JP4887245B2 - Urea water injection device for exhaust treatment - Google Patents

Description

  The present invention relates to an engine exhaust treatment device, and more particularly to an exhaust treatment device that can efficiently remove nitrogen oxides in exhaust gas using urea water as a reducing agent.

  Conventionally, in a diesel engine, a selective reduction type catalyst having a property of selectively reacting nitrogen oxide (hereinafter referred to as NOx) with a reducing agent even in the presence of oxygen is provided in the middle of an exhaust pipe through which exhaust gas flows. Equip and add the required amount of reducing agent (hydrocarbon, ammonia or its precursor) to the upstream side of this selective catalytic reduction catalyst, and react this reducing agent with NOx in the exhaust gas on the selective catalytic reduction catalyst. In some cases, the NOx emission concentration can be reduced. A NOx reduction method using this selective reduction catalyst is called SCR (Selective Catalytic Reduction), and a method using urea as a reducing agent is particularly called urea SCR. In order to apply this urea SCR to a vehicle, the urea water is stored in a tank, and during operation, the urea water supplied from this tank is injected into the exhaust flue, and the urea water is removed using the heat of the exhaust. A technique for reducing NOx by ammonia produced by the hydrolysis reaction of urea is known (Patent Document 1).

Urea injected from the urea water injection device generates ammonia (NH ₃ ) from urea by the following hydrolysis reaction.

(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂
There are several types of reactions in which NOx is reduced by ammonia on a denitration catalyst (= selective reduction catalyst), but the following denitration reaction mainly occurs at relatively low temperatures.

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O
The hydrolysis reaction of urea occurs in high-temperature exhaust gas. However, when the exhaust gas temperature is relatively low, it does not proceed sufficiently in the exhaust gas and occurs on the denitration catalyst. For this reason, the denitration catalyst bears two functions of a hydrolysis reaction and a denitration reaction at a low exhaust temperature. In general, since the reaction rate decreases at a low temperature in a chemical reaction, a denitration catalyst at a low exhaust temperature causes a significant decrease in denitration performance due to a double effect of an increase in burden and a decrease in reaction rate.

  If the exhaust gas temperature is high, the urea water is sufficiently vaporized by the heat of the exhaust gas even if the urea water is directly injected into the exhaust flue. Vaporization becomes difficult. In that case, the sprayed urea water spray adheres to the wall surface of the flue and may cause precipitation. Precipitation of urea means that urea becomes solid and stays in the flue, and accordingly, the reducing agent necessary for the denitration reaction is insufficient, leading to a decrease in denitration performance. Furthermore, if the exhaust temperature rises rapidly with deposits deposited, the urea that has been precipitated will rapidly sublimate, producing more ammonia than required for the denitration reaction, and the risk of discharging ammonia to the outside. Occurs.

  In order to solve this problem, a technique has been invented in which urea water is forced into ammonia gas and then injected into exhaust gas. In the exhaust gas treatment device described in Patent Document 2, by adding an electric heater and a hydrolysis catalyst to the urea water injection device, the vaporization of urea water and the ammonia ammonia are promoted, and the denitration performance at a low exhaust temperature. We are trying to improve.

Japanese Patent No. 3685063 JP 2004-353523 A

  In the exhaust treatment system of an engine, if the urea water is vaporized with an electric heater, the energy consumption of the engine is reduced in order to consume electric power. Therefore, it is necessary to increase the amount of power generation, and there is a problem of increasing the equipment burden such as the necessity of increasing the size of the generator. In order to reduce this problem, it is necessary to reduce the electric power of the electric heater consumed for vaporizing urea water.

  When the electric heater power is reduced under a fixed amount of urea water injection, the amount of heat given to the urea water decreases, so the vaporization rate decreases and urea that could not be vaporized becomes precipitates. There is a risk of depositing as a solid in the flue. When urea water is gently heated on a wall surface of about 200 ° C., only moisture is vaporized and solid urea is deposited. If further gentle heating is continued, the solid urea is transformed into a stronger solid material such as cyanuric acid, and the removal from the wall surface becomes more difficult. If the precipitation of urea continues, the flow path may be blocked due to the accumulation of solid matter, and the function as a urea water injection device may not be achieved.

  Since the amount of heat necessary to vaporize urea water per unit mass is determined physically, it is extremely difficult to reduce the power consumption of the electric heater without changing the amount of urea water to be vaporized.

  Under such conditions, as a means of reducing the power consumption of the electric heater, paying attention to the fact that the heat generated by the heater is lost without being used for the vaporization of urea water, reducing the heat loss, the power consumption It is conceivable to reduce. Since the heat loss of the electric heater is caused by heat being radiated to the outside, it is conceivable that the electric heater generates heat in the internal space of the flue where the urea water spray exists. However, since the electric wiring for supplying electric power to the electric heater is outside the exhaust flue, it is necessary to arrange the terminal of the electric heater to which the electric wiring is connected in the external space of the flue. In addition, it is desirable to electrically insulate the terminal of the electric heater and the exhaust flue from the viewpoint of preventing leakage. In order to perform electrical insulation, it is effective to use a non-metallic material such as a resin at the location to be insulated, but the electric heater becomes hot because it generates heat, and at the same time the exhaust flue However, a material that cannot withstand high temperatures such as resin cannot be used. It is also possible to achieve electrical insulation with a material such as ceramic, but it is difficult to seal between the exhaust flue and the electric heater with a ceramic material, which causes a problem of exhaust gas leakage. . In particular, ammonia gas is generated in the space where the urea water spray is vaporized, so exhaust gas leakage may lead to ammonia gas leakage, and the seal between the exhaust flue and the electric heater is highly reliable. Sex is required. For this reason, it is very difficult to reduce heat loss and power consumption by generating heat from the electric heater in the internal space of the flue.

  For this reason, a heater for vaporizing urea water has been a very difficult task to reduce power consumption while avoiding precipitation of urea and maintaining vaporization performance.

  In order to solve the above problems, the present invention mainly adopts the following configuration.

  An injection device that injects urea water in a spray form and an electric heater that heats and vaporizes the urea water injected from the injection device, and injects ammonia components generated from the urea water into the exhaust flue of the engine In the urea water injection device for exhaust treatment, the electric heater has a non-heat generating portion and a terminal for connecting to a conductive wire at both ends of the heat generating portion, and the heat generating portion and the non-heat generating portion are the terminals and Consists of a sheath heater covered with an electrically insulated protective tube, the heat generating part of the sheath heater is arranged in the space inside the exhaust flue, and the terminals at both ends are arranged in the space outside the exhaust flue. The non-heat generating part at both ends is sealed and fixed to a member connected to the exhaust flue.

  Further, by making the member for fixing the sheath heater and the member for fixing the injection device in common, the place where the sheath heater is fixed approaches the injection point of the urea water, and the temperature of the sheath heater part cooled by the urea water spray Try to fix a lower place. As a result, it is possible to reduce heat generated by the sheath heater from being transmitted to the outside due to heat conduction of the fixing member, resulting in heat loss.

  In addition, by using compression fitting in the structure that fixes the non-heat generating part of the sheath heater, both the function of sealing to prevent the exhaust gas from leaking to the outside and the function of fixing the sheath heater can be used. .

  Moreover, the heat generating part of the sheath heater is formed in a double-wound coil shape folded back at the center so that both ends are on the same side, and further, the direction of the non-heat generating part at both ends is aligned, thereby fixing the injection device The structure for fixing the non-heat generating part to the common member becomes efficient.

  In addition, by arranging the coil-shaped central axis formed by the heat generating portion of the sheath heater on the injection axis of the injection device, the sheath heater can be uniformly present in the circumferential direction of the spray of urea water, and the sheath heater The heat load can be made uniform, and heat loss can be reduced.

  In addition, after the coil-shaped central axis formed by the heat generating part of the sheath heater is arranged on the injection axis of the injection device, the coil pitch of the sheath heater is small on the side close to the urea water injection point, and the injection point By increasing the winding pitch on the side far from the sheath heater, the sheath heater will exist according to the density of the spray that changes according to the distance from the injection point, and the heat load of the sheath heater can be made uniform, resulting in heat loss. Reduction is possible.

  In addition, after the coil-shaped central axis formed by the heat generating part of the sheath heater is arranged on the injection axis of the injection device, the coil diameter of the sheath heater is larger on the side near the injection point of the urea water, and the injection point By reducing the winding diameter on the side far from the coil, the space around the central axis of the coil is narrowed and spraying is more easily applied to the heat generating part of the sheath heater, so that the heat resistance until the heat generation of the sheath heater is transmitted to the spray is reduced. Reduction can be achieved and heat loss can be reduced.

  In addition, by installing the sheath heater and the injection device at a location where the exhaust flue is diverted, it becomes possible to carry out exhaust gas while vaporizing the urea water spray, and to prevent precipitation due to stagnation of urea. It becomes possible.

  In addition, by covering at least a part of the surface of the heat generating part of the sheath heater with a catalyst component having a function of promoting urea hydrolysis, urea water vaporization and urea hydrolysis reaction can occur simultaneously. Acceleration of urea ammoniating makes it possible to prevent urea precipitation.

  When heating and vaporizing the urea water spray with an electric heater, use a sheath heater covered with a protective tube in which the heat generating part and the non-heat generating part are electrically insulated, and the heat generating part is placed in the internal space of the exhaust flue, The terminal of the heater is arranged outside the exhaust flue, and the non-heat generating part is sealed and fixed to a member connected to the exhaust flue, so that the heat generating part of the heater is not leaked to the outside of the flue. Can be arranged. Also, regarding the electrical insulation from the flue when supplying electric power to the electric heater, the contact with the member connected to the exhaust flue is not covered by the insulated protective tube of the sheath heater. Since it is a heat generating part, electrical insulation is maintained, and it becomes possible to withstand the high temperature of the heat generating part of the heater and the exhaust flue and to maintain a seal. As a result, while the connection terminal with the electrical wiring is arranged in the external space of the flue, the heating part of the heater is not leaked to the outside even if it is arranged in the internal space of the flue, and the flue and the terminal Can satisfy the electrical insulation. In addition, when the heat generating part is outside the flue, there is a thermal resistance for transferring heat inside, and the heater temperature needs to rise accordingly, making it easier for heat to escape. Arranging the part in the internal space of the flue eliminates the thermal resistance for transferring heat to the inside, and at the same time increases the thermal resistance against the escape of heat to the outside, so that the heat loss is remarkably reduced. Moreover, in order to arrange the heat generating portion of the sheath heater inside the flue, fixing the non-heat generating portion with the flue member can suppress the heat generation of the heater from escaping to the outside due to solid heat conduction.

  In the present invention, when the urea water spray is heated and vaporized by the electric heater, a sheath heater covered with a protective tube in which the heat generating portion and the non-heat generating portion are electrically insulated is used, and the heat generating portion is placed in the internal space of the exhaust flue. Arranged, the terminals at both ends are arranged outside the exhaust flue, and the non-heat generating part is sealed and fixed to the member connected to the exhaust flue, so that the exhaust is not leaked to the outside, and inside the flue It becomes possible to arrange the heating part of the heater. Also, regarding the electrical insulation from the flue when supplying electric power to the electric heater, the contact with the member connected to the exhaust flue is not covered by the insulated protective tube of the sheath heater. Since it is a heat generating part, electrical insulation is maintained, and it becomes possible to withstand the high temperature of the heat generating part of the heater and the exhaust flue and to maintain a seal. As a result, while the connection terminal with the electrical wiring is arranged in the external space of the flue, the heating part of the heater is not leaked to the outside even if it is arranged in the internal space of the flue, and the flue and the terminal Can satisfy the electrical insulation. In addition, when the heat generating part is outside the flue, there is a thermal resistance for transferring heat inside, and the heater temperature needs to rise accordingly, making it easier for heat to escape. Arranging the part in the internal space of the flue eliminates the thermal resistance for transferring heat to the inside, and at the same time increases the thermal resistance against the escape of heat to the outside, so that the heat loss is remarkably reduced. In addition, there is a method of fixing the heat generating part with the flue member in order to arrange the heat generating part of the sheath heater inside the flue, but by fixing the non-heat generating part with the flue member, the heat of the heater can be obtained by solid heat conduction. Heat generation can be prevented from escaping to the outside.

  Further, by using a sheath heater having terminals at both ends, it becomes possible to have two non-heat generating portions, and the sheath heater can be fixed at two locations. Even if the structure is not fixed, the structure can withstand the vibration of the exhaust flue, and the heat generating portion arranged in the internal space of the flue can be structured to float from the flue member. When the heat generating part is floating from the flue member, the heat generated by the heater does not escape to the outside due to the solid heat conduction, and the heat loss can be further reduced. Due to these heat loss reduction effects, it is possible to reduce the electric heater power consumed to vaporize the same amount of urea water.

  Moreover, the heat generating part of the sheath heater is formed in a two-winding coil shape that is folded back at the center, and the spraying shape is an axial object by aligning the axis of the coil and the injection axis of urea water, and the heat generating part is an axial object. When the heater is fixed to the flue, it becomes a structure in which spraying is uniformly applied to the heat generating portion, and the non-heat generating portions at both ends of the heater can be aligned in one direction. It becomes possible to fix the non-heat generating part by inserting in one direction.

  Specific embodiments according to the present invention will be described below in detail with reference to FIGS.

  A urea water injection device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an overall configuration of the urea water injection apparatus according to the first embodiment, FIG. 2 is a front view of the apparatus, FIG. 3 is a cross-sectional view taken along the line AA of the apparatus, and FIG. CC sectional view of the device, FIG. 5 is a sectional view of the device taken along arrow BB.

  In FIG. 1, exhaust gas 201 discharged from a diesel engine is injected with urea water 202 or 203 and passes through a downstream denitration catalyst (not shown), so that nitrogen oxides (NOx) in the exhaust gas. ) Is reduced. Since exhaust gas from a diesel engine contains a large amount of NOx and particulate matter (PM), the exhaust aftertreatment system may reduce both of them. As an example of the aftertreatment system in that case, exhaust gas can be purified by providing an oxidation catalyst, a filter, a urea water injection device, a denitration catalyst, and a slip ammonia treatment catalyst in this order from the upstream. In the above catalyst configuration, PM is removed by the filter, NOx is removed by the denitration catalyst, and ammonia slipping the denitration catalyst is also removed by the ammonia treatment catalyst, whereby the exhaust gas is purified.

  In injecting urea water in this embodiment, two methods are used in combination: a method in which urea water is directly injected into exhaust gas and a method in which urea water is vaporized by an electric heater. In the method of injecting urea water directly into the exhaust, there is no problem when the exhaust gas is hot, but when the exhaust gas is low, there is a problem that urea adheres to the flue wall and precipitates. The method of injecting urea water after vaporizing it with an electric heater has the advantage of not causing urea precipitation even when the exhaust gas is at a low temperature. However, by consuming electric power, the total energy efficiency of the engine is reduced. There is a problem to make. Therefore, it is possible to solve both of the above problems by providing both the direct injection method of urea water and the vaporization injection method. That is, the injector 5 directly injects urea water into the exhaust, the injector 6 injects urea water into the diversion pipe 8, and the urea water is vaporized by the electric heater 9 in which the heat generating portion is arranged inside the diversion pipe 8.

  FIG. 2 is a front view of the apparatus shown in FIG. 1, in which a broken line AA indicates a cross-sectional position for showing a diverted gas flow path, and a broken line BB directly injects urea into the exhaust pipe. The cross-sectional position for showing is shown. The shunt gas flow path for branching the exhaust gas branches using the introduction portion 7 as an inlet, and merges with the main exhaust gas using an outlet hole provided on the back side of the swirl vane 11 as an outlet. The urea water spray 101 injected from the injector 5 is dispersed in the flue, and then passes through the flow path in which the swirl vanes 11 are arranged, so that it is more uniformly dispersed in the exhaust gas. The swirl vanes 11 are composed of eight blades, and each of them is fixed at an angle of attack with respect to the flow of exhaust gas, so that the gas flow passing around the vanes is swirled, and It becomes a swirl flow.

  FIG. 3 is a cross-sectional view in the direction indicated by the arrow AA in FIG. 2 and shows the structure of the shunt gas flow path. When a part of the exhaust gas flows in from the introduction part 7, the shunt gas flows through the shunt pipe 8. Urea water is injected by the injector 6 into the space in which the diverted gas flows to form a urea water spray 102, and the spray is vaporized by the electric heater 9. The gas vaporized by the electric heater 9 is conveyed to the diverted gas and passes through the hydrolysis catalyst 10a. Urea is decomposed to some extent by being heated and generates ammonia, but in order to achieve complete ammoniation only with heat, the heating amount must be increased. For this reason, a hydrolysis catalyst is used to reduce the power consumption of the heater. When urea passes through the hydrolysis catalyst in a state containing water vapor, sufficient hydrolysis reaction proceeds even at a relatively low temperature, and ammonia conversion is promoted. Therefore, the use of the hydrolysis catalyst saves heater power consumption. it can.

  FIG. 4 is a cross-sectional view taken along the line CC in FIG. 3 and shows the location where the ammonia gas generated in the branch passage joins the main exhaust gas. The diversion passage is bent at a right angle after passing through the hydrolysis catalyst 10a and connected to the flue outer wall 2 after passing through the hydrolysis catalyst 10b. The inside of the flue outer wall 2 has a double pipe structure with the throttle channel 4, and the ammonia gas conveyed by the shunt gas fills the space between the outer wall 2 and the throttle channel 4, By blowing out from the diverted gas blowout hole in the path 4, it merges with the mainstream exhaust gas. Since the swirl vane 11 in FIG. 4 is a cross-section on the rear side of the swirl vane, it has a separate figure as a figure, but is formed of eight blades integrally. For each of the blades, an outlet 17 is provided. In the case of eight blades, eight outlets are provided. The ammonia gas blown out from the blowout port 17 is uniformly mixed with the mainstream exhaust gas by the effect of the swirl vane 11. The reason why the diverted gas is required when ammonia is produced from urea by heating with an electric heater and a hydrolysis catalyst is because the ammonia gas needs to be conveyed. That is, since the amount of NOx contained in the exhaust gas is very small, only a small amount of ammonia is required to treat this, and the volumetric flow rate of ammonia resulting from the injection of urea water is also very small. This is because it takes a long time to pass through the space. In order to produce ammonia from urea, a space for heating and a space for the catalyst are necessary, and if a diverted gas flows in the space, the flow rate increases due to the increase in volume flow rate, and the transit time is short. Therefore, as a result, the ammonia gas is transported to the shunt gas. For this reason, by introducing the diverted gas, the time from when the urea water is injected by the injector until the ammonia comes out to the outlet of the diverted passage is shortened, the responsiveness of the ammonia supply is improved, and the exhaust gas It becomes possible to improve the purification performance.

  FIG. 5 is a cross-sectional view at the position indicated by the arrow BB in FIG. 2 and shows the structure of a portion that directly injects urea water into the exhaust gas. The urea water 202 is jetted from the injector 5 held by the injector holder 12 to form the urea water spray 101, and urea is injected into the exhaust gas 201. By attaching the injector head 16 to the injector holder 12, the pressurized urea water 202 is supplied to the injector 5, and the metered urea water is injected by opening and closing the valve inside the injector 5. I can do it. The injector holder 12 is connected to the flue outer wall 1 so that the urea water spray 101 injected by the injector 5 is directly injected into the flue, but the flue 1 has a temperature according to the rise of the exhaust gas temperature. Since it rises, the function which protects the injector 5 from the temperature is also needed. For this reason, the injector holder 12 is provided with a cooling water circulation passage inside thereof, prevents the temperature of the electric circuit of the injector from rising, prevents the temperature rise of the urea water passage in the injector, and vaporizes only the water of the urea water. The urea precipitation accompanying this is prevented, and clogging by precipitation does not occur. The cooling water circulated in the injector holder 12 can be engine cooling water or urea water. The urea water spray 101 injected from the injector 5 passes through the throttle channel 4 in which the swirl vanes 11 are arranged while being vaporized by receiving heat from the exhaust gas. Due to the narrowing of the flow path and the mixing action by swirling, the spray 101 is uniformly dispersed in the exhaust gas, and the denitration reaction is sufficiently performed on the denitration catalyst downstream of the urea water injection device. . Since the denitration reaction is a reaction with NOx and ammonia, it is necessary to meet NOx and ammonia on the catalyst. If the urea water spray is not uniformly dispersed in the exhaust gas, NOx that cannot meet ammonia will come out, Denitration performance decreases. For this reason, since the uniform dispersion of the spray directly affects the denitration performance, the urea water injection device has an important function of uniformly dispersing the spray.

  FIG. 5 also shows the positional relationship between the swirl vane 11 disposed in the throttle channel 4 and the diverted gas blowing hole 17. That is, the blade 11a, which is one of the swirling blades composed of eight blades, is disposed at an angle of attack with respect to the mainstream exhaust gas 201, but is separated from the exhaust gas flow on the back side of the blade 11a. The blowout hole 17a is arranged in a place where The relationship between the blades of the swirl vanes 11 and the diverted gas blowing holes 17 is the same. Since the shunt gas passage has a large flow resistance, such as being bent or passing through the hydrolysis catalyst, it is in a situation that requires some ingenuity to ensure the flow rate of the shunt gas. . Therefore, a structure is adopted in which the shunt gas is blown out to a location constricted from the mainstream exhaust gas flow path. When the mainstream exhaust gas enters the throttle channel 4, the channel cross-sectional area becomes narrower, and the flow velocity increases than when it is in front of it. Since the fluid has a property that the pressure (= static pressure) decreases as the flow velocity increases, the pressure in the throttle channel 4 decreases compared to before the throttle. Furthermore, a separation vortex is generated on the back side of the swirl vane 11 to further reduce the static pressure. By using this negative pressure, the flow rate of the diverted gas is ensured by sucking out the diverted gas. In addition, the swirling action of the swirling blades and the action of the separation vortex on the back side of the blades uniformly mix the ammonia gas and exhaust gas blown out from the blowout hole, and the denitration reaction is performed on the denitration catalyst downstream of the urea water injector It will be done well. In the case of ammonia gas as well as the dispersion of the urea water spray, the ability to uniformly mix the ammonia with the urea water injection device is particularly important because the uniform mixing with the exhaust gas directly affects the denitration performance. . The use of the throttle channel 4 and the swirl vane 11 has the function of promoting the mixing of ammonia gas and exhaust gas in addition to ensuring the flow rate of the diverted gas, and one structure performs two functions. It has a reasonable structure.

  FIG. 6 is an exploded view of the urea water vaporizer in the urea water injection apparatus according to the first embodiment, and is a diagram for mainly explaining the structure related to the electric heater. The injector holder 13 is connected to the branch pipe 8 provided with the branch gas inlet 7 via a flange 13a. The injector holder 13 has a structure in which the injector 6 is inserted in the center, and is provided with two places 13b for allowing the electric heater 9 to pass through and being fixed. The compression heaters 14 are respectively attached to the two fixed places 13b, and the electric heater 9 is passed therethrough. The compression fitting 14 has a function of sealing and fixing an object that has been penetrated by the seal member being compressed by pushing a screw. In the present invention, the non-heat generating portion of the electric heater 9 is sealed and fixed. To do. In the present invention, since the heat generating portion of the sheath heater is formed in a coil shape, when the electric heater is passed through the compression fitting, it is inserted from the lower side in FIG. Further, in the present invention, since the sheath heater provided with the terminal and the non-heat generating part on both sides is used, if the terminals on both sides do not face the same direction, the assembly by “insertion” cannot be performed. For this reason, when the heat generating portion is formed into a coil shape, a two-winding structure is used. In other words, the double-winding structure folded at the center of the heat generating portion has the non-heat generating portions at both ends on the same side, and by placing the non-heat generating portions in parallel, when inserting into the compression fitting, By inserting both non-heat generating parts at the same time, it is possible to perform assembly without difficulty. Further, since the non-heat generating portion of the sheath heater 9 penetrates the seal portion, the terminal can be disposed outside the flue while the heat generating portion is disposed inside the flue.

  Further, by arranging the coil-shaped axis formed by the heat generating part of the sheath heater 9 and the axis of the injector 6 to coincide with each other, the conical shape of the spray with the injection axis as the central axis and the heat generating part of the heater are concentric. Therefore, when vaporizing the spray, it is possible to make the load on the heater heat generating portion uniform. If the load on the heat generating part of the heater is non-uniform, the temperature will rise at light places and the temperature will fall at places where the load is heavy. . Further, at a portion where the load is light and the heater temperature rises, heat is easily transferred to the outside by the temperature rise, and heat loss increases. For this reason, the equalization of the heat load on the heat generating part is directly connected to the reduction of the power consumption of the heater, and the power consumption can be lowered as the uniformity is achieved.

  Further, since the shunt gas flowing into the shunt passage is a branch of the exhaust gas, when the exhaust gas temperature rises, the temperature of the shunt gas naturally rises and the temperature of the shunt pipe 8 also rises. Also in this case, it is necessary to protect the injector 6 which is an electrical component from high temperature, and a cooling water circulation passage is provided inside the injector holder 13. For this reason, a cooling water inlet / outlet 13c is provided to prevent the temperature of the electrical circuit of the injector from rising and to prevent the urea water passage in the injector from rising, thereby preventing urea precipitation associated with vaporization of only the water of the urea water. Thus, clogging due to precipitation does not occur. As the cooling water circulated in the injector holder 13, engine cooling water or urea water can be used. In addition, urea water to be injected by the injector 6 is supplied through the injector head 15.

  FIG. 7 is a diagram illustrating the detailed structure of the electric heater used in the first embodiment. The sheath heater 9 is composed of a heat generating portion 9a, a non-heat generating portion 9b, an insulator 9c, and a terminal 9d. The heat generating portion 9a and the non-heat generating portion 9b are covered with a protective tube. Is electrically insulated from the terminal 9d by contacting the insulator 9c. Further, the inside of the heat generating portion 9a includes a heat generating wire that generates heat due to an electrical resistance such as a nichrome wire and an insulating material surrounding it, and these are covered with a protective tube. The inside of the non-heat generating portion 9b has a conductive wire and an insulating material surrounding it, and these are covered with a protective tube. The conducting wire functions to electrically connect the heating wire and the terminal 9d, and has a low electrical resistance, so that it does not generate heat even when a current flows. Since the electrical wiring for supplying power to the heater is electrically connected only to the terminal 9d, the protective tubes of the heat generating portion 9a and the non-heat generating portion 9b are electrically insulated. Since the protective tube is electrically insulated, it is possible to use metal for the material of the protective tube, and it can withstand high temperatures. However, since it is electrically insulated, there is no need to worry about leakage into the flue. Further, the insulator 9c is also protected by the injector holder 13 being forcibly cooled by the cooling water. That is, since the insulator 9c cannot be made of metal and cannot withstand high temperatures, the temperature of the diverted gas is reduced by cooling the injector holder 13 that may transmit heat to the non-heat generating portion 9b in contact with the insulator 9c. The temperature rise of the insulator 9c due to the rise is prevented, and reliability can be ensured.

  The right side of FIG. 7 is a view of the left sheath heater as viewed from directly below, and it is possible to wrap one heating part in two lines by folding it back into an S shape at a location 9e which is the center of the heating part 9a. ing. In performing the folding, the S shape is an effective shape for obtaining a maximum bending radius in a limited space. The heating portion 9a of the heater includes a heating wire, an insulating material, and a protective tube in the cross section. The smaller the bend radius, the more the heating wire 9 is deformed, and the heat generation is more likely to be stressed due to thermal expansion. Increase the possibility of breaking the wire. For this reason, for the durability of the heater, it is desirable that the bending radius when bending is increased as much as possible so that the heating wire is not deformed. Therefore, forming the S-shape at the center of the heat generating portion 9a has the effect of increasing the durability of the heater.

  As for the coil shape of the heat generating portion 9a, the winding pitch on the non-heat generating portion side is made fine, and the winding pitch on the side far from the non-heat generating portion is made large. This is because the urea water injection device is arranged on the non-heating part side, and the spray injected from the injection device is radiated concentrically, so that the density of the spray is closer to the injection point And the density of spray decreases as the distance from the injection point increases. This means that for a heater intended to vaporize the spray, the side closer to the injection point absorbs heat more and the side far from the injection point absorbs less heat. Therefore, on the injection point side where heat absorption is large, the heater winding pitch is reduced to increase the amount of heat generated per space, and on the side far from the injection point where heat absorption is small, the heater winding pitch is increased. Thus, by reducing the amount of heat generated per space, the heat load of the heater can be made uniform, and the power consumption of the heater is reduced.

  An electric heater in the urea water injector according to the second embodiment of the present invention will be described with reference to FIG. FIG. 8 shows only the electric heater of the urea water injector, and other parts are the same as those in the first embodiment, and the method of attaching the electric heater is also the same as in the first embodiment.

  The sheath heater 20 shown in FIG. 8 is composed of a heat generating portion 20a, a non-heat generating portion 20b, an insulator 20c, and a terminal 20d, and the heat generating portion 20a and the non-heat generating portion 20b are covered with a protective tube. The protective tube is electrically insulated from the terminal 20d by contacting the insulator 20c. Moreover, the inside of the heat generating portion 20a includes a heat generating wire that generates heat due to an electrical resistance such as a nichrome wire and an insulating material surrounding it, and these are covered with a protective tube. The inside of the non-heat generating part 20b has a conducting wire and an insulating material surrounding it, and these are covered with a protective tube, and the conducting wire electrically connects the heating wire and the terminal 20d. The right side of FIG. 8 is a view of the left sheath heater as viewed from directly below, and is folded back into an S shape at a location 20e corresponding to the center of the heat generating portion 20a.

  Further, the heat generating portion 20a has a coil shape but a shape in which the winding diameter is changed, and the winding diameter on the non-heating portion side is large and the winding diameter on the side far from the non-heating portion is small. This is because the urea water injection device is disposed on the non-heat generating portion side, and the spraying is uniformized on the side closer to and away from the non-heat generating portion. The amount of spray that reaches the heater far from the injection point is reduced from the near side, but by reducing the winding diameter, the surface of the heat generating part of the heater is positioned more visible from the injection point. It becomes possible to compensate for the decrease in the arrival of the spray. At the same time, a combination of a smaller winding pitch on the side closer to the injection point and a larger winding pitch on the far side makes it possible to further equalize the heat load of the heater and reduce the power consumption of the heater. ing.

It is a figure showing the whole urea water injection device composition concerning a 1st embodiment of the present invention. It is a front view of the urea water injection | pouring apparatus which concerns on the 1st Embodiment of this invention. It is AA arrow sectional drawing in FIG. 2 of the urea water injection apparatus which concerns on the 1st Embodiment of this invention. It is CC arrow sectional drawing in FIG. 3 of the urea water injection apparatus which concerns on the 1st Embodiment of this invention. It is BB arrow sectional drawing in FIG. 2 of the urea water injection apparatus which concerns on the 1st Embodiment of this invention. It is an exploded view of the urea water vaporizer in the urea water injection apparatus which concerns on the 1st Embodiment of this invention. It is the front view and bottom view of the sheath heater single-piece | unit in the urea injection apparatus which concerns on the 1st Embodiment of this invention. It is the front view and bottom view of the sheath heater single-piece | unit in the urea injection apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

1, 2, 3 Exhaust flue outer wall 4 Exhaust flue constriction flow path 5, 6 Injector 7 Split gas introduction part 8 Split pipe 9 Electric heater 10 Hydrolysis catalyst 11 Swirling blades 12, 13 Injector holder 14 Compression fittings 15, 16 Injector head 17 Split gas blowing holes 101, 102 Urea water spray 201 Exhaust gas 202, 203 Urea water

Claims (7)

An injection device that injects urea water in a spray form and an electric heater that heats and vaporizes the urea water injected from the injection device, and injects ammonia components generated from the urea water into the exhaust flue of the engine In the urea water injection device for exhaust treatment,
The electric heater, the opposite ends of the heat generating portion, and a non-heat generating portion, and a terminal for connection with the wire, with a protective tube the non-heat generating portion and the heating portion is electrically insulated from said terminal The sheath heater is covered, and the heating portion of the sheath heater is formed in a two-winding coil shape that is folded at the center, and the heating portion is injected into the internal space of the exhaust flue from the injection device with the urea water injection shaft The conical shape of the spray with the central axis and the heat generating part of the sheath heater are arranged so as to face each other concentrically , the non-heat generating parts at both ends are aligned, and the terminals at both ends are connected to the exhaust flue. located outside the space, the urea water injection device of the non-heat generating portions at both ends for exhaust treatment, characterized in that fixed to seal the member connected to the exhaust flue.   The urea water injection device for exhaust treatment according to claim 1, wherein a member for fixing the injection device and the sheath heater is common.   2. The urea water injection device for exhaust treatment according to claim 1, wherein a non-heat generating portion of the sheath heater is sealed and fixed by compression fitting. 2. The urea water injection device for exhaust treatment according to claim 1, wherein the sheath heater and the injection device are installed at a location where the exhaust flue is diverted. . 2. The exhaust gas treatment apparatus according to claim 1 , wherein at least a part of a surface of the heat generating portion of the sheath heater is coated with a catalyst component having a function of promoting urea hydrolysis. Urea water injection device. An injection device that injects urea water in a spray form and an electric heater that heats and vaporizes the urea water injected from the injection device, and injects ammonia components generated from the urea water into the exhaust flue of the engine In the urea water injection device for exhaust treatment,
The electric heater has a non-heat generating portion and a terminal for connecting to a conductive wire at both ends of the heat generating portion, and the heat generating portion and the non-heat generating portion are covered with a protective tube that is electrically insulated from the terminal. constituted by dividing sheath heater, and the two rows turn coil shape of the heating portion was folded back at the center of the sheath heater, non-heating portions at both ends is shaped to align the orientation, turns of the coil shape formed by the heating portion of the sheath heater the pitch, the injector side is small close to the larger side far from the injection device, the heating portion of the sheath heater disposed in the internal space of the exhaust duct, the coil shape formed by the heating portion of the sheath heater The central axis of the exhaust device is arranged on the injection shaft of the injection device, the terminals at both ends are arranged in the external space of the exhaust flue, and the non-heat generating portions at both ends are sealed to members connected to the exhaust flue. Urea water injection device for an exhaust process, which comprises a constant. An injection device that injects urea water in a spray form and an electric heater that heats and vaporizes the urea water injected from the injection device, and injects ammonia components generated from the urea water into the exhaust flue of the engine In the urea water injection device for exhaust treatment,
The electric heater has a non-heat generating portion and a terminal for connecting to a conductive wire at both ends of the heat generating portion, and the heat generating portion and the non-heat generating portion are covered with a protective tube that is electrically insulated from the terminal. constituted by dividing sheath heater, and the two rows turn coil shape of the heating portion was folded back at the center of the sheath heater, non-heating portions at both ends is shaped to align the orientation, turns of the coil shape formed by the heating portion of the sheath heater diameter, side is larger closer to the injector, the small side far from the injection device, the heating portion of the sheath heater disposed in the internal space of the exhaust duct, the coil shape formed by the heating portion of the sheath heater The central axis of the exhaust device is arranged on the injection shaft of the injection device, the terminals at both ends are arranged in the external space of the exhaust flue, and the non-heat generating portions at both ends are sealed to members connected to the exhaust flue. Solid Urea water injection device for an exhaust process, which comprises.

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