DE3923640A1 - Filtering out soot particles from IC engine exhaust gas flow - using existing and specified polarity conditioned retention power and/or related reaction with positive and negative charged filters - Google Patents

Abstract

The soot particles (1) are charged with the same polarity by devices (5, 6) in a first reaction section, in addition the particles are filtered out with at least one filter (3) of opposing polarity. The soot particles (1) having a different polarity, after leaving the engine, flow through a filtering system formed of filters (2, 3, 4), in which in zones (2, 3) a specified electric polarity rules, and/or an intermittently opposing electrical polarity (4a) is made available. The devices (5, 6) are electrically conducting in the first reaction section, the filters (2, 3, 4) carrying out the separation are at least electrically insulated at the surface. USE/ADVANTAGE - Method for filtering out of soot oarticles. Regeneration process with high separation efficiency. Soot is reliably retained also with strongly changing temp. and/or throughput.

Description

Technical field

The invention relates to a method for filtering out Soot particles according to the preambles of claims 1 and 2.

State of the art

Although the field of soot filtering in motor vehicles today is processed very intensively worldwide, are the necessary Requirements in all known proposals are only partial fulfilled wisely:

• a) - The widespread filter of the "Wall Flow" type, as z. B. SAE paper 8 90 179, M. Signer, "Laboratory Results in Particulate Trap Technology" is described, it reaches very high separation levels and can be placed reliably in the vehicle at the desired location, but generates high thermal stresses due to the system during regeneration whose operational control has not yet been achieved:
  • · A regeneration fire always only occurs island-like. The surrounding area remains perfectly isolated. The high temperatures lead to thermal stresses and thus to fractures of the matrix, possibly even to a partial melting of the walls.
  • · The larger the filter, the more serious this problem becomes (see SAE paper 8 90 173, J. Ketagawa, "Effects of DPF-Volume...").
  • The filters can only be used with very carefully controlled regeneration (complex systems with burners and the like), but do not enable an inexpensive car concept.
• b) - foam filter made of ceramic materials, such as. in SAE paper 8 90 172, T. Mizrah, "Open Pore Ceramic Foam as Diesel Pariculate Filter "are suggested a much higher mechanical and thermal stability lity, but achieve with acceptable back pressures only very modest separation rates from 50% to 60% and often show the "blow off" problem.
• c) - Electrostatic soot separator, see e.g. B. FISITA Paper 8 45 080, W. Pollach, "Results with the electrostatic soot separator on a car diesel engine", show quite high degrees of separation and low back pressure. However, they are unable to solve the regeneration problem. In addition, their space requirement is large.
  • · In the usual design, as described in the paper mentioned, a corona discharge path is connected upstream in the filter, which imparts a uniform polarity to the soot particles.
  • In contrast, it has been shown in (SAE Paper 8 60 009, Kittelson, "Electrostatic Collection of Diesel Particles" that the soot particles are highly bipolar when they leave the engine, so that an electrostatic precipitator, directly connected to the engine, can do without a corona line and, with a suitable design, can achieve a separation rate of more than 80% in a simple separator, made up of a concentric tube. However, the impinging particles will release their charge on the catcher electrode and lose their attraction and thus leave the system again along the electrode surface. However, the particles will be agglomerated, so that a subsequent coarse separator (eg a cyclone) will have a discharge effect. Again, there is neither the problem of the definite separation of the soot from the gas flow, still resolved that of regeneration.
• d) - The one in diesel particle filters the cells or too the type of foam usually used are electrically insulating (codierite). However, it is possible to choose suitable ceramic materials that have sufficient electrical conductivity. This technique is generally known and is described, for example, in "Modern Ceramic Engineering", David W. Richerson publ. Marcel Dekker Inc. 1982, technically described. they can be used as semiconductors, as heating elements, for electrical Fuses or capacitors can be used. A An example is the use of a heatable catalyst (SAE paper 8 90 799, K. Hellmann, "Resistive Materials Applied to quick Light-Off Catalysts "), for example the use of a doped silicon carbide material.
• e) - The generation of high DC voltages in the range of some KV is using modern electronic Medium no technical problem. Can be used as a voltage source the DC voltage of the vehicle battery can be used. Using an electronic switch and one Leave the transformer with downstream rectification the required potential with selectable polar represent in a vehicle-accessible technology.
• - The regeneration of one stored in the ceramic filter The amount of soot is determined according to SAE Paper 8 80 008, A. Mayer / E. Pauli, "Emissions Concept for Vehicle Diesel Engine", then reliably possible if the filter pla is decorated, its volume is sufficiently small, the upper surface is coated catalytically and by Throttling or exhaust gas recirculation of the engine throughput  reaching exhaust gas temperatures at any load points be fathered.

Object of the invention

The invention aims to overcome the disadvantages derived above Remedy. The invention as set out in the claims is characterized, the task is one regenerable, due to a high degree of separation to provide characterized exhaust gas particle filter, which is able to remove the deposited soot during the storage phase at strongly changing temperatures and / or throughputs reliably withheld.

The main advantage of the invention is that the filter does not allow "blow-off" behavior, d. H. the Soot particles are along the flow length of the basic measure trix of the filter reliably filtered, even with a porosity of the filter of about 50 ppi, which is a pore size of approx. 0.5 mm.

This is basically achieved by filtering out of the soot particles using their existing ones and predetermined polarity-related holding forces and / or through an action in this regard, as far as these holding forces oppose the drag force of the exhaust gas flow able to contribute. Advantageous and expedient training Solutions of the task solution according to the invention are in the dependent claims marked.

In the following, exemplary embodiments will be described with reference to the drawing of the invention explained. All for immediate understanding Elements not necessary to the invention are omitted. The direction of flow of the exhaust gases is indicated by arrows. In the figures are the same elements with the same reference numerals Chen provided.  It shows

Fig. 1 four different basic structures (I-IV) from filtering out soot particles.

Fig. 1 shows four schematic basic structures (I-IV) of filtering out soot particles.

Soot particles are mostly electrically charged when they leave the internal combustion engine. If there is a filtering of the same after the internal combustion engine, there is an inherent risk that these particles, after they have been caught, lose their charge to the electrically conductive surface of the exhaust gas particle filter, for example to the ceramic surface thereof. The adhesive force of these soot particles would be lost, the desired effect would disappear, and the soot particles could be entrained by the gas flow. In order to prevent this danger, a foam filter 2, 3, 4 made of conductive material is selected beforehand and subsequently covered with an electrically highly insulating, ceramic layer 2 a. This can be done, for example, by immersing in an aluminum oxide bath, as a result of which the open-pore structure of the filter can also be detected well. Furthermore, for example, the "gamma phase" could be selected, which at the same time made possible a very high internal surface for the eventual application of a catalyst. At the required electrical contact points 7 , the foam filter 2, 3, 4 serving for the separation is slightly processed in order to remove the surface insulation layer. According to a first basic structure I, two porous filter plates 2, 3 , which are led out as described above, are connected in series in terms of flow. In addition, they are at a different poten tial: the positively charged exhaust gas particle filter 2 catches the negatively charged soot particles 1 from the exhaust gas flow; the downstream, equally highly negatively charged exhaust gas particle filter 3 will retain the positively charged residual soot particles 1 . In the latter process, it can be said that it can be assumed that part of the positively charged soot particles 1 are already mechanically collected in the first, positively charged exhaust gas particle. In the case of the neutral soot particles from the exhaust gas flow, it can be said that these will either filter out via the positive charge of the exhaust gas particle filter 2 or via a mechanical action taking place there in the same degree of separation as the electrically charged soot particles. The two exhaust particulate filters 2, 3 are provided with a physical insulation relative to their carrier bodies or housings, the leads 8 serving for electrical charging also being guided through the insulation layer. Because of the electrical breakdown voltage, the two filters must be properly spaced: At 10 kV, about 10 mm apart.

Alternatively, a second basic structure II can be provided for the configuration described above. Here, a single exhaust gas particle filter 4 is used, which is brought to different potentials 4 a in rapid time change. The time interval of the pulses +/- should be smaller than the residence time of the soot particles 1 in the filter area. When a positive voltage is applied, the negatively charged soot particles 1 are captured; when changing to a negative voltage, the positively charged soot particles are then filtered out. With regard to the neutrally charged soot particle 1 applies what has been said above under the description of the basic structure I. It can be expected that the charges of these soot particles are not lost in the loose structure of the soot particles 1 . The "cake" thus formed from soot particles 1 will thus remain overall in the exhaust gas particle filter 4 if the adhesive force varies rapidly. In this regard, one benefits from another phenomenon: Due to the mutual attraction of the soot particles 1 , which have been approximated to one another via the filtering process and have already been largely pre-compressed, intensive agglomeration will take place. The much larger soot particles thus formed are easily captured in a large-pored, insulated foam filter.

It has been recognized that when the Ab gas particle filter the original charges of the Soot particles are largely lost. This will be remedied created by the soot particles elec be reloaded.

According to basic structure III, the new electrical charging to be undertaken is done in a first electrically conductive exhaust gas particle filter 5 , in which all soot particles 1 are brought to a positive charge, in order to then filter them out in the following isolated exhaust gas particle filter 3, 2a with a negative charge. This filter 3 is at least superficially electrically isolated.

Of course, the electrically conductive filter 5 can be negatively charged, so that the filter 3 that follows it must then have a positive electrical charge. If the exhaust gas particle filter 5 is primarily to perform the task of loading the soot particles 1 , the size of its porosity can be chosen to be permeable to soot particles.

In itself, this technique can also be used if, as the basic structure IV symbolizes, the negatively charged and insulated exhaust gas particle filter 3, 2 a is preceded by a suitable Ko rona section 6 . Here too, what has been said above regarding the explanations of the basic structure III applies to polarity.

Generally speaking, the formation of a foam ceramic filter as a precipitation electrode of an electrostat only made it possible to take advantage of the foam filter benefits: Use formation of coarser pores, thus lowering the pressure loss and still no "blow-off" risk. In particular, it turns out the resulting reduction in pressure loss in the filter  in a pressure-charged internal combustion engine, its scarf device has a charger placed downstream of the filter, as very beneficial.

The above-mentioned basic structures I-IV can easily with Measures are expanded which are aimed at improving the mechanical filtering and / or regeneration of the Ab Aim gas particle filter. The printing below Fonts and designs form an integrating Be part of this document.

In the document EP-A1-00 72 059 an exhaust gas particle filter is arranged in the high-pressure part of the exhaust gas system in front of the pressure wave machine to limit the gas particle emission in an internal combustion engine charged with pressure wave machines. Through increased self-fuel supply and / or short-term closing of the charge air flap or the recirculation flap and / or short-term opening of the exhaust gas bypass valve, the exhaust gas reaches that flame temperature which makes it possible for the soot particles deposited in the exhaust gas particle filter to ignite and burn, in such a way that the exhaust gas particle filter automatically regenerates. This exhaust gas particle filter can be laid out according to one of the basic concepts I-IV according to FIG. 1.

In a further publication EP-A2-01 52 870, exhaust gas recirculation is generally aimed at minimizing exhaust emission; at the same time, the regeneration of the exhaust particle filter can be designed quasi-continuously with this measure. The exhaust gas recirculation increases the exhaust gas temperature in the entire partial load range: the ignition of the filtered exhaust gas particles starts at a temperature of 500-550 ° C, provided that an oxygen concentration of at least 3% -6% is available. The exhaust gas particle filter provided in this circuit can easily be designed according to a basic concept I-IV, as described above under FIG. 1.

In the publication CH-PS-6 63 253 there is an exhaust gas particle filter for internal combustion engines has been proposed in several floods connected in parallel is divided. A control flap, which can be controlled depending on the engine load, the Mo exhaust gases to one or more of these floods. During the entire company is therefore a complete exhaust gas particle file guaranteed. A controlled application of the flu through the control flap enables complete burning of the exhaust gas particles captured there.

The filters placed in the various floods can be designed according to one of the basic concepts I-IV, as described under FIG. 1.

In the document EP-A1-01 83 066 the proposed here exhaust particle filter has a recess in its core, which ensures that the inflow of exhaust gases to Zen tralfilterteil can be channeled. In addition to the central filter part an external filter part is provided: the one facing the other this, due to larger filter porosity and smaller ones Mass, a smaller degree of separation, so that the exhaust gases choose the path of least resistance in the initial phase will flow through the central filter section. His big Greater filter porosity and the smaller mass mean that the Temperature reduction of the exhaust gases flowing through remains small, so that, even here, a downstream loader speaks quickly will be able to. Because the soot particles are separated for the time being takes place primarily in the central filter section, despite its lower degree of separation, quickly a strong one Deposition result, causing resistance after the Acceleration phase that of the surrounding outside filter part will adjust. This external filter part offers then the capacity over a longer period without regeneration tion to ensure the filtering of the soot particles.

To start the regeneration of the filter alternatively or possible at the same time as the other recognized concepts, the  Exhaust particle filter body with a heatable element to be pieces, with which periodically or continuously the ignition of the filtered soot is initiated. This rain ration turns out to be effective in that one Foam filter the fire started once through the whole Filters can spread. The installation of this exhaust gas particle Filter body is designed so that the filter can set a diffuser-like outflow.

To optimize the regeneration of the filter, one or more filter elements can be provided in the cross section of a housing through which exhaust gases flow. If a single filter element is preferably selected, its front filter zone in the flow direction is coated with a catalyst to reduce the ignition temperature of the soot particles to approximately 360 ° C. The remaining filter zone, which is connected downstream of the front filter zone, is coated with a catalyst for post-oxidation of the gaseous pollutants. This ensures continuous regeneration at the lowest Zündtem temperature, at the same time it also ensures that the burnup, especially with a foam filter because of its open-pore structure, can spread freely through the whole Fil terelement in such a way that the downstream in the front filter zone Filter zone soot particles excreted also for combustion. The possibilities described above for the respective design of the filtering can easily be designed according to one of the basic concepts I-IV, as described under FIG. 1.

In general, it can be said that the basic concept I according to FIG. 1 will not be used for an intentional and necessary choice of a single filter element serving for separation.

The filter concept is for all variants and configurations not on an internal combustion engine charged with a supercharger  limited. It can be used in both petrol engines and Diesel engines with or without supercharging are used.

Claims (7)

1. A method for filtering out soot particles from the combustion in an internal combustion engine, these soot particles having a different electrical polarity, characterized in that the soot particles ( 1 ) are charged with the same polarity in a first action section by means ( 5, 6 ), then the soot particles are filtered out in at least one filter ( 3 ) with opposite polarity. 2. Process for filtering out soot particles from the combustion in an internal combustion engine, these soot particles having a different polarity, characterized in that the soot particles ( 1 ) flow through a filtering path formed by filters ( 2, 3, 4 ) after the internal combustion engine, in which zones ( 2, 3 ) a predetermined opposite electrical polarity prevails, and / or an intermittent opposite electrical polarity ( 4 a) is provided. 3. Apparatus for carrying out the method according to claims 1 and 2, characterized in that the means ( 5, 6 ) in the first action section are electrically conductive, the filter serving for separation ( 2, 3, 4 ) at least superficially electrically isolated are. 4. Apparatus for performing the method according to claims 1 and 2, characterized in that the fil ter ( 2, 3, 4, 5 ) are foam ceramic filters. 5. The device according to claim 4, characterized in that the foam filter ( 2, 3, 4, 5 ) have an open-pore structure. 6. The device according to claim 4, characterized in that the porosity of the foam filter ( 2, 3, 4, 5 ) carries 50 ppi. 7. Apparatus for carrying out the method according to claims 1 or 2 and 3, characterized in that the filters ( 2, 3, 4 ) serving to separate the soot particles are placed in a housing through which exhaust gas flows, where these filters are physically opposite the housing are insulated.