U.S. patent application number 12/120935 was filed with the patent office on 2008-12-25 for segmented particulate filter for an engine exhaust stream.
Invention is credited to Erik Paul Johannes, Xuantian Li, Campbell R. McConnell, Paul Sebright Towgood.
Application Number | 20080314032 12/120935 |
Document ID | / |
Family ID | 40001653 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080314032 |
Kind Code |
A1 |
Li; Xuantian ; et
al. |
December 25, 2008 |
Segmented Particulate Filter For An Engine Exhaust Stream
Abstract
A particulate filter is fluidly connected to and disposed
downstream from a diesel engine exhaust stream outlet. The filter
has a plurality of filter segments that have differing physical
properties or structural characteristics such that the engine
exhaust stream to fuel stream ratio is maintained substantially
consistent among segments during their regeneration. A method for
regenerating a segmented filter comprises maintaining the engine
exhaust stream to fuel stream ratio substantially consistent among
segments during their regeneration.
Inventors: |
Li; Xuantian; (Vancouver,
CA) ; Towgood; Paul Sebright; (Vancouver, CA)
; McConnell; Campbell R.; (Vancouver, CA) ;
Johannes; Erik Paul; (Vancouver, CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET, SUITE 3400
CHICAGO
IL
60661
US
|
Family ID: |
40001653 |
Appl. No.: |
12/120935 |
Filed: |
May 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60938106 |
May 15, 2007 |
|
|
|
60953856 |
Aug 3, 2007 |
|
|
|
Current U.S.
Class: |
60/297 |
Current CPC
Class: |
F01N 3/0253 20130101;
B01D 46/2459 20130101; B01D 46/2451 20130101; F01N 3/022 20130101;
B01D 46/2455 20130101; B01D 2046/2433 20130101; B01D 46/2429
20130101; F01N 2330/60 20130101; B01D 46/247 20130101; B01D 46/2466
20130101 |
Class at
Publication: |
60/297 |
International
Class: |
F01N 3/021 20060101
F01N003/021 |
Claims
1. An engine exhaust stream particulate filter comprising at least
two filter segments wherein said segments are structured so that if
they were each supplied with a gas stream under identical
conditions, the gas stream mass flow through each of said segments
would be different.
2. The engine exhaust stream particulate filter of claim 1 wherein
said segments differ from each other in at least one structural
characteristic selected from the group consisting of
cross-sectional area, longitudinal filter length, filter porosity
and filter cell density.
3. The engine exhaust stream particulate filter of claim 1 wherein
said at least two filter segments are unequal in their in
cross-sectional area.
4. The engine exhaust stream particulate filter of claim 1 having a
longitudinal axis, wherein said at least two filter segments are
unequal in length in the longitudinal direction.
5. The engine exhaust stream particulate filter of claim 1 wherein
said segments differ from each other in at least one structural
characteristic such that the engine exhaust stream mass flow rate
through each segment during their sequential regeneration is
approximately equal.
6. The engine exhaust stream particulate filter of claim 1 wherein
said at least two filter segments are housed in a common
enclosure.
7. A method for operating a particulate filter comprising a
plurality of filter segments, the method comprising: (a) directing
an exhaust stream from a combustion engine through said plurality
of filter segments; (b) selectively introducing a
hydrogen-containing gas stream at least periodically into each of
said filter segments to regenerate said segment; (c) maintaining
the engine exhaust stream to hydrogen-containing gas stream heat
value ratio used for regeneration of each segment substantially
consistent among said plurality of segments.
8. The method of claim 7 wherein said hydrogen-containing gas
stream is introduced into said plurality of segments sequentially
in a regeneration sequence.
9. The method of claim 8 wherein the engine exhaust stream mass
flow rate through each segment is different so that said heat value
ratio is maintained substantially consistent among segments during
their regeneration.
10. The method of claim 9 wherein said segments are structured so
that if they were supplied with a gas stream under identical
conditions, the gas stream mass flow through each one of said
plurality segments would be different.
11. The method of claim 7 wherein said heat value ratio is
maintained substantially consistent among segments during their
regeneration by varying the mass flow rate of said
hydrogen-containing gas stream that is introduced to regenerate
each segment.
12. The method of claim 11 wherein said hydrogen-containing gas
stream is introduced into said plurality of segments sequentially
in a regeneration sequence.
13. The method of claim 12 wherein the mass flow rate of said
hydrogen-containing gas stream that is introduced to regenerate
each segment depends upon its position in the regeneration
sequence.
14. The method of claim 7 wherein the duration of regeneration of
each segment is substantially the same.
15. The method of claim 7 where said hydrogen-containing gas stream
is being introduced into at least one filter segment at a given
time so that at least one filter segment is undergoing regeneration
during operation of said particulate filter.
16. The method of claim 8 further comprising (d) monitoring at
least one of a pressure P.sub.1 of said engine exhaust stream
upstream of said particulate filter, a temperature T.sub.1 of said
engine exhaust stream, and a time interval t.sub.1 related to
operation of said particulate filter, and initiating said
regeneration sequence by selectively introducing a
hydrogen-containing gas stream into a first segment in said
sequence when at least one of P.sub.1, T.sub.1 or t.sub.1 is
greater than a predetermined threshold value.
17. The method of claim 8 further comprising: (d) monitoring at
least one of pressure differential .DELTA.P across said particulate
filter, a temperature T.sub.1 of said engine exhaust stream, and a
time interval t.sub.1 related to operation of said particulate
filter and initiating said regeneration sequence by selectively
introducing a hydrogen-containing gas stream into a first segment
in said sequence when at least one of .DELTA.P, T.sub.1 or t.sub.1
is greater than a predetermined threshold value.
18. The method of claim 17 further comprising: (e) ceasing
regeneration of said first filter segment and each subsequent
segment in said regeneration sequence when .DELTA.P falls below a
predetermined threshold value.
19. The method of claim 17 further comprising: (e) ceasing
regeneration of said first filter segment and each subsequent
segment in said regeneration sequence when the rate-of-decrease in
.DELTA.P falls below a predetermined threshold value.
20. The method of claim 8 wherein the flow of said
hydrogen-containing gas stream to each segment in said regeneration
sequence is ceased after a predetermined segment regeneration
time.
21. The method of claim 8 further comprising (d) monitoring a
temperature T.sub.2 of said exhaust stream downstream of said
particulate filter and the flow of said hydrogen-containing gas
stream to a particular segment is ceased when said temperature
T.sub.2 exceeds a predetermined third threshold value.
22. The method of claim 7 wherein said hydrogen-containing gas
stream is selectively introduced into each of said plurality of
segments depending on a monitored operating parameter of each said
segment.
23. The method of claim 22 wherein said operating parameter is a
temperature of said engine exhaust stream passing through each
segment.
24. An engine and exhaust after-treatment system comprising: (a) a
combustion engine; (b) a particulate filter connected to receive an
exhaust gas stream from said engine via an exhaust stream conduit,
said particulate filter comprising a plurality of filter segments
with different structural characteristics from one another, wherein
during operation of said particulate filter said exhaust gas stream
is directed through said segments in parallel; (c) a syngas
generator for producing a syngas stream; (d) a controller
configured to selectively direct said syngas stream to each of said
segments in sequence to regenerate said segment.
25. The engine and exhaust after-treatment system of claim 24
wherein said filter segments are structured so that if they were
each supplied with a gas stream under identical conditions, the gas
stream mass flow through each of said segments would be different.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is related to and claims priority benefits
from U.S. Provisional Patent Application Ser. No. 60/938,106,
entitled "Control System And Method For Regenerating A Diesel
Particulate Filter", filed on May 15, 2007, and U.S. Provisional
Patent Application Ser. No. 60/953,856, entitled "Engine Exhaust
Stream Particulate Filter With Unequal Segmentation", filed on Aug.
7, 2007, each of which is hereby incorporated by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to engine exhaust stream
particulate filters and, more particularly, to diesel engine
exhaust stream particulate filters. A diesel particulate filter
(sometimes abbreviated herein as a "DPF") is a device designed to
remove diesel particulate matter or soot from the exhaust gas
stream of a diesel engine.
BACKGROUND OF THE INVENTION
[0003] Diesel engines, during combustion of the fuel/air mixture,
produce a variety of particles, generically classified as diesel
particulate matter, due to incomplete combustion. The composition
of the particles varies widely depending upon engine type, age and
the emissions specification that the engine was designed to
meet.
[0004] Historically, diesel engine emissions were not regulated
until 1987 when the first California Heavy Truck rule was
introduced capping particulate emissions at 0.60 g/BHP hour. Since
then, progressively stricter standards have been introduced for
diesel engine particulate emissions. While particulate emissions
from diesel engines were first regulated in the United States,
similar regulations have also been adopted by the European Union,
most Asian countries, and the rest of North and South America.
[0005] A DPF cleans an exhaust gas stream by forcing the gas stream
to flow through the filter. There are a variety of diesel
particulate filter technologies on the market. Each is designed
around similar requirements: [0006] (a) fine filtration; [0007] (b)
minimal pressure drop; [0008] (c) low cost; [0009] (d) mass
production suitability; and [0010] (e) product durability.
[0011] Filters generally require more maintenance than catalytic
converters. Particulates trapped by the filter will eventually clog
the pores. This increases the pressure drop across the filter
which, when it reaches or exceeds a critical value, is capable of
reducing the efficiency of the engine. Regular filter maintenance
or regeneration therefore becomes necessary.
[0012] Regeneration is the process of removing accumulated
particulates from a filter. This is done either passively or
actively by intentionally increasing the temperature of the trapped
particulates. On-board active filter management can employ a
variety of strategies, for example: [0013] (1) Engine management to
increase the exhaust gas temperature. [0014] (2) A fuel burner to
increase the exhaust gas temperature. [0015] (3) A catalytic
oxidizer to increase the exhaust gas temperature. [0016] (4)
Resistive heating coils to increase the exhaust gas temperature.
[0017] (5) Microwave energy to increase the particulate
temperature.
[0018] On-board active regeneration systems consume extra fuel,
whether through burning the fuel to heat the DPF or providing extra
power to the associated electrical system. Typically a computer
monitors one or more sensors that measure back-pressure and/or
temperature and, based on pre-programmed set points, makes
decisions on when to activate and end the regeneration cycle.
Running the regeneration cycle too often, although keeping the
back-pressure in the exhaust system low will use extra fuel. Not
regenerating the DPF sufficiently frequently can increase the risk
of engine damage, can reduce engine efficiency due to high back
pressure, and can result in excessive regeneration temperatures and
possible DPF failure.
[0019] Typically without the use of catalysts, diesel particulate
matter combusts when temperatures around 600.degree. C. and above
are attained. The start of combustion causes a further increase in
temperature. In some cases the combustion of particulate matter can
raise the temperature of the DPF above a threshold temperature that
can cause damage to the DPF. Unlike spark-ignited engines, which
typically have less than 0.5% oxygen in the exhaust gas stream
upstream from the emission control device(s), many diesel engines
typically have 8% to 18% oxygen in the exhaust stream pre-filter.
While the amount of available oxygen makes fast regeneration of a
filter possible, it can also contribute to runaway regeneration
problems.
[0020] The particulate filter can be divided into segments which
can be regenerated at different times by the selective introduction
of a fuel into the particular segment(s) being regenerated, while
the engine exhaust stream continues to flow though all segments of
the filter including those that are being regenerated. Regenerating
a segment or portion of the filter at a given time, compared to the
entire filter, reduces the required mass flow rate of the fuel used
for regeneration. If, for example, syngas is used as the fuel, this
approach can offer the advantage of reducing the size and cost of a
syngas generator required by the system. Furthermore, there are
advantages to regenerating segments of the filter sequentially in a
continuous cycle, so that syngas is being directed into at least
one filter segment at a given time during operation of said
particulate filter. This enables an essentially continuous
requirement for the syngas stream and can offer the advantage of
reducing the fluctuations in demand for the syngas stream.
[0021] If a DPF is segmented into equal segments of the
substantially same dimensions and structure, when all segments are
equally loaded with soot the flow rate of exhaust gas passing
through each of the segments will be about the same. For example,
if the DPF is segmented into four quadrants then about 25% of the
exhaust gas flow will pass through each segment when all segments
are equally loaded with soot.
[0022] If only one segment has been regenerated, then more than 25%
of the exhaust gas stream will pass through the "clean" segment,
thereby leaving less exhaust gas to pass through each of the other
segments when they are being regenerated. If a fixed mass flow rate
of fuel is supplied during regeneration, the result is that the
fuel-to-exhaust gas ratio will be higher in the next segment to be
regenerated, and the temperature associated with combusting a fixed
amount of fuel, for example syngas (a mixture of hydrogen and
carbon monoxide), will be higher and thus potentially damaging to
the DPF's catalyst, washcoat and/or substrate.
[0023] As progressively more and more segments are regenerated, the
ratio of syngas to exhaust gas will increase further, thereby
resulting in higher temperatures and more of a chance of damage to
the DPF. The present approach utilizes the benefits of a segmented
particulate filter while addressing this issue.
SUMMARY OF THE INVENTION
[0024] In a preferred method for regenerating a segmented engine
exhaust stream particulate filter, the heat value ratio of the
engine exhaust stream to the fuel stream introduced into each
individual segment during regeneration is maintained substantially
consistent among segments. This offers the advantages of reducing
the risk of thermal damage to the filter during regeneration (by
decreasing the variation in the maximum regeneration temperatures
reached in each segment), increased regeneration consistency
between the segments, and reduced fuel consumption.
[0025] In one aspect, the filter comprises a plurality of filter
segments that have differing physical properties or structural
characteristics such that the engine exhaust stream to fuel stream
ratio is maintained substantially consistent among segments during
their regeneration. The segments can be designed and constructed so
that if they were each supplied with a gas stream under the same
conditions, the mass flow of that gas stream through each of them
would be different. Such filters are described herein as "unequally
segmented filters".
[0026] In another aspect, the mass flow rate of the fuel stream or
syngas stream introduced to each individual segment can be varied
to enable a substantially consistent heat value ratio of the
streams introduced into each segment during regeneration.
[0027] Thus, in preferred embodiments an engine exhaust stream
particulate filter comprises at least two filter segments wherein
the segments are structured so that if they were each supplied with
a gas stream under identical conditions, the gas stream mass flow
through each of the segments would be different. For example, the
segments can differ from each other in at least one structural
characteristic selected from the group consisting of
cross-sectional area, longitudinal filter length, filter porosity
and filter cell density. Preferably, the segments differ from each
other in at least one structural characteristic such that the
engine exhaust stream mass flow rate through each segment during
their regeneration is approximately equal. In compact designs, the
filter segments can be housed in a common enclosure.
[0028] In embodiments of a method for operating a particulate
filter comprising a plurality of filter segments, the method
comprises: [0029] (a) directing an exhaust stream from a combustion
engine through the plurality of filter segments; [0030] (b)
selectively introducing a hydrogen-containing gas stream at least
periodically into each of the filter segments to regenerate the
segment; [0031] (c) maintaining the engine exhaust stream to
hydrogen-containing gas stream heat value ratio used for
regeneration of each segment substantially consistent among the
plurality of segments.
[0032] In some embodiments of the above method, the engine exhaust
stream mass flow rate through each segment is different so that the
heat value ratio is maintained substantially consistent among
segments during their regeneration. The segments can be structured
as described above, so that if they were supplied with a gas stream
under identical conditions, the gas stream mass flow through each
one of the plurality segments would be different.
[0033] In other embodiments of the above method, the heat value
ratio is maintained substantially consistent among segments during
their regeneration by varying the mass flow rate of the
hydrogen-containing gas stream that is introduced to regenerate
each segment. For example, the mass flow rate of the
hydrogen-containing gas stream that is introduced to regenerate
each segment can depend upon its position in a regeneration
sequence
[0034] In the above-described methods, the hydrogen-containing gas
stream can be introduced into the plurality of segments
sequentially in a regeneration sequence.
[0035] In the above-described methods, the duration of regeneration
of each segment can be substantially the same.
[0036] The above-described methods can be employed in a
non-continuous regeneration cycle or in a continuous regeneration
cycle in which the hydrogen-containing gas stream is being
introduced into at least one filter segment at a given time, so
that at least one filter segment is undergoing regeneration during
operation of the particulate filter.
[0037] In embodiments of an engine and exhaust after-treatment
system, the system comprises: [0038] (a) a combustion engine;
[0039] (b) a particulate filter connected to receive an exhaust gas
stream from the engine via an exhaust stream conduit, the
particulate filter comprising a plurality of filter segments with
different structural characteristics from one another, wherein
during operation of the particulate filter the exhaust gas stream
is directed through the segments in parallel; [0040] (c) a syngas
generator for producing a syngas stream; [0041] (d) a controller
configured to selectively direct the syngas stream to each of the
segments in sequence to regenerate the segment.
[0042] Preferably the filter segments are structured so that if
they were each supplied with a gas stream under identical
conditions, the gas stream mass flow through each of the segments
would be different.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0043] FIG. 1 is a photographic image showing an end view of a
diesel particulate filter with one of four equal segments
regenerated.
[0044] FIG. 2a is a simplified end view of a diesel particulate
filter divided into four equal segments. FIG. 2b is a simplified
end view of a diesel particulate filter divided into four unequal
segments.
[0045] FIG. 3 is a table that summarizes the exhaust gas flow
splits, temperature and pressure drop history at various phases in
a regeneration cycle of a four-segment, equally divided diesel
particulate filter.
[0046] FIG. 4 is a plot of exhaust gas flow splits over a DPF
regeneration test cycle, at the various phases in the regeneration
cycle that is tabulated in FIG. 3.
[0047] FIG. 5 is a plot of exhaust gas outlet temperatures from the
various segments of a diesel particulate filter at the various
phases in the regeneration cycle that is tabulated in FIG. 3.
[0048] FIG. 6 is a table that summarizes the exhaust gas flow
splits, temperature and pressure drop history at various phases in
a regeneration cycle of a four-segment, unequally divided diesel
particulate filter.
[0049] FIG. 7 is a plot of exhaust gas outlet temperatures from the
various segments of a diesel particulate filter at the various
phases in the regeneration cycle that is tabulated in FIG. 6.
[0050] FIG. 8 illustrates a schematic view of a combustion engine
system comprising a segmented diesel particulate filter.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0051] A diesel particulate filter (DPF) can be segmented into at
least two segments, for example, by providing a baffle on the
upstream side of the filter monolith, or by having separate filter
segments housed in a common enclosure or not. This enables the
introduction of a fuel, for example, a syngas stream, selectively
into different portions or segments of the filter and the
regeneration of each segment separately or independently from
another. With this type of filter regeneration of the segments can
be conducted sequentially and in a continuous cycle. In another
variation the segments can be regenerated in sequence, one after
the other, and then the DPF can be operated for a period without
any segments being regenerated, with the regeneration sequence
repeated only when regeneration is required. The engine exhaust
stream flows through all segments of the DPF, whether the segment
is being regenerated or not. As each segment is regenerated, the
mass flow of the engine exhaust stream through the segment being
regenerated tends to change as a result of the removal of
particulate matter. This in turn can alter the heat value ratio of
the engine exhaust stream to the fuel stream during the
regeneration of subsequent segments.
[0052] The following discussion describes a shortcoming of an
"equally" segmented DPF, in which the segments are regenerated
sequentially in a continuous or non-continuous cycle. For example,
if a DPF is loaded with soot and there are four equally divided
segments the total engine exhaust stream flow will be equally split
with about 25% of the total engine exhaust stream flowing through
each segment. After regeneration of the first segment, the first
segment which now has less soot will have a lower resistance to the
flow of the engine exhaust stream. FIG. 1 is a photographic image
showing an end view of a diesel particulate filter with one of four
equal segments regenerated. Significantly more that 25% of the
total engine exhaust stream flow will pass through the first
regenerated (cleaned) segment, while less than 25% of the total
engine exhaust stream flow will flow through each of the remaining
segments. This type of flow behavior will continue as each segment
is regenerated. When the fourth or last segment in the regeneration
sequence is regenerated, only a small fraction of the total engine
exhaust stream flow will pass through the fourth segment (about 12%
in an example described below). The lower flow rate in the final
segment is a result of the lower resistance to flow in the other
segments that have been previously regenerated. If the flow rate of
the fuel or syngas stream supplied is substantially consistent
among segments during the regeneration process, the segments
regenerated later in the sequence will receive more fuel relative
to engine exhaust (that is, an increased heat value ratio), with
the potential to over-heat and thermally damage the segment.
[0053] The present approach reduces the variation in the heat value
ratio of the streams flowing through the various segments during
regeneration, by factoring into the filter design and/or
regeneration technique the change in the engine exhaust stream flow
rate through the segments that occurs as they are regenerated or
cleaned.
[0054] In one embodiment of an improved segmented filter design, a
diesel particulate filter is divided into at least two segments
having different cross-sectional areas. FIG. 2a (prior art) is a
simplified end view of a diesel particulate filter that has a
substantially circular or round cross-sectional profile, and that
is divided into four equal segments, A, B, C and D. FIG. 2b is a
simplified end view of an improved diesel particulate filter
divided into four unequal segments with differing cross-sectional
areas where the smallest segment AA would be regenerated first,
followed in sequence by the progressively larger segments BB, CC
and then DD. The appropriate relative cross-sectional area of the
segments will be dependent upon the operating parameters of the DPF
and/or the engine exhaust gas after-treatment system, including the
regeneration control strategy and sequence. The segments are
preferably sized so that there is a substantially consistent heat
value ratio during regeneration, if the rate of fuel flow supplied
for regeneration is consistent among segments (for example, so that
the ratio is consistent at the start of regeneration of each
segment, or on average over the regeneration of each segment).
[0055] Unequal segmentation of the diesel particulate filter can
reduce the variation in the heat value ratio, and thus the
variation in temperature of the regeneration process, among
individual segments as they are regenerated. It can also
substantially reduce the overall fuel consumption associated with
filter regeneration. For example, if the first segment AA was at
approximately 65.degree. compared to an equally segmented filter
segment at 90.degree., the mass flow rate of the engine exhaust
stream flowing through the first segment would be 65/90 or
approximately 72% of the amount it would be in an equally segmented
filter segment. Therefore, the required flow rate of the fuel
stream or syngas stream would be about 72% of the amount required
for an equally segmented filter, in order to maintain a similar
heat value ratio. In the foregoing example the overall fuel saving
would be about 28%.
[0056] The table in FIG. 3 summarizes modeled data from a DPF
regeneration test cycle of a four segment, equally divided DPF (of
the type illustrated in FIG. 2a), at various phases of a test
cycle. The test starts off with a clean DPF (phase 1) which then
becomes loaded with soot (phase 2). Data is provided for subsequent
phases as and after each of the four segments (seg.) is regenerated
in sequence by supplying syngas at about the same flow rate. FIG. 4
illustrates the mass flow rate of the engine exhaust gas stream
(EG) through the four DPF segments during the various phases of the
test cycle that are tabulated in FIG. 3, as well as the overall
pressure drop across the DPF at the various phases. This data is
included in FIG. 3. FIG. 4 shows that, as would be expected, the
overall pressure drop decreases as each segment is regenerated.
When all segments are clean or all segments of the DPF are loaded
with soot, the EG flow is split about equally among the four
segments (as at phase 1, 2, 3 and 10 where approximately 25% of the
EG flow passes through each segment). Once one segment has been
regenerated, a larger proportion (about 45%) of the EG passes
through the cleaned segment with only about 18% passing through
each of the three loaded segments (see phase 4 data points).
Similarly, once two more segments have been regenerated (phases 6
and 8) the proportion of EG passing through the remaining loaded
segment(s) drops even further to about 12%. FIG. 5 illustrates the
temperatures of the various segments during the various phases of
the test cycle that are tabulated in FIG. 3. The outlet temperature
for the segment being regenerated gets hotter for each of the four
segments. This is because the ratio of fuel (syngas) to EG is
lowest in the first segment to be regenerated but increases with
regeneration of each of the remaining three segments, because
proportionately less of the EG is passing through the remaining
loaded segments, but the supply of fuel (syngas) is the same.
[0057] The data shown in FIGS. 6 and 7 illustrates how an unequally
divided DPF (of the type illustrated in FIG. 2b) can be used to
reduce the variation in outlet temperature from the segments as
they are regenerated in sequence. FIG. 6 summarizes data modeled
for a similar DPF regeneration test cycle of a four segment,
unequally divided DPF. The test starts off with a clean DPF (phase
1) which then becomes loaded with soot (phase 2). The EG mass flow
rate through the four DPF segments during the various phases of the
test cycle is shown in FIG. 6, as well as the overall pressure drop
across the DPF at the various phases. When the DPF is clean or all
segments are loaded with soot, the EG flow is split unequally among
the four segments (approximately 19%, 22% 27% and 32% at phases 1,
2 and 10). Once one segment has been regenerated, a larger
proportion of the EG (about 33%) passes through that first segment
(see phase 4 data points). However, the proportion of EG passing
through a segment during regeneration of that segment is
consistently about 14% for all four segments (see phases 3, 5, 7
and 9). FIG. 6 shows that, as would be expected, the overall
pressure drop decreases as each segment is regenerated. Temperature
data is also provided for the various phases as and after each of
the four segments is regenerated in sequence by supplying syngas at
about the same flow rate. FIG. 7 illustrates the outlet
temperatures (date also shown in FIG. 6) from the various segments
during the various phases of the test cycle that are tabulated in
FIG. 6. Unlike for the equally divided DPF (data in FIG. 5), the
outlet temperature for the segment being regenerated is
substantially the same for each of the four segments as they are
regenerated. This is because the ratio of fuel to EG is
substantially the same for each of the four segments during
regeneration because of the variation in cross-sectional area of
the segments.
[0058] In other embodiments of improved segmented filter designs,
other physical properties or structural characteristics of the
filter segments can be different from one another, besides or in
addition to their cross-sectional area. For example, the mass flow
of the engine exhaust stream can be made more consistent among the
different segments during regeneration by having segments with
differing filter cell density, differing filter porosity and/or
differing longitudinal filter lengths or volumes.
[0059] Ceramic wall-flow monoliths used for DPFs can be
manufactured by extruding a large unitary section or by cementing
or bonding together multiple smaller sections or "bricks" to form
one complete larger section. The DPF in FIG. 1 is constructed of
multiple bricks; the joints between the bricks are visible in FIG.
1. If the DPF is constructed of smaller bricks rather than being
one complete extrusion, preferably the divisions between the
segments do not coincide with the area or joints where individual
bricks are joined to form the DPF, or at least care is taken to
reduce the degree of overlap. This reduces the thermal gradient and
thermal stress across the adhesive or cement that joins the
individual bricks of a DPF together.
[0060] In embodiments of a regeneration technique for a segmented
particulate filter, the heat value ratio during the regeneration of
an individual segment can be held substantially consistent among
segments by controlling and varying the mass flow rate of the fuel
stream introduced to each individual segment. The mass flow rate of
the fuel stream can be adjusted depending on the mass flow rate of
the engine exhaust stream flowing through an individual segment
during regeneration to maintain the desired heat value ratio. This
technique can reduce the overall fuel consumption associated with
filter regeneration, but can cause a fluctuating demand for fuel
(for example, syngas) for regeneration purposes, and requires a
more complex control system. The technique can be used with an
equally segmented particulate filter to reduce the variation in the
heat value ratio, and thus the variation in temperature of the
regeneration process, among individual segments as they are
regenerated. It can also be used with unequally segmented
particulate filters of the types described herein, to provide
further non-passive control of the heat value ratio.
[0061] The present segmented filter designs and regeneration
techniques can provide some or all of the following advantages over
those used in conventional DPFs: [0062] (A) Reduced potential of
thermal damage to the filter substrate and catalyst during
regeneration. [0063] (B) Reduced fuel penalty associated with
filter regeneration due to reducing the amount of fuel (for example
syngas or diesel fuel) required to heat the individual filter
segments during regeneration. [0064] (C) If syngas is used for
regeneration, reduced syngas generator size and cost due to the
reduced mass flow rate of the engine exhaust stream flowing through
an individual segment, which reduces the amount of syngas required
to heat the individual filter segments during regeneration.
[0065] In the above described embodiments the segments can be
regenerated by various methods, for example, conducted sequentially
until all segments have been regenerated, conducted in a specific
order, conducted in a continuous cycle, conducted in a
non-continuous cycle, and/or conducted only when regeneration is of
the filter required. The regeneration process can be controlled
through an open-loop control method and/or a closed loop control
method employing sensors and/or pre-determined regeneration
algorithms.
[0066] FIG. 8 illustrates a schematic view of a combustion engine
system 100 comprising an exhaust after-treatment sub-system 101.
Engine 110 produces an engine exhaust stream which travels through
conduit 111, through an optional turbo-compressor 112, and through
conduit 113 to DPF assembly 120 where the engine exhaust stream is
filtered by a filter 121 to reduce the level of regulated
particulate emissions therein. The filtered engine exhaust stream
is then released to the atmosphere via an exhaust conduit 114.
Conduit 113 and exhaust conduit 114 can comprise additional exhaust
after-treatment devices, not shown in FIG. 8.
[0067] As particulates collect in filter 121, the flow of the
engine exhaust stream is impeded, increasing the backpressure of
the engine exhaust stream upstream of filter 121. An optional
sensor can be employed to monitor the temperature of the engine
exhaust stream and can be located near the engine outlet, for
example, sensor 133. An optional pressure sensor 131 monitors the
pressure of the engine exhaust stream upstream of filter 121 and
can be located along conduits 111 or 113. An optional pressure
sensor 132 monitors the pressure of the engine exhaust stream
downstream of filter 121 and can be located along conduits 114 or
other optional conduits located downstream of filter 121 (not shown
in FIG. 8). Alternatively, a pair of pressure sensors 131 and/or
132 can be located within DPF assembly 120 upstream and downstream
of filter 121. Alternatively a differential pressure sensor (not
shown in FIG. 8) can be employed to monitor the pressure of the
exhaust stream upstream and downstream of filter 121.
Alternatively, an optional sensor can be employed to monitor the
temperature of the engine exhaust stream near the DPF outlet, for
example, sensor 134, or at other locations along conduits 113 or
114 or within DPF assembly 120. A controller 130 receives signals
from optional pressure sensors 131 and 132, and optional
temperature sensors 133 and 134.
[0068] The following paragraphs describe control strategies that
can be used to initiate and terminate regeneration of filter 121.
These strategies are applicable to unsegmented filters, and equally
divided segmented filters or unequally divided segmented filters of
the type described herein.
[0069] In preferred control strategies, controller 130 initiates a
regeneration process for filter 121 based on employing one of
equations (1), (2), (3) or (4).
[0070] Initiate DPF regeneration when:
n<[(P.sub.1-P.sub.2)/P.sub.3], (1)
n<[(P.sub.1-P.sub.2)/P.sub.3] and t.sub.1>x.sub.1 (2)
n<[(P.sub.1-P.sub.2)/P.sub.3] and T.sub.1>y.sub.1 (3)
n<[(P.sub.1-P.sub.2)/P.sub.3] and t.sub.1>x.sub.1 and
T.sub.1>y.sub.1 (4)
where [0071] n=predetermined value [0072] P.sub.1=pressure of
engine exhaust stream upstream of the DPF filter [0073]
P.sub.2=pressure of engine exhaust stream downstream of the DPF
filter [0074] P.sub.3=predetermined first pressure value, which
represents a pressure differential between the inlet and outlet of
a clean DPF (without trapped particulates or a regenerated DPF)
during the present operating condition of the engine. This value
can be pre-programmed or stored in a look-up table, or calculated
(as a function of the mass flow of exhaust stream or mass flow of
the inlet air steam of the engine, temperature of exhaust stream at
the inlet to DPF, cross-sectional area of DPF, and a constant).
[0075] t.sub.1=time since last regeneration [0076]
x.sub.1=predetermined first time value [0077] T.sub.1=temperature
of engine exhaust stream at, for example: engine outlet, DPF
outlet, or other position along engine exhaust stream conduits
[0078] y.sub.1=predetermined first temperature value.
[0079] Alternatively, in equations (1), (2), (3) or (4), P.sub.1
can be employed in place of P.sub.3.
[0080] In other embodiments of a control strategy, controller 130
initiates a regeneration process for filter 121 based on employing
one of equations (5), (6), (7) or (8).
n<P.sub.1 (5)
n<P.sub.1 and t.sub.1>x.sub.1 (6)
n<P.sub.1 and T.sub.1>y.sub.1 (7)
n<P.sub.1 and t.sub.1>x.sub.1 and T.sub.1>y.sub.1 (8)
[0081] Alternatively, in equations (5), (6), (7) or (8),
P.sub.1-P.sub.2 can be employed in place of P.sub.1.
[0082] In yet other embodiments of a control strategy, controller
130 initiates a regeneration process for filter 121 based on
employing one of equations (9), (10), (11) and (12).
n<[(P.sub.1-P.sub.2)/m.sub.1], (9)
n<[(P.sub.1-P.sub.2)/m.sub.1] and t.sub.1>x.sub.1 (10)
n<[(P.sub.1-P.sub.2)/m.sub.1] and T.sub.1>y.sub.1 (11)
n<[(P.sub.1-P.sub.2)/m.sub.1] and t.sub.1>x.sub.1 and
T.sub.1>y.sub.1 (12)
where m.sub.1=mass flow of engine exhaust stream.
[0083] Alternatively, in equations (9), (10), (11) or (12), P.sub.1
can be employed in place of P.sub.1-P.sub.2.
[0084] Alternatively, in equations (9), (10), (11) or (12), m.sub.2
can be employed in place of m.sub.1
where m.sub.2=mass flow of engine intake air stream.
[0085] In equations (1) through (12) the parameters that are
actually monitored and associated signals sent to the controller
can be indicative of another parameter, for example, in equation
(9) a pressure sensor can be employed to monitor the engine exhaust
stream in order to indicate the mass flow rate of the engine
exhaust stream.
[0086] In further embodiments of a control strategy, controller 130
initiates a regeneration process for filter 121 based on employing
at least one of equations (1) through (12) and at least one of
equations (13) (14).
T.sub.1<y.sub.2, (13)
.lamda.>[O.sub.2], (14)
where [0087] y.sub.2=predetermined second temperature value [0088]
.lamda.=oxygen concentration of engine exhaust stream [0089]
[O.sub.2]=predetermined oxygen concentration value.
[0090] In preferred embodiments of a control strategy for
terminating regeneration, controller 130 terminates a regeneration
process for filter 121 based on at least one of equations (15),
(16), (17) or (18).
[0091] Terminate DPF regeneration when:
T.sub.2>y.sub.3, (15)
dT.sub.2>z (16)
t.sub.2>x.sub.2 (17)
P.sub.4(P.sub.1-P.sub.2) (18)
P.sub.4<P.sub.3 (19)
where [0092] T.sub.2=temperature of engine exhaust stream at, for
example: exhaust stream conduit downstream of DPF outlet [0093]
y.sub.3=predetermined third temperature value, which can be the
same as y.sub.2 or different. [0094] dT.sub.2=rate of change to
T.sub.2 [0095] z=predetermined rate of change value [0096]
t.sub.2=time since initiation of regeneration [0097]
x.sub.2=predetermined second time value [0098]
P.sub.4=predetermined second pressure value.
[0099] Preferably in the above described control strategies, DPF
assembly 120 is divided into equally or unequally divided segments
which enables the regeneration of at least one segment or portion
of filter 121 at a given time. In FIG. 8, DPF assembly 120
comprises a baffle 122 which is a means to divide and channel the
flow of the syngas stream through a segment within filter 121,
while allowing the engine exhaust stream to flow though all
segments of filter 121 including those that are being regenerated.
Alternatively or in addition, DPF assembly 120 comprises a baffle
downstream (not shown in FIG. 8) of filter 121 in order to divide
and channel the engine exhaust stream as it exits a segment within
filter 121. This allows the engine exhaust stream exiting each
individual segment to be monitored. For example, the temperature of
the engine exhaust stream exiting each segment can be monitored and
regeneration of individual segments can be triggered depending on
the monitored value for that segment.
[0100] In FIG. 8, syngas generator assembly 140 can be operated
essentially continuously when engine system 100 is in operation. A
fuel and oxidant reactant supply and control system (not shown in
FIG. 8) supplies the necessary reactants to syngas generator
assembly 140. The syngas stream produced by syngas generator
assembly 140 flows through conduit 141 to valve 142 where it is
diverted to flow selectively through at least one of conduits 143,
144, 145 or 146 and the respective segments within DPF assembly
120. Alternatively syngas can be directed to DPF assembly 120 via a
single conduit and the selective flow of syngas to the different
segment accomplished by flow diverters or other devices within DPF
assembly 120. Valve 142 is controlled by controller 130.
[0101] Various algorithms can be used for controlling regeneration
of a segmented DPF. The algorithm can include factors such as:
[0102] (a) the regeneration cycle of DPF. This can be, for example,
continuous, periodic or only as required; [0103] (b) the order of
regenerating the different segments. This can be, for example,
sequential (for example, for an unequally segmented filter) or
non-sequential (for example, done as required as determined by
monitoring of individual segments); [0104] (c) the component to be
monitored in order to control the regeneration. This can be, for
example, individual segment or overall DPF assembly; [0105] (d) the
control system employed for regeneration. This can be, for example,
closed-loop or open-loop systems or some combination; and [0106]
(e) the operating parameter(s) to be monitored for the regeneration
control system. This can be, for example, duration of regeneration
or temperature of exhaust gas stream for DPF assembly or filter or
an individual segment thereof; or pressure drop across the filter
or DPF assembly.
[0107] Table 1 illustrates examples of various regimes that can be
used to control the regeneration of an equally or unequally
segmented DPF assembly. One or more of these regimes can be
used.
TABLE-US-00001 TABLE 1 Example of Regeneration Regimes for a
Segmented DPF DPF Segment Component Regeneration Regeneration to be
Control Operating Regime Cycle Order Monitored System Parameter A
as required sequential DPF closed-loop differential pressure
assembly across DPF assembly or its rate of change B as required
sequential segment closed-loop temperature or its rate of change
downstream of segment C as required sequential segment open-loop
duration of flow of syngas stream to each segment D as required
sequential DPF open-loop duration of flow of assembly syngas stream
to DPF assembly E continuous sequential segment closed-loop
temperature downstream of segment F continuous sequential segment
open-loop duration of flow of syngas stream to each segment G
periodic sequential segment open-loop duration of flow of syngas
stream to each segment H periodic sequential DPF open-loop duration
of flow of assembly syngas stream to DPF assembly I as required
sequential DPF closed-loop mass flow rate of assembly engine
exhaust stream
[0108] As the syngas stream exits conduit 143, 144, 145 or 146, and
enters a respective chamber created by baffle 122, the syngas
stream mixes with and is carried by a portion of the engine exhaust
stream through the respective segment of filter 121. The remaining
portion of the engine exhaust stream flows through the remaining
segments of filter 121, where particulates are trapped, exits DPF
assembly 120 and is then released to the atmosphere via exhaust
conduit 114. As the syngas stream and engine exhaust stream mixture
flows through a segment of filter 121 it undergoes combustion
reactions and heats the segment of filter 121, enhancing the
regeneration process. The combustion reactions can be promoted by a
catalyst (not shown in FIG. 8) within DPF assembly 120, for
example, on filter 121 or on a substrate upstream of filter 121.
Alternatively, the combustion reactions can occur without the use
of a catalyst, for example, through flame combustion by employing a
fuel burner and/or ignition source. A suitable mass flow rate and
volume of syngas is required to heat the segment to the desired
temperature for a predetermined period. During the regeneration
process, the particulates trapped in the segment of filter 121 are
oxidized and carried away from filter 121 and DPF assembly 120 via
conduit 114 to the atmosphere by the portion of the engine exhaust
stream. Controller 130 employing at least one programmed control
regime and/or signals received from various sensors, determines
when to terminate the regeneration process for the particular
segment(s) of filter 121 and sends a signal to valve 142. The
controller that controls regeneration of the filter can be
dedicated for that purpose or can be part of another controller,
for example, an overall engine control module.
[0109] In FIG. 8, exhaust after-treatment sub-system 101 can
optionally comprise one or more additional exhaust after-treatment
devices which at least periodically utilize a syngas stream (for
example, for regeneration and/or heating), The controller can
determine where the syngas is to be directed, and may need to
assign different priorities to the various devices and their
requirements or demands for syngas. For example, in a system with a
DPF and a lean NOx trap (LNT) the syngas stream can be preferably
directed by the controller in order of priority for:
[0110] (1) Regeneration process of DPF;
[0111] (2) De-sulfation process of LNT;
[0112] (3) Regeneration process of LNT.
[0113] Furthermore, syngas generator assembly 140 can from time to
time require a regeneration process which would be a higher
priority over the above stated processes.
[0114] The present filter segmentation designs and techniques have
the following potential commercial applications, end-uses and/or
markets (present and future): [0115] (1) Diesel engine retrofit
markets. [0116] (2) Diesel engine original equipment manufacturer
(OEM) markets. [0117] (3) Segmentation of lean NOx traps during
desulfation heating processes.
[0118] The fuel employed to regenerate the DPF can be another fuel
(other than syngas) for example diesel, gasoline, natural gas,
propane, ethanol, methanol or kerosene can be used.
[0119] The engine can be a lean burn combustion engine fueled by
suitable fuels, for example, diesel, fuel oil, kerosene, natural
gas, propane, liquefied petroleum gas (LPG), methanol, ethanol or
gasoline. The engine system can comprise additional devices which
utilize a syngas stream for example, a lean NOx trap, selective
catalytic reactor (SCR), diesel oxidation catalyst (DOC) and or a
fuel cell. A diverter valve can be used to selectively direct the
flow of syngas stream to such additional devices.
[0120] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood, that the invention is not limited thereto since
modifications can be made by those skilled in the art without
departing from the scope of the present disclosure, particularly in
light of the foregoing teachings.
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