US20100212299A1 - Methods for determining when to regenerate exhaust gas particulate filters - Google Patents
Methods for determining when to regenerate exhaust gas particulate filters Download PDFInfo
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- US20100212299A1 US20100212299A1 US12/392,341 US39234109A US2010212299A1 US 20100212299 A1 US20100212299 A1 US 20100212299A1 US 39234109 A US39234109 A US 39234109A US 2010212299 A1 US2010212299 A1 US 2010212299A1
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- filter
- microwave
- pressure drop
- residual amount
- particulates
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
- F01N9/002—Electrical control of exhaust gas treating apparatus of filter regeneration, e.g. detection of clogging
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present invention relates to exhaust gas particulate filters, and in particular to methods for determining when to regenerate exhaust gas particulate filters, for regenerating, and for calibrating a pressure drop across such filters.
- Exhaust gas particulate filters are used to remove exhaust gas particulates generated by combustion engines.
- diesel particulate filters are designed to accumulate diesel exhaust particulates (“soot”) from diesel engines and are used in a variety of diesel applications, including motor vehicles.
- DPFs are ceramic-based structures that generally comprise a network of interconnected web walls that form a matrix of elongated, gas-conducting cells that can have a variety of cross-sectional shapes.
- Other types of filters e.g., for gasoline engines have a similar type of cellular structure designed to capture exhaust gas particulates.
- Filter performance depends in part on the amount of particulates that the filter accumulates. Filters can be “regenerated” via thermal processing once the amount of accumulated particulates reaches a certain maximum allowed (i.e., threshold) level. The success of the regeneration process, however, requires accurately determining this threshold level.
- threshold a certain maximum allowed
- One method of determining the maximum allowable amount of accumulated particulates in a filter involves measuring the pressure drop across the filter. However, this method tends to be inaccurate and often leads to either an under or over prediction of the amount of particulates accumulated in the filter. A main source of this inaccuracy is due to the variability of the regeneration process, which leaves different amounts of residual particulates in the filter after each regeneration.
- One aspect of the invention is a method of determining when to regenerate a filter disposed in a microwave resonant cavity, wherein the filter has a particulate mass accumulation limit.
- the method includes reducing a first amount of particulates accumulated in the filter to a residual amount.
- the method also includes measuring the residual amount by exciting the microwave resonant cavity with microwave radiation and monitoring a cavity response.
- the method also includes using the measured residual amount to determine a pressure drop threshold representative of the particulate mass accumulation limit in the filter.
- Another aspect of the invention is a method of regenerating a filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates when operably arranged in an engine exhaust system.
- the method includes measuring a first residual amount of particulates in the filter by exciting the microwave resonant cavity with microwave radiation and monitoring the cavity response.
- the method also includes using the measured first residual amount to establish a pressure drop threshold across the filter that is representative of a predetermined amount of particulate accumulation in the filter.
- the method further includes operating the engine and monitoring the pressure drop across the filter as the filter accumulates particulates.
- the method also includes regenerating the filter when the pressure drop reaches the pressure drop threshold to reduce the particulate accumulation to a second residual amount.
- the filter is a DPF and the residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C.
- Another aspect of the invention is a method of calibrating a pressure drop across a filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates that cause a pressure drop when the filter is operably arranged in an engine exhaust system.
- the method includes reducing an initial amount of accumulated particulates in the filter to be equal to or less than a residual amount, wherein the initial amount is greater than the residual amount.
- the method also includes measuring the residual amount by exciting the microwave resonant cavity with a microwave signal having at least one microwave frequency and measuring at least one of a microwave signal resonant frequency shift and a microwave signal attenuation.
- the method also includes, based on the measured residual amount, establishing a pressure drop threshold across the filter that corresponds to an allowable amount of accumulated particulates.
- the method also includes measuring the pressure drop across the filter while the filter is operably arranged in the engine exhaust system, and reducing the accumulated particulates to be less than or equal to the residual amount when the pressure drop reaches the pressure drop threshold.
- FIG. 1 is a perspective side view of a filter in the form of a DPF
- FIG. 2 is a cross-sectional view of a DPF similar to that shown in FIG. 1 , showing the longitudinal cells and the alternating plugged cell ends;
- FIG. 3 is a close-up end view of the DPF of FIG. 1 ;
- FIG. 4 is a close-up perspective cut-away view of an end portion of a DPF and shows the flow of unfiltered diesel exhaust into the DPF, the flow of filtered diesel exhaust out of the DPF, and the accumulation of particulates within the DPF;
- FIG. 5 is a schematic diagram of an example diesel engine system that includes a DPF and in which the method of the present invention is applied by way of illustration;
- FIG. 6 is a schematic close-up view of a portion of the diesel engine system of FIG. 5 showing the filter housing and DPF arranged therein, and the controller;
- FIG. 7 is a plot of the microwave signal spectrum showing the microwave signal intensity I (dBm) vs. Frequency (GHz) as deduced from the detected microwave signal S M for various amounts of select diesel particulate loading of an example DPF at 300° C.; and
- FIG. 8 is a plot of the microwave signal intensity I (dBm) vs. diesel particulate concentration (g/l) at a frequency of 1.6 GHz for a variety of temperatures ranging from 25° C. to 600° C.
- FIG. 1 is a perspective side view of a filter 10 in the form of a DPF (hereinafter, “DPF 10 ”). Cartesian coordinates are shown for the sake of reference.
- FIG. 2 is a cross-sectional view of DPF 10 similar to that of FIG. 1
- FIG. 3 is a close-up end view of the DPF of FIG. 1 .
- the typical DPF 10 has a honeycomb structure 12 with an axial length L, a diameter or width D and a central axis A 1 that defines an axial (longitudinal) direction.
- Honeycomb structure 12 is formed by a matrix of intersecting, thin, porous walls 14 surrounded by an outer wall 15 . Walls 14 extend across and between opposing ends 16 and 18 , and form a large number of adjoining hollow channels or “cells” 20 that also extend between ends 16 and 18 .
- Cells 20 are plugged with plugs 30 in an alternating fashion at ends 16 and 18 so that each cell has one open end and one plugged end.
- DPF 10 can have any type of cross-sectional shape, including square, rectangular, oval, circular, and the circular cross-sectional shape is shown by way of example.
- An example DPF 10 has between about 100 and 400 cells per square inch and walls 14 that are generally on the order of 10-25 mils (e.g., about 0.25-0.65 mm) thick.
- the corresponding cell widths W C ( FIG. 3 ) are typically in the range from about 8 mm to about 1.25 mm.
- Typical diameters D range from about 6 inches (about 15.24 cm) to about 15 inches (about 38.1 cm).
- DPFs 10 are manufactured, for example, by extruding a plasticized ceramic-forming precursor of, for example, cordierite, mullite, silicon carbide, or aluminum titanate, through an extrusion die. The extruded “green body” is then cut and dried. Such green bodies are quite fragile and must be transported to a kiln, wherein the heat transforms the relatively soft and fragile green body into hardened, fired ware with rigid honeycomb structure 12 , which is then plugged with plugs 30 .
- a plasticized ceramic-forming precursor of, for example, cordierite, mullite, silicon carbide, or aluminum titanate
- FIG. 4 is a close-up, perspective cut-away view of an end portion of DPF 10 and shows the flow of unfiltered diesel exhaust gas (“diesel exhaust”) 50 into end 16 of the DPF.
- Unfiltered diesel exhaust 50 contains particulates (specifically, diesel particulates) 52 .
- each cell 20 is blocked at one of its ends, the flow of diesel exhaust 50 into a given cell builds up pressure in a given cell, which causes the diesel exhaust to flow through porous walls 14 .
- Porous walls 14 have a porosity designed to allow the gaseous constituents of diesel exhaust 50 to pass and trap diesel particulates 52 .
- diesel particulates 52 accumulate on and in walls 14 , while the “cleaned” or “filtered” diesel exhaust 50 ′ that passes through the walls 14 exits DPF 10 through the adjacent channel 20 at (open) end 18 .
- the accumulation of diesel particulates 52 in DPF 10 ultimately reduces the performance of the engine in which the DPF resides, and reduces the DPF's durability.
- diesel particulates 52 cause a pressure drop across the DPF.
- limit T DP maximum accumulation limit
- An example regeneration process is a “controlled” regeneration that involves heating DPF 10 to burn off the accumulated diesel particulates 52 .
- the regeneration step is initiated when the pressure drop ⁇ P across DPF 10 reaches a threshold pressure drop ⁇ P TH .
- each regeneration step leaves different residual amounts RA DP of diesel particulates 52 in DPF 10 .
- This causes errors in the correlation between the threshold pressure drop ⁇ P TH and the limit T DP of diesel particulates 52 allowed to accumulate in DPF 10 .
- FIG. 5 is a schematic diagram of an example engine system in the form of a diesel engine system (“system”) 100 that includes a diesel engine 106 and an exhaust system 110 operably connected thereto.
- System 100 may be part any of the various types of engine-based apparatus, such as motorized vehicles (cars, trucks, tractors, trains, etc.), marine vessels, or stationary systems, such as a generator.
- Exhaust system 110 includes a filter housing 120 that houses DPF 10 .
- the phrases “upstream” and “downstream” used below in connection with system 100 refer to locations in the system that are relatively closer to or farther away from engine 106 , which is the source of diesel particulates 52 .
- the “upstream” side of DPF 10 is the diesel-engine side of the filter, while the downstream side of the DPF is the filter side opposite the diesel engine.
- the upstream side of DPF 10 has an associated upstream pressure P U while the downstream side has an associated downstream pressure P D .
- FIG. 6 is a close-up view of a portion of system 100 of FIG. 5 , showing filter housing 120 and DPF 10 arranged therein, and also showing a controller 200 , which is introduced and described in detail below.
- filter housing 120 includes a central cylindrical section 122 in which filter 120 resides. Central cylindrical section 122 is capped at its ends by respective upstream and downstream frustro-conical end sections 124 U and 124 D, which are each operably connected to an exhaust conduit 130 , shown in FIG. 5 .
- Filter housing 120 is preferably made of metal and defines a microwave resonant cavity 126 having a microwave resonant frequency f R .
- a metal screen 136 is provided at one end of central cylindrical section 122 and serves to define an end boundary of microwave resonant cavity 126 by reflecting microwave radiation 182 .
- frustro-conical end sections 124 U and 124 D are configured to act as microwave reflectors that define respective ends of microwave resonant cavity 126 .
- DPF 10 and diesel particulates 52 trapped therein serve as an artificial dielectric having a dielectric permittivity that changes with the concentration of diesel particulates.
- Such changes in the dielectric permittivity alter the microwave resonant frequency f R of microwave resonant cavity 126 , thereby providing an indirect measure of diesel particulate content in DPF 10 .
- system 100 also includes a regeneration unit 140 operably disposed between engine 106 and exhaust system 110 and operably coupled to each via respective exhaust conduits 130 .
- Regeneration unit 140 is responsive to a control signal S R and is adapted to regenerate DPF 10 by removing diesel particulates 52 therefrom.
- regeneration unit 140 is configured to perform a controlled regeneration by generating an amount of heat sufficient to burn off diesel particulates 52 trapped in DPF 10 .
- regeneration unit 140 comprising an external heater, or employing a diesel oxidation catalyst (DOC) that burns injected hydrocarbons.
- DOC diesel oxidation catalyst
- a non-limiting example of an engine system that includes a regeneration unit (“regeneration device”) is described in U.S. Pat. No. 7,260,930, which patent is incorporated by reference herein.
- System 100 also includes upstream and downstream pressure sensors 150 U and 150 D respectively disposed upstream and downstream of DPF 10 , e.g., in respective upstream and downstream frustro-conical end sections 124 U and 124 D, as shown by way of example in FIG. 5 and FIG. 6 .
- system 100 includes a temperature sensor 160 arranged within filter housing 120 and located relative to DPF 10 so that it can accurately measure the temperature of the DPF.
- System 100 further includes at least one microwave probe (antenna) 180 arranged within filter housing 120 and microwave resonant cavity 126 formed thereby.
- microwave probes 180 Two microwave probes 180 A and 180 B are shown by way of illustration and are referred to herein below collectively as “microwave probes 180 .”
- Microwave probes 180 are connected to a microwave generator 181 .
- Microwave generator 181 generates a microwave signal S 1 and one of microwave probes 180 is used to generate microwave radiation 182 having one or more microwave frequencies (including, for example, a frequency sweep) in response to microwave signal S 1 .
- One of microwave probes 180 is also adapted to receive or detect microwave radiation 182 and generate therefrom a detected microwave signal S M representative of the response (“cavity response”) of microwave cavity 126 .
- microwave probes 180 are high-temperature coaxial probes that extend into microwave resonant cavity 126 .
- Microwave generator 181 includes a directional coupler or circulator 184 to direct detected microwave signals S M back to controller 200 .
- a non-limiting example of a microwave-based technique for measuring diesel particulate concentration is described in U.S. Pat. No. 4,477,771, which patent is incorporated by reference herein.
- System 100 further includes the aforementioned controller 200 , which is electrically connected to engine 106 , regeneration unit 140 , pressure sensors 150 U and 150 D, temperature sensor 160 , and microwave generator 181 .
- Controller 200 is, for example, a personal computer or other type of computer, and generally includes a processor 202 (e.g., a central processing unit (CPU), or an engine control unit (ECU)), and a computer-readable storage medium 204 (e.g., a memory unit such as a DRAM, ROM, CD-ROM, etc.) operably connected to the processor.
- Computer-readable storage medium 204 is adapted for storing computer-readable instructions (e.g., software) that direct processor 202 to control the operation of system 100 and to carry out the methods described below.
- controller 200 includes other various known circuitry (not shown), known in the art such as power supply circuitry, control circuitry, signal-processing circuitry, and the like.
- the combustion associated with running diesel engine 106 generates diesel particulates 52 . These particulates enter DPF 10 and are trapped therein in the manner described above in connection with FIG. 4 .
- the pressure drop ⁇ P across DPF 10 is measured using upstream and downstream pressure sensors 150 U and 150 P. These pressure sensors send to controller 200 respective pressure signals S PU and S PD , which are representative of the respective pressure measurements P U and P D on the upstream and downstream sides of DPF 10 .
- Controller 200 monitors the measured pressure drop ⁇ P across DPF 10 based on pressure signals S PU and S PD .
- ECU revolutions per minute
- controller 200 sends a regeneration signal S R to regeneration unit 140 to activate the regeneration unit and to initiate the regeneration of DPF 10 .
- pressure drop threshold ⁇ P TH corresponds exactly to limit T DP of diesel particulates 52 that DPF 10 can accumulate and still adequately perform its filtering function.
- the problem with this prior art approach is that the residual amount RA DP varies with each regeneration step. These variations mean that a fixed value for the pressure drop threshold ⁇ P TH leads to a miscalculation of when to perform the next DPF regeneration process.
- the next regeneration process will have either less than or more than the actual limit T DP of diesel particulates 52 . If there are more diesel particulates 52 than the limit T DP , then the combustion from the regeneration process will generate more heat than expected and possibly damage DPF 10 . If there are less diesel particulates 52 than the limit T DP , then the DPF will be regenerated sooner than necessary.
- the method described herein calibrates (i.e., re-sets) the pressure drop threshold ⁇ P TH after each regeneration step so that it is more consistent with the actual limit T DP of diesel particulates 52 that can accumulate in the DPF before regeneration is necessary. This allows for the regeneration step to be performed at the right time. While the methods described herein may not always yield a theoretically exact limit T DP , it provides a much closer estimate of the exact theoretical amount as compared to simply setting the pressure drop threshold ⁇ P TH at a set value for a given filter regardless of the number of regenerations performed on the filter.
- the method of the present invention involves performing a sensitive measurement of the residual amount RA DP .
- the measurable residual amount RA DP is less than or equal to about 3 g/l at a filter temperature of about 300° C., while in another exemplary embodiment, the measurable residual amount RA DP is less than or equal to about 9 g/l at a filter temperature of about 25° C.
- the measurable residual amount RA DP for a given temperature within 25° C. and 300° C. is based on an interpolation (e.g., a linear interpolation) of the above values.
- controller 200 activates microwave generator 181 so that one of microwave probes 180 generates microwave radiation 182 of at least one microwave frequency.
- a single probe (say, probe 180 A) that serves as both transmitter and receiver of microwave radiation 182 is used, while in another example embodiment two probes 180 A and 180 B are used, with one probe serving as a transmitter and the other as a receiver.
- either a single microwave frequency or a small range of frequencies is used, and attenuation of microwave signal S M is measured either at the single frequency or at two or three frequencies in the small range of frequencies.
- a relatively large range of microwave frequencies is used (e.g., as in a frequency sweep), and the frequency shift in one of the resonant frequencies f R is measured.
- both a single-frequency attenuation measurement and a resonant-frequency-shift measurement are taken and the results are combined. Any or all of the aforementioned approaches involve exciting microwave resonant cavity 126 with microwave radiation 182 in a manner that yields a measurement of the microwave cavity response.
- FIG. 7 is a plot of the microwave signal spectrum showing the microwave signal intensity I (dBm) vs. Frequency (GHz) as deduced from the detected microwave signal S M for various amounts of select diesel particulate loading of an example DPF 10 .
- the measurements for the microwave signal spectrum were obtained using two microwave probes 180 A and 180 B.
- the filter temperature was measured at 300° C.
- the plot of FIG. 7 shows how the magnitude and position (resonant frequency f R ) of resonant peak RP changes most strongly and in a correlated manner for diesel particulate concentrations of about 3 g/l or less. It also shows that at 300° C. the microwave measurement technique loses its sensitivity at larger diesel particulate concentrations. Decreasing measurement sensitivity with increasing filter temperature is the main reason why methods that solely rely on microwave measurements of diesel particulate accumulation to determine when to perform filter regeneration tend to be inaccurate.
- One example microwave measurement technique employed herein involves tracking the location (or both the location and attenuation) of resonant peak RP to measure the residual amount RA DP in the range over which the microwave measurement technique has the greatest sensitivity, namely RA DP of about 3 g/l or less at a temperature of about 300° C. Data taken at room temperature of 25° C. (not shown) indicate that the microwave measurement technique provides adequate sensitivity to accurately measure RA DP of equal to or less than about 9 g/l at a temperature of about 25° C.
- FIG. 8 plots the microwave signal intensity I (dBm) vs. diesel particulate concentration (g/l) at a frequency of 1.6 GHz for a variety of temperatures ranging from 25° C. to 600° C.
- the microwave signal intensity I was obtained by using a single microwave probe 180 as both transmitter and receiver.
- a look-up table, calibration curve, or other type of database or file is created (and preferably stored in computer-readable medium 204 ) based on calibrated microwave measurements.
- An example method of obtaining such a calibrated microwave measurement uses controlled diesel particulate concentrations and taking accurate measurements of DPF temperature T F to provide a temperature calibration or correction for the measurement of residual amount RA DP .
- a temperature signal S T from temperature sensor 160 that is representative of the measured temperature T F of DPF 10 is provided to controller 200 .
- the DPF temperature T F is kept constant so that the calibration for the measurement of residual amount RA DP stays constant.
- the particular single microwave frequency chosen for creating data depends on the particular geometry of filter housing 120 .
- different DPF materials e.g., Cordierite, SiC and AT, for example, show slightly different signal spectra. However, they all experience a change in the spectra with increasing diesel particulate concentration similar to that shown in FIG. 7 and FIG. 8 .
- the microwave measurement method is very sensitive to small amounts of diesel particulates 52 due to their high dielectric loss factor.
- the loss factor of a particulate-filled filter becomes too large, the penetration depth of microwave radiation 182 drops to below the cavity length. This means that microwave radiation 182 no longer “monitors” the entire cavity—i.e. portions of the accumulated diesel particulates 52 are not taken into account and the method becomes invalid, or at least less valid.
- the onset of this self-shielding phenomenon is determined by the diesel particulate mass and the DPF temperature T F , since both have a strong influence on the loss factor.
- controller 200 re-sets the pressure drop threshold ⁇ P TH . It should be noted, however, there may be occasions where the pressure drop threshold ⁇ P TH remains the same, or substantially the same, because the measured residual amount RA DP is the same, or substantially the same. Nevertheless, this re-set step is performed because it is not desirable to regenerate DPF 10 prior to when the limit T DP of diesel particulates 52 has been reached because it unnecessarily interrupts the regular operation of system 100 and also imposes unnecessary wear and tear on the DPF. On the other hand, it is not desirable to regenerate DPF 10 after the limit T DP of diesel particulates has accumulated because the DPF will be operating in an overloaded and inefficient manner and will be more difficult to regenerate without damaging the filter.
- controller 200 sends another engine control signal S E to engine 106 to allow the engine to adjust to a different operating state, such as an operating state more favorable for normal engine operation.
- a different operating state such as an operating state more favorable for normal engine operation.
- controller 200 While system 100 is running, the pressure drop ⁇ P is again monitored across DPF 10 by controller 200 as described above. System 100 is allowed to run until the (re-set) pressure drop threshold ⁇ P TH is reached.
- controller 200 once again sends an engine control signal S E to re-set the operating state of engine 106 as described above. Controller 200 once again initiates another regeneration step by sending control signal S R to regeneration unit 140 , as described above.
- Another DPF regeneration is then initiated, which reduces the diesel particulate accumulation from substantially the limit T DP of diesel particulates down to the variable residual amount RA DP left behind due to an inherently variable regeneration process.
- the regeneration step is carried out so that residual amounts RA DP are within ranges where the microwave measurement is most sensitive.
- the acts of re-setting the pressure drop threshold ⁇ P TH , running system 100 until the re-set pressure drop threshold ⁇ P TH is reached, adjusting the operating state of engine 106 , and then regenerating DPF 10 are repeated multiple times.
- DPF 10 is regenerated while still residing in system 100 , while in another example embodiment, the DPF it is removed and regenerated by a regeneration unit 140 other than the one residing in system 100 .
Abstract
Methods for determining when to regenerate an exhaust gas particulate filter (10), for regenerating, and for calibrating a pressure drop across such filters are disclosed. An example method involves reducing a first amount of particulates (52) accumulated in the filter to a residual amount RADP. The method also includes measuring the residual amount RADP by exciting the microwave resonant cavity (126) in which the filter resides with microwave radiation (182) and then monitoring the microwave cavity response. The method also includes using the measured value of RADP to calibrate a pressure drop threshold ΔPTH SO that it is representative of a limit (TDP) of particulate accumulation in the filter. The methods may also include regenerating the filter a number of times and each time re-setting the pressure drop threshold ΔPTH based on measurements of RADP taken after each filter regeneration.
Description
- The present invention relates to exhaust gas particulate filters, and in particular to methods for determining when to regenerate exhaust gas particulate filters, for regenerating, and for calibrating a pressure drop across such filters.
- Exhaust gas particulate filters (“filters”) are used to remove exhaust gas particulates generated by combustion engines. In a particular example, diesel particulate filters (DPFs) are designed to accumulate diesel exhaust particulates (“soot”) from diesel engines and are used in a variety of diesel applications, including motor vehicles. DPFs are ceramic-based structures that generally comprise a network of interconnected web walls that form a matrix of elongated, gas-conducting cells that can have a variety of cross-sectional shapes. Other types of filters (e.g., for gasoline engines) have a similar type of cellular structure designed to capture exhaust gas particulates.
- Filter performance depends in part on the amount of particulates that the filter accumulates. Filters can be “regenerated” via thermal processing once the amount of accumulated particulates reaches a certain maximum allowed (i.e., threshold) level. The success of the regeneration process, however, requires accurately determining this threshold level.
- One method of determining the maximum allowable amount of accumulated particulates in a filter involves measuring the pressure drop across the filter. However, this method tends to be inaccurate and often leads to either an under or over prediction of the amount of particulates accumulated in the filter. A main source of this inaccuracy is due to the variability of the regeneration process, which leaves different amounts of residual particulates in the filter after each regeneration.
- One aspect of the invention is a method of determining when to regenerate a filter disposed in a microwave resonant cavity, wherein the filter has a particulate mass accumulation limit. The method includes reducing a first amount of particulates accumulated in the filter to a residual amount. The method also includes measuring the residual amount by exciting the microwave resonant cavity with microwave radiation and monitoring a cavity response. The method also includes using the measured residual amount to determine a pressure drop threshold representative of the particulate mass accumulation limit in the filter.
- Another aspect of the invention is a method of regenerating a filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates when operably arranged in an engine exhaust system. The method includes measuring a first residual amount of particulates in the filter by exciting the microwave resonant cavity with microwave radiation and monitoring the cavity response. The method also includes using the measured first residual amount to establish a pressure drop threshold across the filter that is representative of a predetermined amount of particulate accumulation in the filter. The method further includes operating the engine and monitoring the pressure drop across the filter as the filter accumulates particulates. The method also includes regenerating the filter when the pressure drop reaches the pressure drop threshold to reduce the particulate accumulation to a second residual amount. In one case, the filter is a DPF and the residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C.
- Another aspect of the invention is a method of calibrating a pressure drop across a filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates that cause a pressure drop when the filter is operably arranged in an engine exhaust system. The method includes reducing an initial amount of accumulated particulates in the filter to be equal to or less than a residual amount, wherein the initial amount is greater than the residual amount. The method also includes measuring the residual amount by exciting the microwave resonant cavity with a microwave signal having at least one microwave frequency and measuring at least one of a microwave signal resonant frequency shift and a microwave signal attenuation. The method also includes, based on the measured residual amount, establishing a pressure drop threshold across the filter that corresponds to an allowable amount of accumulated particulates. The method also includes measuring the pressure drop across the filter while the filter is operably arranged in the engine exhaust system, and reducing the accumulated particulates to be less than or equal to the residual amount when the pressure drop reaches the pressure drop threshold.
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FIG. 1 is a perspective side view of a filter in the form of a DPF; -
FIG. 2 is a cross-sectional view of a DPF similar to that shown inFIG. 1 , showing the longitudinal cells and the alternating plugged cell ends; -
FIG. 3 is a close-up end view of the DPF ofFIG. 1 ; -
FIG. 4 is a close-up perspective cut-away view of an end portion of a DPF and shows the flow of unfiltered diesel exhaust into the DPF, the flow of filtered diesel exhaust out of the DPF, and the accumulation of particulates within the DPF; -
FIG. 5 is a schematic diagram of an example diesel engine system that includes a DPF and in which the method of the present invention is applied by way of illustration; -
FIG. 6 is a schematic close-up view of a portion of the diesel engine system ofFIG. 5 showing the filter housing and DPF arranged therein, and the controller; -
FIG. 7 is a plot of the microwave signal spectrum showing the microwave signal intensity I (dBm) vs. Frequency (GHz) as deduced from the detected microwave signal SM for various amounts of select diesel particulate loading of an example DPF at 300° C.; and -
FIG. 8 is a plot of the microwave signal intensity I (dBm) vs. diesel particulate concentration (g/l) at a frequency of 1.6 GHz for a variety of temperatures ranging from 25° C. to 600° C. - Reference is now made in detail to various or different embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like elements or components. It will be understood that the drawings are for the purpose of describing particular embodiments and are not intended to limit the disclosure thereto.
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FIG. 1 is a perspective side view of afilter 10 in the form of a DPF (hereinafter, “DPF 10”). Cartesian coordinates are shown for the sake of reference.FIG. 2 is a cross-sectional view ofDPF 10 similar to that ofFIG. 1 , andFIG. 3 is a close-up end view of the DPF ofFIG. 1 . - The
typical DPF 10 has ahoneycomb structure 12 with an axial length L, a diameter or width D and a central axis A1 that defines an axial (longitudinal) direction. Honeycombstructure 12 is formed by a matrix of intersecting, thin,porous walls 14 surrounded by anouter wall 15.Walls 14 extend across and betweenopposing ends ends Cells 20 are plugged withplugs 30 in an alternating fashion atends - An
example DPF 10 has between about 100 and 400 cells per square inch andwalls 14 that are generally on the order of 10-25 mils (e.g., about 0.25-0.65 mm) thick. The corresponding cell widths WC (FIG. 3 ) are typically in the range from about 8 mm to about 1.25 mm. Typical diameters D range from about 6 inches (about 15.24 cm) to about 15 inches (about 38.1 cm). -
DPFs 10 are manufactured, for example, by extruding a plasticized ceramic-forming precursor of, for example, cordierite, mullite, silicon carbide, or aluminum titanate, through an extrusion die. The extruded “green body” is then cut and dried. Such green bodies are quite fragile and must be transported to a kiln, wherein the heat transforms the relatively soft and fragile green body into hardened, fired ware withrigid honeycomb structure 12, which is then plugged withplugs 30. - DPFs are used in diesel engines to filter diesel engine exhaust, which includes diesel particulates, also referred to in the art as “soot.”
FIG. 4 is a close-up, perspective cut-away view of an end portion ofDPF 10 and shows the flow of unfiltered diesel exhaust gas (“diesel exhaust”) 50 intoend 16 of the DPF.Unfiltered diesel exhaust 50 contains particulates (specifically, diesel particulates) 52. Because eachcell 20 is blocked at one of its ends, the flow ofdiesel exhaust 50 into a given cell builds up pressure in a given cell, which causes the diesel exhaust to flow throughporous walls 14.Porous walls 14 have a porosity designed to allow the gaseous constituents ofdiesel exhaust 50 to pass and trapdiesel particulates 52. Thus,diesel particulates 52 accumulate on and inwalls 14, while the “cleaned” or “filtered”diesel exhaust 50′ that passes through thewalls 14exits DPF 10 through theadjacent channel 20 at (open)end 18. - The accumulation of
diesel particulates 52 inDPF 10 ultimately reduces the performance of the engine in which the DPF resides, and reduces the DPF's durability. In particular,diesel particulates 52 cause a pressure drop across the DPF. There is typically a preset threshold value or maximum accumulation limit TDP (hereinafter, “limit TDP”) of an accumulation amount (e.g., mass) ADP ofdiesel particulates 52, beyond whichDPF 10 either needs to be replaced or “regenerated” by reducing the amount of diesel particulates to a minimal level. An example regeneration process is a “controlled” regeneration that involvesheating DPF 10 to burn off the accumulateddiesel particulates 52. - Typically, the regeneration step is initiated when the pressure drop ΔP across
DPF 10 reaches a threshold pressure drop ΔPTH. However, each regeneration step leaves different residual amounts RADP ofdiesel particulates 52 inDPF 10. This causes errors in the correlation between the threshold pressure drop ΔPTH and the limit TDP ofdiesel particulates 52 allowed to accumulate inDPF 10. It is therefore desirable to have an accurate measure of the residual amount RADP of accumulated diesel particulates after the regeneration step has been performed so that measuring the pressure drop ΔP acrossDPF 10 provides accurate information (“feedback”) so that DPF regeneration can be carried out at the proper time. - Diesel Engine System with DPF and Pressure Drop Feedback
-
FIG. 5 is a schematic diagram of an example engine system in the form of a diesel engine system (“system”) 100 that includes adiesel engine 106 and anexhaust system 110 operably connected thereto.System 100 may be part any of the various types of engine-based apparatus, such as motorized vehicles (cars, trucks, tractors, trains, etc.), marine vessels, or stationary systems, such as a generator. -
Exhaust system 110 includes afilter housing 120 that housesDPF 10. The phrases “upstream” and “downstream” used below in connection withsystem 100 refer to locations in the system that are relatively closer to or farther away fromengine 106, which is the source ofdiesel particulates 52. Thus, the “upstream” side ofDPF 10 is the diesel-engine side of the filter, while the downstream side of the DPF is the filter side opposite the diesel engine. Insystem 100, the upstream side ofDPF 10 has an associated upstream pressure PU while the downstream side has an associated downstream pressure PD. The pressure drop acrossDPF 10 is thus given by ΔP=PU−PD. -
FIG. 6 is a close-up view of a portion ofsystem 100 ofFIG. 5 , showingfilter housing 120 andDPF 10 arranged therein, and also showing acontroller 200, which is introduced and described in detail below. In an example embodiment, filterhousing 120 includes a centralcylindrical section 122 in which filter 120 resides. Centralcylindrical section 122 is capped at its ends by respective upstream and downstream frustro-conical end sections exhaust conduit 130, shown inFIG. 5 .Filter housing 120 is preferably made of metal and defines a microwaveresonant cavity 126 having a microwave resonant frequency fR. - In an example embodiment, a
metal screen 136 is provided at one end of centralcylindrical section 122 and serves to define an end boundary of microwaveresonant cavity 126 by reflectingmicrowave radiation 182. In another example embodiment, frustro-conical end sections resonant cavity 126. - As discussed in greater detail below,
DPF 10 anddiesel particulates 52 trapped therein serve as an artificial dielectric having a dielectric permittivity that changes with the concentration of diesel particulates. Such changes in the dielectric permittivity alter the microwave resonant frequency fR of microwaveresonant cavity 126, thereby providing an indirect measure of diesel particulate content inDPF 10. - With reference again to
FIG. 5 ,system 100 also includes aregeneration unit 140 operably disposed betweenengine 106 andexhaust system 110 and operably coupled to each viarespective exhaust conduits 130.Regeneration unit 140 is responsive to a control signal SR and is adapted to regenerateDPF 10 by removingdiesel particulates 52 therefrom. In an exemplary embodiment,regeneration unit 140 is configured to perform a controlled regeneration by generating an amount of heat sufficient to burn offdiesel particulates 52 trapped inDPF 10. There are multiple ways to generate the heat needed to initiate a controlled regeneration, and examples includeregeneration unit 140 comprising an external heater, or employing a diesel oxidation catalyst (DOC) that burns injected hydrocarbons. A non-limiting example of an engine system that includes a regeneration unit (“regeneration device”) is described in U.S. Pat. No. 7,260,930, which patent is incorporated by reference herein. -
System 100 also includes upstream anddownstream pressure sensors DPF 10, e.g., in respective upstream and downstream frustro-conical end sections FIG. 5 andFIG. 6 . In addition,system 100 includes atemperature sensor 160 arranged withinfilter housing 120 and located relative toDPF 10 so that it can accurately measure the temperature of the DPF. -
System 100 further includes at least one microwave probe (antenna) 180 arranged withinfilter housing 120 and microwaveresonant cavity 126 formed thereby. Twomicrowave probes microwave generator 181.Microwave generator 181 generates a microwave signal S1 and one of microwave probes 180 is used to generatemicrowave radiation 182 having one or more microwave frequencies (including, for example, a frequency sweep) in response to microwave signal S1. One of microwave probes 180 is also adapted to receive or detectmicrowave radiation 182 and generate therefrom a detected microwave signal SM representative of the response (“cavity response”) ofmicrowave cavity 126. - Detected microwave signals SM are then analyzed to determine a measured amount of
diesel particulates 52 inDPF 10. In an example embodiment, microwave probes 180 are high-temperature coaxial probes that extend into microwaveresonant cavity 126.Microwave generator 181 includes a directional coupler orcirculator 184 to direct detected microwave signals SM back tocontroller 200. A non-limiting example of a microwave-based technique for measuring diesel particulate concentration is described in U.S. Pat. No. 4,477,771, which patent is incorporated by reference herein. -
System 100 further includes theaforementioned controller 200, which is electrically connected toengine 106,regeneration unit 140,pressure sensors temperature sensor 160, andmicrowave generator 181.Controller 200 is, for example, a personal computer or other type of computer, and generally includes a processor 202 (e.g., a central processing unit (CPU), or an engine control unit (ECU)), and a computer-readable storage medium 204 (e.g., a memory unit such as a DRAM, ROM, CD-ROM, etc.) operably connected to the processor. Computer-readable storage medium 204 is adapted for storing computer-readable instructions (e.g., software) thatdirect processor 202 to control the operation ofsystem 100 and to carry out the methods described below. In an example embodiment,controller 200 includes other various known circuitry (not shown), known in the art such as power supply circuitry, control circuitry, signal-processing circuitry, and the like. - With continuing reference to
FIG. 5 andFIG. 6 , during the operation ofsystem 100, the combustion associated with runningdiesel engine 106 generatesdiesel particulates 52. These particulates enterDPF 10 and are trapped therein in the manner described above in connection withFIG. 4 . During the operation ofsystem 100, the pressure drop ΔP acrossDPF 10 is measured using upstream anddownstream pressure sensors 150U and 150P. These pressure sensors send tocontroller 200 respective pressure signals SPU and SPD, which are representative of the respective pressure measurements PU and PD on the upstream and downstream sides ofDPF 10.Controller 200 monitors the measured pressure drop ΔP acrossDPF 10 based on pressure signals SPU and SPD. - When
controller 200 measures a pressure drop ΔP=ΔPTH, it sends an engine control signal SE toengine 106 to change the engine running conditions to be favorable for filter regeneration. For instance,engine 106 keeps running and the system in which the engine resides keeps operating. For example, in the case wheresystem 100 is part of a motor vehicle,engine 106 operates to keep the vehicle in motion if it is already in motion. However, certain engine operating parameters, such as the air intake, fuel consumption, revolutions per minute (RPM), various exhaust gas temperatures, and like engine parameters, are tightly controlled during regeneration according to instructions stored in computer-readable storage medium 204 and executed by processor (ECU) 202. - Once
engine 106 is set to run under conditions favorable for filter regeneration,controller 200 sends a regeneration signal SR toregeneration unit 140 to activate the regeneration unit and to initiate the regeneration ofDPF 10. Ideally, pressure drop threshold ΔPTH corresponds exactly to limit TDP ofdiesel particulates 52 that DPF 10 can accumulate and still adequately perform its filtering function. - At this point, the prior art methods that use pressure-drop feedback to trigger DPF regeneration assume that only a negligible residual amount RADP of
diesel particulates 52 is left inDPF 10 after a regeneration step is carried out. In this case,DPF 10 is placed back in operation and once again starts to accumulatediesel particulates 52 until the same pressure drop threshold ΔPTH is reached. - The problem with this prior art approach, however, is that the residual amount RADP varies with each regeneration step. These variations mean that a fixed value for the pressure drop threshold ΔPTH leads to a miscalculation of when to perform the next DPF regeneration process. In particular, the next regeneration process will have either less than or more than the actual limit TDP of
diesel particulates 52. If there aremore diesel particulates 52 than the limit TDP, then the combustion from the regeneration process will generate more heat than expected and possibly damageDPF 10. If there areless diesel particulates 52 than the limit TDP, then the DPF will be regenerated sooner than necessary. - The method described herein calibrates (i.e., re-sets) the pressure drop threshold ΔPTH after each regeneration step so that it is more consistent with the actual limit TDP of
diesel particulates 52 that can accumulate in the DPF before regeneration is necessary. This allows for the regeneration step to be performed at the right time. While the methods described herein may not always yield a theoretically exact limit TDP, it provides a much closer estimate of the exact theoretical amount as compared to simply setting the pressure drop threshold ΔPTH at a set value for a given filter regardless of the number of regenerations performed on the filter. - Accordingly, after the DPF regeneration is terminated by
controller 200, the method of the present invention involves performing a sensitive measurement of the residual amount RADP. In one exemplary embodiment, the measurable residual amount RADP is less than or equal to about 3 g/l at a filter temperature of about 300° C., while in another exemplary embodiment, the measurable residual amount RADP is less than or equal to about 9 g/l at a filter temperature of about 25° C. In one exemplary embodiment, the measurable residual amount RADP for a given temperature within 25° C. and 300° C. is based on an interpolation (e.g., a linear interpolation) of the above values. - To measure the residual amount RADP,
controller 200 activatesmicrowave generator 181 so that one of microwave probes 180 generatesmicrowave radiation 182 of at least one microwave frequency. In one example embodiment, a single probe (say,probe 180A) that serves as both transmitter and receiver ofmicrowave radiation 182 is used, while in another example embodiment twoprobes - In one example embodiment, either a single microwave frequency or a small range of frequencies is used, and attenuation of microwave signal SM is measured either at the single frequency or at two or three frequencies in the small range of frequencies. In another example embodiment, a relatively large range of microwave frequencies is used (e.g., as in a frequency sweep), and the frequency shift in one of the resonant frequencies fR is measured. In an example embodiment, both a single-frequency attenuation measurement and a resonant-frequency-shift measurement are taken and the results are combined. Any or all of the aforementioned approaches involve exciting microwave
resonant cavity 126 withmicrowave radiation 182 in a manner that yields a measurement of the microwave cavity response. -
FIG. 7 is a plot of the microwave signal spectrum showing the microwave signal intensity I (dBm) vs. Frequency (GHz) as deduced from the detected microwave signal SM for various amounts of select diesel particulate loading of anexample DPF 10. The measurements for the microwave signal spectrum were obtained using twomicrowave probes FIG. 7 shows how the magnitude and position (resonant frequency fR) of resonant peak RP changes most strongly and in a correlated manner for diesel particulate concentrations of about 3 g/l or less. It also shows that at 300° C. the microwave measurement technique loses its sensitivity at larger diesel particulate concentrations. Decreasing measurement sensitivity with increasing filter temperature is the main reason why methods that solely rely on microwave measurements of diesel particulate accumulation to determine when to perform filter regeneration tend to be inaccurate. - One example microwave measurement technique employed herein involves tracking the location (or both the location and attenuation) of resonant peak RP to measure the residual amount RADP in the range over which the microwave measurement technique has the greatest sensitivity, namely RADP of about 3 g/l or less at a temperature of about 300° C. Data taken at room temperature of 25° C. (not shown) indicate that the microwave measurement technique provides adequate sensitivity to accurately measure RADP of equal to or less than about 9 g/l at a temperature of about 25° C.
-
FIG. 8 plots the microwave signal intensity I (dBm) vs. diesel particulate concentration (g/l) at a frequency of 1.6 GHz for a variety of temperatures ranging from 25° C. to 600° C. The microwave signal intensity I was obtained by using a single microwave probe 180 as both transmitter and receiver. In an example embodiment, a look-up table, calibration curve, or other type of database or file is created (and preferably stored in computer-readable medium 204) based on calibrated microwave measurements. An example method of obtaining such a calibrated microwave measurement uses controlled diesel particulate concentrations and taking accurate measurements of DPF temperature TF to provide a temperature calibration or correction for the measurement of residual amount RADP. In an example embodiment, a temperature signal ST fromtemperature sensor 160 that is representative of the measured temperature TF ofDPF 10 is provided tocontroller 200. In another example embodiment, the DPF temperature TF is kept constant so that the calibration for the measurement of residual amount RADP stays constant. - The particular single microwave frequency chosen for creating data, such as the data shown in the plot of
FIG. 8 , depends on the particular geometry offilter housing 120. For example, for a typicalcylindrical filter housing 120 that accommodates a 5.66″diameter DPF 10, the corresponding microwaveresonant cavity 126 supports microwave frequencies around 1 GHz, with a strong resonance peak RP at about fR=1.4 GHz. For a given geometry forfilter housing 120, different DPF materials (e.g., Cordierite, SiC and AT, for example,) show slightly different signal spectra. However, they all experience a change in the spectra with increasing diesel particulate concentration similar to that shown inFIG. 7 andFIG. 8 . - Aside from filter housing size and geometry, another important factor in choosing the correct microwave frequency for single-frequency cavity response measurements is the dielectric loss factor of
dielectric particulates 52, which loss factor increases with decreasing frequency. Thus, there is a trade-off between measurement sensitivity and signal saturation. - Generally, the microwave measurement method is very sensitive to small amounts of
diesel particulates 52 due to their high dielectric loss factor. However, when the loss factor of a particulate-filled filter becomes too large, the penetration depth ofmicrowave radiation 182 drops to below the cavity length. This means thatmicrowave radiation 182 no longer “monitors” the entire cavity—i.e. portions of the accumulateddiesel particulates 52 are not taken into account and the method becomes invalid, or at least less valid. The onset of this self-shielding phenomenon is determined by the diesel particulate mass and the DPF temperature TF, since both have a strong influence on the loss factor. - It is desirable to carry out microwave-based measurements of the residual amount RADP at a DPF temperature above 100° C. because of the adverse impact of liquid water on the measurements at low temperatures. It is also desirable that any water in
DPF 10 be in the form of water vapor. For the above reasons, it is desirable to perform the microwave measurement of the residual amount RADP as soon as possible after the regeneration of the DPF. - Once residual amount RADP in
DPF 10 has been determined,controller 200 re-sets the pressure drop threshold ΔPTH. It should be noted, however, there may be occasions where the pressure drop threshold ΔPTH remains the same, or substantially the same, because the measured residual amount RADP is the same, or substantially the same. Nevertheless, this re-set step is performed because it is not desirable to regenerateDPF 10 prior to when the limit TDP ofdiesel particulates 52 has been reached because it unnecessarily interrupts the regular operation ofsystem 100 and also imposes unnecessary wear and tear on the DPF. On the other hand, it is not desirable to regenerateDPF 10 after the limit TDP of diesel particulates has accumulated because the DPF will be operating in an overloaded and inefficient manner and will be more difficult to regenerate without damaging the filter. - Once pressure drop threshold ΔPTH is re-set,
controller 200 sends another engine control signal SE toengine 106 to allow the engine to adjust to a different operating state, such as an operating state more favorable for normal engine operation. Whilesystem 100 is running, the pressure drop ΔP is again monitored acrossDPF 10 bycontroller 200 as described above.System 100 is allowed to run until the (re-set) pressure drop threshold ΔPTH is reached. At this point,controller 200 once again sends an engine control signal SE to re-set the operating state ofengine 106 as described above.Controller 200 once again initiates another regeneration step by sending control signal SR toregeneration unit 140, as described above. Another DPF regeneration is then initiated, which reduces the diesel particulate accumulation from substantially the limit TDP of diesel particulates down to the variable residual amount RADP left behind due to an inherently variable regeneration process. As discussed above, the regeneration step is carried out so that residual amounts RADP are within ranges where the microwave measurement is most sensitive. - In an example embodiment, the acts of re-setting the pressure drop threshold ΔPTH, running
system 100 until the re-set pressure drop threshold ΔPTH is reached, adjusting the operating state ofengine 106, and then regeneratingDPF 10 are repeated multiple times. In an example embodiment,DPF 10 is regenerated while still residing insystem 100, while in another example embodiment, the DPF it is removed and regenerated by aregeneration unit 140 other than the one residing insystem 100. - While the description above refers to DPFs as a particular example of an exhaust gas particulate filter, one skilled in the art will understand that the methods described above apply generally to particulate-accumulating exhaust gas filters that are amenable to regeneration and to having their particulate concentration measured using microwave-frequency radiation. It will thus be apparent to those skilled in the art that various modifications to the example embodiments as described herein can be made without departing from the spirit or scope of the defined disclosure and in the appended claims. Thus, it is intended that the disclosure covers the modifications and variations, provided they come within the scope of the appended claims and the equivalents thereto.
Claims (20)
1. A method of determining when to regenerate an exhaust gas particulate filter disposed in a microwave resonant cavity, the filter having a particulate mass accumulation limit, comprising:
a) reducing a first amount of particulates accumulated in the filter to a first residual amount;
b) measuring the first residual amount by exciting the microwave resonant cavity with microwave radiation and monitoring a cavity response; and
c) using the measured first residual amount to determine a pressure drop threshold representative of the particulate mass accumulation limit in the filter.
2. The method according to claim 1 , wherein the filter comprises a diesel particulate filter, and wherein the first residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C.
3. The method according to claim 1 , further comprising:
measuring a pressure drop across the filter as the filter accumulates a second amount of particulates; and
reducing the second amount of accumulated particulates to a second residual amount when the measured pressure drop equals the pressure drop threshold.
4. The method according to claim 1 , wherein reducing at least one of the first and second amounts of particulates includes applying heat to the filter.
5. The method according to claim 1 , further comprising:
performing a temperature measurement of the filter; and
performing a temperature correction to the measured first residual amount based on the temperature measurement.
6. The method according to claim 1 , further comprising performing at least one of acts a) through c) while the filter and microwave resonant cavity are operably arranged in an engine exhaust system.
7. The method according to claim 1 , further comprising:
operably arranging the filter and the microwave resonant cavity in an engine exhaust system;
operating the engine exhaust system and measuring a pressure drop across the filter as the filter accumulates a second amount of particulates; and
reducing the second amount of accumulated particulates to a second residual amount when the measured pressure drop equals the pressure drop threshold.
8. The method according to claim 7 , further comprising:
measuring the second residual amount by exciting the microwave resonant cavity with microwave energy and monitoring the cavity response; and
using the measured second residual amount to re-set the pressure drop threshold.
9. A method of regenerating an exhaust gas particulate filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates when operably arranged in an engine exhaust system, the method comprising:
a) measuring a first residual amount of particulates in the filter by exciting the microwave resonant cavity with microwave radiation and monitoring the cavity response;
b) using the measured first residual amount to establish a pressure drop threshold across the filter that is representative of a predetermined amount of particulate accumulation in the filter;
c) operating the engine and monitoring the pressure drop across the filter as the filter accumulates particulates; and
d) when the pressure drop reaches the pressure drop threshold, thermally regenerating the filter to reduce the particulate accumulation to a second residual amount.
10. The method according to claim 9 , further comprising:
performing a temperature measurement of the filter; and
calibrating the measurement of at least one of the first and second residual amounts based on the temperature measurement.
11. The method according to claim 9 , further comprising repeating acts a) through d) one or more times.
12. The method according to claim 9 , wherein at least one of the first and residual amounts is one of i) about 3 g/l or less at a filter temperature of about 300° C., and ii) about 9 g/l or less at a filter temperature of about 25° C.
13. The method according to claim 9 , further comprising performing at least one of acts a) through d) while the filter resides within the engine exhaust system.
14. The method according to claim 9 , wherein the microwave resonant cavity defines a microwave cavity resonance peak, and wherein monitoring the cavity response further includes measuring a frequency shift in the microwave cavity resonance peak due to the presence of particulates in the filter.
15. The method according to claim 9 , further comprising maintaining the filter at a substantially constant temperature when monitoring the cavity response.
16. The method according to claim 9 , wherein the filter comprises a diesel particulate filter.
17. A method of calibrating a pressure drop across an exhaust gas particulate filter disposed in a microwave resonant cavity, wherein the filter accumulates particulates that cause a pressure drop when the filter is operably arranged in an engine exhaust system, the method comprising:
a) reducing an initial amount of accumulated particulates in the filter to be equal to or less than a residual amount, wherein the initial amount is greater than the residual amount
b) measuring the residual amount by exciting the microwave resonant cavity with a microwave signal having at least one microwave frequency and measuring at least one of a microwave signal resonant frequency shift and a microwave signal attenuation;
c) based on the measured residual amount, establishing a pressure drop threshold across the filter that corresponds to an allowable amount of accumulated particulates;
d) measuring the pressure drop across the filter while the filter is operably arranged in the engine exhaust system; and
e) reducing the accumulated particulates to be within the residual amount when the pressure drop reaches the pressure drop threshold.
18. The method according to claim 17 , wherein the residual amount is either less than or equal to about 3 g/l at a filter temperature of about 300° C., or is less than or equal to about 9 g/l at a filter temperature of about 25° C.
19. The method according to claim 17 , further comprising generating and receiving the microwave signal using first and second high-temperature coaxial probes arranged at one end of the microwave resonant cavity.
20. The method according to claim 17 , further comprising measuring a temperature of the filter and performing a correction of the measured residual amount based on the measured temperature.
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US12/392,341 US20100212299A1 (en) | 2009-02-25 | 2009-02-25 | Methods for determining when to regenerate exhaust gas particulate filters |
PCT/US2010/024972 WO2010099076A1 (en) | 2009-02-25 | 2010-02-23 | Method for determining when to regenerate exhaust gas particulate filters |
EP10708448A EP2401488A1 (en) | 2009-02-25 | 2010-02-23 | Method for determining when to regenerate exhaust gas particulate filters |
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US12/392,341 US20100212299A1 (en) | 2009-02-25 | 2009-02-25 | Methods for determining when to regenerate exhaust gas particulate filters |
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EP2401488A1 (en) | 2012-01-04 |
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