Exhaust purification system for internal combustion engine

Disclosed is an exhaust purification system (2) for an internal combustion engine (1), which comprises: a reduction catalyst (6) that is arranged in an exhaust pipe (exhaust passage) (3) of the internal combustion engine (1); and a reducing agent spraying device (4) for spraying a reducing agent within the exhaust pipe (3) in the upstream of the reduction catalyst (6). A dispersing member (member for promoting evaporation of the reducing agent) (5) is arranged at a position, which is in the upstream of the reduction catalyst (6) within the exhaust pipe (3), and to which the reducing agent is sprayed from the reducing agent spraying device (4). The dispersing member (5) is formed of a porous member and affixed within the exhaust pipe (3) such that the dispersing member (5) is parallel to the flowing direction of the exhaust gas.

TECHNICAL FIELD

The present invention relates to an art of an exhaust purification system purifying exhaust gas discharged from an internal combustion engine via an exhaust pipe.

BACKGROUND ART

Conventionally, as a method for purifying nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine via an exhaust pipe, an art is known in which urea water as a reducing agent is injected into the exhaust pipe and the nitrogen oxides are reduced and purified by a reduction catalyst arranged at the downstream side (Selective Catalytic Reduction).

For increasing purification efficiency of exhaust gas by this method, it is necessary to evaporate efficiency the urea water injected into the exhaust pipe and generate ammonia uniformly in the exhaust pipe.

For example, when the temperature of exhaust gas in the exhaust pipe is low, the urea water injected into the exhaust pipe cannot be evaporated efficiency. Accordingly, time is required for generating ammonia uniformly in the exhaust pipe, whereby the length of the exhaust pipe must be long.

However, since the length of the exhaust pipe is long in this construction, there is a problem in that large space is required for establishing the exhaust pipe. Furthermore, there is a problem in that the urea water tends to adhere to the wall surface inside the exhaust pipe and the adhering urea water is crystallized.

Then, an art is known in which a metal mesh member and a dispersing member mixing and dispersing urea water are arranged in the exhaust pipe oppositely to flow direction of exhaust gas (for example, see the Patent Literature 1).

According to this art, urea water injected into the exhaust pipe collides with the mesh member and fragmentized, and then mixed with the exhaust gas passing through the mesh member. The fragmentized urea water collides with the dispersing member provided downstream the mesh member so as to be mixed and dispersed efficiently in the exhaust pipe. Since the metal mesh member is heated by the heat of the exhaust gas, the evaporation of the urea water colliding with the mesh member is promoted.

Therefore, according to this art, ammonia can be generated uniformly in the exhaust pipe. Namely, it is not necessary to extend the length of the exhaust pipe, and large space for setting up the exhaust pipe is not required. Furthermore, the urea water is prevented from adhering to the wall surface inside the exhaust pipe and being crystallized.

However, according to the art described in the Patent Literature 1, the exhaust gas in the exhaust pipe passes through the mesh member and the dispersing member arranged oppositely to the flow direction of the exhaust gas. Accordingly, pressure loss of the exhaust gas occurs when the exhaust gas passes through the mesh member and the dispersing member. As a result, there is a problem in that pressure upstream the mesh member and the dispersing member in the exhaust pipe rises so that the performance of the internal combustion engine is decreased.

Therefore, according to the art described in the Patent Literature 2, a metal mesh member formed platy is established rotatably in the exhaust pipe. Then, when urea water is not injected, the mesh member is rotated so as to be directed in parallel to flow direction of exhaust gas. On the other hand, when the urea water is injected, the mesh member is rotated so as to be directed oppositely to the injection direction of the urea water (in other words, not parallel to the flow direction of the exhaust gas), whereby the urea water collides with the mesh member.

According to this art, when the urea water is not injected, the mesh member is rotated so as to be directed in parallel to the flow direction of the exhaust gas. Accordingly, pressure loss of the exhaust gas does not occur when the exhaust gas passes through the mesh member so that pressure upstream the mesh member in the exhaust pipe is prevented from rising, whereby the performance of the internal combustion engine is prevented from being decreased.Patent Literature 1: the Japanese Patent Laid Open Gazette 2009-41371Patent Literature 2: the Japanese Patent Laid Open Gazette 2010-38020

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, according to the art described in the Patent Literature 2, when the urea water is injected, the mesh member is rotated so as to be directed in non-parallel to the flow direction of the exhaust gas. Accordingly, there is a problem in that pressure loss occurs when the exhaust gas passes through the mesh member and pressure upstream the mesh member in the exhaust pipe rises so that the performance of the internal combustion engine is decreased.

The present invention is provided in consideration with the above problems, and the problem to be solved by the invention is to provide an exhaust purification system for an internal combustion engine in which ammonia is generated uniformly in an exhaust pipe, nitrogen oxides in exhaust gas are reduced and purified efficiently by a reduction catalyst, and it prevents decrease of performance of the internal combustion engine caused by rising of pressure in the exhaust pipe.

Means for Solving the Problems

According to claim1, an exhaust purification system for an internal combustion engine includes a reduction catalyst arranged in an exhaust passage of the internal combustion engine, and a reducing agent injecting device injecting a reducing agent into the exhaust passage upstream the reduction catalyst. A reducing agent evaporation promotion member is established upstream the reduction catalyst in the exhaust passage and at a position to which the reducing agent injected from the reducing agent injecting device is sprayed. The reducing agent evaporation promotion member is formed by a porous member and fixed to the inside of the exhaust passage so as to be in parallel to flow direction of exhaust gas.

According to claim2, the reducing agent is urea water.

According to claim3, the reducing agent injecting device has an injection nozzle, and the injection nozzle is a single-fluid nozzle.

Effect of the Invention

The present invention constructed as the above brings the following effects.

According to claim1, in the exhaust purification system of the internal combustion engine, ammonia is generated uniformly in the exhaust passage, nitrogen oxides in the exhaust gas are reduced and purified efficiently by the reduction catalyst, and the decrease of performance of the internal combustion engine caused by the increase of pressure in the exhaust passage is prevented.

According to claim2, the exhaust purification system of the internal combustion engine can be built more easily.

According to claim3, the exhaust purification system of the internal combustion engine can be built with easier construction.

DESCRIPTION OF NOTATIONS

DETAILED DESCRIPTION OF THE INVENTION

An explanation will be given on construction of an exhaust purification system2for an internal combustion engine1according to an embodiment of the present invention referring toFIG. 1.

The exhaust purification system2for the internal combustion engine1is a system (so-called SCR) purifying nitrogen oxides in exhaust gas generated in the internal combustion engine1. The exhaust purification system2for the internal combustion engine1includes an exhaust pipe3which is an exhaust passage of exhaust gas, a reducing agent injecting device4, a dispersing member5and a reduction catalyst6.

The internal combustion engine1has one or more cylinders12. In the internal combustion engine1, fuel injected to the cylinders12is burnt and energy generated by this combustion is exchanged into rotational power. In the internal combustion engine1, outside air supplied via an intake pipe8and fuel supplied via four fuel injection valves11are mixed and burnt in the four cylinders12, whereby exhaust gas is generated. The exhaust gas is discharged to the outside of the internal combustion engine1via the exhaust pipe3. In this embodiment, the internal combustion engine1is an in-line four-cylindered engine, but the internal combustion engine1is not limited thereto.

The reducing agent injecting device4injects reducing agent to exhaust gas flowing in the exhaust pipe3. The reducing agent injecting device4includes a reducing agent tank41, a reducing agent pump42and an injection nozzle43.

The reducing agent is supplied into the exhaust gas so as to reduce and purify components of the exhaust gas with the reduction catalyst6. In this embodiment, urea water is used as the reducing agent.

The reducing agent injecting device4is an embodiment of the “reducing agent injecting device” according to the present invention.

The reducing agent tank41stores the urea water. The reducing agent tank41is communicated with the reducing agent pump42via a supply passage44.

The reducing agent pump42sends with pumping the urea water stored in the reducing agent tank41toward the injection nozzle43. The reducing agent pump42is communicated with the injection nozzle43via a supply passage45. In this embodiment, an electric pump is used as the reducing agent pump42. The reducing agent pump42is connected electrically to a control means (not shown in figures) and controlled pressure in the supply passage45to be predetermined pressure with the urea water pressingly sent toward the injection nozzle43.

The injection nozzle43injects the urea water into the exhaust pipe3. In this embodiment, a single-fluid nozzle is used as the injection nozzle43. The injection nozzle43injects the urea water in the supply passage45aslant toward the downstream side of the exhaust gas in the exhaust pipe3corresponding to the pressure in the supply passage45pressingly sent by the reducing agent pump42(the urea water is not mixed with gas).

The dispersing member5mixes and disperses the urea water in the exhaust gas and promotes evaporation of the urea water. The dispersing member5is formed platy by a porous member including ceramic or metal. The dispersing member5is provided horizontally at the downstream of the injection nozzle43and in the vertical middle portion of the inside of the exhaust pipe3. Namely, the dispersing member5is provided in parallel to the flow of the exhaust gas so that the plane center of the dispersing member5is positioned on the extension of the injection center line of the injection nozzle43. Accordingly, the urea water injected from the injection nozzle43collides with (is sprayed to) the dispersing member5aslant.

By injecting the urea water from the injection nozzle43to the dispersing member5shower-like or atomizingly, fine grains of the urea water before colliding with the dispersing member5evaporate easily. When the urea water collides with the dispersing member5and rebounds, the urea water is fragmentized and dispersed in the exhaust pipe3, and evaporates easily. Since the temperature of the dispersing member5becomes high by the heat of the exhaust gas, the evaporation of the urea water colliding with the dispersing member5is promoted (seeFIG. 3).

Accordingly, ammonia is generated uniformly in the exhaust pipe3, and the urea water is prevented from adhering to the wall surface in the exhaust pipe3and crystallizing. “The position with which the injected urea water collides” is not the position with which the injected urea water collides after riding on the flow of the exhaust gas but the position with which the urea water collides by the force of the injection.

The dispersing member5is an embodiment of the “reducing agent evaporation promotion member” according to the present invention.

The reduction catalyst6reduces and purifies nitrogen oxides in the exhaust gas so as to make them harmless. The reduction catalyst6is provided in the exhaust pipe3and arranged downstream the dispersing member5. In this embodiment, a selective reduction catalyst is used as the reduction catalyst6. The urea water supplied to (mixed with and diffused in) the exhaust gas is hydrolyzed by the heat of the exhaust gas flowing in the exhaust pipe3, whereby ammonia is generated. Then, the generated ammonia is reacted with the nitrogen oxides in the exhaust gas so that the nitrogen oxides are reduced and resolved into nitrogen and water (made harmless).

The reduction catalyst6is an embodiment of the “reduction catalyst” according to the present invention.

A particulate filter (hereinafter, referred to as “DPF”) (not shown) may be provided in the exhaust purification system2of the internal combustion engine1. The DPF collects particulate matters (hereinafter, referred to as “PM”) in the exhaust gas. The DPF is provided in the exhaust pipe3and arranged upstream the exhaust purification system2(SCR) of the internal combustion engine1. In the DPF, an oxidation catalyst such as platinum and a honeycomb structure are stored in series in a filter casing substantially cylindrical in a casing made by heat-resistant metal. The DPF collects the PM with the honeycomb structure and makes the collected PM burn so as to remove it with the oxidation catalyst.

In the above-mentioned construction, in the exhaust purification system2of the internal combustion engine1, against the exhaust gas generated in the internal combustion engine1, the urea water stored in the reducing agent tank41is pressingly sent toward the injection nozzle43by the reducing agent pump42and injected into the exhaust pipe3from the injection nozzle43. The urea water colliding with (sprayed to) the dispersing member5in the exhaust pipe3is mixed and dispersed in the exhaust pipe3. The evaporation of the urea water is promoted by the dispersing member5heated by the heat of the exhaust gas, ammonia is generated uniformly in the exhaust pipe3. Then, the ammonia is reacted with the nitrogen oxides in the exhaust gas by the reduction catalyst6so that the nitrogen oxides are reduced and purified.

As mentioned above, when the DPF is attached to the exhaust purification system2of the internal combustion engine1, the urea water is injected to the exhaust gas in which the PM has been collected by the DPF, whereby the nitrogen oxides in the exhaust gas are reduced and purified.

Next, explanation will be given on construction of a dispersing member50which is an example of a conventional dispersing member referring toFIGS. 4 to 6so as to clarify the construction of the dispersing member5.

In the graphs ofFIGS. 5 and 6, a reference letter (a) indicates “exhaust pipe pressure loss”. A reference letter (b) indicates “urea water amount crystallized on a wall surface”. A reference letter (c) indicates “ammonia generation amount”.

In the conventional dispersing member50, a metal mesh member is formed plate-like. The dispersing member50is arranged so as to be rotatable in the exhaust pipe3by a rotating device (not shown). The dispersing member50is rotated so as to be directed oppositely to the flow direction of the exhaust gas (inFIG. 4, rightward direction). When the urea water is not injected from the injection nozzle43, the dispersing member50is rotated so as to be directed in parallel to the flow direction of the exhaust gas. On the other hand, when the urea water is injected from the injection nozzle43, the dispersing member50is rotated so as to be directed oppositely to the injection direction of the urea water (not parallel to the flow direction of the exhaust gas).

According to the construction, though the dispersing member50is formed by the mesh member having high air-permeability, as shown inFIG. 5, when the urea water is injected from the injection nozzle43, pressure loss is caused when the exhaust gas passes through the dispersing member50(see the bold arrow inFIG. 4). As a result, the pressure at the side upstream the dispersing member50in the exhaust pipe3is raised, whereby the performance of the internal combustion engine is decreased.

For preventing the pressure loss of the exhaust gas in the exhaust pipe3, for example, when the dispersing member50is not provided in the exhaust pipe3, that is, the urea water injected into the exhaust pipe3collides with anybody, the pressure loss of the exhaust gas in the exhaust pipe3can be reduced as shown inFIG. 6. However, in this case, as shown inFIG. 6, the urea water injected into the exhaust pipe3is hard to be mixed and dispersed. Namely, the urea water becomes easy to adhere to the wall surface inside the exhaust pipe3, and the adhering urea water is crystallized.

Next, explanation will be given on the construction of the dispersing member5in more detail referring toFIGS. 2 and 3.

In the graph ofFIG. 3, a reference letter (a) indicates “exhaust pipe pressure loss”. A reference letter (b) indicates “urea water amount crystallized on a wall surface”. A reference letter (c) indicates “ammonia generation amount”.

As mentioned above, the dispersing member5in this embodiment is formed by the porous member including ceramic or metal.

According to the construction, when the urea water collides with the dispersing member5, the urea water can be evaporated in a moment by the heat of the exhaust gas stored in the dispersing member5.

The dispersing member5is formed plate-like and arranged in the exhaust pipe3so as to be in parallel to the flow direction of the exhaust gas. In more detail, while the exhaust gas generated in the internal combustion engine1flows in the exhaust pipe3from the left side to the right side inFIG. 2, the dispersing member5formed plate-like is arranged so that a pair of obverse and reverse plate surfaces5ais in parallel to the lateral direction. Namely, the part of the dispersing member5opposite to the flow direction of the exhaust gas is a side surface5bwith small area.

According to the construction, as shown inFIG. 3, the pressure loss generated when the exhaust gas passes through the dispersing member5from the left side to the right side is decreased further in comparison with the conventional dispersing member50.

In the exhaust pipe3, the dispersing member5can be constructed so that the pair of obverse and reverse plate surfaces5aare parallel in the lateral direction and in parallel to the horizontal direction. In this case, the dispersing member5is established in the wall surface of the exhaust pipe3while the pair of obverse and reverse plate surfaces5aare directed respectively upward and downward in the vertical direction.

The dispersing member5is fixed to the wall surface of the exhaust pipe3. Namely, the dispersing member5is not rotated as the conventional dispersing member50. As a result, the two end surfaces of the dispersing member5at the side of the wall surface in the exhaust pipe3can be provided continuously to the wall surface in the exhaust pipe3, whereby any gap is not formed between these members.

For example, if the dispersing member5is rotated, that is, gaps are formed between the two end surfaces of the dispersing member5at the side of the wall surface in the exhaust pipe3and the wall surface in the exhaust pipe3, the urea water injected from the injection nozzle43into the exhaust pipe3may enter the gaps, adhere to the wall surface and be crystallized.

However, as this embodiment, the two end surfaces of the dispersing member5at the side of the wall surface in the exhaust pipe3can be provided continuously to the wall surface in the exhaust pipe3, whereby any gap is not formed between these members. Namely, the urea water is prevented from entering gaps between these members, adhering to the wall surface in the exhaust pipe3and being crystallized.

The method for fixing the dispersing member5to the wall surface of the exhaust pipe3is not limited. Namely, the dispersing member5may be provided integrally with the exhaust pipe3. For example, it may alternatively be constructed so that a dispersing member casing9is established inside the exhaust pipe3and the dispersing member5is exchangeably fixed to the dispersing member casing9. According to this construction, when the dispersing member5is polluted by the PM in the exhaust gas, the dispersing member5can be exchanged with a new dispersing member5or can be removed from the wall surface of the exhaust pipe3, washed and then attached to the wall surface of the exhaust pipe3again.

In this embodiment, the dispersing member5is fixed to the wall surface of the exhaust pipe3, whereby any rotating device for the dispersing member50is not necessary in comparison with the conventional exhaust purification system having the dispersing member50provided rotatably. Therefore, the exhaust purification system2of the internal combustion engine1can be built with very small number of parts and easy construction. Especially, the temperature of the inside of the exhaust pipe3becomes high by the exhaust gas at the time of driving the internal combustion engine1and becomes low (the same as the temperature of the outside air) at the time of not driving the internal combustion engine1, whereby the inside of the exhaust pipe3is bad environment with intense change of temperature. Therefore, in the exhaust pipe3, the high durability of the exhaust purification system2is required. The exhaust purification system2does not have the rotating device for the dispersing member50so as to make the number of parts very small, thereby improving the durability.

In this embodiment, the dispersing member5is arranged so that the center of the plane of the dispersing member5is positioned on the extension of the axis of injection of the injection nozzle43. However, the dispersing member5may alternatively be arranged so that the center of the plane of the dispersing member5is positioned behind the extension of the axis of injection of the injection nozzle43. Namely, when the urea water injected from the injection nozzle43flows along the flow direction of the exhaust gas (the rightward direction inFIG. 1) by the flow of exhaust gas and collides with the dispersing member5(while keeping the force of the injection), the dispersing member5is arranged at the position at which the urea water flows. Namely, it is only necessary to arrange the dispersing member5at the position at which the urea water injected from the injection nozzle43collides with the dispersing member5, and the position of the dispersing member5in the flow direction of the exhaust gas is not limited.

As mentioned above, the exhaust purification system2of the internal combustion engine1according to the embodiment of the present invention includesthe reduction catalyst6arranged in the exhaust pipe3(exhaust passage) of the internal combustion engine1, andthe reducing agent injecting device4injecting the reducing agent into the exhaust pipe3from the side upstream the reduction catalyst6.

The dispersing member5(reducing agent evaporation promotion member) is established upstream the reduction catalyst6in the exhaust pipe3and at the position to which the reducing agent injected from the reducing agent injecting device4is sprayed.

The dispersing member5is formed by the porous member and fixed to the inside of the exhaust pipe3so as to be in parallel to the flow direction of the exhaust gas.

According to the construction, in the exhaust purification system2of the internal combustion engine1, ammonia is generated uniformly in the exhaust pipe3, the nitrogen oxides in the exhaust gas are reduced and purified efficiently by the reduction catalyst6, and the decrease of performance of the internal combustion engine1caused by the increase of pressure in the exhaust pipe3is prevented.

In the exhaust purification system2of the internal combustion engine1according to the embodiment of the present invention, the reducing agent is preferably the urea water.

According to the construction, in the exhaust purification system2of the internal combustion engine1, the reduction catalyst can be handled easily in comparison with the case in which ammonia being virulent and difficult to be handled for example. Accordingly, the exhaust purification system2of the internal combustion engine1can be built more easily.

In the exhaust purification system2of the internal combustion engine1according to the embodiment of the present invention,the reducing agent injecting device4has the injection nozzle43, andthe injection nozzle43is preferably a single-fluid nozzle.

According to the construction, in the exhaust purification system2of the internal combustion engine1, the reducing agent can be injected into the exhaust pipe3only by the pressure of liquid (reducing agent) (without being mixed with gas) in comparison with the case of using a double-fluid nozzle for example. Accordingly, the exhaust purification system2of the internal combustion engine1can be built with easier construction without increasing the number of parts.

As another embodiment, as shown inFIG. 7, dispersing members with different fineness of nets (meshes) may alternatively be arranged at upper and lower sides.

In more detail, upper and lower two dispersing members (hereinafter, the upper dispersing member is referred to as “upper dispersing member51” and the lower dispersing member is referred to as “lower dispersing member52”) are arranged. The plane center of each of the upper dispersing member51and the lower dispersing member52is arranged on the extension of the axis of injection of the injection nozzle43. The upper dispersing member51is arranged horizontally near the vertical center of the inside of the exhaust pipe3. The lower dispersing member52is arranged horizontally below and downstream the upper dispersing member51. Each of the upper dispersing member51and the lower dispersing member52is formed by metal so as to be a mesh or a plate in which many holes are opened. The fineness of the meshes of the upper dispersing member51and the lower dispersing member52is constructed so that the mesh of the upper dispersing member51is rough and that of the lower dispersing member52is fine. Preferably, a pair of obverse and reverse plate surfaces52aof the lower dispersing member52are larger than a pair of obverse and reverse plate surfaces51aof the upper dispersing member51in proportion to the extent of the urea water injected from the injection nozzle43.

The number of the dispersing members is not limited and may alternatively be three or more. Namely, it is only necessary to construct the plurality of the dispersing members so that the fineness of the meshes of the dispersing member closer to the injection nozzle43is finer and the dispersing members are arranged in parallel to each other so that the plane center of each of the dispersing members is positioned on the extension of the axis of injection of the injection nozzle43.

According to the construction, when the urea water is injected from the injection nozzle43to the upper dispersing member51, a part of the urea water may collide with and adhere to the upper dispersing member51or be reflected and fragmentized. Namely, the urea water becomes to tend to be evaporated so as to generate ammonia uniformly in the exhaust pipe3.

The remaining urea water passing through the upper dispersing member51collides with the lower dispersing member52. Since rough parts of the mesh of the lower dispersing member52are close, the urea water passing through the lower dispersing member52is very small, and the passing urea water is fragmentized so as to be evaporated easily. The urea water colliding with the lower dispersing member52adheres or is reflected and fragmentized. Namely, the urea water becomes to tend to be evaporated so as to generate ammonia uniformly in the exhaust pipe3. Therefore, by increasing the number of row of the dispersing members, ammonia becomes easy to be generated uniformly in the exhaust pipe3. Since the upper dispersing member51and the lower dispersing member52are in parallel to the flow direction of the exhaust gas, the pressure loss of the exhaust gas is not increased.

INDUSTRIAL APPLICABILITY

The present invention can be employed for an art of an exhaust purification system purifying exhaust gas discharged from an internal combustion engine via an exhaust pipe.