Note: Descriptions are shown in the official language in which they were submitted.
~L2~S3~
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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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,
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~ 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
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~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 $6 not ~llowed to proceed to
,
` 1rrever~ib11ity, lt~ ~ccurr~nce lead~ to ch~k~ng of~ ~f the
.
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31 Z~753~
exhau~t ~low through the f~lter. 8i~c~ ~o be effect~ve the
fllter must ~e po~i~ivned ~n the exhaust 6~ream,
filter-clogging thus tend~ ~o ~ncrea~e the pre~ure
differential acros~ the filter element ~nd ~mpede the
exhau~t operat~on - which detrimentally effect~ oper~tion of
the die~el eng~ne. Accordingly, ~t ~8 ne~e~ary, lf
filtrat~on ifi to be A pra~tical ~olution, to remove ~olid
particula~e matter which clog~ exhau~t flow filtering
elements, i.e., regenerate the filter.
It is not Gurprising~ therefore, that filter-
regeneration is central to the above-mentio~ed filtration
techniques. But, while they addre~s filter-regeneration,
those techniques do not make i~ oommercially attractive.
~or example, thermal and catalytic oxidation of
filter-trapped particulate matter to regenerate the filter
is problematical inasmuch as the ~pace-, cost- and energy
consumption-re~uirements which accompany them are
substantial. ~hese filtration techniques are no more
acceptable than the direct, in-stream oxidation techniques
which do not make use of ~ilters.
As an indication of the direction the art has
taken, see a recent ~urvey and evaluation of the
above-discussed propo~al~ - Murphy et ~1., "Assessment of
.,
Diesel Particulate Control - Direct And Catalytic
Oxidation~, pre~ented at the International Congress and
Expo~ition, Cobo Hall, Detroit, Michigan (February 23-27,
1981~, SAE ~echnical Paper 5er~e~, No~ 810,112 - ~n which it
is ~tated that the technique apparently hold~ng greatest
promise for removal of ~ol$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~ ~$610dgment ~f ~ai~ ~lid
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p~xticulate ~at~er fro~ sal~ part of ~he 11ter m~an3~ ~n~
~ean~ ~or tran~por~lng ~al~ dislodged ~olia part~culate
~atter to the lntak~ of 8a4~ eng~ne 80 that ~aid ~atter can
be co~busted ln the engln~
In ~ further aspect, the lnvention 18 ln a method
for removing solid particulate matter ~rom th~ exhaust of
diesel engine, which comprises the steps of p~s$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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., ~ . . , :
~Z8~S3;~
~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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~ n a cer~mic honeycomb ~ilter ~oli~ part~cle~
,, . ~ , . . . .
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
-17-
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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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,
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- ~ . - . ,.. : . ...
` . ' ~ ~ , ' '. , ' , , . . ! .
7S32
... . . . . , _ .
~ . ~ 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,
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~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
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-: ~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 $8
advantageou~ly removed ~rom the ~ilter by pas~ing ~ pul~e of
backflush fluid through the f~lter unit in a ~iroction
~pposite to that of the exhau~t flow. ~he ~oncept o~
pul~tion ~8 under~to~ in the ~rt, ~nd normally refer~ to
the generation of one or ~ore ~mpul~e~ or ~urges of ~luid
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r
lZ~;7S~2
~ a~ng ~uff~cle~tly great power ~o that wh~n the ~mpuls~ or
~'P- .
surge strlk~s ~nd passea through the filter unit the
particles residing in the trap are d~sloaged. It i 8 ~
concom~tant advantage of utillz~g a backglu~h fluid pulse
that the 1ui~ also serveæ as a ~edium ln wh~ch di~lodged
particles ~re entra~ed and carrie~ back to th2 ~ngine for
incineration. Accord$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
:
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37532
... . . .~"~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-
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., .. . :. ~ . . . :
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
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7532
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-
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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
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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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~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
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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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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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532
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 $s connected to line 134 between vslve
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142 an the trap 132. ~he pressure drop across trap 132 i~
monitored by a conventional sensor (not shown for the sa~e
of simplicity) sensor. When the pres~ure drop ~cross the
exhaust filter reaches a predetermined value, valves 140 and
142 - which are normally open to permit intake flow to the
engine and transportation of the exhaust stream to the trap
for filtration - are ~losed simultaneously. ~hi~ can be
accomplished by actuating a Eolenoid on each valve by means
of a differential pressure switch placed across the ~ilter.
~alve 144 is positioned acros~ line 138, and is movable
between an open position permitting flow through line and a
closed position preventing flow. When valves 140 and 142
are closed the engine quickly reduces the pressure in the
volume of line between the engine and valve 144. During
this time, exhaust from the engine is accumulated in the
v~lume of line between the engine ~nd ~alve 142.
Yalve 144 is an automatie valve that opens when
the pressure differential across i~ reaches a predetermined
value. When valve 144 opens in response to ~he drawing down
of pressure by the engine in line 138 (valve 144 opens very
quickly)~ambient air flows through line 146, trap 132, line
13~ line 138 and line 136, ~nd eventually to the engine, in
a direction opposite that of n~rmal exhau~t flow. This
surge of gas constitutes a pulsed backflushing of trap 132,
which curge carries particle6 dislodged from the tr~p back
to the engine for incineration.
Valves 140 ~nd 142 open in response to valve
144'~s automatic opening, after a suitable delay. Valve 144
automatioally clo~es ~ter the pressure different$al ~cross
. :
it i5 removed,~and the y tem is restored to $ts original
condition.~ The entire clean~ng sequence is completed in
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lesa than one secona, an~ preferably les~ th~n 0.25 seconds.
Indeed, regeneratlon p~rlods o~ no more than one ~econ~, ~nd
preferably no ~ore than 0.25 secona~, are advantageously
employed ~n many other embodiment~ o~ the lnvention also.
It can re~d~ly be apprec~Ated that the ~ystem~ of
~xample~ 1 and 2, espe~iully ~ha~ of Example 2, can be
~odified by appropriate sub~titution of ~utomatic valve
~equencing as ae~cribed ln connection with the embodiment
depicted in ~ig. 6. Thi~ would of cour~e eliminate the
necessity ~f using a foil diaphra~m, which i5 an expedient
adopted for experimentation only. It i5 al~o clear that,
due to the benefit~ deriving from pulsed backflu~hing, the
filter mean6 of the claimed invention need not b~ limited to
only one flltex zone. Several of those ~dvantages accrue
even when two or more filter elements ~or two or more filter
zones of one element) ~re employed, although u~e of only one
filter zone ~ffords clear commercial advantageR.
Yet another embodiment i8 illustrated in Fig. 7.
A filtered yRtem 150 includes diesel engine 152 connected
to trap 154 by line 156. Intake line 158 lead~ from the
ambient atmosphere to engine 152, to provide ~mbient ~ir for
combustion wi~hin the engine. Line 160 is conne~ted to line
156 and to l~he 158 to provide an alternate flow path around
the engine. Valve 162 i6 positioned across line 158, ~nd i~
movable from an open position permitting flow through the
line, to ~ closed po~ition ~nterruptlng ~low. Valve 164 i8
positioned acro~s l~ne 156, ~nd ~8 movable betw~en an open
po ition permi:tt~ng flow through the line and ~ ~lo~ed
.
position preventing uch flcw. ~lne 160 ls ¢onnected to
line 158 between valve 162 ~nd sng$ne 152, an~ i8 connected
to l$ne 156 ~etween valve 16~ ~nd trap 154. The pre~ ure
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37S32
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
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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.
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