WO2020079095A1

WO2020079095A1 - Measuring a catalytic function of an object for cleaning an exhaust gas of an internal combustion engine

Info

Publication number: WO2020079095A1
Application number: PCT/EP2019/078116
Authority: WO
Inventors: Hanspeter Mayer
Original assignee: Ceramex Ltd
Priority date: 2018-10-16
Filing date: 2019-10-16
Publication date: 2020-04-23
Also published as: EP3640445A1

Abstract

A method for measuring a catalytic function of an object suitable for cleaning an exhaust gas of an internal combustion engine, wherein a test gas which contains nitrogen oxides and/or hydrocarbons, is moved through the object and a concentration of at least one constituent of the test gas is measured before and after flowing through the object. The object is additionally charged with a reactant which causes a catalytic reaction in the object to reduce NOx in the test gas, to determine the catalytic function of the object through the action of the reactant and/or an HC light-off temperature.

Description

MEASURING A CATALYTIC FUNCTION OF AN OBJECT FOR CLEANING AN EXHAUST GAS OF AN INTERNAL COMBUSTION ENGINE

The invention relates to a method for measuring a catalytic function of an object suitable for cleaning an exhaust gas of an internal combustion engine, in particular of a catalytic converter or a particulate filter for a motor vehicle or a work machine, wherein a test gas which contains nitrogen oxide and/or hydrocarbon, is moved through the object and a concentration of at least one constituent of the test gas is measured before and after flowing through the object.

The invention further relates to a device for measuring a catalytic function of an object suitable for cleaning an exhaust gas of an internal combustion engine, in particular of a catalytic converter for a motor vehicle wherein with the device a test gas can be transported through the object and at least one constituent of the test gas can be measured before and after passing the object.

In order to clean exhaust gases of internal combustion engines it is known from the prior art to insert filters and catalytic converters into an exhaust train. In order to reduce the nitrogen oxides in an exhaust gas from by way of example a diesel engine so that the increasingly stringent exhaust gas standards can be observed, denitrification catalysers or storage catalysers are used inter alia in which nitogen oxides are reduced by means of selective catalytic reduction. Alternatively, or additionally, a three-way catalyser can also be used.

Catalytic converters of this kind have as a result of ageing effects with increasing service life or operating time a reduced catalytic reactivity so that certain nitric oxide threshold values can no longer be observed after a specific ageing. With catalytic converters of this kind, in order to reduce the nitrogen oxides urea or an aqueous solution containing urea, which is known by the trade name AdBlue is mixed in in order by forming ammonia to reduce nitrogen oxides by means of selective catalytic reduction.

In order to achieve with motor vehicles having correspondingly aged catalytic converters nitrogen oxide threshold values according to current standards, by way of example the exhaust gas standard Euro 6c, it is thus necessary to either replace the aged catalysers by new ones or to reprocess the aged catalysers so that they have a catalytic reactivity or catalytic function which is sufficient to reach the threshold value and at the same time so that no ammonia slip occurs. Up until now there has however been no method with which such evidence can be efficiently carried out.

The invention addresses this. The object of the invention is to provide a method of the type mentioned at the beginning with which a catalytic function of a corresponding object can be measured in a particularly efficient way.

Furthermore, a device is to be provided for carrying out such a method.

The first object is achieved by a method of the type mentioned at the beginning in which the object is charged additionally with a reactant which cause a catalytic reaction in the object for reducing the nitrogen oxide in the test gas in order to determine the catalytic function of the object under the action of the reactant and/or an HC-light-off temperature.

It was recognized within the scope of the invention that the catalytic function of a reprocessed object, which for reprocessing is dismantled from an exhaust tract of a motor vehicle in which it was inserted for the after treatment of exhaust gas, can be analysed in simple manner even outside of the exhaust tract of the motor vehicle by way of example in a test device, whereby the object is charged on the one hand with a test gas which contains nitrogen oxide and/or hydrocarbons, and on the other hand with the reactant which causes or intensifies a catalytic reaction in the catalyser for reducing the nitrogen oxide in the test gas. Alternatively or additionally an HC-light-off temperature or a hydrocarbon conversion can be determined in the object at different temperatures through the action of the reactant in order to be able to determine particularly accurately the catalytic function of the object and to accurately characterise the object. The HC-light-off temperature is determined as that temperature from which a significant conversion of the hydrocarbons takes place in the catalyser. By way of example a 50%-light-off-point can be determined which corresponds to a temperature from which 50% of the pollutant substances, in particular 50% of the hydrocarbons supplied in the catalyser are converted. With the method according to the invention the hydrocarbon- or HC- conversion can thus be judged at different temperatures under the action of the reactant in order to determine the exhaust gas threshold values which can be achieved with the object when used in a motor vehicle. An aged object for exhaust cleaning such as a catalytic converter has by way of example a higher light-off temperature than a new or reprocessed object. By determining the light-off temperature or a 50% light-off point it is thus possible to classify the object for further use, wherein higher quality objects naturally have a lower light-off temperature or a 50% light-off point at a lower temperature.

It is thus then possible by way of example with a device in which the object is arranged after reprocessing for testing the catalytic function to check in a simple and efficient manner whether a catalytic function is provided during a renewed use of the object in a motor vehicle by using a reactant such as by way of example urea or AdBlue. It is thereby efficiently avoided that reprocessed objects are used again in motor vehicles which despite the reprocessing do not have a sufficient catalytic reactivity or were not sufficiently reprocessed, by way of example because these are damaged in such a way that a better reprocessing is not possible. An important improvement is thus reached compared with the prior art according to which it may happen that an insufficient catalytic function of a reprocessed object is only discovered when used in the motor vehicle through a corresponding exhaust gas measurement, which is connected however with high expense and corresponding costs.

It is expedient if the object is first charged only with the test gas, preferably for at least ten seconds, more particularly for at least one minute, after which the object is charged additionally with the reactant preferably for at least ten seconds, more particularly for at least one minute, wherein a time path of a catalytic reaction in the object is detected, more particularly up to at least ten seconds, preferably up to at least one minute, after ending the charging of the object with the reactant. A function of the object can thereby be determined particularly accurately. A selective catalytic reduction in the catalyser is thus always used only after a certain time after which the reactant was introduced into the catalyser, because the reactant has first to be stored in a coating and/or a substrate of the catalyser after which the corresponding reactions take place in the coating or the substrate. With the method according to the invention it is thus possible to detect the storage effects of the test gas in the coating and/or the substrate of the object which is to be tested. If the temperature has changed, then the storage or extraction of the reactant, more particularly ammonia, in the coating can be measured. By measuring the relevant constituents of the test gas, in particular of the nitrogen oxides in the test gas before and after passing through the object or in a flow path before and after the object it is further possible to determine which catalytic reactivity can still be reached after ending the mixing of the reactant, normally urea or ammonia, with the object. It is thus possible to assess which reactant quantity is required when using the object in a motor vehicle in order to achieve specific exhaust gas threshold values.

It has been proved expedient that nitrogen oxides, in particular nitrogen monoxide and/or nitrogen dioxide, are measured both in a supply line through which the test gas is applied to the object, and also in a discharge line through which the test gas flows after passing the object. By measuring nitrogen oxides in a stream of test gas before and after the object it is easily possible to determine which proportion of the nitrogen oxides was reduced in the object with selective catalytic reduction in order to conclude on the catalytic function of the object.

It has been proved expedient that nitrogen oxides are measured, preferably continuously, in the supply line and in the discharge line before, during and after charging the object with the reactant. Preferably a time path of nitrogen oxides both in the supply line and also in the discharge line, as well as a time path of adding in the reactant, which is normally applied together with the test gas, are measured in order to conclude on a catalytic function of the object. As a rule, a concentration of the reactant as well as of the nitrogen oxides are measured both in the supply line through which the test gas and the reactant are supplied to the object, and also in the discharge line through which a gas supplied to the object leaves the object again. A transient measurement is also obviously possible.

Naturally in addition, further gas constituents, which occur in an exhaust gas of an internal combustion engine, can also be applied and measured at the same time with the nitrogen oxides in the supply line and discharge line, by way of example carbon monoxide and hydrocarbons.

It is expedient if the reactant contains ammonia and/or a constituent, more particularly urea, which is suitable for forming ammonia in the object, or consists of ammonia or urea. The reactant can be introduced into the test gas and supplied to the object via a common supply line or can be applied separately to the object. The reactant can also contain methane or consist of methane.

It is advantageously proposed that the reactant is mixed with the test gas prior to charging the object. Normally the reactant and the test gas are applied through a common supply line to the object and are mixed as homogeneously as possible in the supply line.

In order to achieve a homogenous mixing of the normally fluid or gaseous reactant with the test gas prior to charging the object, a mixing device, in particular a mixer for homogenizing the fluid mixture or gaseous mixture, is normally provided in a common supply line via which both the test gas and also the reactant are applied. The mixing device can comprise by way of example a mixing chamber with devices creating flow vortices or turbulences, and/or one or more ventilators. In the case of diesel vehicles, the solvent containing urea, or AdBlue, is normally introduced into the exhaust gas flow and is converted there in particular into ammonia. By suitably mixing the test gas with the reactant it is thus possible with the method according to the invention to achieve a virtual-reality operation and thus to carry out a measurement under approximately real operating conditions, even if the method according to the invention is carried out in a closed housing within the scope of an automated method for cleaning and reprocessing a corresponding object.

The method according to the invention can be carried out basically both on an object installed in an exhaust gas tract of a motor vehicle, and also on an object dismantled from the exhaust gas tract. The method can further also be used with several objects arranged in serial or parallel connection.

It is advantageous if a concentration of ammonia and/or a constituent suitable for forming ammonia, is measured in a reactant supply line through which the object is charged with the reactant, and optionally also in the discharge line through which the test gas flows after passing the object, wherein several measurements are preferably carried out staggered in time in order to determine a time path. As a rule the reactant supply line is also the supply line through which the test gas is applied to the object, so that the measurement of a gas composition in this common supply line can be sufficient in order to determine a composition both of the test gas and also of the reactant or a concentration of nitrogen oxides and ammonia or urea in the gas supplied to the object.

In order to obtain a particularly good assessment on a behaviour of the object during operation in an exhaust tract of a motor vehicle, it is preferred if the object has at least in a partial region during at least a part of the method a temperature which corresponds to a normal operating temperature of the object during the intended use when cleaning an exhaust gas of an internal combustion engine, more particularly 180° C to 600°C. The object is preferably brought to the desired temperature through heated air or a gas of a specific composition, by way of example to prevent exothermic reactions of carbon dioxide or the like. As a rule, the object is brought to the desired temperature before the test gas is applied to the object in order to achieve test results with a low use of test gas. The object, or if only a partial region of the object is examined, the partial region, preferably remains at the desired temperature until the measurement is concluded, more particularly for at least ten minutes.

It is expedient if the test gas is brought to the object at a temperature which corresponds to a normal temperature of an exhaust gas with which the object is charged during the intended operation, in particular 180°C to 600°C, preferably 200°C to 500°C, and more particularly 250°C to 350°C. This ensures particularly conclusive measurement results. The measured object can thus not only be classified according to whether certain exhaust gas threshold values can be reached, but also according to the temperatures at which the exhaust gas threshold values can be reached, particularly as a reactivity of catalysers is normally higher at higher temperatures. It is then possible to conclude on a fuel consumption which is required to reach the exhaust gas threshold values.

The object can be heated by way of example electrically to a corresponding temperature. It can also be proposed that the object is brought to the corresponding temperature through a hot gas, preferably heated air. For this an electric heater can be provided by way of example in a supply line through which a gas is supplied to the object, for the regulated heating of the gas and thus of the object. For regulation purposes a temperature of the object can be detected directly or indirectly, by way of example optically or with one or more sensors attached to the object. A particularly accurate assessment on the actual behaviour can be performed because a catalytic reactivity is dependent on a temperature of the coating.

A regulation can naturally also be provided for introducing a quantity of test gas, which can contain nitrogen oxides and/or hydrocarbons. A deliberate charging of the object with test gas, in particular with nitrogen oxides and/or hydrocarbons, can thereby be carried out in order to be able to determine the behaviour in real operation with particular accuracy.

In order to obtain a particularly accurate assessment on a catalytic function of the object, it can be proposed that a temperature of the object is changed during the measurement, in particular by at least 10°C. A catalytic function of the object can thereby also be determined at different temperatures. Furthermore, a particularly short test time can thereby also be achieved if the object is analysed during heating up or cooling down. Through a change in temperature over the time it is possible to detect a characteristic injection and withdrawal of gases into the object or into a coating or a substrate of the object.

In order to determine a catalytic function of individual partial regions of the object it is preferably proposed that the test gas is supplied to the object via a supply line with which only a partial region of an end side of the object is charged, in order to detect a catalytic function of a partial region of the object. The partial region can comprise by way of example less than 80%, in particular less than 50%, preferably less than 10% of surface of an end side of the object. Filters and catalysers used in a motor vehicle generally have a more or less circular cross-section and a diameter of less than 40 cm. The supply line is thus preferably designed at the end for bringing gas supplied in the supply line to a correspondingly small region of by way of example less than 160 cm². By measuring the nitrogen oxides and the reactant in the supply line as well as at a position downstream of the object it is thus possible to determine the catalytic function of individual partial regions. It can then be established whether and where applicable which partial region of the object has still not been sufficiently reprocessed in order to regenerate specific individual partial regions, so that an efficient method of reprocessing is ensured.

It is evident that the test gas can basically be applied through any end side of the object and in any flow direction through the object. It could basically also be proposed that the test gas is applied through both end faces simultaneously.

Normally it is proposed that the test gas is supplied sequentially to different partial regions of the object in order to determine a catalytic function of the complete object. For this the supply line for the test gas can be designed to be movable relative to one end side of the object, in particular movable by a multi-axle movable robot or a Cartesian robot relative to the object. The supply line is preferably freely movable in all spatial directions, in particular in a plane parallel to the end sides of the object, generally of a cylindrical shape, through which gas can be injected into and withdrawn from the object, in order to be able to analyse objects of different sizes.

As a rule, a composition of the gas with which the object is charged and which is normally comprised of a test gas containing air, a nitrogen and/or hydrocarbon for testing a light-off temperature as well as of a reactant in certain time sections, or contains these constituents, is analysed both in the supply line and also in the discharge line with a gas analysis measuring device which can be formed by way of example as a UV spectrometer, as a Fourier Transform infrared spectrometer or as a chemo-electrical measuring cell. A UV spectrometer with a wavelength of 200 nm to 600 nm is preferably used since this spectrum has a high sensitivity to ammonia and the concentration of the relevant constituents of the gas can thus be dissolved very accurately. A device can furthermore also be provided for detecting particles, in particular a particle counter both in the supply line and also in the discharge line in order to detect a particle trap rate of the object.

Judgement on a catalytic function of the object is preferably carried out by detecting one or more function thresholds from measured values of nitrogen oxides before and after the object in conjunction with the supplied amount of reactant and producing a correlation with a function of the object on an engine during proper use of the object in order to be able to conclude from the measured values the function of the object during proper use.

By way of example it is possible to contrast a function threshold from a ratio of nitrogen oxides in the discharge line to nitrogen oxides in the supply line in the case of a defined quantity of reactant supplied and a specific temperature with the exhaust values which are achieved when using the same object in a motor vehicle, in order to be able to attain, particularly in the case of objects of the same type, from the function thresholds determined with the method according to the invention, a reliable assessment on the threshold values which can be reached with the object when used in the motor vehicle. The measurement at a partial region of an object can then also be sufficient to conclude through correlations with objects already measured, such as used or new particulate filters, exhaust gas thresholds which can be reached with the corresponding object and to classify the measured object already after a short examination, by way of example in a test cycle of less than 10 minutes, and to be able to indicate a service life with proper use in a vehicle.

For this it can be proposed that exhaust gases of motor vehicles in which individual reprocessed objects are used, are measured. Furthermore, exhaust gas data of vehicles or of internal combustion engines in general, from the exhaust tract of which one or more objects were dismantled for reprocessing, can also be brought in connection with measured data prior to reprocessing in order to determine a correlation. Measured results from several objects analysed according to the invention are preferably stored in a data base with clear assignment to the object so that it is possible to determine with repeated reprocessing a time path of the function attained. It is then possible through corresponding data to gain a prognosis on an anticipated remaining service life after reprocessing. Thus, immediately after the reprocessing and from the measured function thresholds and the correlation, a classification is possible, good or poor, of the reprocessed object as well as details of an anticipated remaining life span. The catalytic function of a reprocessed object can thereby be determined with high precision within few minutes.

The further object is achieved according to the invention through a device of the type mentioned at the beginning in which in addition to the test gas a reactant can be applied with the device to the object.

The device is normally configured for carrying out a method according to the invention and is used for carrying out a method according to the invention.

The device normally comprises a housing in which the object can be arranged. The housing is as a rule configured so that the object can be positioned between a discharge line and a supply line so that a gas or gas mixture of air, test gas and reactant supplied via the supply line can be moved through the object and then brought substantially entirely into the discharge line. For this the discharge line is preferably configured at the end with a funnel-shaped gas trap with a circumferential seal and via which all the gas emerging from the object is directed into the discharge line.

The supply line has as a rule at the end a seal in order to ensure that the supply line can be press-fitted tight on the object, in particular on an end side of a particulate filter, so that gas emerging from the supply line can be pressed substantially completely through the object, in particular through channels in the particulate filter, and does not flow past the object at the sides. The housing is furthermore preferably configured so that a gas exchange is possible between an interior of the housing and an ambient surrounding substantially only through pipelines connected to the supply line or discharge line. The device can thereby also be arranged in an industrial unit by way of example for cleaning and reprocessing particulate filters or a vehicle workshop without toxic gases flowing into the atmosphere.

The object can normally be positioned in the device so that the test gas flows more or less vertically through the object wherein an alternating flow direction can also be provided in order to determine different catalytic reactivities over a length of the object.

Furthermore, normally a supply line is arranged in a multi-axle movable manner in the object in order to charge a partial region of an end side of the object with test gas and reactant. The supply line can have a seal at the end with which the supply line can be pressed tightly against the object so that it is guaranteed that gas emerging from the supply line flows into the surface of the object defined by the seal and an accurately defined region can be measured. Normally the supply line has at the end a smaller cross-section than the object under investigation, by way of example a particulate filter for a diesel vehicle with a diameter of less than 40 cm.

Furthermore, a heater, more particularly an electric heater, can be provided in the supply line in order to bring the gas applied to the object through the supply line to a predefined temperature, normally 250°C to 500°C so that the object can be at the controlled temperature. Normally the heater can be regulated via a temperature measured at the object so that targeted temperature changes can be produced on the object with the heater.

An object to be investigated, such as a catalytic converter or a particulate filter of a motor vehicle, normally has a plurality of channels which extend between a first end side and a second end side. The test gas as well as the reactant are preferably applied to the object at a first end side and emerge again from the object at a second end side of the object, where applicable after a chemical reaction. The gas mixture which normally consists of air, the test gas and temporarily a reactant such as ammonia, is normally introduced into the object through the supply line which is pressed tightly onto the first end side. As a rule, a circumferential seal is provided at the end on the supply line so that the entire gas transported through the supply line is directed into the object and is transported through the object. The object which is generally designed as a particulate filter can have a porous or gas-permeable configuration.

A by way of example funnel-shaped gas trap with a circumferential seal can be provided on the second end side which is generally arranged opposite the first end side, whereby the seal sealingly surrounds the entire second end surface so that all the gas emerging from one or more channels of the second end side is directed via the gas trap into a discharge line through which the gas can be directed out from the device via a suction system, where applicable to a filter unit or the like. Thus, all the gas emerging from the object at the second end surface is directed through the gas trap into the discharge line, namely independently of in which partial region of the first end surface of the object the supply line is positioned. It is thereby ensured that when analysing the gas transported in the discharge line, any gas can be analysed which had been transported through the object. If the object is supplied with gas through the supply line to only one partial region then using the measurement in the supply line and the discharge line it is possible to determine a catalytic function of the corresponding partial region of the object.

It is expedient if the test gas can be applied via a supply line to the object, with which supply line the test gas can only be applied to a partial region of the object in order to determine a catalytic function of a partial region. With the supply line, the test gas or a mixture of test gas, air and where applicable reactant, can be brought to a defined number of channels of an end side of the object whilst at the same time other channels are not charged with the gas mixture. This is normally achieved with a supply line which has a smaller cross-section than the first end surface and which supply line is surrounded at the end by a seal so that when pressing the supply line onto the first end side only the channels opening inside the seal into the end side are charged with a gas flowing through the supply line, whilst the channels opening into the first end side outside of the seal are not charged with the gas or gas mixture.

A flow speed of the test gas can correspond to the flow speed in the original use, by way of example in an exhaust tract of a motor vehicle in order to obtain comparable spatial speeds and to set similar reaction speeds.

The supply line is normally movable with a positioning device in order to determine catalytic functions of different partial regions in sequence. In order to detect nitrogen monoxide, nitrogen dioxide and the like as well as the reactant, more particularly ammonia, in a gas flow before and after the object, gas analysis measuring devices are normally provided in the supply line and/or in the discharge line. A gas analysis measuring device can be designed in particular as a UV spectrometer with a wavelength of 200 nm to 600 nm in order to detect nitrogen monoxide, nitrogen dioxide and ammonia in a particularly accurate manner. Furthermore temperature sensors can be provided both in the supply line and also in the discharge line. It can also furthermore be proposed that a temperature on a surface of the object is measured, by way of example via an optical measuring process.

BRIEF DESCRIPTION

Further features, advantages and actions of the invention will be apparent from the following exemplary embodiment. In the drawings, to which reference is made:

Fig. 1 shows a diagrammatic view of a device according to the invention;

Fig. 2 shows by way of example time paths of measured values detected in a method according to the invention.

DETAILED DESCRIPTION

Fig. 1 shows a device according to the invention for carrying out a method according to the invention. As can be seen, the device comprises a supply line 2 through which air, a test gas as well as a reactant, normally ammonia, can be applied to a partial region of a first end face of an object, designed here as a particulate filter 1 , which is provided with a catalytic coating, of a diesel motor vehicle. Air is hereby supplied via an air supply 29 and is then compressed with a compressor 24 or the like. A heating unit, designed as an electric heater 13, is arranged after the compressor 24 in order to heat up the supplied air and to bring the object for testing the function of the catalytic reactivity to a predefined temperature or to test the catalytic reactivity at different temperatures.

A test gas which contains nitrogen oxides is added to the air via a test gas supply line 25 so that a mixture of air and test gas can be formed which is by way of example analogous to an exhaust gas of an engine in which the particulate filter 1 is normally used for cleaning exhaust gas, in particular is analogous to an exhaust gas of a diesel engine of a motor vehicle. In order to achieve a particularly simple method it is preferably proposed that the gas applied was not produced by combustion in an internal combustion engine.

Furthermore a preferably gaseous reactant, in particular ammonia or a hydrocarbon gas, is supplied via a reactant supply line 3 to the mixture of air and test gas at least temporarily and causes a chemical reaction which reduces the nitrogen oxides in the particulate filter 1 or in a coating of the particulate filter 1 in order to analyse the behaviour of the particulate filter 1 or catalytic coating thereof. The mixture of air, the test gas and the reactant is thus pressed with the compressor 24 through the particulate filter 1 . A suction unit 1 1 is furthermore provided downstream of the particulate filter 1 in the flow direction 23 and via which the mixture can be sucked out from the particulate filter 1 .

A funnel-shaped gas trap 6 is provided in the flow direction 23 immediately after the object to be analysed and as is apparent covers the entire second end side 5 of the object so that any gas emerging from the second end side 5 passes through the gas trap 6 into the discharge line.

Gas analysis measuring devices which are configured as UV spectrometers with a wavelength of 200 nm to 600 nm are provided in both the supply line 2 and the discharge line. Furthermore a particle counter is arranged in the discharge line in order to determine a particle trap rate of the object. A gas analysis connection 9 and a particle counter connection 10 through which the gas flowing through the object can be analysed are shown diagrammatically in the discharge line.

The gas containing air, a test gas as well as the reactant is normally applied under excess pressure to the object via the first end side 4 and emerges from the object at the second end side 5. Channels 27 extend as shown in the longitudinal direction of the particulate filter 1 between the first end side 4 and the second end side 5. Naturally it is also possible for the direction of the gas flow to be reversed. The gas can furthermore naturally also be sucked out only through the object.

The supply line 2 which has a smaller cross-section than the first end side 4 can be movable through a positioning device configured as a Cartesian robot 12 up to various different partial regions of the first end side 4 so that by charging different partial regions and measuring a concentration of nitrogen oxides and ammonia in the supply line 2 as well as the discharge line it is possible to conclude on a catalytic function or NOx conversion of individual partial regions, by way of example in order to subject partial regions which do not exhibit sufficient reactivity or catalytic function to a renewed reprocessing. The supply line 2 can for this purpose be set tightly on the first end side 4 via a seal 7 so that it is ensured that a gas emerging from the supply line 2 enters into the region of the first end side 4 delimited by the seals 7 or the corresponding channels 27. Using the robot 12 the first supply line 2 can normally be freely positioned in a plane parallel to the first end surface and perpendicular to the first end surface so that the device can be adapted to objects of various different sizes, more particularly to different passenger vehicle and industrial vehicle particulate filters 1 .

Temperature sensors 28 are furthermore provided both on the first end side 4 and also on the second end side 6 in order to be able to conclude on a catalytic reactivity of the catalytic converter by way of the temperature changes. A temperature sensor 28 is shown diagrammatically on the second end side 5.

It is furthermore apparent that a mixing device configured as a mixer 8 is provided in the supply line 2 for homogenizing the gas mixture which consists of air, test gas and ammonia or reactant. A situation is reached which is very similar to the real operating conditions in a motor vehicle, particularly as urea or a corresponding reactant, as a rule AdBlue, is added to the exhaust stream in motor vehicles before the exhaust stream meets the catalyser so that corresponding reactions can take place in the catalyser to reduce the nitrogen oxides.

With this method, the particulate filter 1 is first brought to a predefined temperature, by way of example 250°C after which the particulate filter is charged with a gas mixture with a defined composition, which gas mixture contains nitrogen oxides. After about a minute ammonia is additionally introduced into the supply line 2 as a reactant so that air, nitrogen oxides and ammonia are introduced through the supply line 2 into the object. Both in the supply line 2 and also in the discharge line a time path of nitrogen oxides and ammonia is measured in order to be able to judge an NOx conversion of the catalytic coating. It can thereby also be ascertained whether, and where applicable if, a so-called NH3 slip has happened wherein ammonia flows through the particulate filter 12. The device according to the invention can have a closed housing 26 as shown diagrammatically so that the method can also be efficiently used with dismantled particulate filters 1 , more particularly with just reprocessed particulate filters 1 , by way of example within the scope of an industrial reprocessing and cleaning and testing system. An automated cleaning can then take place by way of example until the catalytic function detected in the method according to the invention cannot be further improved or a desired catalytic reactivity is reached.

Fig. 2 shows a time path of measured values of an exemplary measuring method according to the invention. This shows a time path of nitrogen monoxide in the supply line 2, here marked as the NOx inlet 19, nitrogen monoxide in the discharge line, here marked as the NOx outlet 20, ammonia supplied, here marked as the NFb dosage 21 , and ammonia in the discharge line, here marked as the NFb outlet 22.

A delay can be seen between the NOx inlet 19 and the NOx outlet 20. This time delay is conditioned by the injection behaviour of the particulate filter 1 which can initially store nitrogen oxides up to saturation. The measured time delay between nitrogen oxides at the inlet and nitrogen oxides at the outlet can thus already be used as a quality criterion for judging a quality of the particulate filter 1 .

As can be seen, the object, after pre-heating to about 250°C after about four minutes, is initially charged at a first test point 14 with test gas which contains nitrogen monoxide with a concentration of about 200 ppm so that nitric oxide rises both in the supply line 2, NOx inlet 19, and also in the discharge line, NOx outlet 20.

About a minute later at a second time point 15, ammonia is directed into the supply line 2, by way of example with a concentration of about 300 ppm. Roughly at the same time the measured value of the nitrogen monoxide, NOx outlet 20, starts to drop in the discharge line because a selective catalytic reaction takes place in the catalyser.

At a later, third time point 16, the NOx proportion in the discharge line, here marked as the NOx outlet 20, drops to a minimum. From this time point, an NOx conversion is maximum. A ratio of NOx outlet 20 to NOx inlet 19 at this time point is thus an indicator for the denoxification capacity of the particulate filter 1 with an NFb injection.

Furthermore, an increase of the ammonia in the discharge line, NFb outlet 22, also follows the rise of NFb in the supply line 2, NFb dosage 21 , only after a time delay. The reason for this is that ammonia is deposited in the coating and the substrate of the particulate filter 1 between the second time point 15 and the third time point 16. Often only then when the depositing has finished is the complete catalytic function reached.

At the end of mixing in the ammonia at a fourth time point 17, which is about two minutes after the second time point 15, the proportion of nitrogen monoxide in the discharge line, NOx outlet 20, rises only slowly again. The ammonia in the discharge line, NFI3 outlet 22, only reaches the level of before the start of the N FI3 dosage 21 at a later fifth time point 18. The reason for this is that after the end of mixing in the ammonia with the test gas, ammonia is discharged from the coating so that the selective catalytic reaction abates slowly. It is not shown that prior to applying the test gas the catalyser is brought to a temperature of about 250°C by heating up the air which is supplied. As is apparent, the concentration of NOx outlet 20 clearly sinks in the presence of NH3, since by way of example nitrogen monoxide reacts to nitrogen, water and where applicable to further reaction products.

A stronger reaction with higher NOx conversion is naturally achieved with a higher temperature of the particulate filter 1 of by way of example 350°C.

A measuring sequence of this kind thus takes a total duration of less than ten minutes within which a complete classification of the reprocessed object is carried out in a fully automated manner. An examination of the catalytic function is thus possible significantly faster than with methods of the prior art.

Corresponding measuring sequences can also be undertaken directly on an engine and can be compared with those determined in the method according to the invention in order to arrive at a correlation between values measured in the method according to the invention and exhaust threshold values which can be achieved during real operation.

A time point from which NH3 can also be measured after the particulate filter 1 , is dependent on a functional capacity of the coating or a storage capacity and takes place earlier at higher temperatures. This NH3 slip or time point from which the NH3 slip takes place can also be used as a criterion for judging the quality of the particulate filter 1 .

Ammonia is further discharged from the coating when the temperature of the object drops. A discharge of this kind thus leads with a constant concentration of ammonia before the particulate filter 1 or with a constant NH3 dosage 21 to a rise of the ammonia after the particulate filter 1 or to a rise of the NH3 outlet 22 when the temperature drops by way of example from 300°C to 250°C.

Measured values determined with a method according to the invention for reprocessed objects as well as for new objects for cleaning exhaust gas can be contrasted with measured values which the corresponding objects reached during real-time use in a motor vehicle, in order to determine a correlation. It is thereby possible in a reliable manner through the values determined in the method according to the invention to gain in respect of the catalytic reactivity an assessment on the exhaust gas thresholds which can be reached during operation in actual motor vehicles.

With a method according to the invention as well as a device for this it is possible for the first time to provide an assessment on the exhaust gas values which can be achieved with SCR catalytic converters without having to install the objects for this after a reprocessing again into a corresponding vehicle. An assessment is also provided on the storage effects as well as an anticipated remaining service life and functioning period. Furthermore, for the first time a catalytic reactivity can be determined for individual partial regions of the object which is to be investigated so that individual partial regions can be purposefully treated where applicable in order to achieve the desired reactivity. With a method of the prior art for measuring exhaust gases of an internal combustion engine, however, only a catalytic function can be indicated for an entire cross-section of the filter or catalyser.

The method can be carried out both with objects dismantled from an exhaust tract and also with objects which are arranged in the exhaust tract of a motor vehicle. It is furthermore also possible to use the method with objects arranged in a canning wherein a filter and a catalyser are normally positioned in series in a canning.

Claims

1 . A method for measuring a catalytic function of an object suitable for cleaning an exhaust gas of an internal combustion engine, in particular a catalytic converter or a particulate filter (1 ) for a motor vehicle or a work machine, wherein a test gas which contains nitrogen oxides and/or hydrocarbons, is moved through the object and a concentration of at least one constituent of the test gas is measured before and after flowing through the object, characterised in that the object is additionally charged with a reactant which causes a catalytic reaction in the object in order to reduce the nitrogen oxides in the test gas, in order to determine the catalytic function of the object through the action of the reactant and/or an HC light-off temperature.

2. Method according to claim 1 characterised in that the object is first charged only with the test gas preferably for at least ten seconds, in particular for at least one minute, after which the object is additionally charged with the reactant, preferably for at least ten seconds, more particularly for at least one minute, wherein a time path of a catalytic reaction in the object is detected, in particular for up to at least ten seconds, preferably up to at least one minute, at the end of charging the object with the reactant.

3. Method according to claim 1 or 2 characterised in that nitrogen oxides, in particular nitrogen monoxide and/or nitrogen dioxide, are measured both in a supply line (2) through which the test gas is brought to the object, and also in a discharge line which the test gas flows through after passing the object.

4. Method according to one of claims 1 to 3 characterised in that nitrogen oxides in the supply line (2) and in the discharge line are measured, preferably continuously, before, during and after charging the object with the reactant.

5. Method according to one of claims 1 to 4 characterised in that the reactant contains ammonia and/or a constituent, in particular urea, suitable for forming ammonia in the object.

6. Method according to one of claims 1 to 5 characterised in that a concentration of ammonia and/or a constituent suitable for forming ammonia, is measured in a reactant supply line (3) through which the object is charged with reactant, and optionally also in the discharge line through which the test gas flows after passing the object, wherein several measurements are preferably carried out at staggered time intervals in order to determine a time path.

7. Method according to one of claims 1 to 6 characterised in that the object has at least in a partial region during at least a part of the method a temperature which corresponds to a normal operating temperature of the object during operation as intended during cleaning of an exhaust gas of an internal combustion engine, more particularly 180°C to 600°C, wherein the object is preferably brought to the temperature by heated air before the test gas is applied to the object.

8. Method according to one of claims 1 to 7 characterised in that the test gas is applied to the object at a temperature which corresponds to a normal temperature at which the object is charged during operation as intended, in particular 180°C to 600°C.

9. Method according to one of claims 1 to 8 characterised in that the reactant is mixed with the test gas prior to charging the object.

10. Method according to one of claims 1 to 9 characterised in that a temperature of the object is changed during the measuring, in particular by at least 10°C.

1 1 . Method according to one of claims 1 to 10 characterised in that the test gas is supplied to the object via a supply line (2) with which only a partial region of an end side of the object is charged in order to detect a catalytic function of a partial region of the object.

12. Method according to claim 1 1 characterised in that the test gas is supplied sequentially to different partial regions of the object in order to determine a catalytic function of the entire object.

13. Device for measuring a catalytic function of an object suitable for cleaning an exhaust gas of an internal combustion engine, in particular of a catalytic converter for a motor vehicle, wherein with the device a test gas can be transported through the object and at least one constituent of the test gas can be measured before and after passing the object, in particular for carrying out a method according to one of claims 1 to 12, characterised in that a reactant can be applied with the device to the object in addition to the test gas.

14. Device according to claim 13 characterised in that the test gas can be applied via a supply line (2) to the object, with which supply line (2) the test gas can be applied only to a partial region of the object in order to determine a catalytic function of a partial region.

15. Device according to claim 13 or 14 characterised in that the supply line (2) can be moved with a positioning device in order to determine sequentially the catalytic function of different partial regions.