Patent Application
20060196172
The invention relates to an injection device for injecting a dispersion of an active component into exhaust fumes, in particular exhaust fumes from combustion engines, in particular diesel engines, for the catalytically reduction of the levels of unwanted components, in particular nitrogen oxides, from the exhaust fumes.
There is an increasing demand in a significant reduction of nitrogen oxide emissions from combustion engines, in particular from diesel combustion engines, in motor vehicles, such as for examples trucks, passenger cars, and motor bikes. The nitrogen oxide content in exhaust fumes can be reduced by selective catalytic reduction (SCR) wherein the exhaust fumes are directed together with an aqueous urea solution over a catalytic converter. At the converter the reaction of nitrogen oxides with the urea solution to less toxic compounds is catalysed. A fine dispersion of the aqueous urea solution in the exhaust fumes is required for achieving a most efficient conversion. The amount of urea solution required for efficient conversion depends on the operation status of the vehicle. Therefore, the urea solution is injected into the exhaust fumes intermittently and in small doses, which requires precise and homogeneous dosing and reproducible pulsing.
In common exhaust treatment systems using SCR for reducing the nitrogen oxide levels the required amount of the aqueous urea solution is pumped from a storage tank and introduced into the exhaust fumes by means of an injection valve at a certain pressure. For an efficient conversion of nitrogen oxide to be achieved the aqueous urea solution must be finely dispersed when it joins the exhaust fumes. In the injection valves of the prior art dispersion of the aqueous urea solution is achieved by introducing compressed air into the urea solution upon which a fine dispersion may be formed. The use of compressed air is costly and furthermore makes necessary the use of additional components and specific configurations of the injection valve.
Other devices avoid the use of compressed air by using an orifice plate or metal diaphragma for the generation of a dispersion. In these devices the urea solution is fed through the orifice plate or the diaphragma at high pressures upon which a dispersion is formed.
Several disadvantages are associated with this approach. For generating a fine dispersion using orifice plates or metal diaphragma comparatively high pressures need to be applied. As a consequence, the materials of which the injection valve is made must withstand these pressures. Therefore, inexpensive materials, such as components made of plastic or rubber may not be used. Instead rather expensive materials such as for example steel may be required for the fabrication of the injection valve or its components. Additionally, the use of orifice plates or diaphragmas requires the injection valve to have a comparatively large inner volume such that the required pressures can be realized. This again may add to the fabrication costs of the device. Moreover, standard urea solutions used for the catalytic conversion of nitrogen oxides in exhaust fumes using SCR may contain up to 65% water. Due to the high water content the urea solution freezes at low temperatures. Freezing of the solution impacts the efficiency and may even damage components of the injection device. Reducing the volume of the injection valve is one way of avoiding premature freezing of the solution.
It is an object of the present invention to provide a device for injecting a fine dispersion of a liquids into exhaust fumes of combustion engines, in particular diesel combustion engines, that is constructively simple and inexpensive.
It is another object of the present invention to provide a device for injecting a fine dispersion of liquids into exhaust fumes of combustion engines, in particular diesel combustion engines, that allows the intermittent injection of the dispersion at short pulsing periods.
It is a further object of the present invention to provide a device for injecting a fine dispersion of a liquid into the stream of exhaust fumes of combustion engines, in particular diesel combustion engines, that operates at low pressures, i.e. pressures above 1 but less than 10 bar, preferably less than 5 bar allowing for the use of cheap materials (like plastic and rubber) in the fabrication of the device.
It is also an object of the present invention to provide a method for injecting a fine dispersion of a liquid into the exhaust fumes of combustion engines, in particular diesel combustion engines, wherein the liquid is injected intermittently in low amounts.
It is also an object of the present invention to provide a method for injecting a fine dispersion of a liquid into the exhaust fumes of combustion engines, in particular diesel combustion engines, wherein the device has a reduced inner volume (i.e. a reduced volume of the chamber receiving the liquid from the supply means and from which the liquid is fed into a dispersion chamber where it is dispersed) for avoiding premature freezing of the solution.
This invention describes apparatus and methods for injecting a fine dispersion of a liquid into exhaust fumes from combustion engines, in particular diesel combustion engines.
Accordingly, in a first embodiment the invention comprehends a device for injecting a fine dispersion of liquid into exhaust fumes of combustion engines, said device comprising a means for supplying a liquid, in particular an aqueous urea solution, a pumping means for directing the liquid into a pressure swirl atomizer where the liquid is dispersed, and an outlet through which the dispersion is fed into an exhaust manifold prior to the exhaust fumes being directed over a catalytic converter. The device further comprises means for controlling the pumping means such that the liquid is intermittently and reproducibly pulsed into the pressure swirl atomizer allowing for the dosage of the liquid that is fed into the pressure swirl atomizer to be precisely metered. The pressure swirl atomizer allows for a dispersion to be formed through directing the liquid through tangential pathways prior to directing it again through an axial pathway before the outlet at appropriate pressure and geometrical configuration.
The pressure swirl atomizer according to the invention is a liquid only system, i.e. the dispersion is formed without the addition of a second fluid medium such as for example compressed air. Such liquid-only pressure swirl atomizers are known but have been only used in applications of permanent or comparatively long pulsing periods. An example of a suitable liquid only pressure swirl atomizer is shown in
It was surprisingly found that a pressure swirl atomizer can be used in an application where short pulsing period, precise dosing and relative low operating pressures might be required.
Examples of suitable components of the injection device—with the exception of the pressure swirl atomizer and the outlet nozzle—such as for example pumping means, controlling means, housing, actuating means and their suitable configuration are disclosed in US 2004/0103641 A1 and may also be used in the device according to the invention. The content of US 2004/0103641 A1 is incorporated herein by reference.
The liquid to be injected may be any aqueous, Newtonian liquid that may be needed to achieve a catalytic conversion of a toxic component in exhaust fumes of combustion engines. Thus, the invention also contemplates the device for other catalytic conversion systems that require the addition of a dispersion to a gas stream other than nitrogen oxide reduction by SCR.
A preferred liquid according to the invention is an aqueous urea solution.
The toxic component of the exhaust fumes may be any toxic component but preferably is a nitrogen oxide, preferably a mixture of nitrogen monooxide and nitrogen dioxide. The treatment of the exhaust fumes preferably comprises the reduction of nitrogen oxide levels. The catalytic converter is a catalytic reduction converter as known in the art. The invention also contemplates other catalytic conversion systems in which a liquid is to be added intermittently to reduce the amount of unwanted, preferably toxic, components in exhaust fumes.
The injection of the dispersed liquid into the exhaust fumes is carried out at intermittent periods. Typical periods are 1 to 1000 preferably 10 to 100 milliseconds.
The amount of liquid injected into the pressure swirl atomizer is typically from about 0.1 to about 10 milligram per millisecond, preferably from about 0.1 to about 2 milligram per millisecond, more preferably from about 0.5 to about 1.5 milligram per millisecond.
The amount of the dispersed liquid infected into the exhaust fumes are typically from about 0.1 to about 10 milligram per millisecond, preferably from about 0.1 to about 2 milligram per millisecond, more preferably from about 0.5 to about 1.5 milligram per millisecond.
The operation pressure, i.e. the pressure at which the liquid fed into the pressure swirl atomizer is typically from more than 1 to about 20 bar, preferably from about 2 to less than about 6 bar, preferably less than about 5 bar.
By reducing the amount of pressure necessary for injecting the liquid into the dispersing means, i.e. the pressure swirl atomizer or to obtain a fume dispersion of that liquid, materials can be used which allow a cost effective construction of the injection device, such as for example rubber, plastic, rubber tubing, plastic tubing. Also the construction of smaller sized pumping means and chambers comprising these pumping means may be possible. Thus, the device or one or more of its components may be made of cheaper materials, and the components or even the entire device may be reduced in size or volume. Preferably at least one of the following components of the device according to the invention is made of plastic: the pumping means, at least one component of the pumping means, the pressure swirl atomizer, at least one component of the pressure swirl atomizer, the liquid supply means, at least one component of the liquid supply means, tubing a sealing means, the housing.
The invention also relates to a method of reducing the levels of nitrogen oxides in exhaust fumes of combustion engines in motor vehicles, comprising the steps of
(i) leading the exhaust fumes over a selective catalytic reduction converter which converts the nitrogen oxides in the presence of at least another reactive component into components that are less toxic to humans than nitrogen oxide, and wherein the other reactive component is added as a dispersion of a solution containing said reactive component,
(ii) forming a dispersion by pumping the solution containing the reactive component at controlled amounts and during controlled pulse periods into a pressure swirl atomizer
(iii) directing the dispersion into the stream of exhaust fumes before it contacts the catalytic converter.
The indications given wit respect to the device also apply for steps of the process of the invention, in particular apply the pulse periods, operation pressure, and the amount of liquid injected or dispersed.
The liquid (in this case an aqueous urea solution) is feed into the first chamber 6 via the supply means 6 connected to the housing 7. This figure shows one supply means only but several supply means are also contemplated. The liquid can be introduced into the first chamber already as a mixture but the invention also contemplates to introduce several liquids into the chambers such that mixing can take place in that chamber. In the first chamber there is the piston 5 which functions as a pumping means. The piston is pressed against an adapter plate 23 in the closed position. The adapter plate is shown
The position of the piston (i.e. opening position or closed position) is controlled by one or more control devices (not shown) which may act on the piston, for example via a spring. Any known control device can be used (such as for example piezoelements, magnetic elements or eletromagnetic elements, possibly combined with transmitting elements) which allows reproducible and precise pulsing, i.e. the frequency and the speed at which the piston is moved back from and towards the pressure swirl atomizer (leading to injection of liquid in the pressure swirl atomizer and to injection of the dispersion into the exhaust fumes, respectively. En the opening position the piston may be pushed (caused by a suitable control device, e.g. by a magnetic or electromagnetic attraction force) against a spring. If the force pushing the piston against the spring ceases (again caused by the control device) the piston is driven by the tension of the spring towards the adaptor plate and pressure swirl atomizer, respectively, forcing the liquid which in the meantime has been injected into the first chamber through the supply means into the pressure swirl atomizer.
The device as shown in
| Number | Date | Country | |
|---|---|---|---|
| 60658352 | Mar 2005 | US |
