U.S. patent application number 12/892970 was filed with the patent office on 2012-03-29 for fuel-fired burner for no2 based regeneration.
Invention is credited to Steven Beesley, Nicholas J. Birkby, Navin Khadiya, Mark Ramsbottom.
Application Number | 20120073268 12/892970 |
Document ID | / |
Family ID | 45869236 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120073268 |
Kind Code |
A1 |
Khadiya; Navin ; et
al. |
March 29, 2012 |
FUEL-FIRED BURNER FOR NO2 BASED REGENERATION
Abstract
A fuel-fired burner in a vehicle exhaust system is selectively
activated to increase exhaust gas temperature to a desired
reference temperature. The fuel-fired burner can be either a
partial range burner or a full range burner. A control strategy
activates the fuel-fired burner only when needed to provide
NO.sub.2 based passive regeneration of a diesel particulate filter
in a fuel efficient manner. The control strategy includes at least
one of a look-up table which outputs the desired reference
temperature as a function of engine operating conditions, a
comparison of pressure characteristics to predetermined thresholds,
and a steady-state model or a transient model that outputs the
desired reference temperature as a function of exhaust
back-pressure and estimated exhaust oxygen flowrate.
Inventors: |
Khadiya; Navin; (Columbus,
IN) ; Birkby; Nicholas J.; (Goosnargh, GB) ;
Beesley; Steven; (Cottam, GB) ; Ramsbottom; Mark;
(Millhead, GB) |
Family ID: |
45869236 |
Appl. No.: |
12/892970 |
Filed: |
September 29, 2010 |
Current U.S.
Class: |
60/277 ; 60/311;
60/320 |
Current CPC
Class: |
F01N 2240/14 20130101;
Y02T 10/47 20130101; F01N 2900/1402 20130101; F01N 3/025 20130101;
F01N 2900/08 20130101; F01N 3/035 20130101; Y02T 10/40 20130101;
F01N 9/002 20130101; F01N 2900/1404 20130101; F01N 2900/1406
20130101 |
Class at
Publication: |
60/277 ; 60/320;
60/311 |
International
Class: |
F01N 3/025 20060101
F01N003/025; F01N 9/00 20060101 F01N009/00 |
Claims
1. A method of operating a fuel-fired burner in a vehicle exhaust
system comprising the steps of: (a) associating a fuel-fired burner
with a diesel particulate filter assembly; (b) monitoring at least
one engine operating condition; (c) monitoring exhaust gas
temperature; (d) communicating engine operating condition
information and the exhaust gas temperature to a controller
including a control strategy to identify when the fuel-fired burner
should be activated to achieve a desired reference temperature to
increase NO.sub.2 levels sufficiently to regenerate the diesel
particulate filter; and (e) generating a control signal to activate
the fuel-fired burner to raise exhaust gas temperature to the
desired reference temperature only when the control strategy
identifies that the fuel-fired burner should be activated.
2. The method according to claim 1 wherein the fuel-fired burner
comprises a partial range fuel-fired burner.
3. The method according to claim 2 including monitoring at least
two engine operating conditions, and wherein the control strategy
comprises a look-up table which outputs the desired reference
temperature as a function of the engine operating conditions, and
including generating the control signal to inject fuel into the
partial range fuel-fired burner until the desired reference
temperature is achieved.
4. The method according to claim 2 wherein the control strategy
comprises a steady-state model that outputs the desired reference
temperature as a function of exhaust back-pressure and estimated
exhaust oxygen flowrate.
5. The method according to claim 5 including generating the control
signal to operate the partial range fuel-fired burner at
temperatures of 250 degrees Celsius or greater as a function of
estimated oxygen by mass flowrate and measured back-pressure.
6. The method according to claim 2 wherein the control strategy
comprises a transient model that outputs the desired reference
temperature as a function of exhaust back-pressure and estimated
exhaust oxygen flowrate.
7. The method according to claim 6 including generating the control
signal to operate the partial range fuel-fired burner at
temperatures of 250 degrees Celsius or greater as a function of
estimated oxygen by mass flowrate and measured back-pressure.
8. The method according to claim 6 wherein the transient model
comprises a pre-filter and a steady-state model that outputs the
desired reference temperature as a function of model inputs
including exhaust back-pressure and estimated exhaust oxygen
flowrate, and wherein the pre-filter attenuates noise and
disturbances from model input signals.
9. The method according to claim 1 including continuously
monitoring a pressure drop across the diesel particulate filter,
comparing the pressure drop to a look-up table of pressure drop
versus the engine operating condition, and only activating the
fuel-fired burner if the pressure drop exceeds a predetermined
threshold, exhaust gas temperature is below 300 degrees Celsius,
and a rate of pressure of pressure increase exceeds a predetermined
rate threshold.
10. The method according to claim 9 including deactivating the
fuel-fired burner when the pressure drop falls below the
predetermined threshold and/or exhaust temperature increases above
300 degrees Celsius.
11. A vehicle exhaust system comprising: a fuel-fired burner; a
diesel particulate filter assembly; and a controller electrically
coupled to the fuel-fired burner, the controller including a
processor and a memory device electrically coupled to the
processor, the memory device storing a plurality of instructions
that include a control strategy to identify when the fuel-fired
burner should be activated to achieve a desired reference
temperature to increase NO.sub.2 levels sufficiently to regenerate
the diesel particulate filter, and wherein when the processor
executes the plurality of instructions, the processor is caused to:
receive engine operating condition information and exhaust gas
temperature information, and generate a control signal to activate
the fuel-fired burner to raise exhaust gas temperature to the
desired reference temperature only when the control strategy
identifies conditions are proper for activating the fuel-fired
burner.
12. The vehicle exhaust system according to claim 11 wherein the
control strategy comprises a look-up table which outputs the
desired reference temperature as a function of the engine operating
conditions, and wherein fuel is injected into the fuel-fired burner
in response to the control signal until the desired reference
temperature is achieved.
13. The vehicle exhaust system according to claim 12 wherein the
control strategy comprises a steady-state model that outputs the
desired reference temperature as a function of exhaust
back-pressure and estimated exhaust oxygen flowrate.
14. The vehicle exhaust system according to claim 11 wherein the
control strategy comprises a transient model that outputs the
desired reference temperature as a function of exhaust
back-pressure and estimated exhaust oxygen flowrate.
15. The vehicle exhaust system according to claim 14 wherein the
transient model comprises a pre-filter and a steady-state model
that outputs the desired reference temperature as a function of
model inputs including exhaust back-pressure and estimated exhaust
oxygen flowrate, and wherein the pre-filter attenuates noise and
disturbances from model input signals.
16. The vehicle exhaust system according to claim 11 wherein the
controller continuously monitoring a pressure drop across the
diesel particulate filter, compares the pressure drop to a look-up
table of pressure drop versus the engine operating condition, and
only activates the fuel-fired burner if the pressure drop exceeds a
predetermined threshold, exhaust gas temperature is below 300
degrees Celsius, and a rate of pressure increase exceeds a
predetermined rate threshold.
17. The vehicle exhaust system according to claim 11 wherein the
diesel particulate filter comprises a catalyzed diesel particulate
filter.
18. The vehicle exhaust system according to claim 11 wherein the
fuel-fired burner comprises one of a partial range fuel-fired
burner or a full range fuel-fired burner.
19. A method of operating a fuel-fired burner in a vehicle exhaust
system comprising the steps of: (a) continuously monitoring a
pressure drop across a diesel particulate filter; (b) continuously
monitoring exhaust temperature; (c) comparing the pressure drop to
a look-up table of pressure drop versus an engine operating
condition and comparing the exhaust temperature to a threshold
temperature; and (d) selectively activating a fuel-fired burner to
increase NO.sub.2 levels sufficiently to regenerate the diesel
particulate filter only when predetermined pressure and temperature
criteria are met.
20. The method according to claim 21 wherein the fuel-fired burner
comprises a partial range fuel-fired burner and wherein step (d)
further includes activating the partial range fuel-fired burner if
the pressure drop exceeds a predetermined threshold, exhaust gas
temperature is below 300 degrees Celsius, and a rate of pressure
increase exceeds a predetermined rate threshold.
Description
TECHNICAL FIELD
[0001] The subject invention relates to a vehicle exhaust system,
and more specifically to a system with a fuel-fired burner to
enable NO.sub.2 based regeneration of an exhaust system component
such as a diesel particulate filter, for example.
BACKGROUND OF THE INVENTION
[0002] Exhaust systems are widely known and used with combustion
engines. Some exhaust systems utilize a fuel-fired burner that can
be a full range or partial range burner. An active full range
burner unit enables regeneration of a diesel particulate filter
(DPF) as well as providing exhaust thermal management under various
operating conditions. A partial range burner elevates the exhaust
temperature of exhaust gas to assist with regeneration of the
DPF.
[0003] Passive regeneration, i.e. NO.sub.2 based regeneration, is
advantageous due to the lack of a large exotherm as well as for not
incurring a high fuel penalty. For non-EGR (exhaust gas
recirculation) engines, such as off road engines having less than
75 horsepower for example, sufficient NO.sub.2 is available such
that only a passive system would be required for regeneration.
However, for most vehicle applications the exhaust gas temperature
does not consistently stay above 300 degrees Celsius, which is
required to support a system that only uses passive
regeneration.
[0004] In one example, the partial range burner heats the exhaust
gases when possible, or when required, to enable passive
regeneration of the DPF. One control strategy activates the burner
every time exhaust gas temperatures fall below 300 degrees Celsius.
This control strategy is disadvantageous from a fuel conservation
perspective. Further, NO.sub.2 formation in a DOC to support DPF
regeneration can only occur if DOC temperatures exceed
approximately 250 degrees Celsius, hydrocarbon (HC) and carbon
monoxide (CO) concentrations levels are limited, and NOx levels are
sufficient.
SUMMARY OF THE INVENTION
[0005] A control strategy for a fuel-fired burner considers the
various aforementioned factors to provide NO.sub.2 based
regeneration in a fuel efficient manner.
[0006] In one example, the vehicle exhaust system includes a
partial range fuel-fired burner, a diesel oxidation catalyst (DOC),
a diesel particulate filter (DPF) assembly, and a controller. In
another example, the system includes a partial range fuel-fired
burner and a catalyzed DPF. In another example, the system includes
a full range fuel-fired burner with DOC/DPF assembly or a catalyzed
DPF.
[0007] In one example, a method of operating a fuel-fired burner in
a vehicle exhaust system includes monitoring at least one engine
operating condition, monitoring exhaust gas temperature, and
communicating engine operating condition information and the
exhaust gas temperature to a controller. The controller includes a
control strategy to identify when the fuel-fired burner should be
activated to achieve a desired reference temperature to increase
NO.sub.2 levels sufficiently to regenerate the diesel particulate
filter. The controller generates the control signal to activate the
fuel-fired burner to raise exhaust gas temperature to the desired
reference temperature only when the control strategy identifies
that the fuel-fired burner should be activated.
[0008] The control strategy can take various forms. For example,
the control strategy could include one or more of a look-up table
which outputs the desired reference temperature as a function of
engine operating conditions, and a steady-state model or a
transient model that outputs the desired reference temperature as a
function of exhaust back-pressure and estimated exhaust oxygen
flowrate.
[0009] In another example, the control strategy includes
continuously monitoring a pressure drop across a diesel particulate
filter, continuously monitoring exhaust temperature, comparing the
pressure drop to a look-up table of pressure drop versus an engine
operating condition, and comparing the exhaust temperature to a
threshold temperature. The fuel-fired burner is then selectively
activated to increase NO.sub.2 levels sufficiently to regenerate
the diesel particulate filter only when predetermined pressure and
temperature criteria are met.
[0010] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a schematic view of a vehicle exhaust system
incorporating the subject invention.
[0012] FIG. 2 shows a schematic diagram of one example of a control
strategy for a fuel-fired burner.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] FIG. 1 shows a vehicle exhaust system 10 with a DOC (diesel
oxidation catalyst 12)/DPF (diesel particulate filter 14) assembly.
Optionally, the system 10 could include a catalyzed DPF with no
DOC. A fuel-fired burner 16 is located upstream of the DOC 12 and
the DOC 12 is located upstream of the DPF 14. A fuel-fired burner
16 could comprise, for example, a THERMAL REGENERATOR.TM. or
THERMAL ENHANCER.TM. that is manufactured and sold by FAURECIA
EMISSIONS CONTROL TECHNOLOGIES. The THERMAL ENHANCER.TM. is a
partial range fuel-fired burner that elevates the exhaust
temperature of exhaust gas to assist with regeneration of the DPF.
The THERMAL REGENERATOR.TM. is a full range fuel-fired burner that
enables regeneration of a DPF as well as providing exhaust thermal
management under various operating conditions. When the fuel-fired
burner 16 is a partial range burner or a full range burner, it
includes a housing 18 defining a combustion chamber 20. The housing
18 includes an exhaust gas inlet 22 and an exhaust gas outlet 24.
Exhaust gases generated from an engine E flow through any upstream
exhaust components to the exhaust gas inlet 22. Exhaust gases flow
through the fuel-fired burner to the exhaust gas outlet 24 and then
on to any downstream exhaust system components.
[0014] The fuel-fired burner 16 includes an air/fuel supply system
26 that is selectively activated to inject/spray a mixture of air
and fuel into the combustion chamber 20. The mixture is sprayed
into existing exhaust gases within the combustion chamber 20 and an
igniter 28 then ignites the fuel to increase heat. In one example,
the igniter 28 comprises one or more electrodes, however, other
types of igniters could also be used. Further, an airless fuel
supply could also be used where only fuel would be injected/sprayed
and then ignited.
[0015] The fuel-fired burner 16 is selectively activated by a
controller 30 to elevate the exhaust temperature of exhaust gas to
increase NO.sub.2 based regeneration, i.e. passive regeneration of
the DPF 14. The controller 30 includes a control strategy for the
fuel-fired burner 16, which considers various factors to provide
the NO.sub.2 based regeneration in a fuel efficient manner.
[0016] The controller 30 includes various electronic components
that cooperate to provide a electronic control unit to control an
electromechanical system. For example, the controller 30 may
include, amongst other electronic components typically included in
such units, a processor and a memory device. The processor can
comprise one or more microprocessors or microcontrollers, for
example. The memory device can comprise a programmable read-only
memory device (PROM) including erasable PROM's (EPROM, EEPROM), for
example. The memory device is provided to store instructions in the
form of one or more software routines and/or algorithms, which when
executed by the processor, allow the controller 30 to control
operation of the fuel-fired burner 16 using a specific control
strategy.
[0017] In one example, a method of operating the fuel-fired burner
16 includes monitoring at least one engine operating condition,
monitoring exhaust gas temperature, and communicating engine
operating condition information and the exhaust gas temperature to
the controller 30. Examples of engine operating conditions that are
monitored include engine speed, engine load, mass flow rate,
temperature, etc. The controller 30 utilizes the control strategy
to identify when the fuel-fired burner 16 should be activated to
achieve a desired reference temperature to increase NO.sub.2 levels
sufficiently to regenerate the DPF 14. The controller 30 generates
a control signal to selectively activate the fuel-fired burner 16
to raise exhaust gas temperature to the desired reference
temperature only when the control strategy identifies that
conditions require the fuel-fired burner 16 to be activated.
[0018] The control strategy can take various forms. For example,
the control strategy could include one or more of a look-up table
which outputs the desired reference temperature as a function of
engine operating conditions, and a steady-state model or a
transient model that outputs the desired reference temperature as a
function of exhaust back-pressure and estimated exhaust oxygen
flowrate. Each of these will be discussed in more detail below.
[0019] In another example, the control strategy includes
continuously monitoring a pressure drop across the DPF 14 via
pressure sensors P1, P2 and continuously monitoring exhaust
temperature with a temperature sensor T. The pressure drop is
compared to a look-up table of pressure drop versus a specified
engine operating condition. The current pressure drop is compared
to a predetermined pressure threshold and the exhaust temperature
is compared to a predetermined threshold temperature. The
fuel-fired burner 16 is then selectively activated to increase
NO.sub.2 levels sufficiently to regenerate the DPF only when
predetermined pressure and temperature criteria are met.
[0020] Specifically, the controller 30 only activates the
fuel-fired burner 16 if the following criteria are met: 1) the
pressure drop exceeds the predetermined pressure threshold; (2) the
exhaust temperature is below 300 degrees Celsius; and (3) the rate
of pressure increase exceeds a certain rate threshold. The
fuel-fired burner 16 is turned off when the pressure drop falls
below the predetermined pressure threshold and/or the exhaust
temperature from the engine E increases above 300 degrees Celsius.
As the output from the fuel-fired burner 16 is low in hydrocarbon
species, the DOC 12 is selective for the NO to NO.sub.2 reaction
required for passive regeneration.
[0021] NO.sub.2 formation in the DOC 12 to support DPF regeneration
can only occur if DOC temperatures exceed approximately 250 degrees
Celsius, hydrocarbon (HC) and carbon monoxide (CO) concentrations
levels are limited, and NOx levels are sufficient. The control
strategies utilized by the controller 30 function to schedule the
desired reference/outlet temperature of the partial range burner,
i.e. fuel-fired burner 16, to manage the conversion of NO.sub.2,
HC, and CO.
[0022] One proposed control strategy utilizes a look-up table that
outputs a mapped reference or desired outlet temperature of the
fuel-fired burner 16 as a function of one or more engine operating
conditions, such as engine speed, load, etc. Based on the
determined outlet temperature of the fuel-fired burner 16, the
controller 30 activates the fuel-fired burner 16 to inject the
fuel/air mixture until the outlet temperature is achieved, and then
the fuel-fired burner 16 is shut off. Once the desired outlet
temperature is reached, NO.sub.2 levels are sufficient for passive
regeneration of the DPF 14.
[0023] Another proposed control strategy utilizes a steady-state
and model-based control scheme that outputs a reference or desired
outlet temperature as a function of exhaust back-pressure measured
by one or more pressure sensors and as a function of estimated
exhaust oxygen flow rate. This steady-state and model-based
controls scheme schedules the operating temperature of the
fuel-fired burner 16 such that that it is operated at output
temperatures of 250 degrees Celsius or greater as a function of
estimated exhaust oxygen by mass flow rate and measured exhaust
back-pressure, and limited by a pre-defined exhaust oxygen velocity
threshold. This offers the benefit that a reference temperature map
look-up table, such as that discussed above, would not be required
for each different engine. Also, this strategy has the effect that
calibration effort is reduced as a consequence of being applicable
for controllers for any partial range burner associated with the
engine.
[0024] This steady-state and model based strategy includes an
algorithm stored within the controller 30 which compiles data based
on steady-state engine operating conditions. The controller
analyzes the data and then generates the control signal to activate
the fuel-fired burner 16 by injecting the fuel only or the air/fuel
mixture until the desired outlet temperature is reached. Once the
temperature is reached the controller 30 turns off the fuel-fired
burner 16.
[0025] Another proposed control strategy utilizes a transient and
model-based control scheme that outputs a reference or desired
outlet temperature as a function of exhaust back-pressure and
estimated exhaust oxygen flow rate. This transient and model-based
control scheme comprises a steady-state model, as discussed above,
and a pre-filter 40 (FIG. 2). The pre-filter 40 provides a basis
for attenuating noise and/or disturbances from model input signals
S1, S2 as shown in FIG. 2. Implementation of a transient and
model-based control scheme would constitute what is termed a model
reference control scheme and would offer an off-line controller
tuning approach, i.e. a minimized calibration effort, for any
partial range burner based on the pre-filter 40 and sensitivity
design techniques. The transient configuration works on a real time
basis compiling data as the engine conditions change over time.
[0026] In each of the control strategies, the controller 30 issues
a control signal to selectively activate the fuel-fired burner 16
to raise exhaust gas temperatures to promote NO.sub.2 based
regeneration as needed. As shown in FIG. 2, the controller
activates a switch 5 and includes a feedback loop to monitor the
fuel-fired burner outlet temperature and fuel-fired burner fuel or
air/fuel flow rate until the desired reference temperature is
achieved.
[0027] Although an embodiment of this invention has been disclosed,
a worker of ordinary skill in this art would recognize that certain
modifications would come within the scope of this invention. For
that reason, the following claims should be studied to determine
the true scope and content of this invention.
* * * * *