CA1187814A

CA1187814A - Method for cyclic rejuvenation of an exhaust gas particulate filter and apparatus

Info

Publication number: CA1187814A
Application number: CA000366733A
Authority: CA
Inventors: Kashmir S. Virk; Martin Alperstein
Original assignee: Texaco Development Corp
Current assignee: Texaco Development Corp
Priority date: 1979-12-13
Filing date: 1980-12-12
Publication date: 1985-05-28
Also published as: GB2064983B; GB2064983A; IT1141592B; DE3046258A1; FR2471806A1; IT8026635A0; FR2471806B1; JPS5698519A; SE8008527L

Abstract

METHOD FOR CYCLIC REJUVENATION
OF AN EXHAUST GAS PARTICULATE FILTER, AND APPARATUS
(D#77,028-F) ABSTRACT OF THE DISCLOSURE

A system for filtering combustible particles of matter from an exhaust gas stream, and for periodically rejuvenating the filter by thermally incinerating retained particles from the filter bed through which the exhaust gas stream has passed. At least a part of the exhaust gas entering the filter bed is periodically heated by measured injections of a combustible fluid into the exhaust gas stream, prior to the latter contacting a catalytic surface. The heated gas will thus ignite the combustible particles.

-I-

Description

~'7~

B~CK~RO~ND OF THE INVENTION
_ ~ ith any internal combustion eng~ne it is desirable to treat the exhaust gases so that they can be safely dissharged into the atmosphere. In some engines, particularly of the diesel type~ among the most prevalent operating problems is the presence of particulates which are carried in the exhaust gas stream.
Primarily, the particulates are normally bits of carbon. They result from the incomplete combustion of the hydrocarbon ~uel under certain engine operating conditions.
However, the operating efficiency of the engine is also a contributing factor to the amount of carbon produced.
The presence of relatively large amounts of carbon particles in any exhaust gas stream may be evidenced by a dark, smoky, undesirable effluent. Such smoke is not only offensive aesthetically; in large quantities it can be unhealthy.
Means have been provided and are known to the prior art, for the elimination or minimization of the particulate content in exhaust discharge streams. However, it has been found that whlle the particulates can be eliminated by a suitable fllter of proper construction, eventually the latter can become saturated and/or inoperable due to excessive particulate accumulations.
It is further known that the overall engine exhaust gas treating process can be expedited. This is achieved not only b~ passing the hot gas stream through a filter medium, but by providing the filter With a catalyst which ~ill promote combustion of the retained particles.

~1 'i '7~

It should be appreciated that the generation of carbon particles is pre~alent under all diesel engine operating conditions. It is further appreciated that the quantity and quality of an exhaust gas stream created in any internal combustion engine will vary in accordance with the operating characteristics of the engine.
For example, the temperature range experienced by the diesel exhaust gas stream can vary between slightly above ambient air temperature, and temperatures in excess of 1200 F. When the exhaust gas is hot enough, the carbon particles trapped in a filter will be combusted.
However, the engine operating condition where this rejuvena-tion can occur is seldom reached in diesel passenger cars.
Where it is ~ound that an engine continuously operates under such circumstances that the particulates are continuously produced and accumulated in the filter, the particulate trapping filter bed must be occasionally re~uvenated.
Under usual circumstances, rejuvenation will conslst of merely introducing the hot exhaust gas stream, containing su~ficient oxygen, into the filter bed to contact and ignite or incinerate the retained carbon particles~
The combustion of any large and contained carbon accumulation can, however~ produce temperatures greatly in excess of that of the exhaust gasO The result is that at such excessive temperatures, the filter bed or element is susceptible to thermal shock, damage or distortiQn.
Toward achieving a satisfactory or limited rate of carbon removal from an exhaust gas system without 0 incurring resultlng damage to the filter, the unit presently ~7~

disclosed is provided. The instant system thus comprises in brief`, the reaction chamber or section which contains a catalyst bed through which at least a portion of the exhaust gas stream is passed. This catalyst segment can be incorporated within the particulate trapping bed, or it can precede it.
To assure that the main or primary filter bed or beds always remain functional, the exhaust gas stream is periodically and regularly heated to a temperature in excess of the temperature required to initiate combustion of retained particles.
Physically, the heating step is achieved by adding a desired amount of a flammable fluid directly into the exhaust gas stream. This fuel mixes with the diesel exhaust, which has excess oxygen. When the mixture contacts the catalyst, an exotherm will occur and raise the temperature of the exhaust gas stream at least to the combustion temperature of the carbon particles which are retained in the main filter bed.
The main filter bed will thus be regularly and at periodic intervals, reJuvenated. Such treatment, i~
repeated at predetermined intervals will preclude any carbon accumulation which might otherwise lead to thermal stress or damage to the bed at such time as the accumulation is combusted.
It is therefore an ob~ect of the invention to provide a filter of the type disclosed which is capable of containing combustible particulates from an exhaust gas stream, and subsequently being periodically re~uvenated by burning said particulates.

A Eurther object is -to provide a particulate filter of the type disclosed which is capable of removing solid ele-ments from an exhaust gas stream while permitting periodic rejuvenation of the filter element. ~he rejuvenation can be accomplished while the engine is operating at conditions that would normally not result in exhaust gas temperatures suffi-cient to accomplish the task.
A still further object is to provide an exhaust gas treating unit which ls capable of removing particulates from ]0 an exhaust gas stream without jeopardizing -~he integrity of the filter bed by subjecting the latter to thermal shock or damage.
In summary, the invention provides, according to a first aspect, the combination with an automotive internal com-bustion engine which operates on an air/fuel mixture, -the com-bustion of which forms and discharges from the engine exhaust manifold a stream of hot exhaust gas containing an amount of particulate combus-tible matter, of; a filter element having a reaction chamber with an inlet port communicated to a source of said exhaust gas, and having a main filter bed positioned in said reaction chamber to receive a unidirectional flow of said exhaust gas and to contact and retain particulate matter therefrom, a pre-filter bed disposed upstream of said filter bed and having a catalytic Eiltering media therein, an injec-tion means including an injection metering apparatus having an inlet communicated with a source of combustible fluid and having a discharge port openiny into said filter element upstream of said pre-filter bed, injection control means controllably con-nected to said injection means and being operable to periodical-ly actuate the latter to inject an amount oE combustible fluid into said pre-filter bed~ to form a fuel/exhaust mixture there-in, whereby contact of said fuel/exhaust gas mixture with said catalytic filtering media will cause said mixture to be ignited, thereby to raise the temperature of -the exhaust gas passing through the pre-filter bed to a temperature in excess of the ignition temperature of said combus-tible particulate matter thus to incinerate the latter.
According to a second aspect, the invention provides a method for removing combustible particulate matter from a stream of exhaust gas which comprises the steps of; passing a continuous, unidirectional flow of said exhaust gas stream into a filter bed -to retain within the bed at least a portion of said particulate matter/ periodically heating at least a por-ti.on oE said exhaust gas stream prior to its entering said bed to a temperature in excess of the ignition temperature of said retained combustible particulate matter, and passing heated exhaust gas into contact with said particulate retaining fil-ter bed to combust said retained particles~
The invention will now be described in greater detail with reference to the accompanying drawings, in which:
Figure 1 illustrates a diesel engine of the type contemplated with whi.ch the present filter cooperates; and Figure 2 is an enlarged view in cross-section, of the filter element shown of Figure 1.
To facili-tate the present description, the internal combustion engine 10 or source of exhaust gas, will be consid-ered to be of the diesel type. In the latter, air is sequen-tially introduced to the various combustion chambers~ from an air filter 11, by way of manifold 1~. Fuel is thereafter injected into each combustion chamber from a fuel pump 13 by way of an engine control lin~age 14.
The hot exhaust gas stream is carried from exhaust manifold 16 and conducted through an exhaust pipe 18 to a -~a-'7~ ~

t smoke ~ilter 17. Although a sound absorbing ~luffler could be inserted into the exhaust pipe, su~h an element is not essen-tial to the instant system.

-4b-C

~7~

The exhaust gas stream, subsequent to lea~ing exhaust manifold 16, will be at a temperature within the range of about 200 to 1200F. The precise temperature will depend on the operating conditions of the engine. For example, at low and idle speeds, the exhaust gas will be relatively cool or only slightly heated. Consequen~ly, as the exhaust gas stream enters filter 17, the particulates carried in the stream will be retained along the many diverse passages within the filter bed 19.
While the exhaust gas is comprised primarily of a combination of gases, it normally embodies sufficient oxygen content to support at least a limited degree of combustion within the stream itself.
~ilter 17 comprises in essence an elongated metallic casing 21 having opposed end walls 22 and 23 which define an internal reaction chamber 24 therebetween.
The latter chamber is occupied to a large e~tent by at least one bed 19 ~ormed of material particularly adapted to provide a plurality of irregular passages.
The function of this bed, or similar beds which supplement it, is to define a series o~ passages along which the gas will pass. During such passage, the particulate matter carried on the stream will be retained along the various passage walls.
In one embodiment, bed 1~ can be ~ormed of a metallic mesh-like mass such as steel wool or the like which is shaped to substantially fill the ~ilter reaction chamber.
Bed 1~ can be optionally supported at its 0 upstream and downstream ends by perforate panels 26 and 27 or other similar transverse members. The latter are carried on the casing 21 wall to support the one or more beds therein.
The ~ilter upstream wall 23 is provided with inlet port 2~ for introducing gas to the ups-tream side of the bed 19. In a similar manner the downstream panel 26 is communicated with an outlet port 29 to carry away gases which leave the bed.
To best achieve the filtering action on the exhaust 1~ gas stream, filter bed 19 can be comprised as noted of a suitable medium which is oapable of retaining the solid particles from the stream. However, to facilitate subsequent combustion of the retained particles, the filter medium can be provided on its surface with a suitable catalyst of the type which will promote oxidation of fuel and the combustible particles.
When filter bed 19 is utilized without the benefit of a catalyst, in accordance with the present invention, the forward or upstream end thereof is provided with a pretreating segment 19a. The latter includes a catalyst materlal which will be capable of producing the desired oxidation of fuel and the particles. This pre-filtering chamber l9a can be physically a part of the filter bed 19, or it can be a discrete segment thereof.
The pre-filter segment l9a can for example be positioned in the for~rard portion of the casing 21 whereby to contact incoming exhaust gas as soon as the ]atter enters the filter casing.
Toward achieving the present preheating of the G exhaust gas stream, an in~ection system is provided which 7~

embodies primarily a source of a com~ustible fuel together wlth means for insertlng a measured amount of said fuel into the heated exhaust gas stream. Said fuel source can be in either liquid or gaseous form to achieve the desired preheating function.
The supplementary fuel source can, as presently shown, be diesel fuel utilized for powering internal combustion engine 10. Alternatively it can be a compressed gas such as propane or the like which is carried for the express purpose of in~ection into the pre-~iltering chamber.
In brief, the supplementary fuel can be any of a number of known volatile substances, hydrocarbon or otherwise, which are capable of reacting in the catalyst chamber.
The in;ection system thus is provided with a pump 31, or other suitable metering means, having the inlet side 32 thereof co~nected to the fuel source 13. The pump 31 in turn is communicated with an in~ector 33 which can be provided with one or more nozzles 37 disposed at the forward end of the catalyst-containing pre-filtering ~ l9 chamber ~
C As pump 31 is periodically actuated by the in~ector control means 36, a measured amount of the combustible fluidized fuel will be passed directly into the pre-filtering ~ q~
chamber ~ wherein it will be ignited by contact with the heated exhaust gas in the presence of the oxidizing catalyst.
~ o achieve the periodic exhaust gas heating step, pump 31 control system 36 is designed particularly to actuate the pump at regular preset periods o~ time. These intervals can be determined on the basis of the mileage the engine has logged or on the actual time the engine has run.

~:~87~

Further actuation can be a function of the tempe~ature within the filter element. In any instance, the purpose of the injection timing is such that the carbon will be periodically incinerated from the filter regardless of engine operating conditions. The spacing of the intervals is such as to avoid any excess accumulation o~ carbon even under the worst engine operating conditions.
Other modifications and variations o~ the invention as hereinbefore set forth can be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The combination with an automotive internal combustion engine which operates on an air/fuel mixture, the combustion of which forms and discharges from the engine exhaust manifold a stream of hot exhaust gas containing an amount of particulate combustible matter, of; a filter element having a reaction chamber with an inlet port communicated to a source of said exhaust gas, and having a main filter bed positioned in said reaction chamber to receive a unidirectional flow of said exhaust gas and to contact and retain particulate matter therefrom, a pre-filter bed disposed upstream of said filter bed and having a catalytic filtering media therein, an injec-tion means including an injection metering apparatus having an inlet communicated with a source of a combustible fluid and having a discharge port opening into said filter element upstream of said pre-filter bed, injec-tion control means controllably connected to said injection means and being operable to periodically actuate the latter to inject an amount of combus-tible fluid into said pre-filter bed, to form a fuel/exhaust mixture therein, whereby contact of said fuel/exhaust gas mixture with said catalytic filter-ing media will cause said mixture to be ignited, thereby to raise the tem-perature of the exhaust gas passing through the pre-filter bed to a temper-ature in excess of the ignition temperature of said combustible particulate matter thus to incinerate the latter.

2. The combination as defined in claim 1, wherein said pre-filtering bed is integral with said main filter bed.

3. The apparatus as defined in claim 1, wherein said pre-filter in a bed is contiguous with said main filter bed.

4. The apparatus as defined in claim 1, wherein said injection meter-ing apparatus is communicated with a source of liquid fuel.

5. The apparatus as defined in claim 1, wherein said injection metering apparatus is communicated with a source of a pressurized gas.

6. The apparatus as defined in claim 5, wherein said gas is propane.

7. The apparatus as defined in claim 1, wherein said injection con-trol means includes a timer, being operable to actuate said injection meter-ing apparatus as predetermined timed intervals.

8. The apparatus as defined in claim 1, wherein said injection con-trol means is operable to actuate said injection means at predetermined exhaust gas temperatures.

9. A method for removing combustible particulate matter from a stream of exhaust gas which comprises the steps of; passing a continuous, unidirec-tional flow of said exhaust gas stream into a filter bed to retain within the bed at least a portion of said particulate matter, periodically heating at least a portion of said exhaust gas stream prior to its entering said bed to a temperature in excess of the ignition temperature of said retained combustible particulate matter, and passing heated exhaust gas into contact with said particulate retaining filter bed to combust said retained par-ticles.

10. The method as defined in claim 9, wherein said gas heating step includes, injecting an amount of a combustible fuel into said exhaust gas stream prior to the latter entering said filter bed.

11. The method as defined in claim 10, wherein said combustible fluid is a liquid fuel.

12. The method as defined in claim 10, wherein said combustible fluid is diesel fuel.

13. The method as defined in claim 10, wherein said combustible fluid is a gaseous fuel.

14. The method as defined in claim 13, wherein said combustible fluid is propane.