JP2014227860A - Exhaust emission control system and its radiation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system and an exhaust emission control method capable of preventing a reduction in the NOx eliminating rate of an exhaust emission control device such as a selective reduction type catalyst, and of compatibly improving a fuel consumption rate and exhaust gas performance without reducing the NOx eliminating rate during the light load operation of an engine and during the high load operation of the engine to be good in the fuel consumption rate, as well.SOLUTION: An exhaust gas passage 12 between a turbine 13t and an exhaust emission control device 30 is formed with a radiation exhaust gas pipe 12A. Radiation surface area increasing members 12Ba, 12Bb are provided on the radiation exhaust gas pipe 12A. Thus, when an internal combustion engine 10 continuously operates at a rated output, a radiation surface area S of a portion of the radiation exhaust gas pipe 12A becomes an optimum radiation surface area S1 to keep a temperature Tg of exhaust gas G flowing into the exhaust emission control device 30 to be a preset eliminating rate holding upper limit temperature T2 or lower.

Description

  The present invention relates to an exhaust gas purification system that purifies nitrogen oxide (NOx) and the like in exhaust gas of an internal combustion engine such as a diesel vehicle, and a heat dissipation method thereof.

  An exhaust gas aftertreatment device disposed in an exhaust gas passage of a diesel engine or the like mounted on a vehicle has a urea water addition type selective reduction type catalyst device (hereinafter referred to as an SCR catalyst device) as a catalyst for purifying NOx (nitrogen oxide). Is used. This SCR catalyst device is a device that reduces and purifies NOx by the catalytic action of the SCR catalyst by using ammonia that is generated by the urea water injected into the exhaust gas from the urea water injector reacting with the exhaust gas and being decomposed. It is.

  In this SCR catalyst, at present, as shown in FIG. 12, when the temperature of the exhaust gas discharged from the engine and flowing into the SCR catalyst is low (for example, 200 ° C. (deg. C) or less), or When the temperature of the exhaust gas is high (for example, 480 ° C. or higher), the NOx purification rate is significantly reduced. As described above, the current SCR catalyst has a temperature range (in the vicinity of 300 ° C. to 450 ° C. in FIG. 12) Rt between the purification rate maintenance lower limit temperature T1 and the purification rate maintenance upper limit temperature T2 with good activity. Exists. Therefore, the NOx purification rate is lowered not only when the engine load is low and the exhaust gas temperature is low, but also when the engine load is high and the exhaust gas temperature is high.

  In this regard, in the prior art, attention has been focused on improving the purification rate of the exhaust gas when the engine is warming up or idling, etc., for example, suppressing the accumulation of solid matter generated from urea water In addition, in order to ensure a good exhaust gas purification rate, the bent part provided between the urea water injector and the ammonia reduction catalyst in the exhaust passage is made into a double pipe structure, and heat is radiated from the inside to the outside during that time. There has been proposed an exhaust emission control device provided with a heat dissipation suppressing member that suppresses (see, for example, Patent Document 1).

  However, recently, in order to improve the fuel consumption rate of the engine, the frequency of operation in the region where the engine load is high has increased, and when the engine is operating at a high load, that is, the temperature of the exhaust gas becomes high. Under such conditions, it has become important to develop a technique for preventing a reduction in the NOx purification rate.

  For example, in order to be able to use the NOx catalyst in a temperature range with a high NOx purification rate regardless of the operating state of the engine, the exhaust passage is branched into the first passage and the second passage, and then merged, In order to increase the heat dissipation effect, an exhaust cooling promoting portion having an arcuate cross section is provided, and the exhaust gas temperature in the first passage is decreased more than the exhaust gas temperature in the second passage, so that the exhaust gas There has been proposed an exhaust purification device for an internal combustion engine that selectively uses a first passage and a second passage according to temperature (see, for example, Patent Document 2).

  However, in this exhaust gas purification apparatus for an internal combustion engine, it is necessary to branch the exhaust passage, and in addition, an exhaust temperature sensor, a first exhaust gas switching valve, a second exhaust gas switching valve, and control thereof are required. There is a problem that the size is easily increased and the control is complicated.

JP 2010-31718 A JP 2001-214734 A

  The present invention has been made in view of the above situation, and an object of the present invention is to adjust the heat radiation amount in the exhaust gas piping to an exhaust gas temperature within a temperature range having a high purification rate. Even when the load is light, the NOx purification rate is not reduced, and even when the engine has a high fuel consumption rate, the NOx purification rate is not lowered. It is an object of the present invention to provide an exhaust gas purification system and a heat dissipation method thereof that can achieve both improvement in performance.

  In order to achieve the above object, an exhaust gas purification system according to the present invention is an exhaust gas system in which an exhaust gas purification device for purifying exhaust gas is disposed downstream of a turbine of a turbocharger in an exhaust gas passage of an internal combustion engine. In the purification system, an exhaust gas passage between the turbine and the exhaust gas purification device is formed by a radiating exhaust gas pipe, and a radiating surface area increasing member is provided in the radiating exhaust gas pipe so that the internal combustion engine is continuously operated at a rated output. When operating, the heat radiating surface area of the heat radiating exhaust gas piping portion is set to an optimum heat radiating surface area that keeps the temperature of the exhaust gas flowing into the exhaust gas purifying device below a preset purification rate maintenance upper limit temperature. Configure.

  As this heat radiating surface area increasing member, for example, a heat radiating fin, a heat radiating plate, a heat radiating wire mesh or the like can be used. It should be noted that the heat radiation surface area of the heat radiation exhaust gas piping portion does not always need to be the optimum heat radiation surface area, and may be any structure that provides the optimum heat radiation surface area when the internal combustion engine is continuously operated at the rated output. . In other words, the surface area of the heat dissipation is small so that the temperature of the exhaust gas exhaust pipe is not too low so that the temperature of the exhaust gas does not decrease too much, and the temperature of the exhaust gas does not rise too much only when the temperature of the exhaust gas exhaust pipe is high. It is preferable that the heat dissipation surface area be increased.

  According to this configuration, when the internal combustion engine is continuously operated at the rated output due to the arrangement of the heat radiating surface area increasing member, the heat radiating surface area of the radiating exhaust gas piping portion becomes the optimum heat radiating surface area, so the temperature of the exhaust gas is high. Even if it becomes, the temperature of the exhaust gas flowing into the exhaust gas purification device can be maintained below the preset purification rate maintenance upper limit temperature, the exhaust gas purification efficiency can be tampered with in a good state, and the exhaust gas is purified efficiently can do.

In the exhaust gas purification system, the optimum heat radiation surface area S1 (m ² ) is determined based on the exhaust gas volume flow rate V (m ³ / s) discharged when the internal combustion engine is operated at a rated output. When the cross-sectional area A (m ² ) of the radiating exhaust gas pipe is 30 (m / s) ≦ V / A ≦ 70 (m / s), and A = πR ² and C = 2πR, 4 .5 × C ≦ S1 ≦ 7.5 × C. The optimum heat radiation surface area S1 (m ² ) is an area including the surface area of the heat radiation exhaust gas pipe.

Here, the exhaust gas volume flow rate V is the exhaust gas volume flow rate (m ³ ) that passes through the radiating exhaust gas pipe part during engine rated operation, and 30 (m / s) is the exhaust gas volume assumed during engine rated operation. It is a lower limit flow velocity (m / s), and 70 (m / s) is an upper limit flow velocity (m / s) of the exhaust gas assuming the engine rated operation.

Based on the cross-sectional area A (m ² ) of this heat radiation exhaust gas pipe, the perimeter length C (C ² = (2πR) ² = 4πA, C = 2√ (πA)) when the exhaust gas pipe is circular. The surface area C × L (m ² ) of the circular pipe is determined from the temporarily set pipe length L (m), and the heat radiating surface area S is a parameter based on the surface area C × L (m ² ) of the circular pipe. The exhaust gas NOx with respect to the engine load is calculated with reference to the NOx purification rate of the selective reduction catalyst (SCR catalyst) of the selective reduction catalyst device (SCR catalyst device) with respect to the exhaust gas temperature. The purification rate is estimated, and the optimum heat radiation surface area S1 of the heat radiation exhaust gas piping portion is calculated from the estimation result of the NOx purification rate, and 4.5 × C ≦ S1 ≦ 7.5 × C is obtained.

If the optimum heat radiation surface area S1 (m ² ) is less than “4.5 × C”, the heat radiation amount in the heat radiation exhaust gas pipe is insufficient, and the temperature of the exhaust gas flowing into the selective catalytic reduction device becomes too high. As a result, the NOx purification rate of the selective catalytic reduction catalyst may be reduced. Further, if the optimum heat radiation surface area S1 (m ² ) is larger than “7.5 × C”, the heat radiation amount in the heat radiation exhaust gas piping becomes excessive, and the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst becomes low. As a result, the NOx purification rate of the selective catalytic reduction catalyst may decrease.

  In other words, in order to prevent a decrease in the NOx purification rate during high-load operation, the heat dissipation amount of the exhaust gas piping is increased, but excessive heat dissipation reduces the temperature of the exhaust gas, so the purification rate at light loads is reduced. There is a fear. Therefore, calculate the amount of heat radiation so that the optimal NOx purification rate can be maintained even at light loads and at high loads, even when the load is light or high, and the optimum heat dissipation surface area is obtained. It was set.

  According to this structure, the exhaust gas temperature becomes high by adding a heat radiation surface area increasing member so that the heat radiation surface area when the internal combustion engine is continuously operated at the rated output becomes the optimum heat radiation surface area. However, the exhaust gas can be cooled by the heat radiation of the exhaust gas exhaust pipe part, and the exhaust gas temperature flowing into the exhaust gas purification device can be kept below the preset purification rate maintenance upper limit temperature, so the exhaust gas purification efficiency is good The exhaust gas can be purified in a safe state.

  In the above exhaust gas purification system, a part or all of the heat radiating surface area increasing member is constituted by a first heat radiating member provided fixed to the heat radiating exhaust gas pipe. In this configuration, the first heat radiating member such as the heat radiating plate and the heat radiating fin is fixed to the heat radiating exhaust gas piping by welding or the like, so that the thermal conductivity between the heat radiating exhaust gas piping and the first heat radiating member is maintained well. Efficient heat dissipation.

  In the exhaust gas purification system, a part or all of the heat radiation surface area increasing member is separated from the heat radiation exhaust gas pipe when the internal combustion engine is stopped, and the internal combustion engine is rated. In the state of continuous operation with output, the second heat radiating member is in contact with the heat radiating exhaust gas pipe.

  According to this configuration, in a state where the exhaust gas temperature is low and the temperature of the radiating exhaust gas pipe is low, or the internal combustion engine is stopped, the radiating exhaust gas pipe and the second heat radiating member are separated from each other. Therefore, there is no heat conduction between the two, and the amount of heat radiation from the second heat radiating member can be reduced. Therefore, when the temperature of the exhaust gas is low, the amount of heat released from the heat radiating exhaust gas pipe can be significantly reduced. As a result, the amount of heat released when the exhaust gas is low can be reduced, and at the time of warm-up, the purification rate maintenance lower limit temperature can be quickly reached, and even when the engine load is small and the exhaust gas temperature is low, It can be maintained above the purification rate maintenance lower limit temperature with less fuel consumption.

  On the other hand, when the exhaust gas temperature is high and the temperature of the radiating exhaust gas pipe is high, the radiating exhaust gas pipe and the second radiating member are thermally expanded, and the radiating exhaust gas pipe and the second radiating member are in contact with each other Therefore, heat conduction occurs between the two. Therefore, the amount of heat released from the second heat radiating member can be increased, and when the exhaust gas temperature is high, the amount of heat released from the heat radiating exhaust gas piping can be remarkably increased, and the purification rate maintenance upper limit temperature can be reached.

  In other words, by utilizing the thermal expansion of the heat radiating exhaust gas pipe and the second heat radiating member, the presence or absence of heat conduction to the second heat radiating member can be automatically switched depending on the temperature of the heat radiating exhaust gas pipe. Since the temperature of the exhaust gas piping and the exhaust gas passing through this portion can be maintained within a temperature range in which the purification rate is good, the exhaust gas can be purified efficiently.

  In addition, if the area where the second heat radiating member and the heat radiating exhaust gas pipe are in contact with each other is formed in a shape larger than the cross-sectional area of the second heat radiating member, for example, a V shape or a semicircular shape, the contact surface increases, It is more preferable because heat conduction between the two is easily performed well.

  In the exhaust gas purification system, the first heat radiating member or the second heat radiating member is formed of a material whose shape changes depending on temperature. For example, if the temperature rises with bimetal or shape memory alloy, etc., the heat sink made of bimetal or shape memory alloy will open, the surface area will be doubled, the heat sink facing each other will bend, and the heat dissipation surface will be Or try not to face each other.

  According to this structure, the 1st heat radiating member or the 2nd heat radiating member from which a heat radiating surface area changes greatly with temperature can be comprised easily, and the heat radiation effect by a 1st heat radiating member or a 2nd heat radiating member becomes large as a temperature rises. It can be constituted as follows.

  And the heat dissipation method of the exhaust purification system of the present invention for achieving the above object is an exhaust gas purification device for purifying exhaust gas downstream of the turbine of a turbocharger in an exhaust gas passage of an internal combustion engine. In the heat dissipation method of the exhaust gas purification system, the internal combustion engine is continuously operated at a rated output with respect to the heat dissipation surface area of the heat dissipation exhaust gas pipe forming an exhaust gas passage between the turbine and the exhaust gas purification device. The temperature of the exhaust gas flowing into the exhaust gas purification device is set to a preset purification rate maintenance upper limit temperature or less with a preset optimum heat radiating surface area.

  According to this method, when the internal combustion engine is continuously operated at the rated output, the heat radiating surface area of the radiating exhaust gas piping portion becomes the optimum heat radiating surface area, so even if the exhaust gas temperature becomes high, the exhaust gas purification device The exhaust gas flowing into the exhaust gas can be maintained at a temperature equal to or lower than a preset purification rate maintenance upper limit temperature, and the exhaust gas can be purified with a good exhaust gas purification efficiency.

  According to the exhaust gas purification system and the heat dissipation method thereof according to the present invention, the temperature of the exhaust gas is adjusted by optimizing the heat radiation amount in the exhaust gas piping between the turbine of the turbocharger and the exhaust gas purification device such as the selective reduction catalyst device. By setting the temperature within a temperature range with a high purification rate, the NOx purification rate is not lowered even when the engine is lightly loaded, and the NOx purification rate is also obtained during high-load operation of the engine with a good fuel consumption rate. The fuel consumption rate and the exhaust gas performance can be improved at the same time.

It is a figure which shows the structure of the exhaust-gas purification system of embodiment of this invention. It is a figure which shows typically the relationship between the load of an engine and a NOx purification rate with respect to the change of the surface area of heat radiation exhaust gas piping. FIG. 3 is a diagram schematically showing the relationship between the engine load and the NOx purification rate at a heat radiation surface area of 1.5 and 2.5 magnifications of the surface area of the radiant exhaust gas pipe in FIG. 2. It is a figure which shows an example of a structure of the 1st heat radiating member formed with the heat sink. It is a figure which shows an example of a structure of the 1st heat radiating member formed with the heat sink and the heat radiating wire mesh. It is a figure which shows an example of a structure of the 2nd heat radiating member formed with the heat sink, and is a figure which shows the state spaced apart from the thermal radiation exhaust gas piping. It is a figure which shows the state which the 2nd heat radiating member of FIG. 6 contact | abutted with the thermal radiation exhaust gas piping. It is a figure which shows an example of a structure of the 1st heat radiating member formed with the bimetal plate, and is a figure which shows a state with low temperature. It is a figure which shows the state with the high temperature of the 1st heat radiating member of FIG. It is a figure which shows the other example of a structure of the 1st heat radiating member formed with the bimetal plate, and is a figure which shows a state with low temperature. It is a figure which shows the state with the high temperature of the 1st heat radiating member of FIG. It is a figure which shows typically the relationship between the temperature of a SCR catalyst, and a NOx purification rate.

  Hereinafter, an exhaust gas purification system and a heat dissipation method thereof according to embodiments of the present invention will be described with reference to the drawings. Here, the selective reduction type catalyst (SCR catalyst) is a urea water addition type selective reduction type catalyst (urea SCR catalyst) and the ammonia type solution is urea water. However, the present invention is not limited to this, and the hydrocarbon addition type A selective reduction catalyst (HC-SCR catalyst) or the like may be used.

  As shown in FIG. 1, an exhaust gas purification system 1 according to an embodiment of the present invention includes PM (particulate matter), NOx (in the exhaust gas G of an internal combustion engine (hereinafter referred to as an engine) 10 such as a diesel engine. An exhaust gas purification system for purifying exhaust gas G in the exhaust gas passage 12 of the engine 10 on the downstream side of the turbine 13t of the turbocharger 13. Composed.

  In the configuration of FIG. 1, the turbine 13 t of the turbocharger (turbo supercharger) 13 and the exhaust gas purification device 30 are provided in the exhaust gas passage 12 of the engine 10 in order from the exhaust manifold 11 a connected to the engine body 11. Deploy. The exhaust gas purification device 30 includes a upstream oxidation catalyst (front DOC) 32, a PM collection filter device 33, a urea selective reduction catalyst device (hereinafter referred to as SCR device) 34, a rear oxidation catalyst (rear DOC) from the upstream side. ) 35 is arranged. A urea injection nozzle 31 that is an ammonia-based solution supply device is disposed upstream of the SCR device 34.

  Further, an EGR passage 14 is provided to perform EGR for NOx reduction, and the EGR gas Ge, which is a part of the exhaust gas G, flows into the intake manifold 11b, and together with the air A sucked in the intake passage 14, the engine 10 Supply to the cylinder.

  Further, the exhaust gas purification system 1 includes a temperature sensor 41 that measures the temperature Tg of the exhaust gas G at the inlet of the SCR device 34, a NOx concentration sensor 42 that measures the NOx concentration downstream of the SCR device 34, and a PM. A differential pressure sensor 43 that measures the differential pressure ΔP across the collection filter device 33 is provided. In addition, an exhaust gas purification control device 40 that inputs the measurement values of the temperature sensor 41, the NOx concentration sensor 42, and the differential pressure sensor 42 and controls the purification of the exhaust gas G is provided.

  The exhaust gas purification control device 40 is commonly used as an engine control device (ECU) 50 called an ECU (engine control unit) that controls the overall operation of the engine 10. That is, the exhaust gas purification control device 40 is incorporated in the engine control device 50.

  In the exhaust gas purification system 1 illustrated in FIG. 1, when the temperature Tg of the exhaust gas G is low, the temperature Tg of the exhaust gas G is increased by in-cylinder combustion injection of the engine 10 to increase the temperature of the preceding oxidation catalyst device. If Td is set to the activation temperature Tdc or higher, and the temperature Td of the preceding oxidation catalyst device is equal to or higher than the activation temperature Tdc, carbon monoxide (CO) or carbonization in the exhaust gas G is detected by the previous oxidation catalyst device. Hydrogen (HC) is oxidized, and the temperature Tg of the exhaust gas G is increased by these oxidation heats, and the temperature Ts of the SCR device 34 and the temperature Tp of the PM collection filter device 33 are increased. When carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas G are insufficient, hydrocarbons are supplied into the exhaust gas G by post injection or the like.

  If the temperature Ts of the SCR device 34 is equal to or higher than the activation temperature Tsc of the SCR catalyst, the urea water F is discharged from the urea injection nozzle 31 so that the NOx concentration detected by the NOx concentration sensor 42 becomes zero. The ammonia generated by the decomposition of the urea water F is supplied to the SCR device 34 to reduce and purify NOx.

  Further, the PM collection filter 33 collects PM (particulate matter) in the exhaust gas G. When the PM collected by the PM collection filter 33 exceeds a preset accumulation upper limit amount, exhaust is performed by post injection or the like. Hydrocarbon is supplied into the gas G, this hydrocarbon is oxidized by the preceding oxidation catalyst device, the exhaust gas G is heated by this oxidation heat, and the temperature Tp of the PM collection filter 33 is changed to the PM combustion temperature Tpc. The PM collection filter device 33 is regenerated by raising the above and burning and removing the collected PM.

  Further, in the subsequent oxidation catalyst device, excess ammonia in the exhaust gas G flowing out from the exhaust gas purification device 30 is oxidized and decomposed to suppress ammonia slip, and hydrocarbons in the exhaust gas G ( HC) is oxidized to suppress HC slip.

  In the present invention, the exhaust gas passage 12 between the turbine 13t of the turbocharger 13 and the exhaust gas purification device 30 is formed by the radiating exhaust gas pipe 12A, and the radiating exhaust gas pipe 12A has a radiating surface area increasing member 12Ba, 12Bb is provided.

  When the engine 10 is continuously operated at the rated output, the heat radiating surface area S of the portion of the heat radiating exhaust gas pipe 12A has a purification rate in which the temperature Tg of the exhaust gas G flowing into the exhaust gas purifying device 30 is set in advance. The optimum heat radiation surface area S1 is set to the maintenance upper limit temperature T2 or lower. In other words, in the configuration in which the heat radiation surface area increasing members 12Ba and 12Bb are added to the heat radiation exhaust gas pipe 12A, the entire heat radiation surface area S including the surface area of the heat radiation exhaust gas pipe 12A is set to the optimum heat radiation surface area S1. As the heat radiating surface area increasing members 12Ba and 12Bb, for example, heat radiating fins, a heat radiating plate as shown in FIG. 4, a heat radiating wire net as shown in FIG.

This optimum heat radiating surface area S1 (m ² ) is based on the exhaust gas volume flow V (m ³ / s) discharged when the engine 10 is operated at the rated output, and the exhaust gas assumed for the engine rated operation is assumed. The lower limit flow velocity (m / s) is 30 (m / s) and the upper limit flow velocity (m / s) is 70 (m / s). Thus, the cross-sectional area A of the heat radiating exhaust gas pipe 12A is set so as to satisfy 30 (m / s) ≦ V / A ≦ 70 (m / s).

Further, C (C ² = (2πR) ² = 4πA, C = 2√ (πA)) is calculated based on the cross-sectional area A of the heat radiating exhaust gas pipe 12A, and the optimum heat radiating surface area S1 (m ² ) is calculated. It is set within the range of 4.5 × C ≦ S1 ≦ 7.5 × C.

The range of the optimum heat radiation surface area S1 (m ² ) is set based on the following idea. That is, assuming that the radius when the radiating exhaust gas pipe 12A is a circular pipe is R, the sectional area A (m ² ) of the radiating exhaust gas pipe 12A is A = πR ² , and the outer periphery C (m) is C = 2πR. In other words, based on the cross-sectional area A (m ² ) of the radiating exhaust gas pipe 12A, the perimeter length C (C ² = (2πR) ² = 4πA, C = 2 when the radiating exhaust gas pipe 12A is a circular pipe. √ (πA)) (m) is obtained.

Further, the surface area C × L (m ² ) of the circular pipe is determined from the temporarily set pipe length L (m), and the heat radiation surface area S is set as a parameter based on the surface area C × L (m ² ) of the circular pipe. As shown in FIG. 2, the amount of change in the engine load is calculated by calculating the temperature T of the exhaust gas G by calculating the temperature T of the exhaust gas G and referring to the purification rate of the SCR catalyst from the temperature T of the exhaust gas G. The purification rate of the exhaust gas G was calculated.

  In FIG. 2, the exhaust gas G changes with respect to the amount of change in the engine load (horizontal axis) when the surface area is 1.0 to 5.0 times the total exhaust pipe area 1 when the current circular pipe is used. The purification rate is shown on the vertical axis. From the estimation result of this purification rate, it was found that a good purification rate can be obtained at both light and high loads by setting the exhaust pipe total area 1 to 1.5 to 2.5 times. As shown in Fig. 4, the optimum heat radiating surface area S1 range Rs of the heat radiating exhaust gas pipe 12A is extracted, and the case where the surface area is 1.5 times to 2.5 times is selected, and 4.5 × C ≦ S1 ≦ 7.5 × C.

  For example, the length L of the radiant exhaust gas pipe 12A from the outlet of the turbine 13t of the engine 10 to the inlet of the SCR device 34 is 3.00 m, and the pipe diameter of the radiant exhaust gas pipe 12A is 0.10 m (100 mm). Then, it is a trial calculation which should just install ten 1st heat radiating member 12Ba of height 0.03m (30mm) and width 0.01m (10mm) along the length L of 12 A of heat exhaust gas piping.

  The heat radiating surface area S of the heat radiating exhaust gas pipe 12A does not always need to be the optimum heat radiating surface area S1, and is the optimum heat radiating surface area S1 when the engine 10 is continuously operated at the rated output. If it is good. In addition, by setting the time when the engine 10 is continuously operated at the rated output as a reference state when the temperature Tg of the exhaust gas G becomes high, the optimum heat radiation surface area S1 can be easily set.

  As a configuration in which the heat radiation surface area S of the heat radiation exhaust gas pipe 12A is always the optimum heat radiation surface area S1, a part or all of the heat radiation surface area increasing members 12Ba and 12Bb are fixed to the heat radiation exhaust gas pipe 12A. 1 heat dissipating member 12Ba.

  In this configuration, as shown in FIG. 4, the first heat radiating member 12Ba of the heat radiating plate or the heat radiating fin is fixed to the heat radiating exhaust gas pipe 12A by welding or the like. Further, as shown in FIG. 5, the first heat dissipating member 12Ba of the heat dissipating wire mesh is fixed to the heat dissipating exhaust gas pipe 12A by welding or the like. Thereby, the heat conductivity between the heat radiating exhaust gas pipe 12A and the first heat radiating member 12Ba can be maintained well, and efficient heat radiation can be performed.

  Further, the heat radiation surface area S of the heat radiation exhaust gas pipe 12A is optimum when the engine 10 is continuously operated at a rated output, not always, and the heat radiation exhaust gas pipe 12A is at a temperature higher than a preset temperature. As a structure used as the thermal radiation surface area S1, there exist the following structures, for example.

  In a state where the engine 10 is stopped, as shown in FIG. 6, the engine 10 is separated from the radiating exhaust gas pipe 12A. In a state where the engine 10 is continuously operated at the rated output, as shown in FIG. The second heat radiating member 12Bb is in contact with the heat radiating exhaust gas pipe 12A.

  When the temperature of the exhaust gas G is low and the temperature of the radiant exhaust gas pipe 12A is low, the second radiating member 12Bb is spaced apart from the radiant exhaust gas pipe 12A and the second radiating member 12Bb as shown in FIG. In this state, there is no heat conduction between the two, and the amount of heat radiation from the second heat radiating member 12Bb can be reduced. Therefore, when the temperature T of the exhaust gas G is low, the amount of heat released from the portion of the heat radiation exhaust gas pipe 12A, that is, the heat radiation exhaust gas pipe 12A and the second heat radiation member 12Bb can be significantly reduced.

  On the other hand, when the temperature T of the exhaust gas G is high and the temperature of the heat radiating exhaust gas pipe 12A is high, the heat radiating exhaust gas pipe 12A and the second heat radiating member 12Bb are thermally expanded, and as shown in FIG. Since 12A and 2nd heat radiating member 12Bb will be in the state contact | abutted, heat conduction will arise between both, and the thermal radiation amount from 2nd heat radiating member 12Bb can be enlarged. Therefore, when the temperature T of the exhaust gas G is high, the heat radiation amount from the heat radiation exhaust gas pipe 12A can be remarkably increased.

  That is, by utilizing the thermal expansion of the radiating exhaust gas pipe 12A and the second radiating member 12Bb, the second radiating member depends on the temperature of the radiating exhaust gas pipe 12A, in other words, depending on the temperature T of the exhaust gas G. The presence or absence of heat conduction to 12Bb can be automatically switched. As a result, the heat exhaust gas pipe 12A and the temperature Tg of the exhaust gas G passing through the heat exhaust gas pipe 12A are maintained within a temperature range Rt having a good purification rate as shown in FIG. Gas G can be purified.

  As shown in FIG. 6, the portion where the second heat radiating member 12Bb contacts the heat radiating exhaust gas pipe 12A has a shape in which the contact area Ac is larger than the transverse area Ab of the second heat radiating member 12Bb, for example, a V shape. It is more preferable that the contact surface area Ac is increased by forming it in a semicircular shape so that the heat conduction between the two increases.

  Further, the heat radiation surface area S of the heat radiation exhaust gas pipe 12A is optimum when the engine 10 is continuously operated at a rated output, not always, and the heat radiation exhaust gas pipe 12A is at a temperature higher than a preset temperature. As another configuration for the heat radiation surface area S1, the shape of the first heat radiation member 12Ba fixed to the heat radiation exhaust gas pipe 12A or the second heat radiation member 12Bb that the heat radiation exhaust gas pipe 12A contacts at a high temperature changes depending on the temperature. The material to be formed.

  For example, when the first heat radiating member 12Ba or the second heat radiating member 12Bb is formed of a bimetal or a shape memory alloy and the temperature is low, as shown in FIG. 8, the heat radiating portion H1 formed of the bimetal or the shape memory alloy is used. When the temperature increases and the temperature rises, as shown in FIG. 9, the heat dissipating part H1 formed of bimetal or shape memory alloy is opened to form a double sheet, and the surface area of the heat dissipating part H1 is doubled. Configure as follows.

  Alternatively, when the temperature is low, as shown in FIG. 10, the heat radiating portions H2 face each other and the heat radiation amount as a whole is small, but when the temperature is high, the heat radiating portion H2 is bent as shown in FIG. Thus, the heat radiation portions H2 are configured such that the surfaces of the heat radiation portions H2 do not face each other and the amount of heat radiation as a whole increases.

  With these configurations, the heat radiating surface area S or the first heat radiating member 12Ba or the second heat radiating member 12Bb having a greatly different heat radiating amount depending on the temperature can be easily configured. The heat radiation effect by the second heat radiation member 12Bb can be increased as the temperature rises.

  According to the exhaust gas purification system 1 having the above-described configuration and its heat dissipation method, the heat dissipation of the heat dissipation exhaust gas pipe 12A portion is achieved when the engine 10 is continuously operated at the rated output due to the arrangement of the heat dissipation surface area increasing members 12Ba and 12Bb. Since the surface area S becomes the optimum heat radiation surface area S1, even if the temperature T of the exhaust gas G becomes high, the temperature T of the exhaust gas G flowing into the exhaust gas purification device 30 is equal to or lower than a preset purification rate maintenance upper limit temperature T2. The exhaust gas G can be purified in a state where the exhaust gas G purification efficiency is good.

  Therefore, in the SCR device 34, the NOx purification rate is not lowered even when the engine 10 is lightly loaded, and the NOx purification rate is lowered even during the high load operation of the engine 10 where the fuel consumption rate is good. Therefore, even when the engine 10 having a good fuel consumption rate is operated at a high load, the NOx purification rate does not decrease, and both the improvement of the fuel consumption rate and the improvement of the exhaust gas performance can be achieved.

  According to the exhaust gas purification system and the heat dissipation method of the present invention, the heat dissipation amount in the exhaust gas piping between the turbine of the turbocharger and the exhaust gas purification device such as the selective reduction catalyst is made appropriate, and the temperature of the exhaust gas is purified. By setting the temperature within a high temperature range, the NOx purification rate is not reduced even when the engine is lightly loaded, and the NOx purification rate is lowered even during high-load operation of the engine with a good fuel consumption rate. Therefore, it is possible to achieve both improvement of the fuel consumption rate and improvement of the exhaust gas performance, so that it can be used as an exhaust gas purification system such as an internal combustion engine mounted on an automobile or the like and a heat dissipation method thereof.

1 Exhaust gas purification system 10 Engine (internal combustion engine)
11 Engine body 12 Exhaust gas passage 12A Heat radiation exhaust gas pipe 12Ba First heat radiation member (heat radiation surface area increasing member)
12Bb second heat radiating member (heat radiating surface area increasing member)
13 Turbo type supercharger 13t Turbine 14 EGR passage 30 Exhaust gas purification device 31 Urea injection nozzle 32 Pre-stage oxidation catalyst (pre-stage DOC)
33 PM collection filter device 34 Urea selective reduction type NOx catalyst device (SCR device)
35 Rear-stage oxidation catalyst (second-stage DOC)
40 exhaust gas purification control device 41 temperature sensor 42 concentration sensor 43 differential pressure sensor 50 engine control device (ECU)
A Cross-sectional area of radiating exhaust gas piping (m ² )
C Perimeter length when the heat exhaust gas pipe is a circular pipe (C ² = (2πR) ² = 4πA) (m)
L Temporarily set piping length (m)
H1, H2 Heat radiation part G Exhaust gas R Radius (m) when heat radiation exhaust gas pipe is a circular pipe
S Heat dissipation surface area of the exhaust heat exhaust gas piping during continuous operation at the rated output of the engine S1 Optimum heat dissipation surface area V Exhaust gas volume flow (m ³ / s)

Claims (6)

  In an exhaust gas purification system in which an exhaust gas purification device for purifying exhaust gas is disposed downstream of a turbine of a turbocharger in an exhaust gas passage of an internal combustion engine, the exhaust gas between the turbine and the exhaust gas purification device When the internal combustion engine is continuously operated at a rated output when the passage is formed by a heat radiation exhaust gas pipe and the heat radiation exhaust gas pipe is provided with a heat radiation surface area increasing member, the heat radiation surface area of the heat radiation exhaust gas pipe portion is: An exhaust gas purification system configured to have an optimum heat radiating surface area that makes the temperature of exhaust gas flowing into the exhaust gas purification device not more than a preset purification rate maintenance upper limit temperature. The optimum heat radiating surface area S1 (m ² ) is determined based on the exhaust gas volume flow rate V (m ³ / s) discharged when the internal combustion engine is operated at a rated output. Is 30 (m / s) ≦ V / A ≦ 70 (m / s), and when A = πR ² and C = 2πR, 4.5 × C ≦ S1 ≦ 7.5 × C is set. The exhaust gas purification system according to claim 1, wherein:   3. The exhaust gas purification system according to claim 1, wherein a part or all of the heat radiating surface area increasing member is configured by a first heat radiating member provided fixed to the heat radiating exhaust gas pipe.   In a state where the internal combustion engine is stopped, a part or all of the heat radiating surface area increasing member is in a state separated from the heat radiating exhaust gas pipe, and in a state where the internal combustion engine is continuously operated at a rated output, 3. The exhaust gas purification system according to claim 1, wherein the exhaust gas purification system is configured by a second heat radiating member in contact with the heat radiating exhaust gas pipe.   5. The exhaust gas purification system according to claim 3, wherein the first heat radiating member or the second heat radiating member is formed of a material whose shape changes with temperature.   In a heat dissipation method of an exhaust gas purification system in which an exhaust gas purification device for purifying exhaust gas is disposed downstream of a turbine of a turbocharger in an exhaust gas passage of an internal combustion engine, the method is provided between the turbine and the exhaust gas purification device. Exhaust gas flowing into the exhaust gas purification device by setting the heat radiating surface area of the radiating exhaust gas pipe forming the exhaust gas passage to a preset optimum heat radiating surface area when the internal combustion engine is continuously operated at a rated output A heat dissipation method for an exhaust gas purification system, wherein the temperature of the gas is set to a preset purification rate maintenance upper limit temperature or less.

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