Particulate trap regeneration

Abstract

A particulate trap is regenerated with a valving mechanism downstream of the trap for periodically creating a reverse pressure of about 15 to 60 psig throughout the entire trap, a reversing apparatus operative after the reverse pressure is created for starting a regeneration cycle by creating a substantially instantaneous reverse pressure drop across the porous walls of the trap to dislodge accumulated particulate cake and by causing the filtered exhaust gas to flow back through the porous walls to remove the dislodged particulate from the trap, and controls for starting and stopping a regeneration cycle.

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to methods and apparatus for removal of particulate from engine exhaust and more particularly to an improved particulate filter system, and a method of operating.

BACKGROUND OF THE INVENTION

[0002] Diesel engines burn diesel fuel to produce power. The exhaust gas from a diesel engine contains carbon dioxide and water. However, the exhaust gas also contains particulates and nitrogen oxides (NOx), both of which are air pollutants. The United States Environmental Protection Agency (EPA) has issued increasingly stringent standards for particulate and NOx emissions from diesel engines. For example, the standards in place in October, 2002 include 0.1 gram per horsepower hour (g/hp-hr) for particulates and 2.0 g/hp-hr for NOx. In 2007 these were further reduced to 0.01 g/hp-hr for particulates and 0.2 g/hp-hr for NOx. Industry has intensive programs aimed at achieving these requirements.

[0003] Bailey, U.S. Pat. No. 7,269,942, Sep. 18, 2007, discloses a method and apparatus for filtering or trapping particulate from engine exhaust and periodically disposing of the collected soot and ash. The system uses a monolithic ceramic trap having passages with porous walls through which the exhaust is passed to filter out the particulates at very high (about 90 to 98%) trapping efficiency. The systems use wall-flow traps in single or multi-trap configurations. Each of these systems can be used with any diesel engine and is capable of achieving the EPA particulate standards for the foreseeable future. Engine manufacturers can concentrate on achieving the very challenging NOx standards without concern for particulate emissions control. The particulate trap system can also be used for retrofit applications. Other particulate trap systems are disclosed in Bailey et al., U.S. Pat. No. 6,233,926, May 22, 2001; Bailey et al., U.S. Pat. No. 6,989,045, Jan. 24, 2006; Bailey et al., U.S. Pat. No. 7,273,514, Sep. 25, 2007; and Bailey, U.S. Pat. No. 7,992,382, Aug. 9, 2011.

[0004] The wall-flow particulate trap systems use cordierite traps, such as Corning EX-80 or RC-200, to filter the exhaust gas by passing it through the porous walls of trap channels. This action removes about 90 to 98% of the particulate and this collects on the inside surfaces of the passages as a layer or cake which after a few hours of operation increases the engine back pressure and must be removed to prevent adverse affect on engine performance. Most prior art trap systems remove this layer by burning the particulate or soot in the trap. To avoid excessive temperatures during this operation, expensive noble metal catalytic coatings are required and ultra low sulfur fuel must be used which will not be broadly available for a number of years. Also, the engines must be operated at a relatively high average load factor to assure that burn-out occurs before too much soot is collected. To assure that light-off temperatures are reached, heaters such as burners or late injection coupled with catalysts are increasingly employed. Finally, the incombustible ash builds up and the traps and must then be cleaned in an expensive and disruptive maintenance operation. It would be desirable to overcome one or more of these problems.

[0005] Igarashi, U.S. Pat. No. 5,853,438, Dec. 29, 1998, discloses a particulate filter regeneration system that employs high pressure compressed air to dislodge accumulated soot and ash. It would be desirable to eliminate the need for a high pressure compressed air source.

OBJECTS AND ADVANTAGES

[0006] Accordingly, objects of the present invention include one or more of the following: (1) provide apparatus for using an instantaneously applied reverse pressure drop pulse of previously filtered exhaust gas for effective dislodging and removal of the soot/ash cake in a single trap or multi-trap particulate trap systems; (2) provide apparatus for utilization of very high reverse pressure drops such as those used with diesel engine exhaust brakes without loss of component life or reliability; (3) provide for regeneration in a simple and inexpensive arrangement which can be independent of the engine or its controls; and (4) provide a regeneration system which in one embodiment obtain the reverse pressure across the porous walls of the trap from the high back pressure utilized in diesel exhaust brake systems and using a commercially available exhaust brake installed downstream of the particulate trap.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention there is provided a system for regenerating a particulate trap in an exhaust system of an internal combustion engine and including a wall-flow particulate trap having a plurality of porous walls for filtering engine exhaust and removing particulates therefrom to form a particulate cake on the porous walls, a valving mechanism downstream of said trap for periodically creating a reverse pressure throughout said entire trap, a reversing apparatus operative after the reverse pressure is created for periodically creating a substantially instantaneous reverse pressure drop across the porous walls of said trap to dislodge accumulated particulate cake and causing the filtered exhaust gas to flow back through the porous walls to remove the dislodged particulate from said trap, controls for starting and stopping a regeneration cycle, wherein the valving mechanism downstream of the trap is operative to increase the back pressure to a range from about 20 to 35 pounds per square inch gauge (psig). The particulate trap system can be located almost anywhere in the exhaust system and may be substantially independent of the engine and its controls.

[0008] In accordance with another aspect of the present invention there is provided a method of regenerating a wall-flow particulate trap having a plurality of contiguous porous walls for filtering particulate from an exhaust system of an internal combustion engine, the method including the steps of: creating a back pressure throughout the entire exhaust system from a location downstream of the trap to a level of at least about 20 psig and preferably in the range of about 20 to 35 psig; releasing the back pressure at a location upstream of the trap to create a pressure drop across the entire trap and reverse flow through the entire trap sufficient to remove particulate matter stored in the trap; collecting the released particulate matter; and thereafter resuming normal filtration.

[0009] The disclosed particulate trap systems avoid the necessity of using high pressure compressed air, used by some companies, by using a reverse flow of filtered exhaust gas to create a pulse-induced reverse pressure drop across the trap of sufficient magnitude and duration to dislodge and erode the accumulated soot and ash cake and to transport the dislodged particles to an external chamber for suitable disposal. A feature of the present invention is that the entire filter is regenerated at once and that the time of regeneration is extremely short.

[0010] These and other objects and advantages will become apparent as the same become better understood from the following detailed description when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a diagrammatic illustration of a system for regenerating a particulate trap embodying the present invention.

[0012] FIG. 1-A is a diagrammatic illustration of a control system utilizable in the FIG. 1 embodiment.

[0013] FIG. 2 is a view similar to FIG. 1 but illustrating a moved position of the valve mechanism downstream of the trap.

[0014] FIG. 3 is a view similar to FIGS. 1 and 2 but illustrating moved positions of valves upstream of the trap.

[0015] FIG. 4 illustrates the system and positions of the various valves when returned to normal filtration.

[0016] FIG. 5 is a diagrammatic cross-section, of a rig used to load traps for testing.

[0017] FIG. 6 is a diagrammatic cross-section of a rig used for evaluating regeneration at various reverse pressures.

[0018] FIG. 7 is a table showing the 35 psig regeneration test data.

[0019] FIG. 8 is a graph of the particulate trap regeneration test results at 35 psig reverse pressure with a loaded Corning DuraTrap.TM. 200/12.

[0020] FIG. 9 is a table showing the 20 psig regeneration test data.

[0021] FIG. 10 is a graph of the particulate trap regeneration test results at 20 psig reverse pressure with a loaded Corning DuraTrap.TM. 100/17.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Reference is now made to the drawings wherein like reference characters represent the same parts or components throughout the several views.

[0023] FIGS. 1 through 4 show the salient features of a new and improved particulate trap system 10 in normal filtration mode. Flow from the engine exhaust enters the particulate trap system from the left side of the drawing as indicated by the arrows. It then passes through a normally-open two-way valve Y, then through porous walls of a wall-flow filter 20, and then through a valving mechanism (valve X) before exiting the particulate trap system and entering the atmosphere. Examples of the wall-flow filter are hereinafter described. The filter 20 generally has a porosity is in the range of about 42 to 52%. Filters of this porosity range are generally required to withstand thermal regeneration. Filters having greater porosities are suitable for use in the regeneration system of this invention which does not employ thermal regeneration.

[0024] Valve X may be an ordinary two-way valve. However, the embodiment illustrated is a D-Celerator.RTM. diesel exhaust brake, generally designated at 21, marketed by United States Gear Corp. for use as a remote actuated relief valve. This exhaust brake is electrically actuated and is available in various sizes. It has been developed to provide pressures up to about 60 psig for diesel engine braking. The maximum exhaust brake pressure is limited by the engine. If the back pressure is too great, the springs operating the engine valves may have insufficient force to close. When regeneration is carried out in concert with exhaust braking, the use of a back pressure of about 20 to 35 psig is generally preferred because the published literature states that this lower pressure is safe for all diesel engines without modification. This pressure exceeds the reverse pressure required for regeneration of a 42 to 52% porosity filter under all conditions that might be expected in service. However, unless used as an exhaust brake, the D-Celerator.RTM. is adjusted to provide only enough pressure to assure adequate regeneration. Greater pressures of about 60 psig or more are suitable for engines having stronger exhaust valve springs.

[0025] A pressure switch 22, open during normal filtration, is operative to close when the particulate trap has been loaded with particulate and the pressure drop across the filter 20 (i.e., upstream pressure P1 minus downstream pressure P2) reaches about 40 inches water gauge (in. W.G.) as sensed by an associated differential pressure sensor diagrammatically illustrated at 22S. Forty inches W.G. is a level that typically is chosen for the particulate to be removed in a process called regeneration.

[0026] A two-position dump valve Z, located in a purge duct 34, is normally closed but is snapped open to create an almost instantly imposed reverse pressure drop across the porous walls of the trap 20 to dislodge and remove the collected soot cake or particulate cake. Hence valve Z operatively provides a reversing apparatus for back flow through the filter. A tank 36 receives and stores the dislodged particulate particles. Tank 36 contains a very high temperature Nichrome wire coil 38 to ignite and burn the collected particulate matter in the tank. Tank 36 and coil 38 together are sometimes herein called a particulate disposal unit. A normally-closed check valve 39 opens to allow effluent from the tank to be recycled through particulate trap 20. Operation of the various moveable components is controlled, in part, by a microprocessor 40 shown in FIG. 1-A.

[0027] Normal filtration shown in FIG. 1 occurs during operation of the diesel engine. EPA standards require that the exhaust particulate be removed to present a clean exhaust to atmosphere. As noted above, during this period the remote actuated relief valve A and an associated Valve B are wide open. Consequently, the unfiltered engine exhaust enters the particulate trap system without restriction and enters the wall-flow porous ceramic trap 20. As the exhaust passes through the porous walls of the trap, the soot is filtered out and collects on the inner surfaces of the inlet passages and accumulates as a cake on these surfaces. The collection of the soot cake results in an exhaust pressure drop which requires the cake to be dislodged and removed when the differential pressure across the trap reaches a pre-selected level, i.e. about 40 in. W.G. This requires the particulate trap system to be regenerated as shown in FIGS. 2 to 4.

[0028] Referring now to FIG. 2, regeneration of the trap 20 will be described. As noted earlier, when the pressure drop sensed by pressure sensor 22S and fed to the microprocessor 40 reaches a pre-selected level this action starts a number of events:

[0029] Electrical power is supplied by microprocessor 40 causes valve X to close and thus increasing back pressure in the exhaust system upstream of valve X to a preselected level hereinafter described.

[0030] Electrical power is supplied to the coil 38 to provide resistance heat sufficient to ignite the dislodged particulate matter.

[0031] The above rise in back pressure will be sensed by pressure sensor 22S and when it reaches a desired level (generally in the range of about 20 to 35 psig for existing filters and engines), the pressure sensor 22S is operative to actuate and close valve Y. As previously discussed, greater pressures (about 60 psig or more) are suitable for engines having stronger exhaust valve springs.

[0032] Turning now to FIG. 3, an on-going part of the regeneration phase will be described. After valve Y is fully closed, dump valve Z is actuated to almost instantly snap open. The pressure at the volume between the closed valve Y and the inlet side of wall-flow trap 20 almost instantly drops to tank 36 pressure. This, in turn, causes a sharp reverse pressure drop across the porous walls of the wall-flow trap 20. Depending upon the preselected pressures described above, the reverse pressure drop is generally in the range of about 20 to 35 psig. This causes a reverse pressure pulse which quickly breaks off (dislodges) the particulate cake and carries the particles out of the trap 20 and into the tank 36.

[0033] Further, this greatly increased pressure (i.e., the range of about 20 to 35 psig) provides an unobvious result. Attention is directed to the description of test results hereinafter in this specification which records that at the lower pressure of the claimed pressure range (i.e., 20 psig or 1.38 bar gauge) the time for regeneration (i.e. time of back-flow through the filter) was reduced to 0.13 seconds! That figure does not represent the total time from the start of build-up of back pressure until normal operation is resumed. However, the total time is very short and, in one measured test, was 2.4 seconds. It can be appreciated that the regeneration is substantially instantaneous. The term "substantially instantaneous" is used herein to mean less than about one second. These times are in stark contrast to the existing commercial units which require burning of the particulate cake in situ and which can take six to thirty minutes in duration (i.e., 360 to 1800 seconds). Further, this reduced time allows regeneration even while the engine is operating under load. Still further, the preferred arrangement which utilizes an exhaust brake 21 allows for a synergistic regeneration each time the exhaust brake is actuated.

[0034] Engine performance, depending on operating conditions and control, can be altered while the engine is producing power through combustion, but the significant reduction in time (0.13 seconds) for the regeneration to be completed allows for operation in this region without significant increase in the total amount of soot generated by the engine and subsequent number of regenerations per day.

[0035] FIG. 4 shows collection and oxidation of the dislodged soot particles in the tank 36. As the dislodged particulate has been carried into the tank 36, the pressure in the tank will increase and will reach a preselected pressure at which pressure the switch will go from closed to open. This will let the holding relay open and cause the main timer to expire and the connection at this time with the DC supply voltage will be broken resulting in deactivation of valve X and valve Y and these will open and the deactivated dump valve will be closed by its spring. These actions will drop the pressure in the particulate trap system to ambient. Also as a result, the accumulated pressure in the settling tank will begin to flow out through the normally closed check valve carrying particulate particles through the 2000 F Nichrome coils to be burned. It will be noted that the products of combustion of the soot will enter the trap and be re-filtered before passing to the atmosphere. However, it is obvious that the igniter coils must not be cooled by the flow and will continue to burn the particulate until the settling tank is empty. To accomplish this, the Nichrome coils will continue to be electrically heated by connecting them to the 12 volt supply by the igniter pressure switch when the settling tank pressure is at or above about 2 psig indicating that the regeneration phase 4 is still in progress. Following the regeneration of the trap or engine shut down the settling tank pressure will drop to ambient and the igniter coils will be removed from the 12 volt supply and turned off.

[0036] FIG. 5 is a cross section of a test rig 200 used to load the trap by connection to the diesel engine exhaust as shown. The test engine (not shown) is a small 3600 rpm Onan diesel engine such as used for a generator set in recreational vehicles. The three cylinder four cycle engine has a displacement of 43.85 cubic inches (0.72 liters) and a rating of 16.6 HP at 3600 rpm and uses conventional No. 2 diesel fuel having less than 500 ppm sulfur. The load of the engine can be varied from idle, one air conditioner operating or two air conditioners operating (actual hp steps unknown). A 5.66 in. diameter by 6.00 in. long particulate trap module T is loaded axially and the gaskets G define a 3.5 in. diameter opening at each end which provides an effective trap volume of 57.73 cubic inches (0.95 liters). As exhaust flows from the engine and through the trap T the pressure drop across the trap is measured by a manometer and the test is ended when the pressure drop totals 36 in. W.G. An effort was made to keep the same overall average load factor during operation, portions of which included idle and with one or two air conditioners.

[0037] The particulate traps T obtained for the tests were two 5.66 in. diameter by 6 in. long Corning DuraTrap.TM. 200/12 modules, one of which was identified as and permanently labeled "A" and the other "B". Also obtained were two Corning DuraTrap.TM. 100/17 modules, one of which was identified as and permanently labeled "C" and the other "D". All of the new traps were dried at 400 degrees Fahrenheit for 4 to 5 hours and then weighed using a scale with an accuracy of plus or minus 0.01 grams. During the tests each of the traps used were similarly weighed following each loading and each regeneration of the traps.

[0038] FIG. 6 is a cross section of a trap regeneration test rig 210. It consists of the same trap holding and sealing arrangement. Two inch pipes are used to provide air under the desired reverse pressure to the clean end of the trap from a 5.5 cubic foot surge tank ST which is supplied from a small air compressor through a pressure reducing control valve V. Flow leaves the dirty end of the trap and, initially, is prevented from leaving the rig by a snap open one inch diameter ball valve. Thus, air pressure is permitted to gradually build up to a desired reverse pressure (e.g., 35 psig, 20 psig, etc.).

[0039] Following stabilization of the air pressure at the desired level, the snap-open ball valve is very quickly snapped open. This results in an almost instantaneously applied reverse pressure across the porous walls and a similarly quick dislodgement of the particulate cake and removal of the resulting particles.

[0040] FIG. 7 lists the results of the various dry weight changes of a Corning DuraTrap.TM. 200/12 trap module starting with a new clean dry trap when regenerated with 35 psi reverse pressure drop.

[0041] FIG. 8 is a graph of the data in FIG. 7 illustrating the dry trap weight gains following loading and the dry trap weight losses following regeneration. It can be seen that after the first two loadings and regenerations the weight gains during loading and weight loss following regeneration are equal. This shows the effectiveness of regeneration at 35 psi reverse pressure. This is a normal reverse pressure during exhaust braking obtained by closing a remote actuated relief valve (e.g. D-Celerator.RTM. 76 diesel exhaust brake).

[0042] FIG. 9 lists the results of the various dry trap weight changes of a Corning DuraTrap.TM. 100/17 trap module starting with a new clean dry trap when regenerated with 20 psi reverse pressure drop.

[0043] FIG. 10 is a graph of the data in FIG. 9 that illustrates the dry trap weight gains following loading and the dry trap weight losses following regeneration. It can be seen that after the first three loadings and regenerations the weight gains during loading and weight loss following regeneration are generally equal. This shows the effectiveness of the 22 psi reverse pressure obtained by closing the remote actuated relief valve (e.g. D-Celerator.RTM.. 76 diesel exhaust brake) during engine low idle operation.

[0044] Movies were made of the reverse flow being emitted from the exit of the ball valve during a 20 psi regeneration and it was found that all of the added particulate was removed from the entire 0.95 liter trap in just 0.13 seconds!

[0045] The method of regenerating a wall-flow particulate trap having a plurality of contiguous porous walls for filtering particulate from an exhaust system of an internal combustion engine, includes the steps of: creating a back pressure from a location downstream of the trap to a level in the range of about 20 to 35 psig; releasing the back pressure at a location upstream of the trap to create a pressure drop across the entire trap and reverse flow through the entire trap sufficient to remove particulate matter stored in the trap; collecting the released particulate matter; and thereafter resuming normal filtration.

[0046] While the exhaust system in which the trap 20 is used can be the usual system of an entire engine; there can be more than one exhaust system for an engine. For example an eight cylinder engine may have dual exhausts. In some very large engines there may be even more exhaust systems. Thus, while the above description discloses increasing the back pressure across the entire exhaust system, it should be understood that separate exhaust systems may or may not be simultaneously so increased.

[0047] It is deemed that there has been shown and described particulate trap systems embodying various operating ranges and methods of operation; however, it is to be understood that variations and modifications can be made thereto within the skill of those skilled in the art.

Claims

1. In a system for regenerating a particulate trap in an exhaust system of an internal combustion engine and including a wall-flow particulate trap having a plurality of porous walls for filtering engine exhaust and removing particulates therefrom to form a particulate cake on the porous walls, a valving mechanism downstream of said trap for periodically creating a reverse pressure throughout said entire trap, a reversing apparatus operative after the reverse pressure is created for periodically creating a substantially instantaneous reverse pressure drop across the porous walls of said trap to dislodge accumulated particulate cake and causing the filtered exhaust gas to flow back through the porous walls to remove the dislodged particulate from said trap, and controls for starting and stopping a regeneration cycle, the improvement comprising: the valving mechanism downstream of the trap is operative to increase the back pressure to a range from about 20 psig to about 35 psig which is within the limit of the exhaust valve operation.

2. A system according to claim 1, further characterized in that the valving mechanism downstream of the trap is also operative as an exhaust brake.

3. A system for regenerating a particulate trap as set forth in claim 1 wherein the valving mechanism includes a relief valve having a first open position permitting flow of filtered exhaust to atmosphere and a second position restricting flow of the filtered exhaust until the pressure throughout the exhaust system reaches a pre-selected level.

4. A system for regenerating a particulate trap as set forth in claim 1 including a purge duct upstream of said trap for receiving the dislodged particulate from said trap, and wherein the reversing apparatus includes a valve associated with the purge duct.

5. A system for regenerating a particulate trap as set forth in claim 4 wherein the controls are operative for opening the purge duct valve to thereby drop the pressure at the inlet side of the filter and thereby create a pressure drop sufficient to dislodge portions of the cake.

6. A particulate trap system according to claim 1 wherein the controls are actuated following attainment of a pre-selected trap exhaust pressure drop during normal filtration operation of the engine.

7. A particulate trap system according to claim 1 wherein the wall-flow particulate trap has a porosity in the range of about 42 to 52%.

8. A particulate trap regeneration system comprising: (a) a particulate trap in an exhaust system of an internal combustion engine, the trap having a plurality of porous walls for filtering engine exhaust and removing particulates therefrom to form a particulate cake on the porous walls; (b) a valving mechanism downstream of the trap for periodically creating a reverse pressure of about 15 to 60 psig throughout the entire trap; (c) a reversing apparatus operative after the reverse pressure is created for starting a regeneration cycle by creating a substantially instantaneous reverse pressure drop across the porous walls of the trap to dislodge accumulated particulate cake and by causing the filtered exhaust gas to flow back through the porous walls to remove the dislodged particulate from the trap; and (d) controls for starting and stopping a regeneration cycle.

9. The system of claim 8 wherein the valving mechanism includes a relief valve having a first open position permitting flow of filtered exhaust to atmosphere and a second position restricting flow of the filtered exhaust until the pressure throughout the exhaust system reaches a pre-selected level.

10. The system of claim 9 additionally comprising a purge duct upstream of the trap for receiving the dislodged particulate from said trap, and wherein the reversing apparatus includes a purge duct valve, associated with the purge duct.

11. The system of claim 10 wherein the controls are operative for opening the purge duct valve to thereby drop the pressure at the inlet side of the filter and thereby create a pressure drop sufficient to dislodge portions of the cake.

12. A method of regenerating a particulate trap in an exhaust system of an internal combustion engine, comprising the steps of: creating a back pressure throughout the entire exhaust system from a location downstream of the trap to a level of at least about 20 psig; releasing the back pressure at a location upstream of the trap to create a pressure drop across the entire trap and reverse flow through the entire trap sufficient to remove particulate matter stored in the trap; collecting the released particulate matter; and thereafter resuming normal filtration.

13. The method of claim 12 wherein the back pressure created is about 20 to 35 psig.

14. The method of claim 12 wherein the back pressure is released to create a substantially instantaneous pressure drop across the entire trap.

15. The method of claim 14 wherein the back pressure is released by opening a purge duct valve.

16. The method of claim 15 wherein the back pressure is created with an exhaust brake.