Process for regenerating soot filters of diesel engines.

p0001The invention relates to a process for the regeneration of soot filters in diesel engines and related internal combustion engines, such as the elsbett.

p0002According to the current state of the art of the exhaust gases of diesel engines are used for cleaning soot filter, which can be regenerated or burned off only at temperatures above 500 ° C. When using a catalytically active soot filter this value can be lowered to about 400 ° C. The ignition temperature lies mostly on the relatively low exhaust temperatures in diesel engines. The combustion of soot can therefore only take place if such increases by increasing occupancy of the filter with soot the exhaust gas temperature. At the same time, the pressure increases before the catalytic converter, thereby increasing the efficiency of the motor decreases. Under certain operating conditions, the filter can become clogged, without the ignition temperature is reached. Controlled regeneration of the filter is then impossible. Moreover, such large amounts of carbon black are often accumulated on the filter, that upon combustion excess temperatures are reached, which can damage the filter.

p0003The induction and maintenance of a controlled Abbrennvorganges the soot particles in the filter can be achieved by introduction of additives into the exhaust stream.

p0004Thus, DE-OS 33 25 391 and DE-PS are described in DE-OS 31 11 228, describes 38 21 143 methods in which copper (I) chloride alone or in conjunction with ammonium nitrite or acetylacetone the exhaust stream can be admixed. However, these methods have the disadvantage that they do not sufficiently lower the ignition temperature and the filter during its operation is not regenerable. In addition, lead copper deposits on the filter to reduce the permeability and thus the loss of engine power. Furthermore, a wide supply of the appropriate additive components is problematic and the use of heavy metal-containing components in any case not environmentally safe.

p0005The invention opens up the possibility to avoid the disadvantages of the known method and a controlled environment-friendly regeneration of the diesel filter during its operation at exhaust gas temperatures to carry out below 100 ° C.

p0006The invention opens up a relatively simple and safe way to solve this problem by a method described in the patent claims 1 - is indicated. 9

p0007according to claim 1, a soot filter the upstream oxidation catalyst be used. This may be embodied as a separate component or else be arranged as a coating on a front portion of a soot filter. If the particulate filter coated with a catalyst zündtemperatursenkenden, one will choose the separately arranged oxidation catalyst or ensure that the soot filter on the front portion bears no Zündkatalysatorbeschichtung. The further possibility of arranging the oxidation catalyst on the entire soot filter is only useful in soot filters without Zündkatalysatorausrüstung, but has the disadvantage that the oxidation catalyst reduces the permeability of the soot filter.

p0008It is the actual diesel filter an ordinary oxidation catalyst as used for example in gasoline engines for use, upstream. This catalyst is advantageously reduced to about half or less of the usual length, z. B. to about 1/4, to achieve a more rapid heating in the regeneration process. Another possibility consists in the filter or its input portion, that is to coat a front portion of the diesel filter, z. B. about 1/4 of the total length with an oxidation catalyst, z. B. based on noble metals. In the flow section upstream of the catalyst, the possibility is provided for a liquid, preferably feeding in vaporized form, as a fuel to inject into the exhaust flow respectively. The fuel is converted at the oxidation catalyst and heated both the oxidation catalyst and the diesel filter. The quantity of fuel is so regulate that an adiabatic final temperature is reached which is sufficient for ignition of the carbon black and is typically at 600 ° C.

p0009In the proposed method can via a control system, the addition of the fuel to be matched to the gas flow of the engine, so that the required ignition temperature is reached without the oxidation catalyst and / or particulate filters are thermally overloaded.

p0010A pressure gauge is the fuel metering at a predetermined control value of the dynamic pressure in operation. A temperature sensor will switch off the metering of the fuel when it reaches the ignition temperature of the soot. Another stop option is to use the undershooting of a second back pressure control value as a control signal.

p0011The ignition temperatures for the candidate fuels are in use, for example, conventional oxidation catalysts for automobile emission between 100 and 200 ° C. The lowest rates are in ethanol (70 ° C) and methanol (20 ° C), but methanol has the disadvantage of lower heat of combustion.

p0012Gasoline with an ignition temperature 150-200 ° C on the other hand has the advantage of wide availability.

p0013For basic testing of the method first the model apparatus shown in Figure 1 was used. When pumps 1, 2 are two Leister blower, with which a gas stream at temperatures between 20 ° C and 500 ° C can be adjusted served. Instead of the engine exhaust was a model exhaust gas (10 vol.% O₂, 90 vol.% N₂) worked.

p0014With two blowers, a GHSV of max. 40,000 hr⁻¹ achieved. The fuel ethanol was evaporated before entering into the exhaust stream. By turbulence-generating baffles 3 between metering point 4 and the oxidation catalyst 5, a better distribution of the fuel and thus a uniform loading of the catalyst was obtained with the fuel vapor. As oxidation catalyst is a platinum / rhodium catalyst was used in which the noble metals were applied to a support material of the total composition 82 wt .-% γ-Al₂O₃, 15 wt .-% CeO₂, 3 wt .-% ZrO₂. The noble metal content was 1.4 g / l catalyst volume at a mass ratio of Pt: Rh = 5: 1. The catalytic coating was applied to a cordierite ceramic honeycomb body having a cell density of 62 cells / cm. In diesel soot filter 6, a commercially available cordierite monolith filter with alternately stoppered at opposite points channels (so-called wall-flow cylindrical, length:. 15.2 cm, Diameter: 14.4 cm, cell density: 31 cells / cm²), were the temperatures at the in the drawing noted measured points; still was determined in the exhaust CO₂ and CH.

p0015exclusively unberußte filters were used as a filter in the model experiment and the experiment limited to temperature detection in the filter. This is necessary here because not enough gas can be forced through the filter when using rußbelegten filters due to the high pressure drop with the blowers used. Preliminary tests ensured that diesel soot always burns away from the filter at temperatures of 600 ° C.

p0016Starting from an exhaust gas temperature of 100 ° C upstream of the catalyst were measured at a space velocity of 10000 hr⁻¹ and a fuel supply of 10 ml of ethanol / min. after about 2 minutes from 600 -. 700 ° C obtained at the filter input. This period is essentially determined by the heat capacity of the catalyst and filter. In this procedure, approximately 20 ml of ethanol were used, the proportion of CO₂ in the exhaust gas was 2.0 - 2.5 Vol.%.

p0017The conversion of fuel was completely within the measuring accuracy. The final temperatures measured corresponded to approximately the adiabatic combustion temperature of the predetermined fuel / gas mixture.

p0018A practical closer experiment was carried out as follows:

p0019The blower 1, 2 (see Fig .. 1) were replaced by a Gasdosierteil, can be dosed with the nitrogen and oxygen. By means of an electric heater, the gas mixture may be preheated before the fuel injection is carried out. This so modified plant sooted wall-flow filters to the geometry described above were the dynamometer regenerated (the filters were not impregnated with catalytically active components). The length of the upstream ignition catalyst was 5 cm. Here is a platinum / palladium catalyst (1,75 g / l catalyst volume, weight ratio of Pt: total precious metal loading Pd = 3: 1) as an oxidation catalyst on a finely divided support material of the total composition of 10 wt .-% CeO₂, 60 percent. -% TiO₂ (= SO₂-resistant), 30 wt .-% WO₃ used.

p0020The regeneration of the filter was carried out under the following conditions: Gas flow rate: 20 m³ / h (GHSV = 10,000 hr⁻¹) Temperature before catalyst: 150 ° C Fuel supply: 10 ml of ethanol / min Oxygen content of the gas: 10% by volume.

p0021Under these conditions, temperatures were achieved of about 650 ° C after the oxidation catalyst. The burning of the soot, the temperature rises in the filter to continue. The reached the filter maximum temperatures are highly dependent on the amount of the deposited soot.

p0022In these studies, the fuel supply at a temperature of 800 ° C in the filter center is exceeded has been interrupted. The maximum temperatures were then 850-1000 ° C.

p0023Under these conditions, the filters were completely regenerated. The entire procedure lasted over a period of about 5 min. With approximately 50 ml of fuel consumed. Higher gas flow rates and higher gas temperatures have a shorter recovery time and a lower fuel consumption.

p0024In Figure 2, a practical control system for tuning the amount of fuel is shown on the gas flow of the engine.

p0025A flowmeter 7 measures the volume flow, which is sucked in by the engine eighth For this purpose, commercially available flow meter can be used for. B. be used for similar purposes to injection gasoline engines for controlling the injection pump. In most cases these are hot wire anemometer or mechanical devices with a throttle valve, eventually issuing a voltage as a function of the volume flow.

p0026Using the thus obtained value for the volume flow of a metering pump is controlled such that the quantity of fuel with the desired proportionality constant increases linearly with the air flow, so that the desired adiabatic final temperature is always achieved. As metering pump 9 for the liquid fuel are, for example small, about electromagnets operated piston pumps that can be produced cheaply. The delivered volume is determined by the frequency of the pulses to the electromagnet or through a displacement of the piston stroke. In the former case, the control unit has to transform the signal of the flowmeter 7 into a clock signal having an appropriate frequency.

p0027The smoothing of the liquid pulse can be carried out via a damping element in the outlet line of the pump.

p0028A pressure gauge 10 is the mechanism in a given pressure range (as measured before the catalytic converter) in operation while a temperature sensor 11 when it reaches the ignition temperature, the metering of the fuel off.

p0029The described regeneration method has over conventional methods following advantages:<ul><li>1. The diesel filter can be ignited at any engine exhaust gas temperature;</li><li>2. The pressure in the exhaust passage of the engine can be kept small, whereby the motor efficiency increases;</li><li>3. It may Diesel filter without and with catalytically active coatings, such as silver vanadate or doped vanadium oxide used;</li><li>4. Part of the pollutants (CO and hydrocarbons) are implemented already at the oxidation catalyst;</li><li>5. The aging of the oxidation catalyst remains low, since it is exposed, with proper adjustment of the fuel dosing to extremely high temperatures. Excessive temperatures in the soot filter can also be avoided, as can be regenerated in time before collection to large quantities of soot on the filter. The result is an increased durability of the entire exhaust gas purification system.</li></ul>