Ashing a particulate filter in a motor vehicle

Abstract

A method is provided for operating an internal combustion engine in a motor vehicle, The internal combustion engine has at least one cylinder with a combustion chamber, a water injection unit with a tank and at least one injection nozzle for directly or indirectly injecting water into the combustion chamber, an exhaust gas system with at least one exhaust gas catalytic converter and a particulate filter device which has a particulate filter for filtering particles out of an exhaust gas flow guided in the exhaust gas system. A control unit is provide for a state monitoring process and for controlling the combustion in the cylinder.

Claims

1. A method for operating an internal combustion engine in a motor vehicle, wherein the internal combustion engine has: at least one cylinder with a combustion chamber, a water injection system with a tank and at least one injection nozzle for directly or indirectly injecting water into the combustion chamber, an exhaust-gas system with at least one exhaust-gas catalytic converter and a particulate filter device which has a particulate filter for filtering particulates out of an exhaust-gas flow conducted in the exhaust-gas system, a control unit for condition monitoring and for controlling the combustion in the cylinder, wherein the method comprises: filling the tank of the water injection system with a mixture of water and an ash former; and operating the internal combustion engine using the mixture.

2. The method according to claim 1, wherein the ash former has a metal salt.

3. The method according to claim 1, wherein a concentration of the ash former in the mixture is between 100 ppm and 2000 ppm.

4. The method according to claim 1, wherein the mixture is an aqueous solution of the ash former in the water and/or a water-based suspension of the ash former and of the water.

5. The method according to claim 1, further comprising: influencing the operation of the water injection system such that less or no water and ash-former mixture is injected if an exhaust-gas temperature in the exhaust-gas flow lies within a predetermined exhaust-gas temperature range.

6. The method according to claim 5, wherein the predetermined exhaust-gas temperature range is above a limit temperature of 500° C.

7. The method according to claim 1, wherein the water injection system is metered such that a concentration of the ash former in a mixture of the injected fuel and the injected water and ash-former mixture is less than 100 ppm.

8. The method according to claim 1, further comprising: triggering a loading operating state of the water injection system if an unused particulate filter is installed in the particulate filter device; and during the loading operating state, influencing the operation of the water injection system in such a manner that more water and ash-former mixture is injected and/or water and ash-former mixture is injected for a longer time.

9. The method according to claim 8, wherein an oxygen percentage in the air and fuel mixture is increased in such a manner that sufficient oxygen is provided for forming ash.

10. An internal combustion engine, for a motor vehicle, comprising: at least one cylinder with a combustion chamber; a water injection system with a tank and at least one injection nozzle for directly or indirectly injecting water into the combustion chamber, wherein, for the injection, use is made of a mixture of water and an ash former; an exhaust-gas system with at least one exhaust-gas catalytic converter and a particulate filter device which has a particulate filter for filtering particles out of an exhaust-gas flow conducted in the exhaust-gas system; a control unit for condition monitoring and for controlling the combustion in the cylinder, wherein the control unit is configured to influence operation of the water injection system in such a manner that less or no water and ash-former mixture is injected if an exhaust-gas temperature in the exhaust-gas flow lies within a predetermined exhaust-gas temperature range.

11. The internal combustion engine according to claim 10, wherein the injection nozzle is arranged on the combustion chamber of the cylinder and/or in a feed pipe for a fuel and air mixture, or the injection nozzle for the water and ash-former mixture is formed together with a fuel injection nozzle.

12. A motor vehicle comprising an internal combustion engine according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an internal combustion engine according to an exemplary embodiment of the invention with a water injection system and an exhaust-gas system which has a particulate filter device, in a schematic view.

(2) FIG. 2 shows an internal combustion engine according to a further exemplary embodiment of the invention with a water injection system and an exhaust-gas system which has a particulate filter device, in a schematic view.

(3) FIG. 3 shows a diagram in which time profiles of a volume flow of the water and ash-former mixture, of an exhaust-gas temperature upstream of the first lambda probe and of a degree of loading are plotted, in order to explain a method according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 illustrates an internal combustion engine 1 with an exhaust-gas system 2. In the exemplary embodiment, the internal combustion engine 1 is a four-cylinder spark-ignition engine, but it may also be a different type of engine, for example a diesel engine, and/or may have a different number of cylinders. The engine 1 is supplied with charge air by means of a charge air supply 4 (the top arrow with two dashed lines represents the supply of fresh air 5 in a simplified manner). Charge air and fuel and a water and ash-former mixture are provided in a jointly formed fuel and water injection system 40 into the cylinders 6 at the cylinder heads via a common rail 8.

(5) After the combustion, the exhaust-gas flow is removed from the cylinders 6 by means of the exhaust-gas system 2, wherein the exhaust-gas system 2 has at least one first lambda probe 12 and a three-way catalytic converter 10 downstream of the latter. The regulating circuit of the catalytic converter 10, optionally taking measurement values of the lambda probe(s) 12 into consideration, is not the subject matter of the invention, and therefore the activation thereof is also not illustrated here.

(6) A particulate filter 14 of a particulate filter device 16 of the internal combustion engine 1, which particulate filter can optionally be regenerated in respect of soot particulates and at any rate can be exchanged, is arranged in the exhaust-gas flow downstream of the catalytic converter 10. Downstream of the particulate filter 14, the after-treated and ash-filtered exhaust gas is blown out into the environment, for example at an exhaust tail pipe (the bottom arrow with two dashed lines represents the exhaust tail pipe system for the exhaust gases 3 in a simplified manner). The exemplary embodiment is described with a particulate filter 14 arranged downstream of the catalytic converter 10; in other exemplary embodiments, not illustrated, of the invention, the particulate filter device may, of course, also be operated with a particulate filter which has a catalytic coating, and therefore the catalytic converter 10 and the particulate filter 14 are combined.

(7) The particulate filter device 16 is designed in such a manner that the particulate filter 14 can be exchanged. Newly inserted particulate filters 14 normally do not have any soot and/or ash loading, and therefore, after the particulate filter 14 has been exchanged and also when the vehicle is started up with a new particulate filter 14, the degree of loading BG of the particulate filter is 0 (zero). At a degree of loading BG of 0 and also at a low degree of loading, the particulate filter 14, however, achieves only a filtration efficiency FE of approximately 50% to 85% depending on the substrate and operating point (within the context of the invention, customary particulate filters which are known per se, for example customary Otto particulate filters OPFs are preferably used). In order to permit operation of the internal combustion engine 1 with as low a level of pollutants as possible and therefore in particular also to be able to meet the existing pollutant standards, a higher filtration efficiency FE, in particular in the maximum range above approximately 99%, is, however, required. For this purpose, it is necessary for the particulate filter 14 to be loaded with a certain amount of ash which corresponds here to a required minimum degree of loading BG.sub.min. For example, in the case of conventional OPF sizes and types, an absolute loading with approx. 1 to 2 grams of ash may be required for this purpose.

(8) The combined fuel and water injection system 40 has a dedicated combined fuel and water injection nozzle 9 for each cylinder 6. Each of the combined injection nozzles 9 is connected to a fuel and water pump 41 by means of a pressure line. The pump 41 is fed both by a fuel tank 26 and by a water tank 32. The fuel supply to the pump 41 is regulated by means of an infinitely regulable fuel valve 27, the water supply by means of an infinitely regulable water valve 33.

(9) In an alternative refinement, not illustrated, of the combined fuel and water injection system 40, the water and ash mixture is injected into the fuel line downstream of a low-pressure fuel pump, but upstream of a high-pressure fuel pump, in particular via a water injection valve. The water and ash fuel mixture is then injected into the cylinder/the cylinders via the high-pressure fuel pump and the common rail.

(10) In addition, the internal combustion engine 1 has a control unit 20 in which, at least in the exemplary embodiment, a filter operating model 22 is stored. The filter operating model 22 and/or sensors, not illustrated, can be used to undertake filter condition monitoring 21, by means of which, for example, a current degree of loading of the filter can be determined. The control unit 20 is connected to the particulate filter device 16 by means of a double-dotted dashed line, in particular for detecting a newly inserted particulate filter 14. Furthermore, the control unit 20 is connected to these components (see double-dotted dashed lines) in order to activate the valves 27 and 33 and the pump 41.

(11) In order, by means of a method according to an exemplary embodiment of the invention, to achieve as rapid a preliminary ashing of the particulate filter 14 as possible (i.e. in order as rapidly as possible to achieve the minimally necessary degree of loading BG.sub.min, and therefore to ensure sufficiently high filtration efficiency FE), according to one embodiment of the invention, the water tank 32 of the water injection system 40 is not filled with pure water or with the mixture customary for a pure water injection system, but rather with a water and ash-former mixture 31 within the context of the invention.

(12) For this purpose, the exemplary embodiment makes use of a modern spark-ignition engine which is known per se and which in any case has an indirect or direct water injection 30, 40 into the combustion chamber of each cylinder 6 in order to reduce the temperature in the combustion chamber and therefore also to reduce the emissions. Structural adaptations of such a modern spark-ignition engine to the use of the water and ash-former mixture 31 are not required in the exemplary embodiment.

(13) In order to produce the water and ash-former mixture 31 used, a portion of 750 ppm of magnesium is added to the water in the exemplary embodiment, in particular in the form of magnesium nitrate or in the form of another magnesium salt, wherein the magnesium nitrate or the other magnesium salt is dissolved in the water.

(14) The interaction of tank size (or tank filling) and quantity of ash former is balanced out in such a manner that, in the combination of internal combustion engine and exhaust-gas system of the exemplary embodiment, the introduced ash former suffices to load the particulate filter with this tank filling with 1-2 grams of magnesium oxide ash.

(15) When other ash formers are used, other quantities of ash may be required for filling a standard particulate filter, for example, approx. 5× the quantity of ash, i.e. 5-10 grams in the case of CaO, ZnO or other ash.

(16) Which metal salt or which other suitable compound or which combination of elements or compounds in which portions by volume is added as ash former in an individual case can be decided by a person skilled in the art depending on the type of engine and/or the existing combination of catalytic converters.

(17) FIG. 2 shows another internal combustion engine 1 according to a further exemplary embodiment of the invention. The internal combustion engine 1 illustrated in FIG. 2 differs from that according to FIG. 1 primarily in that the fuel 25 and the water and ash-former mixture 31 are injected into the respective cylinders 6 in separate injection nozzles 29 and 39, respectively. For this purpose, a separate fuel injection system 24 and a separate water injection system 30 are provided. The fuel injection system 24 has a separate fuel pump 28. The water injection system 30 has a separate water pump 34.

(18) Apart from these differences, the two internal combustion engines 1 illustrated are formed in a manner corresponding to each other in respect of the exemplary method described in FIG. 3, and therefore the method can be carried out for both internal combustion engines.

(19) FIG. 3 illustrates a diagram 50 in order to explain an exemplary method for operating an internal combustion engine 1 in a motor vehicle. The internal combustion engine 1 can be designed in particular as illustrated in FIG. 1 or as illustrated in FIG. 2.

(20) The diagram 50 illustrates mutually associated time profiles 52, 54 and 56 of a volume flow Q of the water and ash-former mixture 31 (profile 54), of an exhaust-gas temperature T upstream of the first lambda probe 12 (profile 52) and of a degree of loading (BG) of the particulate filter 14 with ash (profile 56).

(21) The diagram shows the operation of the internal combustion engine of a new vehicle in which a brand-new particulate filter 14 having a degree of loading BG of 0 is installed. For as rapid a preliminary ashing of the particulate filter 14 as possible, the water tank 32 has been filled with a water and ash-former mixture 31 as described in FIG. 1.

(22) The control unit 20 recognizes that a new empty (BG=0) particulate filter 14 is installed in the particulate filter device 16 and triggers a loading operating state 58. In order to ash the particulate filter 14 as rapidly as possible such that the desired filtration efficiency of 99% is reached, the control unit 20 triggers a maximum volume flow Q.sub.max of the water injection system 30, 40 during the normal operation of the internal combustion engine 1.

(23) For as long as the exhaust-gas temperature T remains beyond a predetermined exhaust-gas temperature range above a limit value T.sub.g, an ash former is introduced into the combustion chambers of the cylinder 6 such that rapid ashing of the particulate filter 14 causes a rapid rise in the degree of loading BG.

(24) When the exhaust-gas temperature T reaches the limit value T.sub.g or lies above the latter (and therefore lies within the predetermined exhaust-gas temperature range), the operation of the water injection system 30 or 40 is influenced in such a manner that no more water and ash-former mixture is injected. This makes it possible to avoid damage to the lambda probes 12 and/or to the catalytic converter 10 for as long as the exhaust-gas temperature T remains within the harmful range.

(25) It can also be gathered from the diagram 50 that the loading operating state 58 is triggered again and therefore the water injection system is switched on again as soon as the exhaust-gas temperature T is non-critical again.

(26) The water injection system is switched off at the time t.sub.1. The time t.sub.1 can be defined, for example, by the filter operating model 22 being used, depending on the preceding operation of the water injection system, to determine that the required degree of loading BG.sub.min is reached. Alternatively, the time t.sub.1 can also be defined by the fact that the filling of the water tank 32 with water and ash-former mixture is used up. For example, pure water and/or the water mixture normally used for a water injection system in order to reduce the exhaust-gas temperatures can subsequently be introduced again into the tank 32.

(27) In a further exemplary embodiment, not illustrated, it can be provided that the water tank 32 is filled only with water or with a conventional water mixture for the water injection system for reducing the exhaust-gas temperature and in addition an ash-former tank is provided from which ash former can be added when required to the water in the tank 32 in order to assist a rapid preliminary ashing of the particulate filter 14 if this is necessary. For example, the addition of the ash former can be ended when the required degree of loading BG.sub.min is reached.

LIST OF REFERENCE SIGNS

(28) 1 Internal combustion engine 2 Exhaust gas system 4 Charge air supply 6 Cylinder 8 Common rail 9 Common fuel and water injector 10 Three-way catalytic converter 12 First lambda probe 14 Particulate filter 16 Particulate filter device 20 Control unit 21 Filter state determination 22 Filter operating model 24 Fuel injection system 25 Fuel filler neck 26 Fuel tank 27 Fuel valve 28 Fuel pump 30 Water injection system 31 Water filler neck 32 Water tank 33 Water valve 34 Water pump 29 Water injector 40 Combined fuel and water injection system 41 Combined fuel and water pump 50 Diagram 52 Profile of the exhaust-gas temperature T over time 54 Profile of the volume flow Q over time 56 Profile of the degree of loading BG over time 58 Loading operating state BG Degree of loading of the particulate filter FE Filtration efficiency of the particulate filter T Temperature of the exhaust gas upstream of the first lambda probe Q Volume flow of the water and ash-former mixture t Time