Method For The Non-destructive Control Of A Particle Filter And Associated Device

Abstract

A nondestructive method for detecting internal defects of a filter, for example a catalytic filter, and a device for implementing the method. The method may be used in particular for treating a gas laden with soot particulates. The filter includes a honeycomb filter element or a plurality of honeycomb filter elements. In the method the presence or absence of the defects is determined by measuring a propagation of a gas stream such as air through the filter element or elements.

Description

[0001] The invention relates to the field of particulate filters having honeycomb structures used in an engine exhaust line for removing soot, typically produced by the combustion of a diesel fuel in an internal combustion engine. More particularly, the invention relates to a method or process for detecting and characterizing internal defects of the filter, such as porous, absent or supplementary plugs, cracks and, in general, any defect liable to cause a deterioration of the performance or even a deactivation of said filter.

[0002] Structures for filtering soot present in the exhaust gases of an internal combustion engine are well known in the prior art. A typical filter usually has a honeycomb structure, one of its sides allowing the inflow of the exhaust gases to be filtered, and the other side the removal of the filtered exhaust gases. Between the inlet and outlet sides, the structure comprises a series of adjacent channels or ducts having parallel axes and separated by porous filtration walls, said ducts being sealed at one or the other of their ends to delimit inlet chambers opening via the inlet side and outlet chambers opening via the outlet side. For a proper seal, the peripheral part of the structure is advantageously surrounded by cement, called coating cement in the rest of the description. The channels are alternately sealed in an order such that the exhaust gases, when passing through the honeycomb body, are forced to pass through the side walls of the inlet channels to reach the outlet channels. In this way, the solid soot particulates are deposited and accumulate on the porous walls of the filter body. Advantageously, the filter bodies are made from a porous ceramic, for example from cordierite or silicon carbide.

[0003] In a manner known per se, the particulate filter is subjected during its use to a succession of filtration (soot accumulation) and regeneration (soot removal) phases. During the filtration phases, the soot particulates emitted by the engine are retained and deposit inside the filter. During the regeneration phases, the soot particulates are burned inside the filter, in order to restore its filtration properties. The porous structure is then subjected to intense thermal and mechanical stresses, which may cause microcracks that are liable, over time, to cause a severe loss of the unit's filtration capacities, or even its complete deactivation. This process is observed in particular on large-diameter monolithic filters.

[0004] To solve these problems and to lengthen the service life of the filters, more complex filtration structures were more recently proposed, associating a filter block with a plurality of monolithic honeycomb elements. The elements are usually assembled together by an adhesive using a ceramic cement, called joint cement in the rest of the description. Examples of such complex filter structures are described, for example, in patent applications EP 816 065, EP 1 142 619, EP 1 455 923 or even WO 2004/090294 and WO 2004/065088.

[0005] The soot filters or filter blocks as previously described are mainly used at large scale in devices for preventing pollution by the exhaust gases of a diesel internal combustion engine. In the rest of the description, mention is made equally of filters, filter structures or blocks, to designate the filtration structure according to the invention.

[0006] It is admitted that the industrial production of such structures is complex in that it requires numerous steps, each step having to be carried out under optimized conditions, for the final production of a structure suitable for the filtration function, that is, free of internal defects. A typical succession of the main steps in a conventional production process comprises, inter alia, the extrusion of a paste based on SiC or cordierite in monolithic elements of the honeycomb type, the sealing of some ends of the ducts, the firing, optionally a machining, the application of a coating and joint cement between said elements, followed by their assembly, and the solidification of said cement, generally by an appropriate heat treatment. A typical succession of such steps is, for example, described in patent applications WO 2004/065088 and EP 1 142 619. It is clear that these steps (and others) are all sources of potential defects in the internal structure of the filter, for example break(s) in the walls in a honeycomb element or of the joints between elements, incomplete sealing of the ducts, crack(s) in the walls or joints, missing, porous or supplementary plug(s), inhomogeneous distribution of the wall or joint thicknesses, imperfect seal of the coating cement. In the production stage and also after an optional recycling process, the detection and preferably the characterization of these defects are therefore crucial, because they may significantly affect the effectiveness and integrity of the filter, upon its commissioning or after a few successive regeneration cycles, during which the filter is subjected to high thermomechanical stresses.

[0007] It has been found that most of the defects observed are internal defects of the filter.

[0008] Furthermore, most of the nonintrusive methods known for the time being are not sufficiently discriminating, and only the destruction of the filter serves to visually characterize the internal defects of the filter.

[0009] One known method is based on measurements of the pressure drop across the two sides of the structure. However, this measurement does not permit sufficient discrimination, because it is too dependent on the intrinsic variation in the porosity and thickness of the walls.

[0010] Patent application FR 2 840 405 describes a nondestructive method for detecting defects in a particulate filter by the use of ultrasound. It is stated that he measurement of the ultrasound travel time and/or the variations in power and amplitude of the ultrasonic signal during the crossing of the porous mass, is representative of the intrinsic defects of the structure.

[0011] An object of the present invention is to provide a method for nondestructively characterizing a particulate filter as described above.

[0012] More particularly, the present invention relates to a nondestructive method that is simple, economical and sufficiently discriminating, for characterizing and distinguishing, for example, during a production process, the honeycomb structures free of internal defects, from the structures having internal defects liable to make them unacceptable for use as particulate filters.

[0013] More precisely and according to a first aspect, the present invention relates to a nondestructive method for detecting internal faults of a filter, optionally catalytic, used in particular for treating a gas laden with soot particulates, said filter comprising a honeycomb filter element or a plurality of honeycomb filter elements, said element or elements comprising a set of adjacent ducts or channels having parallel axes and separated by porous walls, said ducts being sealed by plugs at one or the other of their ends, to delimit inlet chambers opening via a gas inlet side and outlet chambers opening via a gas removal side, in such a way that the gas crosses the porous walls, said method being characterized in that the presence or absence of said defects is determined by measuring the propagation of a gas stream such as air through said filter element or elements. In the context of the present invention, "propagation of a stream" means the variation of the flow of a gas passing through the structure via its porous walls.

[0014] Said defects may be of the type: break in the walls in a honeycomb element or of the joints between elements, incomplete sealing of the ducts, cracks in the walls or joints, missing, porous or supplementary plug, inhomogeneous distribution of the wall or joint thicknesses, imperfect seal of the coating cement.

[0015] For example, the presence or absence of said defects is determined by comparison with a reference value corresponding to a filter not having any internal defects.

[0016] According to a first possible embodiment of the present method, the propagation of the gas stream through the filter is evaluated by analyzing the transmission spectrum of an infrared radiation at the filter outlet, in particular by infrared thermographic analysis.

[0017] According to another possible embodiment, the propagation of the gas stream through the filter is evaluated by at least one measurement of the gas velocity at the outlet of said filter.

[0018] Obviously, the preceding two embodiments are not limiting for the present invention, and any known means for analyzing the propagation of the gases through the filter is included within the scope of the present invention.

[0019] For example, according to the second embodiment, a series of measurements of the gas velocity are taken in order to obtain a profile of said velocities at the filter outlet.

[0020] The presence or absence of said defects is determined by comparison between the various gas velocity values obtained on the filter.

[0021] The measurement pitch is advantageously equal to or lower than the width of a duct.

[0022] Optionally, in certain embodiments of the invention, the porous walls of the filter are previously loaded with a soot concentration of at least 1 gram per liter.

[0023] According to another aspect, the present invention relates to a device for implementing the method described above, comprising in particular

[0024] means for sending a gas such as air into the filter,

[0025] means for confining the air flow introduced into the filter,

[0026] means for regulating the flow rate and/or pressure of the air introduced into the filter,

[0027] means at the filter outlet for measuring the propagation of a gas stream such as air through the filter element or elements.

[0028] The measurement means are for example means for measuring the gas velocity, selected for example from propeller anemometers, hot wires, Pitot tubes, hot ball systems, hot film systems, PIV (Particle image velocimetry) type systems, LDA (laser doppler anemometry) type systems measuring the doppler effect associated with the air velocity.

[0029] The control means may comprise a butterfly valve associated with a precision valve.

[0030] The measurement means may also be systems in which the propagation of the gas stream is evaluated by analyzing the transmission spectrum of an infrared radiation at the filter outlet, in particular systems for infrared thermographic analysis.

[0031] The method or the device described above is particularly applicable

[0032] for controlling particulate filter production methods,

[0033] for controlling particulate filter recycling methods,

[0034] for studies for the design, characterization or development of novel particulate filters, particularly with regard to the selection of the novel or improved materials usable in said filters,

[0035] for filter endurance control studies.

[0036] The invention will be better understood from a reading of the following description, illustrated by FIG. 1, of an exemplary embodiment of a device according to the invention for implementing the present method.

[0037] The device has been designed for the primary purpose of visualizing the defects of the filter developing in a radial direction. However, the experiments conducted by the applicant have demonstrated that other types of defect, present in the structure along a longitudinal direction, also affect the signal detected by the present method and its associated device, and can consequently also be characterized.

[0038] According to the principles of the present invention, a gas, typically air, is blown into a particulate filter. The gas velocity profile is measured and analyzed at the filter outlet. In the rest of the description, the case is considered in which the gas is air, but obviously, other gases can be used without going outside the scope of the invention.

[0039] The measurements are taken at constant flow rate and, ideally, at constant pressure, at the inlet (upstream) of the particulate filter, in the gas propagation direction.

[0040] More precisely, and as shown in FIG. 1, the device comprises a tubular member 1 on which the following are placed in succession:

[0041] 1) an air filter 2:

[0042] This filter is optional and has the function of preventing the dust present in the surrounding air from accumulating in the system

[0043] 2) a butterfly valve 3:

[0044] This valve serves roughly to regulate the flow rate and pressure at the inlet of the particulate filter 4.

[0045] However, for the lowest values of the air flow rate, it may be advantageous to combine this valve 3 with a precision valve 5. Said valve 5 is, for example, of the guillotine type, and serves to operate with an air stream of which the temperature is substantially constant. The contribution of this valve 5 advantageously allows for an accuracy on the flow rate better than 1 m.sup.3/h (cubic meters per hour) and easier control of the pressure close to and upstream of the particulate filter 4, in the air travel direction. The accuracy on the pressure obtained is about 1 mbar (1bar=0.1 MPa).

[0046] 3) a blower 6:

[0047] The blower serves to send the air into the filter 4. The blown air flow rate generally depends on the type of defect to be characterized. For example, in a configuration in which the filter is not laden with soot or with a powdery material, the air flow rate blown by the blower may typically range between 10 and 700 m.sup.3/h, preferably between 200 and 400 m.sup.3/h.

[0048] In a configuration in which the filter is laden with soot or another powdery material, the air flow rate blown by the filter varies between 10 and 700 m.sup.3/h, preferably between 10 and 100 m.sup.3/h.

[0049] 4) a flowmeter 7:

[0050] The flowmeter serves to check and control the air flow rate during the operation.

[0051] 5) a length of tube 8 adjusted between the blower 6 and the divergent nozzle 9:

[0052] The length of tube 8 between the blower and the divergent nozzle is advantageously higher than about 50 times the tube diameter. Such a configuration serves in particular to obtain a substantially constant velocity of the gas flow lines leaving the tube 8, that is, a stabilized stream of gas at the inlet of the divergent nozzle.

[0053] 6) a divergent nozzle 9:

[0054] To prevent any separation of the air stream at the walls of the divergent nozzle and any turbulence, the divergent apex angle is preferably smaller than 7.degree., for example 6.degree.. Such a configuration serves in particular to make the gas flow lines uniform upon reaching the inlet of the particulate filter.

[0055] In a preferred embodiment of the invention, the filter inlet and the divergent nozzle outlet are directly abutting. However, it is still within the scope of the invention if the housing 10 of the filter (called "canning" in the trade) has a length greater than that of the filter 4, so that a space exists between the outlet 11 of the divergent nozzle 9 and the inlet 12 of the filter 4. For example, tests conducted by the applicant demonstrated satisfactory results when a 6'' long filter (1 inch=2.54 cm) was placed at a distance of 4'' from the filter inlet, a 10'' long canning being used (cf. FIG. 1).

[0056] 7) a pressure sensor 13:

[0057] The pressure sensor has the function of checking and controlling the absolute and/or gauge pressure in the part of the divergent nozzle located immediately upstream of the particulate filter, in the air flow direction.

[0058] 8) optionally, a temperature sensor 14, close to the filter inlet 12.

[0059] 9) a system 15 for measuring the air velocity:

[0060] The measurement system may be selected according to the invention from any system known in the field of fluid mechanics for measuring the velocity of a gas stream. Without this being considered as restrictive, it is possible, for example, according to the invention to use

[0061] one or more mobile propeller anemometers sweeping the downstream surface of the particulate filter at the outlet of the present device,

[0062] a series or battery of anemometers that are fixed or mobile and/or placed at various locations at the back of the filter,

[0063] one or more hot wires, or even a set of hot wires, the gas velocity being measured as a function of

[0064] the heat loss of the wire(s),

[0065] one or more Pitot tubes,

[0066] hot ball systems,

[0067] hot film systems,

[0068] PIV (Particle Image Velocimetry) type systems,

[0069] LDA (laser doppler anemometry) type systems measuring the doppler effect associated with the air velocity.

[0070] According to the invention, the presence or absence of defects is determined by measuring the propagation of the gas stream through the structure. For example, and as previously described, with regard to FIG. 1, this measurement is associated with an analysis of the velocity of the gases leaving the structure. However, any other means for taking said measurement known for this purpose can be used according to the invention. In particular, systems can be used in which the propagation of the gas stream through the filter is evaluated by analyzing the transmission spectrum of an infrared radiation at the filter outlet, particularly systems of infrared thermographic analysis. As the variations obtained are linked to the gas flow conditions through said filter, a characteristic spectrum of the presence or absence of defect(s) is obtained.

[0071] The distance between the back 16 of the filter and the air measurement system 15 is generally a compromise between the overall dimensions engendered by the dimensions of the measurement system itself and the power of the air stream leaving the filter.

[0072] In practice, a configuration is selected in which this distance is minimized to avoid any "backmixing" of the exit gas streams that could hinder the measurement of the gas velocity.

[0073] In general, the filter/measurement system distance is between 0 and a few centimeters, preferably between 0 and 2 cm.

[0074] According to one possible embodiment, it is further possible, without going outside the scope of the present invention, to chart a two- or three-dimensional mapping of the gas velocities at the filter outlet by associating, with the measurement system, a software developed for the purpose.

[0075] The method according to the invention for controlling a particulate filter can be implemented in various ways, particularly according to the type of defect investigated.

[0076] According to a first embodiment, an attempt is made to visualize non-filtering defects of the broken, porous, supplementary or wall plug type. According to this embodiment, the filter is placed directly in the measurement device as described above, without prior loading.

[0077] In this embodiment, the air flow rate is generally between 200 and 400 m.sup.3/h.

[0078] The analysis may be comparative, for example comparison with a reference value corresponding to a filter not having this type of defect. The experiments conducted by the applicant have in fact demonstrated that the gas velocity values obtained at the filter outlet were particularly reproducible if the flow rate and, ideally, the pressure of the gas entering the filter were substantially identical for the two filters (reference filter and filter to be analyzed). According to the invention, it is preferable to work at constant pressure for a better characterization of the filter.

[0079] According to an alternative embodiment, the analysis can also be conducted by comparison between the various velocity values obtained, a substantial deviation from a mean measured velocity indicating the presence of the defect investigated. For example, a local relative deviation of at least 5%, preferably at least 10% from the mean gas velocity measured at the filter outlet may be sufficient to detect, characterize and locate an internal defect. In the context of the present invention, relative deviation means the absolute value of the difference in velocity related to the velocity observed on the reference filter of the same format, multiplied by 100.

[0080] According to another possible embodiment in which an attempt is typically made to visualize defects such as cracks or breaks in the walls, the filter is placed in the measurement device previously described after a prior step in which it has been loaded with soot or preferably with a model powdery material that is less harmful than soot but whereof the characteristics (particle size distribution, grain shape, etc.) are similar.

[0081] In this embodiment, the air flow rate may be between 20 and 40 m.sup.3/h. As in the previous embodiment, the analysis may be comparative with regard to a known reference, under the same air flow rate and preferably pressure conditions, measured immediately at the filter inlet, in the gas propagation direction.

[0082] As in the previous embodiment, the analysis may also be conducted by comparison of the velocities obtained on the filter analyzed, for example with regard to a mean velocity observed. In this arrangement, a local relative deviation of at least 10%, preferably at least 20% from the mean gas velocity measured at the filter outlet, serves to detect, characterize and locate an internal defect of the crack type, in the measurement conditions.

[0083] Obviously, the invention is not limited to these embodiments. In particular, it is possible, without going outside the scope of the invention, to visualize the defects of the crack, break type, etc., on a filter not laden with soot and, conversely, of the broken, porous plug type, etc., on a filter previously laden with soot.

[0084] The invention and its advantages are illustrated by the nonlimiting examples that follow.

[0085] The filter used in the examples that follow combines in one filter block a plurality of monolithic honeycomb elements. The extruded elements are made from silicon carbide (SiC). After firing, they are machined and then joined together by adhesive using a cement based on silicon carbide SiC, the structure thereby obtained being then coated with a coating cement, according to well known techniques. The fabrication of such filter structures is described in particular in patent applications EP 816 065, EP 1 142 619, EP 1 455 923 and even WO 2004/090294.

[0086] The characteristics of the filter used in the following examples are given in Table 1:

TABLE-US-00001 TABLE 1 Channel geometry Square Channel density 180 cpsi (channels per square inch, 1 inch = 2.54 cm) Dimensions of a 1.8 .times. 1.8 mm channel Wall thickness 350 .mu.m Number of elements 16 assembled Structure shape cylindrical Length 6'' (15.2 cm) Volume 2.48 liters

[0087] The device used is of the type described with regard to FIG. 1. The divergent nozzle has an apex angle of 6.degree.. The system for measuring the gas velocity consists of a Schiltknecht propeller anemometer from RBI Instrumentations, mounted on two cylinders in a crosswise arrangement, enabling it to move along two travel directions X and Y.

[0088] The system performs a stepwise movement on a first line in the X direction, the step being set at 1.8 mm. The step is selected as equal to the width of a channel, in order to obtain optimal discrimination. Once the line along X is completed, the system descends by one notch along Y. At each movement of the anemometer in the X or Y direction, a local measurement is taken of the gas velocity. A complete XY mapping of the flows is thus obtained.

Example 1

[0089] In this example, an attempt was made to detect defects of the defective plug type (for example broken or porous) The analysis was carried out on a filter intentionally comprising defective plugs. A reference filter, without defect, was also analyzed under the same conditions. The main parameters and results are given in Table 2.

TABLE-US-00002 TABLE 2 Reference filter/ Parameters and positions of plugs Positions of results without defect defective plugs Gauge pressure 7.4 mbar (at filter inlet) Air flow rate 301 m.sup.3/h 301.5 m.sup.3/h (at filter inlet) Temperature 40.degree. C. (at filter inlet) Measured velocity 10 m/s 12 m/s (at filter outlet) (.+-.0.3 m/s) Relative deviation of 20% measured velocities Distance between 1 cm anemometer and filter Movement of the 1.8 mm: the step is equal to the width anemometer of a channel Diameter of propeller 9 mm anemometer

[0090] The results obtained show that, for equivalent air flow rate and pressure conditions at the filter inlet, the velocities measured at each step by the anemometer:

[0091] a) for the reference filter,

[0092] b) for the parts of the filter without defect,

are substantially identical (10 m/s) with a slight absolute variation (0.3 m/s).

[0093] Furthermore, the relative deviation between the reference value thus determined and the velocity value obtained when the measurement is taken at the defective plugs, is significant (20%) and allows the determination, characterization and even location of the defective plugs.

[0094] It was also checked by the destruction of the filter and the real visualization of the defects that the positions of the defects found by the gas velocity measurement corresponded to the exact positions of the defective plugs.

Example 2

[0095] In this example, an attempt was made to detect defects of the additional plug or non-filtering wall type. The analysis was carried out on a filter intentionally comprising supplementary plugs. A reference filter, without defect, was also analyzed under the same conditions. The main parameters and results are given in Table 3.

TABLE-US-00003 TABLE 3 Reference Parameters and filter/positions of Positions of results normal plugs supplementary plugs Gauge pressure 10.3 mbar (at filter inlet) Air flow rate 352 m.sup.3/h 351 m.sup.3/h (at filter inlet) Temperature 40.degree. C. (at filter inlet) Measured velocity 12 m/s 10.5 m/s (at filter outlet) (.+-.0.3 m/s) Relative deviation of 12.5% measured velocities Distance between 1 cm anemometer and filter Movement of the 1.8 mm: the step is equal to the width anemometer of a channel Diameter of propeller 9 mm anemometer

[0096] As in the preceding example, the results obtained show that, for equivalent air flow rate and pressure conditions at the filter inlet, the velocities measured at each step by the anemometer:

[0097] a) for the reference filter,

[0098] b) for the parts of the filter without defect,

are substantially identical (12 m/s) with a slight absolute variation (0.3 m/s).

[0099] Furthermore, the relative deviation between the reference value thus determined and the velocity value obtained when the measurement is taken at the defective plugs, is still significant (12.5%) although the air flow rates are high, and allows the determination, characterization and even the location of the supplementary plugs.

[0100] The positions of the defects found by the measurement of the gas velocities correspond to the exact positions of the supplementary plugs intentionally added.

Example 3

[0101] In this example, an attempt was made to detect defects of the cracked wall type, observed after several filter regeneration cycles. A reference filter, without defect, was also analyzed under the same conditions. Before the measurement, the walls of the two filters were loaded with soot until reaching a quantity of 7 grams of soot per liter in the filter. The main parameters and results obtained are given in Table 4.

TABLE-US-00004 TABLE 4 Reference Parameters and filter/normal Positions of results positions "cracked walls" Gauge pressure 12.4 mbar (at filter inlet) Air flow rate 39.6 m.sup.3/h 39.6 m.sup.3/h (at filter inlet) Temperature 40.degree. C. (at filter inlet) Measured velocity 1.9 m/s 2.65 m/s (at filter outlet) (.+-.0.1 m/s) Relative deviation of 39% measured velocities Distance between 1 cm anemometer and filter Movement of the 1.8 mm: the step is equal to the width anemometer of a channel Diameter of propeller 9 mm anemometer

[0102] The filters being laden with soot, the air pressure at the filter inlet is substantially higher than in the first two examples, and the velocities measured at the gas outlet are much lower. The results obtained under these conditions show that, for equivalent air flow rate and pressure conditions at the filter inlet, the velocities measured at each step by the anemometer between the reference filter and the parts of the filter without defect are substantially identical (1.9 m/s) with a slight absolute variation (0.1 m/s).

[0103] Furthermore, the relative deviation between this reference value and the velocity value obtained when the measurement is taken at the defective part of the filter is significant (39%) and allows the determination, characterization and location of the internal cracks.

[0104] The conventional analysis of the filter by destructive methods showed that the positions of the defects found by the gas velocity measurements clearly correspond to locations where the walls were cracked.

[0105] The device and the method according to the invention can serve to rapidly evaluate a particulate filter on completion of its production. For example, the device can be installed alongside a production line, the analysis of a portion of the filters produced serving to validate a complete production batch. According to another example, a device according to the invention can be placed at the exit of the production line, and all the filters produced can be inspected at the end of the line, in order to meet product quality targets.

[0106] The invention is also applicable to the search for defects on the filter after its recycling, thereby providing a less expensive and more accurate technique than the one described in FR 2 840 405.

[0107] In the most general manner, the method and the device according to the invention can be applied not only to the control of filter fabrication or recycling processes as previously described, but also

[0108] to studies for the design, characterization or development of novel particulate filters, particularly with regard to the selection of novel or improved materials usable in said filters,

[0109] to filter endurance control studies, etc.

[0110] The present invention is applicable for the detection of defects present both in simple particulate filters, that is, only performing a soot filtration function, and in catalytic filters, combining the soot filtration function with the conversion of polluting gases such as nitrogen oxides, sulfur oxides and carbon monoxide. Such catalytic filters are obtained, for example, by impregnating the initial structure in a solution comprising the catalyst or a precursor thereof.

Claims

1-14. (canceled)

15. A nondestructive method for detecting internal defects of a filter, or a catalytic filter, or a filter used for treating a gas laden with soot particulates, the filter including a honeycomb filter element or a plurality of honeycomb filter elements including a set of adjacent ducts or channels having parallel axes separated by porous walls, the ducts being sealed by plugs at one or other of their ends, to delimit inlet chambers opening via a gas inlet side and outlet chambers opening via a gas removal side, such that gas crosses the porous walls, the method comprising: determining presence or absence of the defects by measuring a propagation of a gas stream or air through the filter element or elements.

16. The method as claimed in claim 15, in which the defects are at least one o: a break in the walls in a honeycomb element or of joints between elements, incomplete sealing of the ducts, cracks in the walls or joints, missing, porous or supplementary plug, inhomogeneous distribution of the wall or joint thicknesses, imperfect seal of a coating cement.

17. The method as claimed in claim 15, in which the presence or absence of the defects is determined by comparison with a reference value corresponding to a filter not having any internal defects.

18. The method as claimed in claim 15, in which the propagation of the gas stream through the filter is evaluated by analyzing a transmission spectrum of an infrared radiation at an outlet of the filter, or by infrared thermographic analysis.

19. The method as claimed in claim 15, in which the propagation of the gas stream through the filter is evaluated by at least one measurement of gas velocity at an outlet of the filter.

20. The method as claimed in claim 19, in which a series of measurements of the gas velocity are taken to obtain a profile of the velocities at the filter outlet.

21. The method as claimed in claim 20, in which the presence or absence of the defects is determined by comparison between the series of gas velocities obtained on the filter.

22. The method as claimed in claim 20, in which the measurement pitch is equal to or lower than the width of a duct.

23. The method as claimed in claim 15, in which the porous walls of the filter are previously loaded with a soot concentration of at least 1 gram per liter.

24. A device for implementing a method as claimed in claim 15, comprising: means for sending a gas or air into the filter; means for confining gas flow introduced into the filter; means for regulating flow rate and/or pressure of the air introduced into the filter; and means at an outlet of the filter for measuring the propagation of a gas stream or air through the filter element or elements.

25. The device as claimed in claim 24, in which the measurement means for measuring includes means for measuring gas velocity, selected from propeller anemometers, hot wires, Pitot tubes, hot ball systems, hot film systems, PIV (Particle image velocimetry) type systems, LDA (laser doppler anemometry) type systems measuring the doppler effect associated with the air velocity.

26. The device as claimed in claim 25, in which the means for regulating includes a butterfly valve associated with a precision valve.

27. The device as claimed in claim 24, in which the means for measuring includes systems in which the propagation of the gas stream is evaluated by analyzing transmission spectrum of an infrared radiation at an outlet of the filter, or by infrared thermographic analysis.

28. Application of the method as claimed in claim 15, for controlling particulate filter production methods, for controlling particulate filter recycling methods, for studies for design, characterization or development of particulate filters, with regard to selection of materials usable in the filters, for filter endurance control studies.

29. Application of the device as claimed in claim 24, for controlling particulate filter production methods, for controlling particulate filter recycling methods, for studies for design, characterization or development of particulate filters, with regard to selection of materials usable in the filters, for filter endurance control studies.