Patent Application
20090107120
The present invention relates to a method and a device for treating the exhaust gas of an internal combustion engine, in which the content of nitrogen oxides in the exhaust gas of the internal combustion engine is reduced through selective catalytic reduction.
The emission into the environment of substances contained in the exhaust gas from internal combustion engines, is undesirable. In many countries, for example, nitrogen oxides (NOX) may only be contained in the exhaust gas of internal combustion engines up to a certain limit value. In addition to engine-internal measures, through the use of which the emissions of nitrogen oxides can be reduced by a selection of a suitable operating point of the internal combustion engine, aftertreatment methods have been established which make a further reduction of the nitrogen oxide emissions possible.
One option for further reducing the nitrogen oxide emissions is so-called selective catalytic reduction (SCR). In that case, a selective reduction of the nitrogen oxides to form molecular nitrogen (N2) takes place by using a selectively acting reducing agent. One possible reducing agent is ammonia (NH3). In that case, ammonia is often stored not in the form of ammonia but instead, an ammonia precursor is stored, which is converted to ammonia when required. Possible ammonia precursors are, for example, urea ((NH2)2CO), ammonium carbamate, isocyanic acid (HCNO), cyanuric acid and the like.
Urea, in particular, has proven to be simple to store. Urea is preferably stored in the form of a urea/water solution. Urea and, in particular, urea/water solution is hygienically harmless, simple to distribute and to store. A urea/water solution of that type is already marketed under the trademark “AdBlue”.
German Published, Non-Prosecuted Patent Application DE 199 13 462 A1 discloses a method in which a urea/water solution is dosed, upstream of a hydrolysis catalytic converter, into a partial flow of the exhaust gas of an internal combustion engine. The dosing-in process takes place in that case in the form of droplets. When the droplets impinge on the hydrolysis catalytic converter, hydrolysis and thermolysis of the urea takes place to form ammonia, which is used as a reducing agent in an SCR catalytic converter situated downstream. The method described therein has the disadvantage that the hydrolysis catalytic converter is cooled by the evaporation of the urea/water solution. In particular, where large quantities of ammonia are required, it is thus possible, at least in regions of the hydrolysis catalytic converter, for such intense cooling to take place that, in that case, the hydrolysis reaction no longer takes place or no longer takes place completely. Furthermore, as a result of the locally severely discontinuous cooling of the hydrolysis catalytic converter generated due to the evaporation of the individual droplets, the hydrolysis catalytic converter can be damaged, and in particular a catalytically active coating can become detached.
It is accordingly an object of the invention to provide a method and a device for treating the exhaust gas of an internal combustion engine, which overcome or at least alleviate the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for treating exhaust gas of an internal combustion engine passing through an exhaust line. The device comprises a reducing agent solution evaporator which is disposed outside the exhaust line and is to be connected to the exhaust line. The reducing agent solution evaporator includes an evaporator unit configured for evaporating an aqueous solution which includes at least one reducing agent precursor and configured for providing a gaseous substance mixture including at least one of the following substances:
A hydrolysis catalytic converter is connected to the reducing agent solution evaporator for the hydrolysis, in particular, of urea to form ammonia, is disposed outside the exhaust line and is to be connected to the exhaust line. An SCR catalytic converter is disposed in the exhaust line for selective catalytic reduction of nitrogen oxides.
A particulate filter can be provided upstream of the SCR catalytic converter. The particulate filter, during operation, can likewise be traversed by the reducing-agent-containing gas flow from the hydrolysis catalytic converter.
This means that, in operation, the SCR catalytic converter is regularly traversed by exhaust gas, while this is not normally the case for the hydrolysis catalytic converter and the reducing agent solution evaporator. The latter are embodied in such a way that they can be connected to the exhaust line in such a way that a gaseous substance mixture which includes a reducing agent can be introduced into the exhaust line, but at most small quantities of exhaust gas can penetrate into the hydrolysis catalytic converter and/or the reducing agent solution evaporator. A reducing agent precursor urea is preferably used as a precursor for the reducing agent ammonia.
In conventional systems known from the prior art, the hydrolysis catalytic converter is also traversed by at least a part of the exhaust gas. That requires a hydrolysis catalytic converter of that type to have, due to the large mass flow rate of the exhaust gas, a certain volume, often half a liter and more, and a certain surface which is to be utilized for the catalytic reaction. The volume and the surface can be considerably smaller in a hydrolysis catalytic converter according to the present invention, since the hydrolysis catalytic converter need merely be constructed to be large enough to ensure that it can convert the maximum required quantity of reducing agent precursor in the evaporated aqueous solution. In this case, the mass flow rates through the hydrolysis catalytic converter are considerably lower.
An evaporation of the urea-water solution takes place In the evaporator unit, during operation. The urea-water solution can contain even further substances which, for example, reduce the freezing point of the solution. In this case, it is possible for, in particular, formic acid and/or ammonium formate to be contained in the solution. In this case, the evaporator unit is embodied in such a way that, in operation, at least an evaporation of the urea/water solution takes place. Depending on the setting of the corresponding temperature and the corresponding quantity of urea/water solution which is supplied to the evaporator unit, it is also already possible, in addition to the pure evaporation of the urea/water solution, for at least partial thermolysis of the urea to take place to form ammonia. The reducing agent solution evaporator is provided upstream of the hydrolysis catalytic converter and the latter is provided upstream of the SCR catalytic converter, so that, in operation, the evaporated aqueous solution which includes a reducing agent precursor and/or a reducing agent, flows from the reducing agent solution evaporator into the hydrolysis catalytic converter, where at least a partial hydrolysis takes place to form the reducing agent. The hydrolysis catalytic converter leaves or yields a gas mixture which includes at least reducing agent. The gas mixture is conducted into the SCR catalytic converter and serves there as a selective reducing agent for reducing nitrogen oxides (NOX).
The internal combustion engine can be mobile or stationary. The internal combustion engine is, in particular, a part of a land vehicle, water vehicle or aircraft, preferably of an automobile such as, in particular, a passenger or truck or utility vehicle. The hydrolysis catalytic converter and the SCR catalytic converter denote catalyst carrier bodies which are correspondingly catalytically active. The catalyst carrier bodies, in particular, have coatings which are catalytically active or which contain catalytically active substances. The catalyst carrier bodies particularly preferably have ceramic coatings, for example in the form of a washcoat in which the correspondingly catalytically active particles are distributed. In particular, the hydrolysis catalytic converter has a coating which includes titanium dioxide (anatase) and/or iron-exchanged zeolites. The SCR catalytic converter particularly preferably has a coating which includes at least one of the following components: titanium dioxide, tungsten trioxide, molybdenum trioxide, vanadium pentoxide, silicon dioxide, sulphur trioxide, zeolite. So-called honeycomb bodies, in particular, are used as catalyst carrier bodies. The honeycomb bodies have channels or cavities through which a fluid can flow. It is particularly preferable for a honeycomb body to be formed as a catalyst carrier body which is constructed from ceramic and/or metallic material. One option for a honeycomb body is a honeycomb body which is composed of thin sheet metal layers, with at least one structured and one substantially smooth sheet metal layer being wound or stacked with one another, and at least one of the stacks being coiled. Other catalyst carrier bodies, for example bulk material catalytic converters, carrier bodies made from wire mesh or the like, are possible and according to the invention. The construction, in particular, of a hydrolysis catalytic converter in the form of a tube which is provided on the inside with a coating that catalyses the hydrolysis of the reducing agent precursor to form reducing agent, is also preferable. The provision of a separate evaporator unit advantageously makes it possible to continuously ensure a defined dispensing of reducing agent without non-uniform and/or incomplete hydrolysis of the ammonia precursor to form ammonia taking place in the event of increased demand for reducing agent.
According to one advantageous embodiment of the device according to the invention, the evaporator unit is connected through the use of a delivery line to a reservoir for the aqueous solution, with the delivery line and the evaporator unit being connected to one another through the use of a connecting unit.
The connecting unit forms the interface between the delivery line and the evaporator unit. The connecting unit is constructed so as to ensure a sealed connection between the delivery line and the evaporator unit in order to avoid leakage of the aqueous solution and of the gaseous substance mixture. Furthermore, the connecting unit is constructed in such a way that, at the same time, a deposition of substances in the interior of the connecting unit, for example as a result of precipitations of components of the corresponding aqueous solution, is suppressed or occurs to such a small extent that a flow through the connecting unit remains possible. The connecting unit is preferably constructed in such a way that it can be cooled. The connecting unit is, for example, connected to a corresponding cooling element. Temperature control, that is to say cooling or heating, of the connecting unit, is generally possible.
According to a further advantageous embodiment of the device according to the invention, the connecting unit is formed at least partially from a material with a thermal conductivity of less than 10 W/m K (Watt per meter and Kelvin).
A material with a low thermal conductivity, which is in particular lower than that of metals, advantageously permits the formation of a connecting unit which permits both a high temperature in the evaporator unit as well as a low temperature in the delivery line to the evaporator unit. It is possible, in particular, for the delivery line to have a temperature of up to 70° C., up to 80° C. or even up to 90° C. while the evaporator unit has a temperature of more than 300° C., preferably more than 350° C. and preferably even more than 400° C. A temperature of approximately 380° C. is particularly preferable. In this case, the low thermal conductivity of the material of the connecting unit, in particular, ensures that no excessive heating of the delivery line occurs. Such excessive heating would on one hand lead to heat losses in the evaporator unit and could on the other hand already cause an at least partial evaporation of the aqueous solution in the delivery line, which is often undesirable. As a result of the aqueous solution being present in the delivery line, particularly reliable and precise regulation of the quantity of the aqueous solution supplied to the evaporator unit, and therefore of the quantity of ammonia being provided, is possible. In this case, materials are preferable which have a thermal conductivity of only 2 W/m K or less, particularly preferably only 1 W/m K or less, in particular between 0.1 W/m K and 0.4 W/m K, in particular approximately 0.25 W/m K or less. In particular, the connecting unit is constructed in such a way that its diameter changes by less than 0.25% even if flown through by pulsatile flows. Preferably, the connecting unit is constructed in such a way that the diameter through which a fluid can flow is 0.5 to 6 mm in case of a substantially circular shape of the region to be flown through. The diameter through which a fluid can flow is preferably 3 to 5 mm, in particular approximately 4 mm. The region of the connecting unit to be flown through preferably has a cross section of 0.2 to 28 square millimeters irrespective of the shape of the region of the connecting unit to be flown through. Preferably, the connecting unit includes at least one Peltier element for cooling and/or heating the connecting unit. The connecting unit is, in particular, galvanically isolated from the evaporator unit.
According to a further advantageous embodiment of the device according to the invention, the connecting unit is constructed in such a way that a temperature gradient of 40 K/mm (Kelvin per millimeter) and greater can be maintained over a length of the connecting unit.
This is obtained, in particular, by construction from a corresponding material, by using a coating made from a corresponding material and/or through the use of a corresponding topological configuration of the connecting unit. It is alternatively or additionally possible for the connecting unit to be equipped with or connected to a corresponding active or passive temperature control device which allows the temperature gradient to be maintained.
A temperature gradient of 40 K/mm and greater advantageously permits a high temperature of 350° C. or more to be maintained in the evaporator unit, with a more moderate temperature of, for example, 70° C., 80° C. or 90° C. being maintained in the delivery line. It is thereby possible on one hand to ensure good and preferably complete evaporation of the aqueous solution with, at the same time, a small spatial extent of the evaporator unit, and a good capability for dosing of the aqueous solution.
The formation of the connecting unit with a very low thermal conductivity and/or a very large possible temperature gradient advantageously permits the generation of a very constant temperature level within the evaporator unit without a significantly reduced temperature in the region adjacent the connecting unit. Such a constant temperature level of the evaporator unit is advantageous since the formation of depositions or deposits within the evaporator unit can be effectively avoided or reduced in this way.
According to a further advantageous embodiment of the device according to the invention, the connecting unit is constructed from at least one material including at least one of the following materials:
The materials particularly advantageously have, on one hand, a low thermal conductivity, for example of less than 10 W/m K, and on the other hand advantageously permit the formation of a connecting unit with temperature gradients of 40 K/mm and greater. It is advantageous, in particular, when using a ceramic material to use an additional sealing and/or adhesive device in order to increase the impermeability of the connecting unit.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a heat capacity of at most 60 J/K.
In this case, the heat capacity of the hydrolysis catalytic converter is preferably understood to mean the heat capacity without any casing tube which may be provided. Such a heat capacity has the effect of permitting the hydrolysis catalytic converter to be heated and cooled quickly. This advantageously makes it possible to use the hydrolysis catalytic converter as the regulating element, or one of several regulating elements, in a temperature regulating circuit. It has additionally been proven that, in particular when the hydrolysis catalytic converter is not used in the exhaust gas flow, that is to say in a situation in which the hydrolysis catalytic converter is not traversed by exhaust gas of the internal combustion engine, an embodiment of the hydrolysis catalytic converter other than in the exhaust system, where the hydrolysis catalytic converter can also be traversed by exhaust gas, is possible. A hydrolysis catalytic converter is even preferably formed with a heat capacity of at most 45 J/K, at most 30 J/K or even of 25 J/K and less.
The hydrolysis catalytic converter preferably includes a metallic honeycomb body made of a steel having a material code 1.4725 according to the German classification of steels and/or aluminum. It is to be understood that a steel with material code 1.4725 is, in particular, a steel having 14 to 16 wt.-% (weight-%) chromium, at most 0.08 wt.-% iron, at most 0.6 wt.-% manganese, at most 0.5 wt.-% silicon, 3.5 to 5 wt.-% aluminum, at most 0.3 wt.-% zirconium, and a remainder of iron which can include usual impurities that add, in particular, up to at most 0.1 wt.-%. In particular, the steel having a material code 1.4725 can be coated and/or bonded with aluminum.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a volume of less than 100 ml (milliliters).
Volumes of the hydrolysis catalytic converter of from 5 to 40 ml, preferably of from 10 to 30 ml, have proven to be particularly advantageous. These volumes are considerably smaller than the volumes of hydrolysis catalytic converters which are traversed by exhaust gas. The volume of the latter is often 500 ml and greater. The device according to the invention is therefore smaller and more cost-effective than systems known from the prior art.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter includes a casing tube.
The casing tube serves to seal off the hydrolysis catalytic converter. A construction of the hydrolysis catalytic converter is preferable in which the latter is composed of a catalytically active coating that is applied to the inner side of the casing tube. It is also advantageous and preferable for the casing tube to serve as a retainer for a conventional structure, for example a honeycomb structure which fills up at least a part of the interior space of the casing tube, or else a structure composed of wire mesh or metal and/or ceramic foam.
According to a further advantageous embodiment of the device according to the invention, at least one at least partially structured metallic layer is provided in the casing tube.
In this case, the hydrolysis catalytic converter can include a conventional honeycomb structure constructed from at least one structured, in particular corrugated metallic layer and if appropriate at least one further, substantially smooth metallic layer. It is alternatively possible for the hydrolysis catalytic converter to have a casing tube and, on the inner face thereof, to have a structured, in particular corrugated metallic layer which encircles the entire periphery of the casing tube at least once, but does not fill up clear or open parts of the cross section of the casing tube, so that a freely traversable cross section remains free in the interior of the layer. This is referred to as a so-called “hot tube”.
The hydrolysis catalytic converter preferably has channels which are delimited by walls, with the walls of the channels being at most 80 μm (micrometers) thick. Wall thicknesses of 60 μm and less or 30 μm and less are preferable in this case, in particular where the hydrolysis catalytic converter is formed at least partially from metallic layers which form the walls of the channels. The wall thicknesses have proven to be particularly advantageous, since they make it possible to provide a hydrolysis catalytic converter with a small heat capacity.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a cell density of less than 600 cpsi (cells per square inch).
In relation to conventional hydrolysis catalytic converters which are traversed by exhaust gas of the internal combustion engine, a hydrolysis catalytic converter which is not traversed by exhaust gas can be provided with smaller volumes and smaller surfaces. It is possible, in particular, in this case for a smaller cell density of the hydrolysis catalytic converter to be used, since the volume flow rate which flows through the hydrolysis catalytic converter even at full load is less than that of exhaust gas. It is thereby possible to use hydrolysis catalytic converters with relatively low cell densities of less than 600 cpsi, of less than 400 cpsi or even of less than 300 or 200 cpsi and less.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter is mechanically connected to the exhaust line, in particular flange-connected thereto. This advantageously permits a stable mechanical mounting of the device according to the invention.
According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter is thermally decoupled from the exhaust line.
Thermal decoupling is advantageous since, in a cold-start phase of the internal combustion engine in which the exhaust line is still relatively cool, it is not necessary for the relatively large thermal mass of the exhaust line to also be heated up during the heating of the hydrolysis catalytic converter. Once the exhaust line has reached its conventional operating temperature, which can be up to 800° C. and more and is greater than the conventional operating temperature of the hydrolysis catalytic converter of approximately 350 to 450° C., heating of the hydrolysis catalytic converter by the exhaust line which, should it arise, is undesirable and complicates the regulation of the temperature of the hydrolysis catalytic converter, is prevented.
The operating temperature of the hydrolysis catalytic converter is, in particular, in the region of 350 to 450° C. whereas the heating of the hydrolysis catalytic converter preferably results from the hot vapor which includes reducing agent and/or reducing agent precursor, from a further electrical heating and/or from waste heat of the evaporator unit having an operating temperature of up to 450° C. or more.
According to a further advantageous embodiment of the device according to the invention, a bar-shaped heating element is provided, through the use of which at least one of the following components can be heated:
According to a further advantageous embodiment of the device according to the invention, at least one bar-shaped heating element is provided, coaxially with which at least one of the following elements is provided:
In this embodiment, the hydrolysis catalytic converter can preferably be embodied as an annular honeycomb body which contains a plurality of channels between an inner casing tube, which is connected to the bar-shaped heating element, and an outer casing tube. The evaporator unit can, in particular, contain a metering line which is, in particular, wound in spiral fashion around the bar-shaped heating element. It is, if appropriate, possible for a further heating element to be provided outside the configuration, so that parts of the evaporator unit and/or of the hydrolysis catalytic converter are situated between two heating elements. Particularly uniform heating can thereby take place.
The bar-shaped heating element preferably has a plurality of heating zones with temperatures that can be controlled independently of one another. The bar-shaped heating element, in particular, has at least two zones, around which are provided, in each case in one zone, the hydrolysis catalytic converter and the evaporator unit or the metering line. In particular, the zone of the evaporator unit or of the metering line is preferably sub-divided further, since different processes take place in this case, specifically for example heating of the liquid, evaporation of the liquid and superheating of the liquid. Accordingly, a configuration of the bar-shaped heating element with 5 or 6 zones is preferable. The boundary between the zones can preferably be adapted as a function of the quantity of aqueous solution which is to be evaporated.
According to a further advantageous embodiment of the device according to the invention, the temperature of at least one of the following components can be controlled:
In this context, temperature control is to be understood, in particular, to mean that the corresponding component(s) can be heated and/or cooled. In this case, at least one of the components can be part of a regulating loop, and it is preferable for a plurality of the components to be parts of a regulating loop. It is possible, in particular, for the regulation of the temperature of the components to be carried out in such a way that one of the components or a plurality of the components are used as a type of actuator. This means, in particular, that the temperature of only one of the components is actively controlled, and the component correspondingly sets the temperature of the respective other components through the use of corresponding reaction kinetics and through the use of the corresponding present fluid-dynamic conditions.
According to a further advantageous embodiment of the device according to the invention, a device for temperature control is provided. This device includes at least one of the following components:
The Peltier element, in particular, can advantageously be used both for heating and for cooling the corresponding component. The cooling body advantageously has a shape which promotes the radiation of heat. The cooling body is preferably made from a material with high thermal conductivity such as, in particular, aluminum or another metal or a metal alloy.
A Peltier element is to be understood, in particular, as an electrical component which, when a current is passed through it, generates a temperature difference based on the so-called Peltier effect. A Peltier element preferably includes one or more elements made from p-doped and n-doped semiconductor material which are connected to one another alternately through the use of electrically conductive material. The sign of the temperature difference is dependent on the direction of the current flow, so that both cooling and heating can be provided by a Peltier element.
In this case, a burner is to be understood, in particular, as a device for burning a fuel, in particular including hydrocarbons and/or hydrogen. Flameless combustion is also advantageously possible. It is to be understood that a material having a positive temperature coefficient, a so-called PTC-resistor, is in particular an electroconductive material having an electric resistance which increases with increasing temperature. These are in use, in particular, as so-called self-regulating heating elements and are, in particular, made of a ceramic material, in particular a barium titanate ceramic. Alternatively, PTC resistors made of a polymeric material being doped with soot particles can be used.
According to a further advantageous embodiment of the device according to the invention, at least one of the following components has a coating which catalyses the hydrolysis of urea:
Hydrolysis is advantageously already catalyzed in one of the specified components as well as in the hydrolysis catalytic converter, by providing a coating which catalyses the hydrolysis of urea and which can be formed, in particular, as specified above. This increases the conversion capacity and makes it possible for the hydrolysis catalytic converter to be provided to have a correspondingly small volume with a smaller catalytically active surface. The formation of a coating, which catalyses the hydrolysis of ammonia, in the dosing line serves, in particular, to ensure as complete a hydrolysis of ammonia as possible, and in particular also prevents significant proportions of a reverse reaction to form urea or another ammonia precursor. A coating which catalyses the hydrolysis of urea is to be understood, in particular, to mean that a metering line for metering the aqueous solution to the hydrolysis catalytic converter and/or an evaporator chamber for evaporating the aqueous solution have, at least in parts, a coating which catalyses the hydrolysis of urea. The components can thereby already cause a partial hydrolysis of the reducing agent precursor to form reducing agent, and thereby improve the effectiveness of the hydrolysis. In addition, the hydrolysis catalytic converter can thereby be fundamentally provided with a smaller volume or with a smaller catalytically active surface than if no corresponding coating were formed on at least one of the components.
The invention encompasses an embodiment of the device in which the evaporator unit and the hydrolysis catalytic converter cannot be traversed by exhaust gas, but rather only the SCR catalytic converter can be traversed by exhaust gas. This results in considerably reduced throughflow rates through the evaporator unit and the hydrolysis catalytic converter, which can advantageously be incorporated in the construction, in particular, of the hydrolysis catalytic converter, so that the latter can be constructed to be smaller and with a lower cell density than hydrolysis catalytic converters which are traversed by exhaust gas. This reduces the costs in the production of the device according to the invention in comparison to devices known from the prior art.
According to a further advantageous embodiment of the device according to the invention, a metering unit is provided, through the use of which the hydrolysis catalytic converter can be flow-connected to an exhaust line of the internal combustion engine.
Through the use of the metering unit, the reducing agent substance mixture including at least one reducing agent is then metered to the exhaust line. The metering unit can, in particular, include the dosing line, but can also have further components. These can, in particular, be a passive mixing device, through the use of which the introducible substances can be mixed with the exhaust gas.
A passive mixing device is to be understood, in particular, to mean that no actively moveable mixing device is provided, but that a mixture of the substances with the exhaust gas can take place only through the use of the provision of a static mixing device together with the characteristics of the exhaust gas flow and the flow of the introducible substances.
It is particularly preferable for the mixing device to include at least one of the following components:
In this case, the guide plate can, in particular, project into the exhaust line. The guide plate can, in particular, be perforated at least in partial regions and/or have a curvature at least in partial regions. The guide plate can project into the exhaust line at an angle with respect to the longitudinal direction of the exhaust line at that point or location.
In particular, the honeycomb body has channels with walls that have perforations. As a result of the perforations, which can if appropriate be complemented by correspondingly formed guide structures, flow can take place at an angle relative to the longitudinal axis of the channel. The honeycomb body can preferably also have a conical construction. In particular, the dosing line may open out in the interior of a corresponding cutout of the honeycomb body, so that the corresponding substances can be dosed directly in the honeycomb body.
According to a further advantageous embodiment of the device according to the invention, the honeycomb body has channels and apertures which can be traversed by a fluid and connect adjacent channels to one another. The apertures can, in this case, be smaller or larger than the conventional dimensions of a channel.
According to a further advantageous embodiment of the device according to the invention, at least one of the following components:
This particularly advantageously has the result that, in operation, the pressure in the exhaust line is lower than in the metering unit or in the dosing line, so that in this case, substantially no exhaust gas flows in the direction of the hydrolysis catalytic converter. A calming zone or dead zone is to be understood to mean a region with a lower pressure than the pressure in the metering unit and/or dosing line. This can be obtained, in particular, in connection with a mixing device which produces a calming zone or dead zone directly in the opening-out region, and promotes a mixture downstream of the opening-out region.
According to a further advantageous embodiment of the device according to the invention, thermal insulation is provided downstream of the hydrolysis catalytic converter. The thermal insulation is preferably provided directly adjoining the hydrolysis catalytic converter.
The thermal insulation prevents thermal contact with the exhaust line, so that on one hand dissipation of heat from the hydrolysis catalytic converter to the exhaust line and thus cooling down, and on the other hand dissipation of heat from the exhaust line to the hydrolysis catalytic converter, can be prevented. In the extreme case, this could have the result that thermal regulation can no longer be carried out, since the exhaust line is always also heated as the hydrolysis catalytic converter is heated.
According to a further advantageous embodiment of the device according to the invention, at least one of the following components includes at least one temperature sensor:
The temperature of the corresponding component can be measured by using the at least one temperature sensor. The temperature sensor preferably includes a thermoresistor. The temperature sensor can preferably be connected to a power supply. The component can be heated in this way. This can, for example, be necessary in an emergency operating mode if substances have been precipitated in the component and block or threaten to block the component. In addition to urea and the like, the substances can also involve soot which has passed into the metering unit with exhaust gas, for example by diffusion.
According to a further advantageous embodiment of the device according to the invention, a delivery device is provided, through the use of which the aqueous solution can be delivered from a reservoir to the evaporator unit. The delivery device preferably includes at least one pump.
As a result of the delivery device, a constant pressure of the aqueous solution can be built up upstream of the evaporator unit, with dosing into the evaporator unit taking place through a valve. In another preferred embodiment, the pump is a dosing pump, with the dosing taking place through the use of a corresponding actuation of the pump. In this case, a dosing pump is to be understood as a pump allowing the metering of a defined volume per time unit or per stroke.
According to a further advantageous embodiment of the device according to the invention, the pump can build up a delivery pressure which is greater than the highest possible exhaust gas pressure on the metering unit and/or on the dosing line during operation of the internal combustion engine.
In this way, exhaust gas can be prevented from penetrating into the evaporator unit and/or into the hydrolysis catalytic converter during operation. A pump is preferably used which has a delivery rate of up to 150 ml/min, preferably of up to 30 ml/min or up to 10 ml/min. A pump is preferably used having a delivery rate per second which can be varied by 0.75 to 2.5 ml/s, in particular which can be increased by these values.
Preferably, a pump is used as a delivery device which can generate a metering pressure of up to 6 bar absolute, preferably up to 2 bar absolute. The volume flow generated by the pump varies with at most 5% around a pretederminable nominal flow. Preferably, the pump is provided in such a way that it is possible to convey back to the reservoir, in particular with a volume flow which corresponds to the conveying volume flow.
With the objects of the invention in view, there is also provided a method for treating exhaust gas of an internal combustion engine. The method comprises:
b) hydrolyzing the at least one reducing agent precursor to obtain a reducing agent substance mixture;
c) subjecting an SCR catalytic converter to the reducing agent substance mixture and the exhaust gas for at least partial selective catalytic reduction of nitrogen oxides contained in the exhaust gas; and
d) mixing the reducing agent substance mixture with at least parts of the exhaust gas after step b).
The method according to the invention can be carried out, in particular, through the use of the device according to the invention. The method according to the invention particularly advantageously permits the provision of ammonia as a reducing agent for use in the selective catalytic reduction of nitrogen oxides, with a highly dynamic method for providing the ammonia being proposed, so that it is possible to react quickly to very rapidly rising and therefore highly dynamic demands for ammonia as a result of high nitrogen oxide concentrations in the exhaust gas. The mixture of the reducing agent substance mixture with the exhaust gas after step b) means, in particular, that an evaporation of an aqueous solution including at least one reducing agent precursor takes place outside the exhaust gas flow, and an addition to the exhaust gas of the internal combustion engine takes place only after the hydrolysis of the reducing agent precursor to form the reducing agent. A variant of the method is preferable in which the reducing agent substance mixture is mixed with the entire exhaust gas of the internal combustion engine. In this case, the reducing agent is preferably ammonia and a reducing agent precursor is preferably urea.
According to an advantageous refinement of the method according to the invention, step a) includes evaporation, in an evaporator unit, of an aqueous solution including at least one reducing agent precursor.
The reducing agent precursor is preferably urea. In addition to urea, the solution can contain further substances, for example substances which lower the freezing point of the solution. These include, for example, ammonium formate and/or formic acid. A corresponding solution is marketed under the trademark “Denoxium”. A further possibility is the use of a solution which is marketed under the trademark “AdBlue”.
According to a further advantageous embodiment of the method according to the invention, step b) at least partially takes place in a hydrolysis catalytic converter. In this case, the hydrolysis catalytic converter includes, in particular, a catalyst carrier body which is provided with a coating that catalyses the hydrolysis of ammonia.
According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is regulated:
The regulation of the temperature of at least one of the components advantageously permits precise control of the reaction kinetics with regard to the generated products and the quantity of generated products. It is, for example, possible to meter quantities of ammonia to the exhaust gas which are precisely matched to the present nitrogen oxide content in the exhaust gas or to a nitrogen oxide content in the exhaust gas which is forecast for a future time, in order to thereby obtain as complete a conversion as possible of the nitrogen oxides in the exhaust gas of the internal combustion engine.
According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is controlled:
As a result of the multiple reaction kinetics processes which take place during the reactions according to the invention, it can be sufficient to control the temperature of only parts of one or more of the above-denoted components or else the overall temperature of one or more of the above-denoted components. In this case, temperature control is to be understood, in particular, to mean heating or cooling of the component. It can be sufficient in this case to use one or more of the above-denoted components as a type of actuator having a temperature which is controlled in such a way that the temperature of the other components is correspondingly changed as a result of the reaction kinetics.
According to a further advantageous embodiment of the method according to the invention, the aqueous solution is delivered through a delivery line to the reducing agent solution evaporator.
The delivery takes place, in particular, through the use of a pump and in particular from a reservoir.
In this context, it is particularly advantageous if the aqueous solution can be returned through the delivery line.
This can be advantageous, in particular, when the corresponding system must be or is switched off. In an automobile, this can for example be the case if the driver switches off the ignition of the vehicle. In this case, the remaining ammonia present in the dosing line would pass unimpeded into the exhaust system and then gradually also into the atmosphere. This is often undesired, and therefore the emissions of ammonia and also of ammonia precursors into the atmosphere can be significantly reduced and, in particular, prevented through the use of a return delivery from the delivery line and if appropriate also from the metering line.
According to a further advantageous embodiment of the method according to the invention, up to 2.5 ml of aqueous solution are evaporated within one second.
The evaporator unit is preferably constructed in such a way that up to 30 ml/min (milliliters per minute) of the aqueous solution can be continuously evaporated. With such a method, a dynamic provision of reducing agent is possible with which it is possible to convert even concentration peaks of the concentration of nitrogen oxides.
According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is determined before the start of a temperature control measure:
and is aligned with at least one further temperature of another component.
The other component is preferably a component which is substantially at the ambient temperature, for example an external temperature sensor of a motor vehicle, or a cooling water thermometer, etc. In this case, the alignment preferably takes place before the evaporation of the aqueous solution is initiated. Alignment is to be understood in this case, in particular, to mean that a comparison of the two temperatures takes place, with it being possible for further factors to be incorporated.
In this case, it is particularly preferable if an evaporation of the aqueous solution takes place only if the temperature alignment yields that the determined temperature level and the temperature of the other component differ at most by a predefinable difference value.
In predefining the difference value, it is taken into consideration, in particular, whether or not the system was in operation in a predefinable timespan and when the system was deactivated. It is also possible to predefine a timespan in which the diagnosis functions do not take place if the system was in operation within the timespan.
The details and advantages disclosed for the device according to the invention can also be transferred and applied to the method according to the invention. The details and advantages disclosed for the method according to the invention can also be transferred and applied to the device according to the invention.
Alternatively, the device and the method according to the invention can be constructed/performed in such a way that a hydrolysis catalytic converter and a reducing agent solution evaporator conduct a flow through them by a partial flow of the exhaust when in use. All advantageous improvements disclosed herein in which the hydrolysis catalytic converter and the reducing agent solution evaporator usually do not conduct a flow through them by exhaust when in use can be transferred to an alternative embodiment in which the hydrolysis catalytic converter and the reducing agent evaporator device conduct a flow through them by a part of the exhaust gas flow when in use.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for treating the exhaust gas of an internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
These are, in particular, the reducing agent ammonia and the reducing agent precursor urea. The device 1 includes a metering line 2 with a dispensing opening 3. Furthermore, a device 4 for heating the metering line 2 is provided. The metering line 2 can be heated with the device 4 above a first critical temperature, which is higher than the boiling temperature of water. The device 1 also includes a reservoir (not shown in
In the present exemplary embodiment, the device 4 for heating the metering line 2 is wound in spiral fashion together with the metering line 2. In this way, a fluid flowing through the metering line 2 is heated and ultimately evaporated. As a result, a gaseous substance mixture which contains at least one reducing agent precursor is dispensed through the dispensing opening 3. Depending on the selection of the temperature by using the device 4 for heating the metering line 2, at least partial thermolysis of the reducing agent precursor can even already take place in the metering line 2, so that the gaseous substance mixture dispensed through the dispensing opening also already contains reducing agent, such as for example ammonia, in addition to a reducing agent precursor, such as for example urea.
Furthermore, the device 1 for providing a gaseous substance mixture also includes a measuring sensor 5, through the use of which the temperature at least at one point of the metering line 2 can be measured. The measuring sensor 5 can, for example, be a conventional thermal element or a conventional thermoresistor. The device 1 and/or the individual components which require an electrical terminal preferably include a cable length for realizing the electrical terminals. A cable length is to be understood, in particular, to mean a cable connection which is at least half of a meter, preferably at least one meter long. This allows plug-type contacts to be formed in regions which, in particular in automobiles, are exposed to only a small extent to environmental influences such as water spray, stone impacts or the like.
In this case, the device 4 for heating the metering line 2 is operated in such a way that, in operation, the temperature across the length of the metering line 2 is at most 5° C. above and below a mean temperature. The mean temperature substantially corresponds in this case to the first critical temperature. The metering line 2 is formed, in particular, from a copper alloy.
The delivery line 6 can be connected to a further component through the use of a connecting unit 11. Depending on the construction of the device, the component can be the metering line 2 as already referred to above, or generally an evaporator unit 12. The metering line 2 can then be part of the evaporator unit 12. In general, the connecting unit 11 is formed at least partially from a material with a thermal conductivity of less than 10 W/m K (Watt per meter and Kelvin). The connecting unit 11 is formed, in particular, from a ceramic material and/or polytetrafluoroethylene (PTFE). The connecting unit 11 is, in particular, constructed in such a way that a temperature gradient of 40 K/mm (Kelvin per millimeter) and greater can be maintained over a length 57 of the connecting unit 11. This permits a method to be carried out in which the evaporator unit 12 and/or the metering line 2 has a considerably higher temperature than the delivery line 6. The evaporator unit can, for example, have a temperature of 300° C. or more, 400° C. or more or of 420° C. or more, and thereby lead to substantially complete evaporation of the aqueous solution within the evaporator unit 12, while the delivery line 6 has a temperature level of only 70° C. or more, 80° C. or more or 90° C. or more in order to ensure that the aqueous solution is not yet evaporated in the delivery line 6.
The SCR catalytic converter 18 therefore attains a mixture of reducing agent and exhaust gas which leads to a reduction of the nitrogen oxides contained in the exhaust gas 13 in the SCR catalytic converter 18. In this case, a quantity of reducing agent substance mixture is preferably provided which is such that as complete a conversion of the nitrogen oxides in the exhaust gas 13 as possible can take place in the SCR catalytic converter 18.
The evaporator chamber 24 is preferably formed from a material including at least one of the following materials: a) copper; b) aluminum; c) noble steel; d) a nickel-based material and e) chrome-nickel steel. The volume of the evaporator chamber 24 is preferably 1.5 to 10 cm3. In operation, the heat conductor 27 is preferably operated with a heating power of up to approximately one kilowatt per second, with the maximum heating power being fixed as a function of the application. In passenger vehicles, the maximum heating power is preferably approximately 500 to 700 W/s, and in trucks or utility vehicles, preferably approximately 1200 to 1500 W/s. The heat capacity of the evaporator chamber 24 is preferably less than 120 J/K, particularly preferably 100 to 110 J/K. The first opening 25 and the second opening 26 preferably enclose an angle of 30 to 70°. The aqueous solution 45 is preferably delivered at up to 150 ml/min into the evaporator chamber 24, preferably at up to 100 ml/min, particularly preferably at up to 30 ml/min. In the region of the second opening 26, the evaporator chamber 24 preferably has a device with which an infiltration of droplets into the second opening 26 can be avoided. The device is, in particular, a device with which a gas film situated between the droplet and the wall of the evaporator chamber 24 can be penetrated. The device is, in particular, projections of the walls or the like. Structures 28 can likewise be provided in this region.
Furthermore, the evaporator chamber 24 has, in the interior, one or more of the above-mentioned structures 28 which serve to produce a larger surface for evaporating the aqueous solution. The structures 28 are illustrated as being relatively large in the present exemplary embodiment. However, the structures 28 can also be a structured surface which is provided, for example, by applying a corresponding coating to the inner surface of the evaporator chamber 24. The structures 28 can alternatively or additionally also include macroscopic structures which have a structure amplitude of a few millimeters or even more. In general, the structures 28 are to be understood as a device for increasing the wetting capacity of the surface of the evaporator chamber 24.
The evaporator unit 12 is connected through the use of the second opening 26 to a hydrolysis catalytic converter 17. The hydrolysis catalytic converter 17 has a device 31 for controlling the temperature of the hydrolysis catalytic converter 17. The device 31 is composed, in the present exemplary embodiment, of a corresponding heating wire which is wound around the hydrolysis catalytic converter 17. A corresponding casing 32, which is disposed around the hydrolysis catalytic converter 17 constitutes, in particular, thermal insulation of the hydrolysis catalytic converter 17 with respect to the environment in order to minimize as far as possible any occurring heat losses. In the present exemplary embodiment, the hydrolysis catalytic converter is connected directly to the exhaust line 14 by virtue of projecting into the latter. A corresponding bore, into which the hydrolysis catalytic converter 17 or its casing 32 can be inserted in as sealed a manner as possible, is formed in the exhaust line 14. A corresponding connecting device 33 produces as sealed a connection as possible between the hydrolysis catalytic converter 17 and the exhaust line 14. A passive mixing device is also provided in the form of a guide plate 34, through the use of which a reducing agent substance mixture 35, which leaves the hydrolysis catalytic converter 17, is mixed with the exhaust gas flowing in the exhaust line 14.
In operation, the evaporator unit 12 serves to produce a gaseous substance mixture from an aqueous solution which contains urea as a reducing agent precursor. The gaseous substance mixture generated in the evaporator unit 12 contains at least urea and if appropriate also already ammonia which has been generated by thermolysis of the corresponding urea. The substance mixture is conducted through the second opening 26 into the hydrolysis catalytic converter 17 in which substantially complete hydrolysis of the urea takes place to form ammonia. In this case, a reducing agent substance mixture 35 which includes ammonia is generated in the hydrolysis catalytic converter. A method is particularly preferred in which 98% and more of the urea is ultimately converted to ammonia.
In operation, an aqueous urea solution 45 is delivered into the metering line 2. The device 4 for heating the metering line 2 serves to heat the metering line 2 and thereby evaporate the aqueous urea solution and, if appropriate, depending on the temperature control, an at least partial thermolysis of the contained urea takes place to form ammonia. The corresponding gaseous substance mixture is introduced through the dispensing opening 3 into the hydrolysis catalytic converter 17, in which hydrolysis, preferably substantially complete hydrolysis of the contained urea takes place to form ammonia. A corresponding reducing agent substance mixture 35 leaves the hydrolysis catalytic converter 17. The reducing agent substance mixture 35 can be introduced into an exhaust line 14 of an exhaust system of an internal combustion engine. A method is preferable in this case in which the temperatures of the evaporator unit 12 and/or of the hydrolysis catalytic converter 17 are monitored through the use of the temperature measuring sensors 39, 43, and both components 12, 17 can be heated by the corresponding devices 4, 31.
All of the temperature control devices 4, 27, 31, 49, 50 and all of the temperature measuring sensors 39, 43, 47, 48 which are provided are connected to a control unit 51. The control unit 51 carries out a regulation of the temperature in a regulating loop which includes at least one device 4, 27, 31, 49, 50 for temperature control and at least one temperature measuring sensor 39, 43, 47, 48. The number of temperature measuring sensors 39, 43, 47, 48 is preferably greater than the number of devices 4, 27, 31, 49, 50 for controlling the temperature of the components 6, 2, 24, 17, 21, 46. The control unit 51 is preferably connected to a controller of the internal combustion engine or is integrated therein. The data of the controller of the internal combustion engine and the operating parameters of the internal combustion engine can advantageously be incorporated in the control of the evaporation and/or of the delivery to the evaporator unit 12.
The evaporator unit 12 preferably has a device 64 for depositing droplets. The device 64 can, for example, be provided within the metering line 2 or in or downstream of the second opening 26 of the evaporator chamber 24.
The hydrolysis catalytic converter 17, which is disposed downstream of the dispensing openings 3, can likewise be heated by a bar-shaped heating element 69. In one advantageous refinement, only one bar-shaped heating element 69 is provided. The heating element 69 is in thermal contact both with the metering line or lines 2 and with the hydrolysis catalytic converter 17. In the present exemplary embodiment, the hydrolysis catalytic converter 17 is embodied as an annular honeycomb body. The hydrolysis catalytic converter 17 is adjoined downstream by a dosing line 21, through which, in operation, the gas flow including at least one reducing agent can be introduced into the exhaust line 14. A mechanical connection to the exhaust line 14 can be produced by a connecting device 71. A thermal insulation 72 is also provided, through which the hydrolysis catalytic converter 17 is thermally decoupled from the exhaust line 14. A heat shield 73 is also provided, through which the hydrolysis catalytic converter 17 is protected from a radiation of heat. Furthermore, air gap insulation 74, which likewise serves as thermal insulation, is provided between an outer housing 75 and an inner housing 76.
In the case, in particular, of a metering line 2 which is heated by a device 4, 69, it is fundamentally advantageous to provide heating from the other side, in addition to single-sided heating. It is, for example, possible for further heating elements to be provided which enclose the metering line from the outside. It is fundamentally advantageous if, at a certain cross section of the metering line 2, the temperature over the periphery differs from a mean temperature at most by +25° C. or −25° C. in operation.
The hydrolysis catalytic converter 17 is fundamentally also a tube which is provided with a coating that catalyses the hydrolysis, in particular, of urea to form ammonia, or else a casing tube having at least one structured metallic layer which is applied on the inside to the outer periphery and which preferably has a freely traversable cross section radially in its interior which is at least 20% of the entire cross section of the casing tube. These embodiments are preferably heated from the outside.
Before the provision of a reducing agent upstream of the SCR catalytic converter 18 commences, the process is fundamentally as follows:
If the temperature of the SCR catalytic converter 18 is above a predefinable limit value, in particular the “light-off” temperature of the SCR catalytic converter 18, the evaporator unit 12 is supplied with the aqueous solution 45. If the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 are still substantially at their operating temperature, then the above-specified diagnosis steps can be omitted.
In operation, the heating power imparted to the evaporator unit 12 correlates with the delivery quantity of the aqueous solution 45. This means, in particular, that it is checked as to what level of nominal heating power is required for the evaporation of the respective delivery quantity. If the measured actual heating power for a timespan is below the nominal heating power, then a warning is output to the user, since a reduction of the cross section of the metering line 2 and/or of the dosing line 21 could then be present.
It is also advantageous, at regular, predefinable time intervals, to heat the evaporator unit 12, the metering line 2, the evaporator chamber 24, the hydrolysis catalytic converter 17, the dosing line 21 and/or the metering unit 46 to a temperature which is above the normal operating temperature, in order to thereby dissolve any depositions which may be present.
When the evaporation is ended, which occurs for example when the internal combustion engine is switched off, the aqueous solution 45 can be returned from the metering line 2. Before the return delivery from the metering line 2, the delivery of aqueous solution 45 is preferably firstly suspended, with the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 however still being heated to the usual temperature in order to thereby carry out complete evaporation and to thereby prevent any impurities present in the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 from passing into the delivery line 6 during the return delivery. After a certain time has elapsed, the return delivery can be initiated by the delivery device. A valve is advantageously provided on or adjacent the connecting unit 11. Air can be sucked in during the return delivery through the use of the valve. The return delivery fundamentally takes place until the delivery line 6 is substantially emptied into the reservoir 20.
In the event of intense changes in the delivery quantity of the aqueous solution 45 which is to be delivered, which can for example be attributed to a sharply-rising concentration of nitrogen oxides in the exhaust gas of the internal combustion engine, situations can occur in which the evaporator unit 12 is not capable of immediately evaporating a considerably higher quantity of aqueous solution 45, since the correspondingly increased heating cannot take place so quickly. In this case, it is preferable to increase the delivery quantity of the aqueous solution 45 only to such an extent that complete evaporation is still possible.
The quantity of reducing agent to be dispensed, and consequently also the quantity of aqueous solution 45 which is to be evaporated, can be determined as a function for example, of at least one of the following conditions:
The reservoir 20, the delivery line 6, the evaporator unit 12, the metering line 2, the evaporator chamber 24 and/or the hydrolysis catalytic converter 17 can be constructed to be in thermal contact, for example with the fuel tank of the internal combustion engine. The fuel tank usually has a heater, for frost protection reasons, which can then also provide frost protection for the above-specified components.
According to a further advantageous aspect, a device 1 is proposed for providing a gaseous substance mixture including at least one of the following substances:
In this case, the device 1 includes a reservoir 20 for an aqueous solution 45 including at least one reducing agent precursor. The aqueous solution 45 can be delivered from the reservoir 20 into at least one metering line 2 with a dispensing opening 3 by a delivery device 19. Advantageously, through the use of the device 4 for heating the metering line 2, the at least one metering line 2 can be heated above a critical temperature which is greater than the boiling temperature of water. The temperature is preferably 350° C. or more, preferably 400° C. or more, in particular approximately 380° C. One advantageous refinement of the device 1 provides that the delivery device 19 includes at least one pump. The latter is preferably a dosing pump. According to a further advantageous refinement of this device, a valve for dosing the quantity of aqueous solution 45 is provided between the delivery device 19 and the metering line 2. The device 4 for heating also advantageously includes at least one of the following elements:
A further advantageous embodiment of the device is distinguished in that the device 1 is constructed in such a way that, in operation, the temperature across the length of the metering line 2 is at most 25° C. above and below a mean temperature.
A further advantageous embodiment of the device is distinguished in that the metering line 2 has a traversable cross section of at most 20 mm2. It is also advantageous if the metering line 2 is formed from a material including at least one of the following materials:
The metering line 2 has, in particular, a length of from 0.1 to 5 m, preferably a length of from 0.3 to 0.7 m, particularly preferably substantially 0.5 m. The metering line 2 preferably has a wall thickness of 0.1 to 0.5 mm. The metering line 2 preferably has a heat capacity of at least 150 J/K (Joule per Kelvin).
According to a further advantageous embodiment of the device 1, the metering line 2 and the device 4 for heating the metering line 2 have, at least in at least one partial region, at least one of the following configurations relative to one another:
According to a further advantageous embodiment of the device 1, the metering line 2 and the device 4 for heating the metering line 2 are connected to one another in a materially joined fashion at least in partial regions. A materially joined connection is to be understood, in particular as a soldered, brazed and/or welded connection.
According to a further advantageous embodiment of the device 1, the metering line 2 is at least partially provided with a coating which catalyses the hydrolysis of a reducing agent precursor to form a reducing agent. The device 1 preferably includes at least one measuring sensor 5 for determining the temperature of the metering line 2. The measuring sensor can preferably be connected to a power source 5 in order to thereby permit, for example within the context of an emergency program, heating of the metering line 2 above the critical temperature.
An advantageous method is also described for providing a gaseous substance mixture including at least one of the following substances:
In this case, an aqueous solution 45 of at least one reducing agent precursor is delivered from a reservoir 20 into a metering line 2. In this case, the metering line 2 is heated in such a way that the aqueous solution 45 is completely evaporated to form the gaseous substance mixture. Completely is to be understood herein, in particular, to mean an evaporation in which 90% by weight and more of the aqueous solution, preferably 95% by weight and more, particularly preferably 98% by weight of the aqueous solution, is evaporated. One advantageous refinement of the method is aimed at least at one of the reducing agent precursors:
being included in at least one of the following components:
It is also advantageous for the temperatures in the metering line 2 to be at a mean temperature between 380° C. and 450° C. The temperature along a length of the metering line 2 is preferably at most 25° C. above or below a mean temperature, preferably a mean temperature of 380° C. to 450° C.
According to a further advantageous embodiment of the method, a heating power which varies by up to 500 W/s is used during the heating process. A quantity of 0.5 ml/s of the aqueous solution 45 is preferably delivered into the metering line 2. It is also preferable for the metering line 2 to have a traversable cross section of at most 20 mm2. The metering line 2 is preferably heated to a second temperature which is higher than the critical temperature at which complete evaporation of the aqueous solution 45 takes place, in order to thereby dissolve, if appropriate, any depositions which may be present.
According to a further advantageous embodiment of the method, the temperature of the metering line 2 is determined before the start of the evaporation, and is aligned with other known temperatures. In this case these can, for example, be other known or measured temperatures in the automobile, such as for example the ambient temperature measured through the use of an external temperature sensor, or the cooling water temperature.
According to a further advantageous embodiment of the method, the heating of the metering line 2 is carried out through the use of an electrical resistance heater, with the resistance of the resistance heater being determined before the start of heating and the heating of the metering line taking place as a function of the determined resistance. A further advantageous refinement of the method is aimed at the introduced heating power during the heating of the metering line 2 being monitored. According to a further advantageous embodiment of the method, the heating is interrupted if, over a predefinable timespan, the heating power remains below a value which is dependent on the quantity of aqueous solution to be evaporated.
According to a further advantageous present aspect, a device 1 is described for providing a gaseous substance mixture including at least one of the following substances:
In this case, a reservoir 20 for an aqueous solution 45 including at least one reducing agent precursor, is provided. The reservoir 20 can be flow-connected to an evaporator chamber 24. Furthermore, a device for dosing the aqueous solution 45 is provided in the evaporator chamber 24. The device 27, 63 for heating the evaporator chamber 24 is provided for heating the evaporator chamber 24 to a temperature greater than or equal to a critical temperature at which the aqueous solution is at least partially evaporated. According to one advantageous refinement of the device 1, the device for dosing the aqueous solution 45 includes at least one nozzle 62. The evaporator chamber 24 advantageously has a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture. According to one advantageous refinement of the device 1, the evaporator chamber 24 encompasses a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution, a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 13. A further advantageous refinement of the device provides that the device 27, 63 for heating the evaporator chamber 24 includes at least one of the following components:
It is also advantageous that the evaporator chamber 24 is substantially spherically symmetrical. In this case, the evaporator chamber 24 preferably has a radius of 2 mm to 25 mm. It is also advantageous for the evaporator chamber 24 to have a volume of 30 to 4,000 mm3. The device 27, 63 for heating the evaporator chamber can impart a heating power of up to 5 kW. A delivery line 6 for delivering the aqueous solution 45 is also advantageously provided. The delivery line 6 connects the evaporator chamber 24 to a reservoir 20 and a delivery device 19 is provided therein, through the use of which a fluid can be delivered through the delivery line 6. According to a further advantageous embodiment of the device, the latter is constructed in such a way that, during operation, the temperature of the evaporator chamber 24 is at most 25° C. above and below a mean temperature. It is also advantageous for the evaporator chamber 24 to have, at least in partial regions, a device 28 for increasing the wetting capacity of the surface. The device 28 can, in particular, include a structuring of the inner surface (projections or the like) of the evaporator chamber 24.
A method is also described for providing a gaseous substance mixture including at least one of the following substances:
An aqueous solution 45 of at least one reducing agent precursor is delivered into an evaporator chamber 24, with the evaporator chamber 24 being heated in such a way that the aqueous solution 45 is completely evaporated to form the gaseous substance mixture. The method can advantageously be further developed in such a way that the evaporator chamber 24 includes a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture.
Alternatively, the evaporator chamber 24 can encompass a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 13.
The methods can advantageously be further developed in such a way that the heating is regulated. The evaporator chamber 24 is, in particular, heated to a mean temperature of 350 to 450° C. It is also advantageous for the evaporator chamber 24 to be heated to a mean temperature in such a way that the temperature does not at any point or location of the evaporator chamber 24 deviate from a mean temperature by more than +25° C. or −25° C.
The device 15 according to the invention advantageously permits the provision of a sufficiently large quantity of reducing agent for the selective catalytic reduction of nitrogen oxides in the SCR catalytic converter 18, with it being possible at the same time for the hydrolysis catalytic converter 17 to be constructed with a smaller volume than is known from the prior art, since the hydrolysis catalytic converter 17 in this case is not traversed by exhaust gas.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 023 145.7 | May 2006 | DE | national |
This is a continuing application, under 35 U.S.C. § 120, of copending International Application No. PCT/EP2007/004359, filed May 16, 2007, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2006 023 145.7, filed May 16, 2006; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2007/004359 | May 2007 | US |
| Child | 12272359 | US |
