CA1287532C - Method and apparatus for filtering solid particulate matter from diesel engine exhaust - Google Patents

Abstract

Abstract of the Disclosure A method for removing solid particulate matter from the exhaust of a diesel engine, which comprises passing the engine's exhaust flow through at least a part of filter means to trap solid particulate matter contained initially in the exhaust, thereby to remove said matter from said exhaust flow, periodically interrupting the exhaust flow through at least said part of the filter mean , passing, during said interruption, at least one backflush fluid pulse through at least said part of the filter means thereby to dislodge from the filter means, and entrain, said solid particulate matter, and transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine; and an apparatus for accomplishing same.

Description

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Field of the Invention The field of the instant invention i~ reduction of the emission level in diesel engine exhaust, and in a more specific vein metho~s and appar~us for removal of ~olid particulate matter found in diesel enqine exh~u~.

Backgr~und of the Invention Over the past few years, the diesel engine has been relied upon in~reasingly t~ power automotive vehicles due to its fuel economy in comparison to conventional gasoline engines. Commercially available diesel engines for highway usage are conveniently classified into two categories, namely, those for use in light-duty vehicles and trucks, and those for use in heavy-duty vehicles.
Light-duty vehicles and trucks are de~ined by the Environmental Protection Agency as passenger cars capable of seating twelve~passengers or fewer, and light-duty trucks and all other vehicles under 8,501 pounds gross weight.
This category includes most cars and pick-up trucks, mini-vans, and some ~peeial purpose vehicles. Heavy-duty vehieles are defined aæ all vehicle~ over 8,500 pounds gross weight. Heavy-duty vehi~les are, typically, trucks, buses, vans and recreational vehicles.
Addltionally, the diesel engine finds ~pplication n lndustrial ~ettings ~uch as storage f~cilities and underground mines, many of which have only limited ventilation. And, diesel engines find further ~gnificant uti:lization in diesel locomotives; industrial ~pplications such as fork l$ft englne~, ~uxiliary engines on large vehicles, generator and pump service, and in logging, miniAg, quarrying ~nd oil field op~r6tl0nb, a6 well DS

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~8'~S~2 w211 drill~ng e~u~pment; construction ~pplications, such ~s use in ~ulldozers, ~otor grader~, tractor~, scrapers, rollers and loaders; and agricultural application~, ~uch as powering agricultural equipment.
However, despite its rising popularity, especially in the heavy-duty vehicle category, ~nd although die~el engine exhaust ~unlike that of gasoline ~ngines) is relatively clean in respect of unburned hydro~arbon- and carbon monoxide-content, several significant difficulties are attendant upon use of ~he diesel engine. They stem essentially from the fact that diesel engine exhaust contains undesirably large amounts of solid particulate matter, for instance, in amounts at least thirty to fifty times greater than amounts present in the exhaust of a qasoline engine.
Typical solid particulate matter from diesel engine exhaust is made up of small, solid, irregularly shaped particles whi~h are agglomerates of roughly spherical subunits. ~he particles often have high molecular weight hydrocarbons absorbed on their eurfaces, and also may have a liquid coating; frequently, the particulate matter is a complex mixture of pure carbon and hundreds ~f organic compvunds. The particulate is often extremely fine and light wlth a flour-like consistency. Size distribution ranges from Yery 6mall single particles of about 0.01 microns to rela~ively large clusters in the range of 10-30 microns. Iliustratively, the particles have ~ ~ulk density of 0.075 gicm3 ~nd h~ve ~ surf~ce srea of 100 m21g.
Generally speaking, the n~ture of solid particulate matter .
emitted from turbo-charged diesel engines is somewhat differ-nt from th~e Df nlturally ospir~t~d die~e~ engines, - ~ . . . . . .

~ 2~532 the former tending to be smaller ~n size w~th much lower level of retained organic compoundR.
Unchecked, the ~forementioned high level of solid particulate emission in diesel exhaust will continue to compound problems caueed by the alre~dy high levels of total suspended particulate~ in the atmosphere, espec$ally in urban areas. For example, ~s the diesel populat~on increases it can be expected that there will be ~ decrease in visibility in major eities. ~hus, the National Research Council estimates visibility loss in l990 to be twenty per~ent in Los Angeles and fifty percent in Denver (Science, page 268, January 1982~. Moreover, certain characteristic com~onents of diesel exhaust par~iculate emissions have been identiied as carcinogens; their presence in the atmosphere thus creates an evident and unacceptable health hazard. In this connection, the National Cancer Institute has published a study which ~howed that truck drivers operating diesel vehicles ran a risk of suffering bladder cancer up to twel~e times that of the normal population ~Wall Street Journal, April ll, l983~.
Responding to the above-described situation, the Environmental Protection Agency has propssed a standard for particulate matter emission ~rom diesel-powered light-duty vehicles of 0.6 g/mile, beginning with the 1987 model year;
the agency has urther proposed (for enforcement beginning with the 1990 ~odel year) ~ st~ndard for ~uch emissions from dlesel-powered heavy-duty vehicles of 0.25 g/bhp-hr ~brake horsepower hour).
One of the options which is available to manufacturers of die~el engines and ~utomotive vehicles for ; combating the aforementi~ned problem i8 deliber~te :; -4-' ~ 7S3~
~uppression of power output in commercially produced diesel engines. Indeed, this technique is simply an exten~ion of methods used to control smo~e and gaseous emissions ~5 previously used by engine manufacturers. Specific examples of such technique are the methods used to minimi~e (1) acceleration smoke and (2) lugdown smoke.
Acceleration smoke is ~hat generated durin~
vehicle acceleration. lt is caused by a higher-than-desired fuel/air ratio and usually manifests itself as a short-duration, black puffo Lugdown smoke is generated during operat on under a hea~y lDad, for instance, duriny hill-climbing. It ean conveniently be considered as full-load, st2ady-state smoke. Manufacturers compensa~e for these difficulties by mechanically limiting the amount of fuel injected under conditions at which the emissions are generated. Thus, smoke reduction is promoted at the cost of lost performance.
By the foregoing technique, engine manufacturers have made some headway in the endeavor to cut back the solid particulate emissions in the exhaust of such engines. But, a~though~these methods have been somewhat helpful, they are not an adequate ~olution. That is, the aforementioned expedients are not effective to eliminate all ~olid particulate emission or even to~decrease it to a desirably ~low levei, unless power output is reduced to an unacceptably low level~. ~
Several 21ternative possibilitiefi for reducing emission levels h~ve be~n inve~tigated. Prominent ~mong those poss~ibilities are thermal and ca~alytic oxidation of ;~ partloulate while it 1~ 6till ~uspended in the exhaust stream, thermal ox1~tion of filter-trapped particulate :: :
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~ tter, ~n~ cutAly~c ox~ation o~ il~er-trapp~d ~ ~ .
partlculate ~atter. ~owever, these po~sibilltie~ g~ner~lly have ~ssoclatea ~hortcom~ng~ which detract from heir suita~ility a8 viable comm~rciMl 801utlon8.
For example, thermal $n-~tream oxld~t~on techniques requ~re ~he provl~lon to the exhaust Gtre~m of large ~mount~ of hea~ energy wh~ch i~ typic~lly unreco~erable~ Catalytic ln-stream oxidation requires devislng a ~uitable mean~ for lntroducing cataly6t material into the exhaust stream, and preliminarily identification of appropriate c~talyts, both difficult problems which to date have defied soluticn.
Other of the aforementioned pos~ibilities involve use Gf a ~ilter to remove ~olid particul~te from a diesel engine exhaust ~tream. Use of filters has generated a relatively large amou~t of interest in the ~rt.
Experi~entation has been conducted with ~ number of different types ~f filter ~aterial~, not~bly ceramic ~aterials, ~tainless ~teel wire mesh, and the like.
Filtration is, of c~ur~e, ~ reasonably direct manner in which to remove particulate emission from an exha~t ~tream.
However, use of filters ifi ~ccompanie~ by 6ignific~n~
difficultie~ re6ulting from the tendency of those filters ~o ~log.
For;~any filtering materials particul~te loading i6 an irrever~ible pr~ce~ ~naofar a8 once lo~ding or clogqing has reached a certain p~int, the filter element mu6t be discarded ~nd replace~ ~lnce the $n$tlal re~triction c~annot be re6tored; for such fllter elements, el~An$n9 i6 ineffective. ~ven lf clogging $6 not ~llowed to proceed to , ` 1rrever~ib11ity, lt~ ~ccurr~nce lead~ to ch~k~ng of~ ~f the .

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exhau~t ~low through the f~lter. 8i~c~ ~o be effect~ve the fllter must ~e po~i~ivned ~n the exhaust 6~ream, filter-clogging thus tend~ ~o ~ncrea~e the pre~ure differential acros~ the filter element ~nd ~mpede the exhau~t operat~on - which detrimentally effect~ oper~tion of the die~el eng~ne. Accordingly, ~t ~8 ne~e~ary, lf filtrat~on ifi to be A pra~tical ~olution, to remove ~olid particula~e matter which clog~ exhau~t flow filtering elements, i.e., regenerate the filter.
It is not Gurprising~ therefore, that filter-regeneration is central to the above-mentio~ed filtration techniques. But, while they addre~s filter-regeneration, those techniques do not make i~ oommercially attractive.
~or example, thermal and catalytic oxidation of filter-trapped particulate matter to regenerate the filter is problematical inasmuch as the ~pace-, cost- and energy consumption-re~uirements which accompany them are substantial. ~hese filtration techniques are no more acceptable than the direct, in-stream oxidation techniques which do not make use of ~ilters.
As an indication of the direction the art has taken, see a recent ~urvey and evaluation of the above-discussed propo~al~ - Murphy et ~1., "Assessment of ., Diesel Particulate Control - Direct And Catalytic Oxidation~, pre~ented at the International Congress and Expo~ition, Cobo Hall, Detroit, Michigan (February 23-27, 1981~, SAE ~echnical Paper 5er~e~, No~ 810,112 - ~n which it is ~tated that the technique apparently hold~ng greatest promise for removal of ~ol$d particulate matter ~rom die6el engine exhau~t i~ catalyt~c oxidation of ~ilter-tr~pped part$culate matter.

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12~75~2 Another proposal for removal of solid particulate matter from diesel engine exhaust appears in U.K~ Patent Application GB 2,Q~7,283 published Novem~er 3, 1982. That application discloses a method for f~ltration of exhaust flow, and corresponding apparatus, which involves use o~ ceramîc filter material and no less than two filter zones ~hich are alternately emplo~ed for ~iltering the exhaust strea~n of an internal com~ustion engine. The essence of that technique is the filtration of the ex~aust stream with one filter zone while simultaneously regeilerating the other filter zone by passing an appropriate fluid (e.g., air1 through it, in a direction opposed to that of exhaust flow, in order to dislodge trapped solid particulate matter. That regeneration technique is known as ~ackflushing. No quantification of ~ackflushing time is givan, it is aPparent that ~ackflushing is effected by continuous, relatively long-term passage of back~lushing fluid t~roug~ t~e ~ilter zone being regenerated. The solid particulate matter removed ~rom the filter is xecycled to the engine fox inc~neration. ~t a desired time the ~egenerated ~lter zone is inserted in the exhaust stream and the other filter zone i5 subjected to ~ackflushing. In this mamler, t~e filter zones are periodically rotated in an attempt to maintain effective engine operation dur~ng filtering.
Ho~ever, even the techni~ue descxi~ed in the a~ove~identifie~d U.K, Patent Application has signif~cant dra~ac~s~ Use of the cont~nuous backflushing p~oceduxe ~ich~the applica~tion p~escribes is ineffective to prevent long~te~ c~ogg~n~ of th~ ~ilter zones e~ployed~ Rather, despite b~ck~lushing~ t~at cl~yin~ ste~dily incXeaseS~ and ~es~1t~ ~n a ~te~dily inc~e~sing pxessuxe dxvp ~cx~ss the . .
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~1ter. 8teady-~tat~ operat~on c~nnot be achleved.
~urthermore~ although with the cont~nuous ~c~flushlng/recycli~g procedure pre~cribed ~n the U,~.
Patent ~pplic~t~on ~he part~ul~te emi~on level ~
somewhat lower, that level ~ still unde~irably high -leaving much room ~or improvement.

Objects of ~he Invent~on It is an object of the instant invention to provide a method of removing solid particulate matter from the exhaus~ of a diesel engine which enables increased utilization of the p~wer output potential of that engine with a ~imultaneous seduction of solid particulate ~mission to an insignificant level, and also to provide ~ppar~tus for accomplishing same.
It is another object of this invention to provide a method ~or removal of olid particulate matter from diesel engine exhaust whioh is direct, simple, relatively inexpensive and highly efficie~t, ~s well as to provide apparatus for accompliohing same.
It 1s yet another object of the instant invention to provide a method for filtration-removal of solid particulate matter ~rom die6el engine exhaust whieh is effective ~o regenerate the ~ilter ~aterial substantially completely and thereby restore an ~cceptably low pressure .
: drop acro6s ~t, ~ well ~8 to provide appar~tus for ~ccomplishing~fiame.
It i6 ~tiIl another object o~ this ~nvention to provlde a~method for filtra~ion-removal of ~olld pnrticulate matter:from~dieRel ~ngine exhau~t wh~ch i~ ef~ective ~n incre~sing the efficlency of eombustion of recycled ~olid ~ .
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lZ~7532 part~ulate ~mlss$on thereby - ln comb~nation ~th filtration of the exhaust str~M - to aecrease soll~
p~rt~ulate levels ~ di~fiel ~ngine ~xhaust ~ynergis~ically.

Statement and Advantages of the Inventlon - The object6 of the ~n~tant ~nvent~on are ~ch~ved a~ follows.
In one of ~ts ~spect~, the present invention ~8 in a method for removing ~olid part~ulate matter from the exhaust of a die~el engine, which compri~es the ~teps of passing the engine's exhau~t flow through at least a part of filter means to trap ~olid part~culate matter in the exhau~., thereby to remove said matter from ~aid exhaust flow: periodi~ally interrupting the exhaust flow to at least ~aid part of the filter means; during ~aid interruption passing a backflush fluid pul e through said ~ilter means to effect dislodgment of ssid ~olid particulate mat~er from said part of ~aid ~ilter means; and tran6porting said dislodged ~olid particulate matter to the intake cf ~aid enqine ~o that ~aid matter ~an be ~ombusted in the engine.
In ~nother of it~ ~pe~t~, the present invention resides in apparatus, in ~ die~el engine, for ~ecreasing exhaust emission, which comprises filter means whi~h is posltioned to intercept the engine's exhaust ~low and which traps ~olid particulate matter ~n the exhaust when that exhau~t flows throu~h ~t lea~ a part of ~a~d f~lter me~ns, thereby to remove ~aid matter from ~aid exhaust flowt means ~or periodically~nterrupt~ng the exhaust ~low t~rough ~t least 6aid~part of the filter means~ means for p~s~ng, during ~id i~nterruption, ~ b~ckflu~h fluid pul~e through the filter ~ean6 to cffeo~ ~$610dgment ~f ~ai~ ~lid . -~O-~, .
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p~xticulate ~at~er fro~ sal~ part of ~he 11ter m~an3~ ~n~
~ean~ ~or tran~por~lng ~al~ dislodged ~olia part~culate ~atter to the lntak~ of 8a4~ eng~ne 80 that ~aid ~atter can be co~busted ln the engln~
In ~ further aspect, the lnvention 18 ln a method for removing solid particulate matter ~rom th~ exhaust of diesel engine, which comprises the steps of p~s$ng the engine's exhaust 10w t~rough ~$1ter means containing a ~ingle filter zone to tr~p $n the filter zone ~olid particulate matter in the exhaust, thereby to remove said matter from the exhaust flow; periodically interrupting the exhaus~ flow through ~aid ~ilter zone; during said interrupti~-~, passing through said filter zone a backflush fluid pul6e sufficient to effect di~lodgment of said 601id particulate matter from the filter means; and transport~ng ~aid dlslodged ~olid particul~te matter to the intake of said engin~ so that s~id matter c~n be combusted in the engine.
In yet ~nother of it~ aspects, the invention is in apparatus, in e diesel engine, Por decreasing exhaust emission, which compri~es filter means having a single filter zone~which is po~itioned to in~ercep~ the exhaugt flow of Eaid engine and which traps solid particulate ma~ter in the exhaust of ~aid engine when that exhaust flows through 6aid filter zone, thereby to remove s~ld matter from the exhau~t flow; means for periodic~lly interrupting the exhau-t flow through 6a~d filter zone; means for pa~sing, darlng ~ald interruption, through ~aid f~lter ~one a ba~ckflush fluld pulse sufficlent to effect ~l~lodgmnnt of ~ai~:-olld p~rtioul~te ~atter ~rom the filter ~esn6i and ~eans for tran6p~rtlng ~a$d ~-lodged olid p~rticul~te : : :

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~atter to the intake of said engine 80 that ~aid ~atter c~n be combuste~ ln the englne.
Numerous ~v~nt~ge~ ~ccrue to the practitioner sf the in~tan~ lnvention. The presen~ method ~nd apparatus embodiment~ re~ult ~n ~ reduction o~ sol~d partlculate emi~sion levels in ~iesel engine exhau~t to aD in~gnificant level~ gener~l~y, 90% or more of the ~olid part~culate emissions are removed, and particulate emi~sion~ are well under maximum emission levels proposed for implementation in the foreseeable future~ ~hi~ obviate~ the need to ~uppress potential power output of the engine in order to reduce emission levels; hence, ~ significantly increased utilization of the diesel engine'~ potential power output is enabled. ~urthermore, the present invention provides a method and appar~tus for controlling solid particulate emission which are direct, ~imple, relatively inexpen~ive and efficient through the u~e of widely avail ble.filtration materials and the elimination of the need to introduce large amounts of thermal energy, ~atalytlc agent~ and the like into the filtering sy~tem. Additionally, the pre¢ent invention, through employment of pulsed backflushing, effects a ~ubstantially complete regeneration of the filter ~aterial utilized. This confers ~ 6ignificant benefit inasmuch as steady deterioration oP the filter material due to i~rremediable long-term clogg$ng effects, experienced when employing~oontinuous backflushing, i8 ellminated ~nd high ~iltration eficiency 1~ maint~ned (thereby $mprov~ng in-u~e per~ormance and prolonging life expectancy of the ; ~filter).~ A15D~nd significantly, the pre~ent invention'~
employment of pul-ed back~lushing to regener~te ~he filter material, nd the con~ommitant recycling of trapped solid ' .
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128~S32 partioulate matter to ~he engine for combu8tion, ACtU~lly result ln a synergistic ~ncre~se in the ~ ciency of incineration of tha~ ~ol~d par~iculate ~atter vis-a-vis ~he efficiency of inc~ner~tion of recycléd solid particulate emissions when empl~ying contlnuous back1u~h~ng. The instant invention i8, therefore, ~ substantl~l $~chn~cal and commercial advance.
In the following ~ections, the invent~on i8 described in greater det~il to illustrate ~everal of its preferred embodiments.

Brief Descript_on of the Drawinq~
~ i~. 1 is a perspecti-~ view of a ~ceramic honeycomb~ filter ele~ent suitable for practicing the invention.
Fig. 2 is a ~chematic view of ~everal individual passages within the filter element of Fig. 1.
Fig. 3 is a s~hematic view of one embodiment of , : the invention, namely, a diesel engine exhaust gas filter arrangement employing a ~ingle filter zone.
Fig. 4 is a curve ~howing the results of filter regeneration with the present inven ion.
Fig. 5 illu~tr~tes an another embodiment in accordance with the presen~ invention.
~ ig. 6 i~ a whematic illustration of yet another embodime~t ~f the ~nventi~n.
~ ~ Fig. 7~i6 ~ whemAtic illustration of ~n al:ternative embodiment of the invention in wh~h pul~ed backflushing is cbrried out with compressed a~r.

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~ F$g. 8 ~ a schemati~ illu~trat$on of still . . .
a~other alternativ2 embo~iment of the ~nvent~on ~ which two filter 20ne~ are employ~.
Description of Certa~n Preferred Embodiment~
The pre~ent ~nvention i~ ~uitable for u~e ln conjunction with both natur~lly ~sp$r~ted a~d turbo-charged diesel engines of ~11 6izQs, but particularly ~ith l~rger turbo~charged die~el engine~ ut~lized in heavy-duty vehicles, such a~ trucks, buses a~d the li~e, or in heavy industrial applic~tions of the sort in which ~olid particulate emissions are e6pecially high and especially intolerable due to poor ventil~tion or the like.
The principal cr$terion of fiuccess w~th the present invention (~s with all ~iltering 5y6tem5 ~or combustion engine emi~ion) i8 the sttainment of the desired radieal minimization of solid particulate emi~sion levels under ~onditions of ~teady-state operation conducive to commercial, automotive and other industrial applications.
Put another way, filtering ~ethods and apparatus which involve a filter element that irrever~ibly (even if gradually) clogc to a level beyond that at which the filtration i~ comp~t1ble with e~ect~ve engine operation, or the utiliz~tion of which rc~ult in the collection of solid pareiculate emis~ion~ elzewhere ln the sy~tem until efficient operation of the ~ngine i8 foreclosed, ~re not oapable of ~u~iciently long-term operat$on to make them easible Bolution to the pollution problem~ discu6scd hereinabove. By way of ex~mple, those of ordlnary ~kill in the ~rt oan re~dily ~ppreciate that partlcul~te ~mi~ion clogging~of:~ fllter elament or trap will rc~ult in unworkably large lncYea~e ln pre8~ure di~ferential acros~

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12~7532 the trap, thereby introducing into the system an unacceptably high backpressure so as to impede the operation of the engine itself. ~ccordingly, the desideratum is to achieve equilibrium, i.e., a condition in which the amount of part;culate emission from the engine is equivalent to an amount which is disposed of in a manner minimizing atmospheric pollution to the greatest degree possible. Pollution minimization in accordance with the instant invention is accomplished by returning the solid particulate matter (except for the -amount which accumulates in the system itself) to the engine for combustion (incineration).
Hence, design choices made in the course of implementing utilization of the invention will be geared toward maintaining the particulate emission inventory in the system at a feasibly low level and maximizing the amount of particulate emissions returned to the engine and there incinerated.

One important point to consider is the filter element or trap which is utilized to remove solid particulate matter from the exhaust stream emitted by the engine. Suitable materials for filtering the exhaust stream in accordance with the invention are ceramic honeycomb, sintered metal particles, coated and uncoated metal mesh, ceramic fiber, ceramic foam, and packed beds. Of these, ceramic honeycomb and sintered metal particle materials act as surface filters inasmuch as particles larger than the effective pore size of the honeycomb are normally collected on its upstream surface. In contrast, the other four filter media can be considered to function as depth filters because particle removal is not ]imited to the surface, but is continuous throughout part or all of the filter materials's thickness or depth.
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- ! lZ ~7 S ~2 ~ n a cer~mic honeycomb ~ilter ~oli~ part~cle~
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larger th~n the approximate mean pore ~ize of ~he mater~al are ~ntercepted ~ the ma~eri~l'3 fiurace and preven~ed from passing throug~ the ~aterlal. A~ par~icle~ collect on the surface, the effective pore size ~ redueed ~h~ch, ln turn, leads to ~n incxeased efficiency A~ smaller 8iZ~ particle6 ~re cGllected. In qeneral, ceramic honeycomb trap~ have three zones of activity fir~t, a period of rel~tively rapi~
back pressure increa6e, ~o~t likely result$ng from early pore plu~ging and in~tial cake formation on the upstream surface sf the filter mater$al; second, a prolonged period characterized by a relatively constant loading 810pe;
fin~. ly, a shorter period during which b~ck pressure agair.
increases rapidly, pr~bably due to complete plugging of many cells. Illustratively, the leading one inch or 60 of the filter ~aterial~ when used in a typical ~ilter assembly ~ee Fig~ 1 or 2, described hereinafter3 usually becomes more heavily loaded ~han does the rem~inder of the fil~er which carries only a lighter and relatively uniform film of the ~olid particulate filtrate. Dislodgment of trapped ~olid particulate matte~ ~n accordance with the invention i5 pre~erably accompli6hed in the fir~t or early ~econd ~ta~e.
~owever, de-ign of the cera~ic honeycomb filter to optimize air flow within each channel of th~t f.lter element in order to di~tribu e the loading more evenly does, in certain embodiments, incre~e the ~ffectivene5s of dislodgment ~nd/or the t~me period which c~n be permitted to elap~e between di610dgment events.
Sintered porou~ metal filter ~aterials are .
advantageou~ ln th~t they exhibit the ~tructursl ~ntegrity~
corro~lon r~ t~nce ~n~ tcmperature re~i~tanc~ required in . , - . . , ................ ~, . .. , - ~
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- certaln embodlment of the lnvention. Thses ~teri~l~ sre - ~6 ~ade typically by pr*comp~c ~ a~d then ~intering st~inle~s teel, nic~el-b~se ~n~ other types o~ alloy ~e~l powders.
~hey are commercially av~lable, for lnst~nce from ~ott Metallurgical Corporation, and are well-adapt~ to regeneration ll.~., cleaning) in accordance wlth the present invention. The$r ~re-entrainmen~U characteri6tics ~n be highly useful ~n removing trapped particles with a relative minimum of dificulty.
In both wire mesh and cer~mic fiber filter ~aterials, the primary trapping mechani~ms are impaction and diffusion. That is, during oper~tion larger parti~les collide with .he filament~ of the mesh or fiber material and adhere to filament ~urfaces, or to particles already collected on those surface~. Addition~lly, some ~maller particles migrate by diffusion to the surf~e of the me~h or fiber material or ~o previously collected particles, and are slso retained in the filter. Mesh and fiber traps of this 60rt are aavantageous in that the back pre~sures attendant upon their u6e are relatively l~w. While their tendency to exhibit a ~blowoff" phenomena - that i~, a reentrainment in the exhaust stream of previously collected particles - can : be somewhat d advantag~ou~, its controlled occurrence operates, in certain e~bodiment~ of the pre~ent lnvention, t~ the advantage of the invention'6 pr~ctit~oner ~6 controlled reentrainment ~ one of the objects o~ the invention. In an ~ltern~t~ve em~odiment metnl ~sh ~ilter material $B coated with ~ctivated alumina whi~h prov$des a highly porou~ surf-ce ~tructure of large ~ur~Ace ~rea.
Addition~lly, the porou ~urface tend6 to di~rupt boundary l~yer flow thereby encouraging di~fu~ion to the mesh ''`- ' '. . . :
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--- - f~lament. ~he ~oreqoing resul~ ln ~ncrea~ea collectlon , .
effi~i~ncy and holding power.
Ceram~c foam f~lter material~, such ~8 ~lica fo~m materials~ are ~180 useful. Thefie materiDls provide ~
three-dimensional, open por0 network which collects sol~d particulate matter efficien~ly, The main trapp~ng mech~nisms ~re ~nterc~ption and diffusion. In general, trapping efficiency incre~se~ as the number of cell~ per linear inch and dep~h increa~es. Pres~ure drvp across the ceramic foam filter increases with cell number and depth, but substantially decrRases with increasing cross-rectional a~ea for a given volumetric flow rate. Dit;lodgment of trapped particle~ in ~cordance ~ith the present invention is, in many instances more difficult when employing a ceramic foam material; however, in ~ome emhodiment~, this di~ficulty i8 more than off~et by the decreased back pressure zttendant upon use Qf ceramic ~oam material in comparison with ceramic honeycomb material, due to the fact that cell ~ize in the ceramic foam materials i5 often larger than the pore ~ize in ceramic honeycomb ~tructures, Granular bed filters lend themselves to practicing of certain embodiment6 of the invention. They are particularly interesting for their ~apacity to function either in a tationary or fluidized mode. It follows that the granul~r bed can be operated ~n ~ ~tationary m~de during loading~or tr~pping to enhance collection ~ficiency, and then be operated in ~ 1uidized mode during cle~ning to enh~nce di-lodgment ~nd reentr~inment, Th$s b~ne~it ie a result of the f~ct that penetration in a moving bed usually ~gnificantly hlgher than p~netration in an otherwise equ$valent tationary bed, the lncreaæe being `~ .

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lZ~3~S32 attributable to better reentrainment through mechanical agitation in the flwidized mode In an advantageous embodiment, collection efficiency of a stationary granw]ar bed is increased by the intergranular deposits in the bed, that is solid particles which ~ecome interstitially lodged during filtering; the bed operates as a graded media filter, larger particles typically being collected on granules at the bed's surface and smaller particles collected within the bed~s pores by an increasingly dense deposit. Shallow beds are favored because they can be designed to provide high collection efficiency with relat*ely low back pressure and easily dislodgment and reentrainment.

An especially preferred filter material is a ceramic honeycomb unit with parallel channels running its entire length. The cells are advantageously square in shape, but are suitably otherwise configured to be circular, elliptical, etc. The ceramic filter unit is suitably fabricated of a porous cordierite (2MgO-2A1203-5SiO2), but is also acceptably made of any other ceramlcs, such as mullite, alumina, forsterite, aluminum titanate, mullite and aluminum titanate, spinel, zirconia and spinel, calcia partially stabilized zirconia, and alurnina and silica Units fabricated of the foregoing materials which are suitable for the invention typically have physical features such as cell density, porosity~ mean pore size, coefficient of thermal expansion, and compressive strength corresponding to those of commercially available units of such materials employed in filtering particulate from diesel engine exhaust The overriding requirements are that the material has the necessary mechanical strength, chemical resistance, thermofracture resistance, and melt resistance to survive effect*ely in the hostile environment presented by diesel engine exhaust ., ,` : - 19-. ~
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... . . . . , _ .
~ . ~ In F~. 1 ther~ epict~d one typ~ o~ ceram~c . .
honeyGomb f~lter unit ~u~tablo for practlcing oP t~e present ~nvent~n. The un~t 10 ha~ ~ monoli~h face 12. On the f~e~ openings 14 ~lternate ~ith eolld ceramic plugs 16 to form a checkerboard arrangemen~. ~he opening~ perm~
ingress to and egress fro~ p~rallel channel~ whlch extend the entire lenqth of the un~t. ~he channels term~nate ~t the opposi~e end of the unit (not ~hown), and ~re blocked nt ~hat end ~y ceramic plugs ~o as to create a set of bl~nd passages. The ~pposite end of the filter unit is also m~de up of alternating pores and ceramic plugs. The pores in the opposite end permit ingress to and egress ~rom a corresponding parallel ~et of channel~ running the entire length of the uni~ and termina~ing in ceramic plugs 16 ~n face 12. ~hus the ceramic channels opening at the opposite end of the filter unit 10 provide ~nother ~et of parallel blind passages, and are ~ituated in the filter unit to alternate with ~he blind passages which open on face 12.
Fig. 2 ~chematically depicts channel arrangement 20 of the type shown ~n Fiy. 1. ~articulate l~den exhaust 22 is directed ~t ~he upstream face of the unat 24. The exhaust enters bli~d channel~ 26 through openings 28 in the upstream fac~ ~f the unit. Channel~ 26 sre blocked at the downstream face 30 by ceramic plugs 32. At the downstream face 30, openings 34 permit inqres~ to and egress from ch~nnels 36. ~ho~e ch~nnel~ sre clo~ed at the upstream f~ce 24 by ~eramic plug6 3~. Channels ~6 and 36 are aeparated ~y : common w~ 40. ~he~e common wall~ are hufficie~tly porous to permit p~6sag~ of cxhsu6t g~s; however, ~he wAll pores are 6uffic1ently ~mall to prevent passage of the v~
majority of ~ol~d p~rt~cul~te matter ~n the exhau~t. Thus, ~- ''' :: , ,.' .

~2~53Z
a8 can be ~een fro~ the arr~ws in F~g. 2, exhau~t g~3 CArry~ng ~ol~d p~rticu1ate matter enter~ opening~ 28 and passes alony ~hanne1E 26. 801~ partic1es 42 ~re trapped on t~e wall~ of the ch~nne1s 26 wh~12 the ga~ passe~ through the porous wall6 and proceed~ along channe1 36 to opening6 3~ where it i~ released downstream of the fi1ter unlt.
Plugs 38 at the up~tream fac~ 24 of the fi1ter unlt prevent passage of the particulate laden exhau~t into channe1s 36 directly. Corresponding1y, plug~ 32 prevent e~cape of particu1ate laden exhaust a~ ~he down~tream face 30 of the unit.
In order to cle~n the filter unit depicted in Figs. 1 and 2, a backf1ush fluid pul~e ~s passed through such unit in a direction opposite that of the aforementioned exhaust. ~hus, the backflush fluid pul6e first encounters what is normally downstream end 30 of the unit, passes through opening~ 34 and into channels 36, diffuses through common walls 40, di~lodges partic1es ~2 from the common walls in channel~ 26, entrains those particle~ and carries them along channels 26 through openings 28 and out of the trap. In this manner, the trap ~ cleaned, that is regenerated.
In certain preferred embodiment~ of the invention, particu1arly its app1ication to ~utomotive uses, the collection eff~clency of the trap must be ba1anced against, and not ~coompl$~hed at~the expense of, exces~ive introduction of back pres~ure in the exhaust ~y~tem. In ~uch c~ses, lt ~8 adv~nt~geou~ to design the trap ~nd ~ssociated exhau~t ~y~tem to malntain ~a~k pre~ure at as low ~ 1eve1 ~ poh~ib1e. Rela~edly, the time period allowed to elap~e between filter unit~c1e~nings ~u~t not ~e ~o great :` :

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8~ S~
as ~o permi~ the accumulatlon of a layer of sol~d particulate matter on the filter materlal sur~ace ~o as to increa~e the pressure drop to an unacceptable level. A8 readily understood by those of ordlnary ak~ll in th~ ar~, increasing the pressure drop ~cross the filt~r unlt ~
accompanied by ~ncreasing back pre~sure ln the ex~aust system. ~ackpressure ha~ ~ direct And detr~mental effect on the operation ~f the invention, and its occurrence should be minimized whenever possib~e. Pres~ure drop can be maintained at lower levelç through the ~hoice of appropriate desisn features. Illu~tratively, it is a function of cell geometry, wall propertie~ and volume of a ceramic filter unit. Those features are advantageously ~et ~uch that a balance is struck between minimizing pre~sure drop and maintaining the required filter efficiency.
It i~ important to ~ote that practicing of the instant invention free- the ~killed artis~n from filter design constraints which would otherwise be imposed upon him due to the use of on~entional regenera~ion technigues.
More specifically, in regeneration processing which involves burning of soot ~nd othsr ~olid particulate matter trapped in the filter unit, the fllter must be configured in order to obtain regeneration times and peak pressures which fit within desired ranges for engine and/or environmental requirements. Furthermore, ~n 2utomotive applications the filter m-terial must exblb$t Gtructural ~ntegrity for the u~eful lifetime of the vehicle.
Burning collec~ed ~oot vff the filter plnc~s greater~physical dem~nd on the filter th~n the conditions i~
i~ normally ~ubject~d to in the cour~e of filter~ng ~xhaust.
That 18 to ~ay, burning of a~c~mul~ted ~oot and ~ther ~olid . '. . :

,, '!_~t - '' , .
-: ~Z~S~2 par~lculate ma~ter ~urlng regener~tion releases ~ larg~
oun~ of energy and gener~te~ o rap~d temperature r~se.
Moreover, thnt ~emperatur~ riBe i8 not neces~arily evenly ai~tr~butsd throughout the filter u~t, th~reby ~etting up thermal gradient6 ~n both radial and ~x~al direct~ons.
Additionally, exce~sive buildup of ~olid p~rticul~te ~atter can result ln release of an excess~vely large nmount of energy ~pon burning, thu~ su~ecting the material (e.g.
ceramic material) of the filter unit to temperature~
exceeding its melting point. The quest for schievement of acceptabl~ operating characteri~tic~ ~nd filter life using certain conventional regeneration processing i~
prohibitively lmpeded, if not defe~ted, by the necessity to strike a balance among the competiny considerations of filtration time be~ween regeneration cycles, filter pressure drop, and degree of particulate loading.
Of course, since with the instant invention regeneration is accomplished without the use of ignition of trapped 601id particulate matter in the filter unit, the foregoing problems ~re eliminated. Attainment of the stated objective o~ providinq method and ~pparatus fvr removal of fiolid particulate matter from diesel engine exhaust which are direct, ~imple, relatively inexpensive and highly e~ficient is manifest.
Once trapped by the ~ilter unit during exhau~t flow therethrough, ~olld part~culate mat~er $8 advantageou~ly removed ~rom the ~ilter by pas~ing ~ pul~e of backflush fluid through the f~lter unit in a ~iroction ~pposite to that of the exhau~t flow. ~he ~oncept o~
pul~tion ~8 under~to~ in the ~rt, ~nd normally refer~ to the generation of one or ~ore ~mpul~e~ or ~urges of ~luid -:. i . .-~, . .. ~ . . . ..

r lZ~;7S~2 ~ a~ng ~uff~cle~tly great power ~o that wh~n the ~mpuls~ or ~'P- .
surge strlk~s ~nd passea through the filter unit the particles residing in the trap are d~sloaged. It i 8 ~
concom~tant advantage of utillz~g a backglu~h fluid pulse that the 1ui~ also serveæ as a ~edium ln wh~ch di~lodged particles ~re entra~ed and carrie~ back to th2 ~ngine for incineration. Accord$ngly, in order for part~cle dislodgment to be carried out successfully ln order to reduce ystem backpressure and renew filter efficiency, the ~eparation forces exerted by pul~ed ba~kflu~h fluid mu~t be in excess o the forces by which ~olid particulate matter ~dheres to the filter materi~ n ~ddition o any direct mechanical for~es th~t might result ~rom flow reversal (depending on the filter material), movement of the backflush fluid s~ream in the immediate vicinity of trapped particulate matter is significant. Gener~lly, in order to initiate particle ~ovement the particle must receive ener~y from an external source, for instance from the impact of another partlcle or object or from drag forces of the moving backflush fluid ~tream.pa t the exposed profile of the particle. A con~enient way of looking at this phenomenon is that the bac~flush ~luid pulse mu~t be composed of ~
sufficient amount of ~lu~d ooll~dinq with and pa~sing through the filter unlt at a ~ufflcient velocity to dislodge trapped partlcle~. ~lternatively, the pulse c~n be ~iewed A W Ve; the pulsed backflushing must be of ~ufficient power (i.e. ~ ufficient ~mount of en~rgy must pas~ by ~ome point:in the filter per u~it t~me) to dislodge trapped p~reic~ Yet another w~y of conceptu~ ing thi~
phenOmeDOn i6 thbt the ch~nge ~n pres~ure ~t any one point ~n the~fi~l~ter un~t due to the passa~e of the w~ve ::

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:.: ~'' ' ' ' '. ' ' ' ' ' . ', . ': ' ' ' t~ 7 S 3~
there~hrough ~houl~ oocur 1~ ~n amount sf ~ime wh~ch ~8 suffici~ntly shor~ that the flul~ pulse ~B c~p~ble o~
dislodging trapped par~icle~. ~t can, of course, be readily ~ppreciate~ by tho~e of ordinary sklll 1~ the art that the m~nimum requirement~ for the bac~fl~h fluia pula~ to be effeotive in di~lodging part~cles wlll v~ry from ~y~tem to system ~nd filter unit to filter unit depending on ~ize, configur~tion and the like. ~owever, equipped with the ~eachings of this ~pplicatlon, and knowledgable of the parameters and dimension~ of his particular ~ysSem, the skilled arti~an will be ~ble to determine - whatever his characterization of the parameter8 defining the pulse -without undue experimentation th1e extent and magnitude of pulsed baekflushing necessary to practice the instant invention (see working example~, infra).
Pul~ed backflush$ng flui~ flow is suitably generated in any convenient manner which lends it~elf to u~ilization in the particular environment to which the invention is applied. Preliminarily, it i8 important to note that, while ~mbient air presents ~ ~onvenient nnd highly useful backflushing fluid, the fluid is not necessarily limited to ~ame. Alternatively, the fluid is ~uitably any one whieh can be pa~sed ~hrough the filter material ~o as to dislodge trapped particles, ~d the presence of which does not otherwise $nterfere with or detriment~lly ~ffect ~he operat~on o~ the engine 8y8tem.
Oxygen, or ~n ~ner~ ges su~h as n~trogen, i~ ~n ~xample of fiuitable lternative 1u~d. (Of cour6e, a~ will be ~pparent fzom the following, ~f ~ backflu~h~ng fluid not ~ontaining oxygen i6 u~ed ~o di~lodge the part$cle~ and tr~n~port Iby ~ean6 of entrainment~ the part~cle~ ~ck to the ~ngine, then `:

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3~
;~. . " . . . . . . - .
,.~`,, the engine ~8 a~vantage~u-~ly suppilea w~th oxyge~ fr~m r~ ~ . ~ .. . .
~no~her ~our~e ~n ~rder tha~ combu8t~0n ~e opt~mize~) ~ n an e~p2~i~11y advant~geous embodiment of the invention, the ~ckflush ~lui~ pul~e ~8 generate~ by inducing a vacuum ~on~it$on, or ~ lea~ very l~w pressure, ~n the exhaust ~ystem on the upstream slde of the trap, and then effe~t~ng a sudden r~lease of bac~flush flu~d into the ~acuum or low pressur~ volume ~uch th~t ~ ~ufficlent m~s of the backflush fluid rushes ~hrough the trap ~t high velocity (in a short t~me peri4dl to dislodge trapped parti~les. An especially ~dvantageous manner for ~ccomplishing this i~ to e~ toy the int~ke pull of ~he engine to ~raw dGwn the pressure on the upstream side of trap or filter unit. A
valve in the e~hau~t system ifi ~ctuated, and moved into the open position 9 in respon6e to the attainment of a suitably low pressure~ the valve's opening ~auses ambi~nt ~ir or other ba~kflushing fluid to be drawn through the filter unit or trap in a direction opposite *o that of the exhaust flow (the exhaust fl~w has of ~ourse been interrupted during this ba~kflushing ~ycle) by the low pres-ure conditions on the upstream side of the ~ilter unit or trap.
: Alternatively, the backflu~h fluid pulse can be a burst or ~urge of pressurized flui~d, ~or ~nstance compressed gas lillustra~ively, air). The pul~e is ~cceptably dr~wn from~a~pres~urized eon~ainer or other ~uitable source;
conveni~ent;ly: oomprefised a~r ~rAwn from the hydrAulic or turbo-charglng~ y~tem of a dl~6el-powered veh~cle w~ll do.
The cGmpre~-~ea gn~ pul~e $~;in~ected into the ~xh~ust sy6tem on the downstre~m ~dc of the 11ter unit or trap ~o AS to flow~through the trAp ln a ~irection which ~a the rever~e of that t-ken by the æxhau~t flow dur~ng normal filter~ng :

~ -26-::`
' --,. . . . . .

... . . . ~"~r~", ' r - operat~ons. ~g~in, the compres~ed g~s pulse i8 ~n~cte~
nto ~he ~y~tem auri~g interruptlon of norm~l exhau~t fl~w.
The compressed gas pula~ mu~t be of ~ufficient mass ana traveling ~t ~uf~icient veloc~ty to dislodge the pArticles trapped ln the ~ilter unit.
- With the foregoing ex~mple~ in minfi, lt is readily appreciable to the ~kille~ arti~an that ~ny other su~table ~anner of drawing or forcing pulsed bac~flush ~luid through the trap in a directlon opposite to that taken by the exhaust flow can be utilized, the principal crlteria of selection being only that the me2ns employed i~ ~ufficient to dislodge trapped par~icle~ and it does not unduly interfere with the engine' 8 opexation.
In addition to providing ~ means for dislodging trapped parti~les from the filter unit for purpo~es of cleaning ~ame, it i8 necessary in ~ccordance with the present invention to transport those particle~ bac~ to the diesel engine for incineration. This is t~pically accomplished by entraining the particles in a fluid stream conducted through a line of the exhaust system leading to the engine's air intake port. A~ter ~nitial dislodgment, the dislodged particles are in ~ery ~hort order brought under the influence of ~he flow of the afor2mentioned fluid tream. That flow ~u~t be ~ufficient to maintain ~floatation-, that 1~, keep the partl~les free ~rom rec~pture by the trap or filter unit, until they leve the unit. ~Recapture $~ dis~dvantageou~ in th~t it lowcrfi the effioiency of the regener~tion operation durlng the cleaning ; ~ycle.
In an adv~ntageou~ ref~nement of the pre~ent ~nvention the bAckflush ~luid pulse employed to di~lodge -~7-, , . . .
, ., .. . :. ~ . . . :

1~7~3;~
trapped solid particulate matter is also utilized as an entrainrnent vehicle, i.e. a carrier, for the dislodged particulate matter in order to transport same back to the diesel engine.
Typically, the backflush fluid pulse is air, the oxygen component of which is sufficient, upon reaching the engine along with the particles entrained in the air, to enable the incineration (oxidation) of those particles.

Further objects and features of the invention will be apparent from the following examples Exnmple 1 A diesel engine exhaust filtering arrangement 60 as schematically depicted in Figure 3 was constructed to demonstrate the invention. A Mack diesel engine 62 having a solid particulate emission level of about 1 gm/min. under normal steady-state operational conditions was connected by lines 78, 66 and 68 to trap 64. The trap was a ceramic filter having a single filter zone which was positioned across the engine's exhaust stream flowing through lines 68 and 70. The filter unit was fabricated of cordierite and had the fo]lowing features: mean pose size - 12 ,~6m; cell density - 100 cells per in2; average wall thickness -17 mils; porosity - 52/56%; coefficient of thermal expansion - 9.5/11.0 x 10 -7 in/in/c (25-1000c); and compressive~strength - 1140 psi, 250 psi, 15 psi along the longitudinal, lateral, and diagonal axis, respectively. Solid particulate matter contained initially in the exhaust was trapped in the filter zone when that exhaust flowed through such zone. Lines 70 and 72 were connected to provide a path from the downstream end of the filter means to main exhaust line 74 leading to the atmosphere. Line 78 was connected between the engine's exhaust port and main exhaust line 74. Intake line 76 conducted air from the ambient atmosphere to the engine 62. Line 68 connected the upstream side of the trap 64 and the intake line 76.
:~.; ' ' Valve 80 was positioned across line 66 at a location intermediate the port from which exhaust is emitted from the engine and line 66's connection with line 68. The ~` ~ ', ~-' '` ' ' ' ' ' , ,' :' , ,, valve was movable between an open 6tate permitting flow through line 66 and ~ closed sta~e lnterrupt~ng flow.
Valve 82 was posit~oned scross line 7~ between main exhaust line 74 ~nd the connection of line 70 with line 72. This valve too was movable between an open st~te permitting flow through line 72 ~nd a closed ~tate interrupting flow.
Valve 84 was positioned across line 78 between main exhaust line 74 ~nd the connection between lines 78 and 66. This valve was likewi e movable between an open state permitting flow through line 78 and a closed ~tate ir. rrupting flow.
Va.'m~e 86 was positioned across intake line 76, and was movable bet.ween an open state permitting flow through line 76 and a closed etate interrupting flow along said intake path.
Valve 88 was positioned across line 68~ and was movable between an open state permitting flow through line 68 and a closed state interrupting 10w.
An aluminum foil diaphragm 92 was positioned across the end of line 70. The thickness and strength of the foil diaphragm were selected so that it would rupture when one sid~ of it was subjected to atmospheric pressure and the other side to a reduced pressure ~ondition resulting from the intake pull of the engine.
Valve 9D was positioned across line 70 between diaphragm~92 and the connection of the line 70 w~th line 72.
The~valve was movable between an open state perm~tting flow through line 70 and ~ ~lo ed state interrupting flow.
Sampler 94 (an 1sokinetic ~ampler1 was connected to~line~7B for the~purpo-e of obtaining a profile o~ ~olid ; ~ -29-. ' ' , ~ ,:: , .

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~287S~Z
particulate emission from the engine before and during pulsed backflushing. Sampler 96 (also an isokinetic sa~pler) was connected to line 70 for the purpose of ascertaining the amount of solid particulate matter passing through trap 64, and thus into the atmosphere. Pr2sgure sensor 98 was connected ~o line 68 for the purpo~e of determining when a pressure ri~e (signalling the passage of a backflush fluid pulse on $ts way to engine 62) occurred in the line.
In operation of the engine, for periods of approximately 10 minutes valves 80, 82 and 86 were maintained in the open state to permit ambient air to flow to the engine through line 76, and exhaust flow from the engine through lines 78 r 66 and 68, the trap 64, lines 70 and ~. ~- the main exhaust line 74. Valves 88, 90 and 84 were maintained in the closed ~tate. It can readily be appreciated, of course, that the approximate ten minute filtering period is only an example; perlods of longer and shorter duration are suitable in this and other embodiments of the invention~depending on the configuration of the system, type and size of trap used, size and nature of the engine, and like considerations.
~ :Typically, after a ten-minute cycle during which exhaust was passed through trap 64, valves 84 and 88 were opened~and valves 82 and 80 were closed to redirect exhaust through line 7:8. After ten to twenty seconds, valve 90 was :` : :
opened,:and then valve 86 closed, the engine'~ intake pull thus being redirected through line 68, trap 6~ ~nd line 70.
The lntake pull Gf the engine drew down the pre~ure in lines 68~and 70, and when ~uffic$ently low pre~sure was ~chieved the foil 92 ruptured. ~hat rup~ure caused a pulse ., .
: -30-' :

s~z of ambient a~r to be pulled through line 70, trap 64, line 68 and line 76, into engine 62. When the pulse passed through the trap it d~lodged ~olid particulate matter therein. ~he part$culate was entr~ined in the backflush air pulse and also carried to the engine 62. When sensor 98 ascertained passage of the pulse in line 68, a fiignal was generated (by conventional means not shown for ~implicity) in response to which the valves were reSurned to their normally open ~nd ~losed states (as described in the preceding paragraph).
The system WAS operated for approximately 1040 minutes during which 100 cycles were completed, the cycles generally comprising about 10 minutes OL passage of the engine's exhaus~ ~hrough trap 64 and then about ten to twenty ceconds during whioh exhaust was redirected through line 78 and ultimately the trap was cleaned by a backflushing~pulse of ambient air.
From measurements taken with sampler 96 during passage of the engine's~exhaust through trap 64, it waC
found that~the trap was 93 to 96 percent effective in filtering out solid particulate emission. Purthermore, , monl ring of the pressure differential across trap 64 during operation of the exhaust filtering system showed that regeneration by pulsed backflushing is highly effective in restoring acceptable pressure drop ch~racteristics to the ~r~p~while maintaining suitable filtering efficiency. More ~peci~fically, as ~n be seen from the plot o~ ~ime ver~us :
upstream~pressure (b~ckpre6sure) trepresented by ~o~) and ~pressure differenti~l acrosC the trap (represented by ~x~) which appeArs in ~ig. 4 - an excerpt, for minutes 140 to 230, of the~trip~hart record~tion of pressure readings ~or . . :
:: .

~ Z ~ ~ 3~
the trap during the e~tire 1040 minute~ of o~era~ion - the pattern which emerged ~s typical of trap regeneration was as ~ollows. Over a set of perhaps fiv~ to nine cycles, upstream pressure (engine backpressure) and di~ferential pressure would increase somewhat during each (approximately) ten-minute period of exhaust filtra~ion ~pul~ed backflushing is represented on the strip chart by the portions of the eurve at which pressure drops precipitously). Over the course of several cycles the maximum backpressure and pressure differential reachcA during each succeeding cycle would generally be higher than he last, until one backflushing pulse would dielodge an unusually large number of particles and thus be particularly effective _n cleaning the filter and restoring a low pressure di~ferential. A
recurrent pattern of such behavior indicates the attainment of a steady-state condition in which the system is not gradually deteriorating due to gradually increasing and irreversible filter loading, but rather is continually regenerated so as to remain in an equilibrated and effective state such that fiitration can ~e continued i~definitely.
In addition, it was calculated based on d ata obtained through the use of isokinetic sampler 94, that the amount of solid particulate matter being released into the atmospbere when employing the above-described experimental system was at most forty percent ~i.e., about four grams every ten minutes) of that which would have been released into the atmosphere by the engine (a~out ten gram~ every ten minutes) hsd the exhaust not been filtered. Ina~much as thi~ condition was ob~erved to hold over ~ lons period of operation during vhich the engine prQduced ~everal hundred grams of 601id particulate emis~ion, ~t i6 cl~ar th~t the :

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lZ~3753~

~ystem reached a ~teady-st~te condition in which the ma~ority of the 601id particulate emlssion was belng incinerated upon it~ return to the engine. This establishes the clear advantages ~nd benefits of the present invention.
Moreover, in interpreting the data obtained in ths aforementioned example, it must be realized that the efficiency of the ~ystem was deliberately decreased by releasing unfiltered engine exhaust into the atmosphere for periods of up to ~wenty seconds, i.e., through line 78 while valve B4 was open, in order to measure the amount of ~olid particulate matter being emitted by the engine before and during re~eneration (with i~okinetic 6~mpler 94). It can readily be appreeiated that elimination of this procedure lwhieh is unnecessary except for experimentation) ~ould increase to an even qreater extent the effi~iency of the present invention in filtering solid particulate emission from diesei engine exhaust.
Yet another factor also merits attention. Because of the fact that, during the time valve 86 is closed and before foil 92 ruptures the air ~upply to the engine is reduced, while pxovision of fuel thereto is not abated, the output of uncombusted earbon from the engine during that time is increased ~îgnifi~antly. Of course, with the experimental eet-up described above, thi~ increased outpu~
occurs duriny ~he ime that valve 84 is open, and thus the increased solid particulate output is passed unfiltered through~line 78 and into the atmosphere. A~cordingly, the actual solid particulate emi~sion from the diesel engine is .~
greater tban the 1 g./min. figure assumed for the above-mentioned ~alcul~tions; the divisor should thus have been greater than 1 g./min. It f~llows that the percent of . __ 3'753;~

solid matter emitted (quotient) actually was smaller than forty percent. It also follows that the experimental system was more than sixty percent effective in reducing solid particulate emission.

Of course, in preferred embodiments of the invention which lend themselves to commercial application, engine exhaust would not be released directly into the atmosphere for any substantial period of time, if at all, and thus filtration efficiency should be greatly improved. This is, in fact, the case, as shown by following Example 2.

Exnmple 2 Figure S is a schematic depiction of a diesel engine exhaust emission filtrationsystem 100 actually constructed to demonstrate the invention.

, A Cummins diesel engine 102, having a solid particulate emission level of about 1.1 g/min. was connected by lines 106 and 108 to trap 104. The trap was a ceramic filter (the same filter unit as employed for example 1) having a single filter zone which was positioned across the engine's exhaust stream flowing through lines 106 and 108. Solid particulate matter contained initially in the exhaust was trapped in the filter zone when that exhaust flowed through the zone.
'~
The downstream end of trap 104 and line 110 were connected to provide a direct path to the atmosphere. Intake line 112 was connected to the engine 102 and conducted air from the ambient atmosphere to the engine. Line 108 was connected between the upstream side of trap 104 and the intake line 112. Valve 114 was positioned across line 108, and was movable between an open state~permitting flow through line 108 and a closed state interrupting flow. Valve 116 was positioned across intake line 112, and was :

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~: :

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lZ~37S3Z~
mo~able between ~n open s~ate permitting flow through tha~
l~ne and a closed ~t~te interrupting flow.
An aluminum foil diaphragm 118 wa~ posltioned across line 108 be~ween valve 114 ~nd the conneckion of line~ 108 and 112, The thickness and strength of the foil diaphragm were seleeted ~o that ~t would rupture when one side of it was ~ubjected to a reduced pressure condition resulting from the intake pull of the engine.
In operation, the engine was run for 91 ~ycles of the type described in connection with example 1 - i.e., each cycle comprising a relatively long period during which the engine's exhaust was directed through the tr~p 104 (usually about ten minL_es but sometimes up to one-half an hour or more) and a shorter period (about .2 ~econds) during which exhaust flow through the trap was interrupted to accsmmodate regeneration. During the longer period, valve 116 was maintained in the opened state and valve 114 was maintained in the closed state, thereby causing the engine's exhaust to flow through lines~106 and 108 to the upstream side of trap 104, through the trap and through line 110 for release into the atmosphere. To regenerate the trap, valve 114 was opened and valve llS closed~ the engine's ~ntake pull thus being redirected through li~e 108. The intake pull of the engine drew down the pressure in line 108, ~nd when sufficiently low pressure was achieved the foil 118 ruptured. The rupture e~used ~ pulse of ~mbient ~ir to be pulled through line 110, trap 104, and lines 108 And 112, lnto engine 102. When the pulse p~ssed through the ~rap it dislodged solid partlcul~te mDtter therein. ~he p~rticulate was entr~ined in the backflush ~ir pulse ~nd ~ls~ cnrried to ~nglne 102.

., :

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Sampler 122 (isol~inetic sampler) was connected to line 11~) for the pwrpose o~ ascertaining the amo~lnt of solid particulate matter passing through trap 104, and thus into the atmosphere. Sensor 120 (a pressure sensor) was connected to line 108 for the purpose of determining when a pressure rise (signaling the passage of a backflush fluid pulse on its way to engine 102) occurred in the line. When sensor 120 ascertained passage of the pulse in line 1U8, a signal was generated (by conventional means not shown for the sake of simplicity) in response to which the valves were returned to their normally opened and closed states.

During the first several runs of the abo~e-described exhaust filtration system the fresh ceramic cordierite trap was being broken in, i.e., the trap was equilibrating. Over the course of those cycles the upstream pressure from one cycle to the next gradually rose from about 2.1 inches of mercury up to about 3.5 inches of mercury. In subsequent runs, equilibrium had been attained and the upstream pressure varied from about 3.4 to about 4 inches of mercury in a recurring pattern as described for the trap of example 1. (It can be readily appreciated that the reported pressures were the result of trap size and can be changed as a matter of design). Additionally, because (in contrast to the embodiment of Example 1) the embodiment of this example did not release unfiltered exhaust to the atmosphere, the obser~ed emission was even more radically reduced. It is noteworthy that during the running of the Example 1 system, a puff of black smoke was observed to emerge from the main exhaust line, corresponding to the release of unfiltered exhaust during the ten to twenty second period in which .
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regeneration was accompli~hed. ~ince exhaust was not released directly to the atmosphere in example 2, but instead held in the ~ystem (~n line 106) until the interruption for regeneration was completed, no such puff of black ~moke was emitted from main exhaust line 110.
Sampler 122 $ndicated that trap 104 wa~ effective in removing 93 to 96% of golid particulate emis~ion from the filtered exhaust during the firs~ 54 cycles. Since sQlid particulate emission is not released from the system in any other manner, it is clear that the system was at least 90%
effective in removinq solid particulate ~mis~ion from diesel engine exhaust. In succeeding runs trap efficiency decreased to abou~ 85~; this was viewed as an aberration of the trap material itself and not of the invention~
Accordingly, later results can be discounted. However, even including those questionable data, the average fil~ering efficiency was at least 88.9~ on aver~ge.
Yet another embodiment suitable for commercial application is ilIustrated in Fig. 6. A diesel engine 130 is connected to trap 132 by line 134. Intake line 136 leads from the ambient atmosphere to engine 130, to provide ambient air for combustion within the engine. Line 138 is connected to~line 134 and to line l36 to provide an alternate flow path ~round ~he engine. Valve 140 is positioned ~cross line 136,~and is movable from ~n open position permitting ~low through the line, to A c108ed positiDn interrupting flow. Valve 142 is position~d across ne 134,; and i mov~ble between an open position permitting ~flow~through the line and a clo~ed position prevonting ~uch flow. ~Line:138:i~ connected to line 136 ~etween valve 140 And~the~eng1ne, ~nd $s connected to line 134 between vslve . ~ :
~ , . ., ~, .,. . -. ,: , .: , ~z~s~z 142 an the trap 132. ~he pressure drop across trap 132 i~
monitored by a conventional sensor (not shown for the sa~e of simplicity) sensor. When the pres~ure drop ~cross the exhaust filter reaches a predetermined value, valves 140 and 142 - which are normally open to permit intake flow to the engine and transportation of the exhaust stream to the trap for filtration - are ~losed simultaneously. ~hi~ can be accomplished by actuating a Eolenoid on each valve by means of a differential pressure switch placed across the ~ilter.
~alve 144 is positioned acros~ line 138, and is movable between an open position permitting flow through line and a closed position preventing flow. When valves 140 and 142 are closed the engine quickly reduces the pressure in the volume of line between the engine and valve 144. During this time, exhaust from the engine is accumulated in the v~lume of line between the engine ~nd ~alve 142.
Yalve 144 is an automatie valve that opens when the pressure differential across i~ reaches a predetermined value. When valve 144 opens in response to ~he drawing down of pressure by the engine in line 138 (valve 144 opens very quickly)~ambient air flows through line 146, trap 132, line 13~ line 138 and line 136, ~nd eventually to the engine, in a direction opposite that of n~rmal exhau~t flow. This surge of gas constitutes a pulsed backflushing of trap 132, which curge carries particle6 dislodged from the tr~p back to the engine for incineration.
Valves 140 ~nd 142 open in response to valve 144'~s automatic opening, after a suitable delay. Valve 144 automatioally clo~es ~ter the pressure different$al ~cross . :
it i5 removed,~and the y tem is restored to $ts original condition.~ The entire clean~ng sequence is completed in . .
, :;_ . .~' '. ,`, ' . ' lesa than one secona, an~ preferably les~ th~n 0.25 seconds.
Indeed, regeneratlon p~rlods o~ no more than one ~econ~, ~nd preferably no ~ore than 0.25 secona~, are advantageously employed ~n many other embodiment~ o~ the lnvention also.
It can re~d~ly be apprec~Ated that the ~ystem~ of ~xample~ 1 and 2, espe~iully ~ha~ of Example 2, can be ~odified by appropriate sub~titution of ~utomatic valve ~equencing as ae~cribed ln connection with the embodiment depicted in ~ig. 6. Thi~ would of cour~e eliminate the necessity ~f using a foil diaphra~m, which i5 an expedient adopted for experimentation only. It i5 al~o clear that, due to the benefit~ deriving from pulsed backflu~hing, the filter mean6 of the claimed invention need not b~ limited to only one flltex zone. Several of those ~dvantages accrue even when two or more filter elements ~or two or more filter zones of one element) ~re employed, although u~e of only one filter zone ~ffords clear commercial advantageR.
Yet another embodiment i8 illustrated in Fig. 7.
A filtered yRtem 150 includes diesel engine 152 connected to trap 154 by line 156. Intake line 158 lead~ from the ambient atmosphere to engine 152, to provide ~mbient ~ir for combustion wi~hin the engine. Line 160 is conne~ted to line 156 and to l~he 158 to provide an alternate flow path around the engine. Valve 162 i6 positioned across line 158, ~nd i~
movable from an open position permitting flow through the line, to ~ closed po~ition ~nterruptlng ~low. Valve 164 i8 positioned acro~s l~ne 156, ~nd ~8 movable betw~en an open po ition permi:tt~ng flow through the line and ~ ~lo~ed .
position preventing uch flcw. ~lne 160 ls ¢onnected to line 158 between valve 162 ~nd sng$ne 152, an~ i8 connected to l$ne 156 ~etween valve 16~ ~nd trap 154. The pre~ ure .

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drop across trap 154 is monitored by a conventional sensor (not shown for the sake of simplicity). When the pressure drop across trap 154 reaches a predetermined value, valves 162 and 164 - which are norma~ly open to permit intake flow to the engine and transportation of the exhaust stream to the trap for filtration - are closed simultaneously.
This can be accomplished by actuating a solenoid on each va]ve by means of a differentia]
pressure switch placed across the filter. After a suitable but short delay a pulse of compressed air is released from source 170 and injected through line 168 into ]ine 166, through trap 154 and lines 156, 160 and 158 into engine 152. This surge of air constitutes a pulsed backflushing of trap 154, which surge carries particles dis]odged from the trap back to the engine for incineration.

During this time, exhaust from the engine is accumulated in the vo]ume of line between the engine and valve 164.

Valves 162 and 164 open a suitable time after injection o~ the compressed air pulse. The entire c]eaning sequence is completed in less than one second, and preferab]y less than 0.25 seconds.

A still further embodiment of the invention is illustrated in Figure 8. A
filtered system 180 includes diesel engine 182 connected alternately to trap 184 by lines 192 and 198 and to trap 186 by ]ines 192 and 202. Intake ]ine 188 ]eads from the ambient atmosphere to engine 182, to provide ambient air for combustion within the engine; valve 190 is positioned across ]ine 188 and is movable between open and closed states permitting and interrupting flow, respectively. Line 194 is connected to line 188 and to line 202 to provide an alternate flow path around the engine.
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Line 192 connects with valve 214, and i8 mov~ble to direct flow into either llne 198 or 202 while closing of flow to the other. Line 200 connects to valve 212, which is mova~le to direc~ flow from either line 198 or 20~ into line 200, and to close off flow from the line not selec~edO L~ne 194 i6 connected to line 188 between valve 190 and the engine.
The pressure drop across traps 184 and 186 is monitored by conventional sensors (not shown for the ~ake of simplicity).
Assume trap 184 is filtering exhaust. When the pressure drop across traps 184 reaches a predetermined value, valves 214 and 212 - which have been oriented to permit transportation of the exhaust stream to txap 184 ~or filtratiGn and drawing of air through trap 186, lines 202, 204, 200 and 194, and line 188 back to the engine - are moved simultaneouslyO The system is then set so that exhaust flows through lines 192 ~nd 202 to trap 186, and then into line 208 to the atmosphere while flow from the atmosphere through trap 184, lines 198, 200 and 194, and line 188 back to the engine is permitted. Periodically valve 190 is closed9 Valve 210 is positioned across line 200, and is movable between an open position permitting flow through line and a closed position preventing flow. When valve 190 is closed the engine quickly redu~es the pressure in the volume of line between the engine and valve 210, which is normally closed.
Valve 210 is an automatic valve that opens when the~pressure differential ~cross it reaches ~ predetermined value. When valve 210 opens in response to the dr~wing down of pressure by the engine in line 194 (valve 210 opens very ::
quicklyi~mbien~ a~r flows through line 206, trap 184, line 198, line 20D and line l94, and eventually ~through line l88) to the eDgine. This 6urge of gas constitutes a pulsed . , . . , . ' I
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~7~2 backflushing of trap 184, which surge carries particle~
dislodged ~r~m the trap back to the engine for incineration.
When valve 190 i5 opened, v~lve 210 automatically closes after the pressure differential across it is removed, and the system is re6tored to its initial condi~ion. ~he entire cleaning sequence ig completed in le85 than one second, and preferably less than C.25 seconds. In some embodiments each trap is ~leaned by a plurality of such sequences. When trap 186 needs regeneration, valves 212 and 214 are operated to direct exhaust to trap 184 and permit backflushing of trap 186 in like manner. It can be readily appreciated from the foregoing example that numerous alternative systems containing a plurality of filter zones are conflgurable depending on the needs of the practitioner and his environmental constraints.
The terms and expressions which have been employed :
: are used as~terms of description and not of limitation, and there is no intention in the use of such terms and expressions of;excluding any equivalents of the features ;

; shown and described or portions thereof, its being recognized that various modifications ore possible within the~scope~of~the lnvention. Thus, it can readily be appreciated~that the invention;is not limited to dislodgment of~particles from the filter unit by means of a pulse of backflu;shing fluid. Rather, any mechanical wave which is of suffi~cient ;power:to~effect dislodgment of ~olid particulate matter trapped ~n ehe ilter unit, and which can feasibly be employed~in the particulAr opplication to which the i~nvention~1s put,~is suitable for pra~tice o~ the invention.
~For~inst~n~ce~,~1n certain embodiments of the inventi~n the partic~les are aooeptably di510dged from the filter unit by A

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sonic wave generated by appropriate convent~onal apparatu~.
The principal and basic criterion for such mechanical waves are that the filter unit mugt be subjected ~o a wave o~
~ufficient power, that i~ of 6ufficiently high energy passing by any point wi~hin the filter unit in a selected unit of time, to di~lodge the trapped particulate material.
Waves which fulfill ~his requirement are ~uitable~
In accordance with the foregoing, a method ~nd apparatus are pxovided which enable direct, simple, relatively inexpensive and efficien~ filtration of diesel engine exhaust to remove solid particula~e matter. More specifically, the present method and apparatus embodiments result in a reduction of solid particula.e emission levels in diesel engine exhaust to an insignificant level, i~e., filtering out of 90% or more of the particulate. Thus, the present invention obviates the need for deliberate suppression of engine power, or reliance on other disadvantageous conventional filtration techniques, in order ~o reduce solid particulate exhaust emission. The attainment of effective filtration of solid particulate matter from diesel engine exhaust along with a significantly increased utilization of the die~el engine's potential power output is a substantial advance in the art.

Claims (15)

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

1. A method for removing solid particulate matter from the exhaust of a diesel engine, which comprises passing the engine's exhaust flow through at least a part of filter means to trap solid particulate matter contained initially in the exhaust, thereby to remove said matter from said exhaust flow, periodically interrupting the exhaust flow through at least said part of the filter means, passing, during said interruption, at least one baakflush fluid pulse through at least said part of the filter means thereby to dislodge from the filter means, and entrain, said solid particulate matter, and transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine.

2. A method as defined in claim 1, which comprises providing a pulse which is a surge of pressurized fluid from an external source, and passing the pressurized fluid, during the interruption of exhaust flow, through at least said part of the filter means.

3. A method as defined in claim 1, which comprise interrupting the exhaust flow for a period of up to on second.

4. A method as defined in claim 1, wherein said filter means contains no more than one filter zone.

5. In a diesel engine apparatus for decreasing exhaust emissions, which comprises filter means which is positioned to intercept the engine's exhaust flow and which traps solid particulate matter contained initially in the exhaust when that exhaust flows through at least a part of said filter means, thereby to remove said matter from said exhaust flow, means for periodically interrupting the exhaust flow through at least said part of the filter means, means for passing, during said interruption, at least one backflush fluid pulse through at least said part of the filter means thereby to dislodge from the filter means, and entrain, said solid particulate matter, and means for transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine.

6. In a diesel engine apparatus for decreasing exhaust emissions, which comprises filter means having a single filter zone which is positioned to intercept the exhaust flow of said engine and which traps solid particulate matter contained initially in the exhaust of said engine when that exhaust flows through said filter zone, thereby to remove said matter from the exhaust flow, means for periodically interrupting the exhaust flow through said filter zone, means for passing, during said interruption, a backflush fluid pulse through said filter zone thereby to dislodge from the filter means, and entrain, said solid particulate matter, and means for transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine.

7. An apparatus as defined in claim 6, wherein said pulse is generated by the intake pull of the diesel engine.

8. An apparatus as defined in claim 6, wherein the filter means includes a ceramic honeycomb filter structure fabricated of cordierite.

9. An apparatus as defined in claim 6, which comprises means for providing a pulse which is a surge of pressurized fluid form an external source, and for passing the pressurized fluid, during the interruption of exhaust flow, through at least said part of the filter means.

10. An apparatus as defined in claim 6, which comprises means for interrupting the exhaust flow for a period of up to one second.

11. An apparatus as defined in claim 6, wherein said period is .25 seconds or less.

12. In a diesel engine, apparatus for decreasing exhaust emissions, which comprises filter means having a single filter zone which is positioned across the engine's exhaust stream and which traps solid particulate matter contained initially in the exhaust when that exhaust flows through said filter zone, thereby to remove said matter form the exhaust flow, a first exhaust line connecting the exhaust inlet end of said filter means and port from which exhaust from the engine's combustion chamber is emitted, a second exhaust line connected to the exhaust outlet of said filter means and leading to the atmosphere, a first intake line through which air flows from the ambient atmosphere to said combustion chamber, and a second intake line connecting the first exhaust line and the first intake line;
first exhaust valve means positioned across the first exhaust line at a location between the port from which exhaust is emitted form the combustion chamber of said engine and the first exhaust line's connection with the second intake line, said valve means being movable between an open state permitting flow through said first exhaust line and a closed state interrupting exhaust flow to the filter means, first intake valve means positioned across the first intake line in such a manner that the second intake line is connected to the first intake line between the first intake valve means and the engine said first valve means being movable between an open state permitting flow through said intake line and a closed state interrupting flow through said intake line, second intake valve means positioned across the second intake line, said valve means being movable between an open state permitting flow through the second intake line and a closed state interrupting flow through the second intake line, said second valve means opening responsive to a predetermined pressure differential being exerted across it, and closing responsive to the relaxation of said pressure differential;

said first intake and first exhaust valve means normally being in the open stake to permit intake flow through the first intake line and exhaust flow from the engine's combustion chamber through the first exhaust line, the filter means and the second exhaust line, and said second intake valve means normally being in the closed state, means for periodically closing the first intake and first exhaust valve means substantially simultaneously, to redirect the engine's intake pull through the second intake line, create said predetermined pressure differential and open said second intake valve means, thereby to generate a pulse of intake flow passing through said filter means and to dislodge solid particulate matter from said filter means and transport it to the intake of the engine for combustion in the engine, means for opening said first intake and first exhaust valve means in response to the closing of said second intake valve means upon relaxation of said pressure differential.

13. In a diesel engine apparatus for decreasing exhaust emissions, which comprises filter means having a single filter zone which is positioned across the engine's exhaust stream and which traps solid particulate matter contained initially in the exhaust when that exhaust flows through said filter zone, thereby to remove said matter from the exhaust flow an exhaust line connecting the exhaust inlet end of said filter means and a port from which exhaust form the engine's combustion chamber is emitted, a second exhaust line connected to the exhaust outlet of said filter means and leading to the atmosphere, a first intake line through which air flows from the ambient atmosphere to said combustion chamber, and a second intake line connecting the first exhaust line and the first intake line;
first intake valve means positioned across the first intake line in such a manner that the second intake line is connected to the first intake line between the first intake valve means to the engine, said first valve means being movable between an open state permitting flow through said intake line and a closed state interrupting flow through said intake line, second intake valve means positioned across the second intake line, said valve means being movable between an open state permitting flow through the second intake line and a closed state interrupting flow through the second intake line, said second valve means opening responsive to a predetermined pressure differential being exerted across it, and closing responsive to the relaxation of said pressure differential;
said first intake valve means normally being in the open state to permit intake flow through the first intake line and exhaust flow form the engine's combustion chamber through the first exhaust line, the filter means and the second exhaust line, and said second intake valve means normally being in the closed state, means for periodically closing the first intake valve means to redirect the engine's intake pull through the second intake line, create said predetermined pressure differential and open said second intake valve means, thereby to generate a pulse of intake flow passing through said filter means and to dislodge solid particulate matter from said filter means and transport it to the intake of the engine for combustion in the engine, means for opening said first intake valve means in response to the closing of said second intake valve means upon relaxation of said pressure differential.

14. A method for removing solid particulate matter form the exhaust of a diesel engine, which comprises the steps of passing the engine's exhaust flow through at least a part of filter means to trap solid particulate matter in the exhaust, thereby to remove said matter from said exhaust flow;
periodically interrupting the exhaust flow to at least said part of the filter means;
during said interruption striking said filter means with one or more mechanical waves of sufficient power to effect dislodgement of said solid particulate matter form said part of said filter means; and transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine.

15. In a diesel engine, apparatus for decreasing exhaust emission which comprises filter means which is positioned to intercept the engine's exhaust flow and which traps solid particulate matter in the exhaust when that exhaust flows through at least a part of said filter means, thereby to remove said matter form said exhaust flow means for periodically interrupting the exhaust flow through at least said part of the filter means;
means for striking, during said interruption, the filter means with one or more mechanical waves of sufficient power to effect dislodgement of said solid particulate matter from said part of the filter means;
and means for transporting said dislodged solid particulate matter to the intake of said engine so that said matter can be combusted in the engine.