the control valve 22a and the control valve 22b are “closed” (step S6), and the process returns to step S2. During this time, the engine is operated without returning the exhaust gas G to the intake air.

  In step S4, the ECU determines whether the value of the engine speed and the amount of fuel injection are in the large NOx generation region. If the ECU determines that the value of the engine speed and the fuel injection amount are within a predetermined large NOx generation region (YES in step S4), the control valve 22a is "open" and the control valve 22b is also "open". (Step S5). As a result, the exhaust gas g is introduced into the first flow path 16a and the second flow path 16b, so both the water vapor f separated by the component separation means 18 and the exhaust gas g are returned (mixed) to the intake air A. Can be made. The amount of water vapor to be returned is controlled by the pressure of the pump 20.

  If the ECU determines in step S4 that the region is low in NOx generation (NO in step S4), the ECU sets the control valve 22a to “closed” and the control valve 22b to “open” (step S7). As a result, the exhaust gas g bypasses the component separation means 18 and is introduced into the second flow path 16b, so that it can be returned (mixed) to the intake air A as it is. The amount of exhaust gas g (EGR) to be returned is controlled by the pressure of the pump 20.

  As described above, since water vapor and exhaust gas can be mixed in the intake air in accordance with the operating state of the engine, the generation of NOx can be more effectively reduced.

  The intake component control device of the present invention is not limited to the above-described embodiment, and can be changed without departing from the gist of the present invention.

  For example, although the separation membrane 34 is formed on the upstream surface of the substrate 32 in FIG. 2B, it may be integrally formed on the downstream surface.

  The intake component control device of the present invention can be suitably used for automobiles and stationary internal combustion engines. Above all, it is extremely effective as a countermeasure against NOx in diesel vehicles.

It is explanatory drawing which shows schematic structure of the aspect of 1st Embodiment. It is explanatory drawing which shows the outline | summary of a honeycomb structure. (A) is a perspective view which shows the whole shape of a honeycomb structure. (B) is a schematic diagram which shows a part of longitudinal section. (C) It is a plane schematic diagram which illustrates cell shape. It is explanatory drawing explaining isolation | separation of the water vapor molecule | numerator by a zeolite membrane. It is the graph which showed notionally the relation between pump pressure and the amount of water vapor. It is a schematic diagram which shows the structure of the aspect of 2nd Embodiment. It is a flowchart explaining operation | movement of the 2nd embodiment.

Explanation of symbols

12: Intake pipe 14: Exhaust pipe 16: EGR pipe 18: Component separation means 20: Differential pressure generation means (pump) 22: Control valve 26: Cell 28: Sealing part 30: Opening part 32: Septum 34: Separation membrane ( Zeolite membrane)
A: Intake air G: Exhaust gas f: Water vapor H: Honeycomb structure

Claims (10)

An EGR pipe which is connected to an intake pipe and an exhaust pipe of the internal combustion engine and forms a flow path for circulating a part of the exhaust gas of the internal combustion engine to the intake pipe; and a predetermined amount in the exhaust gas which is interposed in the EGR pipe In an intake component control apparatus for controlling an intake component of the internal combustion engine, comprising: a component separation unit that separates components; and a differential pressure generation unit that is interposed in the EGR pipe and introduces the exhaust gas into the component separation unit.
The intake component control apparatus according to claim 1, wherein the component separation means includes a zeolite membrane that permeates and separates water vapor in the exhaust gas.   The intake component control device according to claim 1, wherein the component separation means is a honeycomb structure in which the zeolite membrane is integrally formed on a substrate surface.   The air intake according to claim 2, wherein the honeycomb structure is arranged in parallel so that the openings and the sealing parts of the cells having the sealing part on one end side and the opening part on the other end side are alternately adjacent to each other. Component control device.   4. The intake component control device according to claim 2, wherein a cell density of the honeycomb structure is 400 to 900 / inch 2 (62 to 140 / cm 2).   The intake component control device according to claim 1, wherein the zeolite membrane has pores having a pore diameter of 0.26 to 0.5 nm.   The intake component control device according to any one of claims 2 to 5, wherein the base material is a porous body having a through hole having a diameter of 0.1 to 50 µm.   The intake component control device according to claim 6, wherein the porous body is ceramic.   The intake component control device according to claim 7, wherein the ceramic is cordierite.   The EGR pipe includes a first flow path through which the exhaust gas circulates to the intake pipe via the component separation means, and a second flow path through which the exhaust gas circulates to the intake pipe by bypassing the component separation means. The intake component control device according to claim 1.   10. The intake component control device according to claim 9, wherein the EGR pipe includes switching means for switching the flow path of the exhaust gas between the first flow path and the second flow path.

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