JP4216673B2 - Exhaust purification equipment - Google Patents

Description

  The present invention relates to an exhaust purification device equipped with a NOx storage reduction catalyst in the middle of an exhaust pipe.

  Conventionally, when the exhaust air-fuel ratio is lean, NOx in the exhaust gas is oxidized and temporarily stored in the form of nitrate, and when the oxygen concentration in the exhaust gas is reduced, NOx is intervened by unburned HC, CO, etc. NOx storage reduction catalysts having the property of decomposing and releasing and reducing and purifying are known.

  In this NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded. Therefore, the oxygen concentration of the exhaust gas that periodically flows into the NOx occlusion reduction catalyst is reduced. It is necessary to reduce and release NOx by decomposition. For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the oxygen concentration in the exhaust gas and unburned HC in the exhaust gas. Reduction components such as CO can be increased to promote decomposition and release of NOx.

  However, when a NOx storage reduction catalyst is used as an exhaust purification device for a diesel engine, it is difficult to operate the engine at a rich air-fuel ratio, so fuel is added to the exhaust gas upstream of the NOx storage reduction catalyst. Therefore, it is necessary to reduce the oxygen concentration in the exhaust gas by evaporating the added fuel in high-temperature exhaust gas to produce a large amount of hydrocarbon and reacting with oxygen using this hydrocarbon as a reducing agent. Yes (in this case, a rich air-fuel ratio is also required in this case because it is necessary to desorb the sulfur content in the fuel accumulated on the catalyst).

  The idea of adding fuel to the upstream side of an aftertreatment device such as a NOx occlusion reduction catalyst installed in the middle of the exhaust pipe has been proposed in the past. Means in which an injector for fuel addition is provided in the exhaust port of the head, fuel is added to the exhaust gas by exhaust port injection by the injector, and the added fuel is stirred by the turbine and then supplied to the aftertreatment device Has been proposed.

However, in large vehicles equipped with diesel engines, from the viewpoint of ensuring the reliability of EGR devices and turbochargers, fuel is added by installing an injector on the inlet side of the aftertreatment device in the middle of the exhaust pipe, and a rich atmosphere It has been desired to form a fuel cell, and a means for adding fuel with an injector in the middle of an exhaust pipe has already been proposed in Patent Document 2 below.
JP 2001-280125 A Japanese Patent Laid-Open No. 2000-240429

  However, when fuel is added by an injector in the middle of the exhaust pipe to form a rich atmosphere, the fuel injected from the nozzle of the injector at the required injection angle is simply by simply injecting the fuel into the exhaust pipe. Since most of the water just wets the inner peripheral surface of the exhaust pipe and does not achieve good vaporization and mixing into the exhaust gas, a rich atmosphere suitable for regenerating the NOx storage reduction catalyst (the oxygen concentration in the exhaust gas is low) In addition, an atmosphere with a large amount of reducing components such as unburned HC and CO in the exhaust gas) cannot be formed efficiently in a short time, and in particular, when fuel is added as a reducing agent, fuel consumption deteriorates. There was a problem.

  The present invention has been made in view of the above-described circumstances. Exhaust gas purification in which a reducing agent injected from a nozzle of an injector is well mixed in exhaust gas so that a rich atmosphere can be efficiently formed in a short time. The object is to provide a device.

  The present invention provides a NOx occlusion reduction catalyst that oxidizes NOx in exhaust gas and temporarily stores it in the form of nitrate, and decomposes and releases NOx by the intervention of a reducing agent when the oxygen concentration in the exhaust gas decreases. An exhaust pipe shaft installed at a position downstream of the nozzle tip of the injector and close to the nozzle tip is provided with an injector for adding fuel into the exhaust gas upstream of the NOx storage reduction catalyst of the exhaust pipe. The present invention relates to an exhaust emission control device characterized by adopting a concave curved surface structure over a required range in a central direction.

  Thus, in this way, when the reducing agent injected from the tip of the nozzle of the injector approaches the inner peripheral surface of the exhaust pipe, it rides on the flow of the exhaust gas along the concave curved surface structure. Since it is returned to the center side of the exhaust pipe in the second half, adhesion of the reducing agent to the inner peripheral surface (concave surface structure) of the exhaust pipe is avoided as much as possible, and the reducing agent is well mixed in the exhaust gas, A rich atmosphere will be formed efficiently.

  Furthermore, in the present invention, it is preferable to carry the oxidation catalyst over a required range in the axial direction of the exhaust pipe at a position downstream from the nozzle tip of the injector and close to the nozzle tip. When the reducing agent injected from the tip of the nozzle adheres to the inner peripheral surface of the exhaust pipe, an oxidation catalyst is supported on the attached portion, so that the oxidation reaction of the reducing agent is promoted and ignition of the reducing agent occurs. Combustion is assisted, thereby reducing the oxygen concentration in the exhaust gas immediately and promoting vaporization by the reaction heat so that a rich atmosphere is efficiently formed in a short time.

  According to the above-described exhaust purification device of the present invention, the reducing agent injected from the nozzle of the injector can be well mixed in the exhaust gas, and a rich atmosphere can be efficiently formed in a short time. The amount of consumption can be suppressed to the minimum necessary, and particularly when the reducing agent is a fuel, an excellent effect that deterioration of fuel consumption can be avoided as much as possible can be achieved.

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

  FIG. 1 and FIG. 2 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 led from an air cleaner 3 is taken into an intake pipe. 5 is introduced to the compressor 2a of the turbocharger 2 and pressurized, and the pressurized intake air 4 is distributed and introduced to each cylinder of the diesel engine 1 via the intercooler 6.

  Further, exhaust gas 8 discharged from each cylinder of the diesel engine 1 through the exhaust manifold 7 is sent to the turbine 2b of the turbocharger 2 through the exhaust pipe 9, and the exhaust gas 8 driving the turbine 2b is sent to the NOx storage reduction catalyst. 10 is used to reduce NOx and discharge the vehicle outside the vehicle.

  Here, the NOx occlusion reduction catalyst 10 may be constituted by a flow-through type catalyst monolith, or may be carried on a particulate filter having a porous honeycomb structure made of ceramic such as cordierite.

  Further, the fuel injection direction follows the flow direction of the exhaust gas 8 with respect to an appropriate position in the middle of the exhaust pipe 9, that is, a bent portion of the exhaust pipe 9 bent in an L shape in the example shown here. The injector 11 is inserted through.

  Here, the injector 11 does not inject fuel into a high-pressure atmosphere unlike the injector used for in-cylinder injection of the diesel engine 1, so that the fuel can be injected against the exhaust pressure close to atmospheric pressure. For example, an injector used for in-cylinder injection of a gasoline engine can be used as it is.

  In this embodiment, about 3 to the inner peripheral surface of the exhaust pipe 9 over the required range in the axial direction of the exhaust pipe 9 at a position downstream from the nozzle tip of the injector 11 and close to the nozzle tip. The concave curved surface structure 16 is employed with a depth of about 20 mm.

  More specifically, when the pipe diameter of the exhaust pipe 9 is D, the concave curved surface structure extends from a position about 1.5D downstream to a position about 3D away from the nozzle tip of the injector 11 as a starting point. 16 is preferably applied.

  In this way, when the fuel 13 (reducing agent) injected from the tip of the nozzle of the injector 11 approaches the inner peripheral surface of the exhaust pipe 9, the flow of the exhaust gas 8 along the concave curved surface structure 16 occurs. And is returned to the center side of the exhaust pipe 9 in the second half of the concave curved surface structure 16, so that the fuel 13 is prevented from adhering to the inner peripheral surface (concave curved surface structure 16) of the exhaust pipe 9 and the fuel 13 is The exhaust gas 8 is well mixed, and a rich atmosphere is efficiently formed within a short time.

  Therefore, according to the present embodiment, the fuel 13 injected from the nozzle of the injector 11 can be mixed well in the exhaust gas 8 and a rich atmosphere can be efficiently formed in a short time. The amount can be suppressed to the minimum necessary, and deterioration of fuel consumption can be avoided as much as possible.

  Further, it is preferable that an oxidation catalyst is supported on the concave curved surface structure 16 for the purpose of more efficiently forming a rich atmosphere, and in this way, injection is performed from the nozzle tip of the injector 11. When the deposited fuel 13 is attached, an oxidation catalyst is supported on the attached portion, so that the oxidation reaction of the fuel 13 is promoted and the ignition combustion of the fuel 13 is assisted. The oxygen concentration is immediately reduced and vaporization is promoted by the reaction heat, so that a rich atmosphere is efficiently formed in a short time.

  The exhaust emission control device according to the present invention is not limited to the above-described embodiment. The injector does not necessarily have to be disposed at the bent portion of the exhaust pipe, and the fuel added by the injector is used. Of course, it is possible to use different types of fuel such as kerosene as well as light oil which is a general diesel engine fuel, and various modifications can be made without departing from the scope of the present invention. is there.

1 is an overall view schematically showing an example of an embodiment for carrying out the present invention. It is sectional drawing which shows the detail of the fuel addition position by the injector of FIG.

Explanation of symbols

8 Exhaust gas 9 Exhaust pipe 10 NOx storage reduction catalyst 11 Injector 13 Fuel (reducing agent)
16 Concave surface structure

Claims (2)

  Equipped with a NOx occlusion reduction catalyst in the middle of the exhaust pipe that oxidizes NOx in the exhaust gas and temporarily stores it in the form of nitrate, and decomposes and releases NOx through the reduction agent when the oxygen concentration in the exhaust gas decreases. An injector for adding fuel to the exhaust gas upstream of the NOx occlusion reduction catalyst in the exhaust pipe, and a required position in the exhaust pipe axial direction at a position downstream from the nozzle tip of the injector and close to the nozzle tip An exhaust emission control device characterized by adopting a concave curved surface structure over a range.   The exhaust emission control device according to claim 1, wherein an oxidation catalyst is supported over a required range in the axial direction of the exhaust pipe at a position downstream from the nozzle tip of the injector and close to the nozzle tip.

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