Particulate filter cleaning methods and apparatus

Abstract

An internal combustion engine is run to emit an exhaust flow containing particulate. The exhaust flow passes through a filter element to remove at least a portion of the particulate from the exhaust flow. The removed particulate accumulates on the filter element. The filter element is cleaned. The cleaning includes detonating a fuel-oxidizer combination in a conduit and impacting the filter element with a wave from the detonation.

Description

BACKGROUND OF THE INVENTION

The invention relates to particulate filtering. Particular examples relate to the filtering of particulate from diesel engine exhaust.

The US Environmental Protection Agency (EPA) is implementing New Source Performance Standards for mobile and stationary diesel engines. The new rules limit the amount of diesel particulate matter or soot and ash that can be emitted to the atmosphere. Exemplary diesel engines are used in trucks, locomotives, school buses, generators, tractors, and other off-road construction equipment. The California Air Resources Board (CARB) has dictated that the soot and ash limits be 0.1 gram per brake horsepower per hour. This will require 85-90% of the particulate to be eliminated from exemplary exhaust. Engine modifications alone may not be practical to achieve the required reduction. Thus, particulate filters have been developed for future equipment and for retrofit installations on existing diesel engines.

Trapped particulates would quickly buildup and clog a filter, blocking exhaust flow and shutting down the engine if the particulates were not removed. Removing the trapped particulate is called regeneration. Filter regeneration can be accomplished by burning the trapped soot by various processes. U.S. Pat. No. 5,566,545 discloses a filter cleaned by reverse flow from an air feeder. When air is supplied to the filter in a reverse flow direction, the air may remove captured particulates from the filter. A second filter may capture the reversed flow of particulates.

Some filters use a metal mesh filter as an electric resistance heating element to burn the soot. Extra fuel can also be allowed to pass through the engine to burn the soot in the exhaust system particulate filter. A recent example of an added fuel system is found in US Pregrant Publication 20060254262A1. Such thermal regeneration processes turn the larger soot particles into a fine ash on the filter. This fine ash may be periodically washed off, vacuumed off or blown off with high-pressure air during a shop maintenance cycle. Yet other regeneration processes exist.

SUMMARY OF THE INVENTION

One aspect of the invention involves running an internal combustion engine to emit an exhaust flow containing particulate. The exhaust flow passes through a filter element to remove at least a portion of the particulate from the exhaust flow. The removed particulate accumulates on the filter element. The filter element is cleaned. The cleaning includes detonating-a fuel-oxidizer combination in a conduit and impacting the filter element with a wave from the detonation.

Another aspect involves an apparatus having an internal combustion engine. An exhaust system is coupled to the internal combustion engine. A particulate filter element along is along an exhaust flowpath. A conduit has a first end and a second end, the second end being an outlet facing the filter element. A source of fuel and oxidizer is coupled to the conduit to deliver the fuel and oxidizer. An ignitor is coupled to the conduit to ignite the fuel and oxidizer in the conduit. The ignition may produce a wave impacting the filter element to clean the filter element.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first pollutant source in a normal mode of operation.

FIG. 2 is a schematic view of the source of FIG. 1 during a filter cleaning mode of operation.

FIG. 3 is a schematic view of an alternate source during a filter cleaning mode of operation.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a pollutant source 20 having a powertrain 22 including an engine 24. Exemplary sources are fixed (e.g., stationary power generators, tools, and the like) or mobile (e.g., vehicular, mobile generators, and the like). Exemplary engines are internal combustion engines, more particularly, multi-cylinder compression ignition or diesel engines. The engine receives diesel fuel from a fuel source (e.g., tank) 26.

An exhaust system 30 extends in a primary downstream direction 500 from the engine 24 to an outlet 32 to define a primary exhaust flowpath 502. At an upstream end of the flowpath 502, the exhaust system 30 includes an exhaust manifold 34. A filter system 40 is downstream of the manifold. The exemplary filter system includes a filter element 42 within a filter housing 44 and extending across the flowpath 502. In a normal operational mode, the exhaust flow 504 passes through an upstream exhaust inlet port 46 of the housing, then through the filter element 42, and then through an exhaust outlet port 48 of the housing. An exhaust pipe 50 extends downstream from the outlet port 48 to the outlet 32.

Other exhaust system components (e.g., sound mufflers, catalytic emissions control devices, exhaust gas recirculation devices, and the like) may be present but are not shown for ease of illustration.

The filter exemplary element has first and second surfaces or boundaries 60 and 62. In the normal operational mode, the surfaces 60 and 62 are respectively upstream and downstream along the flowpath 502. Thus, particulate (e.g., soot) 64 will accumulate on the surface 60 and/or within the filter element, forming an accumulation 66. The accumulation increases the flow restriction presented by the filter element. Increased restriction, causes increased backpressure (the pressure difference between a higher pressure location or space 70 upstream of the filter and a lower pressure location or space 72 downstream of the filter). The pressures at these two locations may be measured by pressure sensors 74 and 76 coupled to a controller 78. The exemplary controller is shown as a dedicated controller of the system 40. However, the controller may be integrated with an overall controller of the source 20, or otherwise. Various, microcontrollers, computers, or lesser control systems are appropriate for use as the controller 78. The controller 78 may be configured by one or both of software and hardware configuration to operate as discussed further below.

In exemplary implementation, upon reaching a predetermined differential pressure across the filter element the controller 78 will initiate a clearing of the accumulation from the filter element. An exemplary clearing involves directing a shock wave 100 (FIG. 2) through the space 72 (e.g., the portion of the housing interior downstream of the filter element). The exemplary wave 100 impacts the surface 62. The wave 100 and associated combustion gas (discussed further below) may incinerate the accumulation 66. The incineration may form ash 104 which dislodges and may fall from the surface 60. The falling ash may be directed to a trap 106, forming an ash accumulation 108 in the trap.

The exemplary ash accumulation 108 is held in bulk (i.e., not in a separate filter that must be disposed of or cleaned), although other trap configurations are possible. The ash accumulation 108 may be removed in bulk (e.g., via a door 110) when the trap 106 is full (or earlier) as part of manual maintenance. The required interval for clearing the accumulation 108 may be substantially longer than the typical filter cleaning interval (e.g., ten times or more). To facilitate the falling, the exemplary filter element 42 is oriented so that the surface 60 is partially downward-facing.

An exemplary wave generator system 120 for generating the wave 100 includes a detonation conduit 122 having a first end 124 and a second end 126. The exemplary second end 126 is an outlet end positioned in the space 72 and aimed at the surface 62. An exemplary fuel and oxidizer source 128 comprises a fuel source 130 and an oxidizer source 132. An exemplary fuel is propane or MAPP gas. Small replaceable and/or refillable oxygen cylinders of these gases are readily commercially available (e.g., for welding applications). Alternatives include, hydrogen, ethylene, diesel fuel, kerosene, and gasoline. Diesel fuel has the advantage of being available from the fuel source 26. Gasoline is, at least, readily available where the diesel fuel for the source 26 is obtained.

An exemplary oxidizer is essentially pure oxygen. Small replaceable and/or refillable oxygen cylinders are readily commercially available (e.g., for welding applications). Alternatively, nitrous oxide may similarly be used. Air may be used and may be compressed on board for delivering enhanced quantities. One or more inlet valves 140 controlled by the controller 78 may admit the fuel and oxidizer near the conduit inlet end. After the conduit 122 is filled with a desired volume of fuel and oxidizer, an ignitor 142 (e.g., a spark plug) is triggered by the controller to initiate combustion of the fuel-oxidizer mixture.

Initially, combustion near the ignitor is via deflagration. The wave 100 is initially formed as a deflagration pressure wave that passes toward the conduit second end (outlet) 126. During travel of the wave, the deflagration transitions into a detonation. The detonation wave travels down the remainder of the conduit at a supersonic velocity and is discharged from the outlet 126.

As the detonation wave exits the outlet 126, it forms a quickly decaying, high pressure blast wave. The blast wave is followed by a blowdown jet of relatively high pressure/temperature combustion products exiting the conduit. Depending on the fuel and oxidizer utilized the exit pressure (at the outlet 126) can be on the order of 150 psi and the temperature can be in the 400&-4900° F. range. The pressure pulse duration is very short on the order of a few milliseconds.

The shock and high temperature nature of the blast wave 100 and trailing blowdown jet may be used to regenerate the filter. The very quick pressure pulse created by the blast wave and blowdown jet may remove the soot and ash from the filter by momentarily reversing the flow through the filter. The resulting ash may fall into the particle trap 106 as discussed above. The relatively short duration of the blast wave 100 and trailing blowdown jet may advantageously incinerate the soot particles but not affect the filter element. An exemplary filter element is a metal mesh filter element having a much larger thermal mass than the soot accumulation 66 so as to survive the heating by the blowdown jet. Alternative filter elements made from sintered metal material may be the easiest to use because they may be readily fabricated in a desired shape.

The conduit may be sized and fueled so that a single firing is unlikely to provide the necessary cleaning. For example, to produce a single firing of sufficient magnitude may take a large, impractical system. A single firing of sufficient magnitude might also damage system components or create so much back pressure as to interfere with engine operation. Thus, an exemplary system is configured to typically require multiple firings for a full cleaning. For example, a closed loop control may initiate a first firing upon backpressure reaching a first predetermined level or threshold value. After the first firing, the backpressure is remeasured, and firings repeated until the backpressure has decreased to a second predetermined level (e.g., a baseline level associated with a nominally clean filter element), less than the first backpressure level.

FIG. 3 shows an alternate combustion conduit 200 otherwise similar to the conduit 122, but concentrically surrounding an upstream portion of the exhaust pipe. Combustion thus occurs in an annular space 202 surrounding the exhaust pipe. This configuration may allow greater exposure of the filter element to the wave 100. The FIG. 3 configuration may also provide enhanced heat transfer from the exhaust pipe to the conduit 200 and its fuel/air charges. This would allow the heat from the exhaust assist in vaporizing the fuel used in the detonation process. This would be particularly useful for less volatile liquid fuels such as diesel fuel and kerosene. Such heating might eliminate the need for a high pressure injector to achieve fuel vaporization.

In other alternative embodiments, the orientation of the conduit could vary from the illustrated horizontal orientation (e.g. a downwardly directed vertical orientation). A non-straight conduit having one or more turns to accommodate to existing structure is also possible as the deflagration/detonation wave can travel around corners and still be effective.

In other control variations, instead of using a closed loop feedback system based on differential pressures, the control system could activate the cleaner periodically (e.g., based on the engine hour meter or other interval calculated by an engine computer based upon use history). The system could activate after a predetermined engine run time for a set cleaning period (e.g., number of firings) and then shut off. Another option would be to include a manual mode (e.g., to allow a mechanic to activate the system in the shop during scheduled or other maintenance).

One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented in the reengineering of an existing source configuration or the retrofit of an existing source, details of the existing configuration/source may influence details of the particular implementation. In a reengineering or retrofit of a system having an existing filter, the reengineering or retrofit may achieve one or more of: reduced filter size, lengthened maintenance interval; or increased filtration. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A method comprising:

operating an internal combustion engine in a first mode comprising: running the engine to emit an exhaust flow containing particulate from the engine; passing the exhaust flow through a filter element to remove at least a portion of

the particulate from the exhaust flow, the removed particulate accumulating on the filter element;

cleaning the filter element, the cleaning comprising: detonating a fuel-oxidizer combination in a conduit; and impacting the filter element with a wave from the detonation.

2. The method of claim 1 wherein:

the removed particulate accumulates as soot; and

the impacting and an associated blowdown jet incinerate the soot to form ash.

3. The method of claim 2 wherein the cleaning further comprises:

collecting the ash in a trap.

4. The method of claim 3 wherein the cleaning comprises:

a plurality of said detonations and impacts.

5. The method of claim 4 further comprising:

removing collected ash from the trap after a plurality of the cleanings.

6. The method of claim 1 wherein:

the cleaning comprises: measuring a pressure difference across the filter element; responsive to the pressure difference reaching a first predetermined value,

initiating said detonating; and

repeating the detonating until the measured pressure difference decreases to a second predetermined value, lower than the first predetermined value.

7. The method of claim 1 wherein:

the cleaning occurs while the internal combustion engine is running.

8. The method of claim 1 wherein:

the cleaning occurs while the internal combustion engine is not running.

9. The method of claim 1 wherein:

the cleaning comprises: introducing the fuel as at least one of propane and MAPP gas; and introducing the oxidizer as essentially oxygen.

10. The method of claim 1 wherein:

the running comprises running as a compression ignition engine.

11. The method of claim 1 wherein:

heat is transferred from the exhaust flow to the fuel-oxidizer combination in the conduit.

12. An apparatus comprising:

an internal combustion engine; and

an exhaust system coupled to the internal combustion engine and including: an exhaust flowpath; a particulate filter element along the exhaust flowpath; a conduit having a first end and a second end, the second end being an outlet facing the filter element downstream of the filter element along the exhaust flowpath; a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer; and an ignitor coupled to the conduit to ignite the fuel and oxidizer in the conduit.

13. The apparatus of claim 12 wherein:

the exhaust system further comprises: a first pressure sensor positioned to measure a pressure upstream of the filter element; a second pressure sensor positioned to measure a pressure downstream of the filter element; and a controller coupled to the first pressure sensor, second pressure sensor, source, and ignitor, and configured to operate the conduit responsive to outputs of the first and second pressure sensors to discharge waves from the conduit to impact the filter element.

14. The apparatus of claim 12 wherein:

the fuel consists essentially of at least one of propane and MAPP gas; and

the oxidizer consists essentially of pure oxygen.

15. The apparatus of claim 12 wherein:

the fuel consists essentially of diesel fuel; and

the oxidizer consists essentially of pure oxygen.

16. The apparatus of claim 12 wherein:

the filter element does not have a separate heater; and

there is no separate second filter element positioned for blowback filtering of ash from said filter element.

17. The apparatus of claim 12 wherein:

the apparatus is a wheeled vehicle.

18. An apparatus comprising:

an internal combustion engine; and

an exhaust system coupled to the internal combustion engine to pass an exhaust flow from the internal combustion engine and comprising: a filter element positioned to filter particulate from the exhaust flow; and detonative cleaning means for cleaning the filter element.

19. The apparatus of claim 18 wherein:

the internal combustion engine is a diesel engine;

the detonative cleaning means comprises: a conduit having a first end and a second end, the second end being an outlet facing the filter element; a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer; and an ignitor coupled to the conduit to ignite the fuel and oxidizer in the conduit;

the exhaust system further comprises:

a controller coupled to the source and ignitor and configured to discharge waves from the conduit responsive to a measured pressure difference across the filter element.

20. A method for retrofitting a pollution source or reengineering a configuration of the pollution source, the pollution source having an internal combustion engine, the method comprising:

adding a filter element in an exhaust gas flowpath from the internal combustion engine;

adding a detonative cleaning apparatus positioned to discharge a wave to impact the filter element.

21. The method of claim 20 wherein:

the filter replaces a larger baseline filter.

22. The method of claim 20 wherein:

the detonative cleaning apparatus comprises: a conduit having a first end and a second end, the second end being an outlet facing the filter element; a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer; and an ignitor coupled to the conduit to ignite the fuel and oxidizer in the conduit.

23. The method of claim 1 wherein:

the cleaning comprises momentarily reversing flow through the filter element.

24. The method of claim 2 wherein:

the blowdown jet passes through the filter element in a reverse direction from the exhaust flow.

25. The apparatus of claim 12 wherein:

the particulate filter element has, along the exhaust flowpath, an upstream surface and a downstream surface; and

the second end faces the downstream surface.

26. The method of claim 11 wherein:

the heat is transferred from an exhaust pipe to the fuel-oxidizer combination in a space within the conduit surrounding the exhaust pipe.