EP1451452B1 - Method and system for regenerating diesel particle filters - Google Patents

Description

State of the art

The present invention relates to a method and a Arrangement for the regeneration of diesel particulate filters after the preamble of claim 1 and the preamble of claim 8.

Particulate limit values of the Euro IV emission standard (0.05 g / km) may be used of heavy vehicles only with diesel particulate filters (DPF). Cut DPF systems typically 90-95% of the emitted particles. The As a result, particles stored in the filter increase the level Exhaust back pressure, which is why the diesel particulate filter in Intervals between 200-500 km must be regenerated. The Regeneration takes place by burning (oxidation) of the embedded particles. For this, the particles must typically heated to about 600 ° C. Appropriately, the heating of the particles takes place via convective heat input through the exhaust gas flow. The Temperature of the exhaust stream consumption optimized However, diesel engines (TDI, CDI) only exceed a few Operating points 300 ° C. The exhaust gas must therefore during the regeneration be reheated. This can be electric or with Help a burner done. As the residual oxygen content of the exhaust gas varies between 3 and 18%, is the use a diesel burner in the direct exhaust flow without additional Fresh air blower problematic, because not everyone Time enough oxygen for the combustion of the fuel is available.

From DE 197 48 561 is known, the ignition temperature the particles by adding the diesel fuel with Iron or cerium compounds to lower to about 300 ° C. It should be noted, however, that such additives are inorganic Leave ashes in the particle filter, which too a continuous increase in the through the diesel particulate filter generated counterpressure, causing premature Replacement of the filter may be necessary.

From DE 197 48 561 is also known, in particular electrically use heated diesel particulate filter. at Full flow systems is used in the regeneration of the entire exhaust stream passed through the diesel particulate filter and electrically heated. Such full-flow systems do without switchable flaps and are relatively inexpensive and compact produced. A disadvantage of such solutions, however, is that the complete exhaust gas mass flow over the ignition temperature of the diesel soot needs to be heated. As an an example be of a stroke volume of 2.5 liters, an engine speed of 2000 rpm and a boost pressure of 1.4 bar. This results in an exhaust gas flow of 250 kg / h. For a warming this typically obtained mass flow around 400K the minimum heat output is neglected Losses 33 kW. As with a 12 volt electrical system a maximum of 2-2.5 kW electric heating power can be realized in usually partial flow solutions preferred.

From JP 2000 13 67 13 is an exhaust aftertreatment device with two parallel heated filters known.

Another possible partial flow system is shown in FIG. You can see two parallel connected Diesel Particulate Filter 1, 2. In the exhaust gas supply line 3 of this Diesel particulate filter is a flap 4 introduced by means of the exhaust gas in the supply line 3 optionally via a supply line 3a in the diesel particulate filter 1, or via a supply line 3b in the diesel particulate filter 2 is inserted. The Diesel particulate filters 1, 2 are each equipped with electric heaters 1a, 2a formed. About a fan 5 is fresh air into the supply lines 3a, 3b can be introduced. From the diesel particulate filters 1, 2 exiting exhaust gas is discharged via discharge lines 6a and 6b, which open into a conduit 6, dissipated. at Such an arrangement will be the diesel particulate filters expediently individually undergone regeneration. For example, during the regeneration of the diesel particulate filter 1 by means of the flap mechanism 4 of the majority (For example, 90%) of the exhaust gas flow through the diesel particulate filter 2 headed. The remaining residual current becomes electric, or also fossil, heated and heated the diesel particulate filter. 1 and the diesel soot stored therein. If the residual oxygen content the exhaust stream is too low, can by the Blower 5 fresh air to be supplied. The maximum pressure build-up of the blower, typically up to 150 hPa however, its use on relatively small overpressures in the exhaust tract. The size of the partial flow can be adjusted or be dimensioned that the diesel particulate filter 1 in short time with the maximum realizable electrical Heating power brought about the ignition temperature of the diesel soot becomes. After the end of the regeneration of the diesel particulate filter 1, the diesel particulate filter 2 can then be regenerated become. It is also possible between regeneration provide the individual diesel particulate filter phases, in which both diesel particulate filter according to a Normal operation are applied uniformly with exhaust gas. The aim of the invention is a regeneration of diesel particulate filters in a simple and inexpensive way perform. This goal is achieved through a process with the features of claim 1 and an arrangement with the features of claim 7.

The measure according to the invention, the regeneration in at least one partially closed, hereinafter referred to as circulating air circulation perform designated circulation circuit, allows regeneration essentially independent of the size of the exhaust stream, the residual oxygen content and the pressure level. Characterized in that the exhaust gas by means of the circulating air circulation several times through the diesel particulate filter is carried out, the heating time is greatly shortened, thereby Energy can be saved.

It is envisaged to mix ambient air with the circulating air circuit. By the inventively realizable small Mass flow in Umluftkreislauf and such a limited Frischluftzumessung can despite low electrical Heating power high temperatures in the diesel particulate filter be realized very quickly. This makes it possible the diesel particulate filter without additive of a diesel fuel to regenerate effectively, so that too Ash formation in the diesel particulate filter due to inorganic additive residues can be avoided. The controlled Fresh air or oxygen addition to the circulating air flow In addition to the size of the circulating air flow, which by a Blower speed is adjustable, and the electric heating power another parameter for the temperature control of the Diesel particulate filter during the "Durchzündens" of soot By an appropriate regulation of these parameters can local and temporal temperature peaks in the diesel particulate filter be avoided, thereby increasing its life expectancy extended.

Advantageous embodiment of the method according to the invention or the device according to the invention are the subject of Dependent claims.

Conveniently, it is possible to parallel to the introduction of fresh air in the substantially closed circuit to provide the purging of circulating air from the circuit.

According to a preferred embodiment of the invention Method is a detection of the as part of the regeneration of the least produced a diesel particulate filter Rußabbrandes about a difference oxygen measurement at the Inlet or outlet side of the diesel particulate filter. This measuring method proves to be very reliable in practice. In the context of the inventive arrangement are as appropriate means, for example, in front and behind The diesel particulate filter positionable oxygen sensors intended.

It proves to be advantageous if the quantity supplied Fresh air corresponds to the amount of blown circulating air.

According to a particularly preferred embodiment of the invention Method or the inventive arrangement is acting on a two parallel diesel particulate filter Exhaust flow diverted so that a first Diesel particulate filter substantially with the complete Exhaust gas flow is applied and simultaneously with respect to the second diesel particulate filter a closed air circulation is produced. As a substantially complete exhaust gas stream in particular shares between 80 and 100% of the total exhaust gas flow.

Figur 1, wie bereits erwähnt, ein Blockschaltbild zur Erläuterung einer elektrischen Regeneration von Dieselpartikelfiltern,

Figur 2 ein Blockschaltbild einer bevorzugten Ausführungsform einer erfindungsgemäßen Anordnung zur Regeneration von zwei Dieselpartikelfiltern,

Figur 3 das Blockschaltbild gemäß Figur 2, wobei zur Darstellung einer ersten Phase einer bevorzugten Ausführungsform des erfindungsgemäßen Regenerationsverfahrens die hierbei auftretenden Abgas- bzw. Gasströme dargestellt sind, und

Figur 4 das Blockschaltbild gemäß Figur 2, wobei zur Darstellung einer zweiten Phase einer bevorzugten Ausführungsform des erfindungsgemäßen Regenerationsverfahrens die hierbei auftretenden Abgas- bzw. Gasströme dargestellt sind.

The invention will now be explained with reference to the accompanying drawings. In this shows

FIG. 1, as already mentioned, is a block diagram for explaining an electrical regeneration of diesel particulate filters,

FIG. 2 shows a block diagram of a preferred embodiment of an arrangement according to the invention for the regeneration of two diesel particulate filters,

FIG. 3 shows the block diagram according to FIG. 2, wherein the exhaust gas or gas streams occurring in this case are shown to represent a first phase of a preferred embodiment of the regeneration method according to the invention, and

FIG. 4 shows the block diagram according to FIG. 2, wherein the exhaust gas or gas streams occurring in this case are shown to represent a second phase of a preferred embodiment of the regeneration method according to the invention.

In Figure 2 it can be seen that the illustrated preferred Embodiment of the inventive arrangement analogous to the arrangement already described according to the prior Technique two diesel particulate filters 21, 22 with each associated electrical heating 21a, 22a. The Diesel particulate filters 21, 22 are via an exhaust gas supply line 23 exhaust gas fed. The line 23 is via a flap 24th with a first exhaust gas feed line 23a, which with the Diesel particulate filter 21, and one of a second Exhaust pipe 23 b, which with the diesel particle 22 connected, can be connected. By appropriate Position of the flap 24, it is possible by the Exhaust gas inlet 23 flowing exhaust gas flow in any way to distribute to the diesel particulate filters 21 and 22, respectively.

It can also be seen that discharge lines 26a and 26b, respectively, which from the respective diesel particulate filters lead out, apply a flap 27. The flap 27 can guarantee, in a first position, that the Discharge lines 26a, 26b in a common discharge line 26 lead. In a second position, the flap 27 adjustable so that the lines 26a or 26b flowing gas (exhaust gas) via a line 30 a Flap 28, in a line 32, a fan 25 and the Flap 24 back into the respective diesel particulate filter 21, 22 can be performed.

About the flap 28 is by means of a feed line 29th Fresh air can be introduced into the exhaust gas flow.

By appropriate adjustment of the flaps 24, 27 and 28 it is possible in a simple manner, the gas flows to To lead realization of the method according to the invention. This will be described below with reference to FIGS. 3 and 4 explained.

In FIG. 3, the first phase of an example is shown by way of example Regeneration of the lower diesel particulate filter 22 shown. The flaps 24 and 27 are set that the entire incoming via the supply line 23 Exhaust gas flow to the upper diesel particulate filter 21, and of this is passed into the discharge line 6. This stream is illustrated by the dashed arrows. These Adjustment of the flaps 24 and 27, and an additional closed position of the flap 28 causes simultaneously with respect to the lower DPF 22 a closed line system is generated. By Switching on the fan 25, it is thus possible, the Diesel particulate filter 22 in recirculation mode with exhaust gas too apply. The fan 25 must be only a relative promote small mass flow, namely the mass flow, the at the time of the mentioned setting of the flaps 24, 27th and 28 within the diesel particulate filter 22 and the closed conduit system (lines 23b, 26b, 30, 32nd and 31). For typical dimensions of Regeneration systems can be assumed that the maximum to be promoted mass flow here at about 20 kg / h, whereby the pressure drop over the filled with soot Diesel particulate filter 22 is relatively small, typically maximum 50 hPa.

By switching on the electric heater 22a of Diesel particulate filter 22, it is now possible that the Diesel particulate filter in recirculation mode flowing exhaust gas to heat effectively.

The electric heater 22a, which expediently as electric heating coil is formed, heats the Diesel particulate filter 22 via radiation injection as well convective via the circulating air flow. There is no air at first exits the system, the heating takes place, as mentioned, very fast.

The flow paths for realizing the circulating air mode are in Figure 3 illustrated by the solid arrows.

When reaching a maximum for the fan Temperature, eg. 300 ° C, opens the flap 28 and mixes the recirculation circuit controlled fresh air. By corresponding opening of the flap 27 is simultaneously Recirculated air from the closed circuit into the exhaust tract (Discharge line 6) blown out, expediently a Balance between sucked fresh air and ejected circulating air is adjusted. The position of the Flap 28 is in this case controlled such that the maximum permissible temperature for the fan 25 at no time is exceeded. This state is shown in FIG. 4 shown, wherein the fresh air flow and the Ausblasstrom illustrated by dotted arrows.

The diesel particulate filter 22 becomes in this mode of operation continue until reaching the ignition temperature of the warmed up soot. The "Durchzünden" of the Diesel soot can be measured by measuring the oxygen consumption due to oxidation within the diesel particulate filter 22 are performed. For this it turns out to be expedient, input side and output side of the Diesel particulate filter 22 lambda sensors 40, 41 provided. It is also possible via appropriate input and output pressure measurements the pressure drop within of the diesel particulate filter. The finding of "Durchzündens" of the diesel soot is finally with a Output-side temperature measurement possible. A corresponding temperature measuring device, by means of a the steeper characterizing steeper Temperature increase is detected, is in Figure 3 schematically designated 42.

The temperature of the diesel particulate filter 22 can by Control of the heating power of the electric heater 22a or the delivery volume of the blower 25 controlled become. Furthermore, over the controlled Frischluftzumessung (by controlling the flap 28) of the Oxygen content of the circulating air and thus the speed the Rußabbrandes be controlled. With these measures can effectively overheat and damage the Diesel particulate filter 22 by the burning of the Diesel soot released combustion enthalpy prevented become.

By appropriately switching the flaps 24 and 27 it is then possible, fed from the supply line 23 Exhaust gas flow substantially completely over the Diesel particulate filter 22 dissipate and a closed Recirculation circuit with respect to the particulate filter 21 to produce. The switching of the flaps 24 and 27 can immediately after completion of the regeneration procedure for the diesel particulate filter 22. It is too possible, after the regeneration of the diesel particulate filter 22nd initially both diesel particulate filter with exhaust gas too apply and the appropriate regeneration of the Diesel particulate filter 21 only at a later date initiate. Of course it is possible for the Diesel particulate filter 21 analogous to the diesel particulate filter 22 Lambda sensors and / or a temperature measuring device to provide, which, however, in Figure 3 for the sake of Clarity are not shown in detail.

The advantages resulting according to the invention are finally summarized as follows:

The regeneration of the diesel particulate filter takes place in at least partially closed recirculation independently from the height of the exhaust stream and from Residual oxygen content and pressure level of the exhaust gas stream. One used blower only has the back pressure or the Overcome pressure drop of a diesel particulate filter. Further The heating time for a diesel particulate filter can be strong be shortened, whereby energy is saved. By the small mass flow in the circulating air circuit as well as the limited Frischluftzumessung can despite low electrical Heating power high temperatures in the diesel particulate filter be achieved. This allows the diesel particulate filter also without additive of the diesel fuel be regenerated.

The controlled addition of fresh air or oxygen to the Circulating air flow, in addition to the size of the circulating air flow, which is adjustable by the fan speed, and the electric heating power another actuator for Temperature control of the diesel particulate filter during the "Durchzündens" of soot dar. This local and temporal temperature peaks in a diesel particulate filter be avoided, thereby increasing its life expectancy significantly extended.

Claims (10)

1. Method for regenerating at least one diesel particulate filter (21; 22), in which exhaust gas is introduced into the at least one diesel particulate filter (21; 22) via a feed line (23, 23a, 23b) and is discharged from it via a discharge line (26, 26a, 26b), the exhaust gas which flows through the at least one diesel particulate filter (21; 22) being heated, characterized by the creation of a closable recirculated-air circuit, via which exhaust gas which emerges from the at least one diesel particulate filter (21; 22) can be reintroduced into it, it being possible for ambient air to be added to the recirculated-air circuit.
2. Method according to Claim 1, characterized in that air which circulates within the recirculated-air circuit can be blown out of the circuit in a regulated or controlled way.
3. Method according to Claim 2, characterized in that the quantity of fresh air supplied corresponds to the quantity of recirculated air which is blown out.
4. Method according to one of the preceding claims, characterized in that particulate burn-off which is produced as part of the regeneration of the at least one diesel particulate filter (21; 22) is carried out via differential oxygen measurement at the inlet and outlet sides of the at least one diesel particulate filter (21; 22).
5. Method according to one of the preceding claims, characterized by at least two diesel particulate filters (21; 22) connected in parallel, with an exhaust-gas stream which acts on the two diesel particulate filters optionally being diverted in such a manner that the substantially complete exhaust-gas stream is passed via the first diesel particulate filter (21), and a closed recirculated-air circuit is provided with respect to this second diesel particulate filter (22).
6. Method according to Claim 5, characterized in that the diversion of the exhaust-gas streams is effected by flaps (24, 27) which are introduced into the feed line or discharge line of the exhaust-gas stream.
7. Arrangement for regenerating at least one diesel particulate filter (21; 22), which is in communication with a feed line (23, 23a; 23, 23b) for supplying exhaust gas and a discharge line (26a, 26; 26, 26b, 26) for discharging exhaust gas, means (21a; 21b) for heating the exhaust gas flowing through at least one diesel particulate filter being provided, characterized by means (24, 23a, 26a, 27, 30, 28, 32, 25, 31; 24, 23b, 26b, 27, 30, 28, 32, 25, 31) for creating a closable recirculated-air circuit, via which exhaust gas which emerges from the at least one diesel particulate filter (21; 22) can be reintroduced into it, means (28, 29) for adding ambient air to the recirculated-air circuit being provided.
8. Arrangement according to Claim 7, characterized by means (27) for blowing exhaust gas out of the recirculated-air circuit in a regulated or controlled way.
9. Arrangement according to Claim 7 or 8, characterized by means (40, 41) for differential oxygen measurement at the inlet and outlet sides of the at least one diesel particulate filter (21; 22).
10. Arrangement according to one of Claims 7 to 9, in which two diesel particulate filters (21, 22) that are connected in parallel can be acted on by an exhaust-gas stream in such a manner that substantially the entire exhaust-gas stream can be passed via a first diesel particulate filter, and a closed recirculated-air circuit can be provided with respect to the second diesel particulate filter, flaps (24, 27) which can be introduced into the feed line and/or discharge line being provided as means for correspondingly diverting the exhaust-gas streams.

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