U.S. patent application number 12/546994 was filed with the patent office on 2011-03-03 for partial coating of platinum group metals on filter for increased soot mass limit and reduced costs.
This patent application is currently assigned to International Engine Intellectual Property Company, LLC. Invention is credited to Brad J. Adelman, Shyam Santhanam, Vadim Strots.
Application Number | 20110047992 12/546994 |
Document ID | / |
Family ID | 43383644 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110047992 |
Kind Code |
A1 |
Adelman; Brad J. ; et
al. |
March 3, 2011 |
PARTIAL COATING OF PLATINUM GROUP METALS ON FILTER FOR INCREASED
SOOT MASS LIMIT AND REDUCED COSTS
Abstract
A diesel particulate filter has a thin band of washcoated filter
material either on the inlet of the upstream side or the outlet of
the downstream side. The washcoating is with platinum group metals
(PGM), e.g., Pt and Pd added to the surface and pore structure of a
DPF. The PDF should provide comparable or improved distance between
active regeneration and/or should prevent HC/CO slip during active
DPF regeneration.
Inventors: |
Adelman; Brad J.; (Chicago,
IL) ; Strots; Vadim; (Forest Park, IL) ;
Santhanam; Shyam; (Aurora, IL) |
Assignee: |
International Engine Intellectual
Property Company, LLC
Warrenville
IL
|
Family ID: |
43383644 |
Appl. No.: |
12/546994 |
Filed: |
August 25, 2009 |
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
F01N 3/035 20130101;
B01D 53/9454 20130101; B01D 53/9472 20130101; F01N 2370/02
20130101; F01N 2510/0682 20130101; F01N 13/0097 20140603; B01D
2255/9032 20130101; F01N 3/0231 20130101; Y02T 10/22 20130101; B01D
2255/1023 20130101; Y02T 10/12 20130101; F01N 13/009 20140601; F01N
3/106 20130101; B01D 2255/1021 20130101 |
Class at
Publication: |
60/299 |
International
Class: |
F01N 3/28 20060101
F01N003/28 |
Claims
1. A diesel particulate filter, comprising: a housing having an
inlet and an outlet and containing a diesel particulate filter
material therein wherein a band of said filter material includes a
washcoat with platinum group metals added to the surface and pore
structure of the filter material.
2. The diesel particulate filter according to claim 1, wherein said
band is located adjacent to said inlet.
3. The diesel particulate filter according to claim 1, wherein said
band is located adjacent to said outlet.
4. The diesel particulate filter according to claim 1, wherein said
platinum group metals comprises at least one metal selected from Pt
and Pd.
5. An exhaust gas after treatment system for a diesel engine,
comprising: a containment defining a flow path for exhaust gas; a
diesel oxidation catalyst unit arranged in the flow path; a diesel
particulate filter unit arranged in the flow path downstream of the
diesel oxidation unit, wherein the diesel particulate filter
comprises a housing having an inlet and an outlet and containing a
diesel particulate filter material therein wherein a band of said
filter material includes a washcoat with platinum group metals
added to the surface and pore structure of the filter.
6. The diesel particulate filter according to claim 5, wherein said
band is located adjacent to said inlet.
7. The diesel particulate filter according to claim 6, wherein said
platinum group metals comprises at least one metal selected from Pt
and Pd.
8. The diesel particulate filter according to claim 5, wherein said
band is located adjacent to said outlet.
9. The diesel particulate filter according to claim 8, wherein said
platinum group metals comprises at least one metal selected from Pt
and Pd.
10. The diesel particulate filter according to claim 5, wherein
said platinum group metals comprises at least one metal selected
from Pt and Pd.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to motor vehicles, such as
trucks, that are powered by internal combustion engines,
particularly diesel engines that have exhaust gas treatment devices
for treating exhaust gases passing through their exhaust
systems.
BACKGROUND OF THE INVENTION
[0002] A known system for treating exhaust gas passing through an
exhaust system of a diesel engine comprises a diesel oxidation
catalyst (DOC) that oxidizes hydrocarbons (HC) to CO2 and H2O and
converts NO to NO2 , and a diesel particulate filter (DPF) that
traps diesel particulate matter (DPM). DPM includes soot or carbon,
the soluble organic fraction (SOF), and ash (i.e. lube oil
additives etc.). The DPF is located downstream of the DOC in the
exhaust gas flow. The combination of these two exhaust gas
treatment devices prevents significant amounts of pollutants such
as hydrocarbons, carbon monoxide, soot, SOF, and ash, from entering
the atmosphere. The trapping of DPM by the DPF prevents black smoke
from being emitted from a vehicle's exhaust pipe.
[0003] The DOC oxidizes hydrocarbons (HC) and converts NO to NO2 .
The organic constituents of trapped DPM within the DPF, i.e.,
carbon and SOF, are oxidized within the DPF, using the NO2
generated by the DOC, to form CO2 and H2O, which can then exit the
exhaust pipe to atmosphere.
[0004] The rate at which trapped carbon is oxidized to CO2 is
controlled not only by the concentration of NO2 or O2 but also by
temperature. Specifically, there are three important temperature
parameters for a DPF.
[0005] The first temperature parameter is the oxidation catalyst's
"light off" temperature, below which catalyst activity is too low
to oxidize HC. Light off temperature is typically around
180-200.degree. C.
[0006] The second temperature parameter controls the conversion of
NO to NO2 . This NO conversion temperature spans a range of
temperatures having both a lower bound and an upper bound, which
are defined as the minimum temperature and the maximum temperature
at which 40% or greater NO conversion is achieved. The conversion
temperature window defined by those two bounds extends from
approximately 250.degree. C. to approximately 450.degree. C.
[0007] The third temperature parameter is related to the rate at
which carbon is oxidized in the filter. Reference sources in
relevant literature call that temperature the "Balance Point
Temperature" (or BPT). It is the temperature at which the rate of
oxidation of particulate, also sometimes referred to as the rate of
DPF regeneration, is equal to the rate of accumulation of
particulate. The BPT is one of the parameters that determines the
ability of a DPF to enable a diesel engine to meet expected
tailpipe emissions laws and/or regulations.
[0008] Typically, a diesel engine runs relatively lean and
relatively cool compared to a gasoline engine. That factor makes
natural achievement of BPT problematic.
[0009] Therefore, a DPF requires regeneration from time to time in
order to maintain particulate trapping efficiency. Regeneration
involves the presence of conditions that will burn off trapped
particulates whose unchecked accumulation would otherwise impair
DPF effectiveness. While "regeneration" refers to the general
process of burning off DPM, two particular types of regeneration
are recognized by those familiar with the regeneration technology
as presently being applied to motor vehicle engines.
[0010] "Passive regeneration" is generally understood to mean
regeneration that can occur anytime that the engine is operating
under conditions that burn off DPM without initiating a specific
regeneration strategy embodied by algorithms in an engine control
system. "Active regeneration" is generally understood to mean
regeneration that is initiated intentionally, either by the engine
control system on its own initiative or by the driver causing the
engine control system to initiate a programmed regeneration
strategy, with the goal of elevating temperature of exhaust gases
entering the DPF to a range suitable for initiating and maintaining
burning of trapped particulates.
[0011] Active regeneration may be initiated even before a DPF
becomes loaded with DPM to an extent where regeneration would be
mandated by the engine control system on its own. When DPM loading
beyond that extent is indicated to the engine control system, the
control system forces active regeneration, and that is sometimes
referred to simply as a forced regeneration.
[0012] The creation of conditions for initiating and continuing
active regeneration, whether forced or not, generally involves
elevating the temperature of exhaust gas entering the DPF to a
suitably high temperature.
[0013] There are several methods for initiating a forced
regeneration of a DPF such as retarding the start of main fuel
injections or post-injection of diesel fuel to elevate exhaust gas
temperatures entering the DPF while still leaving excess oxygen for
burning the trapped particulate matter. Post-injection may be used
in conjunction with other procedures and/or devices for elevating
exhaust gas temperature to the relatively high temperatures needed
for active DPF regeneration.
[0014] These methods are able to increase the exhaust gas
temperature sufficiently to elevate the catalyst's temperature
above catalyst "light off" temperature and provide excess HC that
can be oxidized by the catalyst. Such HC oxidation provides the
necessary heat to raise the temperature in the DPF above the
BPT.
[0015] However, during such short rich operation, the exhaust gas
in enriched with hydrocarbons (HC) and carbon monoxide (CO) while
the oxygen concentration in the exhaust gas is drastically
depleted.
[0016] The amount of HC and CO generated by the engine during the
rich operation typically exceeds the stoichiometric quantity of NOx
that is to be reduced over the catalyst. This excess of reductant,
while necessary for high NOx reduction efficiencies, leads to HC
and CO breakthroughs at the DOC outlet ("HC/Co slip"), wherein the
HC/CO slip cannot be oxidized to CO2 and H2O.
[0017] Traditional coated DPF have a washcoat throughout the filter
to prevent HC/CO slip and increased emissions. However, a coated
DPF has a lower soot-mass-limit to prevent deactivation of the
catalyst from high bed temperatures generated during active
regeneration.
[0018] Uncoated DPF are used in conjunction with a DOC and operated
in a passive manner (no active filter regeneration) or if used with
an active regeneration then have a reduced rate of passive
regeneration compared to a coated filter or have an increased risk
of HC/CO slip. The time elapsed between active filter regeneration
is decreased as a result of the lower rate of passive soot
oxidation.
SUMMARY
[0019] The disclosed embodiments of the invention provide a DPF
which has a thin band of washcoated filter material either on the
inlet of the upstream side or the outlet of the downstream side.
The washcoating is with platinum group metals (PGM), e.g., Pt and
Pd added to the surface and pore structure of a DPF. The PDF should
provide comparable or improved distance between active regeneration
and/or should prevent HC/CO slip during active DPF regeneration.
The embodiments of the invention should also reduce the cost of the
after treatment system by minimizing the PGM applied to the filter.
The after treatment system should operate and function in the same
manner as a fully coated DPF although the interval between active
regeneration could be increased or alternatively the size of the
filter can be reduced.
[0020] According to a first embodiment, a coating of platinum group
metals (PGM), e.g., Pt and Pd is applied to the surface and pore
structure of a relatively thin band of filter media within an inlet
portion of the DPF media on the upstream side. Due to the presence
of the coating, additional NO2 can thus be formed and therefore
increase the rate of passive regeneration. In addition, since the
coating is only on a front portion of the filter, it will be able
to burn any HC/CO slip from the DOC during active regeneration
while not being exposed to the exotherm from burning the HC/CO slip
coupled with the burning of the storage soot on the filter. It is
known that the temperature rise within the DPF is greater towards
the rear of the DPF as opposed to the front. This exotherm becomes
pronounced in situations where regeneration has been initiated but
then is quickly interrupted (e.g. drop-to-idle). By having the
coating only at the front of the filter, it will be possible to
minimize HC/CO slip, maintain passive regeneration and increase the
soot-mass-limit of the filter.
[0021] According to a second embodiment, a coating of platinum
group metals (PGM), e.g., Pt and Pd is applied to the surface and
pore structure of a relatively thin band of filter media within an
outlet portion of the DPF media on the downstream side. Although
this will not increase the rate of passive regeneration other than
that from the DOC, it will allow for HC/CO slip mitigation during
active regeneration. Since the coating is on the downstream side,
HC/CO will be in contact with a catalyst even if it traverses the
filter wall toward the inlet. Also, since the coating will not be
in direct contact with soot, there will not be any accelerated soot
burn during conditions such as drop-to-idle. This in turn will
minimize the peak bed temperature and prevent ring-cracking,
pitting or melting which could occur if the coating was on the
upstream side and in contact with the soot. Though this
configuration will be exposed to higher peak temperatures than if
the coating was placed on the inlet of the DPF on the upstream
side, the impact will not be as pronounced since this configuration
is not relying on the coating to perform, enhance or promote
passive regeneration. The function of the washcoat in this
configuration is to burn any HC/CO slip during active
regeneration.
[0022] Numerous other advantages and features of the present
invention will be become readily apparent from the following
detailed description of the invention and the embodiments thereof,
from the claims and from the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic illustration of a representative
diesel engine and control with an exhaust after-treatment
device;
[0024] FIG. 2 is a schematic sectional view of a first embodiment
DPF of the invention; and
[0025] FIG. 3 is a schematic sectional view of a second embodiment
DPF of the invention.
DETAILED DESCRIPTION
[0026] While this invention is susceptible of embodiment in many
different forms, there are shown in the drawings, and will be
described herein in detail, specific embodiments thereof with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the invention to the specific embodiments
illustrated.
[0027] FIG. 1 shows a schematic diagram of an exemplary diesel
engine 20 for powering a motor vehicle. Engine 20 has a
processor-based engine control system 22 that processes data from
various sources to develop various control data for controlling
various aspects of engine operation. The data processed by control
system 22 may originate at external sources, such as sensors,
and/or be generated internally.
[0028] Control system 22 includes an injector driver module 24 for
controlling the operation of electric-actuated fuel injectors 26
that inject fuel into combustion chambers in the engine cylinder
block 28. A respective fuel injector 26 is associated with each
cylinder and comprises a body that is mounted on the engine and has
a nozzle through which fuel is injected into the corresponding
engine cylinder. A processor of engine control system 22 can
process data sufficiently fast to calculate, in real time, the
timing and duration of injector actuation to set both the timing
and the amount of fueling.
[0029] Engine 20 further comprises an intake system having an
intake manifold 30 mounted on block 28. An intercooler 32 and a
compressor 34 of a turbocharger 36 are upstream of manifold 30.
Compressor 34 draws air through intercooler 32 to create charge air
that enters each engine cylinder from manifold 30 via a
corresponding intake valve that opens and closes at proper times
during engine cycles.
[0030] Engine 20 also comprises an exhaust system through which
exhaust gases created by combustion within the engine cylinders can
pass from the engine to atmosphere. The exhaust system comprises an
exhaust manifold 38 mounted on block 28. Exhaust gases pass from
each cylinder into manifold 38 via a respective exhaust valve that
opens and closes at proper times during engine cycles.
[0031] Turbocharging of engine 20 is accomplished by turbocharger
36 that further comprises a turbine 40 associated with the exhaust
system and coupled via a shaft to compressor 34. Hot exhaust gases
acting on turbine 40 cause the turbine to operate compressor 34 to
develop the charge air that provides boost for engine 20.
[0032] The exhaust system further comprises a DOC 41 and DPF 42
downstream of turbine 40 for treating exhaust gas before it passes
into the atmosphere through an exhaust pipe 44. Although the DOC 41
and the DPF 42 are shown as separate components, it is also
possible that the DOC 41 and the DPF 42 share a common housing.
[0033] DPF 42 physically traps a high percentage of DPM in exhaust
gas passing through it, preventing the trapped DPM from passing
into the atmosphere. Oxidation catalyst 46 within the DOC 41
oxidizes hydrocarbons (HC) in the incoming exhaust gas to CO2 and
H2O and converts NO to NO2 . The NO2 is then used to reduce the
carbon particulates trapped in DPF 42.
[0034] With regard to passive and active regeneration as mentioned
above, U.S. Pat. No. 6,829,890; and U.S. Published Patent
Applications 2008/0184696 and 2008/0093153 describe systems and
methods for undertaking regeneration. These patents and
publications are herein incorporated by reference.
[0035] A first embodiment DPF 42 is shown in FIG. 2. The DPF
includes a housing 47 having an inlet 48 and an outlet 49 and
containing a filter media or filter material throughout. The filter
media is composed of (but not limited to) cordierite, silicon
carbide, aluminum titanate, mullite or other porous ceramic
material, or woven metal or ceramic fibers.
[0036] Ceramic or refractory materials for diesel particulate
filters are described in U.S. Pat. Nos. 6,942,708; 4,510,265; and
4,758,272, herein incorporated by reference.
[0037] A washcoat 54 of platinum group metals (PGM), e.g., Pt and
Pd is applied to the surface and pore structure of a relatively
thin band 55 of filter media 50 within an inlet portion of the DPF
media on the upstream side of the DPF 42. The relatively thin band
55 can be up to about 25% of the length of the media 50.
[0038] Due to the presence of the PGM, additional NO2 can thus be
formed and therefore increase the rate of passive regeneration
within the DPF 42. In addition, since the coating 54 is only on a
front portion of the DPF 42, it will be able to burn any HC/CO slip
from the DOC during active regeneration while not being exposed to
the exotherm from burning the HC/CO slip coupled with the burning
of the storage soot on the filter. It is known that the temperature
rise within the DPF is greater towards the rear of the DPF as
opposed to the front. This exotherm becomes pronounced in
situations where regeneration has been initiated but then is
quickly interrupted (e.g. drop-to-idle). By having the coating only
at the front of the filter, it will be possible to minimize HC/CO
slip, maintain passive regeneration and increase the
soot-mass-limit of the filter.
[0039] The maximum bed temperature should be limited so that the
PGM does not sinter excessively. Also, the interaction between the
washcoat and filter material may lead to lower tolerance to thermal
events (peak bed temperature, axial/radial thermal gradient). In
order to prevent excessive PGM sintering or filter failure induced
from the washcoat-filter material interaction, the soot mass limit
(SML) can be lowered so that an active DPF regeneration event is
commanded more frequently for equivalent volume of filter.
[0040] A second embodiment DPF 42a is shown in FIG. 3. A washcoat
64 of platinum group metals (PGM), e.g., Pt and Pd is applied to
the surface and pore structure of a relatively thin band 65 of
filter media 50 within an outlet portion of the DPF media on the
downstream side of the DPF 42. The relatively thin band 55 can be
up to about 25% of the length of the media 50. Although this will
not increase the rate of passive regeneration over that generated
by the DOC, it will allow for HC/CO slip mitigation during active
regeneration. Since the coating is on the downstream side, HC/CO
will be in contact with a catalyst even if it traverses the
filter.
[0041] Also, since the coating 64 will not be in direct contact
with soot, there will not be any accelerated soot burn during
conditions such as drop-to-idle. This in turn should minimize the
peak bed temperature and prevent ring-cracking, pitting or melting.
Though the coating of this embodiment will be exposed to higher
peak temperatures than if the coating was placed on the inlet of
the DPF on the upstream side, this should not be detrimental since
this coating is not intended to perform, enhance or promote passive
regeneration. The function of the washcoat in this configuration is
to burn any HC/CO slip during active regeneration.
[0042] From the foregoing, it will be observed that numerous
variations and modifications may be effected without departing from
the spirit and scope of the invention. It is to be understood that
no limitation with respect to the specific apparatus illustrated
herein is intended or should be inferred.
* * * * *