Note: Descriptions are shown in the official language in which they were submitted.
3 I
Filtration SYSTEM FOR DIESEL ENGINE EXHAUST-II
The present invention relates to diesel exhaust
filtration.
State of the art engine technology may allow a
diesel engine to emit as low as .6 gm/mile particulate.
Louvre, with more stringent particulate emission
requirements to come into effect in 1985, such as at a
level of .20 gm/mile, the technology cannot meet such
lower level ox particulate emissions without some form of
particulate trap. The most important materials used to
date by the prior art for the trap material have included
rigid and fibrous ceramic filter materials (see US.
patent 4,276,071, ceramic wall flow monolith particulate
filter) and wire mesh (see US. patent 3,499,269), each
material having its own characteristic mode of trapping.
Some of these filter materials have been coated with
catalysts in the hope it would facilitate incineration of
the collected cation material. unfortunately, the
placement ox the coating as a layer throughout the filter
has proven not to lower the incineration temperature
effectively and, more importantly, has produced unwanted
sulfites.
The particulate emitted and trapped throughout
the life of a vehicle cannot be stored since the amount
25 can be typically 20 cubic feet for each 100~000 miles of
engine use. As the particulate build up, the exhaust
system restriction is increased. Thus, a means is
required to remove the trapped material periodically,
commonly referred to as regeneration of the filter. One
30 of the most promising methods found to date is
rejuvenation of the filter by thermal oxidation of the
carbonaceous particles, which incinerate at about 1200F
(600C).
I
I
-- 2 --
Normal diesel engine exhaust temperatures rarely
reach 1200F during normal driven Therefore, an
auxiliary temperature elevating means is necessary to
carry out thermal oxidation. The types of thermal
5 oxidation means used by the prior art have generally
fallen into the following three categories: use of a fuel
fed burner (see US. patent 4,167,852 and Japanese patent
55-19934~, use of an electric heater (see US. patents
4,~70,936; 4,276,066; 4,319,896), and retuning techniques,
10 which may be combined with any ox the above, for raising
the temperature of the exhaust gas temperature at selected
times (see US. patents 4,211,075; 3,49g,269). These
techniques have been used to burn the collected particles
in the presence of excess oxygen.
With respect to fuel burners, they are
disadvantageous because: pa) they require more fuel than
for normal vehicle operation when they function as the
sole means to raise the temperature of the entire mass of
the filter system, and (b) can only be used for
20 regeneration in certain limited cruise conditions ox the
engine when used in line with exhaust flow. In addition,
such an addition is prone to malfunction and can pose
safety problems unless an adequate control system is
provided.
With respect to electrical heating used as the
sole means to raise the temperature of the entire mass of
the filter system to an incineration temperature: (a) it
is inefficient; and (b) it requires a disproportionate
supply of electrical power, which is not readily available
30 with current vehicles, and would require significant
redesign of the power supply system.
As to deturling techniques, they are difficult to
operate to reliably achieve adequate incineration
temperatures, may have an adverse effect on engine
35 emissions, and may cause premature failure of the filter
material.
~;23(~
-- 3 --
hat it needed is a filtration system for diesel
engines which uses considerably less energy than that
envisioned by the prior art regeneration techniques, has
increased reliability for incineration, does not affect
other measures taken to control engine emissions, reduces
the complexity of the controls needed or the regeneration
system, and is independent of engine operation for optimum
regeneration.
The invention is a filtration system operative to
remove oxidizable particulate from the exhaust gas of a
diesel engine. The system comprises tax filtration
means having a filter element operative to filter out and
collect a substantial portion of the entrained
particulate in the exhaust gas, (b) ignition means
having a source of energy selectively supplied for a
limited period to effect the lighting of a leading portion
of said particulate collection, and (c) means for
conducting a flow of gas with excess oxygen through said
filtration means immediately following said ignition,
without the addition of energy. The flow of gas with
excess oxygen is utilized to support continued oxidation
of the ignited particulate collection.
It is preferred that the ignition means use a
source of energy which is a combustible mixture of
hydrocarbon fuel and a combustion supporting gas, and a
supplementary heated catalyst effective to act upon the
mixture to bring about ignition of the mixture at a lower
temperature. Advantageously, an electrical resistance
heater is coupled with a catalyst to lower the necessary
ignition temperature of the combustible mixture. The
mixture may be formed by the addition of atomized
hydrocarbon fuel to a portion of the exhaust gas (either
at the intake manifold, exhaust manifold, or exhaust
$
23(~;~9~
conduit leading to the filtration system), or by addition
to a separate pressurized flow of air. It is most
advantageous to form the ignition means as a pheromones
nlember having a plurality of closely nested straight flow
channels, the channel walls having an apparent porosity of
at least 25~ with pores of about 5-40 microns with 10 18
microns average diameter. The walls of the pheromones
member carry a catalyst material effective to lower the
ignition temperature ox the combustible mixture passing
there through, thereby requiring less input of energy in
the form of either hydrocarbon fuel or the amount of
electricity required to operate the electrical resistance
heating element. Preferably, the electrical resistance
heating element is embedded within the pheromones member
at the entrance in the form of a flat electrical
resistance wire.
Optimally, the catalyst coated pheromones member
is located in front of the entrance to the filter element
and may be in spaced relation thereto (by as much as 2-
inches. The pheromones catalyst coated member is heated so that it will reach an entrance temperature of about
500-700F and a exit temperature ox at least 1200F. This
latter temperature it attained by the oxidation Ox
hydrocarbon and carbon monoxide gases at the surface of
25 the catalyst, the latter being sufficient to ignite the
carbonaceous material on the filter element.
The filtration system may additionally comprise
a flow control means which has a flow diverter effective
to normally bypass the exhaust gas flow around the
3Q ignition means to avoid sulfite formation, but through
the filter during normal operation of the filtration
system. The diverter is selectively operate to switch
the exhaust gas flow through the ignition means when
regeneration ox the filter is desired in order to heat the
35 catalyst so as to minimize the external heat requirement.
I
-- 5 --
Yet still another alternative has a flow
diverter, again effective to normally bypass the exhaust
gas flow around the ignition means, but through the filter
during normal operation of the filtration system.
5 However, in the regenerative mode, the exhaust gas is
additionally diverted around the filter as well as the
ignition means, while conducting a separate flow of
hydrocarbon fuel and a combustion supporting gas through
the ignition means to initiate regeneration.
The invention is described further, by way of
illustration, with reference to the accompanying drawings,
in which:
Figure 1 is a schematic elevation Al view of a
filtration system for removing the particulate from a
diesel engine embodying the principles of this invention;
Figure 2 is a sectional view taken substantially
along line 2-2 of Figure l;
Figure 3 is another embodiment of this invention
wherein a flow control system is used so that the exhaust
gas is bypassed about the ignition means of the
regenerative system during normal operation;
Figure 4 is yet another alternative embodiment of
this invention wherein a flow control system is used to
bypass the exhaust gas around the catalyst coated
pheromones member and filter element during regeneration
but conducts exhaust gas through the catalyst coated
pheromones member and filter element during normal
operation; and
Figures 5 and 6 each show schematic variations of how
hydrocarbon fuel can be added to the heated gas needed for
regeneration.
The invention is an apparatus system wherein a
small but limited amount of energy is required to ignite
the leading portion of a collection of particulate in a
'. ?,
I
-- 6
diesel engine trap, allowing the exother~lic reaction of
the burning of the remaining particulate to sustain and
continue the oxidation process. Particulate are defined
herein, and by the EPA, as any matter in the exhaust of an
internal combustion engine, other than condensed water,
which can be collected on a special filter after dilution
with ambient air to a temperature of 125F (52C) maximum.
This includes agglomerated carbon particles, adsorbed
hydrocarbons, including known carcinogens, and sulfites.
Particulate are extremely small, having a mass median
diameter of 4-12 micro inches, and are extremely light
(one pound of particulate matter will occupy 350 cubic
inches).
As shown in Figures 1-2, the filtration system
comprises, broadly a filtration means 11, an ignition
means 12, means 13 for conducting an excess oxygen flow,
and a flow control means 14 (see Figures I The
filtration means particularly comprises a filter element
15 which may be comprised of a rigid or fibrous ceramic
such as aluminum silicate, or of fine metallic mesh. The
art of making such ceramic filter materials is well known
(see US. patents ~,340,403; 4,329,162; and 4,324,572).
Similarly, the art of making fine wire mesh trapping
materials is also well known (see So patent 3,~99,269).
One preferred trapping material construction
comprises a porous ceramic honeycomb similar to that used
for monolithic catalysts on gasoline engines. The
parallel aligned open channels of the honeycomb are
alternately blocked with high temperature ceramic cement
30 at the top and bottom so that all of the inlet gas flow
must pass through the porous ceramic walls before exiting
prom the trap. This honeycomb trap provides very high
filtration surface area per unit volume. For example, a
119 cubic inch trap of this configuration with 100 cells
~2~0~9~
per square inch and .017 inch wall thickness has
approximately 1970 square inches of filtering surface
area, and the filtering surface area per unit volume for
such a trap would be 16.6 square inches per cubic inch.
The mechanical trapping mechanism for the filter
element 15 is essentially by interception, although some
form of diffusion may also take place. The filtration
means is preferably formed as a cylinder, one flat end of
the cylinder acting as the frontal interface with the
incoming gas flow. The cylinder is encased in a metallic
housing 16 having entrance walls aye and exit walls 16b.
The alternate channels should preferably be aligned so
that they are aligned with the direction of flow, such as
shown in Figure 1. When the particulate collect on the
trap, they will nest within the porosity of the walls
which are aligned parallel to the direction of flow. Thus
there can be a general uniform distribution of particulate
collections along the length of the trap.
The ignition means 12 is comprised of a
channelized pheromones member 17 which may be similarly
shaped as a cylinder, but having an overall length which
is considerably shorter than that of the filter element,
such as one-fourth. The member 17 is enclosed in a
housing 18 having tapered (i.e., 3-6 inches) diameters,
inlet walls aye/ end an exit which commonly connects with
the housing 16. The member 17 preferably has direct
through channels 19 defined by walls which are not
particularly porous. The member may be formed by winding
aluminum oxide strands into a wall pattern containing the
30 through channels. Any porosity in the aluminum oxide
strands is small, typically AYE in diameter. The
member 17 can also be constructed of other ceramic
materials such as Malta aluminum titan ate.
~Z3(~;~9~
-- 8 --
Most importantly, the element 17 is coated with a
catalyst which may close or partially close the pores of
the pheromones walls. The ~oramina of the element gives a
high surface area for exposure to the gases passing
5 through channels 19. A catalyst is herein defined to mean
finely distributed discrete particles of very high surface
area that promote the reaction of carbon monoxide and
hydrocarbons with oxygen. Preferably the catalyst may be
selected from the group consisting of platinum,
10 platinum-palladium, palladium rubidium.
The catalyst coated pheromones member 17 has an
electrical resistance heating element 20 embedded therein,
preferably in the form of a torus shaped wire as shown in
Figure 2. The heating element, of course, is supplied
15 with a suitable source of electrical energy through
appropriate wiring 21 which may be about 600 watts,
sufficient to raise the temperature of the member 17 to
the range of 500-700F (which is effective to ignite a
combustible mixture of hydrocarbon fuel and exhaust gas or
I air).
The hydrocarbon rich flow of gas 22 is a
necessary part of the ignition means and is passed
uniformly through the catalyst coated pheromones member.
The flow of gas is supplied with atomized hydrocarbon fuel
25 droplets from a nozzle 23, such fuel being preferably
diesel, but can also be in other forms such as propane,
kerosene, or compressed natural gas. Excess hydrocarbon
fuel may be added either to (i) the gas flow through the
intake manifold of the engine (see Figure 6), (ii) the
3Q exhaust gas exiting from the engine (see Figure 5), or
(iii) a separate supply of compressed air fed to the
catalyst (see Figure 4).
The placement of the catalyst coated pheromones
member is of some significance. In the preferred mode the
35 axis 24 of the In ember is aligned with the axis of flow 22;
member 17 has a length of about 2-4.5 inches with the
I
trailing face 24 thereof spaced a distance of about 2-4
inches from the front face 25 of the filter element 15.
In this manner the flow of the combustible hydrocarbon
fuel/gas mixture can be ignited at a temperature of about
~00-700F at the front face 26 of the catalyst coated
pheromones member; by virtue of the exothermic reaction
within member 17, the combusted mixture will reach a
temperature at the trailing face 24 of the catalyst coated
pheromones member of about 1200F. The heated gas will
continue to increase slightly in temperature as it travels
across the gap of 2-4 inches, and assuredly possess
sufficient temperature to light (ignite) the front face
collection of particulate in the filter element.
Collected carbon particles in the filter require an
ignition temperature of at least about 1100F. However,
the trailing face I of the member 17 may be fitted or
juxtaposed the front face 25 of the filter element if the
diameters of housings 18 and 16 are substantially the
same.
The means 13 conducts a slow of gas carrying
excess oxygen for supporting combustion of the
particulate. Means 13 particularly comprises conduit 28
which is effective to conduct a flow 29 derived from
either exhaust gas of the engine itself or a separate
supply of compressed fresh air. The flow 29 is used after
ignition has taken place in the filter for purposes of
sustaining the continued oxidation of the particulate
material, facilitating prorogation of the flame front at
the entrance to the filter element through the entire
length of the filter element. The invention provides a
30 means of economically regenerating a filter at lower
temperatures without sulfite formation and on a periodic
basis. The necessary fuel for regeneration over the life
of a vehicle is extremely small end can be contained in a
small fuel reservoir separate from the engine fuel tank.
~Z3~
-- 10
In the preferred embodiment there is no flow
control means to divert the normal exhaust flow during
regeneration or to bypass the catalyst coated pheromones
member during any stage of operation. However the flow
5 control means lo Tokyo on some lmpo~tclnce in thy
alternative embodiments.
The arrangement shown in Figure 3 has the
catalyst coated pheromones member 17 termed as a tube with
the radial thickness of the tube wall 30 serving similar
to the longitudinal walls of the filter in Figure l; the
flow through the walls 30 is in a radial direction of the
tube. The tube is mounted within a plenum chamber 31
leading to the frontal face 25 of the filter element and
oriented so that its axis 32 is aligned with the direction
of flow of the exhaust gas. Walls of the plenum chamber
31 are arranged 50 that the full front face of the flow
can either enter the central core 33 of the pheromones
member thereby not requiring penetration through the
walls 30 of the member 17 in a radial direction, or go
around the exterior ox the pheromones member and penetrate
radially through the member walls 30 as the result of an
annular stopping plate 34 at the trailing end of the
- plenum chamber 31. The electrical heater 35 is mounted in
a manner which is in the outer surface region of the
25 tubular arrangement. By use of a diverter 36, the exhaust
gas, which is normally treated by the filter element
during engine operation is allowed to pass through the
central core of the pheromones member, thereby bypassing
the catalyst coated material. The diverter can be rotary
3Q operated. When regeneration is selected the diverter is
rotated so as to close off flow through the front core
opening 37 of the core tube 38, forcing the exhaust flow
to go about the exterior of the member 30 radially
passing through the Ermines material and electric
35 heater, into the interior hollow portion 33 and out
through the trailing opening 39.
1.~31~90
With this mode, hydrocarbons may be added to the
incoming gas during a period of regeneration; the
electrical heater, along with the catalyst coated
pheromones member, may ignite such enriched gas at a
relatively low temperature and raise it to an appropriate
ignition temperature for the particulate material. The
diverter structure for controlling the diversion of flow
may also be an axially movable valve as opposed to a
rotary operated valve requiring the plenum chamber to have
lo a slightly different design of the flow channel to permit
the use of an axially movable valve.
With the flow control means of Figure 3, the flow
diverter 36 is effective to normally bypass the exhaust
gas flow around the ignition means and then through the
filter element during normal operation of the system. The
diverter then is selectively operated to divert the
exhaust gas slow through the ignition means when
regeneration of the filter element is desired.
Figure 4 illustrates still another arrangement
for the flow control means 14. In this embodiment, the
plenum 40 comprises walls defining an ignition chamber 41
to receive the catalyst coated pheromones member 17. A
first duct 42 is effective to carry the exhaust gas to
plenum 40 and a second duct 43 to carry the exhaust gas
around the ignition chamber and around the filter element
15 to communicate with the exhaust gas exiting from the
filter element. A third duct 44 is used to carry a feed
gas to the ignition chamber 41 for ignition purposes. A
movable door or valve 45 is positioned to close off duct
I 43 in one position to permit the exhaust gases to enter
the filter 15 via opening 46, and alternatively effective
to open duct 43 in another position to permit bypassing
the jilter 15. To relieve the pressure of actuating valve
45, a coordinated valve 47 is positioned deep in duct 43
35 and closes when valve 45 is closed and vice-versa. Thus,
3~9~
- 12 -
the flow control means 14 has a flow diverter comprised of
valves 45 and 47, which are effective to normally bypass
the exhaust gas flow around the ignition means and through
the filter element 15 during normal operation of the
5 engine. The diverter may then be selectively moved 50
that the exhaust gas flow is directed not only around the
ignition means, but also around the filter element 15
through the channel 43. During the regeneration stage, a
separate flow of air and hydrocarbon enriched feed gas is
10 transmitted through duct 44 to the front face of the
catalyst coated pheromones member 17 in the ignition
chamber 41; the feed gas is ignited by the assistance of
electrical heating element 48 and heats to a temperature
of at least 1100F. Once the front face of the
15 particulate collection is ignited, fuel is no longer added
to the feed gas and air is then conducted through the
heated catalyst and filter element to carry out sustained
incineration of the particulate collection.
The addition of fuel or energy to the flow of
20 heated gas, that is, the gas effective to promote
ignition, may be promoted in two ways, as shown in Figures
5 and 6. In Figure 5, a separate fuel nozzle 50 (fed by a
diesel fuel line I is connected to one of the legs 51 of
the exhaust manifold 52 of the engine, whereby fuel may be
25 injected into the exhaust flow of leg So to create an
atomized fuel/air suspension. The exhaust gas is diverted
from that one leg 51, during regeneration, by a control
valve 53 to enter a passage 54 leading to the filtration
system. Alternatively, the exhaust gas may be enriched
30 with hydrocarbon fuel by a split fuel injection system for
the engine. In this system, diesel fuel is injected a
second time to the combustion chamber of the engine
(during the exhaust stroke) to create a fuel rich exhaust
gas.
~Z3(:~Z~O
In the embodiment of Figure 6, excess hydrocarbon
fuel is added by fuel line and nozzle 57 to the intake
manifold 58 of the engine during the desired regeneration
period. The overly rich mixture is partially combusted by
the engine and a portion of such exhaust gas therefrom is
diverted for regeneration. At a selected regeneration
time, valve 55 is actuated to divert such fuel rich
exhaust gas to the filtration system, while valve 56 is
actuated to bypass the remainder of the exhaust gas.
, . . .
