U.S. patent application number 13/423565 was filed with the patent office on 2013-09-19 for exhaust gas treatment system having a solid ammonia gas producing material.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is Joshua Clifford Bedford, Eugene V. Gonze, Chang H. Kim, Michael J. Paratore, JR.. Invention is credited to Joshua Clifford Bedford, Eugene V. Gonze, Chang H. Kim, Michael J. Paratore, JR..
Application Number | 20130239554 13/423565 |
Document ID | / |
Family ID | 49044159 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130239554 |
Kind Code |
A1 |
Gonze; Eugene V. ; et
al. |
September 19, 2013 |
EXHAUST GAS TREATMENT SYSTEM HAVING A SOLID AMMONIA GAS PRODUCING
MATERIAL
Abstract
An exhaust gas treatment system for an internal combustion
engine is provided, including an exhaust gas conduit, a pressurized
vessel, a selective catalytic reduction ("SCR") device, and a
control module. The internal combustion engine has a plurality of
pistons and an engine off condition that indicates that the pistons
are generally stationary. The exhaust gas conduit is in fluid
communication with, and configured to receive an exhaust gas from
the internal combustion engine. The pressurized vessel stores a
solid ammonia gas producing material. The pressurized vessel is
selectively activated to heat the solid ammonia gas producing
material into an ammonia gas. The ammonia gas is released into the
exhaust gas conduit. The SCR device is in fluid communication with
the exhaust gas conduit and is configured to receive the ammonia
gas.
Inventors: |
Gonze; Eugene V.; (Pinckney,
MI) ; Paratore, JR.; Michael J.; (Howell, MI)
; Bedford; Joshua Clifford; (Farmington Hills, MI)
; Kim; Chang H.; (Rochester, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gonze; Eugene V.
Paratore, JR.; Michael J.
Bedford; Joshua Clifford
Kim; Chang H. |
Pinckney
Howell
Farmington Hills
Rochester |
MI
MI
MI
MI |
US
US
US
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
49044159 |
Appl. No.: |
13/423565 |
Filed: |
March 19, 2012 |
Current U.S.
Class: |
60/286 ;
60/287 |
Current CPC
Class: |
F01N 2610/12 20130101;
Y02T 10/12 20130101; F01N 3/2013 20130101; F01N 3/208 20130101;
F01N 3/103 20130101; F01N 2610/06 20130101; F01N 3/2066 20130101;
Y02T 10/24 20130101; Y02T 10/26 20130101; F01N 3/2026 20130101;
F01N 2900/1808 20130101 |
Class at
Publication: |
60/286 ;
60/287 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1. An exhaust gas treatment system for an internal combustion
engine, the internal combustion engine having a plurality of
pistons and an engine off condition that indicates that the
plurality of pistons are generally stationary, comprising: an
exhaust gas conduit in fluid communication with, and configured to
receive an exhaust gas from the internal combustion engine during
operation; a pressurized vessel storing a solid ammonia gas
producing material, the pressurized vessel selectively activated to
heat the solid ammonia gas producing material into an ammonia gas,
the ammonia gas being released into the exhaust gas conduit; a
selective catalytic reduction ("SCR") device in fluid communication
with the exhaust gas conduit and configured to receive the ammonia
gas, the SCR device having a SCR temperature profile and a SCR
light-off temperature; a control module in communication with the
internal combustion engine and the pressurized vessel, the control
module receiving a signal indicating the engine off condition, the
control module including a memory for storing a value indicating a
target amount of the ammonia gas released into the exhaust gas
conduit by the pressurized vessel and loaded on the SCR device, the
control module comprising: a control logic for determining if the
internal combustion engine is in the engine off condition based on
the signal; a control logic for determining the SCR temperature
profile; a control logic for determining if the SCR temperature
profile is below a threshold value if the internal combustion
engine is in the engine off condition, the threshold value
indicating that the SCR device is a specified amount below the SCR
light-off temperature; a control logic for determining if the
pressurized vessel has released the target amount of the ammonia
gas into the exhaust gas conduit if the SCR temperature profile is
below the threshold value; and a control logic for deactivating the
pressurized vessel if the pressurized vessel has released the
target amount of the ammonia gas.
2. The exhaust gas treatment system of claim 1, wherein the control
module includes control logic for monitoring a pressure transducer
that indicates pressure located internally of the pressure vessel,
and wherein the pressure vessel internally attains a threshold
pressure.
3. The exhaust gas treatment system of claim 2, wherein the control
module includes control logic for activating the pressurized vessel
if the threshold pressure is attained, and if the pressurized
vessel has not released the target amount of the ammonia gas into
the exhaust gas conduit.
4. The exhaust gas treatment system of claim 2, wherein the
threshold pressure creates the gas propagation required for
creating a gas propagation needed to create the target amount of
ammonia gas released into the exhaust gas conduit that is loaded on
the SCR device.
5. The exhaust gas treatment system of claim 1, wherein the target
amount of ammonia gas is an amount needed to create a saturation
amount of ammonia gas that is stored by the SCR device, and wherein
the saturation amount represents a maximum amount of ammonia gas
the SCR device is capable of storing.
6. The exhaust gas treatment system of claim 1, further comprising
an electrically heated catalyst ("EHC") device in fluid
communication with the exhaust gas conduit and configured to
receive the exhaust gas during operation of the internal combustion
engine, and selectively activated to produce heat and induce
oxidation of the exhaust gas, the EHC device having an oxidation
catalyst compound disposed thereon for converting nitrogen oxide
("NO") to nitrogen dioxide ("NO.sub.2").
7. The exhaust gas treatment system of claim 6, further comprising
an oxidation catalyst ("OC") device in fluid communication with the
exhaust gas conduit, the OC device having a front face, the OC
device adsorbing hydrocarbons and selectively activated to induce
oxidation of the hydrocarbons in the exhaust gas during operation
of the internal combustion engine, wherein the EHC device is
located within the OC device.
8. The exhaust gas treatment system of claim 7, wherein at least
one of the EHC device and the OC device has an oxidation catalyst
compound disposed thereon that is one of Palladium ("Pd"), Platinum
("Pt"), and perovskite.
9. The exhaust gas treatment system of claim 7, wherein the control
module includes control logic for selectively activating the EHC
depending on if the SCR device has achieved the light-off
temperature during operation of the internal combustion engine.
10. The exhaust gas treatment system of claim 1, further comprising
a first temperature sensor and a second temperature sensor in fluid
communication with the exhaust gas conduit, the first temperature
sensor situated upstream of the SCR device and the second
temperature sensor situated downstream of the SCR device.
11. The exhaust gas treatment system of claim 10, wherein the
control module includes control logic for monitoring the first
temperature sensor and the second temperature sensor, and a control
logic for calculating the SCR temperature profile based on signals
from the first temperature sensor and the second temperature
sensor.
12. The exhaust gas treatment system of claim 1, further comprising
an ignition switch, wherein the ignition switch sends the signal to
the control module that is indicative of the engine off
condition.
13. An exhaust gas treatment system for an internal combustion
engine, the internal combustion engine having a plurality of
pistons and an engine off condition that indicates that the
plurality of pistons are generally stationary, comprising: an
exhaust gas conduit in fluid communication with, and configured to
receive an exhaust gas from the internal combustion engine during
operation; a pressurized vessel storing a solid ammonia gas
producing material, the pressurized vessel selectively activated to
heat the solid ammonia gas producing material into an ammonia gas,
the ammonia gas being released into the exhaust gas conduit, the
pressure vessel configured for internally attaining a threshold
pressure; a pressure transducer that indicates pressure located
internally of the pressure vessel; a SCR device in fluid
communication with the exhaust gas conduit and configured to
receive the ammonia gas, the SCR device having a SCR temperature
profile and a SCR light-off temperature; an ignition switch that
sends a signal that is indicative of the engine off condition; and
a control module in communication with the internal combustion
engine, the pressurized vessel, the pressure transducer, and the
ignition switch, the control module including a memory for storing
a value indicating a target amount of the ammonia gas released into
the exhaust gas conduit by the pressurized vessel and loaded on the
SCR device, the control module comprising: a control logic for
monitoring the ignition switch for the signal, wherein the control
module includes control logic for determining if the internal
combustion engine is in the engine off condition based on the
signal; a control logic for determining the SCR temperature
profile; a control logic for determining if the SCR temperature
profile is below a threshold value if the internal combustion
engine is in the engine off condition, the threshold value
indicating that the SCR device is a specified amount below the SCR
light-off temperature; a control logic for determining if the
pressurized vessel has released the target amount of the ammonia
gas into the exhaust gas conduit if the SCR temperature profile is
below the threshold value; a control logic for deactivating the
pressurized vessel if the pressurized vessel has released the
target amount of the ammonia gas; a control logic for monitoring
the pressure transducer for pressure located internally of the
pressure vessel; and a control logic for activating the pressurized
vessel if the threshold pressure is attained, and if the
pressurized vessel has not released the target amount of the
ammonia gas into the exhaust gas conduit.
14. The exhaust gas treatment system of claim 13, wherein the
threshold pressure creates the gas propagation required for
creating a gas propagation needed to create the target amount of
ammonia gas released into the exhaust gas conduit that is loaded on
the SCR device.
15. The exhaust gas treatment system of claim 13, wherein the
target amount of ammonia gas is an amount needed to create a
saturation amount of ammonia gas that is stored by the SCR device,
and wherein the saturation amount represents a maximum amount of
ammonia gas the SCR device is capable of storing.
16. The exhaust gas treatment system of claim 13, further
comprising an EHC device in fluid communication with the exhaust
gas conduit and configured to receive the exhaust gas, and
selectively activated to produce heat and induce oxidation of the
exhaust gas during operation of the internal combustion engine, the
EHC device having an oxidation catalyst compound disposed thereon
for converting nitrogen oxide NO to nitrogen dioxide NO.sub.2.
17. The exhaust gas treatment system of claim 16, further
comprising an OC device in fluid communication with the exhaust gas
conduit, the OC device having a front face, the OC device adsorbing
hydrocarbons and selectively activated to induce oxidation of the
hydrocarbons in the exhaust gas during operation of the internal
combustion engine, wherein the EHC device is located within the OC
device.
18. The exhaust gas treatment system of claim 17, wherein at least
one of the EHC device and the OC device has an oxidation catalyst
compound disposed thereon that is one of Palladium Pd, Platinum Pt,
and perovskite.
19. The exhaust gas treatment system of claim 13, further
comprising a first temperature sensor and a second temperature
sensor in fluid communication with the exhaust gas conduit, the
first temperature sensor situated upstream of the SCR device and
the second temperature sensor situated downstream of the SCR
device.
20. The exhaust gas treatment system of claim 19, wherein the
control module includes control logic for monitoring the first
temperature sensor and the second temperature sensor, and a control
logic for calculating the SCR temperature profile based on signals
from the first temperature sensor and the second temperature
sensor.
Description
FIELD OF THE INVENTION
[0001] Exemplary embodiments of the invention relate to exhaust gas
treatment systems for internal combustion engines and, more
particularly, to an exhaust gas treatment system having a
pressurized vessel that is selectively activated to heat a solid
ammonia gas producing material into an ammonia gas.
BACKGROUND
[0002] The exhaust gas emitted from an internal combustion engine,
particularly a diesel engine, is a heterogeneous mixture that
contains gaseous emissions such as carbon monoxide ("CO"), unburned
hydrocarbons ("HC") and oxides of nitrogen ("NO.sub.x") as well as
condensed phase materials (liquids and solids) that constitute
particulate matter ("PM"). Catalyst compositions typically disposed
on catalyst supports or substrates are provided in an engine
exhaust system to convert certain, or all of these exhaust
constituents into non-regulated exhaust gas components.
[0003] One type of exhaust treatment technology for reducing CO and
HC emissions is an oxidation catalyst device ("OC"). The OC device
includes a flow-through substrate and a catalyst compound applied
to the substrate. One type of exhaust treatment technology for
reducing NO.sub.x emissions is a selective catalytic reduction
("SCR") device that may be positioned downstream of the OC device.
The SCR device includes a substrate, having a SCR catalyst compound
applied to the substrate.
[0004] In one approach, a reductant is typically sprayed into hot
exhaust gases upstream of the SCR device. The reductant may be an
aqueous urea solution that decomposes to ammonia ("NH.sub.3") in
the hot exhaust gases and is adsorbed by the SCR device. The
ammonia then reduces the NO.sub.x to nitrogen in the presence of
the SCR catalyst. However, the SCR device also needs to reach a
threshold or light-off temperature to effectively reduce NO.sub.x.
During a cold start of the engine, the SCR device has not attained
the respective light-off temperature, and therefore generally may
not effectively remove NO.sub.x from the exhaust gases.
[0005] Several drawbacks may exist when spraying an aqueous urea
solution into the exhaust gas. For example, the tanks that store
the aqueous urea may be heavy and bulky, and therefore add weight
and cost to a vehicle. Also, during certain operating conditions,
such as low ambient temperatures, the aqueous urea solution may
become frozen (i.e. below the freezing temperature of the urea
solution which is usually at about negative 12.degree. C.). This
causes the urea solution to lose the ability to be injected into
the exhaust gas stream by an injector. Thus, in order to maintain
the effectiveness of the injector, an electrical heater may need to
be provided for thawing the urea solution, which also adds weight
and cost to a vehicle. Accordingly, it is desirable to provide an
efficient, cost-effective approach for effectively removing
NO.sub.x from the exhaust gas.
SUMMARY OF THE INVENTION
[0006] In one exemplary embodiment of the invention, an exhaust gas
treatment system for an internal combustion engine is provided,
including an exhaust gas conduit, a pressurized vessel, a selective
catalytic reduction ("SCR") device, and a control module. The
internal combustion engine has a plurality of pistons and an engine
off condition that indicates that the pistons are generally
stationary. The exhaust gas conduit is in fluid communication with,
and configured to receive an exhaust gas from the internal
combustion engine during operation. The pressurized vessel stores a
solid ammonia gas producing material. The pressurized vessel is
selectively activated to heat the solid ammonia gas producing
material into an ammonia gas. The ammonia gas is released into the
exhaust gas conduit. The SCR device is in fluid communication with
the exhaust gas conduit and is configured to receive the ammonia
gas. The SCR device has a SCR temperature profile and a SCR
light-off temperature. The control module is in communication with
the internal combustion engine and the pressurized vessel. The
control module receives a signal indicating the engine off
condition. The control module includes a memory for storing a value
indicating a target amount of the ammonia gas released into the
exhaust gas conduit by the pressurized vessel and loaded on the SCR
device. The control module includes control logic for determining
if the internal combustion engine is in the engine off condition
based on the signal. The control module includes control logic for
determining the SCR temperature profile. The control module
includes control logic for determining if the SCR temperature
profile is below a threshold value if the internal combustion
engine is in the engine off condition. The threshold value
indicates that the SCR device is a specified amount below the SCR
light-off temperature. The control module includes control logic
for determining if the pressurized vessel has released the target
amount of the ammonia gas into the exhaust gas conduit if the SCR
temperature profile is below the threshold value. The control
module includes control logic for deactivating the pressurized
vessel if the pressurized vessel has released the target amount of
the ammonia gas.
[0007] The above features and advantages and other features and
advantages of the invention are readily apparent from the following
detailed description of the invention when taken in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Other features, advantages and details appear, by way of
example only, in the following detailed description of embodiments,
the detailed description referring to the drawings in which:
[0009] FIG. 1 is a schematic diagram of an exemplary exhaust gas
treatment system; and
[0010] FIG. 2 is a process flow diagram illustrating a method of
activating a pressurized vessel to heat a solid ammonia gas
producing material into an ammonia gas.
DESCRIPTION OF THE EMBODIMENTS
[0011] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, its application or
uses. It should be understood that throughout the drawings,
corresponding reference numerals indicate like or corresponding
parts and features. As used herein, the term module refers to an
application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that
executes one or more software or firmware programs, a combinational
logic circuit, and/or other suitable components that provide the
described functionality.
[0012] Referring now to FIG. 1, an exemplary embodiment is directed
to an exhaust gas treatment system 10, for the reduction of
regulated exhaust gas constituents of an internal combustion ("IC")
engine 12. The exhaust gas treatment system described herein can be
implemented in various engine systems that may include, but are not
limited to, diesel engine systems, gasoline engine systems, and
homogeneous charge compression ignition engine systems. In the
example as illustrated, the engine 12 includes a plurality of
pistons 16. For example, the engine 12 may be an eight cylinder or
a twelve cylinder engine, however it is to be understood that any
number of pistons 16 may be used as well.
[0013] The exhaust gas treatment system 10 generally includes one
or more exhaust gas conduits 14, and one or more exhaust treatment
devices. In the embodiment as illustrated, the exhaust gas
treatment system devices include a hydrocarbon adsorber 20, an
electrically heated catalyst ("EHC") device 22, an oxidation
catalyst device ("OC") 24, a selective catalytic reduction device
("SCR") 26, and a particulate filter device ("PF") 30. As can be
appreciated, the exhaust gas treatment system of the present
disclosure may include various combinations of one or more of the
exhaust treatment devices shown in FIG. 1, and/or other exhaust
treatment devices (not shown), and is not limited to the present
example.
[0014] In FIG. 1, the exhaust gas conduit 14, which may comprise
several segments, transports exhaust gas 15 from the IC engine 12
to the various exhaust treatment devices of the exhaust gas
treatment system 10. The hydrocarbon adsorber 20 includes for
example, a flow-through metal or ceramic monolith substrate. The
substrate can include a hydrocarbon adsorber compound disposed
thereon. The hydrocarbon adsorber compound may be applied as a wash
coat and may contain materials such as, for example, zeolite. The
hydrocarbon adsorber 20 is located upstream of the EHC device 22,
the OC device 24, and the SCR device 26. The hydrocarbon adsorber
20 is configured for reducing the emissions of HC during an engine
cold start condition when the EHC device 22, the OC device 24 and
the SCR device 26 have not heated to the respective light-off
temperatures and are not active, by acting as a mechanism for
storing exhaust emission components. Specifically, the
zeolite-based material is used to store fuel or hydrocarbons during
a cold start.
[0015] The OC device 24 is located downstream of the hydrocarbon
adsorber 20 and may include, for example, a flow-through metal or
ceramic monolith substrate that may be packaged in a stainless
steel shell or canister having an inlet and an outlet in fluid
communication with exhaust gas conduit 14. The substrate can
include an oxidation catalyst compound disposed thereon. The
oxidation catalyst compound may be applied as a wash coat and may
contain metals such as platinum ("Pt"), palladium ("Pd"),
perovskite or other suitable oxidizing catalysts, or combination
thereof. The OC device 24 treats unburned gaseous and non-volatile
HC and CO, which are oxidized to create carbon dioxide and
water.
[0016] In the embodiment as illustrated, the EHC device 22 is
disposed within the OC device 24. The EHC device 22 includes a
monolith 28 and an electrical heater 32, where the electrical
heater 32 is selectively activated and heats the monolith 28. The
electrical heater 32 is connected to an electrical source (not
shown) that provides power thereto. In one embodiment, the
electrical heater 32 operates at a voltage of about 12-24 volts and
at a power range of about 1-3 kilowatts, however it is understood
that other operating conditions may be used as well. The EHC device
22 may be constructed of any suitable material that is electrically
conductive such as a wound or stacked metal monolith 28. An
oxidation catalyst compound (not shown) may be applied to the EHC
device 22 as a wash coat and may contain metals such as Pt, Pd,
perovskite or other suitable oxidizing catalysts, or combination
thereof.
[0017] The SCR device 26 may be disposed downstream of the OC
device 24. In a manner similar to the OC device 24, the SCR device
26 may include, for example, a flow-through ceramic or metal
monolith substrate that may be packaged in a stainless steel shell
or canister having an inlet and an outlet in fluid communication
with the exhaust gas conduit 14. The substrate may include an SCR
catalyst composition applied thereto. The SCR catalyst composition
may contain a zeolite and one or more base metal components such as
iron ("Fe"), cobalt ("Co"), copper ("Cu") or vanadium ("V") which
can operate efficiently to convert NO.sub.x constituents in the
exhaust gas 15 in the presence of a reductant such as ammonia
("NH.sub.3").
[0018] In the example as shown in FIG. 1, a pressurized vessel 40
is provided for storing a solid ammonia gas producing material 42.
In one embodiment, the solid ammonia gas producing material 42 is
ammonium carbamate or ammonium carbonate. The pressurized vessel 40
is selectively activated to heat the solid ammonia gas producing
material 42 into an ammonia gas that is injected or released into
the exhaust gas conduit 14. In the exemplary embodiment as shown in
FIG. 1, the pressurized vessel 40 includes a plurality of heaters
44 that are located along the side walls 46 of the pressurized
vessel 40. In one example, the heaters 44 are 200 Watt resistive
elements that act as heaters. The pressured vessel 40 also includes
a flash heater 48 that the solid ammonia gas producing material 42
rests upon. A space 50 exists in the pressure vessel 40 between the
pressure vessel 40 and the solid gas producing material 42. In one
embodiment, the heaters 44 are activated to heat the solid gas
producing material 42 to a temperature ranging from about
60.degree. C. to about 100.degree. C. Then, the flash heater 48 may
be activated to heat the solid gas producing material 42 to a
relatively high temperature (i.e., in one embodiment to about
110.degree. C.). The temperature created by activation of the flash
heater 48 creates a decomposition of the solid gas producing
material 42 at the interface between the solid gas producing
material 42 and the flash heater 48. Specifically, the activation
of the flash heater 48 converts the solid gas producing material 42
into an ammonia gas and carbon dioxide ("CO.sub.2"). The mixture of
ammonia gas and carbon dioxide are fed through a tube 52 that is
connected to the exhaust gas conduit 14. The mixture of ammonia gas
and the carbon dioxide are then dosed or released into the exhaust
gas conduit 14. Specifically, the ammonia gas and carbon dioxide
are released into the exhaust gas conduit 14 and directed towards
the SCR device 26.
[0019] The pressure vessel 40 also includes a pressure transducer
54 that is used to monitor the pressure of the space 50 located
internally of the pressure vessel 40. Specifically, the space 50
eventually reaches a threshold pressure as the solid gas producing
material 42 decomposes into the ammonia gas. The threshold pressure
indicates the solid gas producing material 42 is being converted
into the ammonia gas and carbon dioxide at a rate that results in a
steady supply of ammonia gas that is required by the SCR device 26.
That is, the pressure vessel 40 includes a normally closed solenoid
valve 56 that is opened in the event the pressure transducer 52
detects that the pressure within the space 50 has exceeded the
threshold pressure. The opening of the solenoid valve 56 allows for
the ammonia gas and carbon dioxide to enter the exhaust gas conduit
14. Thus, the threshold pressure creates the dispersion or gas
propagation needed to create a target amount of ammonia gas
released into the exhaust gas conduit 14 that is loaded on the SCR
device 26. Specifically, in one example, the target amount of
ammonia gas may represent a saturation amount of ammonia gas that
is stored by the SCR device 26. The saturation amount represents a
maximum amount of ammonia gas the SCR device 26 is capable of
storing, however it is to be understood that the target amount of
ammonia gas may be other quantities as well.
[0020] The PF device 30 may be disposed downstream of the SCR
device 26. The PF device 30 operates to filter the exhaust gas 15
of carbon and other particulates. In various embodiments, the PF
device 30 may be constructed using a ceramic wall flow monolith
filter 23 that may be packaged in a shell or canister constructed
of, for example, stainless steel, and that has an inlet and an
outlet in fluid communication with exhaust gas conduit 14. The
ceramic wall flow monolith filter 23 may have a plurality of
longitudinally extending passages that are defined by
longitudinally extending walls. The passages include a subset of
inlet passages that have and open inlet end and a closed outlet
end, and a subset of outlet passages that have a closed inlet end
and an open outlet end. Exhaust gas 15 entering the filter 23
through the inlet ends of the inlet passages is forced to migrate
through adjacent longitudinally extending walls to the outlet
passages. It is through this wall flow mechanism that the exhaust
gas 15 is filtered of carbon and other particulates. The filtered
particulates are deposited on the longitudinally extending walls of
the inlet passages and, over time, will have the effect of
increasing the exhaust gas backpressure experienced by the IC
engine 12. It is appreciated that the ceramic wall flow monolith
filter is merely exemplary in nature and that the PF device 30 may
include other filter devices such as wound or packed fiber filters,
open cell foams, sintered metal fibers, etc.
[0021] A control module 60 is operably connected to and monitors
the engine 12 and the exhaust gas treatment system 10 through a
number of sensors. The control module 60 is also operably connected
to the electrical heater 32 of the EHC device 22, the engine 12,
and the pressurized vessel 40. An engine off condition occurs if
the pistons 16 are generally stationary within the respective
cylinders of the engine 12. In the embodiment as shown, the control
module 60 is in communication with an ignition switch 70. The
ignition switch 70 sends a signal to the control module 60 that is
indicative of the engine off condition. Specifically, the ignition
switch 70 includes a key-on state and a key-off state, where the
key-off state coincides with the engine off condition. In the
key-on state, electrical power is supplied to a propulsion system
of a vehicle (not shown in FIG. 1). In the key-off state,
electrical power is not supplied to the propulsion system. It
should be noted that while the terms key-on and key-off are used, a
key may not be employed with the ignition switch 70 in some
embodiments. For example, in one embodiment the ignition switch 70
may be activated by proximity to a fob (not shown) that is carried
by a user instead of a key. Thus, the key-off state exists when
power is supplied to the propulsion system and the key-off state
exists when power is not supplied to the propulsion system,
regardless of whether an actual key is employed. It should also be
noted that while an ignition switch 70 is illustrated, other
approaches may be used as well to determine the engine off
condition.
[0022] FIG. 1 illustrates the control module 60 in communication
with two temperature sensors 62 and 64 located in the exhaust gas
conduit 14. The first temperature sensor 62 is situated upstream of
the SCR device 26, and the second temperature sensor 64 is located
downstream of the SCR device 26. The temperature sensors 62 and 64
send electrical signals to the control module 50 that each indicate
the temperature in the exhaust gas conduit 14 in specific
locations.
[0023] The control module 60 includes control logic for monitoring
the first temperature sensor 62 and the second temperature sensor
64 and for calculating a temperature profile of the SCR device 26.
Specifically, the first temperature sensor 62 and the second
temperature sensor 64 are averaged together to create the
temperature profile of the SCR device 26. The control module 60
includes control logic for determining if the SCR device 26 is
below a threshold temperature. The threshold temperature is below a
light-off or minimum operating temperature of the SCR device 26
(i.e. in one embodiment the light-off temperature is about
200.degree. C.). Specifically, the threshold temperature is a
specified amount below the light-off temperature of the SCR device
26. That is, the SCR device 26 has been cooled to the threshold
temperature such that ammonia gas may be stored on the SCR device
26. In one example, the threshold temperature ranges from between
100.degree. C. to about 150.degree. C., however it is understood
that the threshold temperature may include other ranges as
well.
[0024] The control module 60 also includes control logic for
determining if the SCR device 26 has the target amount of ammonia
gas loaded therein. Specifically, in one embodiment, the control
module 60 includes control logic for determining if the engine 12
is in the engine off condition by receiving the signal from the
ignition switch 70. In the event that the engine 12 is in the
engine off condition, then the control module 60 includes control
logic for determining if the temperature profile of the SCR device
26 is below the threshold temperature. That is, the control module
60 includes control logic for determining if the SCR device 26 is
cooled to the threshold temperature such that ammonia gas may be
stored on the SCR device 26 when the engine 12 is in the engine off
condition. In the event that the SCR device 26 is below the
threshold temperature, then the control module 60 also includes
control logic for determining the amount of ammonia gas that has
been released into the exhaust gas conduit 14 by the pressurized
vessel 40.
[0025] In the event that the control module 60 determines that the
SCR device 26 has the target amount of ammonia gas loaded therein,
then the control module 60 includes control logic for deactivating
the pressurized vessel 40. Specifically, the control module 60
includes control logic for deactivating the flash heater 48, which
in turn ceases the decomposition of the solid gas producing
material 42 into the ammonia gas and carbon dioxide. This in turn
deactivates the dosing or injection of the ammonia gas into the
exhaust gas conduit 14. In the event that the control module 60
determines that the SCR device 26 does not have the target amount
of ammonia gas loaded therein, the control module 60 includes
control logic for continuing to keep the flash heater 48 of the
pressurized vessel 40 activated to produce the ammonia gas.
[0026] The control module 60 includes control logic for monitoring
the pressure transducer 54. The pressure transducer 54 monitors the
pressure of the space 50 located internally of the pressure vessel
40. The space 50 eventually reaches the threshold pressure as the
solid gas producing material 42 decomposes into the ammonia gas.
Once the control module 60 determines that the threshold pressure
has been attained, the normally closed solenoid valve 56 is opened.
The ammonia gas and carbon dioxide is then released into the
exhaust gas conduit 14.
[0027] The control module 60 also includes control logic for
selectively activating or deactivating the EHC device 22 based on
the temperature profile of the SCR device 26. Specifically, if the
temperature profile of the SCR device 26 is above the light-off
temperature, then the electrical heater 32 is deactivated, and no
longer heats the EHC device 22. However, as long as the temperature
profile of the SCR device 22 is below the light-off temperature the
electrical heater 32 is activated or remains activated, and heat is
provided to the SCR device 26.
[0028] The control module 60 also includes control logic for
monitoring the temperature of the EHC device 22. Specifically, the
control module 60 may monitor the temperature of the EHC device 22
by several different approaches. In one approach, a temperature
sensor (not shown) is placed downstream of the EHC device 22 and is
in communication with the control module 60 for detecting the
temperature of the EHC device 22. In an alternative approach, the
temperature sensor is omitted, and instead the control module 60
includes control logic for determining the temperature of the EHC
device 22 based on operating parameters of the exhaust gas system
10. Specifically, the temperature of the EHC device 22 may be
calculated based on the exhaust flow of the engine 12, an input gas
temperature of the engine 12, and the electrical power provided to
the electrical heater 32. The exhaust flow of the engine 12 is
calculated by adding the intake air mass of the engine 12 and the
fuel mass of the engine 12, where the intake air mass is measured
using an intake air mass flow sensor (not shown) of the engine 12,
which measures air mass flow entering the engine 12. The fuel mass
flow is measured by summing the total amount of fuel released into
the engine 12 over a given period of time. The fuel mass flow is
added to the air mass flow rate to calculate the exhaust flow of
the engine 12.
[0029] The control module 60 includes control logic for determining
if the temperature of the EHC device 22 is above a threshold or EHC
light-off temperature. In one exemplary embodiment, the EHC
light-off temperature is about 250.degree. C. If the temperature of
the EHC device 22 is above the EHC light-off temperature, then the
control module 60 includes control logic for de-energizing an
electrical source (not shown) of the electrical heater 32.
[0030] The SCR device 26 stores the ammonia gas during the engine
off condition. This is because the SCR device 26 has been cooled to
the threshold temperature, which is a specified amount below the
respective light-off temperature of the SCR device 16. Thus, the
ammonia gas will not react with the SCR catalyst composition that
is disposed on the substrate of the SCR device 26 before a cold
start of the engine 12. The SCR device 26 continues to store the
ammonia gas before a cold start of the engine 12. During the engine
on condition, but prior to attaining the light-off temperature, the
SCR device 26 generally acts as a NO.sub.x adsorber. That is, the
SCR device 26 is generally able to adsorb NO.sub.x released into
the exhaust gas 15 as the engine 12 operates.
[0031] The SCR device 26 is eventually heated to the light-off
temperature during operation of the engine 12, which generally
effectively reduces the amount of NO.sub.x in the exhaust gas 15.
Specifically, the NO.sub.x in the exhaust gas 15 is reduced to
nitrogen after light-off of the SCR device 26. As discussed above,
in one embodiment the oxidation catalyst compound applied to the
EHC device 22 and the OC device 24 may contain metals such as Pt,
Pd, or perovskite. These types of oxidation catalysts may convert
NO to NO.sub.2 at a relatively high rate during cold start of an
engine when compared to some other types of oxidation catalyst
compounds that are currently available. The majority of NO.sub.x
emitted from the engine 12 is in the form of NO, however it should
be noted that NO.sub.2 is more easily adsorbed than NO by the SCR
device 26. Thus, the conversion of NO to NO.sub.2 at a relatively
high rate may facilitate or improve the reduction of NO.sub.x in
the exhaust gas 15 by the SCR device 26 once the SCR device 26 is
heated to the light-off temperature.
[0032] The EHC device 22 is also positioned downstream of a front
face 74 of the OC device 24 such that hydrocarbons in the exhaust
gas 15 do not substantially interfere with the generation of NO to
NO.sub.2 by the EHC device 22. In the embodiment as shown, the EHC
device 22 is located within the OC device 24. Specifically, the OC
device 24 is employed in an effort to treat unburned gaseous and
non-volatile HC and CO upstream of the EHC device 22. Hydrocarbons
in the exhaust gas 15 may interfere with the conversion of NO to
NO.sub.2 by the EHC device 22. Thus, the placement of the OC device
24, or a portion thereof, upstream of the EHC device 22 facilitates
reducing the amount of NO.sub.x in the exhaust gas 15 by reducing
or substantially eliminating hydrocarbons that interfere with
NO.sub.2 generation.
[0033] Moreover, the hydrocarbon adsorber 20 is configured for
reducing the amount of HC that reaches the EHC device 22 and the OC
device 24 during a cold start, which also facilitates or improves
the reduction of NO.sub.x in the exhaust gas 15. The hydrocarbon
adsorber 20 acts as a mechanism for storing fuel or hydrocarbons
during a cold start. That is, the hydrocarbons are adsorbed by the
hydrocarbon adsorber 20 prior to reaching the EHC device 22 and the
OC device 24. Thus, the hydrocarbon adsorber 20 may also facilitate
reducing the amount of NO.sub.x in the exhaust gas 15 by reducing
or substantially eliminating hydrocarbons that interfere with
NO.sub.2 generation.
[0034] A method of operating the exhaust gas treatment system 10
will now be explained. Referring to FIG. 2, an exemplary process
flow diagram illustrating an exemplary process of operating the
exhaust gas treatment system 10 is generally indicated by reference
number 200. Process 200 begins at step 202, where the control
module 60 includes control logic for monitoring the engine 12 for
an engine off condition. Specifically, referring to FIG. 1, in one
embodiment, an engine off condition occurs if the pistons 16 are
generally stationary within the respective cylinders. In one
exemplary embodiment, an ignition switch 70 is in communication
with the control module 60, and is used to indicate if the engine
on or engine off condition has occurred, however it is to be
understood that other approaches may be used as well to determine
the engine off condition. If the engine 12 is not in the engine off
condition, process 200 may then terminate. Process 200 may proceed
to step 204 in the event the engine 12 is in the engine off
condition.
[0035] In step 204, the control module 60 includes control logic
for monitoring a temperature profile of the SCR device 26.
Specifically, referring to FIG. 1, the control module 60 is in
communication with two temperature sensors 62 and 64 located in the
exhaust gas conduit 14, where the first temperature sensor 62 is
situated upstream of the SCR device 26, and the second temperature
sensor 64 is located downstream of the SCR device 26. The control
module 60 includes control logic for monitoring the first
temperature sensor 62 and the second temperature sensor 64 and for
calculating a temperature profile of the SCR device 26.
Specifically, the first temperature sensor 62 and the second
temperature sensor 64 are averaged together to create the
temperature profile of the SCR device 26. The threshold temperature
is below a light-off or minimum operating temperature of the SCR
device 26. Specifically, the threshold temperature is a specified
amount below the light-off temperature of the SCR device 26, such
that ammonia gas may be stored on the SCR device 26. If the SCR
device 26 is above the threshold temperature, process 200 may
continue to monitor the temperature profile of the SCR device 26.
In the event that the SCR device 26 is below a threshold
temperature, process 200 may then proceed to step 206.
[0036] In step 206, the control module 60 includes control logic
for determining if the SCR device 26 has a target amount of ammonia
gas loaded therein. Specifically, the control module 60 includes
control logic for monitoring the amount of ammonia gas that has
been released into the exhaust gas conduit 14 by the pressurized
vessel 40 decomposing the solid gas producing material 42 into an
ammonia gas and carbon dioxide. In the event that the control
module 60 determines that the SCR device 26 has the target amount
of ammonia gas loaded therein, then process 200 may proceed to step
208. In step 208, the control module 60 includes control logic for
deactivating the pressurized vessel 40. Specifically, the control
module 60 includes control logic for deactivating the flash heater
48 if the flash heater 48 has been activated. Deactivation of the
flash heater 48 will cease the decomposition of the solid gas
producing material 42 into the ammonia gas and carbon dioxide. This
in turn deactivates the dosing or injection of the ammonia gas into
the exhaust gas conduit 14. Process 200 may then terminate. In the
event that the control module 60 determines that the SCR device 26
does not have the target amount of ammonia gas loaded therein,
process 200 may then proceed to step 210.
[0037] In step 210, the control module 60 includes control logic
for monitoring the pressure transducer 54. The pressure transducer
54 is used to monitor the pressure of a space 50 located internally
of the pressure vessel 40 as the space 50 eventually reaches a
threshold pressure. The threshold pressure indicates the solid gas
producing material 42 is being converted into the ammonia gas and
carbon dioxide at a rate that results in a steady supply of ammonia
gas that is required by the SCR device 26. That is, the pressure
vessel 40 includes the normally closed solenoid valve 56 that is
opened in the event the pressure transducer 52 detects that the
pressure within the space 50 has exceeded the threshold pressure.
Process 200 may then proceed to step 212.
[0038] In step 212, the control module 60 includes control logic
for determining if the threshold pressure has been attained. In the
event that the threshold pressure has not been attained, process
200 may return to step 210, where the control module 60 continues
to monitor the pressure transducer 54. In the event the threshold
pressure has been attained, process 200 may then proceed to step
214. In step 214, a normally closed solenoid valve 56 is opened.
The ammonia gas and carbon dioxide may then enter the exhaust gas
conduit 14. Process 200 may then terminate.
[0039] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiments disclosed, but that the invention will
include all embodiments falling within the scope of the
application.
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