JPH04129829U - diesel engine catalytic converter - Google Patents

Abstract

(57) [Summary] [Purpose] Contained in exhaust gas from diesel engines
An object of the present invention is to provide a catalytic converter for a diesel engine that can simultaneously and optimally purify NOx and particulates. [Structure] A catalytic converter for a diesel engine includes a catalyst unit 14 housed in a casing 10,
This catalyst unit 14 is located on the upstream side in the flow direction of exhaust gas, and includes a lean NOx catalyst region 16 that is heated and maintained at a temperature range that optimizes its purification efficiency, and this lean
It is configured to include a particulate catalyst region 20 located downstream of the Ox catalyst region 16.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This idea is a diesel engine catalyst that can optimally purify exhaust gas. Concerning converters.

0002

[Conventional technology]

In recent years, environmental pollution has become more serious, and due to this, diesel engine exhaust gas Many attempts have been made to purify it. For example, one such attempt is exhaust gas recirculation. There is a method called EGR. This EGR recycles some of the exhaust gas. This is a method of adding it to the air-fuel mixture by returning it to the intake system of the diesel engine. If this method is implemented, nitrogen oxides, so-called NOx, in exhaust gas can be significantly reduced. It has a great effect on reducing

0003

[Problems that the idea aims to solve]

By the way, when EGR is performed, particulates such as soot are produced in the exhaust gas. In response to this, reducing particulates in exhaust gas If the air-fuel ratio, etc. are controlled in this way, NOx will increase, which is not desirable. Therefore, the aim is to simultaneously reduce NOx and particulates in exhaust gas. As a lean NOx catalyst that decomposes NOx in the catalytic converter and particulate It is conceivable to combine it with a trap with a catalyst to collect the However, for lean NOx catalysts, the optimum temperature range for their purification efficiency is below the exhaust gas temperature. Therefore, the NOx purification efficiency was poor.

0004 This idea was made based on the circumstances mentioned above, and its purpose is can simultaneously and optimally purify NOx and particulates in exhaust gas. Our objective is to provide a catalytic converter for diesel engines that can be used.

[0005]

[Means to solve the problem] The diesel engine catalytic converter of this invention consists of a casing and a The catalyst unit is located within the housing, and this catalyst unit is Located on the diesel engine side, it works with nitrogen oxides in the exhaust gas and oxygen in the exhaust gas. The lean NOx catalyst area to purify and the lean NOx catalyst area compared to the exhaust gas flow direction. A putty located downstream of the exhaust gas that oxidizes and purifies particulates in exhaust gas. The catalytic converter area and the lean NOx catalyst area are heated to a predetermined temperature range to maintain them. and heating control means for maintaining the temperature.

[0006]

[Effect]

According to the catalytic converter described above, the lean NOx catalyst region is controlled by the heating control means. It is heated and maintained at a temperature range that optimizes the purification efficiency of NOx in exhaust gas. On the other hand, the particulate catalyst area oxidizes the particulates in the exhaust gas. It has the function of oxidizing and purifying. Therefore, the exhaust gas from the diesel engine When NOx flows through the catalytic converter, the NOx is first purified by the lean NOx catalyst area. After being oxidized, the particulates are located downstream of the lean NOx catalyst region. The particulates are oxidized and purified by the particulate catalyst region.

[0007]

【Example】

Referring to Figure 1, an exhaust gas purification system for a diesel engine is shown. . This exhaust gas purification system includes an intake pipe 4 extending from a diesel engine 2 and It is provided with an exhaust pipe line 6, and in the middle of this exhaust pipe line 6, a catalyst colloid according to an embodiment is installed. A converter 8 is inserted. Note that the exhaust passage 6 on the downstream side of the catalytic converter 8 is , although not shown, is open to the atmosphere via a muffler.

[0008] The catalytic converter 8 includes a casing 10, and inside the casing 10, A catalyst unit 14 is housed with a heat insulating layer 12 in between. Catalyst unit 14 Viewed from the upstream side in the exhaust gas flow direction, the lean NOx catalyst area 16, the non-catalyst area It consists of a holding area 18 and a particulate catalyst area 20. these The regions 16, 18, and 20 are, for example, provided with a heating element made of a material capable of generating heat when energized. For example, in the lean NOx catalyst area 16, the catalyst is distributed and supported. A zeolite-based lean NOx catalyst (Cu/ZSM5, etc.) is supported on the heating element. On the other hand, in the particulate catalyst region 20, platinum (Pt) or the like is used as a heating element. A catalyst such as palladium (Pd) is supported.

[0009] Lean NOx catalysts reduce exhaust gas under conditions where the exhaust gas has an oxygen concentration of several percent. It has a catalytic effect that reduces and decomposes NOx in the exhaust gas, and Pt and Pd are It has a catalytic effect to oxidize and purify particulates. The above-mentioned catalyst has a temperature range in which its catalytic action is optimal, that is, its purification efficiency is Each has an optimum temperature range; for example, in the case of a lean NOx catalyst, the temperature range The temperature range is from T1 (e.g. 350°C) to T2 (e.g. (for example, 550℃), and if the catalyst temperature deviates from between T1 and T2, the purification It can be seen that the conversion efficiency decreases. On the other hand, in the case of particulate catalysts, The temperature range is from T3 (e.g. 500°C) to T4 (e.g. 650°C) .

0010 The temperature range mentioned above is usually higher than the exhaust gas temperature of the diesel engine 2. Therefore, in the catalytic converter 8 of one embodiment, the lean NOx catalyst region 16 and the par The ticulate catalyst region 20 is electrically connected to the controller 22. This controller 22 controls the energization of the heating element to each catalyst region 16. , 20 is maintained within the above-mentioned temperature range. That is, this In the case of the embodiment, in order to facilitate the explanation, each energizing area 16, At the part 20, there are heater parts 24 and 26 whose heating elements are schematically shown by broken lines. These heater parts 24 and 26 are electrically connected to the controller 22. On the other hand, this controller 22 has a function to detect the temperature of each catalyst region 16, 20. Temperature sensors 28 and 30 are connected to each other. Therefore, these temperature sensors Based on the sensor signals from 28 and 30, the controller 22 controls each heater section 24, By controlling the energization to 26, the heating temperature of each catalyst region 16, 20 can be adjusted as described above. temperature range.

[0011] According to the catalytic converter 8 described above, the lean NOx catalyst region 16 and the particulate If the catalyst region 20 is heated and maintained within its optimum temperature range, When exhaust gas from the diesel engine 2 flows into the catalytic converter 8, first, NOx in the exhaust gas is decomposed, that is, returned, by its catalytic action in the lean NOx catalyst region 16. It is restored and purified. Here, as mentioned above, the lean NOx catalyst region 16 is This is because it has the ability to purify NOx under conditions where a few percent of oxygen exists in the gas. It is assumed that the air-fuel ratio of the diesel engine 2 is set to the lean side.

0012 After this, the exhaust gas passes through the unsupported region 18 and enters the particulate catalyst region 20. During the passage, particulates in the exhaust gas are trapped by their catalytic action. The particulates are then burned or oxidized, thereby also purifying the particulates. subordinate Therefore, if the exhaust passage 6 is equipped with the above-mentioned catalytic converter 8, the exhaust gas will be reduced. NOx and particulates can be purified simultaneously and optimally. Environmental pollution caused by diesel engine exhaust gas can be significantly reduced.

[0013] Further, according to the catalyst unit 14 of this invention, the lean NOx catalyst region 16 is Since it is located upstream of the ticulating catalyst region 20, It becomes possible to further improve the NOx purification efficiency by the lean NOx catalyst region 16. In other words, this type of lean NOx catalyst described above does not require the presence of hydrocarbons (HC) in the exhaust gas. For example, because it has the property of increasing NOx purification ability in situations where The particulate catalyst region 20 is located upstream of the lean NOx catalyst region 16. If the particulate catalyst area 20 is installed, the HC in the exhaust gas will be It will be oxidized and removed, and in this case, the lean NOx catalyst area 16 will be This is not preferable because the NOx purification efficiency decreases.

[0014] Further, each catalyst region 16, 20 has its heating temperature maintained within an appropriate temperature range. Because the catalyst and heating element are exposed to high temperatures of 700℃ or higher, There is no risk of heat deterioration. This invention is not limited to the one embodiment described above, and various modifications are possible. It is. For example, in one embodiment, the lean NOx catalyst region 16 and par Although the unsupported region 18 was provided between the ticulate catalyst region 20, This unsupported region 18 is not necessarily necessary, and is These overlapping regions are provided between the region 16 and the particulate catalyst region 20. The catalyst may be distributed such that there are regions. In addition, lean NOx catalyst area 16 and the particulate catalyst region 20 are not necessarily supported on the same heating element. It is not necessary and may be carried on a separate heating element.

[0015] In one embodiment, the lean NOx catalyst region 16 and the particulate catalyst region Heating of the region 20 is controlled independently by heater sections 24 and 26. However, heating control of these catalyst regions 16 and 20 is performed by one heater section. In this case, the heating temperature of the catalytic regions 16, 20 may be as shown in FIG. As such, the temperature will be maintained in the temperature range between T3 and T2.

[0016] Furthermore, the catalytic actions of the lean NOx catalyst and the particulate catalyst can be performed simultaneously. If there is a catalyst material that exhibits The catalysts can be constructed from the same material. Furthermore, the catalytic converter of this invention has a particulate catalyst region 20. It also has various trap structures on the downstream side of the exhaust gas to collect harmful substances in the exhaust gas. It may be.

[0017]

[Effect of the idea]

As explained above, the diesel engine catalytic converter of this invention For example, the catalyst unit in the casing has a lean NOx catalyst area in its upstream region. area, and a particulate catalyst downstream of this lean NOx catalyst. Moreover, the lean NOx catalyst region purifies NOx in exhaust gas. Diesel engines are heated and maintained within the optimum temperature range for When the exhaust gas from the engine passes through the catalytic converter, NOx in the exhaust gas is reduced to lean N The particulate matter in the exhaust gas is decomposed and purified by the Ox catalytic region. The rate is oxidized and purified by the catalytic region. Therefore, the diesel engine The NOx and particulates in the exhaust gas of the engine are removed by the catalytic converter of this invention. Optimum purification can be achieved at the same time.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a catalytic converter inserted into an exhaust pipe of a diesel engine.

FIG. 2 is a graph showing the purification efficiency of a lean NOx catalyst versus catalyst temperature.

[Explanation of symbols]

2 Diesel engine 6 Exhaust passage 8 Catalytic converter 10 Casing 14 Catalyst unit 16 Lean NOx catalyst area 20 Particulate catalyst area 22 Controller 24, 26 Heater part

Claims (1)

[Scope of utility model registration request] 1. A catalytic converter that is inserted into an exhaust passage extending from a diesel engine and purifies exhaust gas flowing in the exhaust passage, the catalytic converter comprising a casing and a catalyst unit disposed within the casing, the catalyst The unit is located on the diesel engine side and works with oxygen in the exhaust gas to purify nitrogen oxides in the exhaust gas.
x A catalyst area, a particulate catalyst area that is located downstream of the lean NOx catalyst area in the exhaust gas flow direction and which oxidizes and purifies particulates in the exhaust gas, and a lean NOx catalyst area at a predetermined temperature. A catalytic converter for a diesel engine, comprising heating control means for heating and maintaining the heating within a range.