Method to purify the exhaust gas of Diesel engines

0001The invention is according to the preamble of claim 1 of EP-A 0405310 from.

0002From this document is a method for regenerating a soot filter in the Exhaust system of a diesel engine is known. Here is the soot filter upstream a assigned adjacent Oxydatlons catalyst whose conversion temperature in Dependence of soot load of the particulate filter is increased controlled by upstream the catalyst additionally injected fuel to increase Conversion rate to at relatively low exhaust gas temperatures, the ignition temperature of the diesel of about 600 ° C safely to achieve.

0003As is known, the diesel is when passing through a conventionally Catalyst acting for a significant portion of the accumulated, volatile compounds HC withdrawn, so that a relatively dry despite heavy flammable additives Soot in the filter reaches the deposition. In the known method are formed in the increased by the fuel additive conversion, excess HC shares supplied to the deposited soot in the filter and thus the Although influenced ignition temperature of the soot low, but not in a desirable Extent.

0004The invention is therefore based on the object, which in the preamble of claim 1 method described with the purpose specified in such funds to improve, that is substantially always to burn off the retained in the filter Soot its lowest ignition temperature is given.

0005This object is achieved with the patent claim 1 in such a way that a liquid Fuel to a relation to the respective usual, maximum catalyst temperature conversion by about 30 - 60% in degrees Celsius lower temperature in such an amount is controlled / regulated is added that in the soot filter a Rußbefeuchtung is achieved.

0006The advantage of the invention is in addition to the significant lowering of the ignition temperature in connection with secure Rußabbrennen further in the free placement of the respective catalyst between soot and diesel engine seen since the Rußbefeuchtung a directly adjacent heating the Soot filter can advantageously be dispensed by a particular catalyst.

0007To achieve an effective Rußbefeuchtung is in embodiment of the invention with the fuel addition to the exhaust duct below the light-off temperature started 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.

0008With the invention it is possible in an advantageous manner, the fuel in the particulate filter and / or add upstream of the soot filter in the exhaust system.

0009Further, the invention provides the additional advantage of each of the catalytic converter arrangement in the exhaust system freely selectable map of fuel charging, wherein the fuel is injected by means of a separate device. Finally, the cycles of the Rußbefeuchtung can vary depending on parameters the soot filter, the exhaust gas and other engine parameters map-controlled be, so with optimum Rußabbrennen minimum fuel consumption is achievable.

0010The invention is described below:

0011In a method for cleanup of diesel emissions by flowing into a Flue exhaust an oxidation catalyst and / or an SCR or DeNOx catalytic converter and a particulate filter. Next is the HC enrichment of Soot temperature controlled in the soot filter in the exhaust system, a liquid fuel added. As is well known, the diesel exhaust as it passes through a acting in the usual way catalyst due to the conversion, the volatile HC-compounds are removed, is with the controlled addition of fuel 0,405,310 tries in accordance with the generic EP-A, the soot in the filter downstream of the respective catalyst gaseous HC-compounds for lowering supplying the soot-ignition temperature, the upstream of the soot filter closely adjacent Catalyst of each type with its conversion heat significantly contributes to Rußentzündung.

0012For reliable ignition of the deposited soot in the soot filter with simultaneous Decoupling of adverse structural combination of respective catalyst and soot is achieved according to such the method of emission control improved in that the fuel to a respective opposite the usual maximum permissible catalyst conversion temperature by about 30 - 60% in degree Celsius lower temperature controlled / regulated in such an amount is added that in the soot filter a Rußbefeuchtung is achieved.

0013To achieve an effective Rußbefeuchtung after a predetermined controlled / regulated introduced Rußentzündung for burning the soot filter in minimal fuel consumption takes the start of the fuel-addition in the Flue substantially below the light-off temperature of each catalyst; as the upper limit of the addition may be as the light-off temperature plus ≈ 200 ° C be selected.

0014The invention enables using in structurally advantageously known separate device for injecting the fuel directly these in the soot filter and / or upstream closely adjacent enter into the exhaust system. Since with this method, the added fuel by any of the foreseeable, individually or through here in a combination which can be arranged catalysts needs are hereby arises advantageously a minimum Consumption of additional fuel, preferably a diesel engine of the may be entrained fuel.

0015the cycles of Rußbefeuchtung and thus to be advantageous the Rußabbrennen map-controlled, travel-distance-dependent and function-dependent parameters Loading intervals and / or the exhaust gas temperature and / or the can serve filter back pressure and / or other engine parameters.

0016The inventive method is particularly advantageous to operate with a Oxidation-catalyst and / or an SCR catalyst with an integrated oxidation catalyst upstream of the soot filter in a close-coupled arrangement in a Exhaust system, in which the fuel Rußbefeuchtungs separate means of a Apparatus downstream of the respective catalyst close before or in the soot filter is injected. The close arrangement of the respective catalyst results in a high conversion rate with an advantageous exhaust gas temperature increase upstream of the moistened soot filter, which advantageously an additive supported regeneration the carbon filter system is achieved even in the lower load range.

0017With the invention targeted Rußkonditionierung allows the regeneration area of additive filter systems on the entire engine operating range advantageously extend with the further advantage of a substantial reduction in the Energy required for regeneration over filter systems with external Regeneration energy.

0018Besides, in the arrangement of a known a high heat capacity with lowered exhaust temperatures having downstream soot filter 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 be achieved.