Exhaust treatment device for internal combustion engine

Abstract

To efficiently utilize urea water in NOx reduction.SOLUTION: An exhaust treatment device applied to an internal combustion engine using hydrogen as fuel includes a selective reduction type SCR catalyst 30 provided in an exhaust passage 20 of the internal combustion engine and purifying NOx, and a urea injection valve 40 arranged on the exhaust upstream side of the SCR catalyst 30 and injecting urea water to the SCR catalyst 30. A urea-water injector 40 is arranged so that a C2 line C1 of spray injected from the urea-water injector 40 is offset in a vertically downward direction with respect to a center line LA of the SCR 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust treatment device for an internal combustion engine that uses hydrogen as fuel. [Background technology]

[0002] An exhaust treatment device is known that has a selective reduction catalyst that is provided in the exhaust passage of an internal combustion engine and purifies NOx, and a urea injection valve that is positioned upstream of the catalyst in the exhaust gas and injects urea water toward the catalyst (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-32970 Summary of the Invention [Problem to be solved by the invention]

[0004] In internal combustion engines that use hydrogen as fuel, hydrogen may be contained in the exhaust gas as unburned gas. When hydrogen is contained in the exhaust gas, the hydrogen is adsorbed onto the catalyst. When the catalyst adsorbs hydrogen, it becomes unable to reduce NOx even when urea water is injected. As a result, there is a risk that urea water will not be used efficiently for NOx reduction. [Means for solving the problem]

[0005] An exhaust treatment device for an internal combustion engine that solves the above-mentioned problems is applied to an internal combustion engine that uses hydrogen as fuel, and is an exhaust treatment device that includes a selective reduction catalyst that is provided in the exhaust passage of the internal combustion engine and purifies NOx, and a urea injector that is positioned upstream of the catalyst in the exhaust and injects urea water into the catalyst, and the urea injector is positioned so that the central axis of the spray injected from the urea injector is offset vertically downward from the central axis of the catalyst.

[0006] Hydrogen contained in exhaust gas has a smaller molecular weight and is lighter than other components contained in exhaust gas. Therefore, when passing through the catalyst, hydrogen tends to pass through the catalyst while being biased toward the upper vertical region of the catalyst. Therefore, even if urea water is supplied to the upper vertical region of the catalyst, hydrogen is adsorbed in that upper region, preventing efficient use of the urea water for NOx reduction. Therefore, in this configuration, the urea injector is positioned so that the urea water spray area is not included in a region up to a predetermined distance from the uppermost end of the catalyst front end face in the vertical upward direction. More specifically, the urea injector is positioned so that the central axis of the spray injected from the urea injector is offset vertically downward from the central axis of the catalyst. Therefore, the urea water injected from the urea injector is injected while avoiding the upper region of the catalyst front end face. This makes it possible to prevent the urea water spray area from being included in the upper region of the catalyst front end face. In this way, urea water is not supplied to areas of the catalyst where hydrogen is easily adsorbed, and urea water is supplied to areas where hydrogen is not easily adsorbed, so that urea water can be used efficiently during NOx reduction. [Effects of the Invention]

[0007] According to the present invention, urea water can be efficiently used in reducing NOx. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating a configuration of an embodiment of an exhaust treatment device. [Figure 2] 1A is a schematic diagram showing a spray area of ​​the urea injector according to the embodiment, which is determined by the distance from the nozzle hole of the urea injector to the front end face of the catalyst and the spray angle of the urea injector, and FIG. [Figure 3] FIG. 10 is a schematic diagram showing the arrangement of urea injectors in a modified example of the embodiment. [Figure 4] FIG. 10 is a schematic diagram showing the arrangement of urea injectors in a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of an exhaust treatment device will be described below with reference to Figures 1 and 2. The exhaust treatment device of this embodiment is applied to the exhaust passage of an internal combustion engine that uses hydrogen as fuel. In Figures 1 and 2, arrow U indicates the vertically upward direction, and arrow D indicates the vertically downward direction.

[0010] <Configuration of exhaust treatment device> As shown in Fig. 1, the exhaust treatment device for an internal combustion engine of this embodiment is provided with a selective catalytic reduction catalyst 30 (hereinafter referred to as SCR catalyst 30) that is provided in an exhaust passage 20 and purifies NOx contained in the exhaust EX. The exhaust treatment device also has a urea injector 40 that is disposed upstream of the SCR catalyst 30 in the exhaust gas and injects urea water toward the SCR catalyst 30. The SCR catalyst 30 adsorbs ammonia and other substances generated from the urea water. The adsorbed ammonia and other substances are then used to reduce NOx in the exhaust gas, thereby purifying the NOx.

[0011] The SCR catalyst 30 is cylindrical, and is supported on the inner wall of the exhaust passage 20 with its outer circumferential surface wrapped in a support mat 50 . A curved portion 22 is provided in the exhaust passage 20 on the exhaust upstream side of the SCR catalyst 30. The curved portion 22 is provided with a bracket 24 to which the urea injector 40 is attached.

[0012] An injection hole 42 for injecting urea water is provided at the tip of the urea injection valve 40. The injection hole 42 is exposed to the inside of the exhaust passage 20. <Spray Area of ​​Urea Injector 40> The urea injector 40 is disposed so that the central axis C2 of the spray H injected from the urea injector 40 is offset vertically downward by a specified amount OF from the central axis C1 of the SCR catalyst 30. As a result, the spray H injected from the urea injector 40 is injected avoiding an upper vertical region at the front end face 31, which is the end face on the exhaust upstream side of the SCR catalyst 30. The central axis of the urea injector 40 in this embodiment is coaxial with the central axis C2.

[0013] With reference to FIG. 2, the spray area of ​​the urea water on the front end surface 31 will be described in detail. As shown in FIG. 2(a), the spray area NR of the urea water on the front end face 31 is determined by the distance L1 from the injection hole of the urea injector 40 to the front end face 31 and the spray angle α of the urea injector 40.

[0014] As shown in FIG. 2(b), the region of the front end face 31 extending from the uppermost end Tp of the front end face 31 in the vertically upward direction to a predetermined distance L2 is defined as a first region HR. More specifically, a line segment passing through the top end Tp and the central axis C1 on the front end face 31 is defined as a straight line RL. A chord of the front end face 31 that is perpendicular to the straight line RL and whose length of a perpendicular line dropped from the top end Tp is the distance L2 is defined as a chord G. An arc that includes the top end Tp is defined as an arc K. In this case, the first region HR is the region enclosed by the chord G and the arc K.

[0015] The urea injector 40 is disposed so that the urea water spray area NR is not included in the first area HR. Here, the area of ​​the first region HR is defined as the first area S1, and the area of ​​the front end face 31 is defined as the second area S2. The percentage (%) of hydrogen contained in the exhaust gas is defined as the hydrogen percentage B. In this embodiment, the hydrogen percentage B is the average value of the percentage of hydrogen contained in the exhaust gas, but it may also be the maximum or minimum value of the percentage of hydrogen contained in the exhaust gas. The ratio of the first area S1 to the second area S2 is a value corresponding to the hydrogen percentage B. For example, the ratio of the first area S1 to the second area S2 is the same as the hydrogen percentage B.

[0016] <Action and effect> The operation and effects of this embodiment will be described. (1) Hydrogen contained in exhaust gas has a smaller molecular weight and is lighter than other components contained in exhaust gas. Therefore, when passing through the SCR catalyst 30, the hydrogen tends to pass through the SCR catalyst 30 while being biased toward the upper side in the vertical direction of the SCR catalyst 30. Therefore, as shown in FIG. 2(a), the upper region Hab, which is the upper region of the SCR catalyst 30 in the direction in which the central axis C1 extends, tends to become a region that adsorbs hydrogen. Note that the range of the upper region Hab on the front end face 31 corresponds to the first region HR described above. Because hydrogen is adsorbed in the upper region Hab, even if urea water is injected into the upper region of the front end face 31 of the SCR catalyst 30 in the vertical direction, more specifically, into the range of the first region HR, the urea water cannot be efficiently used for NOx reduction. This could result in, for example, a decrease in NOx purification performance or an increase in urea water consumption.

[0017] In this regard, in this embodiment, the urea injector 40 is positioned so that the urea-water spray area NR is not included in the first area HR. Therefore, urea water is not supplied to the area of ​​the SCR catalyst 30 where hydrogen is easily adsorbed, and urea water is supplied to the area where hydrogen is not easily adsorbed. This makes it possible to efficiently use urea water during NOx reduction.

[0018] (2) The urea injector 40 is disposed so that the central axis C2 of the spray injected from the urea injector 40 is offset vertically downward from the central axis C1 of the SCR catalyst 30. Therefore, the urea water injected from the urea injector 40 is injected while avoiding the upper region on the front end face 31 of the SCR catalyst 30. Therefore, the urea water spray region NR can be prevented from being included in the first region HR.

[0019] (3) The ratio of the area of ​​the first region HR (first area) to the area of ​​the front end face 31 (second area S2) is the same as the ratio of hydrogen contained in the exhaust, and is a value corresponding to the hydrogen ratio B. Therefore, it is possible to appropriately set the first region HR, which is likely to adsorb hydrogen.

[0020] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0021] The urea injector 40 is positioned so that the central axis C2 of the spray injected from the urea injector 40 is offset vertically downward from the central axis C1 of the SCR catalyst 30, thereby preventing the urea water spray area NR from being included in the first area HR. However, the urea injector 40 may be positioned in other ways. Modified examples are shown in Figures 3 and 4.

[0022] As shown in FIG. 3, the urea injector 40 may be disposed so that the spray H is injected from the vertically upper side (vertically upward side) of the central axis C1 of the SCR catalyst 30. As shown in FIG. 4, the urea injector 40 may be disposed so that the spray H is injected from the vertically lower side (vertically downward side) of the central axis C1 of the SCR catalyst 30.

[0023] The ratio of the area of ​​the first region HR (first area) to the area of ​​the front end face 31 (second area S2) was the same as the ratio of hydrogen contained in the exhaust. Alternatively, the ratio of the area of ​​the first region HR (first area) to the area of ​​the front end face 31 (second area S2) may be increased or decreased by a predetermined value based on the ratio of hydrogen contained in the exhaust.

[0024] Although the central axis of the urea injector 40 is coaxial with the central axis C2, the central axis of the urea injector 40 and the central axis C2 may be different from each other. The urea injector 40 is provided in the curved portion 22 of the exhaust passage 20, but may be provided in another location. [Explanation of symbols]

[0025] 20...Exhaust passage 22...Bend 24…Bracket 30...Catalyst 31…Front end surface 40...Urea injector 42...Nozzle 50...Retaining mat

Claims

[Claim 1] An exhaust treatment device applied to an internal combustion engine fueled by hydrogen, the exhaust treatment device comprising: a selective reduction catalyst that is provided in an exhaust passage of the internal combustion engine and purifies NOx; and a urea injector that is disposed upstream of the catalyst in the exhaust and injects urea water into the catalyst, The urea injector is disposed so that the central axis of the spray injected from the urea injector is offset vertically downward from the central axis of the catalyst. Exhaust treatment device for internal combustion engines.

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