U.S. patent application number 11/589964 was filed with the patent office on 2008-05-08 for method of regenerating a particulate filter.
Invention is credited to Trent J. Cleveland, Jessica Anne Crompton, David Joseph Kapparos, Michael Dennis Lowe, Maarten Verkiel.
Application Number | 20080104948 11/589964 |
Document ID | / |
Family ID | 39148822 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080104948 |
Kind Code |
A1 |
Kapparos; David Joseph ; et
al. |
May 8, 2008 |
Method of regenerating a particulate filter
Abstract
A method of regenerating a particulate filter is disclosed. The
method involves heating the particulate filter to an intermediate
temperature, and maintaining the particulate filter at the
intermediate temperature until substantial temperature equilibrium
is reached. The particulate filter is then heated to a regeneration
temperature higher than the intermediate temperature.
Inventors: |
Kapparos; David Joseph;
(Chillicothe, IL) ; Lowe; Michael Dennis;
(Metamora, IL) ; Cleveland; Trent J.; (Metamora,
IL) ; Verkiel; Maarten; (Metamora, IL) ;
Crompton; Jessica Anne; (Washington, IL) |
Correspondence
Address: |
CATERPILLAR/FINNEGAN, HENDERSON, L.L.P.
901 New York Avenue, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39148822 |
Appl. No.: |
11/589964 |
Filed: |
October 31, 2006 |
Current U.S.
Class: |
60/297 ; 60/295;
60/300 |
Current CPC
Class: |
F01N 2260/10 20130101;
F01N 3/025 20130101; F01N 2240/14 20130101; F01N 2550/04 20130101;
Y02T 10/47 20130101; F01N 9/002 20130101; F01N 2260/04 20130101;
Y02T 10/40 20130101 |
Class at
Publication: |
60/297 ; 60/295;
60/300 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/10 20060101 F01N003/10 |
Claims
1. A method of regenerating a particulate filter comprising:
triggering a regeneration process; determining a value indicative
of an initial temperature of the particulate filter; comparing the
initial temperature to an intermediate temperature; preheating the
particulate filter to the intermediate temperature; maintaining the
particulate filter at the intermediate temperature for a
predetermined period of time; and heating the particulate filter to
a regeneration temperature higher than the intermediate
temperature.
2. The method of claim 1, wherein the triggering of the
regeneration process includes triggering regeneration of the
particulate filter when a pressure drop across the particulate
filter exceeds a threshold pressure drop.
3. The method of claim 1, wherein the triggering of the
regeneration process includes triggering regeneration of the
particulate filter when a time between two successive regeneration
events exceeds a threshold time duration.
4. The method of claim 1, wherein the triggering of the
regeneration process includes triggering regeneration of the
particulate filter based upon a mathematical model estimating a
particulate matter loading of the particulate filter.
5. The method of claim 1, wherein the determination of the value
includes measuring an inlet temperature and an outlet temperature
of the particulate filter.
6. The method of claim 5, wherein the determination of the value
includes computing an overall temperature of the particulate filter
based on the inlet temperature and the outlet temperature.
7. The method of claim 1, wherein the determination of the value
includes determining a temperature variation between different
regions within the particulate filter.
8. The method of claim 7, wherein the triggering of the
regeneration process includes triggering regeneration of the
particulate filter based on the temperature variation within the
particulate filter.
9. The method of claim 1, wherein the comparison of the initial
temperature to the intermediate temperature includes computing the
intermediate temperature.
10. The method of claim 9, wherein the computation of the
intermediate temperature includes determining the intermediate
temperature such that the stresses in the particulate filter due to
heating the particulate filter from intermediate temperature to the
regeneration temperature is below the strength of the particulate
filter.
11. The method of claim 1, wherein the maintaining of the
particulate filter at the intermediate temperature includes holding
the particulate at the intermediate temperature until the
particulate filter substantially equilibrates at the intermediate
temperature.
12. The method of claim 11, wherein the holding of the particulate
filter at the intermediate temperature includes holding the
particulate filter at the intermediate temperature until multiple
temperature sensor readings indicate that the particulate filter
has substantially equilibrated at the intermediate temperature.
13. The method of claim 1, wherein the preheating of the
particulate filter to the intermediate temperature, and the heating
of the particulate filter to the regeneration temperature includes
heating an exhaust gases supplied to the particulate filter using a
fuel driven burner located upstream of the particulate filter.
14. The method of claim 1, wherein heating the particulate filter
to a regeneration temperature includes heating the particulate
filter to a temperature at which an accumulated particulate matter
in the particulate filter begins burning.
15. A method of regenerating a diesel particulate filter
comprising: heating the particulate filter to an intermediate
temperature; maintaining the particulate filter at the intermediate
temperature until substantial temperature equilibrium is reached;
and heating the particulate filter to a regeneration temperature
higher than the intermediate temperature.
16. The method of claim 15, wherein the heating of the particulate
filter to the intermediate temperature and the heating of the
particulate filter to the regeneration temperature includes heating
exhaust gases supplied to the particulate filter.
17. The method of claim 16, wherein the heating of the exhaust
gases includes heating the exhaust gases using a fuel driven burner
located upstream of the particulate filter.
18. An exhaust system of an engine comprising; a particulate filter
through which exhaust gas flows; one or more temperature sensors
attached to the particulate filter, wherein the sensors are
configured to measure a value indicative of a temperature of the
particulate filter; and a control system electrically connected to
the sensors, wherein the control system is configured to: heat the
particulate filter to an intermediate temperature that is higher
than the overall temperature, maintain the particulate filter at
the intermediate temperature until a substantial temperature
equilibrium is reached, and heat the particulate filter to a
regeneration temperature that is higher than the intermediate
temperature.
19. The system of claim 18, further including a fuel driven burner
located upstream of the particulate filter.
20. The system of claim 19 wherein the fuel driven burner is
configured to heat the exhaust gas supplied to the particulate
filter such that the particulate filter is heated to the
intermediate temperature, maintained at the intermediate
temperature, and heated to the regeneration temperature, in
response to one or more commands from the control system.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to particulate
filter regeneration, and more particularly to a method to
regenerate particulate filters.
BACKGROUND
[0002] Diesel engines and other engines known in the art may
exhaust a complex mixture of air pollutants. The air pollutants may
be composed of gaseous compounds and solid particulate matter,
which may include unburned carbon particles called soot. Exhaust
emission standards regulate the amount of particulate matter
emitted from an engine. One method used by engine manufacturers to
comply with these emission standards is to remove particulate
matter from the exhaust flow of an engine using a particulate
filter. Most particulate filters operate by a similar process of
forcing engine exhaust through filter elements in the particulate
filter that are designed to block particulate matter while allowing
the gases to flow through. Periodically the accumulated particulate
matter in the filter elements are burned off, to reduce the
pressure drop within the filter (commonly referred to as
backpressure). Filter regeneration is the process of burning the
accumulated particulate matter in the filter elements. When filter
regeneration is desired, the temperature of the exhaust gas is
increased to raise the temperature of the accumulated soot in the
filter to its combustion temperature. A catalyst is sometimes used
to lower the regeneration temperature.
[0003] Filter regeneration causes different regions of the filter
element to heat up at different rates causing a thermal gradient
between these different regions. The thermal expansion mismatch
between the different regions resulting from these thermal
gradients induce thermo-mechanical stresses in the filter element.
When the magnitude of these stresses exceed the strength of the
filter element, the filter element cracks. In addition to reducing
the useful lifetime of the particulate filter, cracks in the filter
element create a leakage path for particulate to escape, thereby
reducing filtration efficiency.
[0004] U.S. Pat. No. 5,701,735 (the '735 patent) to Kawaguchi
describes a method of regenerating a particulate filter to reduce
the likelihood of the filter "melting" or "cracking" due to
high-temperature thermal stress. When regeneration of the
particulate filter is desired, the method of the '735 patent allows
a regenerative gas to flow through a particulate filter. While
flowing through the upstream side, the regenerative gas cools the
upstream side of the filter to below the regeneration temperature.
Because of the transfer of heat from the upstream side, the
temperature of the regenerative gas increases, reducing the cooling
of the downstream side. This preferential cooling of the upstream
side of the filter causes combustion to initiate on the downstream
side of the filter during a regeneration event. The combustion
flame then propagates to the upstream side of the filter. In the
method of the '735 patent, propagation of the combustion flame
within the filter is opposite to the direction of flow of the
regenerative gas. Therefore, a part of the combustion heat is
transferred upstream by the combustion flame and the remaining part
is transferred downstream by the regenerative gas. This transfer of
heat to both the upstream and downstream regions prevents
overheating of the filter in any one region, thereby preventing the
melting or cracking of the filter due to thermal stress.
[0005] Although the regeneration method of the '735 patent may
reduce the component of thermal stress due to high temperature, it
may introduce thermal stresses in the filter by intentionally
inducing a thermal gradient in the filter. By selectively heating
the down stream side of the filter and cooling the upstream side, a
thermal gradient is created within the filter. This thermal
gradient will cause the upstream side of the filter to expand by a
different amount than the downstream side. This differential
expansion of the filter caused by the thermal gradient induces
thermal stresses in the filter. Further, additional parts, such as
valves, pipes and other components associated with the regenerative
gas, may have to be added to the exhaust system to practice the
method of regeneration of the '735 patent. These additional parts
may increase the cost of the exhaust system.
[0006] The disclosed method of regeneration of a particulate filter
is directed to overcoming one or more of the problems set forth
above.
SUMMARY OF THE INVENTION
[0007] In accordance with one aspect, the present disclosure is
directed towards a method of regenerating a particulate filter. The
method involves triggering a regeneration process and determining a
value indicative of an initial temperature of the particulate
filter. The initial temperature is then compared to an intermediate
temperature, and the particulate filter is preheated to the
intermediate temperature. The particulate filter is then maintained
at the intermediate temperature for a predetermined period of time,
and the particulate filter is heated to a regeneration
temperature.
[0008] According to another aspect, the present disclosure is
directed to a method of regenerating a diesel particulate filter.
The method involves heating the particulate filter to an
intermediate temperature, and maintaining the particulate filter at
the intermediate temperature until substantial temperature
equilibrium is reached. The particulate filter is then heated to a
regeneration temperature higher than the intermediate
temperature.
[0009] In yet another aspect, the present disclosure is directed to
an exhaust system of an engine. The exhaust system includes a
particulate filter through which exhaust gas flows, one or more
temperature sensors attached to the particulate filter, and a
control system electrically connected to the sensors. The sensors
are configured to measure a value indicative of a temperature of
the particulate filter. The control system is configured to heat
the particulate filter to an intermediate temperature that is
higher than the overall temperature, maintain the particulate
filter at the intermediate temperature until a substantial
temperature equilibrium is reached, and heat the particulate filter
to a regeneration temperature that is higher than the intermediate
temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagrammatic illustration of an engine system
having an exhaust treatment system with particulate filters
according to an exemplary embodiment of the present disclosure;
[0011] FIG. 2 is an exemplary method of regenerating a particulate
filter of FIG. 1.
DETAILED DESCRIPTION
[0012] FIG. 1 illustrates an engine system 100 having a power
source 10 having an exemplary exhaust treatment system 12. Power
source 10 may include an engine such as, for example, a diesel
engine, a gasoline engine, a natural gas engine, or any other
engine apparent to one skilled in the art. Power source 10 may
alternately include another source of power such as a furnace or
any other source of power known in the art. Exhaust treatment
system 12 may include an air induction system 14, a recirculation
system 16, and an exhaust system 18.
[0013] Air induction system 14 may be configured to introduce
charged air into a combustion chamber (not shown) of power source
10. Air induction system 14 may include an induction valve 20,
compressor 22, and other components known in the art such as, one
or more air coolers, additional valving, one or more air cleaners,
one or more waste gates, a control system, etc.
[0014] Recirculation system 16 may be configured to redirect a
portion of the exhaust flow of power source 10 from exhaust system
18 into air induction system 14. Recirculation system 16 may
include components such as, an inlet port 24, a recirculation
particulate filter 26, a cooler 28, a recirculation valve 30, and a
discharge port 32. Inlet port 24 may be connected to exhaust system
18 and configured to receive at least a portion of the exhaust flow
from power source 10. Specifically, inlet port 24 may be disposed
downstream of a particulate filter 40. It is contemplated that
inlet port 24 may be located elsewhere within exhaust system
16.
[0015] Exhaust system 18 may be configured to direct exhaust flow
out of power source 10. Exhaust system 18 may include a first
particulate filter 34, a turbine 36, a regeneration assist system
38, and a second particulate filter 40. It is contemplated that
additional emission controlling devices may be included within
exhaust system 18.
[0016] First particulate filter 34 may be connected to power source
10 via a fluid passageway 42 and to turbine 36 via a fluid
passageway 44. First particulate filter 34 may include a first
filter element 46 configured to filter particulate matter from the
exhaust flow. First particulate filter 34 may also be fitted with
sensors to measure different parameters pertaining to the operating
condition of the filter.
[0017] The first filter element 46 may be of any type known in the
art, such as, for example, ceramic cordierite, ceramic foam, other
ceramic, sintered metal, or metal foam type filter. The first
filter element 46 assists in removing particulate matter, such as
soot, from the exhaust flow. The first filter element 46 may be
situated horizontally, vertically, radially, or in any other
configuration that allows for proper filtration. The first filter
element 46 may of a honeycomb, mesh, mat, or any other construction
that allows for proper filtering of particulate matter. The first
filter element 46 may contain pores, cavities or spaces of a size
that allows exhaust gas to flow through while substantially
restricting the passage of particulate matter. The flow of exhaust
through the pores of the first filter element 46 is illustrated by
the arrows 48. In some applications, the first filter element 46
may contain heating elements configured to heat the first filter
element 46 and the exhaust flow during a regeneration event. First
particulate filter 34 may also include a catalyst to catalyze the
particulate matter filtered by the first particulate filter 34. The
catalyst may include, for example, a base metal oxide, a molten
salt, and/or a precious metal that assists in reducing the
combustion temperature of particulate matter.
[0018] The sensors attached to the first particulate filter 34 may
include among others, pressure sensors 58, 60 and temperature
sensors 62, 64. These sensors may be located proximate to the inlet
and the outlet of the first particulate filter 34. The pressure
sensors 58, 60 may measure the pressure drop of the exhaust flow
across the filter, and the temperature sensors 62, 64 may measure
the temperature of the exhaust entering and exiting the first
particulate filter 34. The temperature sensor data may be used to
calculate an overall temperature of the first particulate filter
34. The overall temperature may be a temperature value calculated
from the temperature sensor data based upon a mathematical model.
In some cases, the overall temperature may represent the average
temperature of a particulate filter. It is contemplated that these
sensors may be located at other locations within the first
particulate filter 34. For instance, one or more temperature
sensors may be located at different locations of the first filter
element 46 to measure the temperature variation between the
different locations. The temperature sensor data may also be used
to determine the temperature gradient across the first filter
element 46 or any other thermal characteristic related to the
measured temperatures. It is also contemplated that other sensors,
such as flow rate sensors, mass sensors, etc. may be used to
measure other operating characteristic of the first particulate
filter 34. The pressure sensors 58, 60 and temperature sensors 62,
64 along with other sensor of the first particulate filter 34 may
be electrically connected to a control system 74.
[0019] As noted above, the first particulate filter 34 may be
fluidly connected a turbine 36. The turbine 36 may be located
downstream of the first particulate filter 34 and may be
mechanically coupled to drive the compressor 22 of the air
induction system 14 to form a turbocharger. In particular, as the
hot exhaust gases exiting power source 10 expand against the blades
of turbine 36, the shaft of turbine 36 may rotate and drive the
connected compressor 22. It is contemplated that more than one
turbine 36 may be included within exhaust system 18 and disposed in
parallel or series relationship. It is also contemplated that
turbine 36 may, alternately, be omitted and compressor 22 be driven
by power source 10 mechanically, hydraulically, electrically, or in
any other manner known in the art.
[0020] Downstream to the turbine 36, may be located a regeneration
assist system 38. The exhaust flow exiting the turbine 36 may flow
through the regeneration assist system 38. The regeneration assist
system 38 may include systems, such as a fuel driven burner or an
oxidation catalyst system. The regeneration assist system 38 may
assist in the regeneration of the second particulate filter 40, and
may be configured to increase the temperature of the exhaust
flowing through it. For instance, fuel may be sprayed by the fuel
driven burner and ignited within the regeneration assist system 38
to heat the exhaust flow. The regeneration assist system 38 may
include components, such as spark plugs, spray nozzles, fuel lines,
burners, and any other means that assists in heating the exhaust
flow. In some applications, the regeneration assist system 38 may
heat the exhaust flow electrically and may include electrical
resistive heaters. The regeneration assist system may also include
instrumentation to communicate with and execute instructions from a
control system 74. These instructions may include commands from the
controls system 74 instructing the regeneration assist system 38
begin heating the exhaust flow. The regeneration assist system 38
may also be fitted with sensors (not shown) to measure different
operating conditions, such as temperature, pressure, flow rate,
etc. of the regeneration assist system 38.
[0021] Although the regeneration assist system 38 is depicted as
located between the between the turbine 36 and the second
particulate filter 40 to assist in regeneration of the second
particulate filter 40. The regeneration assist system 38 may also
be located upstream of the first particulate filter 34 to assist in
regeneration of the first particulate filter 34. In some
applications, multiple regeneration assist systems 38 may be
located upstream of different particulate filters to assist in
regeneration of the respective filters. In some applications the
regeneration assist system 38 may not be located upstream of some
particulate filters, and the heat to regenerate those filters may
be provided by other means. For instance, the heat to regenerate
the first particulate filter 34 may be provided by the power source
10, or by heating elements located in first particulate filter
element 34. In some applications, the exhaust flow may be heated by
electromagnetic radiation, such as microwaves. Using a regeneration
assist system 38 to heat the exhaust flow may make the heating of
the exhaust flow more controllable. For example, by using only the
correct amount of fuel necessary to heat the exhaust flow to the
required temperature, good control over the exhaust gas temperature
may be achieved.
[0022] The second particulate filter 40 may be disposed downstream
of the regeneration assist system 38. Specifically, second
particulate filter 40 may be fluidly connected to regeneration
assist system 38 via a fluid passageway 52. The second particulate
filter 40 may include a second filter element 54 to filter
particulate matter from the exhaust flow. Similar to the first
filter element 46, the second filter element 54 may also be of any
type known in the art, may be situated in any configuration, and
may be of any construction that allows for proper filtering of
particulate matter. The flow of exhaust through the pores of the
second filter element 54 is illustrated by the arrows 56. In some
applications, the pore size of the second filter element 54 may be
different than the pore size of the first filter element 46 to
filter a different size of particulate matter particles. Similar to
first particulate filter 34, the second particulate filter 40 may
also include a catalyst to reduce the ignition temperature of
particulate matter trapped by second particulate filter 40, and
heating elements to heat the accumulated particulate matter.
Similar to the first particulate filter 34, the second particulate
filter 40 may also include pressure sensors 66, 68 and temperature
sensors 70, 72 to measure the pressure drop across the second
particulate filter 40 and temperatures at different locations
within the filter. These sensors may also be electrically connected
to the control system 74.
[0023] The control system 74 may include all the components to
manage the exhaust treatment system 12 such as, for example, a
memory, a secondary storage device, and a processor. Various
circuits may be associated with control system 74 such as, for
example, power supply circuitry, signal conditioning circuitry, and
other appropriate circuitry. The control system 74 may be connected
to different components of the exhaust treatment system 12 and may
be configured to send and receive signals to and from the different
components. These signals may include data from different sensors
and commands instructing a component to perform a particular task.
For instance, the control system 74 may be configured to receive
temperature and pressure data signals from the first and second
particulate filters 34, and 40, and send instructions to the
regeneration assist system 38. Signals from other sensors which may
indicate different parameters related to the operating condition of
the exhaust treatment system 12 may also be input to the control
system 74.
[0024] The control system 74 may be configured to store different
parameter values. These stored parameters may include user
specified values and values calculated by the control system 74.
For instance, the stored parameters may include a regeneration
temperature, a step temperature, a limit pressure drop, and a limit
time.
[0025] The regeneration temperature may be an average temperature
at which collected particulate matter in a particular filter burns.
The regeneration temperature may also be the lower limit of a range
of temperatures at which the accumulated particulate matter in a
particulate filter burns. It may be a user-defined value or may be
a value that the control system 74 computes from sensor inputs.
[0026] The step temperature may be a temperature value to which a
particulate filter 34, 40 may be heated prior to regeneration. The
step temperature may be a user-specified constant temperature value
lower than a regeneration temperature of the filter. It may also be
a value that is calculated by the control system 74 based upon the
sensor signals. For instance, based upon the temperature sensors
70, 72 the control system 74 may compute an overall temperature of
the second particulate filter 40. The control system 74 may further
compute the step temperature based on a mathematical model. For
instance, the step temperature may be calculated based upon the
thermo-mechanical stresses induced in a filter element 46, 54.
Specifically, the step temperature may be calculated such that the
stresses generated in the filter element 46, 54 due to a change of
temperature from the step temperature to the regeneration
temperature does not exceed the strength of the filter element 46,
54. The step temperature may be a temperature value which is higher
than the overall temperature and lower than the regeneration
temperature of the filter. The step temperature may be also be
calculated based upon the temperature gradient in a filter element
46, 54.
[0027] The limit pressure drop may be a user specified value or a
value calculated by the control system 74. For instance, the limit
pressure drop may be specified by a user based upon the maximum
permissible pressure drop across a particulate filter. It may also
be calculated by the control system based upon sensor inputs.
[0028] The time limit may indicate a time duration between filter
regenerations. It may be a constant value specified by a user, or
it may be calculated by the control system 74 based upon sensor
inputs. In some cases, it may be a user-defined value based on
prior experience.
[0029] The control system 74 may be configured to perform different
mathematical and logical operations and compare the results with
other calculated results and stored parameters. For instance, based
on signals from the pressure sensors 66, 68 the control system 74
may calculate the pressure drop across the second particulate
filter 40. The control system 74 may then compare this calculated
pressure drop with the stored limit pressure drop. The control
system 74 may also calculate an overall temperature of the second
particulate filter 40 based on signals from the temperature sensors
70, 72 and compare the result with the stored step temperature. The
control system 74 may also do a model based calculation based on
some or all of the sensor data, and may compare the result with
other stored or calculated values. The results of the comparisons
and calculations by the control system 74 may be used to control
different components of the exhaust treatment system 12. For
instance, the control system 74 may trigger the regeneration assist
system 38 to begin heating the exhaust flow through it when the
pressure drop across the second particulate filter 40 reaches or
exceeds the limit pressure drop, when the overall temperature of
the second particulate filter 40 is lower than the step
temperature, or when the time between regenerations of the second
particulate filter 40 exceed the stored time limit. It is also
contemplated that in some applications, the control system 74 may
trigger the regeneration assist system 38 to begin heating the
exhaust flow based on other comparisons, calculations or sensor
inputs. For instance, the control system 74 may use a mathematical
model to determine the particulate matter loading in a filter, and
use these results trigger the regeneration assist system. In some
cases, a sensor signal indicating a mass flow rate through the
fluid passageway 52 below a preset value may also trigger
regeneration of the second particulate filter 40. The control
system 74 may also signal the regeneration assist system 38 to stop
heating the exhaust flow based upon results of the comparisons,
calculations or sensor inputs. For example, when the overall
temperature of the second particulate filter 40 reaches or exceeds
the step temperature, the control system 74 may signal the
regeneration assist system 38 to stop heating the exhaust flow. The
control system 74 may also control the operation of other
components of the exhaust treatment system 12. For instance, the
control system may control the operation of the induction valve 20
and the recirculation valve 30 based upon signal inputs or
calculated values. In some applications, the control system 74 may
be part of the engine computer system. In these applications, the
control system 74 may also control the operation of other
components of the engine system 100.
INDUSTRIAL APPLICABILITY
[0030] The disclosed method of regenerating a particulate filter
34, 40 may be used with any type of engine system 100 that exhausts
exhaust gases containing particulate matter. The engine system 100
may include diesel engines, gasoline engines, gaseous fuel driven
engines, or any other engine known in the art. The engine system
100 may also be a part of a mobile or a stationary machine. Some of
the particulate matter exhausted by the engine system 100 gets
filtered by filter elements 46, 54 within the particulate filters
34, 40. These particulate filters 34, 40 are regenerated
periodically to prevent the accumulated particulate matter from
restricting exhaust flow through the filters. During regeneration,
large temperature gradients are introduced between different
sections of the filter elements 46, 54. The thermo-mechanical
stresses resulting from these temperature gradients induce
micro-cracks in the filter elements 46, 54. These micro-cracks
deteriorate the filtering efficiency and the durability of the
particulate filters 34, 40. The disclosed method of regeneration of
particulate filters preserves the filtering efficiency and
increases the durability of the particulate filters 34, 40 by
reducing the thermal gradients induced in the filter elements 46,
54 during regeneration.
[0031] FIG. 2 illustrates the method 1000 of regeneration of the
particulate filter in accordance with an embodiment of the current
disclosure. To describe the operation of the disclosed method, an
illustration describing the regeneration of the second particulate
filter 40 is used. When the control system 74 triggers a
regeneration process of the second particulate filter 40, any of
the above mentioned methods to regenerate the particulate filter
may be executed. In this disclosure, triggering a regeneration
process is used to indicate an initiation of the regeneration
process. For example, initiation of the regeneration process may
include commands from the control system 74 to begin heating the
exhaust flow. The term regeneration process is used broadly to
encompass all the heating and holding steps that eventually
culminates in the combustion of particulate matter accumulated in
the filter. For example, the regeneration process may include the
steps of heating the exhaust flow to the step temperature, holding
the temperature of the exhaust flow at the step temperature until
the filter media equilibrates at that temperature, and heating the
exhaust flow to the regeneration temperature.
[0032] The control system 74 may trigger a regeneration event when
the pressure drop across a filter reaches or exceeds the pressure
limit, when the time duration between successive regeneration
events reaches or exceeds the time limit, or based upon a model
based calculation. In some applications a regeneration event will
be triggered at the first occurrence of one of the above listed
events. In other applications, a regeneration event may only be
triggered at the occurrence of more than one of the above listed
events. It is also contemplated that the control system 74 may
trigger a regeneration event based upon some other condition. For
example, a regeneration may be triggered when a user initiates a
regeneration event by activating a switch or a button.
[0033] When a regeneration event is triggered, the first step in
the method 1000 of regeneration of a particulate filter is to
determine the overall temperature of the second particulate filter
40 (step 200). Determination of the overall temperature may include
measuring the temperature of the exhaust flow entering and exiting
the second particulate filter 40 using temperature sensors 70 and
72. These measured temperatures may then be used to determine the
overall temperature of the second particulate filter 40 using a
mathematical model. In some applications, the mathematical model
may include averaging the temperature readings from the temperature
sensors 70, 72. In some other applications, a more complex
mathematical model that may use other sensor inputs in addition to
the temperature sensor inputs may be used to calculate the overall
temperature. It is also contemplated that the control system 74 may
directly use a temperature sensor input as the overall temperature
of the second particulate filter 40.
[0034] After determining the overall temperature of the second
particulate filter 40, the control system may compare this overall
temperature with the step temperature (step 300). If the overall
temperature of the second particulate filter 40 is lower than the
step temperature, the second particulate filter 40 may be heated to
the step temperature (step 400). To heat the second particulate
filter 40 to the step temperature, the control system 74 may
instruct the regeneration assist system 38 to start heating the
exhaust flow through it. The heated exhaust flow may in turn heat
the second particulate filter 40 while flowing through it. In some
applications, the control system 74 may instruct the regeneration
assist system 38 to heat the exhaust flow such that the second
particulate filter 40 is heated and maintained at the step
temperature. In some other applications, the control system 74 may
use sensor inputs from temperature sensors 70, 72 or other sensor
inputs to maintain the second particulate filter 40 at the step
temperature. In the comparison of step 300, if the overall
temperature of the second particulate filter 40 is at or above the
step temperature, step 400 will not be executed, and the method
will proceed directly to step 500.
[0035] When the overall temperature of the second particulate
filter 40 reach or exceed the step temperature (that is, when the
condition of step 300 is satisfied), the particulate filter may be
maintained at the step temperature until the particulate filter
equilibrates at the step temperature (step 450). Equilibrating the
second particulate filter 40 at the step temperature may involve
holding the second particulate filter 40 at the step temperature
for a predetermined amount of time until substantially all regions
of the second filter element 54 reaches the step temperature. This
predetermined amount of time may be a user-specified time delay
that may be stored in the control system 74. The predetermined
amount of time may provide sufficient time to allow the second
filter element 54 of the second particulate filter 40 to
substantially equilibrate to the step temperature. The
predetermined amount of time may be determined from prior
experience, experimental studies, analytical calculations or
numerical computations (such as, for example, finite element
analysis). When the second filter element 54 equilibrates at the
step temperature, different sections of the filter element 54 are
at substantially uniform temperature. In some applications, in
place of a preset time delay, the control system 74 may maintain
the second particulate filter 40 at the step temperature until
inputs from temperature sensors indicate that the filter element 54
has substantially equilibrated at the step temperature.
[0036] After the particulate filter equilibrates at the step
temperature (step 450), the control system 74 may instruct the
regeneration assist system 38 to further heat the exhaust flow to
the regeneration temperature (step 500). The regeneration
temperature may be a user specified value of temperature stored in
the control system 74 indicating the temperature at which the
accumulated particulate matter in the second particulate filter 40
burns.
[0037] Although the description above focuses on the method of
regenerating the second particulate filter 40, the disclosed method
can also be used to regenerate any other particulate filter in the
engine system 100. In applications without a regeneration assist
system 38, heating the particulate filter to the step temperature
and then to the regeneration temperature may be accomplished by
other means. For example, heat to regenerate the first particulate
filter 34 may be obtained by using the power source 10 to heat the
exhaust flow to the required temperature or by using heaters
installed in the first particulate filter 34.
[0038] Heating and equilibrating a particulate filter at an
intermediate temperature close to the regeneration temperature
before further heating it to the regeneration temperature,
decreases the temperature difference between different regions of
the filter element during regeneration. This decrease in
temperature difference will decrease the difference in thermal
expansion between different regions of the filter element, thereby
reducing the thermo-mechanical stresses in the filter element. This
reduction of stresses in the filter element will decrease the
likelihood of stress induced micro-cracks in the filter element,
thereby increasing its durability. Since the increase in durability
is achieved without the use of additional parts or processing
treatments, the cost of the particulate filter is not impacted.
[0039] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed method of
regenerating a particulate filter. Other embodiments will be
apparent to those skilled in the art from consideration of the
specification and practice of the disclosed regeneration method. It
is intended that the specification and examples be considered as
exemplary only, with a true scope being indicated by the following
claims and their equivalents.
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