CH661563A5 - Electrostatic device for protecting a built in an exhaust channel and for gasoline engines specific catalyst before poisoning by pollutant particle. - Google Patents

Description

661563

PATENT CLAIMS

1.Electrostatic device for protecting a catalytic converter installed in an exhaust duct and intended for gasoline engines against poisoning by pollutant particles, in which an ionization path formed from an electrode and counterelectrode is provided for the pollutant particles in the direction of flow of the exhaust gases in front of the catalytic converter and the catalyst is negative in the same direction as the pollutant particles is charged and provided with electrical insulation relative to the exhaust gas duct, characterized in that the exhaust gas duct is also provided with electrical insulation on the inside in the region of the ionization path (5) and the positively charged counter electrode (6, 6 ') in front of the catalyst (4) designed to be permeable to flow, is oriented essentially transversely to the direction of flow and essentially fills the cross section of the exhaust gas duct.

2. Device according to claim 1, characterized in that the counter electrode consists of a wire mesh (6 ').

In order to reduce the content of harmful components in the exhaust gas from gasoline engines, it is known to subject the exhaust gas flow to catalytic afterburning on exhaust gas catalysts or to regulate the composition of the fuel-air mixture supplied to the engine by means of sensors, so-called lambda probes, installed in the exhaust gas flow also have a catalytically active zone and react to the content of oxygen and unburned hydrocarbons. If fuels containing lead are used, however, these catalysts are inactivated within a short time by the pollutant particles in the exhaust gas, in particular lead, but also sulfur, soot or heavy metal particles. The electrostatic separation of the particles upstream of the catalytic converter (DE-OS 21 39 775) is also unsatisfactory, since particles are torn off the filter surface at high exhaust gas velocities and heavy filter occupancy and damage the catalytic converter.

It has therefore already been proposed to charge the pollutant particles and the catalyst surface electrostatically in the same direction with a high-voltage DC voltage, so that the pollutant particles and the catalyst surface repel each other and the pollutant particles fly past the catalyst without being deposited on it (patent application P 31 42 481.3). The generation of the ionizing electric field required for the preferably negative charging takes place between a wire electrode mounted concentrically in the exhaust pipe and the exhaust pipe acting as a counter electrode. Immediately behind the charge path is the catalytic converter, which is electrically insulated from the exhaust pipe and to which the same voltage is applied as at the wire electrode. When the exhaust gas flow is ionized between the wire electrode and the exhaust wall in front of the catalytic converter, however, it can happen that individual ionized particles get to the exhaust pipe wall before the catalytic converter and are discharged there. These particles are of course no longer repelled by the catalyst and can settle on it.

The object of the present invention is therefore to find an electrostatic device for protecting the catalysts in the exhaust gas duct of gasoline engines, in which the possibility that charged pollutant particles can discharge before the catalyst is largely eliminated.

This object is achieved by the electrostatic device described in claim 1. The particles are no longer charged in the radial direction (from the minus charged wire-shaped inner electrode to the exhaust wall), but in the axial direction, i.e. from the negatively charged catalyst in the direction against the exhaust gas flow to a gas-permeable planar counterelectrode which is oriented essentially transversely to the flow direction and essentially fills the cross section of the exhaust gas duct. The exhaust duct in the area of the catalyst and the ionization path is provided on the inside with electrical insulation, generally in view of the temperatures of a ceramic layer prevailing there. Perforated plates, wire screens or nets are suitable as counterelectrodes, which are designed in such a way that they provide the lowest possible flow resistance to the exhaust gases, e.g. Sieves with a mesh size of 2 to 4 mm. The counterelectrode should have the largest possible area, i.e. it should generally essentially fill the cross section of the exhaust gas duct. The smaller the area of the counter electrode in relation to the cross section of the exhaust gas duct, the worse the ionization of the pollutant particles. By charging the pollutant particles in the opposite ionization field between the catalyst and counterelectrode, the pollutant particles are negatively charged and cannot discharge at a positive potential before they reach the catalyst. Only the counter electrode is present as a positive potential in front of the catalytic converter. Although negatively charged particles which reach the counterelectrode against the gas flow can accumulate or discharge here, these particles must cross the ionization field again before they reach the catalyst, i.e. that only negatively charged particles can reach the negatively charged catalyst. After passing through the catalytic converter, the negatively charged particles accumulate in the further course of the exhaust gas line and are then "shaken" while driving after discharge at the exhaust wall and released into the open.

The length of the charge path between the catalyst serving as the negative electrode and the counter electrode depends on the gas velocity, the applied potential, the distance between the electrodes and the particle mobility of the pollutant particles and can be used using those known for charging particles for electrostatic particle separation with direct current Formulas (e.g. Perry, Chemical Engineers Handbook, Mc Graw-Hill 1973, pages 20-103 to 20-115) can be easily calculated. Generally, voltages of about 10 to 40 kV are used and the ionization path is 5 to 15 cm long.

Of course, only those catalysts can be used that are deposited on an electrically conductive support, e.g. on a steel net or in particular a honeycomb-shaped steel frame or catalysts which themselves have sufficient electrical conductivity, which can optionally also be brought about by adding electrically conductive substances such as noble metal, copper, aluminum, etc. to the catalyst mass.

Since the electrostatic charge of the pollutant particles is temperature-dependent, the device is expediently arranged at a point in the exhaust line where the temperature of the exhaust gases does not exceed 800 ° C, but the exhaust gases are still hot enough to contact the exhaust gas catalytic converter or the lambda probe to react.

The device according to the invention is shown in the drawing, for example. Here shows

1 is a representation of the entire device in the prin

zip,

2 and 3 show different embodiments

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for the counter electrode.

The device consists of the housing 1, to which the exhaust gases are fed through the pipe 2 and from which the exhaust gases are discharged again through the pipe 3. The catalyst 4, the ionization path 5 and the counterelectrode 6, which is designed as a perforated plate, are located inside the housing. The catalyst, ionization path and counterelectrode are electrically insulated from the housing by the aluminum oxide tube 7. In order to reduce the risk of breakage of the insulating tube 7, there is still a layer of inorganic fiber material 9 between the insulating tube 7, the housing jacket 8 and the catalytic converter 4, which layer is able to absorb length changes caused by temperature changes. The high voltage of minus 10 to minus 30 kV is fed to the catalytic converter 4 through the feed wire 10, which is electrically insulated from the housing by the insulating tube 11. The counter electrode 6 is connected to the housing via the metal rod 12 mounted in the guide 13 and is at the potential 0. By moving the rod 12 in the guide 13, the distance between the counter electrode 6 and the catalytic converter 4 and thus the length of the ionization path 5 can be adjusted change. The ionization path can thus easily adapt to the different conditions in motor vehicles, e.g. with regard to the temperature of the exhaust gases or the level of high voltage generated. So it would be e.g. possible using e.g. circuits known from Perry (I.e.) to determine the sparkovers to control the distance between the counterelectrode 6 and the catalytic converter 4 with the aid of a Servon.otor so that the exhaust gases are always optimally ionized. Normally, however, the counterelectrode 6 will be permanently installed and no displacement options will be provided.

Since high DC voltages of 10 to 40,000 volts are required to operate the device, but only very small currents of about 1 to 10 mA, it is possible to derive the required high voltage from the ignition voltage of the gasoline engines, such as e.g. is described in detail in DE-AS 10 80 349. The operating voltage for the device can also be generated in a power supply device that is independent of the ignition system i5. Chopper devices powered by a battery, so-called inverters, but preferably electronic devices of known design, can be used for this purpose, which, given the very low power consumption, can be implemented without great technical effort.

The advantages that can be achieved with the invention lie primarily in the fact that the ionized pollutant particles have no possibility of being discharged on their way through the ionization section and therefore cannot attach themselves to the catalytic converter.

1 sheet of drawings