Arrangement for supplying a medium into an exhaust gas conduit in an internal combustion engine

(54) Title: Arrangement for supplying a medium to an exhaust gas line of an internal combustion engine (56) Published publications: JP A 2 306 929, EP Al 1 054 139, US B2 6 601 385 (47) Abstract:

The present invention relates to an arrangement for supplying a medium to an exhaust pipe (3) of an internal combustion engine (1). The arrangement comprises a vented exhaust passage (12) defined by at least one vented wall surface (10a'-10d ') of an element (10a-10d) and a metering device (4,5,6,7,9) adapted to supply said medium for the exhaust gas passage (12). The arrangement comprises means adapted to maintain a degree of heating of the first wall surface (10a'1 Od ') so as to obtain a higher temperature than the evaporation temperature of the medium as the liquid medium enters the first exhaust passage (12). This ensures that even the medium that hits the first wall surface (10a'-10d ') is evaporated in the first exhaust passage (12).

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528 119

Summary

The present invention relates to an arrangement for supplying a medium to an exhaust pipe (3) of an internal combustion engine (1). The arrangement comprises a first gas passage (12) defined by at least one first wall surface (10a'-1dO ') of an element (10a-10d) and a metering device (4,5,6,7,9) arranged supplying said medium to the first exhaust passage (12). The arrangement comprises means adapted to maintain a degree of heating of the first wall surface (10a'10d ') so as to obtain a higher temperature than the evaporation temperature of the medium when the liquid medium is supplied in the first exhaust passage (12). This ensures that even the medium that hits the first wall surface (10a'-10d ') is evaporated in the first exhaust passage (12).

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BACKGROUND OF THE INVENTION AND PRIOR ART

The invention relates to an arrangement for supplying a medium to an exhaust line of an internal combustion engine according to the preamble of claim 1.

¹⁵

In order to reduce emissions of nitrogen oxides from diesel engines, a technique called Selective Catalytic Reduction (SCR) is used. This technique means that a solution of urea is supplied at a fixed dose to the exhaust gases in a diesel engine's exhaust line. Urea solution can be sprayed into the exhaust pipe so that it is atomized and the urea solution in contact with the hot exhaust gases is evaporated and ammonia is formed. The mixture of ammonia and exhaust gases is then passed through a catalyst where a chemical reaction takes place. The nitrogen of the nitrogen oxides in the exhaust gases here reacts with the nitrogen in the ammonia to form nitrogen gas. The oxygen of the nitrogen oxides reacts with the hydrogen in the ammonia to form water. The nitrogen oxides in the exhaust gases are thus reduced in the catalyst to nitrogen gas and water vapor. With the correct dosage of urea, the emission of nitrogen oxides by the diesel engine can be greatly reduced.

During large parts of a diesel engine's operating condition, the exhaust gases have a sufficiently high temperature to evaporate the urea solution to form ammonia. However, it is difficult to avoid that part of the supplied urea comes into contact with and adheres to the internal wall surface of the exhaust pipe in a non-evaporated state. Exhaust pipe of a vehicle is usually in contact with ambient air. The exhaust pipe is cooled by ambient air to a lower temperature than the exhaust gases inside the exhaust pipe. In most cases, however, the exhaust pipe has a temperature sufficiently high to evaporate and convert the urea solution that hits the internal wall surface of the exhaust pipe to ammonia. 1 de

528 In cases where the exhaust pipe has a temperature that is too low to evaporate and convert the urea solution to ammonia, the urea solution will accumulate on the internal wall surface of the exhaust pipe. The urea solution may crystallize on the inside of the exhaust pipe or leak out via joints in the exhaust pipe and crystallize on the outside of the exhaust pipe. This can lead to malfunctions.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement which supplies a medium to an exhaust pipe of an internal combustion engine where the supplied medium will substantially be completely vaporized in the exhaust pipe even when the liquid in liquid form hits the internal wall surface of the exhaust pipe.

This object is achieved by arrangement of the kind mentioned in the introduction, which is characterized by the features stated in the characterizing part of claim 1. The exhaust gases have a temperature during large parts of the combustion engine's operating state which makes it possible to evaporate the supplied medium when it is mixed with the exhaust gases. Problems with vaporizing the medium usually arise only when liquid medium hits the internal wall surface of the exhaust pipe and when the internal wall surface has a temperature too low to evaporate the medium. The low temperature of the exhaust pipe may be due to a cold ambient temperature or the combustion engine operating in an operating area where the exhaust gas temperature is relatively low. A strong dosing of the medium can also lower the temperature of the first wall surface of the exhaust pipe considerably as a lot of heat energy is needed to evaporate the medium. According to the present invention, the arrangement comprises means adapted to maintain a degree of heating of the first wall surface such that it obtains a higher temperature than the evaporation temperature of the medium when the liquid medium is supplied in the first exhaust passage. The first wall surface will thus have a higher temperature than the liquid medium that hits the first wall surface. The liquid medium will thus be guaranteed to be heated to a temperature so that it evaporates.

The invention includes a heat source which supplies heat to the first wall surface. The first wall surface can thus, at least if necessary, be heated so as to exhibit substantially continuously a temperature higher than the evaporation temperature of the medium.

Such a heat source can be of an essentially arbitrary but functional nature.

The heat source may be an electric heating element which supplies heat energy to the front wall surface, depending on its prevailing temperature. Advantageously, however, said heat source comprises a second exhaust passage which is limited by a second wall surface located adjacent to the first wall surface. The temperature of the exhaust gases is usually clearly higher than the evaporation temperature of the medium. It is therefore advisable to use the heat energy of the existing exhaust gas as a heat source. By conducting exhaust gases in a second passage adjacent to the first passage, a heat transfer is easily provided to the first wall surface from the exhaust gases in the second exhaust passage. With an element made of a material with good thermal conductivity, heat energy with a slight resistance is passed from the second wall surface to the first wall surface. Thus, the lost wall surface will substantially continuously provide a temperature at least corresponding to the evaporation temperature of the medium.

Said element may be tubular and mounted in a position inside the exhaust pipe so that the first passage is formed inside the tubular element and the second exhaust passage is formed between the outer wall surface of the tubular element and an internal wall surface of the exhaust pipe. Here, the inner wall surface of the tubular member is the first wall surface and the outer surface of the tubular member is the second wall surface. The tubular element is thus flowed here both internally and externally by exhaust gases in the exhaust pipe. Since the tubular element is completely surrounded by exhaust gases, the entire tubular element will obtain substantially the same temperature as the exhaust gases in the exhaust pipe. The internal wall surface of the tubular element thus also obtains substantially the same temperature as the exhaust gases. Since, under most relevant operating conditions, the exhaust gases have a temperature which is clearly higher than the evaporation temperature of the medium, the medium which in liquid form hits the internal wall surface of the tubular element is guaranteed to evaporate. Preferably, the tubular member is relatively thin and made of a metal material with good thermal conductivity. Advantageously, the tubular element is mounted in a central position in the exhaust pipe. Thus, a uniform flow of exhaust gases is provided in the second exhaust passage around the tubular element. The tubular element can be applied in a substantially straight portion of an exhaust pipe. However, it is possible to incorporate the tubular element into exhaust pipe portions having a substantially arbitrary shape.

According to the invention, said element is a wall element which is applied in a helical exhaust pipe and divides part of the exhaust pipe into a first exhaust passage and in a second exhaust passage. A helical exhaust pipe is compact and it is straightforward to transfer heat between adjacent radial portions of the exhaust pipe. However, the sidewalls of a helical exhaust pipe are usually in contact with ambient air. With the wall elements as above, the first exhaust passage can obtain sidewall surfaces heated by ambient exhaust gases. The first passage can thus be caused to be completely surrounded by internal wall surfaces that are heated by ambient exhaust.

The element may form an integral part of the exhaust pipe and said means comprise a heat insulating material applied between the first wall surface and an environment. The element here has a shape like the exhaust pipe, but it can be made of a material with considerably higher heat insulating properties than the exhaust pipe in general. Alternatively, a suitable insulating material of suitable thickness can be applied around the outer surface of the element. With such a heat insulating material, the cooling effect of the environment on the interior wall surface of the tubular element can be substantially eliminated. The interior wall surface of the element here will only be heated by the exhaust gases flowing through the first exhaust passage. However, this heat supply is usually fully sufficient for the medium in liquid to hit the inner wall surface of the tubular element to evaporate when the cooling effect on the first wall surface from the environment is eliminated.

According to another preferred embodiment of the present invention, the metering device comprises a spray nozzle by which the medium is sprayed into said first exhaust passage. With a spray nozzle, a very fine distribution of the liquid medium is obtained as it is injected into the tubular element. Thus, a rapid and efficient evaporation of the medium is obtained when it is mixed with the exhaust gases flowing through the tubular element. Advantageously, the medium is a urea solution and the exhaust conduit comprises a catalyst. In particular, when using the technique referred to as Selective Catalytic Reduction (SCR), a urea solution can be utilized to provide ammonia which is a necessary substance to obtain a chemical reaction in which the nitrogen oxides in the exhaust gases are reduced to nitrogen gas and water vapor. An urea solution is easy to handle and store as it is both relatively odorless and non-toxic. By supplying the urea solution in well-defined doses, the emission of nitrogen oxides by the diesel engine can be significantly reduced. With the present invention, an optimal supply of urea can be provided as all the urea solution supplied is guaranteed to evaporate. It is also possible to supply media other than urea to the exhaust pipe of the present invention as well.

The interior wall surface of the element may comprise at least one area with a non-smooth surface. Thus, the tubular element, in this area, provides a greater interior wall surface than a smooth surface. A non-smooth wall surface retains liquid urea solution until it evaporates. The interior wall surface of the element may comprise at least one depression having a propagation in a direction substantially perpendicular to the flow direction of the exhaust gas in the first exhaust passage. Thus, the liquid medium is effectively retained in the well until it evaporates. With such recesses having suitable positions, the element can be given a reduced length.

BRIEF DESCRIPTION OF THE DRAWINGS

The following are exemplary preferred embodiments of the invention with reference to the accompanying drawings, in which:

Fig. 1 shows a diesel engine with an exhaust pipe fitted with catalytic exhaust gas according to the method called SCR,

Fig. 2 shows an arrangement according to a first embodiment of the invention,

Fig. 3 shows an arrangement according to a second embodiment of the invention,

Fig. 4 shows an arrangement according to a third embodiment of the invention,

Fig. 5 shows an arrangement according to a fourth embodiment of the invention and Fig. 6 shows a cross-section along the plane AA in Fig. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows an internal combustion engine in the form of a diesel engine 1. The diesel engine 1 can, for example, be intended as a drive engine for a heavier vehicle. The exhaust gases from the cylinders of the diesel engine 1 are passed, via an exhaust collector 2, to an exhaust pipe 3. · The exhaust pipe 3 has here been provided with an arrangement which provides a catalytic exhaust gas purification according to the method called Selective Catalytic Reduction (SCR). This method means that a urea solution is supplied to the exhaust gases in the exhaust gas line 3 of the diesel engine.

The urea solution is stored in a tank 4 and passed, via a conduit 5, to the exhaust pipe 3. A control unit 6, which may be a computer unit with an appropriate software, controls the supply of the urea solution which is led to the exhaust pipe 3 by means of a pump 7. The control unit 6 can, with information regarding, for example, current fuel consumption and the temperature of the exhaust gas, calculate the amount of urea solution that needs to be added in order to optimally reduce the content of nitrogen oxides in the exhaust gases. The supplied urea solution is intended to be heated by the exhaust gases in the exhaust pipe 3 so that it evaporates and

528 119 is converted to ammonia. The mixture of ammonia and the exhaust gases is then passed on in the exhaust pipe 3 to a catalyst 8.1 catalyst 8 a chemical reaction takes place. The nitrogen of the nitrogen oxides in the exhaust gases here reacts with the nitrogen in the ammonia to form nitrogen gas. The acid of the nitrogen oxides reacts with the hydrogen in the ammonia to form the water. The nitrogen oxides in the exhaust gases are thus reduced in the catalyst 8 to nitrogen gas and water vapor, which is discharged into ambient air.

Fig. 2 shows an arrangement for supplying urea solution to the exhaust duct 3. The duct 5, which is intended to transport the urea solution, extends here through an opening in a wall of the exhaust duct 3. The duct 5 has a curved end portion at which a spray nozzle 9 is attached. A tubular element 10a having a smaller dimension than the exhaust pipe 3 is mounted by means of suitable fasteners 11 in a substantially central position within the exhaust pipe 3. The exhaust gas flows here in the direction of the arrows inside the exhaust pipe 3. The tubular element 10a has an internal wall surface.

10a 'defining a first passage 12 for the exhaust gases. The first exhaust passage 12 extends between an inlet 12 'and an outlet 12.

The urea solution is sprayed here by means of the spray nozzle 9 into the first exhaust passage 12 in connection with its inlet 12 '. Thus, the added urea solution will be carried by the exhaust gas flow through substantially all of the first exhaust passage 12.1 and with the tubular element 10a having a smaller dimension than the exhaust pipe 3, a second exhaust gas passage 13 is formed radially externally about the tubular element 10a. The second exhaust passage 13 has a radial extension between an outer wall surface 10a of the tubular element 10a and an internal wall surface of the exhaust pipe 3.

The exhaust gases in the exhaust pipe 3 will thus flow in parallel through the first exhaust passage 12 and through the second exhaust passage 13.

Thus, the outer wall surface 10a of the tubular element is in contact with the exhaust gases flowing through the second exhaust passage 13. The outer wall surface 10a of the tubular element thus provides a temperature substantially corresponding to the temperature of the exhaust gases. The tubular member 10a advantageously has relatively thin walls and is advantageously made of a material with good thermal conductivity. Thus, heat can be rapidly transported from the exterior wall surface 10a 'to the interior wall surface 10a' when there is a temperature difference between these surfaces.

Such a difference in temperature can occur temporarily when urea solution is evaporated on the internal wall surface 10a 'because a lot of it is needed in this evaporation process.

528 119 thermal energy. However, by means of the heat supply from the second exhaust passage 13, the internal wall surface 10a 'maintains a temperature which exceeds the evaporation temperature of the urea solution.

As exhaust gases flow through the exhaust pipe 3, urea solution is sprayed into the first exhaust passage 12 inside the tubular element 10a, via the spray nozzle 9, in a dose controlled by the control unit 6. The urea solution has a vaporization temperature which is normally lower than the exhaust gas temperature but higher than the ambient temperature. 14 temperature. The urea solution atomized by spray nozzle 9 is mixed with the exhaust gases flowing through the first exhaust passage 12. The hot exhaust gases heat the atomized urea solution to evaporate to form ammonia. However, some of the liquid urea solution cannot evaporate by the exhaust gases before it hits the internal wall surface 10a '. Thus, the interior wall surface 10a 'maintains a higher temperature than the evaporation temperature of the urea solution.

The urea solution that hits the interior wall surface 10a 'thus provides a heating until it evaporates. With a suitably sized tubular member 10a, substantially all of the urea solution supplied in the first exhaust passage 12 can be evaporated to form ammonia in the first exhaust passage 12. The tubular member 10a may, for example, have a length of 100 to 200 mm and a diameter of 80 to 100 mm. However, the dimensions of the tubular element 10a must also be adapted to the dimensions of the exhaust pipe 3.

Fig. 3 shows an alternative arrangement for supplying a urea solution to an exhaust pipe 3. This arrangement differs from the arrangement in Fig. 2 in that the tubular element 10b shown here has an internal wall surface 10b 'which comprises a plurality of annular depressions 15 which extend in a direction substantially perpendicular to the direction of exhaust flow through the first exhaust passage 12. However, the tubular member 10b has a smooth exterior wall surface 10b. Urea solution which hits an interior wall surface 10b 'will accumulate in said recesses 15 until the urea solution evaporates. With such depressions, the urea solution is guaranteed to be guided by the exhaust gas flow through the first exhaust passage 12 and out through the outlet 12 before being evaporated. The tubular element 10b can here be given a reduced length compared to a tubular element 10a having a smooth internal wall surface 10a '.

Fig. 4 shows a further arrangement for supplying a urea solution to an exhaust pipe 3. Here, a tubular element 10c is used which forms an integral part of the exhaust pipe 3. The pipe-shaped element 10c here has a corresponding shape and dimension as the exhaust pipe 3. A thermal insulation material 16 has been applied externally around the outer wall surface 10c of the tubular member 10c. Possibly, the other parts of the exhaust pipe 3 can also be fully or partially supplied with heat insulating material. The heat-insulating material 16 prevents the internal wall surface 10c 'of the tubular element from being cooled by ambient air, which generally has a significantly lower temperature than the evaporation temperature of the urea solution. By means of a suitable choice of insulating material 16 and of a suitable thickness, the cooling effect of the environment 14 on the inner wall surface 10c 'of the tubular element can be substantially eliminated. The tubular element

10c forms here an exhaust passage 12 which is flowed through all the exhaust gases in the exhaust pipe 3. The exhaust gases heat the internal wall surface 10c 'of the tubular element 10c. Since the insulating material 16 substantially eliminates the heat losses to the environment 14, the internal wall surface 10c 'can maintain a temperature which at least corresponds to the evaporation temperature of the urea solution. When the diesel engine 1 is activated, urea solution is sprayed into the exhaust passage 12 in connection with the inlet 12 '. The exhaust gases heat the finely divided urea solution to evaporate to form ammonia. The urea solution which hits the interior wall surface 10c 'provides a heating of the interior wall surface 10c' until it evaporates. The tubular element 10c has a length such that substantially all of the urea added is evaporated within the tubular element

10c.

Fig. 5 shows a container 17 in the form of a combined silencer and exhaust cleaner intended to be applied in an exhaust system for a diesel-powered vehicle. The container 17 comprises an outer casing 18 having a substantially circular cylindrical shape. The casing 18 forms a closed exterior wall surface except at the places where an inlet 19 and an outlet 20 are provided for the exhaust gases. A circular tube 21 is provided inside the housing 18.

The tube 21 has a length such that it extends from a first end wall 18a of the housing to a module 22 comprising a second end wall 18b of the housing. The container device 17 comprises an exhaust pipe 3 extending from the inlet 19 to the outlet 20. The exhaust pipe comprises, after the inlet 19, a first exhaust pipe portion 3a, which has a substantially straight stretch outside the pipe 21 from the inlet 19 to the module 22. A particle filter 23 is provided in the first exhaust pipe portion 3a. As the exhaust gases pass through the particle filter 23, the soot particles of the exhaust gases get trapped in the particle filter 23 where they are subsequently incinerated.

The exhaust gases purified from soot particles are then passed into the module 22 which comprises a helical wall element 24. The wall surfaces of the helical element 24 define a

528 119 second helical exhaust sealing portion 3b. The lateral extension of the helical second exhaust pipe portion 3b is limited by the second end wall 18b and a wall element 25 of the module 22. The helical element 24 and the wall element 25 have wall surfaces which are in contact with exhaust gases on both sides. However, the exterior wall surface of the gable wall 18b is in contact with ambient air 14. An additional wall element 10d is arranged in a part of the helical exhaust pipe portion 3b. The auxiliary wall element 10d divides this part of the helical exhaust line 3b into a first exhaust passage 12 and a second exhaust passage 13. The first exhaust passage 12 is laterally limited by the extra wall element 10d. The extra wall element 1 Od has wall surfaces that are surrounded on both sides by exhaust gases. The first exhaust passage 12 will thus be completely limited by wall elements 24,25, 10d having wall surfaces which are surrounded on both sides by exhaust gases.

The urea solution is sprayed by means of the spray nozzle 9 into the first exhaust passage 12 in connection with its inlet 12 ', see Fig. 6. Thus, the added urea solution is mixed with the exhaust gases in the first exhaust passage 12. Thus, the first exhaust passage 12 is completely limited by internal wall surfaces 24'. 25 ', 10d * of wall elements 24,25, 10d having external wall surfaces 24, 25, 10d heated by ambient exhaust. By exterior wall surfaces are meant the surfaces of the wall elements 24, 25, 10d which are located on the opposite side of the interior surfaces 24 ', 25', 10d *. The portion of the urea solution supplied 20 carried by the exhaust stream in the first exhaust passage 12 is heated by the exhaust gases so that it is evaporated and converted to ammonia. The portion of urea solution that hits the interior wall surfaces 24 ', 25', 10d 'is heated by the interior wall surfaces 24', 25 ',

10d 'which is supplied with heat from the surrounding exhaust gases. The interior wall surfaces 24 ', 25',

10d 'thus provides a temperature which exceeds the evaporation temperature of the urea solution. Thus, the urea solution that hits the internal wall surfaces 24 ', 25', 10d 'will be vaporized and converted to ammonia. Thus, any added urea solution will evaporate and be converted to ammonia before it flows out through the outlet pipe of the first exhaust passage2.

Thus, the exhaust gases in the second exhaust pipe portion 3b flow in parallel through the first exhaust passage 12 and the second exhaust passage 13. At the outlet 12 of the first exhaust passage, the parallel exhaust streams are joined. The mixture of exhaust gases and ammonia continues to flow radially inwardly into the helical exhaust conduit 3b until it reaches a central position in the module 22. Here, it is discharged from module 22 to a third exhaust pipe portion 3c which has a substantially straight line within tube 21.

528 The third exhaust gas portion 3c comprises a catalyst 8. As the mixture of ammonia and exhaust gases is passed through catalyst 8, the nitrogen of the nitrogen oxides in the exhaust gases reacts with the nitrogen in the ammonia to form nitrogen gas. The oxygen of the nitrogen oxides reacts with the hydrogen in the ammonia to form water. The nitrogen oxides in the exhaust gases are thus reduced in catalyst 8 to nitrogen gas and water vapor before being discharged from the container 17 via the outlet 20.

The invention is not limited to the embodiments shown in the drawings but can be freely varied within the scope of the claims.

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