Patent Application
20100101219
This application claims priority to German application 10 2008 053 669.5, which was filed Oct. 29, 2008.
The present invention relates to an exhaust system, in particular for a vehicle with a diesel engine.
Such exhaust systems typically include a first insert through which exhaust gas flows, a second insert through which exhaust gas flows, and which is arranged downstream thereof in the flow direction, and an injection device arranged between the inserts for injecting a fluid. The inserts are filter units which are usually a block of ceramic material allowing through flow of exhaust gas. The insert can merely provide a filter function and/or have catalytic properties.
To comply with specifications as provided by environmental law, the amount of the particulate matter contained in the exhaust gas of a diesel engine needs to be reduced. To this end, particulate filters are built into the exhaust systems of vehicles for retaining the particles contained in the exhaust gas. To prevent an impairment of the function of the filter and, hence, of the exhaust system by the particles accumulating on the filter surface, the filter must be regenerated from time to time. This is effected by combusting the particles accumulated on the filter surface by the addition of heat.
To generate the temperatures necessary for the combustion, an oxidizable liquid, for example, is introduced into the exhaust gas flow upstream of the particulate filter, the liquid reacting with the residual oxygen contained in the exhaust gas. To achieve a uniform regeneration of the particulate filter, the combustion reaction must proceed distributed as uniformly as possible over the entire cross-section of the exhaust pipe.
It is the object of the present invention to provide an exhaust system which allows a uniform development of heat and thus a uniform combustion of the particles.
The present invention provides an exhaust system, in particular for a vehicle with a diesel engine, including a first insert through which exhaust gas flows, a second insert through which exhaust gas flows, and which is arranged downstream thereof in the flow direction, and an injection device arranged between the first and second inserts for injecting a fluid. A swirling element is provided in the flow path of the exhaust gas downstream of the first insert in the flow direction. In the swirl produced by the swirling element, the fluid introduced is mixed more homogeneously with the exhaust gas stream. This results in a more uniform distribution of the fluid over the entire flow cross-section, so that a better development of heat, and thus a more effective regeneration of the subsequent second insert are achieved.
In one example, the swirling element includes recesses through which the exhaust gas flows. This allows an effective control of the exhaust gas flow and, hence, a good deflection or a good swirling of the exhaust gas flow.
To influence the entire exhaust gas flow and to reach a complete mixing of the exhaust gas and the fluid, the swirling element ideally extends across the entire cross-section of the exhaust pipe.
A particularly uniform distribution of the fluid is attained in that the swirling element produces swirls over the entire cross-section of the exhaust pipe.
In one example, the swirling element includes deflector plates which are inclined in relation to the flow direction. They are arranged in the exhaust gas stream and deflect the exhaust gas stream or parts thereof, so that an eddy is produced downstream of the swirling element.
The angle at which these deflector plates are disposed with respect to the exhaust gas flow has great influence on the effectiveness of the swirling element. It is therefore of advantage for the deflector plates to include at least two portions which are inclined at different angles in relation to the flow direction.
It is especially advantageous if the angle of inclination of the portions increases in the flow direction. This allows the exhaust gas stream to be influenced very effectively.
Ideally, the deflector plates are inclined at an angle of at least 30° in relation to the flow direction.
The deflector elements may, for example, be arranged radially and distributed evenly over the entire cross-section.
The deflector elements are more particularly arranged similarly to a stator of a turbine and generate an eddy downstream of the swirling element in which the fluid introduced can be effectively distributed over the entire cross-section of the exhaust pipe.
The radially arranged deflector elements may, for example, enclose an opening in the middle of the swirling element, through which the exhaust gas stream can flow.
A baffle plate, disposed perpendicularly to the flow direction, may be provided in front of this opening. The baffle plate directs the exhaust gas stream onto the deflector elements.
The deflector elements may, however, also be arranged parallel to each other, so that as a whole they constitute a grid structure by which the exhaust gas stream is diverted.
To enhance the effect of the swirling element, the cross-sectional area of the exhaust pipe, through which exhaust gas flows, tapers in a portion located directly upstream of the swirling element in the flow direction, and/or widens in a portion located directly downstream of the swirling element in the flow direction. A tapering of the cross-sectional area upstream of the swirling element causes an increase in the approach velocity, so that the exhaust gas stream impinges on the swirling element at a higher velocity. In addition, the reduced cross-section results in a more favorable ratio of the pipe cross-section to the vaporizer. The widening of the cross-sectional area downstream of the swirling element, on the other hand, causes the exhaust gas stream to be decelerated, so that the fluid is allowed to mix with the exhaust gas stream over a longer period of time.
The inserts may be particulate filters, for example, more particularly diesel particulate filters. Owing to the swirling element, a fluid introduced can combust homogeneously, so that a uniform regeneration of the entire filter surface is achieved.
The first insert is, e.g., a pre-filter and the second insert may be a diesel particulate filter with a diesel oxidation catalytic converter. Because of such a diesel oxidation catalytic converter, the exhaust gas temperature may be further increased, so that the subsequent filter may be regenerated more effectively. The swirling element arranged upstream swirls the exhaust gas stream with the fluid contained therein, so that the entire surface area of the diesel oxidation catalytic converter can be used.
Preferably, the injection device is part of a regeneration device. By using such a regeneration device, an oxidizable liquid is introduced into the exhaust gas stream which, based on an exothermic reaction with the oxygen of the exhaust gas, leads to an increase in temperature by which a particulate filter arranged downstream can be regenerated.
For this purpose, the injection device includes a fuel vaporizer, which vaporizes the fuel before it is injected into the exhaust pipe, so that the fuel mixes well with the exhaust gas stream and reacts more readily with the residual oxygen in the exhaust gas.
Such an injection device may be arranged upstream or downstream of the swirling element. In this way, the fluid is either introduced into the exhaust gas stream prior to the swirling and is mixed with the exhaust gas stream by the swirling element, or the fluid is introduced downstream of the swirling element into the eddy already generated.
The injection device may also be integrated in the swirling element, for example, for reasons of space.
In one example, the first insert and the second insert along with the swirling element are arranged in a shared housing. This results in a very compact design of the exhaust system.
The swirling element may be a static mixer, i.e. the swirling element does not have any moving parts, and no external control of, for example, the deflector plates is required.
The swirling element is a prefabricated component that is inserted in the exhaust pipe.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The exhaust system 10 shown in
The fluid introduced into the cavity 26 is an oxidizable liquid, in this case a fuel, which combusts with the residual oxygen present in the exhaust gas of a diesel engine in an exothermic reaction at the oxidation catalytic converter. Owing to the heat produced in the process, a particulate filter disposed downstream in the flow direction A can be regenerated, i.e. the residual particles accumulated in this particulate filter are combusted in a controlled manner by the heat generated. This process is assisted by the diesel oxidation filter arranged downstream of the injection device 28, since the exhaust gas temperature is further increased by this filter.
A swirling element 30 is arranged in the exhaust gas stream between the injection device 28 and the second insert 24. The swirling element extends across an entire cross-section of the exhaust system 10. As can be seen in
The exhaust gas stream enriched with the fluid flows through the circular central opening 32 and is swirled downstream thereof. This results in an improved mixing of the exhaust gas stream with the fluid, so that the fluid impinges in an evenly distributed state on the second insert 24 located downstream thereof in the flow direction A.
The exhaust system 10 in
Compared with the first and second housing parts 14 and 16, the intermediate portion 36 of the exhaust system 10 shown in
In addition to the intermediate portion 36 arranged downstream of the swirling element 30, the exhaust system 10 shown in
In each of the embodiments shown, the injection device 28 is arranged upstream of the swirling element 30, so that the liquid or the vapor is introduced into the exhaust gas stream prior to the swirling.
However, the injection device 28 could also be arranged downstream of the swirling element 30.
Embodiments in which the injection device 28 is integrated in the swirling element 30 are also conceivable.
The injection device 28 is part of a regeneration device and includes a fuel vaporizer by which fuel is introduced into the exhaust system 10 in a vaporous condition. But other oxidizable liquids may also be introduced into the exhaust system 10. In particular, the liquid need not be vaporized before it is introduced into the exhaust pipe.
The swirling element 30 in
The number of the deflector elements 34 and the shape and arrangement thereof in the swirling element 30 may be varied as desired. In particular, the number of the portions 42, 44 of a deflector element, as well as the angle thereof in relation to the exhaust gas stream, may be altered as desired. The slope of a deflector element 34 may also be altered continuously, for example, similar to a turbine blade.
A baffle plate 46 is provided in the middle of each swirling element 30. The baffle plate 46 is disposed perpendicularly to the exhaust gas flow. This baffle plate 46 causes the exhaust gas stream to be directed more effectively onto the deflector elements 34. However, embodiments without a baffle plate 46 are also conceivable.
Such an embodiment is shown, for example, in
In addition, the outer casing of the swirling element 30 is designed to be conically tapered in the region of the deflector elements 34. This results in a simultaneous increase in the flow velocity while the exhaust gas stream is deflected by the deflector elements 34.
In a region downstream of the deflector elements 34, the outer casing of the swirling element 30 is conically widened here, so that a deceleration of the flow velocity is brought about again. As can be seen in
A further embodiment of a swirling element 30 is apparent from
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 053 669.5 | Oct 2008 | DE | national |
