EP2169192B1 - Device and method for spraying fuel into the exhaust gas flow of an internal combustion engine, in particular for regenerating a particulate filter - Google Patents

Description

The invention relates to a device for injecting fuel into the exhaust line of an internal combustion engine, in particular for the regeneration of a particulate filter, according to the preamble of claim 1 and a method for operating such a device according to the preamble of claim 6. The use of particulate filters in motor vehicles is general known. However, such particulate filters are prone to clogging by the carbonaceous soot deposited therein, which increases exhaust back pressure and reduces engine performance. An arrangement and a method with particle filter is from the EP 0 341 832 A1 known. There, upstream of the particulate filter, an oxidation catalyst is arranged, which oxidizes the nitrogen monoxide in the exhaust gas with the help of the likewise contained residual oxygen to nitrogen dioxide:

2NO + O ₂ ↔ 2NO ₂

It should be noted that the equilibrium of the above reaction at high temperatures is on the side of NO. This has the consequence that the achievable NO ₂ levels are limited at high temperatures due to these thermodynamic limitations.

This NO ₂ is in turn in the particulate filter with the carbonaceous soot particles to CO, CO ₂ , N ₂ and NO to. With the aid of the oxidizing agent NO ₂ , a continuous removal of the adsorbed fines particles can thus take place. Regeneration cycles, as they must be carried out consuming in other arrangements, thereby eliminated. This is called a passive regeneration. The reaction takes place in accordance with the following reaction equations:

2NO ₂ + C → 2NO + CO2

2NO ₂ + C → 2NO + CO

2C + 2NO ₂ → N ₂ + 2CO ₂

However, if complete oxidation of the carbon stored in the particulate filter is not possible with the aid of NO ₂ , the carbon content and thus the exhaust backpressure increase steadily. To avoid this, the particle filters are currently increasingly provided with a catalytic coating for the oxidation of NO. These are usually platinum-containing catalysts. The disadvantage of this method, however, is that the NO ₂ formed on the particulate filter can only serve for the oxidation of particles which are deposited downstream of the catalytically active layer for NO oxidation, ie within the filter medium. If, on the other hand, a layer of separated particles forms on the filter surface and thus on the catalytically active layer (filter cake), then the NO oxidation catalyst is present downstream of the filter cake so that the deposited soot particles can not be oxidized by NO ₂ from the NO oxidation catalyst applied to the particulate filter. In addition, strictly speaking, only the catalyst layer applied to the top of the system performance is because the NO ₂ catalytically formed on the clean gas side can no longer come into contact with the soot deposited on the raw gas side and within the filter material.

Another problem of the coating of the particulate filter is that the geometric surfaces of the filter are significantly lower than that of the catalyst substrates commonly used. The reason for this is that the filters require relatively large free cross sections and thus free volume on the raw gas side in order to store soot and engine oil ash.

For these reasons, despite the catalytic coating of the filter can not be dispensed with a NO oxidation catalyst in front of the particulate filter, so that there is a relatively large volume of construction. This is the case even if the NO oxidation catalysts and the particulate filter form a structural unit in which the inlet region of the particulate filter is designed as a NO oxidation catalyst, as for example in the DE 103 270 30 A1 the case is.

Although by these measures, a soot oxidation is still possible up to temperatures of 250 ° C, there are still applications in which even these exhaust gas temperatures are not achieved and thus no reliable function of the particulate filter can be guaranteed. This usually occurs in lightly loaded and installed in vehicles engines, such as passenger cars, bus or refuse collection vehicles, which additionally still have high idle proportions, on. Therefore, a second possibility of particulate filter regeneration is used especially in such cases: it consists in actively raising the exhaust gas temperature. This usually succeeds through the Addition of hydrocarbons (HC) upstream of hydrocarbon or HC oxidation catalysts. The exothermic oxidation of the hydrocarbons on the catalysts leads to a significant increase in temperature. If this results in a temperature increase above 600 ° C, oxidation of the carbon occurs with the help of oxygen (active filter regeneration):

C + O ₂ → CO ₂

However, the injection of the fuel into the hot exhaust tract poses problems: since hydrocarbons are only injected during the regeneration, no cooling of the injection nozzle takes place during the regeneration pauses. Due to the high exhaust-gas temperatures in the exhaust-gas tract, this leads to coking of the fuel remaining in the nozzle, in particular in the nozzle holes, so that there is a blockage and thus usually a total failure of the nozzle.

To solve this problem is out of the WO 2007/091969 A1 Already a metering device for fuel known in which a nozzle element or nozzle head is designed so that in this opens a fuel line. This fuel line opens centrally and centrally into the nozzle element and is surrounded by a double-wall arrangement of an air duct, so that they form a double tube arrangement. In the area of the free nozzle head end, branch channels are led from the fuel line into the air channel, so that mixing of the compressed air of the air channel with the fuel of the fuel line can take place in special nozzle directed towards the nozzle tip, whereby atomization of the fuel is to be effected in order to fine this Distributed distributed in the exhaust line.

The dual tube arrangement of fuel line and air channel is arranged from the nozzle tip to a remote from the nozzle tip Valve block out, which has a first valve, by means of which the metered addition of the fuel is controlled to the nozzle member. Furthermore, the valve block comprises a second valve element by means of which two compressed-air connections can be controlled. By means of the two compressed-air connections, air can be introduced into the air duct guided to the nozzle tip either from the inlet side of the internal combustion engine or from a separate compressor. Furthermore, a third valve element is provided by means of which the fuel line can be brought into fluid communication with one of the two compressed air lines in order to blow them through. Thus, the following procedure is possible: Before fuel is metered into the exhaust system, the fuel line is blown with air to clean them. In this case, the, the fuel metering releasing valve element is kept closed. Subsequent to this air supply to the fuel line then fuel is pumped out of the fuel tank of the vehicle via a separate pump and conveyed via the fuel line to the nozzle tip. At the same time air flows through appropriate control of the compressed air valve via the double pipe arrangement air to the nozzle tip, where the mixing between compressed air and fuel takes place.

Obviously, such a construction is relatively complex and component-intensive and thus prone to failure.

The EP 1 676 628 A1 relates to a Dosierpumpenaggregat for admixing a liquid reducing agent in an exhaust stream with a metering pump for conveying the reducing agent and a premixing device, in which in a mixing area the subsidized by the metering pump reducing agent is mixed with a pressurized gas. It is provided that the metering pump unit has a pump head with a central plate, in which at least the metering pump and the premixing device are arranged.

In the EP 971 102 A1 is a NOx reduction system described which includes a NOx catalyst mounted in an exhaust passage of an engine, such as a diesel engine, wherein an air supply communicates with the exhaust passage upstream of the NOx catalyst. The air supply supplies the exhaust passage with a mixture of air and fission gas generated by spraying fuel into the air and heating to 350 to 450 degrees C and partial oxidation. With this mixture added to the exhaust gas, NOx in the exhaust gas can be effectively removed.

It is therefore an object of the present invention to provide an apparatus and a method for injecting fuel into the exhaust line of an internal combustion engine, in particular for the regeneration of a particulate filter, by means of which the clogging of a nozzle element for the fuel metering in the exhaust system of an internal combustion engine to structurally simple and functionally reliable way can be reliably avoided.

This object is achieved with respect to the device with the features of claim 1. Regarding the method, this object is achieved with the

Features of claim 6. Advantageous embodiments thereof are each the subject of the dependent claims.

According to claim 1, an apparatus for injecting fuel into the exhaust line of an internal combustion engine, in particular for the regeneration of a particulate filter, a fuel line and a compressed air line coupled thereto, which are guided to a arranged on or in the exhaust line nozzle member, wherein the compressed air line downstream of a compressor a turbocharger branches and / or fluidly connected to the pressure side of a compressor. Furthermore, at least one controllable by means of a control and / or regulating device control is provided by means of which the compressed air supply and the fuel supply to the nozzle element according to predetermined control and / or control parameters is adjustable. According to the invention, according to a first aspect, the at least one, preferably only a single, compressed-air line upstream of the nozzle element is brought together with the fuel line such that they form a single common supply line guided to the nozzle element. With this measure, the mixing of the compressed air and the fuel is already achieved in a structurally simple manner before the nozzle element, so that manufacturing technically complex nozzle configurations, as they are the subject of WO 2007/091969 are, in which the nozzle member is formed by a double pipe arrangement with fuel line and compressed air line, can be avoided. As a result, the manufacturing costs for the actual nozzle element can be significantly reduced. Due to the early mixing of compressed air and fuel, a mixing and atomization of the fuel in the compressed air is also already achieved relatively early, so that even with the inventive solution a fine distribution of the fuel in the exhaust gas tract of the internal combustion engine can be achieved.

As an alternative or in addition to this first aspect of the present inventive concept, according to a second, essential aspect of the present invention Be provided invention that the fuel line branches off from a guided to the engine fuel supply line downstream of a low pressure pump and upstream of a high pressure pump of a high-pressure fuel injection device. With such, measure explicitly claimed separately, measure according to the invention can advantageously account for a separate feed pump for supplying the fuel to the nozzle element, since an already existing low pressure pump is used in an advantageous dual function to promote the fuel via the fuel line in the direction of the nozzle member. This low-pressure pump of a high-pressure injection device, which is also called a prefeed pump, raises the fuel pressure in the fuel supply line to preferably approximately 5 to 20 bar before it is increased to up to 2,500 bar via the high-pressure pump. This pressure of the prefeed pump is sufficient for metering into the exhaust tract, so that the fuel is advantageously removed at this point.

The compressed air required for the process can be generated by a compressor. Such a compressor is z. B. in commercial vehicles anyway, z. B. in conjunction with a pneumatic brake system. This makes it advisable to remove the compressed air from an already existing on the vehicle compressor. Alternatively or additionally, in turbocharged engines, the compressed air can also be taken downstream of the compressor of the charging group. This eliminates the need for vehicles without compressed air compressor to install a compressor specifically for the addition of the hydrocarbon for the preferred particle filter regeneration.

The nozzle element itself can be arranged directly on the exhaust pipe or within the exhaust pipe. The arrangement in the exhaust pipe is only possible by the possibility of cooling with compressed air. Without these, there would be coking within the nozzle or in a connecting line between a nozzle and an exhaust pipe of the exhaust line.

According to claim 6, the at least one of the fuel line and the compressed air line associated control element according to the invention controlled by the control and / or regulating device that the nozzle element in a Kraftstoffzudosierphase for a predetermined time fuel or a fuel / compressed air mixture is supplied. Subsequently, after completion of the fuel metering phase in a compressed-air phase, exclusively compressed air is supplied to the nozzle element for a predetermined time. With such a process management, the remaining fuel in the nozzle can be safely blown out and thus the clogging of a nozzle element by coking of the fuel can be reliably avoided.

In the regeneration pauses, the compressed air supply is usually deactivated in order to keep the compressed air requirement low. However, this has the consequence that the nozzle element is exposed to the high exhaust gas temperatures. This can lead to the start of the fuel addition to the particle filter regeneration briefly still very high temperatures in and on the nozzle element present, which can lead to a coking of the fuel. Therefore, it is useful to turn on the compressed air prior to activation of the fuel addition and thereby lower the nozzle temperature to a level where coking is no longer possible.

If the cooling effect of the fuel during the regeneration phase is insufficient to reliably prevent coking in the nozzle, a fuel / compressed air mixture is added for safety. Otherwise, the addition of compressed air during the regeneration phase and the metered addition of fuel can be dispensed with.

The invention will be explained in more detail with reference to a drawing.

Fig. 1

schematisch ein Blockschaltbild einer erfindungsgemäßen Vorrichtung zur Eindüsung von Kraftstoff in den Abgasstrang einer Brennkraftmaschine, und

Fig. 2

schematisch eine alternative Ausgestaltung einer erfindungsgemäßen Vorrichtung zur Eindüsung von Kraftstoff in den Abgasstrang einer Brennkraftmaschine.

Show it:

Fig. 1

schematically a block diagram of a device according to the invention for the injection of fuel into the exhaust line of an internal combustion engine, and

Fig. 2

schematically an alternative embodiment of an inventive device for injecting fuel into the exhaust line of an internal combustion engine.

Fig. 1 1 schematically shows a block diagram of a first embodiment according to the invention of a device 1 for injecting fuel into the exhaust gas line 2 of an internal combustion engine 3.

This device has an intake air line 6 leading to a compressor 4 of an exhaust-gas turbocharger 5, via which intake air is led to the compressor 4. The compressed, sucked air then passes through a turbocharger compressed air line 7 to the internal combustion engine 3. From the internal combustion engine 3 is an exhaust pipe 8 from which directs the exhaust gas to a turbine 9 of the exhaust gas turbocharger 5. Downstream of the exhaust gas turbocharger 5, a further exhaust gas line 10 is provided, into which an oxidation catalytic converter 11 and a particle filter 12 are integrated.

The fuel supply of the internal combustion engine 3 via a high-pressure injector 13, the downstream of a fuel tank 14, first a low-pressure pump 15 and then further downstream of a high pressure pump 16 includes. Both the low-pressure pump 15 and the high-pressure pump 16 are integrated in a fuel supply line 17 led from the fuel tank 14 to the engine 3.

Downstream of the low pressure pump 15 and upstream of the high pressure pump 16 branches from the fuel supply line 17 from a fuel line 18, in an actuatable by means of a control and / or regulating device 19 according to specifiable parameters metering valve 20 is integrated.

In this fuel line 18 opens a branched from the turbocharger compressed air line 7 to the compressor 4 compressed air line 21 such that they form a single, common supply line 22 to a nozzle member 23, the nozzle head 24 protrudes into the exhaust pipe 10 of the exhaust line 2. In the compressed air line 21 a controllable with the control and / or regulating device 19 according to predetermined parameters valve element 25 is integrated.

Such a device 1 has a number of advantages: For example, the nozzle element 23 together with the nozzle head 24 can be of relatively simple construction since the pressurization of the nozzle element with compressed air and / or fuel takes place exclusively via the single supply line 22 in each operating phase. Complex double-tube nozzle element configurations with a multiplicity of valve elements and branch channels for the flow connection of air and fuel lines can thus advantageously be dispensed with here.

Another particular advantage is that only a single compressed air line 21 is provided here, which branches off from the fresh air side of the supply line 7, so that the structural complexity of the compressed air supply to the WO 2007/091969 is significantly reduced.

Another particularly preferred advantage of the present invention, which as well as the single supply line to the nozzle member 23 is expressly claimed separately and independently of the feature of the single supply line 22, is located in the branch of the fuel line 18 downstream of the low-pressure pump 15, the dosing valve 20 open has a sufficient delivery pressure to promote fuel via the fuel line 18 to the nozzle member 23.

If particle regeneration is now carried out with such a device 1 according to the invention, compressed air is supplied to the nozzle element 23 in a first compressed-air phase for a predetermined time, according to a particularly preferred process control, before the actual metering of fuel. In this compressed air phase, the metering valve 20 is closed and the valve element 25 is opened.

Subsequently, the nozzle member 23 in a Kraftstoffzudosierphase for a predetermined time fuel or - at particularly high temperatures - fed to a fuel / compressed air mixture, including in the former case the metering valve 20 is opened and the valve member 25 is closed, in the second case, however, opened both valves become.

In order to clean the nozzle element 23 of fuel after this fuel metering phase as the actual regeneration phase, it is again supplied with compressed air in a further, second compressed-air phase for a predetermined time, for which the valve element 25 is opened and the metering valve 20 is closed.

With such a metered addition of fuel into the exhaust pipe 10, a particulate filter regeneration can then take place in the manner described at the outset in the introduction to the description.

In the Fig. 2 an alternative embodiment according to the invention of a device 1 for injecting fuel into an exhaust line 2 of an internal combustion engine 3 is shown, which is substantially identical to the device according to the embodiment of the Fig. 1 is formed, so that reference is made only to the differences below. In contrast to the embodiment according to Fig. 1 is instead of the branching from the supply line 7 to the compressor 4 compressed air line 21 one of a compressed air side of a compressor 26 of a z. B. branch off pneumatic brake system Compressed air line 21 'is provided, over in the previously in connection with the execution of Fig. 1 already described way the compressed air supply takes place. The operation of this device 1 according to Fig. 2 otherwise corresponds to that of Fig. 1 , so that reference is made to avoid repetition of the above statements made in this regard, especially with regard to the aforementioned advantages.

In principle, there would also be the possibility of the compressed air line 21 'of the Fig. 2 also in the compressed air line 21 of the embodiment according to Fig. 1 to let open, in the area of the valve element 25, which would then be designed accordingly as a multi-way valve. In such a structure, however, the structural complexity is greater than in the two in the Fig. 1 and the Fig. 2 illustrated embodiments, each with a single compressed air line.

Claims (6)

1. Device (1) for spraying fuel into the exhaust section of an internal combustion engine (3), in particular for regenerating a particle filter, with a fuel line (18) and with a compressed air line (21; 21') which is coupled thereto, which fuel line (18) and compressed air line (21; 21') are guided to a nozzle element (23) which is arranged on or in the exhaust section, wherein the compressed air line (21; 21') branches off downstream of a compressor (4) of a turbocharger (5) and/or is connected fluidically to the pressure side of a compressor (26), and having at least one control element which can be actuated by means of an open-loop and/or closed-loop control device (19) and by means of which the compressed air supply and the fuel supply to the nozzle element (23) can be adjusted in accordance with predefined open-loop and/or closed-loop control parameters, characterized in that the at least one compressed air line (21; 21') is combined upstream of the nozzle element (23) with the fuel line (18) in such a way that said compressed air line (21; 21') and fuel line (18) form a single common feed line (22) which is guided to the nozzle element (23), and in that the fuel line (18) branches off from a fuel supply line (17) guided to the internal combustion engine (3), downstream of a low-pressure pump (15), and branches off upstream of a high-pressure pump (16) of a fuel high-pressure injection device (13).
2. Device according to Claim 1, characterized in that at least one catalytic converter (11) for oxidizing hydrocarbons and at least one particle filter (12) are arranged downstream of the spraying point in the exhaust section (2).
3. Device according to Claim 1 or 2, characterized in that a metering valve (20) which can be actuated with an open-loop and/or closed-loop control device (19) in accordance with the predefined open-loop and/or closed-loop control parameters and forms a control element is arranged in the fuel line (18).
4. Device according to one of Claims 1 to 3, characterized in that the compressed air line is embodied as a single compressed air line either by means of a compressor compressed air line (21') coming from a compressor (20) of an air supply system or by means of a turbocharger compressed air line (21) coming from a compressor side of a turbocharger (5).
5. Device according to Claim 4, characterized in that a valve element (25) which can be actuated with an open-loop and/or closed-loop control device (19) in accordance with predefined control parameters and which forms a control element is arranged in the compressor compressed air line (21') or in the turbocharger compressed air line (21).
6. Method for operating a device (1) for spraying fuel into the exhaust section of an internal combustion engine (3), in particular for regenerating a particle filter, according to one of the preceding Claims 1 to 5, characterized

   - in that the at least one control element (20, 25) which is assigned to the fuel line (18) and to the compressed air line (21; 21') is therefore actuated by means of the open-loop and/or closed-loop control device (19),

   - in that fuel or a fuel/compressed air mixture is fed to the nozzle element (23) for a predefined time in a fuel metering phase,

   - in that after the conclusion of the fuel metering phase compressed air is fed exclusively to the nozzle element (23) in a compressed air phase for a predefined time, and

   - in that before the start of the metering of fuel compressed air is fed exclusively to the nozzle element (23) in a compressed air phase for a predefined time.

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