Method and apparatus for trapping and incinerating particulate matter found in diesel engine exhaust

A method of 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, interrupting the exhaust flow through at least said part of the filter means, at a time when the preceding period of exhaust flow therethrough is of sufficiently brief duration that the trapped particulate matter has not become resistant to subsequent combustion in the engine, during said interruption backflushing at least said part of the filter means thereby to dislodge from the filter means, and entrain, said solid particulate matter for the purpose of removing it from the 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; and apparatus for accomplishing same.

FIELD OF THE INVENTION 
The field of the instant invention is reduction of the particulate emission 
level in diesel engine exhaust, and in a more specific vein methods and 
apparatus for removal of solid particulate matter found in diesel engine 
exhaust. 
BACKGROUND OF THE INVENTION 
Over the past few years, the diesel engine has been relied upon 
increasingly to 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 defined 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 special purpose vehicles. Heavy-duty 
vehicles are defined as all vehicles of 8,500 pounds or more gross weight. 
Heavy-duty vehicles are, typically, trucks, buses, vans and recreational 
vehicles. 
Additionally, the diesel engine finds application in industrial settings 
such as storage facilities and underground mines, many of which have only 
limited ventilation. And, diesel engines find further significant 
utilization in diesel locomotives; industrial applications such as fork 
lift engines, auxiliary engines on large vehicles, generator and pump 
service, and in logging, mining, quarrying and oil field operations, as 
well as well-drilling equipment; construction applications, such as use in 
bulldozers, motor graders, tractors, scrapers, rollers and loaders; and 
agricultural applications, such as powering agricultural equipment. 
However, despite its rising popularity, especially in the heavy-duty 
vehicle category, and although diesel engine exhaust (unlike that of 
gasoline engines) is relatively clean in respect of unburned hydrocarbon- 
and carbon-monoxide content, several significant difficulties are 
attendant upon use of the 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 gasoline 
engine. 
Typical solid particulate matter from diesel engine exhaust is made up of 
small, solid, irregularly shaped particles which are agglomerates of 
roughly spherical subunits. The particles often have high molecular weight 
hydrocarbons absorbed on their surfaces, and also may have a liquid 
coating; frequently, the particulate matter is a complex mixture of pure 
carbon and hundreds of organic compounds. The particulate is often 
extremely fine and light with a flour-like consistency. Size distribution 
ranges from very small single particles of about 0.01 microns to 
relatively large clusters in the range of 10-30 microns. Illustratively, 
the particles have a bulk density of 0.075 g/cm.sup.3 and have a surface 
area of 100 m.sup.2 /g. Generally speaking, the nature of solid 
particulate matter emitted from turbo-charged diesel engines is somewhat 
different from that of naturally aspirated diesel engines, the former 
tending to be smaller in size with much lower levels of retained organic 
compounds. 
Unchecked, the aforementioned high level of solid particulate emission in 
diesel exhaust will continue to compound problems caused by the already 
high levels of total suspended particulates in the atmosphere, especially 
in urban areas. For example, as the diesel population increases it can be 
expected that there will be a decrease in visibility in major cities. 
Thus, the National Research Council estimates visibility loss in 1990 to 
be twenty percent in Los Angeles and fifty percent in Denver (Science, 
page 268, January 1982). Moreover, certain characteristic components of 
diesel exhaust particulate emissions have been identified 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 showed that truck drivers operating diesel 
vehicles ran a risk of suffering bladder cancer up to twelve times that of 
the normal population (Wall Street Journal, Apr. 11, 1983). 
Responding to the above-described situation, the Environmental Protection 
Agency has proposed a standard for particulate matter emission from 
diesel-powered light-duty vehicles of 0.6 g/mile, beginning with the 1987 
model year; the agency has further proposed (for enforcement beginning 
with the 1990 model year) a standard for such emissions from 
diesel-powered heavy-duty vehicles of 0.25 g/bhp-hr (brake horsepower 
hour). 
One of the options which is available to manufacturers of diesel engines 
and automotive vehicles for combating the aforementioned problem is 
deliberate suppression of power output in commercially produced diesel 
engines. Indeed, this technique is simply an extension of methods for 
controlling smoke and gaseous emissions as previously used by engine 
manufacturers. Specific examples of such technique are the methods used to 
minimize (1) acceleration smoke and (2) lugdown smoke. 
Acceleration smoke is that generated during vehicle acceleration. It is 
caused by an undesirably higher fuel/air ratio and usually manifests 
itself as a short-duration, black puff. Lugdown smoke is generated during 
operation under a heavy load, for instance, during hill-climbing. It can 
conveniently be considered as full-load, steady-state smoke. Manufacturers 
compensate 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, although that technique has been somewhat helpful, it 
is not an adequate solution. That is, the aforementioned expedients are 
not effective to eliminate all solid particulate emission or even to 
decrease it to a desirably low level, unless power output is reduced to an 
unacceptably low level. 
Several alternative possibilities for reducing emission levels have been 
investigated. Prominent among those possibilities are thermal and 
catalytic oxidation of particulate matter while it is still suspended in 
the exhaust stream, thermal oxidation of filter-trapped particulate 
matter, and catalytic oxidation of filter-trapped particulate matter. 
However, these possibilities generally have associated shortcomings which 
detract from their suitability as viable commercial solutions. 
For example, thermal in-stream oxidation techniques require the provision 
to the exhaust stream of large amounts of heat energy which is typically 
unrecoverable. Catalytic in-stream oxidation requires devising a suitable 
means for introducing catalyst material into the exhaust stream, and 
preliminarily identification of an appropriate catalyst, both difficult 
problems which to date have resisted viable solution. 
Other of the aforementioned possibilities involve use of a filter to remove 
solid particulate from a diesel engine exhaust stream. Use of filters has 
generated a relatively large amount of interest in the art. 
Experimentation has been conducted with a number of different types of 
filter materials, notably ceramic materials, stainless steel wire mesh, 
and the like. Filtration is, of course, a reasonably direct manner in 
which to remove particulate emission from an exhaust stream. However, use 
of filters is accompanied by significant difficulties resulting from the 
tendency of those filters to clog. 
For many filtering materials particulate loading is an irreversible process 
insofar as once loading or clogging has reached a certain point, the 
filter element must be discarded and replaced since the initial 
restriction cannot be restored; for such filter elements, cleaning is 
ineffective. Even if clogging is not allowed to proceed to 
irreversibility, its occurrence leads to choking off of the exhaust flow 
through the filter. Since to be effective the filter must be positioned in 
the exhaust stream, filter-clogging tends to increase the pressure 
differential across the filter element and impede the exhaust 
operation--which detrimentally effects operation of the diesel engine. 
Accordingly, it is necessary, if filtration is to be a practical solution, 
to remove solid particulate matter which clogs exhaust flow filtering 
elements, i.e., regenerate the filter. 
It is not surprising, therefore, that filter-regeneration, and the 
concomitant difficulty of disposing of the particulate matter removed from 
the filter, are central to the above-mentioned filtration techniques. But, 
while they address filter-regeneration and particulate disposal, the 
aforementioned techniques are not commercially attractive. For example, 
thermal and catalytic oxidation of filter-trapped particulate matter to 
regenerate the filter is problematical inasmuch as the space-, cost- and 
energy consumption-requirements which are entailed are substantial. These 
filtration techniques are no more acceptable than the direct, in-stream 
oxidation techniques which do not make use of filters. 
As an indication of the direction the art has taken, see a recent survey 
and evaluation of the above-discussed proposals--Murphy et al., 
"Assessment of Diesel Particulate Control--Direct and Catalytic 
Oxidation", presented at the International Congress and Exposition, Cobo 
Hall, Detroit, Mich. (Feb. 23-27, 1981), SAE Technical Paper Series, No. 
810,112--in which it is stated that the technique apparently holding 
greatest promise for removal of solid particulate matter from diesel 
engine exhaust is catalytic oxidation of filter-trapped particulate 
matter. 
Another proposal for removal of solid particulate matter from diesel engine 
exhaust appears in U.K. Patent Application 2,097,283. That application 
discloses a method for filtration of exhaust flow, and corresponding 
apparatus, which involves use of ceramic filter material and no less than 
two filter zones which are alternately employed for filtering the exhaust 
stream of an internal combustion engine. The essence of that technique is 
the filtration of the exhaust stream with one filter zone while 
simultaneously regenerating the other filter zone by passing an 
appropriate fluid (e.g., air) 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 backflushing. No quantification of 
backflushing time is given; it is apparent that backflushing is effected 
by continuous, relatively long-term passage of backflushing fluid through 
the filter zone being regenerated. 
At a desired time the regenerated filter zone is inserted in the exhaust 
stream and the other filter zone is subjected to backflushing. In this 
manner, the filter zones are periodically rotated in an attempt to 
maintain effective engine operation during filtering. 
In order to dispose of the solid particulate matter filtered from the 
exhaust, it is recycled to the engine for incineration. However, there is 
no teaching--for example, description of maximum residence time of 
particulate in the filter during exhaust flow or of the condition of the 
particulate during that residence time--in the above-identified U.K. 
Patent Application to guide the practitioner in preserving the solid 
particulate in a form such that it is suitable for efficient incineration 
in the engine. 
OBJECTS OF THE INVENTION 
It is an object of the instant invention to provide a method of removing 
solid particulate matter from the exhaust of a diesel engine and disposing 
of that particulate which enables substantial and sustained reduction of 
solid particulate emission, and also to provide apparatus for 
accomplishing same. 
It is another object of this invention to provide a method for removal of 
solid particulate matter from diesel engine exhaust and disposal of that 
particulate which is direct, simple, relatively inexpensive and highly 
efficient, as well as to provide apparatus for accomplishing same. 
It is still another object of this invention to provide a method for 
filtration-removal of solid particulate matter from diesel engine exhaust 
which is effective in increasing the efficiency of combustion of recycled 
solid particulate emission thereby--in combination with filtration of the 
exhaust stream--to decrease solid particulate levels in diesel engine 
exhaust. 
STATEMENT AND ADVANTAGES OF THE INVENTION 
The objects of the instant invention are achieved as follows. 
In one of its aspects, the present invention is in a method for removing 
solid particulate matter from the exhaust of a diesel engine. In 
accordance with the method, the engine's exhaust flow is passed 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. The exhaust flow through at least said part of the filter means is 
interrupted, at a time when the preceding period of exhaust flow 
therethrough is of sufficiently brief duration that the trapped 
particulate matter has not become resistant to subsequent combustion in 
the engine. During said interruption at least said part of the filter 
means is backflushed thereby to dislodge from the filter means, and 
entrain, the trapped solid particulate matter for the purpose of removing 
it from the filter means. The dislodged solid particulate matter is 
transported to the intake of said engine so that said matter can be 
combusted in the engine. 
In another of its aspects, the present invention resides in apparatus, in a 
diesel engine, for decreasing exhaust emission. That apparatus comprises 
filter means which is adapted 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. The apparatus also 
comprises means for interrupting the exhaust flow through at least said 
part of the filter means at a time when the preceding period of exhaust 
flow therethrough is of sufficiently brief duration that the trapped 
particulate matter has not become resistant to subsequent combustion in 
the engine. The apparatus further includes means for passing, during said 
interruption, backflush fluid through at least said part of the filter 
means thereby to dislodge from the filter means, and entrain, said solid 
particulate matter for the purpose of removing it from said 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. 
Numerous advantages accrue to the practitioner of the instant invention. 
The present method and apparatus embodiments, through trapping of solid 
particulate matter of the exhaust in a filter material, and removal of the 
trapped particulate from that material in a condition lending itself to 
combustion, enable reduction of solid particulate emission levels in 
diesel engine exhaust to an insignificant level. This obviates the need to 
suppress potential power output of the engine in order to reduce emission 
levels; hence, a significantly increased utilization of the diesel 
engine's potential power output is enabled. Furthermore, the present 
invention provides a method and apparatus for controlling solid 
particulate emission which are direct, simple, relatively inexpensive and 
efficient through the use of widely available filtration materials and the 
elimination of the need to introduce large amounts of thermal energy, 
catalytic agents and the like into the filtering system. Additionally, the 
present invention, through the timely employment of backflushing, effects 
a regeneration of the filter material utilized. The instant invention is, 
therefore, a substantial technical and commercial advance. 
In the following sections, the invention is described in greater detail to 
illustrate several of its preferred embodiments.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS 
The present invention is suitable for use in conjunction with both 
naturally aspirated and turbo-charged diesel engines of all sizes, but 
especially with larger turbo-charged diesel engines utilized in heavy-duty 
vehicles, such as trucks, buses and the like, or in heavy industrial 
applications of the sort in which solid particulate emissions are 
especially high and especially intolerable due to poor ventilation or the 
like. 
The principal criterion of success with the present invention (as with all 
filtering systems for combustion engine emission) is the attainment of the 
desired radical minimization of solid particulate emission levels under 
conditions of steady-state operation conducive to commercial, automotive 
and other industrial applications. Put another way, filtering methods and 
apparatus which involve a filter element that irreversibly (even if 
gradually) clogs to a level beyond that at which the filtration is 
compatible with effective engine operation, or the utilization of which 
results in the collection of solid particulate emissions elsewhere in the 
system until efficient operation of the engine is foreclosed, are not 
capable of sufficiently long-term operation to make them feasible 
solutions to the pollution problems discussed hereinabove. By way of 
example, those of ordinary skill in the art can readily appreciate that 
particulate emission clogging of a filter element or trap will result in 
an unworkably large increase in pressure differential across the trap, 
thereby introducing into the system an unacceptably high backpressure so 
as to impede the operation of the engine itself. Accordingly, the 
desideratum is to achieve equilibrium, i.e., a condition in which the 
amount of particulate 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. 
A fundamental aspect of the present invention is the recognition that solid 
particulate matter trapped by filter material through which diesel engine 
exhaust is passed cannot be allowed to remain on the filter material for 
an indefinite amount of time during exhaust flow without a significant 
loss in the efficiency of incineration of recycled particulate in the 
engine. That is to say, if trapped particulate is allowed to accumulate in 
the filter material for too long a period of time it becomes resistant to 
incineration in the engine after such particulate is dislodged from the 
filter material and transported back to the engine's combustion chamber. 
It appears likely that such resistance stems from the conditions to which 
the trapped particulate is subjected before removal from the filter 
material. One of these conditions is elevated temperature due to the 
relatively high temperature of the exhaust stream passing through the 
filter material. This elevated temperature condition probably results in 
chemical reactions at the surfaces of the trapped particles (e.g., 
oxidation) causing there to be a "crust" or coating which is resistant to 
combustion conditions in the diesel engine and thus decreases the 
efficiency of incineration of recycled trapped particulate. Another 
condition to which trapped particulate is subjected is constant contact 
with gaseous and solid components of the exhaust stream. Such contact is 
likely to result in the gradual enlargement of the individual particles 
due to deposition of additional material on their surfaces and/or to 
particle agglomeration. Increased particle size would have the effect of 
increasing the difficulty of combustion and thus decreasing incineration 
efficiency. And, at least as importantly, is the apparent adverse effect 
on ease of incineration of the particulate's graphitization, i.e., 
conversion from an amorphous carbon form to a far less combustible 
(crystalline) graphite form. It will be appreciated, of course, that the 
reason or reasons for the increased resistance to combustion of trapped 
particulate as a function of residence time in the filter material are not 
known with certainty. The foregoing explanations are voluntarily offered 
in the spirit of giving as full a description of the invention as 
possible. 
In any event, the efficiency and completeness with which recycled trapped 
solid particulate is incinerated in the engine is a function of the 
freshness of the solid particulate material when it is recycled to the 
engine. The guiding consideration in this regard is, therefore, the 
interruption of exhaust flow through the filter material in question 
before particulate matter trapped therein has been subjected to exhaust 
stream conditions for a time sufficient to make its resistance to 
incineration upon recycling unacceptably high for commercial operation of 
a diesel engine. It will be appreciated by the skilled artisan that the 
period of time for exhaust flow during which the trapped particulate can 
be permitted to reside in the filter material, without the particulate's 
undergoing a change making it significantly more incineration-resistant 
such that the commercial feasibility of the particulate filtering and 
disposal arrangement is diminished or lost, will vary from system to 
system--depending on system configuration, speed and amount of exhaust 
flow, exhaust pressure and temperature, and the like. However, the skilled 
artisan will be able, using the teachings herein, to determine for any 
particular system maximum and preferred periods of exhaust flow through a 
trap without undue experimentation. Generally speaking, from a "freshness" 
standpoint the preferred practice is to interrupt exhaust flow after as 
short a time as feasible, i.e., "the sooner, the better." Of course, it is 
readily appreciated that, especially in commercial applications, this must 
be balanced against other operational constraints and considerations, but 
that practice is advantageously followed to the extent possible. 
Accordingly, in an illustrative embodiment, trapped solid particulate 
matter is not allowed to reside in the filter material in question during 
exhaust flow through that material for more than one hour. Preferably, the 
time of exhaust flow is no more than about 0.5 hour. It is especially 
advantageous if the residence time is no more than about 10 minutes. As 
can be seen, observance of these guidelines requires the frequent 
substitution of a regenerated filter material for that containing trapped 
solid particulate matter, in order that the trapped particulate remain 
acceptably combustible. Accordingly, it is important in practicing the 
present invention that its method and apparatus embodiments be adapted for 
meeting the requirement of frequent substitution. 
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 
limited to the surface, but is continuous throughout part or all of the 
filter material's thickness or depth. 
In a ceramic honeycomb filter solid particles larger than the approximate 
mean pore size of the material are intercepted at the material's surface 
and prevented from passing through the material. As particles collect on 
the surface, the effective pore size is reduced which, in turn, leads to 
an increased efficiency as smaller sized particles are collected. In 
general, ceramic honeycomb traps have three stages of activity: first, a 
period of relatively rapid back pressure increase, most likely resulting 
from early pore plugging and initial cake formation on the upstream 
surface of the filter material; second, a prolonged period characterized 
by a relatively constant loading slope; finally, a shorter period during 
which back pressure again increases rapidly, probably due to complete 
plugging of many cells. Illustratively, the leading one inch or so of the 
filter material, when used in a typical filter assembly (see FIG. 1 or 2, 
described hereinafter) usually becomes more heavily loaded than does the 
remainder of the filter which carries only a lighter and relatively 
uniform film of the solid particulate filtrate. 
When using ceramic honeycomb filter material it is, therefore, necessary to 
take into account its propensity for causing an agglomeration of a large 
portion of the particulate material at the upstream side of the filter 
material, in addition to the exposure of the particulate material (in 
general) to the rather severe exhaust conditions, in determining how short 
the duration of exhaust flow through the filter material should be in 
accordance with the invention. 
Sintered porous metal filter materials are advantageous in that they 
exhibit the structural integrity, corrosion resistance and temperature 
resistance required in certain embodiments of the invention. These 
materials are made typically by precompacting and then sintering stainless 
steel, nickel-base and other types of alloy metal powders. They are 
commercially available, for instance from Mott Metallurgical Corporation, 
and are well-adapted to regeneration (i.e., cleaning) in accordance with 
the present invention. Their "re-entrainment" characteristics can be 
highly useful in removing trapped particles with a relative minimum of 
difficulty. Since these sintered metal materials are also surface filters, 
their use (like that of ceramic honeycomb materials) requires provision 
for the combined effects of particle agglomeration and high temperature as 
contributors to the increasing of resistance to incineration in the diesel 
engine. 
Of course (as will be appreciated), although other useful filter materials 
do not apparently function as surface filters (in contrast to ceramic 
honeycomb and sintered porous metal materials), the present invention also 
finds application to the use of such materials because particulate matter 
trapped in them also becomes disadvantageously resistant to incineration 
if not removed from the exhaust flow within an appropriate time period. 
Thus, discussion of various other filter materials which can be utilized 
in the invention is in order. 
In both wire mesh and ceramic fiber filter materials, the primary trapping 
mechanisms are impaction and diffusion. That is, during operation larger 
particles collide with the filaments of the mesh or fiber material and 
adhere to filament surfaces, or to particles already collected on those 
surfaces. Additionally, some smaller particles migrate by diffusion to the 
surface of the mesh or fiber material or to previously collected 
particles, and are also retained in the filter. Mesh and fiber traps of 
this sort are advantageous in that the back pressures attendant upon their 
use are relatively low. While their tendency to exhibit a "blowoff" 
phenomenon--that is, a reentrainment in the exhaust stream of previously 
collected particles--can be somewhat disadvantageous, its controlled 
occurrence operates to advantage in certain embodiments of the present 
invention, as controlled reentrainment is a desideratum. In an alternative 
embodiment metal mesh filter material is coated with activated alumina 
which provides a highly porous surface structure of large surface area. 
Additionally, the porous surface tends to disrupt boundary layer flow 
thereby encouraging diffusion to the mesh filament. The foregoing result 
in increased collection efficiency and holding power. 
Ceramic foam filter materials, such as silica foam materials, are also 
useful. These materials provide a three-dimensional, open pore network 
which collects solid particulate matter efficiently. The main trapping 
mechanisms are interception and diffusion. In general, trapping efficiency 
increases as the number of cells per linear inch and depth increases. 
Pressure drop across the ceramic foam filter increases with cell number 
and depth, but substantially decreases with increasing cross-sectional 
area for a given volumetric flow rate. Dislodgment of trapped particles in 
accordance with the present invention is in many instances more difficult 
when employing a ceramic foam material; however, in some embodiments, this 
difficulty is more than offset by the decreased back pressure attendant 
upon use of ceramic foam material in comparison with ceramic honeycomb 
material, due to the fact that cell size in the ceramic foam materials is 
often larger than the pore size in ceramic honeycomb structures. 
Granular bed filters lend themselves to practicing of certain embodiments 
of the invention. They are particularly interesting for their capacity to 
function either in a stationary or fluidized mode. It follows that the 
granular bed can be operated in a stationary mode during loading or 
trapping to enhance collection efficiency, and then be operated in a 
fluidized mode during cleaning to enhance dislodgment and reentrainment. 
This benefit is a result of the fact that penetration in a moving bed is 
usually significantly higher than penetration in an otherwise equivalent 
stationary bed, the increase being attributable to better reentrainment 
through mechanical agitation in the fluidized mode. In an advantageous 
embodiment, collection efficiency of a stationary granular bed is 
increased by the intergranular deposits in the bed, that is solid 
particles which become 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 
relatively low back pressure and easy dislodgment and reentrainment. 
An especially preferred filter material, and as appears from the foregoing 
one with which the present invention is quite advantageously employed, is 
a ceramic honeycomb unit typically fabricated of a porous cordierite 
(2MgO-2Al.sub.2 O.sub.3 -5SiO.sub.2), but is also acceptably made of any 
other ceramics, such as mullite, alumina, forsterite, aluminum titanate, 
mullite and aluminum titanate, spinel, zirconia and spinel, calcia 
partially stabilized zirconia, and alumina 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 effectively in the hostile environment presented by diesel engine 
exhaust. 
In FIG. 1 there is depicted one type of ceramic honeycomb filter unit 
suitable for practicing of the present invention. The unit 10 has a 
monolith face 12. On the face, openings 14 alternate with solid ceramic 
plugs 16 to form a checkerboard arrangement. The openings permit ingress 
to and egress from parallel channels which extend the entire length of the 
unit. These openings are typically square in shape, but are suitably 
otherwise configured to be circular, elliptical, etc. The channels 
terminate at the opposite end of the unit (not shown), and are blocked at 
that end by ceramic plugs so as to create a set of blind passages. The 
opposite end of the filter unit is also made up of alternating pores and 
ceramic plugs. The pores in the opposite end permit ingress to and egress 
from a corresponding parallel set of channels running the entire length of 
the unit and terminating in ceramic plugs 16 in face 12. Thus the ceramic 
channels opening at the opposite end of the filter unit 10 provide another 
set of parallel blind passages, and are situated in the filter unit to 
alternate with the blind passages which open on face 12. 
FIG. 2 schematically depicts channel arrangement 20 of the type shown in 
FIG. 1. Particulate laden exhaust 22 is directed at the upstream face of 
the unit 24. The exhaust enters blind channels 26 through openings 28 in 
the upstream face of the unit. Channels 26 are blocked at the downstream 
face 30 by ceramic plugs 32. At the downstream face 30, openings 34 permit 
ingress to and egress from channels 36. Those channels are closed at the 
upstream face 24 by ceramic plugs 38. Channels 26 and 36 are separated by 
common walls 40. These common walls are sufficiently porous to permit 
passage of exhaust gas; however, the wall pores are sufficiently small to 
prevent passage of the vast majority of solid particulate matter in the 
exhaust. Thus, as can be seen from the arrows in FIG. 2, exhaust gas 
carrying solid particulate matter enters openings 28 and passes along 
channels 26. Solid particles 42 are trapped on the walls of the channels 
26 while the gas passes through the porous walls and proceeds along 
channel 36 to openings 34 where it is released downstream of the filter 
unit. Plugs 38 at the upstream face 24 of the filter unit prevent passage 
of the particulate laden exhaust into channels 36 directly. 
Correspondingly, plugs 32 prevent escape of particulate laden exhaust at 
the downstream face 30 of the unit. 
In order to clean the filter unit depicted in FIGS. 1 and 2, backflush 
fluid is passed through such unit in a direction opposite that of the 
aforementioned exhaust. Thus, the backflush fluid first encounters what is 
normally downstream end 30 of the unit, passes through openings 34 and 
into channels 36, diffuses through common walls 40, dislodges particles 42 
from the common walls in channels 26, entrains those particles and carries 
them along channels 26 through openings 28 and out of the trap. In this 
manner, the trap is cleaned, that is regenerated. 
In certain preferred embodiments of the invention, particularly its 
application to automotive uses, the collection efficiency of the trap must 
be balanced against, and not accomplished at the expense of, excessive 
introduction of back pressure in the exhaust system. In such cases, it is 
advantageous to design the trap and associated exhaust system to maintain 
back pressure at as low a level as possible. As is readily understood by 
those of ordinary skill in the art, increasing the pressure drop across 
the filter unit is accompanied by increasing back pressure in the exhaust 
system. Backpressure has a direct and detrimental effect on the operation 
of the invention, and its occurrence should be minimized whenever 
possible. Pressure drop can be maintained at lower levels through the 
choice of appropriate design features. Illustratively, it is a function of 
cell geometry, wall properties and volume of a ceramic filter unit. Those 
features are advantageously set such that a balance is struck between 
minimizing pressure drop and maintaining the required filter efficiency. 
It is important to note that practicing of the instant invention frees the 
skilled artisan from filter design constraints which would otherwise be 
imposed upon him due to the use of conventional regeneration techniques. 
For example, consider regeneration processing which involves burning of 
soot and other solid particulate matter trapped in the filter unit. In 
such processing the filter must be configured in order to obtain 
regeneration times and peak pressures which fit within desired ranges for 
engine and/or environmental requirements. Another requirement which 
ordinarily presents difficulty is the need, in automotive applications, to 
design the filter so that its material exhibits structural integrity for 
the useful lifetime of the vehicle. 
Conventional technique for soot-disposal involving burning collected soot 
off the filter places an even greater physical demand on the filter than 
the conditions it is normally subjected to in the course of filtering 
exhaust. That is to say, burning of accumulated soot and other solid 
particulate matter during regeneration releases a large amount of energy 
and generates a rapid temperature rise. Moreover, that temperature rise is 
not necessarily evenly distributed throughout the filter unit, thereby 
setting up thermal gradients in both radial and axial directions. 
Additionally, excessive buildup of solid particulate matter can result in 
release of an excessively large amount of energy upon burning, thus 
subjecting the material (e.g. ceramic material) of the filter unit to 
temperatures exceeding its melting point. 
Since with the instant invention regeneration is accomplished without the 
use of ignition of trapped solid particulate matter in the filter unit, 
the foregoing problems are eliminated. Attainment of the stated objective 
of providing method and apparatus for removal of solid particulate matter 
from diesel engine exhaust which are direct, simple, relatively 
inexpensive and highly efficient is manifest. 
Once trapped by the filter unit during exhaust flow therethrough, solid 
particulate matter is advantageously removed from the filter by passing 
backflush fluid through the filter unit in a direction opposite to that of 
the exhaust flow. It is a concomitant advantage of backflushing that the 
fluid also serves as a medium in which dislodged particles are entrained 
and carried back to the engine for incineration. Accordingly, in order for 
particle dislodgment to be carried out successfully so as to reduce system 
backpressure and renew filter efficiency, the separation forces exerted by 
backflush fluid must be in excess of the forces by which solid particulate 
matter adheres to the filter material. In addition to any direct 
mechanical forces that might result from flow reversal (depending on the 
filter material), movement of the backflush fluid stream in the immediate 
vicinity of trapped particulate matter is significant. Generally, in order 
to initiate particle movement the particle must receive energy from an 
external source, for instance from the impact of another particle or 
object or from drag forces of the moving backflush fluid stream past the 
exposed profile of the particle. A convenient way of looking at this 
phenomenon is that the backflush fluid must be composed of a sufficient 
amount of fluid colliding with and passing through the filter unit at a 
sufficient velocity to dislodge trapped particles. It can, of course, be 
readily appreciated by those of ordinary skill in the art that the 
backflushing requirements will vary from system to system and filter unit 
to filter unit depending on size, configuration and the like. However, 
equipped with the teachings of this application, and knowledgable of the 
parameters and dimensions of his particular system, the skilled artisan 
will be able to determine without undue experimentation the extent of 
backflushing necessary to practice the instant invention. 
As can be appreciated, backflushing is suitably effected in more than one 
different way. Typically, backflushing is accomplished by a continuous 
passage, during the backflushing or regeneration period, of fluid through 
the filter material in a direction opposite that in which the exhaust 
stream flows. This is referred to herein as continuous backflushing. 
However, the present invention is equally applicable to pulsed 
backflushing systems. The concept of pulsation is understood in the art, 
and normally refers to the generation of one or more impulses or surges of 
fluid having sufficiently great power so that when the impulse or surge 
strikes and passes through the filter unit the particles residing in the 
trap are dislodged. In such an embodiment, the backflush fluid pulse is 
conveniently viewed as being composed of a sufficient amount of fluid 
colliding with and passing through the filter material at a sufficient 
velocity to discharge trapped particles. Alternatively, the pulse can be 
viewed as a wave; the pulsed backflushing must be of sufficient power 
(i.e., a sufficient amount of energy must pass by some point in the filter 
unit per unit time) to dislodge trapped particles. Yet another way of 
conceptualizing this phenomenon is that the change in pressure at any one 
point in the filter unit due to the passage of the wave therethrough 
should occur in an amount of time which is sufficiently short that the 
fluid pulse is capable of dislodging trapped particles. A detailed 
description of certain pulsed backflushing embodiments is set forth in 
application Ser. No. 708,260 filed Mar. 5, 1985 and naming as inventors, 
Charles D. Wood et al. In any event, it is readily appreciated that the 
present invention finds wide application to embodiments involving 
filter-backflushing and subsequent recycling of the dislodged trapped 
particulate, and that the mode of backflushing is not critical to the 
functioning of the invention. 
Backflushing fluid flow is suitably generated in any convenient manner 
which lends itself to utilization in the particular environment to which 
the invention is applied. Preliminarily, it is important to note that, 
while ambient air presents a convenient and highly useful backflushing 
fluid, the fluid is not necessarily limited to same. Alternatively, the 
fluid is suitably any one which can be passed through the filter material 
so as to dislodge trapped particles, and the presence of which does not 
otherwise interfere with or detrimentally affect the operation of the 
engine system. Oxygen, or an inert gas such as nitrogen, is an example of 
a suitable alternative fluid. (Of course, as will be apparent from the 
following, if a backflushing fluid not containing oxygen is used to 
dislodge the particles and transport (by means of entrainment) the 
particles back to the engine, then the engine is advantageously supplied 
with oxygen from another source in order that combustion be optimized.) 
In an especially advantageous embodiment of the invention, backflushing is 
generated by inducing a vacuum condition, or at least very low pressure, 
in the exhaust system on the upstream side of a particulate-laden trap, to 
draw backflush fluid into the vacuum or low pressure volume such that a 
sufficient mass thereof passes through the trap at sufficient velocity to 
dislodge trapped particles. An especially advantageous manner in which to 
accomplish this is to employ the intake pull of the engine to draw down 
the pressure on the upstream side of the trap or filter unit in question. 
Alternatively, the backflushing is accomplished by directing a pressurized 
fluid, for instance compressed gas (illustratively, air), through a trap 
to be cleaned. The fluid is acceptably drawn from a pressurized container 
or other suitable source; conveniently, compressed air drawn from the 
hydraulic or turbo-charging system of a diesel-powered vehicle will do. 
The compressed gas is injected into the exhaust system on the downstream 
side of the filter unit or trap so as to flow through the trap in a 
direction which is the reverse of that taken by the exhaust flow during 
normal filtering operations. Again, the compressed gas is injected into 
the system during interruption of normal exhaust flow. The compressed gas 
must be of sufficient mass and traveling at sufficient velocity to 
dislodge the particles trapped in the filter unit. 
With the foregoing examples in mind, it is readily appreciable to the 
skilled artisan that any other suitable manner of drawing or forcing 
backflush fluid through the trap in a direction opposite to that taken by 
the exhaust flow can be utilized, the principal criteria of selection 
being only that the means employed is sufficient to dislodge trapped 
particles and it does not unduly interfere with the engine's operation. 
In addition to providing a means for dislodging trapped particles from the 
filter unit for purposes of cleaning same, it is necessary in accordance 
with the present invention to transport those particles back to the diesel 
engine for incineration. This is typically accomplished by entraining the 
particles in a fluid stream conducted through a line of the exhaust system 
leading to the engine's air intake apparatus. After initial dislodgment, 
the dislodged particles are in very short order brought under the 
influence of the flow of the aforementioned fluid stream. That flow must 
be sufficient to maintain "floatation", that is, keep the particles free 
from recapture by the trap or filter unit, until they leave the unit. 
Recapture is disadvantageous in that it lowers the efficiency of the 
regeneration operation during the cleaning cycle. 
In an advantageous refinement of the present invention the backflush fluid 
employed to dislodge trapped solid particulate matter is also utilized as 
an entrainment vehicle, i.e. a carrier, for the dislodged particulate 
matter in order to transport same back to the diesel engine. Typically, 
the backflush fluid 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. 
It should be realized that the present invention is suitably practiced by 
using one filter zone, or a plurality of filter zones, each comprising a 
suitable filter material. Normally, when the practitioner determines that 
it is advantageous or otherwise desirable to conduct exhaust filtering and 
filter regeneration as separate operations, such that performance of one 
is not mutually exclusive of the other, two or more filter zones are 
utilized. The filter zones suitably are different portions of a single 
filter element; alternatively two or more different filter elements (each 
having one or more different filter zones) can be used. With the multiple 
filter zone arrangement the exhaust stream is passed through at least one 
zone, while at the same time at least one other zone is being backflushed 
(e.g. by passage of the engine's intake stream through it). After a period 
of exhaust flow through the zone(s) which is not so long that trapped 
particulate becomes undesirably incineration-resistant (as previously 
discussed), the exhaust stream's flow to that zone is interrupted. The 
zone(s) can then be regenerated by backflushing, while if desirable one or 
more already-regenerated filter zones can be inserted in the exhaust 
stream to replace (in part or in whole) the filter zones removed for 
regeneration. In another embodiment, the invention is applicable to a 
system employing a single filter zone only. Such an arrangement has clear 
advantages in terms of minimization of filter material, valving, conduit 
and like expenses. In such an arrangement exhaust flow through the filter 
material is interrupted for a period of time during which a suitable 
backflushing fluid is passed through the filter in a direction opposite 
that of exhaust flow; the filter is at all times left in the exhaust line, 
a measure which confers a high degree of simplicity on the system. 
In accordance with the foregoing a more specific embodiment of the 
invention comprises the steps of passing the engine's exhaust through at 
least one of the filter zones of filter means having a plurality cf filter 
zones to trap solid particulate matter contained initially in the exhaust 
and thereby to remove it from the exhaust, while reserving at least one 
other of said filter zones such that the exhaust flow is not passed 
through it; interrupting exhaust flow through at least one said filter 
zone through which exhaust flow is being passed, at a time when the 
preceding period of exhaust flow therethrough is of sufficiently brief 
duration that the trapped particulate matter has not become resistant to 
subsequent combustion in the engine; re-directing exhaust flow through at 
least one said reserved filter zone; backflushing said at least one filter 
zone through which exhaust flow has been interrupted for a period of time 
effective to dislodge therefrom, and entrain, trapped solid particulate 
matter for the purpose of removing it from said filter zone, thereby 
regenerating the filter zone; and transporting said dislodged solid 
particulate matter to the intake of said engine so that said matter can be 
combusted in the engine. 
A corresponding apparatus embodiment comprises filter means having a 
plurality of filter zones which means is positioned so that exhaust flow 
from the engine is passable through each of its filter zones to trap solid 
particulate matter contained initially in the exhaust flow, thereby to 
remove said solid particulate matter from the exhaust. The filter means is 
adapted so that exhaust flow passes through at least one of its filter 
zones while there is reserved at least one other of such filter zones such 
that exhaust flow is not being passed through it. Further, there is means 
for interrupting exhaust flow through at least one of the filter zones 
during the passage of exhaust flow through the zone, at a time when the 
preceding period of exhaust flow therethrough is of sufficiently brief 
duration that the trapped particulate matter has not become resistant to 
subsequent combustion in the engine. Also included are means for 
re-directing exhaust flow to at least one said reserved filter zone, and 
means for backflushing each such filter zone through which exhaust flow 
has been interrupted, thereby to dislodge from each such filter zone, and 
entrain, solid particulate matter trapped in the zone for the purpose of 
removing it from said zone. Additionally, the apparatus contains means for 
transporting said dislodged solid particulate matter to the intake of said 
engine so that said matter can be combusted in the engine. 
A yet more specific embodiment of the foregoing apparatus has the following 
added features. The filter means as aforesaid has two filter zones. The 
apparatus also includes means for directing exhaust flow alternately to 
said filter zones, adapted to re-direct exhaust flow from one filter zone 
to the other in conjunction with an interruption of exhaust flow through 
the former zone. Their is means for continuously backflushing each of said 
filter zones which is adapted to effect backflushing of the filter zone 
through which exhaust is not passing. Also, there is means for 
correspondingly interrupting backflushing of the other of the filter 
zones. 
In a preferred form of each of the immediately preceding method or 
apparatus embodiments, as well as the other embodiments of the invention 
herein disclosed, the sequence of steps is repeatedly performed or the 
apparatus is adapted for repetitious performance--to effect continual 
regeneration of each filter zone when it is in turn backflushed. 
Further objects and features of the invention will be apparent from the 
following. 
In the embodiment illustrated in FIGS. 3A and 3B the invention is applied 
to a naturally-aspirated Diesel engine, i.e., one with no pressure 
charging of the intake air. The engine 50 has an inlet manifold 51 
connected to a main inlet air duct 52 and an exhaust manifold 53 connected 
to a main exhaust gas duct 54. Two filters 56 and 57 are provided. 
The filter units are fabricated of cordierite and have the following 
features: mean pore size--12 um; cell density--100 cells per in.sup.2 ; 
average wall thickness--17 mils; porosity--52/56%; coefficient of thermal 
expansion--9.5/11.0.times.10.sup.-7 in/in/.degree.C. 
(25.degree.-1000.degree. C.); and compressive strength--1130 psi, 250 psi, 
15 psi along the longitudinal, lateral, and diagonal axis, respectively. 
Solid particulate matter contained initially in the exhaust is trapped in 
the filter zone of each unit when that exhaust flows through such zone. 
Two three-port two-way rotating cocks 58 and 59 have their main ports 58A, 
59A connected respectively to the main inlet duct 52 and to the main 
exhaust duct 54 as shown, the two cocks having their rotating members 
coupled together for simultaneous operation as indicated diagrammatically 
at 60. One branch port 58B of the cock 58 is connected by a 
cross-connection pipe 61 to one other branch port 59C of cock 59; and the 
other branch port 58C of cock 58 is connected by a cross-connection pipe 
62 to the other branch port 59B of cock 59. One filter unit 56 is 
connected at one end by a pipe 63 to the cross-connection pipe 62, the 
other end of the filter unit 56 being open either directly or through an 
associated silencer device to the atmosphere. The second filter unit 57 is 
connected at one end by a pipe 64 to the other cross-connection pipe 61, 
and once again the other end of the filter 57 is open either directly or 
through an associated silencer device to the atmosphere. By operation of 
the ganged cocks 58 and 59, each filter 56 and 57 may be operated either 
as an exhaust gas filter, or placed in the inlet air stream with the 
direction of flow through the filter element reversed. 
Thus with the cocks 58 and 59 in the positions shown in FIG. 3A, inlet air 
will be drawn into the open end of the filter 56 and will pass through the 
filter, in the direction indicated by the arrow A, and then by way of 
pipes 63 and 62, cock 58 and pipe 52 to the inlet manifold 51. The exhaust 
gas from the exhaust manifold 53 will travel via pipe 54, cock 59, and 
pipes 61 and 64 to the second filter 57, through which it will pass to the 
atmosphere as indicated by the arrow B. Deposits of carbonaceous matter 
will be intercepted by the element of the filter unit 57 and will collect 
on its upstream side. 
After a preselected time-period of exhaust flow through the filter--chosen 
to be sufficiently short so that trapped particulate is "fresh", i.e. has 
not become infeasibly resistant to combustion, in this case after one 
hour--the two cocks are turned simultaneously by the mechanism 60 into the 
positions shown in FIG. 3B, reversing the directions of gas flow through 
filters 56 and 57. Typically, the means by which the "turning" of cocks 58 
and 59 is effected is an associated microprocessor control system (not 
shown for purposes of simplicity). The pre-selected time period, having 
been determined previously, is programmed into the memory of the 
microprocessor control system. When the time period expires the control 
system commands the movement of mechanism 60 which causes rotation of the 
cocks, thereby interrupting exhaust flow to the filter in question. 
However, it is readily appreciated that the invention is not limited to 
the use of such a microprocessor control system, and that any way of (and 
any apparatus for) accomplishing the desired effect is suitable so long as 
it does not interfere with achievement of the invention's objects. 
At this point, the exhaust gases from the manifold 53 flow via the pipe 54, 
cock 59, pipes 62 and 63 to the filter 56, in which they will be filtered 
before being discharged to the atmosphere in the direction of the arrow 
A1. The inlet air enters the filter 57 in the direction shown by the arrow 
B1, and passes via pipes 64 and 61, cock 58 and inlet duct 52 to the inlet 
manifold 51. The air flow through the filter unit 57 is in the reverse 
direction to that of the previously-filtered exhaust gases, so that the 
partially-blocked filter element of the filter 57 has the inlet air drawn 
through it in the reverse direction "backflushing" the filter so as to 
dislodge collected material from the now-downstream face of the filter 
element and carrying the dislodged material along into the inlet manifold 
11 and thence into the engine where it will be combusted. In this way the 
filter element of the filter 57 will be cleared, or regenerated, by the 
reversed flow of inlet air through it, while simultaneously the other and 
initially-clean filter 56 is in use to filter the exhaust gases and 
collect particulate material from them. Because the particulate matter 
removed from filter 57 is "fresh", the disposal of that particulate matter 
is efficient and substantially complete thereby to eliminate problems 
stemming from its release into the atmosphere. 
Subsequently, the cocks 58 and 59 will be changed over again to switch the 
flow direction and initiate another cycle of operation, which will be 
repeated periodically. 
While two separate three-port two-way cocks 58 and 59 separately installed 
but coupled together are shown in FIGS. 3A and 3B for clarity and 
simplicity, in practice the cocks can be arranged in axial alignment and 
with a common rotary member, or any other convenient valving arrangement 
may be used. Any known arrangement of flow-switching valves and piping may 
be employed, including the use of electrically-operated solenoid valves. 
FIGS. 4A and 4B show an embodiment of the invention in its application to a 
turbocharged Diesel engine. The engine 80 has an inlet manifold 81 
connected to a main inlet air duct 82 and an exhaust manifold 83 connected 
to a main exhaust gas duct 84. Two filters 86 and 87 are provided. 
The filter elements are fabricated of cordierite and have the same features 
as the filter elements shown in FIG. 1. Solid particulate matter contained 
initially in the exhaust is trapped in the filter zone of each unit when 
that exhaust flows through such zone. The gas flow switching means is a 
double spool valve 90 and the turbo-compressor 91 shown diagrammatically, 
is positioned between the mainifolds 81, 83 and the spool valve 94 and 
filters 86, 87. An EGR cross-connection pipe 88 and control valve 89 are 
shown for use if required and an additional pipe 92 is shown connecting 
the main inlet pipe 82 on the intake side of the air compressor 91A to the 
engine crankcase, for use in an emission-controlled engine. This is 
standard practice for ensuring that any blowback of gases past the pistons 
or valve stems of the engine, which will contain unburnt hydrocarbons, 
etc., is passed back through the engine and combusted instead of being 
released into the atmosphere. 
The spool valve 90 has two valve chambers 95, 96 in a common valve housing 
97, and a single valve spool 98 common to both chambers and having one 
land 99 in the valve chamber 95, for cooperation with the valve ports 95B 
and 95C, and a second land 100 in the valve chamber 96 for cooperation 
with the valve ports 96B, 96C. The portion 82A of the main engine inlet 
duct 82 on the intake side of the compressor 91A is connected to the main 
port 95A of valve chamber 95, the portion 84A of the main engine exhaust 
duct 84 on the exhaust side of the exhaust turbine 91B is connected to the 
main port 96A of valve chamber 96, the pipe interconnects the ports 95B 
and 96C, the pipe 100 interconnects the ports 95C and 96B, and the filter 
units 86 and 87 are connected to the pipes 102 and 101 by pipes 103 and 
104 respectively. 
FIG. 4A shows the system with the valve spool 98 in one operative position 
in which the inlet air is drawn in through the filter unit 16, as 
indicated by the arrow A and passes via pipes 103 and 102 to port 95C, 
through valve chamber 95 to port 95A, and then through the inlet pipe 
portion 82A to the intake of the compressor 91A to be compressed and 
delivered to the inlet manifold 81 through the duct 82, while the exhaust 
gas from the manifold 83 drives the exhaust gas turbine 91B (the rotor of 
which is connected by a shaft 105 to the compressor rotor 91A), and passes 
then via pipe 84A, port 96A, chamber 96, port 96C and pipes 101 and 104 to 
the other filter unit 87 to be filtered and discharged to the atmosphere 
as shown by the arrow B. 
When the spool 38 is moved to its other operating position as shown in FIG. 
4B, in response to the command of a microprocessor control system of the 
type discussed in connection with FIGS. 3A and 3B, the gas flow through 
the filters is reversed. The exhaust gas is switched to the filter unit 86 
to be filtered thereby and to emerge in the direction of arrow A1, while 
the inlet air is drawn in through filter 87 (arrow B1) and passes through 
that filter to "backflush" and clean its filter element. The dislodged 
solid matter in "fresh" condition is carried by the inlet air flow through 
the pipe 104 and the pipe 101, the valve chamber 95, the pipe portion 82A 
and the compressor 91A to the duct 82 and the inlet manifold 81 to be 
combusted in the engine. 
In each of the illustrated embodiments described above, in which the 
exhaust gas flow is switched cyclically between the filters 86 and 87, it 
is possible to provide duplicate silencers respectively for the filters 86 
and 87 to ensure adequate silencing of the exhaust gas flow whichever 
filter it is discharged from. The inlet air will then be drawn in through 
the other silencer. Alternatively a single silencer only may be provided, 
in conjunction with a suitable change-over valve arrangement arranged to 
connect it to whichever filter is in use to filter the exhaust gas flow. 
This change-over valve may be operated simultaneously with the switching 
of the change-over cocks or spool valves, and by the same operating 
mechanism. 
Yet another embodiment 120 is illustrated in FIG. 5. A diesel engine 122 is 
connected to trap 124 by line 126. Intake line 128 leads from the ambient 
atmosphere to engine 122, to provide ambient air for combustion within the 
engine. Line 130 is connected to line 126 and to line 128 to provide an 
alternate flow path around the engine. Valve 132 is positioned across line 
128, and is movable from an open position permitting flow through the 
line, to a closed position interrupting flow. Valve 134 is positioned 
across line 126, and is movable between an open position permitting flow 
through the line and a closed position preventing such flow. Line 130 is 
connected to line 128 between valve 132 and the engine, and is connected 
to line 126 between valve 134 and the trap 124. The desired time period of 
exhaust flow through trap 124 such that trapped particulate is maintained 
in a "fresh" condition has previously been determined and stored in the 
memory of a microprocessor control system which directs the operation of 
the valves 132 and 134 (in, for instance, an automotive vehicle this 
microprocessor control system is typically adapted to control many other 
operational features of the vehicle as well). When the time period 
expires, valves 132 and 134--which are normally open to permit intake flow 
to the engine and transportation of the exhaust stream to the trap for 
filtration--are simultaneously closed in response to a command from the 
microprocessor control system. This can be accomplished by actuating a 
solenoid on each valve or in any other conventional manner which is 
consistent with the practice of the present invention. Valve 136 is 
positioned across line 130, and is movable between an open position 
permitting flow through line and a closed position preventing flow. When 
valves 132 and 134 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 volume of line between the 
engine and valve 134. 
Valve 136 is an automatic valve that opens when the pressure differential 
across it reaches a predetermined value. When valve 136 opens in response 
to the drawing down of pressure by the engine in line 130 (valve 136 opens 
very quickly) ambient air flows through line 138, trap 124, and line 126 
in a direction opposite that of normal exhaust flow, and then through line 
130 and line 128, and eventually to engine 122. This surge of gas 
constitutes a pulsed backflushing of trap 124, which surge carries 
particles dislodged from the trap in "fresh" condition back to the engine 
for incineration. 
Valves 132 and 134 open in response to valve 136's automatic opening, after 
a suitable delay. Valve 136 automatically closes after the pressure 
differential across it is removed, and the system is restored to its 
original condition. The entire cleaning sequence is completed in less than 
one second, and preferably less than 0.25 seconds. Indeed, regeneration 
periods of no more than one second, and preferably no more than 0.25 
seconds, are advantageously employed in many other embodiments of the 
invention also. 
Yet another embodiment is illustrated in FIG. 6. A filtered system 150 
includes diesel engine 152 connected to trap 154 by line 156. Intake line 
158 leads from the ambient atmosphere to engine 152, to provide ambient 
air for combustion within the engine. Line 160 is connected to line 156 
and to line 158 to provide an alternate flow path around the engine. Valve 
162 is positioned across line 158, and is movable from an open position 
permitting flow through the line, to a closed position interrupting flow. 
Valve 164 is positioned across line 156, and is movable between an open 
position permitting flow through the line and a closed position preventing 
such flow. Line 160 is connected to line 158 between valve 162 and engine 
152, and is connected to line 156 between valve 164 and trap 154. The 
operation of valves 162 and 164 is governed by a microprocessor control 
system of the type mentioned in connection with the apparatus of FIG. 5. 
When the time programmed for exhaust flow through the trap has expired, 
valves 162 and 164--which are normally open to permit intake flow to the 
engine and transportation of the exhaust stream to the trap for 
filtration--are simultaneously closed in response to a command from the 
microprocessor control system. Again, this can be accomplished by 
actuating a solenoid on each valve, or in any other conventional manner 
which is consistent with the practice of the present invention. After a 
suitable but short delay a pulse of compressed air is released from source 
170 in response to a command from the appropriately programmed 
microprocessor control system, and is injected through line 168 into line 
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 dislodged from the trap in "fresh" condition back to the 
engine for incineration. During this time, exhaust from the engine is 
accumulated in the volume of line between the engine and valve 164. 
In response to another command from the microprocessor control system, 
valves 162 and 164 open a suitable time after injection of the compressed 
air pulse, and normal exhaust flow through trap 154 is resumed. The entire 
cleaning sequence is completed in less than one second, and preferably 
less than 0.25 seconds. 
A still further embodiment of the invention is illustrated in FIG. 7. A 
filtered system 180 includes diesel engine 182 connected alternately to 
trap 184 by lines 192 and 198 and to trap 186 by lines 192 and 202. Intake 
line 188 leads from the ambient atmosphere to engine 182, to provide 
ambient air for combustion within the engine; valve 190 is positioned 
across line 188 and is movable between open and closed states permitting 
and interrupting flow, respectively. Line 194 is connected to line 188 and 
to line 200 which is connected to line 202, to provide an alternate flow 
path around the engine. Line 192 connects with valve (i.e., cock) 214, 
which is movable to direct flow into either line 198 or 202 while closing 
off flow to the other. Line 200 connects to valve (i.e., cock) 212, which 
is movable to direct flow from either line 198 or 204 into line 200, and 
to close off flow from the line not selected. Line 194 is connected to 
line 188 between valve 190 and the engine. 
Valves 212 and 214 are operated in response to commands from a 
microprocessor system of the sort discussed in connection with FIG. 5. 
Assume trap 184 is filtering exhaust. When the time period for exhaust flow 
through the trap (as programmed into the memory of the microprocessor 
control system) expires, valves 214 and 212--which have been oriented to 
permit transportation of the exhaust stream to trap 184 for filtration and 
drawing of air through trap 186, lines 202, 204, 200 and 194, and line 188 
back to the engine--are moved simultaneously in response to a command from 
the control system. That is, the valves are moved so that exhaust flows 
through lines 192 and 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 closed. Valve 210 is positioned across line 200, and is movable 
between an open position permitting flow through the line and a closed 
position preventing flow. When valve 190 is closed the engine quickly 
reduces 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 
across it reaches a predetermined value. When valve 210 opens in response 
to the drawing down of pressure by the engine in line 194 (valve 210 opens 
very quickly) ambient air flows through line 206, trap 184, line 198, line 
200 and line 194, and eventually (through line 188) to the engine. This 
surge of gas constitutes a pulsed backflushing of trap 184, which surge 
carries particles dislodged from the trap in "fresh" condition back to the 
engine for incineration. 
When valve 190 is opened, valve 210 automatically closes after the pressure 
differential across it is removed, and the system is restored to its 
initial condition. The entire cleaning sequence is completed in less than 
one second, and preferably less than 0.25 seconds. In some embodiments 
each trap is cleaned by a plurality of such sequences. When trap 186 needs 
regeneration, valves 212 and 214 are operated in response to a command 
from the microprocessor control system 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 configurable depending on the 
needs of the practitioner and his environmental constraints. 
Thus, the present invention provides method and apparatus for trapping 
solid particulate matter in the exhaust of a diesel engine, and in turn 
removing that particulate from the trap and sending it to the engine for 
combustion in a "fresh" state which maximizes the efficiency of that 
combustion. In this manner, a relatively simple and commercially feasible 
disposal of the trapped particulate is effected. This confers significant 
operational economies, while at the same time preventing environmental 
problems stemming from release of such particulate into the atmosphere. 
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 are possible within the scope of the invention.