JP2022042206A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control system capable of improving stirring efficiency of a reducing agent and exhaust gas by using a rotary blade.SOLUTION: An exhaust emission control system includes: a first rotary blade provided in an exhaust pipe between a reducing agent supply device (urea water injector) and a selective reduction type catalyst (SCR catalyst) and promoting mixing of a reducing agent (urea water) supplied from the reducing agent supply device and exhaust gas; and a second rotary blade provided in the exhaust pipe and coupled to the first rotary blade via a rotating shaft.SELECTED DRAWING: Figure 2

Description

The present invention relates to an exhaust purification system for an internal combustion engine, which has rotary blades (fins) that promote mixing of a reducing agent and exhaust.

As an exhaust gas purification system for purifying NOx in the exhaust gas of diesel engines mounted on vehicles such as trucks and buses, selective reduction type (selective reduction type) that reduces NOx to nitrogen and water using urea water as a reducing agent. SCR: Selective Catalytic Reduction) A system using a catalyst has been developed.

This exhaust purification system supplies urea water stored in the urea water tank to the exhaust pipe upstream of the selective catalytic reduction system (SCR catalyst), and hydrolyzes urea with the heat of the exhaust gas to generate ammonia. NOx is reduced by an SCR catalyst with ammonia. An appropriate amount of urea water is injected, for example, by a urea water injector provided in an exhaust pipe constituting an exhaust passage.

When using an SCR catalyst, it is important to mix the exhaust gas and urea water sufficiently in order to improve the decomposition efficiency of NOx.

Therefore, a technique has been developed in which a rotary blade (fin) is provided in order to disperse and agitate the urea water in the exhaust gas directly downstream of the urea water injector. The rotary wing consists of, for example, a plurality of fins at an angle to the exhaust flow, and by generating a swirling flow in the passing exhaust, the spray-like urea water and the exhaust injected from the urea water injector are combined. (See, for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2006-292333 Japanese Unexamined Patent Publication No. 2012-47119

By the way, conventionally, the above-mentioned rotary blade is rotatably fixed in the exhaust pipe, but it is still insufficient in terms of stirring efficiency.

The present invention has been made in consideration of the above points, and provides an exhaust gas purification system for an internal combustion engine capable of improving the stirring efficiency by a rotary blade.

One aspect of the exhaust gas purification system for an internal combustion engine of the present invention is:
A first rotary blade provided in the exhaust pipe between the reducing agent supply device and the selective reduction catalyst to promote mixing of the reducing agent supplied from the reducing agent supply device and the exhaust.
A second rotary blade provided in the exhaust pipe and connected to the first rotary blade via a rotary shaft,
Equipped with.

According to the present invention, the rotation of the first rotor can be assisted by the rotation of the second rotor, so that the stirring efficiency of the first rotor can be improved.

The figure provided for the explanation of the combustion system and the exhaust system in this embodiment. Schematic diagram showing enlarged parts of the first and second rotors and the axis of rotation. Schematic diagram showing the configuration of other embodiments described above.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a vehicle 1 such as a truck or a bus is equipped with an internal combustion engine 10 and an exhaust system 20. The exhaust system 20 functions as the exhaust gas purification system of the present invention.

First, the configuration of the internal combustion engine 10 will be described. The internal combustion engine 10 is, for example, a diesel engine. The fuel injection injector 13 injects fuel into the combustion chamber 11. The fuel injection injector 13 may inject fuel into the intake port of the combustion chamber 11. Fuel injection is controlled, for example, by an ECM (not shown). The fuel in the combustion chamber 11 is compressed and burned by the operation of the piston 19.

The intake valve 15 and the exhaust valve 17 are configured to be openable and closable. When the intake valve 15 opens, fresh air from the intake pipe 50 is sucked into the combustion chamber 11. Further, when the exhaust valve 17 is opened, the exhaust gas generated by the combustion of fuel in the combustion chamber 11 is sent out to the exhaust system 20 (specifically, the exhaust pipe 21).

Next, the configuration of the exhaust system 20 will be described. The exhaust system 20 has an exhaust pipe 21. The exhaust pipe 21 is mainly made of metal, and is provided at the lower part of the vehicle 1, for example. The exhaust pipe 21 guides the exhaust gas generated by the combustion of fuel in the internal combustion engine 10 to the atmosphere (outside the vehicle).

Further, various post-treatment devices are provided in the middle of the exhaust pipe 21 in order to purify (detoxify) the exhaust gas. In the present embodiment, as the post-treatment apparatus, an oxidation catalyst 23A, a filter 23B, an SCR catalyst 23C (corresponding to the selective reduction catalyst apparatus of the present invention), and an ammonia slip catalyst 23D are provided.

The oxidation catalyst 23A is formed by supporting rhodium, cerium oxide, platinum, aluminum oxide, or the like on a metal carrier. The oxidation catalyst 23A decomposes and removes hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas. Further, the oxidation catalyst 23A also has a function of oxidizing nitric oxide (NO), which occupies most of NOx contained in the exhaust gas, to generate nitrogen dioxide (NO2). By utilizing this function, it becomes possible to promote the combustion (PM regeneration) of PM collected in the filter 23B and improve the NOx purification efficiency of the SCR catalyst 23C.

The filter 23B is formed of a monolith honeycomb type wall flow filter in which inlets and outlets of honeycomb channels (cells) made of porous ceramic are alternately sealed. The filter 23B collects and removes particulate matter (PM) contained in the exhaust gas.

In the exhaust pipe 21, the urea water injector 24 as a reducing agent supply device is on the downstream side of the filter 23B (specifically, the downstream side in the flow direction of the exhaust gas) and on the upstream side of the SCR catalyst 23C. (Also called a dosing valve) is provided.

In the exhaust pipe 21, for example, a temperature sensor (not shown) for detecting the temperature of the exhaust gas is provided near the inlet of the SCR catalyst 23C. This temperature sensor is used for controlling the injection of urea water and the like.

The SCR catalyst 23C has, for example, a cylindrical shape and has a honeycomb carrier made of ceramic. A catalyst such as zeolite or vanadium is supported or coated on the wall surface of the honeycomb.

The SCR catalyst 23C as described above is arranged on the downstream side of the filter 23B in the exhaust pipe 21. Further, in the exhaust pipe 21, urea water as a reducing agent is injected between the filter 23B and the SCR catalyst 23C by the urea water injector 24, and is supplied to the exhaust gas that has passed through the oxidation catalyst 23A and the filter 23B. As a result, urea water is hydrolyzed to ammonia.

While the exhaust gas containing ammonia is passing through the SCR catalyst 23C, nitrogen oxides (so-called NOx) react with nitrogen and water by the action of the catalyst (reduction reaction). This purifies the nitrogen oxides in the exhaust gas.

Here, the hydrolysis occurs when the temperature of the exhaust gas passing through the SCR catalyst 23C is equal to or higher than a predetermined temperature. Therefore, it is preferable that the urea water injector 24 supplies urea water to the exhaust gas in the exhaust pipe 21 when the temperature of the exhaust gas flowing into the SCR catalyst 23C is equal to or higher than a predetermined temperature. Here, the injection of urea water is controlled by DCU (not shown). The predetermined temperature is appropriately and appropriately determined by experiments, simulations, and the like at the design and development stage of the exhaust system 20 while considering the reaction temperature of ammonia and NOx.

The ammonia slip catalyst 23D is a post-stage oxidation catalyst and has the same configuration as the oxidation catalyst 23A, and is arranged immediately downstream of the SCR catalyst 23C in the exhaust pipe 21. The ammonia slip catalyst 23D mainly oxidizes and removes the slipped ammonia in the SCR catalyst 23C so that the slipped ammonia that has not been used in the reduction reaction is not released into the atmosphere. Other than that, the ammonia slip catalyst 23D may have the same function as the SCR catalyst 23C.

Water, nitrogen, and carbon dioxide produced by treating the exhaust gas with each of the above aftertreatment devices are discharged into the atmosphere through a muffler (not shown) or the like.

In addition to this configuration, the urea water injector 24 is contained in the exhaust pipe 21 between the urea water injector 24 and the SCR catalyst 23C (that is, on the downstream side of the urea water injector 24 and on the upstream side of the SCR catalyst 23C). A first rotary blade 31 (which may be called a fin) is provided to promote mixing of the urea water supplied from the vehicle and the exhaust.

Further, a second rotary blade 32 (which may be called a fin) is provided in the exhaust pipe 21. The first rotary blade 31 and the second rotary blade 32 are connected via a rotary shaft 30. In other words, the first rotary blade 31 is fixed to one end of the rotary shaft 30, and the second rotary blade 32 is fixed to the other end of the rotary shaft 30. As a result, the rotational force of the first rotary blade 31 and the second rotary blade 32 is transmitted to the other rotary blade via the rotary shaft 30.

In the case of the present embodiment, the second rotary wing 32 is provided at a position in the exhaust pipe 21 in which the flow velocity of the exhaust gas is larger or the exhaust pressure is larger than in the exhaust pipe 21 in which the first rotary wing 31 is provided. There is. In the case of the present embodiment, the second rotary blade 32 is provided on the downstream side of the ammonia slip catalyst 23D. Here, it is assumed that the flow velocity of the gas in the exhaust pipe 21 provided with the second rotor 32 is larger than the flow velocity of the gas in the exhaust pipe 21 provided with the first rotor 31.

However, since the gas flow velocity and pressure are also affected by the diameter of the exhaust pipe 21, the gas flow velocity of the exhaust pipe 21 on the downstream side of the ammonia slip catalyst 23D is always at the position where the first rotary blade 31 is provided. It is not always greater than the gas flow rate or exhaust pressure. Therefore, essentially, the second rotor 32 is provided at a position where the flow velocity or the exhaust pressure of the exhaust gas is larger than the position in the exhaust pipe 21 where the first rotor 31 is provided at the time of combustion of the internal combustion engine. You can do it.

As an example, in the present embodiment, the second rotary blade 32 is provided in the exhaust pipe 21 on the downstream side of the SCR catalyst 23C and the ammonia slip catalyst 23D. As another example, if there is a position in the exhaust pipe 21 on the upstream side of the urea water injector 24 where the flow velocity or exhaust pressure of the exhaust gas is larger than the position in the exhaust pipe 21 provided with the first rotary blade 31. If so, the second rotary blade may be provided at that position. Further, the second rotor may be provided near the turbo outlet (when the SCR catalyst 23C is close to the engine) or on the upstream side of the exhaust brake (when the SCR catalyst 23C is under the floor).

FIG. 2 is a schematic diagram showing enlarged portions of the first and second rotors 31, 32 and the rotary shaft 30, which are the features of the present invention. As can be seen from this figure, the intermediate portion of the rotating shaft 30 is exposed from the inside of the exhaust pipe 21 to the outside. The rotary shaft 30 is rotatably and airtightly attached to the wall surface of the exhaust pipe 21. For example, an opening and a bearing component are provided in the exhaust pipe 21, and the rotary shaft 30 is rotatably and airtightly supported by the bearing component. The circumference of the rotating shaft 30 exposed to the outside of the exhaust pipe 21 may be separately covered with a cover, a case, or the like. In short, the rotating shaft 30 may be supported by using the wall surface of the exhaust pipe 21.

In the above configuration, when the internal combustion engine 10 is burning, a gas flow is generated in the exhaust pipe 21 as shown by an arrow in the figure. Since the second rotor 32 is provided at a position where the gas flow is faster or the exhaust pressure is higher than that of the first rotor 31, the second rotor 32 tries to rotate faster than the first rotor 31. As a result, the rotational force of the second rotary blade 32 is transmitted to the first rotary blade 31 via the rotary shaft 30, and the rotation of the first rotary blade 31 is assisted by the second rotary blade 32. Therefore, the stirring efficiency of the urea water and the exhaust gas by the first rotary blade 31 can be improved as compared with the case where the first rotary blade 31 is provided alone.

As described above, according to the present embodiment, the reducing agent supply device is provided in the exhaust pipe 21 between the reducing agent supply device (urea water injector 24) and the selective reduction type catalyst (SCR catalyst 23C). The first rotary blade 31 that promotes mixing of the reducing agent (urea water) supplied from the vehicle and the exhaust, and the second rotary blade 31 provided in the exhaust pipe 21 and connected to the first rotary blade 31 via the rotary shaft 30. By providing the rotary blade 32, it is possible to realize an exhaust purification system for an internal combustion engine capable of improving the stirring efficiency of the first rotary blade 31.

The above-described embodiment is merely an example of the embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

In the above-described embodiment, the case where the second rotor 32 is provided at a position where the gas flow is faster or the exhaust pressure is larger than that of the first rotor 31 has been described, but the position where the second rotor 32 is provided is the same. Not exclusively. The second rotary blade 32 may be provided at a position capable of supplementing the rotation of the first rotary blade 31.

FIG. 3 in which the same reference numerals are given to the portions corresponding to those in FIG. 2 is a diagram showing the configurations of other embodiments. In the configuration of FIG. 3, the rotary shaft 30 includes a first rotary shaft 30a connected to the first rotary blade 31, a second rotary shaft 30b connected to the second rotary blade 32, a first rotary shaft 30a, and a first rotary shaft 30. It has a gear 30c interposed between the two rotating shafts 30b. As a result, the stirring efficiency of the first rotary blade 31 can be further improved by appropriately setting the gear ratio of the gear 30c. Since the gear 30c is arranged outside the exhaust pipe 21, the flow of the exhaust gas does not have to be obstructed by the gear 30c.

In addition, a one-way clutch or freewheel (a mechanism that does not transmit the rotation of the first rotor 31 side to the second rotor 32 side) that transmits only the rotation from the second rotor 32 to the first rotor 31 is provided. It may be provided between the rotary blade 32 and the first rotary blade 31. The non-way clutch or freewheel may be provided in place of the gear 30c or in addition to the gear 30c. By doing so, it is possible to suppress the rotational energy on the first rotary blade 31 side from being used on the second rotary blade 32 side, and to efficiently drive the first rotary blade 31.

In the above-described embodiment, the case where urea water is used as the reducing agent has been described, but as the reducing agent, other than urea water such as ammonia water can also be used.

The present invention is widely applicable to an exhaust purification system having rotary blades (fins) that promote mixing of the reducing agent and the exhaust.

1 Vehicle 10 Internal combustion engine 11 Combustion chamber 13 Fuel injection injector 15 Intake valve 17 Exhaust valve 19 Piston 20 Exhaust system 21 Exhaust pipe 23A Oxidation catalyst 23B Filter 23C SCR catalyst 23D Ammonia slip catalyst 24 Urea water injector (reducing agent supply device)
30 rotary shaft 30a 1st rotary shaft 30b 2nd rotary shaft 30c gear 31 1st rotary blade 32 2nd rotary blade

Claims (8)

A first rotary blade provided in the exhaust pipe between the reducing agent supply device and the selective reduction catalyst to promote mixing of the reducing agent supplied from the reducing agent supply device and the exhaust.
A second rotary blade provided in the exhaust pipe and connected to the first rotary blade via a rotary shaft,
An exhaust purification system for an internal combustion engine equipped with. The second rotor is provided in an exhaust pipe on the downstream side of the selective reduction catalyst.
The exhaust gas purification system for an internal combustion engine according to claim 1. The second rotor is provided in an exhaust pipe on the upstream side of the reducing agent supply device.
The exhaust gas purification system for an internal combustion engine according to claim 1. The second rotor is provided at a position where the flow velocity of the exhaust gas is larger than the position in the exhaust pipe where the first rotor is provided at the time of combustion of the internal combustion engine.
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3. The axis of rotation is
The middle part is exposed from the inside of the exhaust pipe to the outside.
Rotatably and airtightly attached to the wall surface of the exhaust pipe.
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3. The axis of rotation is
The first rotary shaft connected to the first rotary blade and
The second rotary shaft connected to the second rotary blade and
A gear interposed between the first rotating shaft and the second rotating shaft,
Equipped with
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 5. The gear is arranged outside the exhaust pipe.
The exhaust gas purification system for an internal combustion engine according to claim 6. Between the first rotor and the second rotor, a one-way clutch that transmits only the rotation from the second rotor to the first rotor, or the rotation of the first rotor is the first. There is a mechanism that does not transmit to the two rotors,
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 7.

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