JP2010106797A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the conversion rate of HC, CO, and NOx through a ternary catalyst in an engine carrying out a lean combustion operation. <P>SOLUTION: The exhaust emission control device includes an after-treatment device 13 provided in the exhaust passage 12 of the engine 11 and having the ternary catalyst 14 purifying HC, CO, and NOx in exhaust gas, and an oxygen separation device 15 provided in the exhaust passage 12 in an upstream side than the after-treatment device 13 and separating oxygen from the exhaust gas for reducing the oxygen concentration of the exhaust gas to be supplied to the after-treatment device 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine exhaust gas purification apparatus including an aftertreatment device that is provided in an engine exhaust passage and has a three-way catalyst that purifies HC, CO, and NOx in exhaust gas.

  As a catalyst for simultaneously purifying three components of HC (hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxide), which are harmful components in the exhaust gas, a platinum-rhodium-based or palladium-rhodium-based ternary Catalysts are known. An exhaust emission control device including a three-way catalyst is described in Patent Document 1 and the like.

  In order to simultaneously purify the above three components of HC, CO, and NOx with a three-way catalyst, it is necessary to control the combustion in the vicinity of the theoretical mixing ratio of low oxygen. In order to control combustion near the theoretical mixing ratio, the oxygen concentration in the exhaust gas is detected by an oxygen sensor or the like, and the fuel injection amount by the injector or the like is adjusted based on the oxygen concentration in the exhaust gas detected by the oxygen sensor. Engine fuel injection control devices are known.

JP 2004-251188 A

In recent years, not only local environmental problems such as exhaust gas but also CO ₂ regulations have been screamed in order to cope with global warming on a global scale, and improving fuel efficiency of automobiles is also a major issue. One of the major improvements for improving the fuel efficiency of automobiles is the lean combustion of gasoline engines and diesel engines. A high purification rate under a theoretical mixing ratio cannot be obtained.

  In some cases, an alkaline base is added to a three-way catalyst to temporarily store NOx in a lean atmosphere, and NOx is released in a short rich operation to obtain a three-way reaction. In the three-way catalyst, a high purification rate cannot be obtained as much as a three-way reaction under a theoretical mixing ratio, and since an alkali base is added, there are problems of exhaust temperature restriction and deterioration of fuel consumption due to rich operation.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an engine exhaust purification device that can improve the purification rate of HC, CO, and NOx by a three-way catalyst in an engine that performs lean combustion operation.

  In order to achieve the above object, the present invention provides an aftertreatment device provided in an exhaust passage of an engine and having a three-way catalyst for purifying HC, CO and NOx in exhaust gas, and an upstream side of the aftertreatment device. And an oxygen separation device that separates oxygen from the exhaust gas in order to reduce the oxygen concentration of the exhaust gas supplied to the aftertreatment device.

  According to the present invention, an engine that performs a lean combustion operation has an excellent effect that the purification rate of HC, CO, and NOx by a three-way catalyst can be improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view of an engine exhaust gas purification apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an exhaust purification device 10 according to the present embodiment includes an aftertreatment device 13 disposed in an exhaust passage (exhaust pipe) 12 of an engine (diesel engine in the present embodiment) 11. .

  In the present embodiment, the aftertreatment device 13 has a three-way catalyst 14 that simultaneously purifies HC, CO, and NOx in the exhaust gas. As the three-way catalyst 14, for example, a platinum-rhodium-based or palladium-rhodium-based one can be used.

  In the present embodiment, exhaust gas is exhausted to the exhaust passage 12 upstream of the post-treatment device 13 (three-way catalyst 14) in order to reduce the oxygen concentration of the exhaust gas supplied to the post-treatment device 13 (three-way catalyst 14). An oxygen separator 15 for separating oxygen from the gas is provided.

  As shown in FIG. 2, the oxygen separation device 15 according to the present embodiment is interposed in the middle of the exhaust passage 12 of the engine 11 and has a crank-shaped casing 16 through which exhaust gas flows, and an oxygen separation composed of a solid electrolyte. And a film 17. Specifically, the oxygen separation device 15 has a structure in which a plurality of membrane electrode assemblies 19 each having a thin film electrode 18 attached to both sides of the oxygen separation membrane 17 are arranged side by side so as to form the wall surface of the casing 16.

  When a potential difference is generated between the exhaust side (inside the casing 16) of the oxygen separation membrane 17 of the membrane electrode assembly 19 and the atmosphere side (outside the casing 16), oxygen is generated on the exhaust side (inside the casing 16) of the oxygen separation membrane 17. The molecules receive and ionize electrons that have moved from the atmosphere side of the oxygen separation membrane 17 (outside of the casing 16), and oxygen ions move to the atmosphere side (outside of the casing 16) of the oxygen separation membrane 17 due to ion conduction. Electrons are emitted on the atmosphere side (outside of the casing 16) and returned to oxygen molecules again. In this way, oxygen can be separated from the exhaust gas and released to the atmosphere side (outside of the casing 16) to obtain exhaust gas with reduced oxygen.

  Further, as shown in FIG. 1, the exhaust gas supplied to the post-treatment device 13 (three-way catalyst 14) passes through the exhaust passage 12 between the post-treatment device 13 (three-way catalyst 14) and the oxygen separation device 15. An oxygen sensor (oxygen concentration detection means) 20 for detecting the oxygen concentration is provided.

  In addition, an injector 21 that injects fuel into the combustion chamber of the engine 11 and a control means 22 called an ECU (engine control unit) that controls the entire engine 11 are provided.

  In the present embodiment, the intake air passes through an air cleaner (not shown) provided in an intake passage (intake pipe) 23, a flow meter 24, and the like, and is introduced into the combustion chamber of the engine 11.

  On the other hand, the exhaust gas generated in the combustion chamber of the engine 11 passes through the oxygen separation device 15 and the like, passes through the aftertreatment device 13 and is purified, and is discharged into the atmosphere through a silencer (not shown). Is done.

  Next, the operation of this embodiment will be described.

  In the present embodiment, the ECU 22 detects the oxygen concentration of the exhaust gas with the oxygen sensor 20, and the oxygen concentration of the exhaust gas supplied to the post-processing device 13 (three-way catalyst 14) becomes a predetermined concentration (for example, zero or zero). The voltage between the exhaust side (inside the casing 16) and the atmosphere side (outside the casing 16) of the oxygen separation membrane 17 of the oxygen separation device 15 is controlled so as to be close to the atmosphere side (outside the casing 16). The oxygen concentration of the exhaust gas supplied to the aftertreatment device 13 (three-way catalyst 14) is adjusted by adjusting the amount of oxygen released into the exhaust gas.

  That is, the exhaust emission control device 10 according to the present embodiment does not adjust the fuel injection amount by the injector 21 according to the oxygen concentration of the exhaust gas, but separates oxygen from the exhaust gas by the oxygen separation device 15, and the aftertreatment device The exhaust gas supplied to the exhaust gas 13 (three-way catalyst 14) is reduced in oxygen, and the three-way catalyst 14 purifies HC, CO and NOx in the reduced oxygen exhaust gas.

  According to the exhaust purification apparatus 10 according to the present embodiment, the post-processing apparatus 13 having the three-way catalyst 14 provided in the exhaust passage 12 of the engine 11 and purifying HC, CO, and NOx in the exhaust gas, and the post-processing apparatus. 13 is provided in the exhaust passage 12 upstream of the 13 (three-way catalyst 14), and oxygen is separated from the exhaust gas in order to reduce the oxygen concentration of the exhaust gas supplied to the aftertreatment device 13 (three-way catalyst 14). Since the oxygen separation device 15 is provided, the oxygen separation device 15 reduces the oxygen concentration of the exhaust gas supplied to the aftertreatment device 13 (three-way catalyst 14). In the engine (diesel engine) 11 that is capable of supplying lean exhaust gas to the aftertreatment device 13 (three-way catalyst 14) and performs a lean combustion operation, the three-way catalyst 14 C, it is possible to improve the purification efficiency of CO and NOx.

  Further, according to the present embodiment, a three-way catalyst can be used alone in a diesel engine that performs lean combustion operation, and it is possible to achieve both high-dimensional conflicts of NOx reduction and fuel efficiency improvement. And Since the known three-way catalyst can only obtain a NOx purification rate of 60 to 70%, it is necessary to greatly reduce the NOx concentration of the exhaust gas supplied to the three-way catalyst. For example, since a NOx purification rate of 95% or more is expected, it is not necessary to extremely reduce the NOx concentration of the exhaust gas supplied to the three-way catalyst, and that amount can be used to improve fuel efficiency. .

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various other embodiments can be adopted.

  For example, in the above embodiment, the engine 11 is a diesel engine. However, the present invention is not limited to this, and the engine 11 may be a lean burn engine (gasoline engine).

FIG. 1 is a schematic view of an engine exhaust gas purification apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the oxygen separator.

Explanation of symbols

10 exhaust purification device 11 engine 12 exhaust passage (exhaust pipe)
13 Post-processing device 14 Three-way catalyst 15 Oxygen separator

Claims (1)

  An aftertreatment device provided in the exhaust passage of the engine and having a three-way catalyst for purifying HC, CO and NOx in the exhaust gas, and provided in the exhaust passage upstream of the aftertreatment device, the aftertreatment device An exhaust gas purification apparatus for an engine, comprising: an oxygen separation device for separating oxygen from the exhaust gas in order to reduce an oxygen concentration of the exhaust gas supplied to the engine.

Images