DE19918591A1 - Engine operation making good use of water from exhaust gases, recovers water with advanced membrane, to be injected in air inlet manifold and to be mixed with solid urea for injection into exhaust ahead of catalyst - Google Patents

Abstract

Exhaust gases (3) are passed over a membrane (4) separating water from them. The water is returned to the process, to reduce pollutant emissions. The term process, here covers both the engine and subsequent exhaust treatment. Preferred features: The water is collected in a storage vessel (5), to be injected (8) into the air inlet manifold (9). It is alternatively injected into a side stream of exhaust gas, which is returned to the air inlet manifold. In a further development, the piston engine is operated with an exhaust gas catalyst. Solid urea is dosed into a water storage vessel and dissolved. The aqueous urea solution is introduced into the flow of exhaust gases, ahead of the catalyst used for after-treatment.

Description

When operating a piston internal combustion engine, it can be used for Optimization of the operating process, especially with regard to expedient to reduce pollutant emissions be to add water to the operating process. Under "Operating process "in the sense of the present invention, both the chemical-physical processes in the combustion chamber of the pistons internal combustion engine as well as the chemical-physical pre gears in the area of one of the piston internal combustion engines switched catalytic exhaust gas aftertreatment device stood.

In the context of reducing pollutant emissions, for example, the reduction of NO _x emissions in piston internal combustion engines, which are operated using the diesel process, represents a great challenge, since the 3-way catalyst technologies used for piston internal combustion engines, who work according to the Otto process cannot be used in the diesel process due to the excess of oxygen.

For this application, there is a possibility of NO _x reduction by means of catalytic exhaust gas aftertreatment via a selective catalytic reduction by adding urea to the exhaust gas, the so-called urea SCR. In this process, an aqueous urea-water solution is injected into the exhaust gas in front of a corresponding catalyst. In previously implemented SCR systems of this type, a premixed aqueous urea-water solution with a mixing ratio of one part by mass of urea to two parts by mass of water is used as the reducing agent. With a reducing agent consumption of about 2.9 g of solution to 1 g of NO _x , about 1 g to 1.5 g of reducing agent per kilometer of travel distance is required in diesel-powered piston internal combustion engines, such as those used in passenger cars, under test conditions. This means that a container volume of 15 to 25 l is required for a travel distance of 15,000 km, i.e. according to an inspection interval common today. In order to cover operating modes with high proportions of high speed, containers with a capacity of up to 40 l would be required for the driving interval mentioned. This is not justifiable for reasons of space or weight.

Although urea is the cheapest reducing agent for the represents its application, because of the above Disadvantages described tried with others, less expensive favorable reducing agents, for example cyanuric acid, the to avoid these disadvantages. Here is by thermal A effect the cyanuric acid in steam and this cyanur acid vapor after further thermal exposure in the Ab gas tract introduced in front of the SCR catalytic converter.

The invention is based on the object of a method to create that enables pollutant reduction to effect when operating a piston internal combustion engine and through the use of water, the ge initially disadvantages described are avoided.

The object is achieved according to the invention by a method ren for operating a piston internal combustion engine, in which during operation from at least part of the exhaust gas flow with at least part of the water content by means of a Separating membrane separated and to reduce pollutants bump at least temporarily back to the operating process leads. It has surprisingly been found that with With the help of modern membrane technology even from one exhaust part current during the operation of the piston internal combustion engine much water can be separated as for the harmful  Reduction of substances by returning them to the operating process is required.

Depending on the mode of operation, it may be appropriate that the Exhaust gas abge by means of a separation membrane and by condensation separated water to collect as stock.

In a first embodiment of the invention, that water from the supply into the intake air of the piston burn engine is introduced. Compared to the familiar What This measure has the advantage of ser injection into the combustion chamber part that the nozzles are not made of the high combustion chamber temperature are set and that beyond the injection with only ge low pressure and thus with correspondingly low energy wall can be done. The injection of the water quantities can be done here in the case of centrally via a single nozzle in the intake tract gen or in the intake manifold to the individual cylinders the piston engine take place, then the on spray nozzles via the usually available engine control can be controlled according to the work cycle. So that is a very precise dosage and adaptation to the respective internal engine operating process possible.

In another embodiment of the method according to the invention it is provided that water from the supply in one. From the partial gas flow is injected, which is returned to the piston internal combustion engine with the intake air. The advantage here is that the water absorption in the recirculated hot exhaust gas is quantitatively very high, and there is rapid evaporation, so that here too no high demands are placed on the spray quality of the nozzles. Another advantage is that the recirculated exhaust gas is cooled without heat exchanger by the heat of vaporization of the water supplied. This results in a simple manner in an engine-based nitrogen oxide reduction through the combination of exhaust gas recirculation and water addition to the recirculated exhaust gas. With the same exhaust gas recirculation, this causes a significant increase in the NO _x reduction in the combustion chamber of the piston internal combustion engine.

In a further embodiment of the invention is provided for a method for operating a piston internal combustion engine with egg ner device for catalytic aftertreatment of the exhaust gases that the urea is metered in and dissolved in the water supply in solid form and that the urea-water solution before Device for the catalytic aftertreatment of the exhaust gases is introduced into the exhaust tract. This procedure offers the advantage that, when using the inexpensive urea as a reducing agent, the water required to dissolve the urea is recovered from the exhaust gas by the process according to the invention, and so the urea can be carried in solid form in a cartridge. The urea is removed from the cartridge and metered to the water supply and dissolved in it, so that a urea-water solution is available in the storage tank for exhaust gas aftertreatment, which can be injected into the exhaust tract via an injection nozzle in front of the SCR catalytic converter . The amount to be injected is determined via the engine control system from a NO _x emission map and the detected air mass flow. A particular advantage of this procedure is also that in addition to the unproblematic solubility of urea in water for carrying the reducing agent urea in the vehicle compared to a premixed urea-water solution, a smaller volume and thus a lower weight is required.

While carrying water in a tank or when Carrying a premixed urea-water solution at Au outside temperatures below -11 ° C cause freezing problems, with the result that an additional for the reservoir Heating must be provided, the Lö invention solution on the advantage that only so much from the exhaust gas Water must be made available, as for the loading drive process is needed. So that the storage container  be kept small, be installed close to the engine and accordingly are warmed up quickly, the Zu drove from warm water immediately after takeoff. Another advantage of this embodiment of the invention ß procedure is that a significantly higher urine substance concentration in the urea-water solution reached can be, so that a much lower fluid volume lumen is to be injected into the exhaust tract and evaporated.

The invention is based on schematic block diagrams ago explained. Show it:

Fig. 1 a method comprising injecting water into the intake tract,

Fig. 2 shows a method with injection of water into the exhaust gas recirculation,

Fig. 3 shows a method for injection of an on-board generated urea-water solution.

In Fig. 1 shows schematically a four-cylinder reciprocating internal combustion engine 1 shown, be according to the diesel process is exaggerated.

A partial stream is branched off from the exhaust tract 2 via a bypass line 3 and is carried out through a separating membrane system 4 . In the separating membrane system 4 of known type, at least part of the water content is separated from the exhaust gas via a separating membrane 4.1 and is condensed out by cooling. The condensed water is fed to a buffer store or storage container 5 . The Abga steep stream dehumidified in this way is returned to the gas tract 2 via a discharge line 6 .

For internal engine nitrogen oxide reduction, water is drawn off from the reservoir 5 with the aid of a pump 7 and injected into the intake duct 9 of the internal combustion engine 1 via an injection nozzle 8 . By means of a motor controller 10, which also all the other operating functions of the piston internal combustion engine controls and / or regulates the requirements of the operation by driving the nozzle 8 and the pump 7 is injected metered water into the air intake passage 9 accordingly.

In the schematic representation here is only the on Injection of water at one point of the air intake duct poses. But it is also possible to inject the water in each case in the individual air leading directly to the cylinders make intake channels, so that each cylinder then own injector is assigned and accordingly ge targets and in the work cycle of the intake air of each cylinder a correspondingly metered amount of liquid can be supplied can.

In Fig. 2, the process of the internal engine nitrogen oxide reduction by injecting water in another configuration is shown schematically. The extraction of water from a partial exhaust gas flow with the help of the separating membrane device 4 and the collection of the separated water in a storage container 5 correspond to the method described with reference to FIG. 1.

The modification in the method of FIG. 1 is that with the exhaust tract 2 an exhaust gas recirculation line 11 is the, which opens into the intake tract 9 , with the engine control 10 and an in the exhaust gas recirculation line 11 to ordered valve 12 according to the requirements of Mo torbetriebes a metered amount of exhaust gas is the intake tract 9 leads.

In this procedure, the required water is injected into the exhaust gas recirculation line 11 from the reservoir 5 via the pump 7 and the injection nozzle 8 , so that the water on the one hand cools the recirculated exhaust gas amount and on the other hand the amount of water evaporates quickly.

If there is not a sufficient temperature gradient available for cooling the separation membrane system or if, as in the process according to. Fig. 1 or Fig. 2 that the process to be introduced into the process water is not required in liquid form, then the reservoir 5 can be omitted. The pump 7 is then not a pump for the conveyance of liquids son to train gases, so that the suction side of the required for the function of the separating membrane device underpressure on the water vapor side of the separating membrane 4.1 is available. In this case, the water required can be supplied to the operating process in vapor form. The supply in vapor form is at least according to the method. Fig. 1 useful, since a supply in liquid form in the air intake must ensure good atomization, which is not so critical when introduced into the hot exhaust gas because of the rapid evaporation caused by temperature.

A further method variant is shown in FIG. 3. In this variant of the method, the exhaust tract 2 of the piston internal combustion engine 1 is connected to an SCR catalytic converter 13 . As described above, a partial exhaust gas stream is withdrawn from the exhaust tract 2 via the branch line 3 and water is separated from the partial exhaust gas stream in the separating membrane device 4 , condensed and collected in the storage container 5 . In this embodiment, liquid is injected from the reservoir 5 with the aid of the pump 7 and the injection nozzle 8 into the exhaust tract 2 in a controlled manner upstream of the SCR catalytic converter 13 .

Via a metering and mixing device 14 , urea present in solid form, for example in the form of granules present urea, is drawn from a storage cartridge 15 and metered into the container 5 . The urea dissolves in the water introduced into the container 5 from the separating membrane device 4 , so that a urea-water solution is formed. The metering of the amount of urea and thus the determination of the urea concentration in the container 5 can be effected via a measurement of the conductivity and / or a measurement (signal line 17 ) of the liquid temperature in the container 5 .

The urea-water solution is again metered into the exhaust tract 2 via engine control.

In particular in the process according to Fig. 3 is the amount of liquid to be injected via a stored in the engine control 10 NO _x emission map and via the air flow measured with a sensor 16 shown only schematically here, otherwise the efficiency of the SCR catalyst would be too low or an NH ₃ slip is to be feared.

In the process according to Fig. 1 or 2, it is sufficient to inject as much water as possible, especially since the separation rate of the separating membrane device is limited anyway.

Claims (6)

1. Method for operating a piston internal combustion engine, in which at least part of the Ab gas flow at least part of the water content by means of egg ner separation membrane and to reduce the damage emissions at least temporarily back to the operating process is fed. 2. The method according to claim 1, characterized in that the separated water is collected as a supply. 3. The method according to claim 1 or 2, characterized in that water into the intake air of the piston internal combustion engine is introduced. 4. The method according to claim 1 or 2, characterized in that water is introduced into a partial exhaust gas flow with of the intake air is returned to the piston internal combustion engine becomes. 5. Method for operating a piston internal combustion engine with a device for the catalytic aftertreatment of the exhaust gases according to claim 1 and 2, characterized in that in the Water in solid form metered in existing urea and is dissolved and that the urea-water solution before the facility for catalytic after-treatment in the Ab gas flow is introduced. 6. The method according to claim 5, characterized in that the Urea concentration of the urea-water to be introduced Solution depending on the given electrical guidelines ability values and / or a predetermined value of the mixed values temperature is determined in a mixing container.