WO2004029424A1

WO2004029424A1 - Method for the post-treatment of exhaust gases and device for the same

Info

Publication number: WO2004029424A1
Application number: PCT/DE2003/003007
Authority: WO
Inventors: Hans-Oliver Ruoss; Patrik Hartherz
Original assignee: Robert Bosch Gmbh
Priority date: 2002-09-18
Filing date: 2003-09-10
Publication date: 2004-04-08
Also published as: DE10243269A1; EP1543224A1

Abstract

A method and a device for the treatment of the exhaust gas from an internal combustion engine are disclosed, whereby an auxiliary agent is introduced into the exhaust gas for purification of the exhaust gas, whereby the auxiliary agent is treated with a plasma before the introduction thereof into the exhaust gas. A high frequency electrical energy is injected into a wave guide structure, such that at one end of the wave guide structure a super-elevation of the electrical field is generated and a plasma can form in the region of the auxiliary agent flowing past said end.

Description

L 0 Method for exhaust gas aftertreatment and device therefor

State of the art

The invention relates to a method and a device for treating the L5 exhaust gas of an internal combustion engine according to the type of the independent claims. From DE 195 10 804 AI it is known to treat a reducing agent introduced in the exhaust tract after the engine before flowing through a catalyst by means of a plasma for the production of radicals.

.0 It is known from WO 00/29727 to treat fuel with a plasma before it is introduced into the exhaust system after the engine.

From WO 00/50743 an arrangement for generating a plasma is known which functions similarly to a conventional spark plug and in which an electrical signal .5 is applied in the kilohertz range.

The article also describes "Aftertreatment of Diesel Vehicle Emissions Using Compact Plasmatron Fuel Converter-Catalyst Systems" by L. Bromberg, D. R. Cohn and A.

Rabinovich, Plasma Science and Fusion Center, Massachusetts Institute of Technology,

30 Cambridge, MA 02139, USA, December 1999 (see http: // www.psfc. Mit. Edu / library / 00rr / 00RR001 / 0QRR001 full. Pd f the excitation of a plasma by means of an arc. When using a conventional spark plug or an arc, there is the disadvantage that sparks which arise, in which a plasma can form, constrict themselves and thus only represent thin areas in which partial oxidation of the hydrocarbons can take place. In addition, such arrangements require a lot of electrical energy. Sparks put a heavy load on the components used and expose them to a rapid aging process. Sparks and arc discharges can be blown out so that continuous and safe operation is not always guaranteed.

Advantages of the invention

The method according to the invention and the device according to the invention with the characteristic

L 5 drawing features of the independent claims, in contrast, have the advantage of providing an energetically favorable method for exhaust gas aftertreatment, in particular for the selective catalytic reduction of nitrogen oxides in exhaust gases. In addition, a device according to the invention is subject to comparatively little wear and tear, and therefore represents a robust arrangement.

.0

A further advantage is that a high-frequency plasma occupies a larger space and thus has a larger cross-section when treating an aid than locally limited spark discharges or arc discharges. In addition, a high-frequency plasma cannot flow in

.5 aids are blown out, as may be the case with an electrical spark. In addition to low electrode wear compared to spark discharges, it is advantageous that any deposits in a combustion chamber are automatically burnt off, since the arrangement can be designed such that the plasma more or less fills the entire combustion chamber. Furthermore

30 proves to be an advantage that the burning time can be controlled exactly in comparison to a spark ignition. Furthermore, a waveguide structure provided according to the invention is easily scalable in a simple manner; in particular the provision of a resonator allows scalability or space-saving miniaturization. This can be achieved by choosing the frequency - and thus the wavelength in the waveguide structure - which in a must have a certain relationship to the geometric dimensions of the waveguide (for example λ / 4 - coaxial resonator). Furthermore, a high-frequency ignition device with a waveguide structure can be handled flexibly, in particular the flame size can be adjusted at any time to the optimum value for the generation of partially oxidized hydrocarbons by appropriate adjustment of the ignition volume. An optimal cross section of action between the plasma and the flowing fuel-air mixture can also be set in a simple manner, resulting overall in a high level of safety in the excitation and operation of the plasma to produce partially oxidized hydrocarbons.

The measures listed in the dependent claims allow advantageous developments and improvements of the methods and apparatus specified in the independent claims. The use of a coaxial waveguide structure is particularly advantageous because, in addition to a compact design, the integration of the power generation into the coaxial structure can be achieved with favorable properties with regard to electromagnetic compatibility.

If frequencies of the high-frequency electrical signal are selected in a range between 100 megahertz and a few gigahertz (10 GHz), preferably in a range between 800 megahertz and 3 gigahertz, an extremely compact size is advantageously achieved.

In particular, it is advantageous that the frequency lies in the ISM frequency band, i.e. in a frequency range around a value of 2.45 GHz with a bandwidth of, for example, +/- 75 MHz. The ISM band (= "Industrial Scientific Medical Band") represents a freely available frequency range and also guarantees a small size.

It proves to be particularly advantageous to introduce the aid into the exhaust tract using a motor and to treat the aid by means of a plasma before it is fed into the exhaust tract. As a result, the plasma does not have to chemically convert any exhaust gas components, which would only unnecessarily absorb energy and would only counter the exhaust gas flow with an additional flow resistance. Further advantages result from the features mentioned in the further dependent claims and in the description.

Drawing 5

The exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it

1 shows a device for exhaust gas aftertreatment, 0

Figure 2 shows a high-frequency plasma reactor and

3 shows a high-frequency ignition device.

.5 Description of the exemplary embodiments

FIG. 1 shows an exhaust gas aftertreatment device 2, the exhaust gas line 5 of which is connected to an internal combustion engine 1 and leads to an exhaust gas purification system 10 which is designed as a catalytic converter arrangement for selective catalytic reduction and / or as a particle filter! 0. One that can be supplied with an aid for exhaust gas aftertreatment

High-frequency plasma reactor 15 has a gas outlet line 17, which opens into the exhaust line 5 between the internal combustion engine 1 and the exhaust gas cleaning system 10 via a metering device 19, in particular via a valve.

15 In the high-frequency plasma reactor 15, a gas rich in partially oxidized hydrocarbons (HC) is generated by the partial combustion of a diesel-air mixture in a high-frequency plasma by introducing high-frequency electrical energy in the megahertz range. The gas enriched with partially oxidized hydrocarbons is introduced via the gas outlet line 17 and the metering device 19 into the exhaust line 0 behind the internal combustion engine 1, in order to support a hydrocarbon-based method for selective catalytic reduction (HC-SCR method) or the downstream exhaust gas cleaning system 10. to ensure particle filtering in a particle filter contained in the exhaust gas purification system 10. In addition, hydrogen and carbon monoxide are generated in the high-frequency plasma reactor. Because of their high reducibility, they are particularly suitable for reducing nitrogen oxides to nitrogen. Due to the highly exothermic oxidation of hydrogen to water and from carbon monoxide to carbon dioxide, hydrogen and carbon monoxide are particularly suitable for quickly heating a catalyst. 5

FIG. 2 shows a special embodiment 150 of a high-frequency plasma reactor with a combustion chamber 151, which has inlet lines 156 for supplying a fuel-air mixture on one side and the gas outlet line 17 already described in FIG. 1 on the opposite side. Protrudes on the side of the inlet lines 156

.0 a high-frequency ignition device 154 with its ignition pin 207a into the combustion chamber 151. The high-frequency ignition device 154 is supplied with high-frequency electrical energy in the megahertz range via a control line 153 by means of a high-frequency generator arrangement 152. The mouth region 158 of the inlet lines 156 is arranged close to the ignition pin 207a relative to the gas outlet line. The arrow 160 illustrates

L5 is the direction of flow of the mixture of air with partially oxidized hydrocarbons.

The high-frequency ignition device 154 ignites a high-frequency plasma in the combustion chamber 151 in the presence of a fuel-air mixture supplied via the inlet lines 156, in which the hydrocarbons are partially oxidized. The resulting mixture of air with partially oxidized hydrocarbons flows in the direction 160 to the exhaust gas line 5. The gas enriched with partially oxidized hydrocarbons, after introduction into the exhaust line, is used in particular in the area of the exhaust gas cleaning system 10 to reduce nitrogen dioxide to nitrogen with the aid of the so-called HC

.5 SCR procedure. The advantages of an HC-SCR process are that no additional auxiliary is required, as is the case, for example, with the ammonia-based process for selective catalytic reduction. This saves an additional tank and the handling is easy for the vehicle operator.

30 Alternative to a catalyst for selective catalytic reduction or to one

Particle filter, the process can also be used in conjunction with a NOx storage catalytic converter. In particular in the case of a storage catalytic converter, there is the possibility of locally in the case of a diesel engine which is normally operated with high lambda values without or without substantial intervention in the internal engine fuel injection Area of the storage catalyst to generate a lambda value of 1 by post-engine injection of partially oxidized hydrocarbons.

Alternatively or in combination with a denitrification system, the high-frequency plasma reactor 150 can also be used with one contained in the exhaust gas purification system 10

Particle filter can be combined to support soot burnup. Alternatively, a metering device 19 can also be omitted if the metering of the aid supply into the exhaust gas tract takes place via a metering of the supply of the fuel-air mixture into the combustion chamber 151. Furthermore, in an alternative embodiment of the high-frequency plasma reactor 150, one or more swirling units can be provided, in particular in the area of the mouth areas 158, in order to swirl the fuel with the air on the one hand and to mix the supplied fuel-air mixture with the high-frequency plasma already present in the combustion chamber 151 to support.

FIG. 3 shows a special embodiment 201 of a high-frequency ignition device 154. Such a high-frequency ignition device is basically already known from the German patent application with the file number 102 39 410.5. The high-frequency generator arrangement 152 has a high-frequency generator 202, the high-frequency signals of which are amplified in the megahertz range by means of an amplifier 203 and then fed to the high-frequency ignition device 201. An inductive coupling 204 of the high-frequency vibrations in a coaxial waveguide structure constructed as a λ / 4 resonator 205 is shown schematically here as an essential component of the high-frequency ignition device. The coaxial resonator 205 consists of an outer conductor 206 and an inner conductor 207, the so-called open end 208 of the resonator 205 with the inner conductor 207 as the ignition pin 207a causing the ignition. The other closed end 209 of the resonator 205 remote from the combustion chamber represents a short circuit for the high-frequency vibrations. The dielectric 210 between the outer conductor 206 and the inner conductor 207 essentially consists of air or a suitable electrically non-conductive material. Only for sealing the open end

208 of the resonator 205 towards the combustion chamber there is a seal 211. The seal 211 also consists of an electrically non-conductive material that withstands the temperatures in the combustion chamber 151, for. B. ceramics. They determine the electrical Properties of the filling material 210 or the seal 211 include the dimensions of the resonator 205.

In this high-frequency ignition device 201, the principle of field elevation in a coaxial resonator 205 of length (2n + 1) • λ eff / 4 with n O O is used, λeff is the effective wavelength of the electromagnetic wave in the resonator. The high-frequency signal generated by a sufficiently strong microwave source as the generator 202 and optionally also the amplifier 203 is mixed inductively, but optionally also capacitively, from the two by the coupling 204 or introduced into the resonator 205 by an aperture coupling. The formation of a voltage node at the short circuit 209 and a voltage antinode at the open end 208 results in a field increase at the ignition pin 207a, which represents an integral continuation of the inner conductor 207, which leads to the plasma in the combustion chamber 151 described above.

Claims

Expectations

1. A method for treating the exhaust gas of an internal combustion engine, in which an aid is introduced into the exhaust gas for cleaning the exhaust gas, the aid being treated by means of a plasma, characterized in that high-frequency electrical energy is introduced into a waveguide structure (205, 206, 207 ) is coupled in and that an elevation of the electrical field is formed at one end (208) of the waveguide structure, so that a plasma can form in the presence of the auxiliary device flowing past the end.

2. The method according to claim 1, characterized in that a coaxial waveguide structure is used.

3. The method according to claim 1 or 2, characterized in that the frequency of the high-frequency electrical signal in a range between 100 MHz and 10 GHz, preferably in a range between 800 MHz and 3 GHz.

4. The method according to claim 3, characterized in that the frequency is 2.45 GHz +/- 75 MHz.

5. The method according to any one of the preceding claims, characterized in that the waveguide structure is designed as a resonator (205).

6. The method according to any one of the preceding claims, characterized in that the end of the waveguide structure (208) projects into a combustion chamber (151) which can be filled with the auxiliary means.

5 7. The method according to any one of the preceding claims, characterized in that the aid is introduced after-motor.

8. The method according to any one of the preceding claims, characterized in that the treatment of the aid by means of a plasma prior to introduction into the

0 exhaust gas occurs.

9. The method according to any one of the preceding claims, characterized in that the aid is used to reduce nitrogen oxides contained in the exhaust gas.

5 10. The method according to any one of the preceding claims, characterized in that the purification of the exhaust gas comprises a selective catalytic reduction of nitrogen oxides.

11. The method according to any one of the preceding claims, characterized in that! 0 hydrocarbons are used as aids, especially the fuel with which the internal combustion engine is operated.

12. Device for treating the exhaust gas of an internal combustion engine, with means for supplying an auxiliary to the exhaust gas for cleaning the exhaust gas, the auxiliary

* 5 can be treated by means of a plasma, characterized in that a waveguide structure (205, 206, 207) which can be supplied with high-frequency electrical energy is provided, so that there is an increase in the electric field at one end (208) of the waveguide structure and in the presence of the can form a plasma at the end of the aid flowing past.

30