DE102010033038A1 - System for injecting reducing agent into effluent stream of e.g. diesel engine of motor vehicle, has electrical heating element that is arranged between reducing agent pump and nozzle for vaporizing reducing agent - Google Patents

Abstract

The system has reducing agent pump (1) that is used to convey the reducing agent stored in reducing agent tank. A nozzle (3) is connected to pressure side of reducing agent pump through spacer (2) for injecting the reducing agent into effluent stream of combustion engine. An electrical heating element (4) is arranged between reducing agent pump and nozzle for vaporizing the reducing agent. An independent claim is included for method for controlling injection of reducing agent into effluent stream of combustion engine.

Description

The invention relates to a Reduktionsmitteldosiersystem for injection of a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering system with a reducing agent tank connectable / connected, removed from the reducing agent and conveyed by a reducing agent pump, wherein at least one nozzle is arranged with the pressure side of the reducing agent pump is connected via a reducing agent line and via which the reducing agent is injected into the exhaust gas stream.

Furthermore, the invention relates to a method for controlling a metering system for metering and injecting a reducing agent into the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering system is connected to a reducing agent tank, removed from the reducing agent and conveyed by a reducing agent pump, wherein at least one nozzle is arranged, which is connected to the pressure side of the reducing agent pump via a reducing agent line and via which the reducing agent is injected into the exhaust gas stream

Selective Catalytic Reduction (SCR) catalysts are used to reduce the NOx emissions of diesel engines, combustion plants, incinerators, industrial plants, and the like. For this purpose, a reducing agent is injected into the exhaust system with a metering device. The reducing agent used is ammonia or an ammonia solution or another reducing agent.

Since the entrainment of ammonia in vehicles is safety-critical, urea is in aqueous solution with usually 32.5% urea content according to DIN 70070 , the so-called AdBlue, used. In the exhaust gas, the urea decomposes at temperatures above 150 ° Celsius into gaseous ammonia and CO ₂ . Parameters for the decomposition of the urea are essentially time (evaporation and reaction time), temperature and droplet size of the injected urea solution. In these SCR catalysts, selective catalytic reduction (SCR) reduces the emission of nitrogen oxides by about 90%.

Characterized in that the commonly used 32.5% urea solution according to DIN 70070 , the so-called AdBlue, freezes at about -11 ° C, can be damaged due to the expansion of the aqueous solution or the water content of the solution components of the dosing. The problem of freezing also concerns any other aqueous reducing agent solution than the 32.5% urea solution often used as a reducing agent.

In order to avoid damage to components of the metering system due to expansion due to freezing of the reducing agent solution, the reducing agent-carrying components are to be cleaned of the solution during metering pauses.

From the DE 10 2008 013 960 A1 It is known to clean by means of compressed air, the reducing agent leading components after completion of the dosage. The disadvantage here is that this procedure requires the presence of a compressed air supply or the arrangement of a compressor.

The object of the invention is to further form a Reduktionsmitteldosiersystem of the type mentioned above and a method for controlling a metering system of the type mentioned in that a cleaning of the endangered in the case of freezing of reducing agent areas of the metering after completion of the dosage of reducing agent solution little effort is possible and damage to components of the dosing is prevented.

This object is achieved by a Reduktionsmitteldosiersystem according to claim 1 and by a method for controlling a metering system according to claim 7. Advantageous developments of the invention are specified in the respective dependent claims.

The terms reducing agent metering system or metering system are used synonymously in the sense of this description. The term reducing agent solution or reducing agent includes any reducing agent suitable for selective catalytic reduction, preferably a urea solution according to DIN 70070 for use. However, the invention is not limited thereto.

Particularly advantageous in the Reduktionsmitteldosiersystem for injecting a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering is connected to a reducing agent tank / connected, removed from the reducing agent and conveyed by a reducing agent pump, wherein at least one nozzle is arranged with the pressure side of the reducing agent pump is connected via a reducing agent line and via which the reducing agent is injected into the exhaust gas flow, it is that between the reducing agent pump and the nozzle in the reducing agent line at least one heating element is arranged, by means of which the reducing agent is locally vaporizable.

According to the invention, a heating element is arranged in the reducing agent line between the reducing agent pump and the nozzle. The term of the reducing agent pump generally encompasses any usable delivery pump, metering pump, delivery unit or metering unit.

A small portion of the urea solution in the line is heated by a local heating element, so that an increased pressure is established by evaporation of ammonia from the solution and / or evaporation of the aqueous solution. By opening the metering, the injection valve or automatically with always open to the exhaust side piping systems, the aqueous solution is pumped into the exhaust system. Alternatively or cumulatively, the reducing agent can be conveyed back via one or more further valves via a return line into the reducing agent tank. The heating element is preferably arranged in the vicinity of the delivery unit of the solution. When evaporating, the gas volume increases by about a factor of 1000. If the heater is switched off, the medium condenses and creates a negative pressure. With this air is sucked into the system. This can be done via the open pipe from the exhaust or a separate check valve. It is possible to specifically ventilate only parts of the line, depending on the arrangement of the check valve.

Preferably, the heating element is an electrical heating element. In an electric heating element, a connection and disconnection of the heating element can be done in a simple manner via a control unit of the dosing.

In a preferred embodiment, a check valve is arranged in the reducing agent line between the heating element and the nozzle.

Via this check valve, exhaust gas from the exhaust tract is introduced into the reducing agent line via the nozzle at the moment when the heating element is switched off and condenses the residual amount of reducing agent solution remaining in the reducing agent line and correspondingly reduces its volume, whereby a negative pressure in the line to the environment arises.

Alternatively or cumulatively, a check valve can be arranged in the reducing agent line between the heating element and the nozzle, via which air can be introduced into the reducing agent line, so that at the moment in which the heating element is switched off and the remaining amount of vaporized reducing agent solution remaining in the reducing agent line condenses again the resulting negative pressure air is sucked in and introduced into the reducing agent line. This may be ambient air or else compressed air of a compressed air supply system, if the reducing agent metering system is in any case a compressed air supply in which the reducing agent solution is atomized by means of compressed air. The simplest variant results when ambient air is drawn in via this check valve and introduced into the reducing agent line.

In a preferred embodiment, a return line opening into the reducing agent tank branches off from the reducing agent line between heating element and nozzle, a switching valve being arranged in the return line.

About this switching valve and the return line can be promoted alternatively or cumulatively to a blowing out of the reducing agent in the exhaust gas reducing agent in the reducing agent tank back.

In a particularly preferred embodiment, a control device for controlling components of the metering system is arranged as a function of operating parameters of the internal combustion engine, wherein at least the reducing agent pump and the heating element are actuated by means of the control device.

By such a control unit can thus on the one hand, the dosage of the reducing agent in response to operating parameters of the engine and after switching off the engine, when the dosage is terminated, can be done via the control unit, a short-term connection in the reducing agent line between the reducing agent pump and nozzle heating element, so that the reducing agent solution is locally evaporated and the volume reduction increases the residual reducing agent via the nozzle into the exhaust gas tract.

Particularly advantageous in the inventive method for controlling a metering system for metering and injection of a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering system is connected to a reducing agent tank, removed from the reducing agent and conveyed by a reducing agent pump, wherein at least one nozzle is arranged, which is connected to the pressure side of the reducing agent pump via a reducing agent line and via which the reducing agent is injected into the exhaust gas stream, it is that when interrupting or ending the dosage, an intervention at least one between the Reduction agent pump and the nozzle disposed in the reducing agent line heating element takes place, by means of which the reducing agent is locally evaporated, wherein the reduction in volume due to the local evaporation, the reductant located in the reducing agent line blown through the nozzle and / or is conveyed back via a return line in the reducing agent tank.

Preferably, after the blowing out of the reducing agent from the reducing agent line, the heating element is switched off, whereby a negative pressure is generated by the condensation of the reducing agent still in the reducing agent line and the concomitant reduction in volume, so that via a valve arranged between the heating element and the nozzle check valve exhaust via the nozzle sucked and introduced into the reducing agent line.

Alternatively or cumulatively, the heating element is switched off after the blowing out of the reducing agent from the reducing agent line, whereby a negative pressure is generated by the condensation of the reducing agent still in the reducing agent line and the concomitant reduction in volume, so that via a non-return valve arranged between the heating element and the nozzle in particular ambient air or compressed air of a compressed air supply of the dosing, sucked and introduced into the reducing agent line.

It can thus be initiated via one or more check valves in the reducing agent line after switching off the heater and condensation of remaining in the reducing agent reductant residual gas from the exhaust gas and / or air, in particular ambient air and / or compressed air.

Thus, a small portion of the urea solution in the line is locally heated by a local heating element, so that an increased pressure sets by evaporation of ammonia from the solution and / or evaporation of the aqueous solution due to the volume increase associated with the evaporation. By opening the metering, the injection valve or automatically with always open to the exhaust side piping systems, the aqueous solution is pumped into the exhaust system. Alternatively or cumulatively, the reducing agent can be conveyed back via one or more further valves via a return line into the reducing agent tank. The heating element is preferably arranged in the vicinity of the delivery unit of the solution. When evaporating, the gas volume increases by about a factor of 1000. If the heater is switched off, the medium condenses and creates a negative pressure. With this air is sucked into the system. This can be done via the open line from the exhaust system or a separate check valve. It is possible to specifically ventilate only parts of the line, depending on the arrangement of the check valve.

Preferably, the reducing agent line is preheated by means of heating provided for the winter operation of the metering system before and / or during the purging of the reducing agent from the reducing agent line in order to avoid condensation of the vapor in the reducing agent line during the heating process by means of the heating element, thus a larger amount of reducing agent blow.

Two embodiments of the invention are illustrated in the figures and are explained below. Show it:

1 a first embodiment of a Reduktionsmitteldosiersystems;

2 a second embodiment of a Reduktionsmitteldosiersystems.

In the 1 and 2 identical components are provided with the same reference numerals.

The reducing agent metering system according to 1 is used for injection of a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction. From a reducing agent tank, not shown, in which on board a commercial vehicle aqueous urea solution with 32.5% urea content is carried, the urea solution is removed for injection and by means of the reducing agent pump 1 promoted.

About the reducing agent line 2 the delivered reducing agent reaches the nozzle 3 , About the nozzle 3 the reducing agent is injected and atomized into the exhaust gas flow of the engine of the commercial vehicle and serves within a downstream not shown in the exhaust gas flow SCR catalyst for the reduction of nitrogen oxides.

To the reducing agent line 2 in dosing breaks or after completion of the dosage of the reducing agent to free is in the reducing agent line 2 a heating element 4 arranged, by means of which, after completion of the dosing remaining in the reducing agent line residual amount of reducing agent solution in the region of the heating element 4 locally heated and localized by heating is evaporated locally. As a result of this evaporation of the reducing agent solution, the volume is locally increased by about a factor of 1000, so that in the reducing agent line 2 remaining Reducing agent through the nozzle 3 is pushed out into the exhaust system.

After a short switch-on time of the heating element 4 the heating element is switched off again so that the remainder of the reducing agent solution, which is in gas phase within the reducing agent line 2 remained, condensed and its volume greatly reduced. Due to the resulting negative pressure in the reducing agent line 2 gets over the nozzle 3 Aspirated exhaust gas from the exhaust tract of the commercial vehicle and thereby passes into the reducing agent line 2 ,

The reducing agent line 2 is now freed from the reducing agent solution and filled to a minimum residual amount of recondensed reducing agent solution with exhaust gases and it can occur even at low ambient temperatures no frost damage by freezing of reducing agent solution.

The second embodiment according to 2 shows a further embodiment of a Reduktionsmitteldosiersystem, also with a feed pump 1 , Starting from the pressure side of the feed pump 1 the further transport of the reducing agent solution takes place via the reducing agent line 2 to the nozzle 3 , About the nozzle 3 the reducing agent solution is injected into the exhaust tract of a commercial vehicle and atomized.

At the in 2 illustrated embodiment is within the reducing agent line 2 near the conveyor unit 1 also a heating element 4 with the same operation as previously in the embodiment according to 1 explained, arranged.

Furthermore, in the embodiment according to 2 check valves 5 and 6 arranged. In non-illustrated embodiments, the check valves 5 respectively. 6 alternatively provided to each other.

About the check valve 5 A suction of exhaust gas from the exhaust system via the nozzle 3 into the reducing agent line 2 at the moment, as explained above, after local evaporation by means of the heating element 4 the reducing agent is blown out and by the recondensation of the remaining residue in the reducing agent line 2 a negative pressure relative to the exhaust tract arises.

About the check valve 6 there is an intake of ambient air in the moment in which the heating element 4 is turned off and in the reducing agent line 2 Remaining residual amount of reducing agent solution recondensed and thereby creates a negative pressure in the reducing agent to the environment.

It is thus possible to use the alternative or cumulative non-return valves 5 respectively. 6 Aspirate exhaust gas from the exhaust system and / or ambient air and into the reducing agent line 2 so that it is frost-resistant even at low ambient temperatures, since there is no or only a minimal residual amount of reducing agent solution in the reducing agent line 2 more is located.

In an alternative, not shown, also via the check valve 6 Compressed air to be supplied to a compressed air system, since in many cases a compressed air supply is provided anyway, by means of compressed air, the reducing agent, which via the nozzle 3 injected into the exhaust tract, to atomize. However, it is quite sufficient ambient air through the check valve in the reducing agent line 2 initiate.

Depending on the arrangement of the check valve, it is also possible, only parts of the reducing agent line 2 specifically to ventilate. Preferably, the heating element 4 near the reducing agent pump 1 arranged as far as possible parts of the reducing agent line 2 by evaporating ammonia from the solution and / or by evaporating the aqueous solution from that in the reducing agent line 2 to free the remaining residue of reducing agent.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008013960 A1 [0007]

Cited non-patent literature

• DIN 70070 [0004]
• DIN 70070 [0005]
• DIN 70070 [0010]

Claims (10)

Reduktionsmitteldosiersystem for injecting a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering system with a reducing agent tank is connected / connected, taken from the reducing agent and by means of a reducing agent pump ( 1 ), wherein at least one nozzle ( 3 ) is arranged, which with the pressure side of the reducing agent pump ( 1 ) via a reducing agent line ( 2 ) and via which the reducing agent is injected into the exhaust gas stream, characterized in that between the reducing agent pump ( 1 ) and the nozzle ( 3 ) in the reducing agent line ( 2 ) at least one heating element ( 4 ) is arranged, by means of which the reducing agent is locally vaporizable. Dosing system according to claim 1, characterized in that it is in the heating element ( 4 ) around an electric heating element ( 4 ). Dosing system according to claim 1 or 2, characterized in that in the reducing agent line ( 2 ) between heating element ( 4 ) and nozzle ( 3 ) a check valve ( 5 ) is arranged. Dosing system according to one of the preceding claims, characterized in that in the reducing agent line ( 2 ) between heating element ( 4 ) and nozzle ( 3 ) a check valve ( 6 ) is arranged, via the air, in particular ambient air or compressed air of a compressed air supply of the dosing, in the reducing agent line ( 2 ) can be introduced. Dosing system according to one of the preceding claims, characterized in that of the reducing agent line ( 2 ) between heating element ( 4 ) and nozzle ( 3 ) branches off a receding into the reducing agent tank return line, wherein in the return line, a switching valve is arranged. Dosing system according to one of the preceding claims, characterized in that a control device for controlling components of the dosing system in dependence on operating parameters of the internal combustion engine is arranged and by means of which at least the reducing agent pump ( 1 ) and the heating element ( 4 ). Method for controlling a metering system for metering and injecting a reducing agent into the exhaust stream of an internal combustion engine for selective catalytic reduction, wherein the metering system is connected to a reducing agent tank, taken from the reducing agent and by means of a reducing agent pump ( 1 ), wherein at least one nozzle ( 3 ) is arranged, which with the pressure side of the reducing agent pump ( 1 ) via a reducing agent line ( 2 ) and via which the reducing agent is injected into the exhaust gas stream, characterized in that when interrupting or terminating the metering, an activation of at least one between the reducing agent pump ( 1 ) and the nozzle ( 3 ) in the reducing agent line ( 2 ) arranged heating element ( 4 ) takes place, by means of which the reducing agent is locally evaporated, whereby the increase in volume due to the local evaporation in the reducing agent line ( 2 ) reducing agent via the nozzle ( 3 ) is blown out and / or conveyed back via a return line in the reducing agent tank. A method according to claim 7, characterized in that after blowing out of the reducing agent from the reducing agent line, the heating element ( 4 ) is switched off and a negative pressure is generated by the condensation of the reducing agent still located in the reducing agent reducing agent, so that via a between the heating element ( 4 ) and the nozzle ( 3 ) arranged check valve ( 5 ) Exhaust via the nozzle ( 3 ) is sucked and introduced into the reducing agent line. A method according to claim 7 or 8, characterized in that after blowing out of the reducing agent from the reducing agent line, the heating element ( 4 ) is switched off and a negative pressure is generated by the condensation of the reducing agent still located in the reducing agent reducing agent, so that via a between the heating element ( 4 ) and the nozzle ( 3 ) arranged check valve ( 6 ), In particular ambient air or compressed air of a compressed air supply of the dosing, sucked and introduced into the reducing agent line. Method according to one of claims 7 to 9, characterized in that the reducing agent line is pre-heated by means provided for the winter operation of the metering before and / or during the blowing out of the reducing agent from the reducing agent line to a condensation of the vapor in the reducing agent line during the heating process by means of the heating element ( 4 ) to avoid.

Images