Note: Descriptions are shown in the official language in which they were submitted.
21Sll 62
.
Title: FYU~T GAS FILTER
FIELD OF ~ INVENTION
This invention is related to the field of gas
filters, more particularly to the field of exhaust gas
filters.
The operation of an internal combustion engine
is accompanied by the generation of exhaust gases. The
exhaust gases emanating from an internal combustion engine
contain unburnt carbon particles ranging in size from the
submicroscopic to a few microns. The emission to the
atmosphere of such unburnt carbon particles are considered
environmentally offensive. A particular type of internal
combustion engine, the diesel engine is very widely used
by the transportation industry. Due to its construction
and the nature of fuel the diesel engine utilizes, the
exhaust gases generated by diesel engines tend to be even
more abundant in unburnt carbon particles. It is therefor
an environmental requirement to provide means for
eliminating carbon particles from exhaust gaæes, before
such gases enter the surrounding atmosphere. The unburnt
carbon particles are usually removed from the exhaust
gases by incorporating some form of a filtering device in
the exhaust gas handling system of an internal combustion
engine, such as a diesel engine.
There are many different materials which are
commonly used for filtering exhaust gases, such as for
example, glass or metallic wool, loose ceramic particles,
and so forth. Other types of filtering devices utilize
discs, cylinders or similar conveniently shaped bodies
which are porous and high temperature resistant as well,
to allow the passage of exhaust gases while simultaneously
trapping the unburnt carbon particles carried by the
gases.
The pores and cavities of the above discussed
filtering devices, however, are likely to be blocked
during use by the retained unburnt carbon particles,
resulting in increased exhaust gas back pressure and in a
21~1 1 62
; - 2 -
carbon particles continues, the magnitude of the exhaust
gas back pressure increases further, while the efficiency
of the engine is reduced even more. The build-up of the
unburnt carbon particles and similar carbonaceous matter
necessitates frequent change of filters utilized in
filtering devices. Thus unburnt carbon particles carried
by exhaust gases affect the operating cost of an internal
combustion engine in two ways: in reducing the efficiency
of the engine and in the expense of having to replace the
filter. One possible way of overcoming such difficulties
lies in regenerating the filter clogged by carbon
particles. In other words, the operation of the filter may
be revitalized by periodically burning off the carbon
particles trapped by the filter elements incorporated in
the filtering devices of the internal combustion engine.
One of the more commonly used methods of regenerating
the filter element incorporated in a filtering device is
increasing the temperature of the filter element in order
to combust the carbon particles trapped within the filter
element. An example of such a method is described in U.S.
patent 4,319,896 issued to W. M. Sweeney on March 16 1982,
which utilizes an electric resistance heater coil embedded
in a ceramic filter element. The operation of the heater
is triggered by pressure and temperature sensing devices.
Another approach in regenerating the filter by
combusting the carbon particles trapped within it, may be
found in a conventional filtering device wherein the
filter is made up of two portions. The first portion of
the filter of this type has relatively large pores and
embeds an electric heater or heaters. The second, usually
larger portion is designed to remove the bulk of the
unburnt carbon particles from the exhaust gas. The
exhaust gases passing through the first portion are
thereby heated during the regeneration step to eliminate
by combustion the carbon trapped by the second portion.
Filtering devices of the above design are described, for
example, in U.S. patent 4,427,418 issued to Takeshi Kogiso
2151162
et al. on Jan. 24 1984 and in U.S. patent 4,662,911 issued
to Tsukasa Hirayama et al. on May 5 1987.
The exhaust gases often contain corrosive components
which may have adverse effect on the embedded heater
element incorporated in a conventional filtering device of
this type. The metallic heating components or wires
comprised in such heaters may become corroded, oxidized or
otherwise damaged when exposed to the exhaust gases,
resulting in malfunction of the heater and breakdown in
the regeneration of the filter element of the device.
U.S.patent 4,535,589, issued to Hitoshi Yoshida et
al. on Aug. 20 1985, utilizes electrically conducting
ceramic heater members in the portion of the filter
element designed to heat the exhaust gases when the filter
element undergoes regeneration. The conductive ceramic
heater members have large apertures for facilitating the
passage of exhaust gases, and each such member is
surrounded and supported by porous ceramic insulators. The
electrically conducting ceramic heaters are equipped with
metallic electrode connections. In the filtering device
described in U.S. 4,535,589 the heater bearing portion is
attached to a larger second portion for trapping the
offending unburnt carbon particles. It is to be noted that
the filtering device of U.S. 4,535,589 also separates the
gas heating function from the gas filtering function,
similar to the filtering devices described hereinabove.
The conductive ceramic heater members may be made
of silic~n carbide or lanthanum chromite, according to
U.S. 4,535,589. Such conductive ceramic substances have
relatively low mechanical strength, and would not
withstand mechanical impact and physical vibrations that
filtering devices are usually subjected to in the absence
of some type of su~o~ing structure. The ceramic heater
members of U.S. 4,535,589 are usually encased or supported
by alumina and porous cordierite bodies.
The common feature of the filtering devices
discussed hereinabove is that in the regenerating cycle of
the filter element, the exhaust gases having been heated
215Il62
by some means, pass into a separate portion containing the
trapped unburnt carbon particles with the objective of
combusting the carbon particles. If the gases entering the
filtering portion are allowed to cool or the temperature
S of the heated gases drops below the combustion temperature
of the trapped carbon, the filter regeneration will be
incomplete.
By one aspect of the present invention a porous
ceramic filter element is provided which allows the
passage of exhaust gases while trapping unburnt carbon
particles, and which may also act as means to burn the
collected carbon particles in the regeneration cycle of
the filter element.
By another aspect of the invention a filter element
is provided which is made of a porous electrically
resistive ceramic substance, which is capable of being
heated to high temperatures by means of passage of
electrical current, is resistant to oxidation and
corrosion and has notable mechanical strength.
By yet another aspect of the invention an exhaust gas
filtering device is provided which houses several ceramic
filter elements, each filter element being made of a
porous electrically resistive ceramic substance and the
exhaust gas filtering device is incorporated in the
exhaust gas handling system of an internal combustion
engine.
SUMNARY OF THE INVENTION
The exhaust gas filtering device of the present
invention comprises at least one porous ceramic filter
element having interconnecting channels for allowing
exhaust gases to flow therethrough and for trapping
particles carried by the exhaust gases. The porous
ceramic filter element is a unitary body made of an
electrically resistive ceramic substance, comprising an
electrically conductive ceramic component homogeneously
dispersed within an electrically insulating ceramic
component. The electrically conductive ceramic component
215II 62
is selected from the group consisiting of molybdenum
disilicide, titanium nitride, titanium carbonitride,
titanium boride and zirconium boride. The electrically
insulating ceramic component is selected from the group
consisting of silicon nitride, zirconia, alumina,
cordierite, an alumina-silicate bearing ceramic
composition and mixtures thereof. The porous ceramic
filter element is defined by an internal face, an external
face and a perimeter. A pair of electrodes are in contact
with the ceramic filter element and each electrode is
connectable to an electrical power source for providing an
electrical current flowing within said porous ceramic
filter element, where~y the temperature of said porous
ceramic filter element can be raised above the ambient
temperature. A housing adapted to enclose the perimeter
of the porous ceramic filter element is further comprised
in the exhaust gas filtering device. The housing has an
inlet port which is in communication with an engine
combustion chamber, thereby facilitating the passage of
exhaust gases from the chamber to the internal face of the
porous ceramic filter element. The filtered exhaust gases
exit the housing through an outlet port.
One of the electrodes may be connected to the housing
and the housing may be grounded.
The housing comprised by the exhaust gas
cleaning device may enclose a plurality of porous ceramic
filter elements, each of the ceramic filter elements
having electrodes, one of each pair of electrodes of each
ceramic filter element may be connected to the electrical
power source, and the other electrode in contact with each
ceramic filter element may be connected to the housing.
DF--~RTPTION OF ~R~ DRAWINGS
Figures l(a) and l(b), and 2 are schematic drawings
showing different embodiments of the filter element of the
present invention.
Figure 3 shows the schematic drawing of an exhaust
filtering device housing four porous ceramic filter
elements in successive arrangement.
2I5ll 62
6 -
The preferred embodiment of the invention will now be
described hereinbelow and illustrated by working examples.
Dl~l'ATT.Rn DESCRIPTION OF l~IE PRI~ KK~v 13~1BODI~IENTS
One of the characteristic features of any gas filter
element utilized in a gas cleaning system is that it has
two faces, one face is facing the gases entering by a
conduit or pipe, and the other face permits the filtered
gases to exit towards the atmosphere. Such two faces of a
filter element are often parallel, but this is not a
requirement for the working of the filter. There is a
multiplicity of apertures, tortuous interconnecting
channels between the two faces of the filter element, to
allow unimpeded passage of the gases through the filter.
For the sake of clarity the apertures, channels, pores,
openings within the filter element regardless of their
size, shape or length within the filter, will be referred
to hereinbelow as channels.
The filter element is usually circular in shape such
as a disc, but it may have elliptical or rectangular
cross-section, or be of any suitable configuration. The
shape depends on and is often but not necessarily decided
by the cross-section of the conduit or pipe that carries
the gases to be filtered from the combustion chamber to
the gas filtering device. The two faces of the filter
element may be parallel, or enclose an angle. These will
be referred to in the discussion hereinbelow as the faces
of a filter plate or a filter element.
The filter plate of the present invention is
essentially made of an electrically resistive ceramic
substance. The electrically resistive ceramic substance
is a mixture of at least two ceramic components. One of
the ceramic components in the mixture is a heat and
substantially oxidation resistant, stable ceramic
insulator. Such ceramic materials are zirconia, hafnia,
alumina, silicon nitride, alumina-silicates, or optionally
a mixture of the above. The insulator ceramic component
may also be mullite, cordierite, and similar conventional
21511 62
- 7 -
ceramic substances which have high strength and insulating
properties. It is generally preferred that when zirconia
or hafnia is used as an insulator component, it is fully
stabilized. Partially stabilized zirconia or hafnia may
also be utilized under certain circumstances.
The other ceramic component comprising the
electrically resistive mixture of which the ceramic filter
plate is made is an electrically conductive ceramic
compound. Examples of such ceramic compounds are:
titanium nitride, titanium carbonitride, molybdenum
disilicide, zirconium and titanium boride or similar
ceramic compounds, which are capable of conducting
electricity, are stable at high temperature and are
relatively resistant to oxidation and corrosion.
It is desirable that the ceramic substance for
ob~ining the ceramic filter plate of this invention has
resistivity values ranging between 10 2 _106 ohm.cm after
firing. It is considered that for best results, the
electrically conducting ceramic component be present in
the mixture making up the ceramic filter plate, in a range
of 30-70 vol.%. The desired porosity is in excess of 50%,
preferably 60%. The mixture is usually made by mixing the
fine dry ceramic insulator component-with the dry powder
of the electrically conductive component and some type of
conventional organic binder. The mixture may additionally
contain other conventional additives which will enhance
the formation of a porous structure and/or improve
sinterability. The mixture is subse~uently compacted by
known methods into a filter plate of any conventional
shape or design.
The compacting pressure applied is governed by the
particle size range of the ceramic mixture and by the
desired porosity of the filter plate obtained, and other
conventional considerations.
The ceramic filter plate may also be rendered
permeable to gases by other methods, such as for example
by introducing a large number of very small apertures in
215II62
- 8 -
the plate, by means of punching or puncturing, or by
other conventional means.
The compacted ceramic filter plate is subsequently
fired. The firing temperature depends on the nature of
- 5 the organic binder, the composition and additives, but is
usually in excess of 1200C.
In one embodiment of the present invention, the
perimeter of the filter plate or element will have two
opposing sections. In case of a filter plate having a
circular perimeter, the opposing sections are understood
to mean opposing arc-sections of the circular perimeter of
the plate. In case of a rectangular filter plate, the
opposing sections are understood to mean opposing sides of
the rectangle. The useable portions of the filter plates
are considered to be located between the two opposing
sections of the filter plate.
In the first embodiment metallic conductors,
such as small metal bars are embedded in the ceramic plate
close to each of the opposing sections of the perimeter of
the compacted plate. The metallic conductors will
conveniently have electrical lead wires attached to them,
usually subsequent to firing of the ceramic plate, thereby
forming what is conventionally understood to be
electrodes. The electrodes may be connected by
conventional means to a battery or similar electric power
source. Thus an electric current may be passed within the
ceramic plate located between the two metallic conductors
embedded in opposing sections of the perimeter of the
ceramic plate.
In another embodiment of the present invention, a
conductive metallic layer is deposited by conventional
means on each face of the compacted and fired filter
plate. Care should be taken that the conductive layers do
not block the apertures of the channels within the filter
plate, that is the flow of the exhaust gases through the
filter is not impeded. An electrode lead, one on each
face, is brazed or attached in a similar manner, to the
partially coated face of the filter plate. The electrode
215116~
g
leads are usually connected to a battery through a switch,
whereby electric current may be passed between the faces
of the filter plate when this is desired.
Electric current may be passed through the portion of
the ceramic plate located between the electrodes, either
continuously or intermittently, as is dictated by
convenience.
As stated above, the current is designed to heat
the ceramic plate to a temperature above 600 C. It is to
be noted, that ambient temperature under the present
circumstances is considered to be the temperature of the
exhaust gases emerging from the engine, which is usually
well below 600C.
The ceramic filter plate equipped with either
embedded or plated electrodes, may be fitted with an
electrically insulating ceramic frame which encloses the
circumference or perimeter of the ceramic filter plate.
The frame or suitably shaped insulator element may be made
of any suitable non-conducting ceramic material, which
may be cast or compacted at the same time as the ceramic
filter plate. The insulator element, or ceramic frame,
may be fired together with the ceramic filter plate
thereby becoming an integral part of the filter plate.
Alternatively, the ceramic insulator element may be fired
separately and fitted around the filter plate
subsequently.
The filter plate, together with the electrode(s) and
insulator element fitted around it, is then placed
according to conventional methods in a suitable metallic
housing. The metallic housing may subsequently be
incorporated in the exhaust cleaning system of an internal
combustion engine. The exhaust gases emitted by the
engine will then be passing through and be filtered by the
filter plate of the present invention.
The housing may have a conventional lining designed
to protect the filter plate from mechanical damage.
Protective lining of this nature is an optional feature of
the present exhaust gas filtering device.
2151162
-- 10 --
In a third embodiment of the exhaust gas cleaning
device the ceramic filter plate or ceramic filter element
has one electrode deposited on one of the faces only, and
an electric- lead wire is brazed or connected by
conventional means to the deposit. The ceramic filter
plate bearing one electrode on one of its faces is
subsequently fitted tightly into the metallic housing.
It is to be noted that in the third embodiment no
insulating frame is fitted around the filter plate or
element and the perimeter of the ceramic filter element is
conductively in contact with the metallic housing. The
housing is the second electrode in the third embodiment,
which is then connected to one terminal of the electric
power source or the housing-may conveniently be grounded
by usual means.
The arrangement whereby only one electrode is
connected to the electric power source and the other
electrode is grounded, is commonly known as a unipolar
arrangement.
In one embodiment shown on Figure l(a), the ceramic
substance comprising the above described mixture of a
ceramic insulator component, an electrically conducting
ceramic component and an organic binder, is cast into a
rectangular ceramic plate (12). Two metallic bars (14')
and (14") are attached to opposing sides of the ceramic
rectangle. The bars usually lie along the shorter sides
of the rectangle, but they may equally be placed along the
longer sides, as long as the sides oppose one another.
The metallic bars, referred to as electrodes hereinabove,
have electrical leads (16), which can be connected to an
electrical power source, conveniently to a battery or a
similar power source (not shown). The rectangular ceramic
filter plate having electrodes attached to its opposing
sides, is fitted into a circular frame ~18), made of an
insulator ceramic material. The circuIar frame (18), has
a rectangular opening into which the f-ilter plate (12),
tightly fits. Alternatively, the circular insulator frame
215I~ 62
11 --
(18), is cast around the rectangular filter plate (12),
having electrodes (14') and (14"), on its opposing sides.
Preferably, the circular insulator frame is of the
same composition as the insulator ceramic component of the
ceramic filter plate; but this is not essential.
The circular ceramic frame embracing the rectangular
ceramic filter plate by its four sides, is subsequently
fired and sintered at a temperature usually above 1200C,
preferably between 1300-1400 C. The firing of the
assembled ceramic elements will cause the organic binder
to burn off, and thus the ceramic assembly will be
rendered both porous and hard.
The metallic electrode bars in the above described
arrangement need to be resistant to corrosion and
oxidation at the temperature of firing. Another method of
producing the filter plate of Figure l(a), may be to fire
the ceramic filter plate and insulating element first and
insert the electrodes later, in a conventional manner.
The fired circular plate is then fitted into a
housing (20), conveniently made of steel or other suitable
metal. The resulting gas filter (10), may then be fitted
to the exit end of a pipe carrying the exhaust gases from
the combustion chamber of an engine. The electrical leads
attached to the electrodes are connected appropriately to
a power source.
Figure l(b) shows a similar exhaust gas filter
element arrangement (10), wherein the rectangular filter
plate (12), has curved sides and thus electrodes (14') and
(14") are also curved. Like numerals represent like
elements of the filter element of the present invention.
Another variant of the above embodiment of the filter
plate of the present invention is shown schematically on
Figure 2. The filter plate of the present invention is
made up of the required composition described above,
containing electrically conductive and insulator ceramic
components. The filter plate is cast into a circular
plate or disc (22). The circular ceramic plate is fitted
into a ceramic ring (28), which is made of an insulator
215I162
- 12 -
material. Preferably the ceramic ring (28), is made of
the same substance as the insulator component of the
circular plate. The circular plate held by the insulator
ring is subsequently fired and sintered, and the binder
within the mixture is burnt off so as to render the filter
plate permeable to gases. The two faces of the fired
filter plate (22), are subse~uently coated with metallized
layers by vaporization, electroless deposition, painting
or by any similar conventional means. Electrical lead
connections (26), are soldered or brazed to each face
(27). Figure 2 shows only one face t24), and one
electrical lead connection (26). It is to be understood
that in this embodiment there is a corresponding metallic
layer on the underside of the filter plate and a
corresponding electrical lead connection. The insulator
ring (28) enclosing the circular filter plate (22), is
subsequently fitted into a housing (20), and the filter
assembly (10), is then attached to the exit end of an
exhaust gas carrying pipe.
As discussed above, in the third embodiment of the
exhaust gas cleaning device, the ceramic ring 28, as shown
on Figure 2, is omitted. In the third embodiment (not
shown) there is no metallic layer deposited on the
underside of the ceramic filter element(22).
There may be other conventional ways to have
electrode connections incorporated in the ceramic filter
element described hereinabove.
The fourth embodiment of the exhaust filtering device
of the present invention is schematically shown in Figure
3. In the fourth embodiment, four ceramic filter
plates(22) each comprising mixtures of electrically
conductive and insulating components, which have been
fired and have electrical resistivity ranging between
102-106 ohm.cm, are held in successive arrangement in a
metallic housing(20). The perimeter of each filter
plate(22) is in contact with the inside of the
housing(20). The housing is shown to be grounded. The
internal face of each filter plate bears a deposited
215I162
- 13 -
metallized area(27), which is of a smaller diameter than
the internal face of the filter plate(22). An electrical
lead wire(26) is brazed to each metallized area(27), and
the lead wires of each filter plate are connected through
a common lead and a switching mechanism(30), to one
terminal of a battery(32). The other terminal of the
battery may also be grounded. Arrows indicate
schematically the flow path of the exhaust gases
proceeding through each successive filter plates.
It is to be noted that the essential function of
any filter is to remove solid particles carried by a
flowing fluid. In the instance of filtering gases issuing
from an internal combustion engine, the fluid is the
exhaust gas and the particles are substantially
combustible carbon particles. It is a particular
advantage of the filter element of the present invention
that the particles removed from the gas and trapped in the
channels and on the face of the filter element may be
eliminated without having to remove or replace the filter.
The particles are eliminated by combustion by means of
passing an electric current between the electrodes
incorporated within the filter, thus raising the
temperature of the filter element portion located between
the electrodes, sufficiently high to allow particles
collected by the filter element to be removed by burning
or combustion.
The accumulation of particles which are trapped by
the filter, i.e. the build-up of the carbon within and on
the surface of the filter element, is a continuous process
resulting from the running of the engine. It may take
hours, days, or even weeks, before the amount of soot or
carbon particles collected, that is before the build-up of
combustible particles within the filter element, becomes
detrimental. The amount of particles collected by the
filter element will depend on the mechanical efficiency
and design of the internal combustion engine, the quality
and nature of the fuel used, and so on. Thus the
fre~uency and duration of burning and eliminating the
21 51 1 62
14 -
trapped carbon particles, or soot, is selected by the
user and it is dictated entirely by convenience.
It is the advantage of the ceramic filter element of
the present exhaust gas cleaning device that it is
capable of trapping the carbon particles carried by the
exhaust gases, and subsequently burning the trapped carbon
particles. Thus the porous ceramic filter element made
according to the present invention is a unitary body
acting both as a filtering means and as a heating means.
It is a further advantage of the filter element of the
present invention, that the combustion of the trapped and
accumulated carbon particles is conducted in a controlled
manner.
Another advantageous property of the filter element
made of the electrically resistive ceramic composition
described hereinabove, is that it acquires a relatively
high fracture toughness, after the ceramic composition has
been fired. The fracture toughness of the fired porous
ceramic filter element was found to be in excess of 5
Mpa.m~.
The high fracture toughness allows the porous ceramic
filter element to withstand the vibrations and normal wear
and tear an exhaust gas filtering device incorporated with
an internal combustion engine, is subjected to.
The exhaust gas cleaning device incorporating the
porous ceramic filter element of the present invention has
been found to be most adaptable to be used in automotive
engines, especially in diesel engines.
The internal combustion device generating exhaust
gases may also be stationary, such as a pump. The only
requirement is that it has a conduit or pipe through which
the combustion gases exit from the combustion chamber.
The exhaust gas cleaning device may be attached to the
exit end of the conduit and the cleaned exhaust gases then
3S exit to the atmosphere through the outlet port of the
housing.
The power source providing the current for generating
heat in the filter is conveniently a battery, which is
215I 1 62
- lS -
usually incorporated into the working system of the
internal combustion engine, or in the device utilizing an
internal combustion chamber.
As discussed above, one advantage of the ceramic
S filter element of this invention is that it removes soot
and combustible carbon particles carried by the exhaust
gases. Another advantage of utilizing the present ceramic
filter element is that it allows the internal combustion
engine to operate continuously at the required level of
efficiency.
The exhaust gas cleaner incorporating the ceramic
filter element described hereinabove may be utilized in
conjunction with conventional pressure sensing devices.
In using a pressure sensor device the carbon trapped by
the filter element may be combusted by allowing the
present filter element to act as a heater when the
pressure sensor indicates a certain drop in the efficiency
of the internal combustion engine.
An alternative arrangement may be that the filter
element is incorporated with some kind of a timer device
which will trigger the connection to the power source
providing the current passing through the filter element.
There are known timing devices to establish such periodic
contact.
In yet another application of the filter element
design of the present invention, the efficiency of an
engine may be monitored by measuring the frequency and the
current requirement for eliminating the build-up of
accumulated carbon particles during the performance of the
engine.
The following examples will illustrate the making and
the utilization of the ceramic filter of the present
invention.
E XA~PT.li~ 1
Fine particles of silicon nitride were mixed with
molybdenum disilicide in a volume ratio of 60:40. The
average particle size of the mixture was 20~m. The
organic binder utilized in this example is marketed under
2151 162
- 16 -
,
the trade name of Durez (marketed by Canadian Occidental
Petroleum Ltd.). An aqueous slurry was made with the
organic binder by mixing it with sufficient amount of
water to render it pourable. The organic binder slurry
was then added to the dry ceramic mixture in 50 vol.%.
Discs having dimensions of 4" diameter and 1" thickness
were cast from the above mixture.
A separate mixture made of silicon nitride particles
and aqueous organic binder slurry in 25 vol.% was
prepared. A ring of 1" thickness, 4" internal diameter
and 4.25" external diameter was cast from the latter
mixture.
The green discs made of silicon nitride and
molybdenum disilicide were inserted into the green ceramic
rings composed essentially of silicon nitride.
The green discs enclosed by the rings were allowed to
dry in air, and subsequently they were fired in air
applying slow heating to attain 700 C. The temperature
was raised gradually to 700 C in a period of 12 hours.
Subsequently the temperature was further increased and the
firing was continued in argon atmosphere at 1600'C for
another two hours. The filter discs so obtained were
found to have 62 vol.% porosity. The surrounding ring
made of non-conducting ceramic material was found to have
less than 20~ porosity.
A layer of copper was deposited on the flat faces of
the disc by electroless deposition. The deposits were
located in the centre of the flat face and had
approximately 1 inch diameter. Care was taken that no
copper was deposited over the surface of the insulator
ring enclosing the ceramic filter discs.
Insulated copper wire was brazed, one to each side to
the copper layer deposited on the face of the filter disc.
The filter discs so obtained and enclosed in an
insulator ring were subsequently encased in a stainless
steel cylinders, which allowed them to be fitted to the
exhaust pipe of an internal combustion engine.
215I162
- 17 -
EXANPLE 2
An exhaust gas filter made as described in Example 1,
was incorporated into the exhaust system of a medium speed
diesel engine. The electrodes located on each side of the
gas filter were connected to the battery of the diesel
engine, which in the present case was a 12 volt battery
having an output of 50 amps. Thus the power of about 0.60
Kw was applied to the filter plate after the engine had
been running for 10 hours. Within 3 minutes of applying
0.60 Kw power, the black soot which was observed to have
deposited on the filter after 10 hours of running, has
been completely burned off and the engine has been
restored to its previous efficiency.
It can thus be seen that the ceramic filter plate
made in accordance with the present invention is not only
efficient in removing carbon particles from the exhaust
gas of the diesel engine, but also efficient in
eliminating the accumulated carbon particles without
having the resort to removal of the ceramic filter plate
for cleaning and thus restoring the performance of the
engine.
Although the present invention has been described
with reference to the preferred embodiments, it is to be
understood that modifications and variations may be
resorted to without departing from the spirit and scope of
the invention, as those skilled in the art will readily
understand. Such modifications and variations are
considered to be within the purview and scope of the
invention and the appended claims.
