Method to purify the exhaust gas of Diesel engines

p0001The invention is based according to the preamble of claim 1 of EP-A 0 405 310th

p0002From this document a method for regenerating a soot filter in the exhaust system of a diesel engine is known. Here, an oxidation catalyst of the soot filter is upstream arranged adjacent, the conversion temperature is increased is controlled as a function of soot loading of the soot filter by upstream of the catalyst additionally injected fuel to the riser below the conversion rate to at relatively low exhaust gas temperatures, the ignition temperature of diesel soot of approx 600 safely reach ° C.

p0003As is known, the diesel soot is removed as it passes through a stop acting in the usual way catalyst for a significant portion of the accumulated, volatile HC connections, so that a relatively dry, despite additives heavily flammable soot reaches the filter for the deposition. In the known method is formed, excess HC-shares are at heightened by the fuel additive conversion supplied to the deposited soot in the filter and thus indeed influenced the ignition temperature of the soot low, but not in a desirable extent.

p0004The invention is therefore based on the object to improve the method described in the preamble of claim 1 with the means for this purpose specified such that substantially always to burn off the soot retained in the filter its lowest ignition temperature is given.

p0005This object is achieved with the patent claim 1 in such a manner that the fuel to a relation to the respective usual, maximum catalyst conversion temperature around 30 - is controlled 60% lower temperature in an amount / added controlled so that the soot filter a Rußbefeuchtung is achieved.

p0006The advantage of the invention is further seen in addition to the significant reduction of the ignition temperature in conjunction with a safe Rußabbrennen in the free placement of the respective catalyst between soot and diesel engine, as the Rußbefeuchtung can be dispensed with an immediately adjacent heating of the soot filter by a particular catalyst advantageous.

p0007To achieve an effective Rußbefeuchtung starting in embodiment of the invention with the fuel addition into the exhaust duct below the light-off temperature of the particular catalyst, as a result the proportion of the added fuel to Rußbefeuchtung with or without the soot filter upstream catalyst is relatively high.

p0008With the invention it is possible advantageously to add the fuel into the soot filter and / or upstream of the soot filter in the exhaust system, wherein upstream in the latter case, the fuel or may be added downstream of the respective catalyst.

p0009Further, the invention provides the additional benefit of the respective catalytic converter assembly in Abgasfühtung freely selectable map of fuel addition, the fuel is injected by means of a separate device and / or added via an engine-side injector. The latter can be done by late position of the respective injection timing or by Nachspritzen of diesel fuel during or after combustion, in particular with a common rail system. Finally, the cycles of the Rußbefeuchtung a function of parameters of the soot filter, the exhaust gas and additional engine parameters may be controlled characteristic field, whereby with optimum Rußabbrennen a minimum of fuel consumption is achieved.

p0010The invention is described below:

p0011In a method for cleanup of diesel emissions flow through a flue exhaust an oxidation catalyst and / or an SCR or DeNOx catalyst and a particulate filter. Next, a liquid fuel is the HC enrichment of the soot in the soot filter in the exhaust system added temperature controlled. As is well known, the diesel soot, volatile HC-compounds are removed during passage through a stop acting in the usual way catalyst due to the conversion, it is attempted with the controlled addition of fuel according to the generic EP-A 0 405 310 the soot in the filter downstream of the respective catalyst gaseous HC supplying compounds for lowering the soot ignition temperature, the upstream of the soot filter catalyst closely adjacent the respective design contributes significantly with its conversion to heat Rußentzündung.

p0012For safe ignition of the deposited in the particulate filter soot with simultaneous decoupling of the adverse structural combination of respective catalyst and soot filter, the method of exhaust gas purification according to the invention improved in a way that the fuel to a compared to the respective conventional maximum permissible catalyst conversion temperature around 30 - 60% lower temperature controlled in such a quantity / is added controlled to a Rußbefeuchtung is obtained in the soot filter.

p0013To achieve an effective Rußbefeuchtung after a predetermined controlled / regulated initiated Rußentründung for burning the soot filter with a minimum fuel consumption of the start of the fuel-addition takes place in the exhaust system significantly below the light-off temperature of each catalyst; as the upper limit of addition may be selected as the light-off temperature plus ≈ 200 ° C.

p0014The invention makes it possible in a structurally advantageous manner using a known separate device for injecting the fuel to enter it directly into the soot filter and / or upstream closely adjacent to the exhaust system. Since with this procedure, the added fuel by any of the foreseeable, individually or can be arranged in a combination of catalysts to be pushed through, hereby arises advantageously a minimum consumption of additional fuel, which can be entrained fuel in a diesel engine preferably.

p0015To avoid an additional device for fuel-injecting the additional fuel may be added by means of a motor-side injector, whereby in this case to achieve a Rußbefeuchtung at upstream of the soot filter arranged catalyst to obtain a sufficient amount of fuel in particular working with high pressures Common Rail system offers. The preferably injected into the exhaust fuel is quantitatively chosen so that a humidification by fuel condensation is achieved in the soot filter.

p0016For the case of motor-side fuel charging is suitable in a combination of catalyst and soot filter for lowering fuel consumption according to the invention to provide the respective catalyst downstream of the soot filter. This gives the advantage that erupted soot particles are converted in soot when burned by a particular fuel overdose produced HC connections and through the filter. The soot filter downstream the catalyst, an oxidation catalyst or to reduce NO_xhis Shares in the exhaust gas serving SCR and DeNOx catalyst.

p0017Advantageously, the cycles of the Rußbefeuchtung and, associated with the map-controlled Rußabbrennen, wherein can serve as function-dependent parameter distance dependent loading intervals and / or the exhaust gas temperature and / or the filter counter-pressure and / or other engine parameters.

p0018The inventive method is particularly advantageous to operate with an oxidation catalyst and / or an SCR catalytic converter with integrated oxidation catalyst upstream of the soot filter in a close-coupled arrangement in a flue, in which the Rußbefeuchtungs fuel by means of a separate apparatus downstream of the respective catalyst will close prior to or injected into the soot filter. The close arrangement of the respective catalyst yields a high conversion rate with advantageous exhaust-gas temperature increase of the humidified upstream soot filter, with which an additive based regeneration of the soot filter system is also achieved in the lower load area in an advantageous manner.

p0019With the invention targeted Rußkonditionierung can be the regeneration area of ​​additive filter systems on the entire engine operating range advantageously extend with the further advantage of a significant reduction of energy consumption for the regeneration towards filtering systems with external regeneration energy.

p0020Besides, in the arrangement of a known a high thermal capacity with lowered exhaust temperatures having a soot filter downstream SCR and DeNOx catalyst a better adaptation of the exhaust temperature curve before this catalyst to the scope of a conventional Pt / Al₂O₃-Denox Catalyst are achieved.