U.S. patent application number 12/105776 was filed with the patent office on 2009-10-22 for enhanced aftertreatment apparatus regeneration using spatially controlled hydrogen-rich gas.
Invention is credited to Leslie Bromberg, Daniel Cohn, John B. Heywood, Victor Wong.
Application Number | 20090260350 12/105776 |
Document ID | / |
Family ID | 41199957 |
Filed Date | 2009-10-22 |
United States Patent
Application |
20090260350 |
Kind Code |
A1 |
Bromberg; Leslie ; et
al. |
October 22, 2009 |
ENHANCED AFTERTREATMENT APPARATUS REGENERATION USING SPATIALLY
CONTROLLED HYDROGEN-RICH GAS
Abstract
Regeneration system in which a hydrogen-rich gas from an onboard
reformer flows into an aftertreatment unit in a direction opposite
to the flow of engine exhaust to regenerate the unit. The
aftertreatment unit is segmented with independent regeneration
capability for each segment. Regeneration is performed with
hydrogen-rich gas produced by an onboard reformer. A hydrogen-rich
gas switchbox is used to direct the flow of the reformate to the
segment of the aftertreatment unit that is undergoing
regeneration.
Inventors: |
Bromberg; Leslie; (Sharon,
MA) ; Cohn; Daniel; (Cambridge, MA) ; Heywood;
John B.; (Newton, MA) ; Wong; Victor;
(Peabody, MA) |
Correspondence
Address: |
Patent Department;Attn: Sam Pasternack, Esq.
Choate, Hall & Stewart, LLP, Two International Place, Suite 34
Boston
MA
02110
US
|
Family ID: |
41199957 |
Appl. No.: |
12/105776 |
Filed: |
April 18, 2008 |
Current U.S.
Class: |
60/286 ; 60/274;
60/295 |
Current CPC
Class: |
F01N 3/36 20130101; F01N
2290/00 20130101; F01N 3/2073 20130101; C01B 2203/0883 20130101;
F01N 2610/14 20130101; C01B 3/34 20130101; F01N 2240/28 20130101;
C01B 2203/025 20130101; B01D 53/96 20130101; B01D 53/9431 20130101;
F01N 2240/30 20130101; C01B 2203/0861 20130101; F01N 2610/04
20130101; F01N 13/009 20140601; B01D 53/90 20130101; B01D 2251/202
20130101; F01N 3/0871 20130101; F01N 3/0253 20130101 |
Class at
Publication: |
60/286 ; 60/274;
60/295 |
International
Class: |
F01N 3/029 20060101
F01N003/029; F01N 3/023 20060101 F01N003/023 |
Claims
1) Regeneration system comprising: an exhaust aftertreatment unit
fitted to the exhaust of an internal combustion engine; and a fuel
reformer providing hydrogen-rich gas to the aftertreatment unit so
as to obtain spatially selective regeneration of the aftertreatment
unit; and including a hydrogen-rich gas switchbox having associated
valves and plumbing for controlling the flow of hydrogen-rich gas,
wherein the valves in the switchbox are used to direct the flow of
hydrogen-rich gas to the appropriate plumbing to regenerate the
associated section of the aftertreatment unit.
2) Regeneration system comprising: an exhaust aftertreatment unit
fitted to the exhaust of an internal combustion engine; and a fuel
reformer providing hydrogen-rich gas to the aftertreatment unit so
as to obtain spatially selective regeneration of the aftertreatment
unit wherein the engine exhaust is prevented from flowing in the
region being regenerated by the hydrogen-rich gas flowing in an
opposite direction to the exhaust flow.
3) The regeneration system of claims 1 or 2 wherein the
aftertreatment unit is segmented in sections that undergo
independent regeneration.
4) The system of claims 1 or 2 wherein the aftertreatment device is
a NOx trap.
5) The system of claims 1 or 2 wherein the aftertreatment device is
a diesel particulate filter.
6) The system of claim 2 further including a hydrogen-rich gas
switchbox having associated valves and plumbing for controlling the
flow of hydrogen-rich gas, wherein the valves in the switchbox are
used to direct the flow of hydrogen-rich gas to the appropriate
plumbing to regenerate the associated section of the aftertreatment
unit.
7) The system of claim 6 wherein the valves are butterfly
valves.
8) The system of claim 6 wherein the valves are poppet valves.
9) The system of claims 7 or 8 wherein the valves are actuated by
either vacuum or compressed air.
10) The system of claim 6 wherein the valves are sleeve valves.
11) The system of claim 10 wherein the sleeve valve is made of flat
surfaces, the moving part having one or more openings.
12) The system of claim 11 wherein the sleeve valve surfaces are
cylindrical shells with the moving part having one or more
openings.
13) The system of claim 11 wherein the moving part is driven by an
electromagnetic actuator.
14) The system of claim 5 wherein, during switching, there are two
or more partially or fully open valves.
15) The system of claims 1 or 2 further including at least one
regeneration sensor located upstream from the exhaust system, the
sensor or sensors monitoring either reformate compounds or
regeneration compounds.
16) The system of claims 1 or 2 wherein the fuel reformer operates
over a wide range of oxygen-to-carbon ratios, from below partial
oxidation to below full combustion.
17) The system of claims 1 or 2 wherein there is a heat exchanger
downstream from the reformer but upstream from the aftertreatment
unit.
18) The system of claim 4 wherein there is ammonia generated in the
region that is being regenerated by the hydrogen rich gas, the
ammonia re-entering other regions of the NOx trap that are not
being regenerated by the hydrogen rich gas.
19) The system of claims 1 or 2 wherein a lean NOx catalyst and an
SCR catalyst are both used and where the SCR catalyst is closer to
the engine, so that the hydrogen rich gas passes over the lean NOx
catalyst before it reaches the SCR catalyst.
20) The system of claims 1 or 2 wherein the fuel reformer is a
plasmatron fuel reformer.
Description
[0001] This application is related to U.S. pending application Ser.
No. 10/868,333 filed on Jun. 15, 2004.
BACKGROUND OF THE INVENTION
[0002] This invention relates to the regeneration of exhaust
aftertreatment devices and more particularly to spatially selective
regeneration of aftertreatment units.
[0003] U.S. pending application Ser. No. 10/868,333 discloses
spatial control of hydrogen-rich gas for improving the regeneration
of devices that clean engine exhaust. This application considered
particular aftertreatment devices--diesel particulate filters (DPF)
and NOx traps.
[0004] As taught in that application, the use of spatially
selective regeneration of aftertreatment units offers advantages in
relation to a decreased fuel penalty, increased options for
regeneration (oxidation/reducing environments, temperature
control), regeneration at reduced loading, increased reliability
from decreased temperatures during regeneration, decreased
temperature gradients, and in some cases, reduced thermal stress.
In addition, the use of spatially selective regeneration can reduce
catalyst cost by allowing the use of a one-leg rather than a
two-leg system with an exhaust valve. High catalyst cost is a key
issue in developing commercially attractive NOx trap systems.
[0005] There is therefore a need for optimization of a device that
can be used to direct the hydrogen-rich gas to a particular region
of the device for regeneration, and has the ability to selectively
direct the hydrogen-rich gas to different sections of the
aftertreatment device. It is also desirable to have a novel means
for determination of end-of-regeneration conditions.
SUMMARY OF THE INVENTION
[0006] In one aspect, the invention is a regeneration system
including an exhaust aftertreatment unit fitted to the exhaust of
an internal combustion engine and a fuel reformer providing
hydrogen-rich gas to the aftertreatment unit to spatially
non-uniformly regenerate the aftertreatment unit. In a preferred
embodiment, the aftertreatment unit is segmented into sections that
undergo independent regeneration. It is preferred that engine
exhaust be prevented from flowing in the region being regenerated
by arranging the hydrogen-rich gas to flow in a direction opposite
to that of the exhaust flow. Appropriate aftertreatment devices for
regeneration according to the invention includes diesel particulate
filters and NOx traps. An SCR/lean NOx trap device is another
device useful for cleaning exhaust, and included in aftertreatment
devices that can benefit from the present invention.
[0007] In a preferred embodiment, a hydrogen-rich gas switchbox
controls the flow of hydrogen-rich gas using appropriate valves and
plumbing to regenerate a desired section of an aftertreatment unit.
Suitable valves include butterfly valves, poppet valves and sleeve
valves. An electromagnetic actuator may be used to control the
valves. In yet another preferred embodiment, at least one
regeneration sensor is located upstream from the exhaust system to
monitor either reformate compounds or regeneration compounds. A
suitable fuel reformer is a plasmatron fuel reformer.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIGS. 1a and 1b are cross-sectional views of an embodiment
of the regeneration system disclosed herein.
[0009] FIG. 2 is a cross-sectional view of a schematic of an
embodiment of a hydrogen-rich gas switchbox for the selection of
flow through multiple outlets to direct hydrogen-rich gas to
specific sections of the aftertreatment unit.
[0010] FIG. 3 is a schematic illustration of an embodiment of the
system disclosed herein using a fuel reformer, a hydrogen-rich gas
switchbox and an aftertreatment unit.
[0011] FIGS. 4a and 4b are perspective and cross-sectional views,
respectively, of a hydrogen-rich gas box illustrating the use of a
flat sleeve valve.
[0012] FIG. 5 is a cross-sectional schematic illustration of an
embodiment of the invention using a sensor to monitor
end-of-regeneration conditions upstream from the aftertreatment
unit.
[0013] FIG. 6 is a cross-sectional view of an embodiment of the
invention including a sensor downstream from the aftertreatment
unit for monitoring end-of-regeneration conditions.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] During regeneration of NOx traps, it is desirable to
minimize the flow of exhaust through the section being regenerated.
Minimization of the exhaust flow is important to reduce additional
reductant that would be wasted by eliminating free oxygen present
in the exhaust flow before any reduction of the nitrogen oxides on
the catalyst can begin. A fuel penalty can be severely impacted by
the presence of even small levels of exhaust (which contain free
oxygen) in a NOx trap region being regenerated.
[0015] With reference first to FIG. 1a, an aftertreatment unit 10
includes a plurality of subsections as shown. The aftertreatment 10
unit may be a diesel particulate filter or an NOx trap. During
normal operation as shown in FIG. 1a, exhaust gas flows through the
individual subsections. When it is time to regenerate the
aftertreatment unit 10, reformate including a hydrogen-rich gas is
introduced through a pipe 12 into a first subsection 13 for
regeneration. The reformate flows in the opposite direction of an
exhaust gas thereby excluding substantially all of the exhaust gas
from the subsection 13 under regeneration. Each of the remaining
subsections can be regenerated in turn.
[0016] For regeneration of NOx traps, it is important to eliminate
as much free oxygen as possible. Co-flow (wherein hydrogen-rich gas
flows in the same direction as the exhaust) will introduce oxygen
into the stream. Counterflow in which hydrogen-rich gas is
introduced downstream from the unit in the opposite direction to
the exhaust flow prevents the entrainment of exhaust gas in the
segment of the aftertreatment section being regenerated as shown in
FIG. 1b. Counterflow decreases the fuel penalty for the
regeneration of NOx traps since hydrogen-rich gas is not wasted on
free oxygen in the exhaust flow.
[0017] With reference now to FIG. 2, a hydrogen switchbox 14
receives hydrogen-rich gas from a fuel reformer 16 that is
preferably a plasmatron fuel reformer. Valves 18, 20 and 22 control
the flow of hydrogen-rich gas through feed lines 24, 26 and 28. The
valves 18, 20 and 22 may be of a butterfly configuration, or they
can be poppet valves or sleeve valves. It is noted that any number
of valves and feed lines may be provided. The three valves in FIG.
2 are merely exemplary. Butterfly valves have the advantage of low
cost. A sleeve valve allows for a single moving unit with one or
more openings that when moved, redirects the flow of hydrogen-rich
gas to the appropriate feed lines or pipes. Sleeve valves minimize
the number of moving parts but have but a single control. Sleeve
valves require substantial motions of the moving part of the
valve.
[0018] FIG. 3 is another schematic illustration showing the
hydrogen-rich gas switchbox 14 receiving hydrogen-rich gas from the
reformer 16 and selectively introducing hydrogen-rich gas into the
aftertreatment unit 10 in a direction opposed to the exhaust gas
flow.
[0019] In order to minimize pressure fluctuations in the reformer
16, it is preferred to switch the flow between different pipes in a
manner in which two or more of the valves are open during the
switching as illustrated in FIGS. 4a and 4b. Valve overlap (wherein
more than one valve is open) minimizes high-speed flows across
narrow (near-closed or near-open) valves, that could result in
deposits or increased heat transfer through regions with high
turbulence because of the high flow speeds. Therefore, the
requirement of fast acting, but soft valve landing required for
engine valves is not needed, and valve motion control is not needed
to minimize noise or vibration. Simple pressurized air or vacuum
actuated valves can be used and are attractive for cost
minimization of the hydrogen-rich gas switchbox 14.
[0020] As shown in FIGS. 4a and 4b, sleeve valves 30 can be a flat
plate 32 with axial pipes, or it can be a cylindrical shell with a
radial pipe activated with angular motion. In the case of the
sleeve valve, overlap is achieved by proper sizing of a pipe
opening 34 and the moving element opening. It should be recognized
that there can be more than one opening in the plate.
[0021] In either case, a valve does not require large forces to
either actuate or close. Spring loaded valves, in the case of
butterfly or poppet valves, are sufficient. Since valve actuation
does not have to be particularly fast, the valves can be actuated
by vacuum or pressurized air as a means of decreasing the cost of
the hydrogen-rich gas switchbox 14.
[0022] In contrast to valves in an exhaust system in a two-leg
configuration that need to be very tight (having little leakage),
it is not required that the valves in the switchbox 14 be very
tight. If there is some leakage, the effect is a linear drop in
efficiency, with minimal effect on any fuel penalty. This situation
is in sharp contrast to a valve in a exhaust system in which a
small leakage may require substantial amounts of hydrogen-rich gas
to combust the free oxygen, much larger than the amount of
hydrogen-rich gas required to regenerate a catalyst in the
aftertreatment unit 10.
[0023] As the duty cycle of each valve is relatively small (at
most, if the reformer is on all the time, the duty cycle is the
inverse of the number of valves), the temperature of the valves can
be maintained sufficiently low to minimize the temperature
requirements of the unit. The use of low temperature valves is
useful for cost minimization of the hydrogen switchbox 14. However,
there can be times, for example, during de-sulfation cycles in
which the temperature of the valves can be high. However, the
number of de-sulfation cycles is typically much smaller than that
of trap regeneration.
[0024] It may be desirable to decrease the temperature of the
reformate before introduction into the aftertreatment unit. A heat
exchanger can be introduced between the reformer and the
aftertreatment unit. One advantage of the decreased temperature is
that thermal stresses in the aftertreatment unit during
regeneration can be decreased. The heat exchanger can be
gas-to-air, gas-to-exhaust, or gas-to-liquid. The heat exchanger
can be incorporated into the reformer, the hydrogen switch box or
placed in-between the reformer and the hydrogen rich box.
[0025] In another embodiment, the reformer can operate over a wide
range of oxygen-to-carbon ratios. Partial oxidation is defined when
the oxygen atoms' flow rate in the air to the reformer is the same
as that of the carbon atoms' flow rate in the fuel to the reformer.
Full combustion is defined as when the fuel is fully combusted with
no excess oxygen (stoichiometric combustion). In the case when the
reformer operates with high oxygen-to-carbon ratios, the hydrogen
yield is decreased but the reformer is at higher temperatures,
which may be advantageous for some applications. On the other hand,
operating at oxygen-to-carbon ratios below partial oxidation may
generate lower temperatures, at the expense of hydrogen flow rate.
Operation with some oxygen in the reformer for the generation of
some oxygen is however desired. The reformer may use the engine
exhaust, which for diesel engines or lean burn gasoline engines has
free oxygen, as well as air, as the fuel oxidizer.
[0026] In still another embodiment, the conditions in the region of
the NOx trap can be sufficiently rich that ammonia is generated in
the region being regenerated. The ammonia thus produced is then
used in the other regions that are not being directly regenerated
by the hydrogen rich gas. This embodiment is allowed because of the
counterflow direction of the of hydrogen rich gas with respect to
the direction of the exhaust flow. In this embodiment, the catalyst
formulation optimized for lean NOx should be closer to the exhaust,
and the catalyst formulation optimized for an SCR catalyst should
be closer to the engine side. In this manner, the hydrogen rich gas
travels over the lean NOx catalyst before it reaches the SCR
catalyst. Under some conditions it would be preferred that the
amount of hydrogen rich gas be adjusted so that little hydrogen
rich gas survives past the lean NOx catalyst.
[0027] High temperature of the reformate results in substantial gas
speeds at the end of the pipe that carries the reformate to an NOx
trap. High speed is needed in order to provide the effect of a
gas-dynamic valve, wherein the reverse flowing reformate excludes
exhaust from the section being regenerated thereby eliminating any
free oxygen. The reformate reverse flow has enough momentum to stop
the exhaust flow.
[0028] It is preferred to provide sensors to determine when the
regeneration has been completed. As shown in FIGS. 5 and 6, a
sensor 40 can be placed in one of two places, either upstream from
the aftertreatment unit 10 (on the side of the aftertreatment
device 10 that is closest to an engine as shown in FIG. 5) or it
can be placed downstream from the aftertreatment unit 10 on the
same side of the aftertreatment unit wherein the hydrogen-rich gas
is introduced as shown in FIG. 6. The sensor 40 can be a chemical
sensor for sensing one or more of the compounds from the reformer
16 (hydrogen, CO) or for sensing one or more of the compounds
resulting from the regeneration process.
[0029] It is recognized that modifications and variations of the
invention disclosed herein will be apparent to those of ordinary
skill in the art and it is intended that all such modifications and
variations be included within the scope of the appended claims.
* * * * *