JP6658165B2 - engine - Google Patents

Description

  The present invention relates to engines, and more particularly, to engines that reduce nitrogen oxide emissions.

  2. Description of the Related Art An engine has been proposed in which ammonia hydrolyzed from urea water injected from a urea water injection valve is used as a reducing agent to reduce nitrogen oxides in exhaust gas by a selective reduction catalyst device (for example, see Patent Document 1). ). In this engine, a selective reduction catalyst device is attached to a casing via a mat material.

  However, in the urea water injection valve, after the urea water is injected, the urea water may drop from the injection port. Then, using the dripped urea water as a raw material, a white product in which urea, melamine, cyanuric acid, biuret and the like are solidified is precipitated.

  As described above, when the white product precipitates around the injection port, the white product blocks the injection port, which hinders appropriate injection of the urea water. As a result, there is a problem that the reduction rate of nitrogen oxides in the selective reduction catalyst device is reduced. In addition, when the white product is thermally decomposed, there is a problem that ammonia is slipped because more ammonia than is obtained from the urea injected by the control is supplied to the selective reduction catalyst device.

JP 2013-167157 A

  An object of the present invention is to provide an engine that suppresses precipitation of a white product using urea water as a raw material and reduces the emission of nitrogen oxides.

An engine of the present invention that achieves the above object has an exhaust passage through which exhaust gas flows, a urea water injection valve arranged in the exhaust passage, and a urea water injection valve arranged downstream of the urea water injection valve with respect to the flow of exhaust gas. A selective reduction catalyst device, wherein the urea water injection valve has an injection port at one end, and injects urea water into the exhaust passage from the injection port to perform the selective reduction. In an engine in which the catalyst device is configured to reduce nitrogen oxides using ammonia decomposed from the injected urea water as a reducing agent, at least the injection port of the injection surface region where the injection port is open A region including a dripping region where the urea water is dripped below is covered with fibers, and a urea decomposition catalyst for decomposing urea is fixed to the fibers .

  According to this engine, the urea water dripping from the injection port of the urea water injection valve permeates into a large number of fibers covering the injection surface due to a capillary phenomenon. The urea water that has permeated the fibers has a larger surface area than that of the liquid droplets, so that the volatility is improved, so that hydrolysis is promoted. Thereby, the generation of ammonia from the dripped urea water is promoted, so that the precipitation of a white product caused by the urea water can be suppressed.

In this way, by suppressing the precipitation of the white product, it is possible to avoid the situation where the injection port is blocked, and to supply the optimal amount of ammonia to the selective reduction catalyst device. The reduction rate of the product can be improved.

  In this engine, it is desirable that a urea decomposition catalyst for decomposing urea is fixed to the fibers. The urea decomposition catalyst further promotes the hydrolysis of urea water permeated into the fiber, which is advantageous for suppressing the precipitation of a white product.

FIG. 1 is a configuration diagram illustrating an engine according to a first embodiment of the present invention. FIG. 2 is an enlarged sectional view of a range indicated by II in FIG. 1. FIG. 3 is a perspective view of one end of the urea water injection valve, with the surface viewed from the direction opposite to the injection direction facing the front. FIG. 4 is an enlarged view of a range indicated by IV in FIG. 3. It is a front view which illustrates the injection surface in the engine of the second embodiment of the present invention. FIG. 10 is an enlarged cross-sectional view illustrating the inside of an exhaust passage on the upstream side of the selective reduction catalyst device in the engine according to the third embodiment of the present invention.

  Hereinafter, an engine of the present invention will be described based on an embodiment. Hereinafter, in the drawing, x indicates the injection direction of the urea water U injected from the injection surface 21, y indicates the direction perpendicular to the injection direction, and the downward direction in which the urea water U attached to the injection surface 21 drips. , Z indicate the depth direction.

  The engine 10 of the first embodiment illustrated in FIGS. 1 to 4 is a diesel engine. As shown in FIG. 1, an engine 10 includes an engine body 12 having a plurality of cylinders 11 arranged in series, and an exhaust gas G generated by burning fuel from the engine body 12 in the cylinders 11. And an exhaust passage 14 that flows in through the exhaust passage.

  The urea water injection valve 15 and the selective reduction catalyst device 16 are disposed in the exhaust passage 14 in order in the direction in which the exhaust gas G flows. Note that the white arrow in FIG. 1 indicates the direction in which the exhaust gas G flows.

  The urea water injection valve 15 has an injection surface 21 having an injection port 17 formed at one end, and a portion including at least the injection surface 21 is inserted into the exhaust passage 14. The selective reduction catalyst device 16 is formed by supporting zeolite or the like on a porous ceramic carrier.

  When purifying the nitrogen oxides contained in the exhaust gas G, the urea water injection valve 15 is controlled by the control device 19 connected to the urea water injection valve 15 via a signal line to a predetermined amount from the injection surface 21. The urea water U is injected in the injection direction x. The injected urea water U is hydrolyzed by the heat of the exhaust gas G to produce ammonia. The selective reduction catalyst device 16 uses the ammonia as a reducing agent to selectively reduce and purify nitrogen oxides.

  As shown in FIG. 2, in the exhaust passage 14 upstream of the selective reduction catalyst device 16, the urea water injection valve 15 is arranged such that the lower part of the injection surface 21 is inclined toward the direction in which the exhaust gas G flows. Have been. That is, the injection direction x of the urea water U is from the upper left to the lower right in the figure.

The injected urea water U exists inside the exhaust passage 14 as droplets having various particle diameters. In the figure, U1 indicates that the particle size is small, and U2 indicates that the liquid jets on the ejection surface 21. Since the urea water U1 having a small particle size has a small inertia force and flows along with the flow of the exhaust gas G, it is diffused into the exhaust gas G regardless of the injection direction x. That is, the urea water U1 is easily hydrolyzed to ammonia. On the other hand, the urea water U3 adhering to the jetting surface 21 and dripping downward in the downward direction y is not diffused into the exhaust passage 14, and a white product is deposited on the jetting surface 21. Note that, when the urea water U3 is radially injected from one injection port 17 in a side view in the depth direction z, the injection direction x is an average direction of the direction in which the urea water U3 travels straight. The same applies to the case where a plurality of injection ports 17 are formed on the injection surface 18.

  Therefore, as shown in FIGS. 2 and 3, in the engine 10, the entire region of the injection surface 21 is covered with the fibers 22 except for the opening surface of the injection port 17.

  The ejection surface 21 is formed in a circular shape in a front view from a direction opposite to the ejection direction x. The same applies to the case where a plurality of injection ports 17 are formed on the injection surface 21. In this embodiment, the ejection surface 21 is formed in a circular shape when viewed from the front, but the shape of the ejection surface 21 is not limited to this and may be formed in a rectangular shape.

  The ejection surface 21 is entirely covered with a large number of fibers 22 except for the opening surface of the ejection port 17. The fiber 22 is a high heat resistant fiber such as a glass fiber or an alumina fiber, and is a fiber whose shape is maintained even when the exhaust gas G reaches a high temperature of 700 ° C. or more.

  More specifically, the urea water injection valve 15 has a nonwoven fabric 24 in which the fibers 22 are accumulated and formed in a sheet shape. The non-woven fabric 24 is fixed to the jetting surface 21 and is formed by bonding or tangling the fibers 22 by mechanical or chemical action to form a cloth. ing. Although the nonwoven fabric 24 is used in this embodiment, a woven fabric formed by weaving the fibers 22 may be used. However, if the fiber 22 is a glass fiber or an alumina fiber having high heat resistance, it is not easy to weave them, so it is preferable to use the nonwoven fabric 24.

  The opening 23 is formed in the nonwoven fabric 24. The opening 23 is formed in a circular shape when viewed from the front in a direction opposite to the ejection direction x. The opening area of the opening 23 is larger than the opening area of the injection port 17. As a result, a region where the fibers 22 do not exist around the periphery of the injection port 17 is formed between the injection port 17 and the nonwoven fabric 24, and the urea water U injected from the injection port 17 Collision with 22 is avoided.

  As shown in FIG. 4, the urea water injection valve 15 has a urea decomposition catalyst 27 fixed to the fiber 22 and hydrolyzing the urea water U. The urea decomposition catalyst 27 can be exemplified by one obtained by adding vanadium oxide, aluminum oxide, silicon oxide, tungsten oxide, and the like based on titanium oxide.

  Next, the function of the fiber 22 will be described. When the urea water U is injected from the urea water injection valve 15, the urea water U1 having a small particle diameter is diffused and hydrolyzed in the exhaust gas G. On the other hand, the urea water U3 attached to the injection surface 18 drips downward y.

  The dripping urea water U3 penetrates to the tips of a large number of fibers 22 covering the ejection surface 21 by capillary action. Next, the urea water U3 that has permeated the fibers 22 has a larger surface area than the state of the liquid droplets, thereby improving the volatility, evaporating water, and promoting hydrolysis.

  Further, the urea from which the moisture has evaporated is hydrolyzed by the urea decomposition catalyst 27 fixed to the fibers 22, and ammonia is generated. Then, the generated ammonia volatilizes and is supplied to the selective reduction catalyst device 16.

  As described above, the engine 10 suppresses the precipitation of the white product, thereby avoiding the situation where the injection port 17 is blocked by the white product, so that the optimal amount of ammonia can be supplied to the selective reduction catalyst device 16. Can be supplied, so that the reduction rate of nitrogen oxides in the selective reduction catalyst device can be improved.

  Further, when the white product precipitates, the urea water U is not hydrolyzed to that extent, and the amount of generated ammonia decreases. When the temperature of the exhaust gas G rises and the precipitated white product is thermally decomposed, ammonia is generated. That is, the amount of ammonia supplied to the selective reduction catalyst device 16 becomes too small or too large due to the precipitation of the white product. However, in the engine 10, as described above, by suppressing the precipitation of the white product, the optimal amount of ammonia is supplied to the selective reduction catalyst device 16, so that the ammonia functions as a reducing agent without excess or shortage. Thus, the reduction rate of nitrogen oxides in the selective reduction catalyst device 16 can be improved.

  In this embodiment, only the ejection surface 21 is covered with the fibers 22, and the fibers function to automatically suppress the precipitation of a white product. This eliminates the need for a device for detecting the temperature of the exhaust gas G or power such as electric power, thereby suppressing an increase in the weight and length of the device.

  The engine 10 according to the second embodiment illustrated in FIG. 5 differs from the first embodiment in the manner in which the fibers 22 cover the injection surface 21. In this embodiment, a plurality of nonwoven fabrics 24 are scattered on the ejection surface 21, and only the dripping region where the urea water U3 is dripped from each ejection port 17 of the ejection surface 21 in the downward direction y, It is covered with fibers 22.

  As a result, the amount of the fibers 22 can be reduced, which is advantageous in reducing the manufacturing cost.

  The engine 10 according to the third embodiment illustrated in FIG. 6 includes, in addition to the configuration of the first embodiment, a urea water injection valve 15 in which a heater 28 warms an injection surface 21 and a temperature sensor that detects the temperature of exhaust gas G. 29.

  The heater 28 is an electric heater and is fixed to a surface opposite to the injection surface 21 inside the urea water injection valve 15 and is connected to the control device 19 via a signal line. The heater 28 may be arranged outside the urea water injection valve 15.

  The temperature sensor 29 is connected to the control device 19 via a signal line. Note that, instead of the temperature sensor 29, a sensor that directly detects the temperature of the ejection surface 21 may be used.

  Hereinafter, the control method of the engine 10 will be described as a function of the control device 19. First, the temperature sensor 29 detects the temperature of the exhaust gas G. Next, control device 19 determines whether or not the temperature is equal to or higher than a preset threshold. The threshold value is set to a value that can determine the temperature at which the hydrolysis of urea is promoted, and is set, for example, to 90 degrees to 100 degrees.

  Next, when it is determined that the temperature is lower than the threshold, the control device 19 energizes the heater 28. Thus, the temperature of the ejection surface 21 is increased by the heater 28. Then, when the temperature of the injection surface 21 rises and becomes equal to or higher than the temperature at which hydrolysis of urea is promoted, urea is hydrolyzed to generate ammonia. The temperature of the injection surface 21 may be maintained at a temperature at which hydrolysis of urea is promoted or higher. That is, when the temperature of the exhaust gas G becomes equal to or higher than the threshold, the power supply to the heater 28 is stopped.

By performing such control, the temperature of the injection surface 21 can be maintained at a temperature at which hydrolysis of urea is promoted. In other words, in this embodiment, the hydrolysis of urea is promoted by the action of both the urea decomposition catalyst 27 fixed on the fibers 22 and the temperature rise of the injection surface 21, so that the precipitation of the white product is more effectively performed. Can be suppressed.

  When the heater 28 is used, the urea decomposition catalyst 27 does not have to be fixed to the fiber 22.

  In the above-described embodiment, a diesel engine has been described as an example of the engine 10, but the present invention can also be applied to a gasoline engine or an engine using liquefied gas as fuel. Further, as a purification device for the exhaust gas G, a collection filter for collecting particulate matter contained in the exhaust gas G and an oxidation catalyst device for oxidizing hydrocarbons and the like are arranged upstream of the selective reduction catalyst device 16. May be. Further, a catalyst device for storing ammonia may be disposed downstream of the selective reduction catalyst device 16.

Reference Signs List 10 engine 14 exhaust passage 15 urea water injection valve 16 selective reduction catalyst device 17 injection port 21 injection surface 22 fiber x injection direction

Claims (3)

An exhaust passage through which exhaust gas flows, a urea water injection valve disposed in the exhaust passage, and a selective reduction catalyst device disposed downstream of the urea water injection valve with respect to the flow of exhaust gas. The urea water injection valve has an injection port at one end, and injects urea water into the exhaust passage from the injection port, so that the selective reduction catalyst device is decomposed from the injected urea water. Engine that is configured to reduce nitrogen oxides using ammonia as a reducing agent,
A region including a dripping region where the urea water is dripped at least from the injection port of the region of the injection surface where the injection port is open is covered with fibers, and the fibers include: An engine , wherein a urea decomposition catalyst for decomposing urea is fixed .   The urea water injection valve has a nonwoven fabric in which the fibers are accumulated and formed in a sheet shape, and the nonwoven fabric covers the entire area of the injection surface except for an opening surface of the injection port. Item 10. The engine according to Item 1. The urea water injection valve, an engine according to claim 1 or 2 has a heater to warm the ejection face.