U.S. patent application number 13/798382 was filed with the patent office on 2014-09-18 for exhaust aftertreatment control system and method for maximizing fuel efficiency while reducing emissions.
This patent application is currently assigned to TENNECO AUTOMOTIVE OPERATING COMPANY INC.. The applicant listed for this patent is TENNECO AUTOMOTIVE OPERATING COMPANY INC.. Invention is credited to John W. DeGeorge.
Application Number | 20140260190 13/798382 |
Document ID | / |
Family ID | 51521025 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140260190 |
Kind Code |
A1 |
DeGeorge; John W. |
September 18, 2014 |
Exhaust Aftertreatment Control System And Method For Maximizing
Fuel Efficiency While Reducing Emissions
Abstract
An engine exhaust treatment and fuel efficiency improvement
system includes a NOx module that determines a quantity of NOx
emitted from an engine. A selective catalytic reduction (SCR)
efficiency module determines a SCR efficiency to reduce the
determined NOx quantity below a predetermined threshold. A reagent
dosing module determines a quantity of reagent required to reduce
the NOx quantity below the predetermined threshold. An injection
optimization module determines whether an increase in system
operating efficiency may be obtained by changing an injected
reagent quantity and an engine operating parameter in cooperation
with each other while maintaining the NOx quantity below the
threshold, the system being operable to change the reagent
injection quantity and engine operating parameter to increase
system efficiency.
Inventors: |
DeGeorge; John W.; (Michigan
Center, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TENNECO AUTOMOTIVE OPERATING COMPANY INC. |
Lake Forest |
IL |
US |
|
|
Assignee: |
TENNECO AUTOMOTIVE OPERATING
COMPANY INC.
Lake Forest
IL
|
Family ID: |
51521025 |
Appl. No.: |
13/798382 |
Filed: |
March 13, 2013 |
Current U.S.
Class: |
60/274 ;
60/286 |
Current CPC
Class: |
Y02T 10/47 20130101;
F02D 41/1461 20130101; F01N 2610/02 20130101; F01N 2900/1404
20130101; F02D 41/0275 20130101; F01N 3/208 20130101; F01N 2900/08
20130101; F02D 41/005 20130101; Y02T 10/12 20130101; Y02T 10/40
20130101; F01N 2900/1406 20130101; F01N 2560/026 20130101; F02D
41/30 20130101; Y02T 10/24 20130101 |
Class at
Publication: |
60/274 ;
60/286 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1. An engine exhaust treatment and fuel efficiency improvement
system, comprising: a NO.sub.x module that determines a quantity of
NO.sub.x emitted from an engine; a selective catalytic reduction
(SCR) efficiency module that determines a SCR efficiency to reduce
the determined NO.sub.x quantity below a predetermined threshold; a
reagent dosing module that determines a quantity of reagent
required to reduce the NO.sub.x quantity below the predetermined
threshold; and an injection optimization module that determines
whether an increase in system operating efficiency may be obtained
by changing both an injected reagent quantity and an engine
operating parameter in cooperation with each other while
maintaining the NO.sub.x quantity below the threshold, wherein the
system injection optimization module outputs a signal to change the
reagent injection quantity and the engine operating parameter to
increase system efficiency.
2. The system of claim 1, wherein the engine operating parameter
includes fuel injection rate.
3. The system of claim 2, wherein the engine operating parameter
includes exhaust gas recirculation flow rate.
4. The system of claim 1, wherein the reagent includes urea.
5. The system of claim 1, wherein the injection optimization module
signals an increase in reagent injection quantity and a decrease in
fuel injection rate.
6. The system of claim 1, wherein the injection optimization module
determines whether the engine NO.sub.x output at the changed engine
operating parameter may be reduced to the predetermined threshold
by the exhaust treatment system and outputs a signal to change the
engine parameter only when so determined.
7. The system of claim 1, wherein the NO.sub.x module, the SCR
efficiency module and the injection optimization module, are
operable on a common control unit that controls the engine
operating parameter.
8. A method of operating an engine exhaust treatment and fuel
efficiency improvements system, the method comprising: determining
an engine operating parameter; calculating engine exhaust NO.sub.x;
calculating a selective catalytic reduction (SCR) conversion
efficiency required to reduce the engine exhaust NO below a
predetermined threshold; determining a quantity of reagent to
inject into the exhaust to reduce the engine exhaust NO below the
threshold; determining whether an operating efficiency of the
system may be increased by changing both the reagent quantity and
the engine operating parameter while maintaining exhaust NO below
the threshold; and changing the reagent quantity and the operating
parameter to reduce engine fuel consumption.
9. The method of claim 8, wherein calculating engine exhaust NO is
accomplished without receiving a NO sensor signal.
10. The method of claim 8, wherein the engine operating parameter
includes fuel injection rate.
11. The method of claim 10, wherein changing the reagent quantity
and the operating parameter includes increasing the reagent
quantity and decreasing the fuel injection rate.
12. The method of claim 8, wherein the engine operating parameter
includes exhaust gas recirculation flow rate.
13. The method of claim 8, wherein the reagent includes urea.
14. The method of claim 8, wherein determining whether an operating
efficiency may be increased includes determining whether the system
includes a capacity to reduce NO.sub.x below the threshold.
Description
FIELD
[0001] The present disclosure relates to exhaust treatment systems
and, more particularly, relates to a system for controlling
injection of a reagent, such as an aqueous urea solution, into an
exhaust stream to reduce oxides of nitrogen (NO.sub.x) emissions
from internal combustion engine exhaust while maximizing engine
fuel efficiency.
BACKGROUND
[0002] This section provides background information related to the
present disclosure which is not necessarily prior art. Lean burn
engines provide improved fuel efficiency by operating with an
excess of oxygen, that is, a quantity of oxygen that is greater
than the amount necessary for complete combustion of the available
fuel. Such engines are said to run "lean" or on a "lean mixture."
However, this improved or increase in fuel economy, as opposed to
non-lean burn combustion, is offset by undesired pollution
emissions, specifically in the form of oxides of nitrogen
(NO.sub.x).
[0003] One method used to reduce NO.sub.x emissions from lean burn
internal combustion engines is known as selective catalytic
reduction (SCR). SCR, when used, for example, to reduce NO.sub.x
emissions from a diesel engine, involves injecting an atomized
reagent into the exhaust stream of the engine in relation to one or
more selected engine operational parameters, such as exhaust gas
temperature, engine rpm or engine load as measured by engine fuel
flow, turbo boost pressure or exhaust NO.sub.x mass flow. The
reagent/exhaust gas mixture is passed through a reactor containing
a catalyst, such as, for example, activated carbon, or metals, such
as platinum, vanadium or tungsten, which are capable of reducing
the NO.sub.x concentration in the presence of the reagent.
[0004] An aqueous urea solution is known to be an effective reagent
in SCR systems for diesel engines. However, use of such an aqueous
urea solution may involve many disadvantages. Urea is highly
corrosive and may adversely affect mechanical components of the SCR
system, such as the injectors used to inject the urea mixture into
the exhaust gas stream. Urea also may solidify upon prolonged
exposure to high temperatures, such as temperatures encountered in
diesel exhaust systems. Solidified urea will accumulate in the
narrow passageways and exit orifice openings typically found in
injectors. Solidified urea may also cause fouling of moving parts
of the injector and clog any openings or urea flow passageways,
thereby rendering the injector unusable.
[0005] During vehicle operation, both internal combustion engine
fuel and aqueous urea are consumed. At the present time, vehicle
engine control and reductant injection control are substantially
autonomous where the exhaust treatment system is tasked with only
reducing undesirable emissions. To reduce the overall cost of
vehicle operation, it may be beneficial to provide a system that
maximizes engine fuel efficiency while providing exhaust
treatment.
SUMMARY
[0006] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0007] An engine exhaust treatment and fuel efficiency improvement
system includes a NO.sub.x module that determines a quantity of
NO.sub.x emitted from an engine. A selective catalytic reduction
(SCR) efficiency module determines a SCR efficiency to reduce the
determined NO.sub.x quantity below a predetermined threshold. A
reagent dosing module determines a quantity of reagent required to
reduce the NO.sub.x quantity below the predetermined threshold. An
injection optimization module determines whether an increase in
system operating efficiency may be obtained by changing an injected
reagent quantity and an engine operating parameter in cooperation
with each other while maintaining the NO.sub.x quantity below the
threshold, the system being operable to change the reagent
injection quantity and engine operating parameter to increase
system efficiency.
[0008] A method includes determining an engine operating parameter,
calculating an exhaust NO.sub.x and calculating a selective
catalytic reduction (SCR) conversion efficiency required to reduce
the engine exhaust NO.sub.x below a predetermined threshold. A
quantity of reagent to inject into the exhaust to reduce the engine
exhaust NO.sub.x below the threshold is determined. The method also
includes determining whether an operating efficiency of the system
may be increased by changing both the reagent quantity and the
engine operating parameter while maintaining exhaust NO.sub.x below
the threshold. The reagent quantity and the operating parameter are
changed to reduce the engine fuel consumption.
[0009] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0010] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0011] FIG. 1 is a schematic depicting an exemplary exhaust after
treatment system constructed in accordance with the teachings of
the present disclosure;
[0012] FIG. 2 is a functional block diagram of a controller
according to the present disclosure;
[0013] FIG. 3 is a functional block diagram illustrating an
alternate controller arrangement according to the present
disclosure; and
[0014] FIG. 4 is flow diagram that illustrates the steps of a
method for improving the operating efficiency of an engine exhaust
treatment and fuel efficiency improvement system.
[0015] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0016] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0017] It should be understood that although the present teachings
may be described in connection with diesel engines and the
reduction of NO.sub.x emissions, the present teachings may be used
in connection with any one of a number of exhaust streams, such as,
by way of non-limiting example, those from diesel, gasoline,
turbine, fuel cell, jet or any other power source outputting a
discharge stream. Moreover, the present teachings may be used in
connection with the reduction of any one of a number of undesired
emissions. For example, injection of hydrocarbons as a NO.sub.x
reducing agent or for the regeneration of diesel particulate
filters is also within the scope of the present disclosure. For
additional description, attention should be directed to
commonly-assigned U.S. Pat. No. 8,047,452, entitled "Method And
Apparatus For Injecting Atomized Fluids", which is incorporated
herein by reference.
[0018] With reference to the Figures, a pollution control system 8
for reducing NO.sub.x emissions from the exhaust of an internal
combustion engine 21 is provided. In FIG. 1, solid lines between
the elements of the system denote fluid lines for reagent and
dashed lines denote electrical connections. The system of the
present teachings may include a reagent tank 10 for holding the
reagent and a delivery module 12 for delivering the reagent from
the tank 10. The reagent may be a urea solution, a hydrocarbon, an
alkyl ester, alcohol, an organic compound, water, or the like and
can be a blend or combination thereof. It should also be
appreciated that one or more reagents may be available in the
system and may be used singly or in combination. The tank 10 and
delivery module 12 may form an integrated reagent tank/delivery
module. Also provided as part of system 8 is a controller 14, a
reagent injector 16, and an exhaust system 18. Exhaust system 18
includes an exhaust conduit 19 providing an exhaust stream to at
least one catalyst bed 17.
[0019] The delivery module 12 may comprise a pump that supplies
reagent from the tank 10 via a supply line 9. The reagent tank 10
may be polypropylene, epoxy coated carbon steel, PVC, or stainless
steel and sized according to the application (e.g., vehicle size,
intended use of the vehicle, and the like). A pressure regulator
(not shown) may be provided to maintain the system at predetermined
pressure setpoint (e.g., relatively low pressures of approximately
60-80 psi, or in some embodiments a pressure of approximately
60-150 psi) and may be located in the return line 35 from the
reagent injector 16. A pressure sensor may be provided in the
supply line 9 leading to the reagent injector 16. The system may
also incorporate various freeze protection strategies to thaw
frozen reagent or to prevent the reagent from freezing. During
system operation, regardless of whether or not the injector is
releasing reagent into the exhaust gases, reagent may be circulated
continuously between the tank 10 and the reagent injector 16 to
cool the injector and minimize the dwell time of the reagent in the
injector so that the reagent remains cool. Continuous reagent
circulation may be necessary for temperature-sensitive reagents,
such as aqueous urea, which tend to solidify upon exposure to
elevated temperatures of 300.degree. C. to 650.degree. C. as would
be experienced in an engine exhaust system.
[0020] Furthermore, it may be desirable to keep the reagent mixture
below 140.degree. C. and preferably in a lower operating range
between 5.degree. C. and 95.degree. C. to ensure that
solidification of the reagent is prevented. Solidified reagent, if
allowed to form, may foul the moving parts and openings of the
injector.
[0021] The amount of reagent required may vary with load, exhaust
gas temperature, exhaust gas flow, engine fuel injection timing,
desired NO reduction, barometric pressure, relative humidity, EGR
rate and engine coolant temperature. A NO sensor or meter 25 may or
may not be positioned downstream from catalyst bed 17. NO sensor
25, if provided, is operable to output a signal indicative of the
exhaust NO content to controller 14 and/or an engine control unit
27.
[0022] Referring to FIGS. 1 and 2, controller 14 is in
communication with engine control unit 27 and is in receipt of
signals representative of measured exhaust parameters as provided
by exhaust sensors 50. The measured exhaust parameters may include
exhaust temperature at a location proximate engine 21 and/or at a
location proximate an inlet to SCR 17. The exhaust temperature
downstream from SCR 17 may also be measured. Other relevant exhaust
information that may be collected by exhaust sensors 50 includes
exhaust pressure, exhaust flow rate and NO.sub.x, if a NO.sub.x
sensor is provided.
[0023] Controller 14 includes a NO.sub.x module 52, an SCR
efficiency module 54, a dosing module 56, an injection optimization
module 58, a fuel combustion control module 60 and a reagent
injection control module 62. Controller 14 may receive input
signals from engine control unit 27 indicative of a number of
engine operating conditions including engine speed, engine load,
fuel injection timing, exhaust gas recirculation system flow, fuel
flow rate, coolant temperature, engine inlet air temperature,
barometric pressure, air flow rate, manifold pressure, and
crankshaft position. Other information may also be provided from
ECU 27 or exhaust system sensors 50. Controller 14 commands an
engine fuel injection system 66 and reagent injector 16.
[0024] NO.sub.x module 52 calculates the NO.sub.x content emitted
by engine 21 based on either the signal output from the NO.sub.x
sensor or one or more of the signals previously discussed including
engine speed, fuel flow rate, intake air temperature, injection
timing and/or coolant temperature. NO.sub.x module 52 may be
programmed with a map generated from empirical test data obtained
from a similar engine operating under like circumstances. Other
purely analytical techniques may be used to calculate a quantity of
engine NO.sub.x, if desired. NO.sub.x module 52 may determine NO
flow, NO.sub.2 flow, and/or a NOx ratio=NO.sub.2:NO.sub.x.
[0025] SCR efficiency module 54 is in receipt of the calculated
engine NO.sub.x provided by NO.sub.x module 52. SCR efficiency
module 54 calculates a required SCR conversion efficiency to assure
that the NO.sub.x content entering the atmosphere is at or below a
predetermined threshold based on the calculated quantity of engine
NO.sub.x. Once the quantity of NO.sub.x has been determined and the
required SCR efficiency to appropriately reduce the NO.sub.x has
been calculated, this information is forwarded to dosing module
56.
[0026] Dosing module 56 calculates the amount of ammonia to provide
to the engine exhaust to reduce the NO.sub.x content below the
predetermined threshold. Several different methods may be used to
calculate the requisite quantity of ammonia. For example, one
method includes executing an ammonia storage model to determine a
target amount of ammonia to be stored in SCR 17. The ammonia
storage model may include a map correlating the required quantities
of ammonia to be dosed to exhaust containing NO.sub.x. The map may
account for reductant type, selective catalytic reduction device
type, SCR temperature, and exhaust mass flow rate, among other
factors. SCR dosing module 56 may alternatively calculate the
amount of ammonia required using purely theoretical models without
the use of a map. The purely analytical and theoretical approach
may incorporate a chemistry and physics based model. Use of this
type of model may significantly reduce the need for prototype
construction and data collection. Some of the models, however, may
have limited applicability.
[0027] Dosing module 56 may also calculate a dosing rate of
reductant to be injected into the exhaust. Dosing module 56 may
account for the particular ammonia storage mechanism employed. For
example, the reductant may be carried on a vehicle as an aqueous
urea solution or as a solid urea. The physical characteristics of
injector 16 may also be considered at this time to define an
energization sequence to the particular injector being used to
supply the reductant to the exhaust.
[0028] Injection optimization module 58 determines whether an
increase in vehicle operation efficiency may be gained by varying
the reductant dosing rate and the rate of engine fuel consumption.
Injection optimization module 58 calculates the extent to which
engine exhaust NO.sub.x may be increased up to the predetermined
NO.sub.x threshold. A further calculation is made regarding the
opportunity to operate engine 21 in a further lean mode by reducing
the quantity of fuel injected into the combustion chambers of the
engine. When the engine operating conditions are further leaned out
to reduce fuel consumption, NO.sub.x output from the engine
typically increases. Injection optimization module 58 evaluates
several combinations and permutations of possible reductant
injection rates and fuel consumption rates that may be possible
while maintaining the NO.sub.x output below the predetermined
threshold.
[0029] At least one of the factors considered by injection
optimization module 58 includes determining the upper limit of the
NO.sub.x reduction system. State another way, injection
optimization module 58 determines the maximum NO.sub.x increase
over the present operating condition that may be counteracted by an
increase in reductant injection rate while maintaining a NO.sub.x
output below the threshold. Injection optimization module 58 also
accounts for the possibility of varying other engine operating
characteristics including air flow, fuel injection timing, EGR flow
and fuel flow rate. Once the optimized engine operating parameters
and reductant injection rates have been determined to minimize
vehicle operation costs, controller 14 recalculates the engine
NO.sub.x that will be emitted to atmosphere based on the projected
changes to fuel injection rate, reagent injection rate, EGR flow,
and any other parameters. Based on the previous calculations,
injection optimization module 58 calculates whether the system
operating efficiency may be increased. If so, the revised target
engine operating conditions are provided to fuel combustion control
module 60. Similarly, the revised reagent quantity is provided to
reagent injection control module 62. Fuel combustion control module
60 outputs a signal to engine fuel injection system 66 to provide
the new target fuel flow rate. This information may be provided to
ECU 27. Fuel combustion control module 60 may account for the
number and type of active fuel injectors associated with engine 21.
Fuel combustion control module 60 may also output signals for
controlling the EGR flow rate and the intake air flow rate.
[0030] Reagent injection control module 62 receives a signal from
injection optimization module 58 relating to the quantity of
ammonia to be injected to meet the target NO.sub.x output. Reagent
injection control module 62 outputs a signal to control the
operation of reagent injector 16. The signal may account for the
type of reagent being injected. For example, reagent injection
control module 62 may consider the percentage of urea within an
aqueous solution or some other parameter depending on the reductant
storage system. After commands have been sent from controller 14 to
engine fuel injection system 66 and reagent injector 16, controller
14 recalculates the engine NO.sub.x at the exhaust system outlet
based on confirmed changes to the engine management parameters. A
reagent dosing quantity is calculated based on the recalculated
NO.sub.x content provided by NO.sub.x module 52. The revised dosing
quantity is provided to reagent injection control module 62 such
that reagent injector 16 delivers the revised and optimized reagent
quantity.
[0031] As depicted in FIG. 3, some modules previously described as
being executed within controller 14 may alternately be included as
part of the engine control unit 27. In particular, it is
contemplated that NO.sub.x module 52, SCR efficiency module 54 and
injection optimization module 58 form a part of ECU 27. Controller
14 would continue to implement dosing module 56 and an input/output
module 68. Input/output module 68 assists with the transfer of
information between ECU 27 and controller 14.
[0032] In operation, and with reference to FIG. 4, the exhaust
treatment and fuel efficiency optimization system of the present
disclosure collects information regarding the present operating
conditions of the exhaust system and measures exhaust sensed
parameters at step 80. Exhaust system sensors 50 provide controller
14 with signals indicative of the relevant exhaust conditions.
Similarly at step 82, controller 14 receives information from ECU
27 including signals indicative of engine speed, engine load, fuel
injection timing, EGR flow, fuel flow rate, engine inlet air
temperature, barometric pressure, engine coolant temperature,
crankshaft position, exhaust manifold pressure and possibly several
other signals indicative of the engine operating condition.
[0033] At step 84, control calculates the engine NO.sub.x using a
NO.sub.x sensor signal or one or more of the methods previously
described. Controller 14 next calculates the SCR conversion
efficiency required to maintain the NO.sub.x output to the
atmosphere at or below a predetermined threshold at step 86. At
step 88, control determines the quantity of ammonia that is to be
injected to reduce the NO magnitude to the threshold quantity. At
step 90, a reagent dosing quantity or reagent dosing rate is
calculated. The dosing rate will typically be determined in grams
of urea per second.
[0034] Control, at step 92, calculates whether an increase in
vehicle operation efficiency may be gained by varying the reductant
dosing rate in combination with changing the engine operating
parameters. In one example, the rate of engine fuel consumption is
reduced by adjusting the air/fuel mixture to be increasingly lean.
Operating the engine at a further lean condition increases the NO
output. To account for the increase in NO output, reductant dosing
rate is increased. The cost of the increase in reductant dosing
rate is less than the cost savings realized by reducing the rate of
engine fuel consumption. As such, the vehicle operating cost may be
reduced by implementing the present teachings. In another example,
the vehicle may operate more efficiently from a cost analysis point
of view if the rate of engine fuel consumption is increased,
thereby reducing NO output and reducing the reductant dosing rate
required to meet emission standards.
[0035] Once an optimized set of engine operating parameters and
reductant injection rates have been determined, control
recalculates the engine NO output based on the projected changes to
engine control which may include injection timing and EGR flow.
Recalculation occurs at step 94. At step 96, control determines
whether the proposed optimized engine operating parameters and
exhaust treatment system operating parameters may be met to improve
the system efficiency based on changing the engine NO output. This
determination may include evaluating the reagent injection system
and ensuring that the system has the capability to reduce the
increased quantity of NO to a magnitude at or below the
predetermined threshold. If the projected changes to the engine
operating conditions and the reductant injection system are not
feasible, control continues to step 98 where reagent is dosed at
the previously calculated rate at step 90 and not the proposed rate
determined at step 92.
[0036] If control determines that system efficiency may be improved
by changing the NO output of the engine, the information is sent to
engine control unit 27 to vary the engine operating parameters at
step 100. Control confirms that the engine operating parameters
have been changed at step 102. Engine NO output is recalculated at
step 104 based on the confirmed changes to the engine operating
parameters that may include injection timing and EGR flow. A
revised reagent dosing quantity is calculated at step 106 to
account for recalculated engine NO quantity determined at step 104.
At step 98, reagent is dosed at the recalculated rate determined at
step 106.
[0037] 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 program, a combinational logic
circuit, and/or other suitable components that provide the
described functionality.
[0038] Furthermore, the foregoing discussion discloses and
describes merely exemplary embodiments of the present disclosure.
One skilled in the art will readily recognize from such discussion,
and from the accompanying drawings and claims, that various
changes, modifications and variations may be made therein without
departing from the spirit and scope of the disclosure as defined in
the following claims.
* * * * *