Claims:1. A method for controlling an emission amount in a gas stream emitted from a power generation system comprising a combustion engine operating at stoichiometric conditions, and a three-way catalyst disposed downstream of the combustion engine, the method comprising:
determining a pre-catalyst emission level using a combustion engine model;
determining a post-catalyst emission level using a three-way catalyst model based on the pre-catalyst emission level;
determining an adjusted post-catalyst emission level based on the post-catalyst emission level;
determining a difference between the post-catalyst emission level and the adjusted post-catalyst emission level and comparing the difference with a threshold value; and
determining whether to adjust an actual value of an engine operating parameter based on the comparison such that the emission amount in the gas stream is maintained below an emission regulatory limit.

2. The method of claim 1, wherein the adjusted post-catalyst emission level is determined based on one or more measured parameters comprising a measured pre-catalyst emission level, a measured post-catalyst emission level, a gas stream humidity, or combinations thereof.

3. The method of claim 1, wherein the engine operating parameter comprises an exhaust gas recirculation (EGR) set-point, a lambda (?) set-point, an engine ignition timing, or combinations thereof.

4. The method of claim 1, comprising determining that adjusting the actual operating parameter is required if the difference is greater than the threshold value, and further comprising sending a signal to adjust the engine operating parameter.

5. The method of claim 4, further comprising determining an estimated value of the engine operating parameter if the difference is greater than the threshold value and adjusting the actual value of the engine operating parameter based on the estimated value of the engine operating parameter.

6. The method of claim 5, comprising determining the estimated value of the engine operating parameter based on the adjusted post-catalyst emission level, the emission regulatory limit, and one or both of a ? curve and an EGR curve.

7. The method of claim 6, wherein the ? curve is indicative of a relationship between the adjusted post-catalyst emission level and a ? set-point, and wherein the EGR curve is indicative of a relationship between at least two of an EGR set-point, an engine load, and the pre-catalyst emission level.

8. The method of claim 6, wherein the estimated value of the engine operating parameter is determined further based on a combustion engine age, a three-way catalyst age, or a combination thereof.

9. The method of claim 6, wherein determining the estimated value of the engine operating parameter comprises:
determining a range of estimated values of the engine operating parameter based on the adjusted post-catalyst emission level, the emission regulatory limit, and one or both of the ? curve and the EGR curve; and
selecting the estimated value of the engine operating parameter from the range of estimated values of the engine operating parameter.

10. The method of claim 5, further comprising adjusting the actual value of the engine operating parameter based on the estimated value of the engine operating parameter such that a number of occurrences of a misfire condition is maintained below a determined number of misfire occurrences.

11. The method of claim 5, further comprising adjusting the actual value of the engine operating parameter based on the estimated value of the engine operating parameter such that a number of occurrences of a knock condition is maintained below a determined number of knock occurrences.

12. The method of claim 1, further comprising:
determining a region of operation of the power generation system based at least on location coordinates determined via a global positioning system sensor; and
determining the emission regulatory limit based on the region of operation of the power generation system.

13. The method of claim 1, wherein an input value to the three-way catalyst model further comprises a gas stream temperature, a gas stream mass flow-rate, or a combination thereof.

15. An engine controller for controlling an emission amount in a gas stream emitted from a power generation system comprising a combustion engine operating at stoichiometric conditions, and a three-way catalyst disposed downstream of the combustion engine, the engine controller comprising:
a memory storing one or more processor-executable routines; and
one or more processors to execute the one or more processor-executable routines which, when executed, cause acts to be performed comprising:
determining a pre-catalyst emission level using a combustion engine model;
determining a post-catalyst emission level using a three-way catalyst model based on the pre-catalyst emission level;
determining an adjusted post-catalyst emission level based on the post-catalyst emission level;
determining a difference between the post-catalyst emission level and the adjusted post-catalyst emission level and comparing the difference with a threshold value; and
determining whether to adjust an actual value of an engine operating parameter based on the comparison such that the emission amount in the gas stream is maintained below an emission regulatory limit.

16. The engine controller of claim 15, wherein the engine operating parameter comprises an exhaust gas recirculation (EGR) set-point, a lambda (?) set-point, an engine ignition timing, or combinations thereof.

17. The engine controller of claim 15, wherein the acts to be performed further comprise determining an estimated value of the engine operating parameter if the difference is greater than the threshold value and adjusting the actual value of the engine operating parameter based on the estimated value of the engine operating parameter.

18. A power generation system, comprising:
a combustion engine operating at stoichiometric conditions;
a three-way catalyst disposed downstream of the combustion engine; and
an engine controller operably coupled to the combustion engine to control an emission amount in a gas stream emitted from the power generation system, wherein the engine controller comprises:
a memory storing one or more processor-executable routines; and
one or more processors to execute the one or more processor-executable routines which, when executed, cause acts to be performed comprising:
determining a pre-catalyst emission level using a combustion engine model;
determining a post-catalyst emission level using a three-way catalyst model based on the pre-catalyst emission level;
determining an adjusted post-catalyst emission level based on the post-catalyst emission level;
determining a difference between the post-catalyst emission level and the adjusted post-catalyst emission level and comparing the difference with a threshold value; and
determining whether to adjust an actual value of an engine operating parameter based on the comparison such that the emission amount in the gas stream is maintained below an emission regulatory limit.

19. The power generation system of claim 18, wherein the engine operating parameter comprises an exhaust gas recirculation (EGR) set-point, a lambda (?) set-point, an engine ignition timing, or combinations thereof.

20. The power generation system of claim 18, wherein the acts to be performed further comprise determining an estimated value of the engine operating parameter if the difference is greater than the threshold value and adjusting the actual value of the engine operating parameter based on the estimated value of the engine operating parameter
, Description:BACKGROUND
[0001] Embodiments of the invention relate to a system and a method for improving engines
operating at a stoichiometric condition. More particularly, embodiments of the invention relate
to an engine controller and related methods for controlling an emission amount in a gas stream
emitted from a power generation system employing an engine operating at the stoichiometric
condition.
[0002] Internal combustion (IC) engines are used in a wide range of applications. The IC
engines use a variety of fuels including, but not limited to, liquid fuels such as gasoline
(sometimes referred to as petrol) and diesel, and gaseous fuels such as liquefied natural gas
(LNG) or liquefied petroleum gas (LPG). Typically, combustion of such fuels in an IC engine
produces by-products that are discharged from the IC engine in the form of a gas stream. The
exhaust gas stream from the IC engine may include contaminants, such as, oxides of nitrogen
(NOx), carbon monoxide (CO), hydrocarbons (HC), or combinations thereof. Such
contaminants, when mixed into the atmosphere, may lead to various environmental hazards.
[0003] Typically, in order to minimize levels of the contaminants (sometimes referred to as
emission levels) in the gas stream, the IC engines operating at stoichiometric condition may
employ a three-way catalyst. The three-way catalyst causes chemical reactions such as, but not
limited to, oxidation and reduction, to treat the gas stream in order to minimize the levels of the
contaminants. Further, use of an exhaust gas recirculation (EGR) along with the use of the threeway
catalyst may help in minimizing levels of the contaminants.
[0004] However, in order to consistently achieve low levels of the contaminants in the
exhaust gas stream, it may be desirable to maintain operation of the IC engine at the
stoichiometric condition. Maintaining the stoichiometric condition during the operation of the
IC engine may be a challenge. Further, maintaining low levels of the contaminants as the IC
engine and the three-way catalyst ages, may be another challenge. Furthermore, when the IC
engine is employed in a mobile application, it may also be desirable that the levels of the
contaminants are maintained to meet emission requirements of a given region. Thus, there is a
need for improved methods and related controllers and power generation systems to maintain the
emission levels in the exhaust stream.
BRIEF DESCRIPTION
[0005] One embodiment of the invention is directed to a method for controlling an emission
amount in a gas stream emitted from a power generation system including a combustion engine
operating at stoichiometric conditions, and a three-way catalyst disposed downstream of the
combustion engine. The method includes determining a pre-catalyst emission level using a
combustion engine model. The method further includes determining a post-catalyst emission
level using a three-way catalyst model based on the pre-catalyst emission level. Furthermore, the
method includes determining an adjusted post-catalyst emission level based on the post-catalyst
emission level. Moreover, the method also includes determining a difference between the postcatalyst
emission level and the adjusted post-catalyst emission level and comparing the
difference with a threshold value. Additionally, the method includes determining whether to
adjust an actual value of an engine operating parameter based on the comparison such that the
emission amount in the gas stream is maintained below an emission regulatory limit.
[0006] Another embodiment of the invention is directed to an engine controller for
controlling an emission amount in a gas stream emitted from a power generation system
including a combustion engine operating at stoichiometric conditions, and a three-way catalyst
disposed downstream of the combustion engine. The engine controller includes a memory
storing one or more processor-executable routines. The engine controller further includes one or
more processors to execute the one or more processor-executable routines which, when executed,
cause acts to be performed including determining a pre-catalyst emission level using a
combustion engine model. The acts to be performed also include determining a post-catalyst
emission level using a three-way catalyst model based on the pre-catalyst emission level.
Further, the acts to be performed include determining an adjusted post-catalyst emission level
based on the post-catalyst emission level. Furthermore, the acts to be performed include
determining a difference between the post-catalyst emission level and the adjusted post-catalyst
emission level and comparing the difference with a threshold value. Moreover, the acts to be
performed also include determining whether to adjust an actual value of an engine operating
parameter based on the comparison such that the emission amount in the gas stream is
maintained below an emission regulatory limit.
[0007] Yet another embodiment of the invention is directed to a power generation system.
The power generation system includes a combustion engine operating at stoichiometric
conditions. The power generation system further includes a three-way catalyst disposed
downstream of the combustion engine. Furthermore, the power generation system includes an
engine controller operably coupled to the combustion engine to control an emission amount in a
gas stream emitted from the power generation system. The engine controller includes a memory
storing one or more processor-executable routines. The engine controller further includes one or
more processors to execute the one or more processor-executable routines which, when executed,
cause acts to be performed including determining a pre-catalyst emission level using a
combustion engine model. The acts to be performed also include determining a post-catalyst
emission level using a three-way catalyst model based on the pre-catalyst emission level.
Further, the acts to be performed include determining an adjusted post-catalyst emission level
based on the post-catalyst emission level. Furthermore, the acts to be performed include
determining a difference between the post-catalyst emission level and the adjusted post-catalyst
emission level and comparing the difference with a threshold value. Moreover, the acts to be
performed also include determining whether to adjust an actual value of an engine operating
parameter based on the comparison such that the emission amount in the gas stream is
maintained below an emission regulatory limit.
DRAWINGS
[0008] These and other features, aspects, and advantages of the present specification will
become better understood when the following detailed description is read with reference to the
accompanying drawings in which like characters represent like parts throughout the drawings,
wherein:
[0009] FIG. 1 is a diagrammatical illustration of a power generation system, in accordance
with one embodiment of the invention;
[0010] FIG. 2 depicts a flowchart illustrating a method for controlling an emission amount in
a gas stream emitted from the power generation system of FIG. 1, in accordance with one
embodiment of the invention;
[0011] FIG. 3 is a graphical representation depicting a lambda curve, in accordance with one
embodiment of the invention;
[0012] FIG. 4 is a graphical representation depicting an exhaust gas recirculation (EGR)
curve, in accordance with one embodiment of the invention; and
[0013] FIG. 5 depicts a flowchart illustrating a method for determining an emission
regulatory limit, in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
[0014] The specification may be best understood with reference to the detailed figures and
description set forth herein. Various embodiments of the invention are described hereinafter
with reference to the figures. However, those skilled in the art will readily appreciate that the
detailed description given herein with respect to these figures is for explanatory purposes as the
method and the system may extend beyond the described embodiments of the invention.
[0015] Unless defined otherwise, technical and scientific terms used herein have the same
meaning as is commonly understood by one of ordinary skill in the art to which this disclosure
belongs. In the following specification and the claims, the singular forms “a”, “an” and “the”
include plural referents unless the context clearly dictates otherwise. As used herein, the term
“or” is not meant to be exclusive and refers to at least one of the referenced components being
present and includes instances in which a combination of the referenced components may be
present, unless the context clearly dictates otherwise.
[0016] As used herein, the terms “may” and “may be” indicate a possibility of an occurrence
within a set of circumstances; a possession of a specified property, characteristic or function;
and/or qualify another verb by expressing one or more of an ability, capability, or possibility
associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a
modified term is apparently appropriate, capable, or suitable for an indicated capacity, function,
or usage, while taking into account that in some circumstances, the modified term may
sometimes not be appropriate, capable, or suitable.
[0017] Approximating language, as used herein throughout the specification and claims, may
be applied to modify any quantitative representation that could permissibly vary without
resulting in a change in the basic function to which it is related. Accordingly, a value modified
by a term or terms, such as “about”, and “substantially” is not to be limited to the precise value
specified. Here and throughout the specification and claims, range limitations may be combined
and/or interchanged; such ranges are identified and include all the sub-ranges contained therein
unless context or language indicates otherwise.
[0018] Some embodiments of the invention are directed to a power generation system and a
method of controlling an emission amount in a gas stream emitted from the power generation
system. The power generation system includes a combustion engine operating at stoichiometric
conditions. The power generation system further includes a three-way catalyst disposed
downstream of the combustion engine. Furthermore, the power generation system includes an
engine controller operably coupled to the combustion engine to control an emission amount in a
gas stream emitted from the power generation system. The engine controller includes a memory
storing one or more processor-executable routines. The engine controller further includes one or
more processors to execute the one or more processor-executable routines which, when executed,
cause acts to be performed including determining a pre-catalyst emission level using a
combustion engine model. The acts to be performed also include determining a post-catalyst
emission level using a three-way catalyst model based on the pre-catalyst emission level.
Further, the acts to be performed include determining an adjusted post-catalyst emission level
based on the post-catalyst emission level. Furthermore, the acts to be performed include
determining a difference between the post-catalyst emission level and the adjusted post-catalyst
emission level and comparing the difference with a threshold value. Moreover, the acts to be
performed also include determining whether to adjust an actual value of an engine operating
parameter based on the comparison such that the emission amount in the gas stream is
maintained below an emission regulatory limit.
[0019] FIG. 1 is a diagrammatical illustration of a power generation system 100, in
accordance with one embodiment of the invention. As illustrated in FIG. 1, in some
embodiments of the invention, the power generation system 100 may include a combustion
engine 102, a three-way catalyst 106 disposed downstream of the combustion engine 102, and an
engine controller 108. The engine controller 108 may be operably coupled to the combustion
engine 102 to control an emission amount in a gas stream 10 emitted from the power generation
system 100.
[0020] In some embodiments of the invention, the power generation system 100 may further
include an intake conduit 104 that may receive an air stream 12 and a fuel stream 16. The intake
conduit 104 may be configured to facilitate mixing of the air stream 12 with the fuel stream 16
thereby generating a mixed stream 18, which may be received by the combustion engine 102.
[0021] The combustion engine 102 may be an internal combustion (IC) engine. In a nonlimiting
example, the combustion engine 102 may be a gas engine. In some embodiments of the
invention, the combustion engine 102 may include one or more cylinders (not shown). Each
cylinder of the one or more cylinders may include a combustion chamber, a piston, and a
crankshaft mechanically coupled to the piston. Further, the combustion engine 102 may also
include one or more fuel injectors (not shown) to inject the one or more fuels directly into the
combustion chamber or via an intake manifold (not shown) to the combustion chamber.
[0022] In some embodiments of the invention, the combustion engine 102 may be fluidly
coupled to the intake conduit 104 to receive the mixed stream 18. The engine controller 108
may, at least in part, control the combustion of the mixed stream 18 in the combustion engine
102 by way of controlling injection of the mixed stream 18 into the combustion engine 102. The
injection of the mixed stream 18 into the combustion engine 102 may be controlled by the engine
controller 104 by controlling one or more of an intake valve (not shown) or the one or more fuel
injectors. In certain embodiments of the invention, the combustion engine 102 may be operated
at a stoichiometric condition. The term “stoichiometric condition” as used herein refers to an
operation of the combustion engine 102 at an air-fuel equivalence ratio (hereinafter, alternatively
referred to as a lambda set-point (???????????????????)) of one (1) or substantially close to one (1). In one
embodiment of the invention, the ? set-point may be represented by a following equation:
[0023] ??????????????????? ?? ??????????????????
??????????????????????????????????
(1)
[0024] where, ?????????????????? represents an actual air-fuel ratio of the mixed stream 18 and
?????????????????????????????????? represents a stoichiometric air-fuel ratio of the mixed stream 18 for a given
fuel. A value of ??????????????????? greater than 1 may be indicative of the mixed stream 18 having a lean
air-fuel mixture and the value of ??????????????????? lower than 1 may be indicative of the mixed stream
18 having a rich air-fuel mixture.
[0025] In response to the combustion at the stoichiometric condition, a reciprocating motion
of the piston may be enabled. The piston may be mechanically coupled to the crankshaft such
that a reciprocating motion of the piston is converted into a rotational motion of the crankshaft.
Accordingly, in one embodiment of the invention, the power generation system 100 may
generate a mechanical power in the form of the rotational motion of the crankshaft using a
chemical energy of the one or more fuels. Combustion residues or by-products of the
combustion may be discharged from the combustion engine 102 as an exhaust gas stream 20.
[0026] In some embodiments of the invention, the exhaust gas stream 20 may include
contaminants such as oxides of nitrogen (NOx), carbon monoxide (CO), and hydrocarbons (HC).
These contaminants, if emitted into the environment, may result in environmental hazards. In
order to reduce levels of such contaminants a three-way catalyst 106 is disposed downstream of
the combustion engine 102. In some embodiments of the invention, a flow path of the exhaust
gas stream 20 may be designed such that at least a portion of the exhaust gas stream 20 may be
directed toward the three-way catalyst 106. The portion of the exhaust gas stream 20 that is
directed toward the three-way catalyst 106 is hereinafter referred to as a pre-catalyst gas stream
22.
[0027] The three-way catalyst 106 may facilitate a chemical reaction of at least a portion of
the pre-catalyst exhaust gas stream 22, thereby forming the emitted gas stream 10 having
reduced levels of such contaminants, for example, by converting at least a portion of the
contaminants into nitrogen (N2), carbon dioxide (CO2) and water (H2O). By way of a nonlimiting
example, the three-way catalyst 106 may include a reduction catalyst and oxidation
catalyst to aid in the chemical reaction with the pre-catalyst exhaust gas stream 22. In some
embodiments of the invention, the reduction catalyst or the oxidation catalyst may have a
ceramic honeycomb structure. Examples of materials used in the three-way catalyst 106 may
include, but are not limited to, platinum (Pt), palladium (Pd), and rhodium (Rh).
[0028] In some embodiments of the invention, the power generation system 100 may employ
an EGR system that facilitates a flow of a portion of an exhaust gas steam 20 back into the
combustion engine 102. The EGR system may include an EGR valve 116 for controlling the
flow of the portion of the exhaust gas stream 20 toward the combustion engine 102. The portion
of the exhaust gas stream 20 that is directed toward the combustion engine 102 via the EGR
valve 116 is hereinafter referred to as an EGR stream 24. In some embodiments of the invention,
the engine controller 108 may control an open position or percentage opening of the EGR valve
to control the flow of the EGR stream 24.
[0029] In certain embodiments of the invention, the EGR stream 24 may be supplied to the
intake conduit 104, where it may be mixed with the air stream 12 and the fuel stream 16. In such
an instance, when the EGR system is employed, the mixed stream 18 may be a mixture of the air
stream 12, the fuel stream 16, and the EGR stream 24. Combustion of such mixed stream 18 in
the combustion engine 102 may result in reduced flame temperature in the combustion engine
102. The reduction in the flame temperature may further reduce generation of the NOx in the
exhaust gas stream 20. Also, a useful life of the combustion engine 102 may be improved due to
the reduced temperature inside the combustion engine 102.
[0030] As noted earlier, the engine controller 108 may control an emission amount in the gas
stream 10 emitted from a power generation system 100, in some embodiments. The engine
controller 104 may include one or more processors, such as, a processor 110. The processor 110
may include a specially programmed general purpose computer, a microprocessor, a digital
signal processor, and a microcontroller. Examples of the processor 110 may include, but are not
limited to, a reduced instruction set computing (RISC) architecture type processor or a complex
instruction set computing (CISC) architecture type processor. Further, the processor 110 may be
a single-core processor or a multi-core processor. The processor 110 may also include, or, has
electrically coupled thereto, one or more input/output ports.
[0031] The engine controller 104 may further include a memory 112 accessible by the
processor 110. In one embodiment of the invention, the memory 112 may be integrated into the
processor 110. In another embodiment of the invention, the memory 112 may be external to the
processor 110 and electrically coupled to the processor 110, as depicted in FIG. 1. The memory
112 may be a non-transitory computer-readable media. The non-transitory computer-readable
media may include tangible, computer-readable media, including, without limitation, nontransitory
computer storage devices. The non-transitory computer storage devices may include,
but are not limited to, volatile and non-volatile media, and removable and non-removable media
such as a firmware, physical and virtual storage, a compact disc read only memory (CD-ROM),
or a digital versatile disc (DVD). The non-transitory computer storage devices may also include
digital source such as a network or the Internet, as well as yet to be developed digital means,
with the sole exception being a transitory, propagating signal. Other non-limiting examples of
the memory 112 include a dynamic random access memory (DRAM) device, a static random
access memory (SRAM) device, and a flash memory.
[0032] The memory 112 may store processor-executable routines that are executable by the
processor 110. The processor-executable routines, when executed by the processor 110, may
cause acts to be performed that contribute to methods described below as well as other variants
that are anticipated, but not specifically listed. In a non-limiting example, processor-executable
routines may be implemented in a variety of programming languages, including but not limited
to C, C++, or Java. In some embodiments of the invention, by executing one or more of the
processor-executable routines, the processor 110 may aid in controlling the emission from the
power generation system 100 such that the emission amount in the gas stream 10 is maintained
below an emission regulatory limit.
[0033] In some embodiments of the invention, the processor-executable routines, when
executed by the processor 110 may cause the acts to be performed. The acts to be performed
may include steps illustrated in flowcharts of Figures 2 and 5. FIG. 2 depicts a flowchart
illustrating a method 200 for controlling the emission amount in the gas stream 10 emitted from
the power generation system 100, in accordance with one embodiment of the invention. As
illustrated in FIG. 2, in some embodiments of the invention, the method 200 may include steps
202-216. The processor-executable routines, when executed by the processor 110, may cause the
processor 110 to perform acts indicated by the steps 202-216 of the method 200.
[0034] Referring now to Figures 1 and 2, in some embodiments of the invention, the method
200 includes determining a pre-catalyst emission level using a combustion engine model at step
202. For example, the pre-catalyst emission level corresponding to one or more of the CO,
NOx, and HC amount may be determined by the processor 110 using the combustion engine
model.
[0035] In some embodiments of the invention, the combustion engine model may be
representative of a relationship among one or more of an EGR set-point, an engine speed, an
engine load, a brake mean effective pressure (BMEP), and a pre-catalyst emission level. In some
embodiments of the invention, the EGR set-point may be the percentage opening or the open
position of the EGR valve 116. The BMEP may be indicative of an intake manifold pressure of
the cooled air-fuel-exhaust mixture. In a non-limiting example, the combustion engine model
may be stored in the memory 112 and represented by following equations:
[0036] ?????????????????? ?? ???????? * ?????????? ?? ?????? * ?????? ?????????????????? ?? ?????? * ???????????????????? ?? ?????? * ??????????????????
???? ?? ??????
(2)
[0037] ???????????????????? ?? ???????? * ?????????? ?? ?????? * ?????? ?????????????????? ?? ?????? * ???????????????????? ?? ?????? * ?????? ????????????????
???? ??
???????? (3)
[0038] ?????????????????? ?? ???????? ?? ???????? * ?????????? ?? ???????? * ?????? ?????????????????? ?? ???????? * ???????????????????? ?? ???????? *
?????? ????????????????
?????? (4)
[0039] wherein, ???? - ?????? represents numeric coefficients, EGR ???????????????? represents an actual
value of the EGR set-point, and ????????????????? represents an actual value of the ? set-point. Although,
not shown above, the combustion engine model may also be represented using equations that are
based on a parameter, such as, but not limited to, the engine load, without limiting the scope of
the present specification.
[0040] In another embodiment of the invention, the combustion engine model may be stored
in the memory 112 as a combustion engine look-up table indicative of the relationship among the
EGR set-point, the engine speed, the engine load, and the pre-catalyst emission level. In a nonlimiting
example, in the combustion engine look-up table, different values of the pre-catalyst
emission level may be stored with respect to corresponding values of the EGR set-point, the
engine speed, and the engine load.
[0041] Accordingly, in some embodiments of the invention, in order to determine the precatalyst
emission level, the processor 110 may determine one or more of the engine speed (rpm),
the engine load (kW), the BMEP (psi or bar), and an actual value of the EGR set-point
(described later). The processor 110 may then use the combustion engine model (for example,
the equations 2-4 or the combustion engine look-up table) to determine the pre-catalyst emission
level corresponding to the determined engine speed (rpm), engine load (kW), BMEP (psi or bar),
and actual value of the EGR set-point. In some embodiments of the invention, the processor 110
may store the pre-catalyst emission level determined at step 202 in the memory 112.
[0042] Further, in some embodiments of the invention, as shown in Fig. 2, the method 200
includes determining a post-catalyst emission level using a three-way catalyst model based on
the pre-catalyst emission level, at step 204. For example, the post-catalyst emission level
corresponding to one or more of the CO, NOx, or HC amount may be determined by the
processor 110 using the three-way catalyst model.
[0043] In some embodiments of the invention, the three-way catalyst model may be indicative
of properties of the three-way catalyst 106. For example, the three-way catalyst model may be a
physics based model of the three-way catalyst 106. In a non-limiting example, the three-way
catalyst model may be represented by following equations:
[0044] g i ? g i s i ?
g i g i A c c
x
c
u
t
c
, ,
, , ? ?
?
?
? ?
?
?
? ? ? (5)
[0045] ? ? ? ? ?
?
? ? ?
?
?
?
N
j
g i g i s i i j
s i A c c r
t
c
1
, , ,
1 ? , ? (6)
[0046] RT
E
i i
N
i
i i
i
r k c k Ae?
?
? ? , ?
1
(7)
[0047] wherein, e represents open frontal area or void fraction of the three-way catalyst 106,
cg represents gas phase concentration of contaminants (for example, NOx, CO, or HC) in the precatalyst
exhaust gas stream 22, cs represents surface phase concentration of the contaminants in
the pre-catalyst exhaust gas stream 22, u represents a measured exhaust gas stream mass flowrate,
Ag represents geometric surface area of the three-way catalyst 106, ß represents mass
transfer coefficient from gas phase to surface phase and vice-versa, ri,j represents rate of reaction
of ith contaminant participating in jth reaction, ki represents reaction rate constant, Ai represents
pre exponential factor, Ei represents activation energy, T represents a measured exhaust gas
stream temperature, and R represents universal gas constant.
[0048] In some alternative embodiments of the invention, the three-way catalyst model may
further be simplified using conservation of contaminants feature. The simplified three-way
catalyst model may be represented using a single equation of gas phase contaminant
concentrations. In a non-limiting example, the simplified three-way catalyst model may be
represented by a following equation:
[0049] ?
?
?
?
?
? ?
?
? N
j
i j
g i g i r
x
c
u
t
c
1
,
, , 1
?
(8)
[0050] In one embodiment of the invention, an input to the three-way catalyst model may
include the pre-catalyst emission level determined at step 202. In some embodiments of the
invention, in addition to the pre-catalyst emission level, the input value to the three-way catalyst
model may further include the measured exhaust gas stream temperature, the measured exhaust
gas stream mass flow-rate, or a combination thereof. Therefore, in order to determine the postcatalyst
emission level, the processor 110 may also determine the measured exhaust gas stream
temperature and the measured exhaust gas stream mass flow-rate.
[0051] Accordingly, in some embodiments of the invention, the power generation system 100
may further include a flow-rate sensor 118 and a temperature sensor 120. The flow-rate sensor
118 and the temperature sensor 120 may be disposed downstream of the three-way catalyst 106.
The flow-rate sensor 118 and the temperature sensor 120 may generate electric signals indicative
of levels of an exhaust gas stream mass flow-rate and an exhaust gas stream temperature,
respectively, of the gas stream 10. The processor 110 may receive the electric signals generated
by the flow-rate sensor 118 and the temperature sensor 120. These electric signals may aid in
determining, by the processor 110, the levels of the exhaust gas stream mass flow-rate and the
exhaust gas stream temperature, respectively. The levels of the exhaust gas stream mass flowrate
and the exhaust gas stream temperature, thus determined, are referred to as the “measured
exhaust gas stream mass flow-rate,” and the “measured exhaust stream gas temperature,”
respectively.
[0052] The processor 110 may then use the three-way catalyst model (for example, the
equations 5-7 or the equation 8) to determine the post-catalyst emission level based on one or
more of the pre-catalyst emission level determined at step 202, the measured exhaust gas stream
mass flow-rate, and the measured exhaust stream gas temperature. In some embodiments of the
invention, the processor 110 may store the post-catalyst emission level determined at step 204 in
the memory 112.
[0053] In some embodiments of the invention, the method 200 further includes determining
an adjusted post-catalyst emission level, at step 206. In a non-limiting example, the processorexecutable
routines executed by the processor 110 to determine the adjusted post-catalyst
emission level may constitute a functionality of an estimator, such as, a Kalman filter or an
extended Kalman filter. In one embodiment of the invention, the Kalman filter or the extended
Kalman filter may have been configured to incorporate therein a behavior of the power
generation system 100. Accordingly, the post-catalyst emission level determined by the
processor 110, at step 204, may further be corrected to determine the adjusted post-catalyst level
using the estimator. Accordingly, in some embodiments of the invention, the adjusted postcatalyst
emission level may be representative of an error corrected form of the post-catalyst
emission level, determined at step 204.
[0054] In some embodiments of the invention, additional inputs to the processor 110 for
determining the adjusted post-catalyst emission level may further include one or more of a
measured pre-catalyst emission level, a measured post-catalyst emission level, a measured
humidity content in the gas stream 10, at least one fuel quality parameter, or combinations
thereof.
[0055] In some embodiments of the invention, in order to determine the measured pre-catalyst
emission level, the power generation system 100 may include a pre-catalyst emission sensor 115.
The pre-catalyst emission sensor 115 may be disposed upstream of the three-way catalyst 106.
In a non-limiting example, the pre-catalyst emission sensor 115 may be disposed at any suitable
location in a flow path of the pre-catalyst exhaust gas stream 22, the exhaust gas stream 20, or
the EGR stream 24. The pre-catalyst emission sensor 115 may generate an electrical signal
indicative of a level of a given contaminant (for example, NOx) in the flow path prior to the
three-way catalyst 106. The electrical signal generated by the pre-catalyst emission sensor 115
may aid in determining, by the processor 110, the level of any of the contaminants (for example,
NOx) in the exhaust gas stream 20, the pre-catalyst exhaust gas stream 22, or the EGR stream 24.
Hereinafter, the level of the given contaminant that is determined based on the electrical signal
generated by the pre-catalyst emission sensor 115 may be referred to as the “measured precatalyst
emission level.” In some embodiments of the invention, the processor 110 may store the
measured pre-catalyst emission level in the memory 112.
[0056] Further, in some embodiments of the invention, in order to determine the measured
post-catalyst emission level, the power generation system 100 may include a post-catalyst
emission sensor 122 disposed downstream of the three-way catalyst 106. In a non-limiting
example, the post-catalyst emission sensor 122 may be disposed at any suitable location in a flow
path of the gas stream 10. The post-catalyst emission sensor 122 may generate another electrical
signal that is indicative of a level of a given contaminant (for example, NOx) in the flow path
downstream of the three-way catalyst 106. The electrical signal generated by the post-catalyst
emission sensor 122 may aid in determining, by the processor 110, the level of any of the
contaminants (for example, NOx) in the gas stream 10. Hereinafter, the level of the given
contaminant that is determined based on the electrical signal generated by the post-catalyst
emission sensor 122 may be referred to as the “measured post-catalyst emission level.” In some
embodiments of the invention, the processor 110 may store the measured post-catalyst emission
level in the memory 112.
[0057] In some embodiments of the invention, in order to determine the measured humidity
content in the gas stream 10, the power generation system 100 may include a humidity sensor
124 disposed downstream of the three-way catalyst 106. The humidity sensor 124 may generate
another electrical signal that is indicative of the humidity content in the gas stream 10. The
electrical signal generated by the humidity sensor 124 may aid in determining, by the processor
110, the level of the exhaust gas stream humidity content. The level of the exhaust gas stream
humidity content determined based on the electrical signal generated by the humidity sensor 124
may is referred to as the “measured exhaust gas stream humidity content”. In some
embodiments of the invention, the processor 110 may store the measured exhaust gas stream
humidity content in the memory 112.
[0058] Additionally, in some embodiments of the invention, the power generation system 100
may further include one or more sensors (not shown) capable of measuring the fuel quality
parameter. In a non-limiting example, the term “fuel quality parameter” may be indicative of
one or more of a fuel energy density, a fuel propensity for knock (for example, a methane
number), fuel contaminants (for example, sulfur and fluorides), a contaminant particle size, or
combinations thereof. In some embodiments of the invention, an information corresponding to
one or more of the fuel energy density, the fuel propensity for knock, the fuel contaminants, the
contaminant particle size, and combinations thereof, may be known for a given fuel and stored in
the memory 112.
[0059] Once one or more of the post-catalyst emission level, the measured pre-catalyst
emission level, the measured post-catalyst emission level, the measured humidity content in the
gas stream 10, and at least one fuel quality parameter are determined, the processor 110 may
determine the adjusted post catalyst emission level, for example, using the Kalman filter or the
extended Kalman filter.
[0060] In some embodiments of the invention, the method 200 further includes determining a
difference between the post-catalyst emission level and the adjusted post-catalyst emission level,
at step 208. The difference may be determined by the processor 110 by subtracting the postcatalyst
emission level from the adjusted post-catalyst emission level, or vice versa. In some
embodiments of the invention, the difference may be an absolute difference.
[0061] Furthermore, in some embodiments of the invention, the method 200 further includes
performing a check to determine if the difference is greater than a threshold value, at step 210.
The processor 110 may perform the check at the step 210. For example, the threshold value may
be indicative of an allowable deviation between the post-catalyst emission level and the adjusted
post-catalyst emission level and is stored in the memory 112. In some embodiments of the
invention, the threshold value may be predefined, for example, by an operator, technician, or
manufacturer of the power generation system 100 or the engine controller 104. Performing the
check at step 210 may include comparing the difference with the threshold value. If the
difference is smaller than the threshold value, the processor 110 may determine that the power
generation system 100 is operating normally and the emission amount in the gas stream 10 is
under control. Accordingly, as shown in FIG. 2, the method 200 may include circling back to
step 202 if the difference is smaller than the threshold value. However, if the difference is
greater than the threshold value, the processor 110 may determine that the emission amount in
the gas stream 10 may need to be controlled, and the method 200 may further include preforming
the step 212 (described later).
[0062] The method 200 further includes, in some embodiments of the invention, at step 214,
determining an estimated value of an engine operating parameter. In one embodiment of the
invention, the engine operating parameter includes the EGR set-point, the ? set-point, an engine
ignition timing, or combinations thereof. The estimated value of the engine operating parameter
may be determined by the processor 110 based on the adjusted post-catalyst emission level, the
emission regulation data, an EGR curve, a ?? curve, or combinations thereof, stored in the
memory 112, in some embodiments. In some embodiments of the invention, the estimated value
of the engine operating parameter may be determined further based on a combustion engine age,
a three-way catalyst age, or a combination thereof. The combustion engine age and the threeway
catalyst age may be determined by the processor 110 and stored in the memory 112, in some
embodiments.
[0063] The ? curve data, that is used to determine the estimated value of the engine operating
parameter, may be obtained from a ? curve. The ? curve may be a relationship between an
adjusted post-catalyst emission level (described later) and the ? set-point. In one embodiment of
the invention, the information of the ? curve may be stored as the ? curve data in the form of a
look-up table or a mathematical relationship. In a non-limiting example, the ? curve data may
include information from a ? curve of FIG. 3. FIG. 3 is a graphical representation depicting a ?
curve 300, in accordance with one embodiment of the invention. As illustrated in FIG. 3, in
some embodiments of the invention, the ? curve 300 may be indicative of a relationship between
the adjusted post-catalyst emission level and the ? set-point.
[0064] The X-axis of the ? curve 300 is represented by a reference numeral 302 and the Yaxis
of the ? curve 300 is represented by a reference numeral 304. The X-axis 302 represents
values of ? set-points. The Y-axis 304 represents the adjusted post-catalyst emission level
corresponding to the contaminants, such as, NOx and CO, for example. A curve 306 may
represent the adjusted post catalyst emission levels of CO corresponding to different values of
the ? set-points. Similarly, a curve 308 may represent the adjusted post catalyst emission levels
of NOx corresponding to different values of the ? set-points. Although not shown, the ? curve
300 of FIG. 3 may also include a curve indicative of the adjusted post catalyst emission levels of
HC corresponding to different values of the ? set-points.
[0065] In certain embodiments of the invention, determining the estimated value of the engine
operating parameter may include determining, by the processor 110, a range of estimated values
of the engine operating parameter based on the adjusted post-catalyst emission level, the
emission regulatory limit, and one or both of the ? curve data and the EGR curve data. In a nonlimiting
example, a ? set-point range 310 may be representative of one such range of estimated
values of ? set-point such that the emission amount in the gas stream 10 is maintained below the
emission regulatory limit. Further, the estimated value of the engine operating parameter, for
example, ? set-point, may be selected from the range of estimated values of the engine operating
parameter.
[0066] The EGR curve may be a relationship between at least two of the EGR set-point, the
engine load, and the pre-catalyst emission level. In one embodiment of the invention, the
information of the EGR curve may be stored as EGR curve data in the form of a look-up table or
a mathematical relationship. In a non-limited example, the EGR curve data may include
information from an EGR curve of FIG. 4. FIG. 4 is a graphical representation depicting an
EGR curve 400, in accordance with one embodiment of the invention. As illustrated in FIG. 4,
in some embodiments of the invention, the EGR curve 400 may be indicative of a relationship
between at least two of the EGR set-point, the engine load, and the pre-catalyst emission level.
[0067] The X-axis of the EGR curve 400 is represented by a reference numeral 402. A first
Y-axis of the EGR curve 400 is represented by a reference numeral 404 and a second Y-axis of
the EGR curve 400 is represented by a reference numeral 406. The X-axis 402 represents the
engine load in kilowatts (kW), for example. The first Y-axis represents 404 the EGR set-points
(for example, EGR valve open position) in percentage, for example. Further, in one embodiment
of the invention, the second Y-axis 406 may represent the pre-catalyst emission level
corresponding to the contaminant, such as, NOx. In another embodiment of the invention, the
second Y-axis 406 may represent the pre-catalyst emission level corresponding to CO or HC.
[0068] In one embodiment of the invention, curves 408, 410, and 412 may represent
maximum values of the EGR set-point, estimated values of the EGR set-point, and minimum
values of the EGR set-point, respectively. Further, curves 414 and 416 may represent values of
the pre-catalyst emission level corresponding to the values of the EGR set-point indicated by
curves 408 and 410, respectively.
[0069] In some embodiments of the invention, the method 200 may further include, at step
216, adjusting an actual value of the engine operating parameter based on the estimated value of
the engine operating parameter. The actual value of the engine operating parameter may be
adjusted such that the emission amount in the gas stream 10 is maintained below an emission
regulatory limit, in some embodiments.
[0070] The emission regulatory limit may refer to allowable level of a given contaminant in
accordance with relevant emission regulation norms. In a non-limiting example, the emission
regulation norms may be governed by United States Environmental Protection Agency (EPA),
Bharat Stage (BS) emission standards, or European emission standards.
[0071] In one embodiment of the invention, the actual value of the engine operating
parameter may be adjusted by the processor 110 by communicating one or more signals to
respective system elements of the power generation system 100. In a non-limiting example, in
order to adjust an actual value of the ? set-point, the processor 110 may communicate a first
control signal to a fuel control valve 114. In one embodiment of the invention, the fuel control
valve 114 may be fluidly coupled to a fuel source (not shown) to receive a fuel 14. The fuel
control valve 114 may further be fluidly coupled to the intake conduit 104 to supply the fuel
stream 16 thereto. The fuel control valve 114 may control the flow of the fuel stream 16 to the
intake conduit 104. The first control signal may be indicative of a required open position of the
fuel control valve 114. Accordingly, the fuel control valve 114 may be operated at the required
open position such that the actual value of the ? set-point may be equivalent to an estimated
value of the ? set-point.
[0072] Further, in another non-limiting example, in order to adjust an actual value of the EGR
set-point, the processor 110 may communicate a second control signal to the EGR valve 116.
The second control signal may be indicative of a required open position of the EGR valve 116.
Accordingly, the EGR valve 116 may be operated at the required open position such that the
actual value of the EGR set-point may be equivalent to an estimated value of the EGR set-point.
[0073] Furthermore, in yet another non-limiting example, in order to adjust an actual value of
the engine ignition timing, the processor 110 may communicate a third control signal to the fuel
injector (not shown), the intake valve (not shown), or a combination thereof, of the combustion
engine 102. The third control signal may be indicative of a desired piston position from a top
dead center (TDC) at which the mixed stream 18 needs to be injected. Accordingly, the mixed
stream 18 may be injected into the combustion engine 102 at the desired piston position such that
the actual value of the engine ignition timing may be equivalent to an estimated value of the
engine ignition timing.
[0074] It is to be noted that, in one embodiment of the invention, the emission amount in the
gas stream 10 may be maintained below the emission regulatory limit by adjusting one of the
EGR set-point, the ? set-point, or the engine ignition timing. In another embodiment of the
invention, two or more of the EGR set-point, the ? set-point, or the engine ignition timing may
be controlled simultaneously to maintain the emission amount in the gas stream 10 below the
emission regulatory limit. Advantageously, a method and system that have the capability of
adjusting two or more of the EGR set-point, the ? set-point, or the engine ignition timing may
facilitate increased degree of freedom while achieving reduced emission amount in the exhaust
gas.
[0075] Referring again to FIG. 4, in some embodiments of the invention, a misfire condition
may occur during the operation of the power generation system 100 for values of EGR set-points
greater than the maximum values indicated by the curve 408 for a given engine load. The term
“misfire condition” as used herein may refer to an instance of one or more processes of a
combustion cycle, in the combustion engine 102, being skipped. Moreover, the misfire condition
and/or a knock condition may occur during the operation of the power generation system 100 for
values of EGR set-points lower than the minimum values indicated by the curve 412, for a given
engine load. The term “knock condition” as used herein may refer to an instance of the
combustion engine 102 generating pinging sounds due to abnormal combustion inside the
combustion chamber of the combustion engine 102.
[0076] Referring again to FIG. 2, in some embodiments of the invention, the method 200, at
step 216 may optionally adjust the actual value of the engine operating parameter based on the
estimated value of the engine operating parameter such that a number of occurrences of the
misfire condition is maintained below a determined number of misfire occurrences. For
example, the determined number of misfire occurrences may be indicative of allowable misfire
occurrences and is stored in the memory 112. In some embodiments of the invention, the
number of allowable misfire occurrences may be predefined, for example, by an operator,
technician, or manufacturer of the power generation system 100 or the engine controller 104. In
some embodiments of the invention, the number of allowable misfire occurrences may be
determined by the processor 110.
[0077] Alternatively, or, in addition, in some embodiments of the invention, the method 200,
at step 216 may optionally adjust the actual value of the engine operating parameter based on the
estimated value of the engine operating parameter such that a number of occurrences of the
knock condition is maintained below a determined number of knock occurrences. For example,
the determined number of knock occurrences may be indicative of allowable knock occurrences
and is stored in the memory 112. In some embodiments of the invention, the number of
allowable knock occurrences may be predefined, for example, by an operator, technician, or
manufacturer of the power generation system 100 or the engine controller 104. In some
embodiments of the invention, the number of allowable knock occurrences may be determined
by the processor 110.
[0078] In a non-limiting example, in order to maintain the pre-catalyst emission level of NOx,
as indicated by curve 418, between the engine loads ranging from 800 kW to 1050 kW, the
processor 110 may determine estimated value of EGR set-point that confirms the values
indicated by the curve 410, thereby avoiding the misfire and knock conditions.
[0079] In some embodiments of the invention, the method may optionally include, at step
212, determining an emission regulatory limit. In some embodiments of the invention, the
processor 110 may determine the emission regulatory limit using an emission regulation data
stored in the memory 112. In some embodiments of the invention, the emission regulation data
may be stored in the memory 112 in the form of a look-up table, hereinafter referred to as, an
emission data look-up table. The emission data look-up table may include information
including, but not limited to, a list of one or more regions and at least a set of location
coordinates corresponding to the one or more regions. For example, a set of location coordinates
may define a region of the one or more regions. Further, the emission data look-up table may
also include an emission regulatory limit of the post-catalyst emission level corresponding one or
more contaminants for the one or more regions. The term “region” as used herein may refer to a
region of operation of the power generation system 100, where the term region may correspond
to any of a jurisdiction, a country, and a state. Further details for the steps of determining the
emission regulatory limit are described later in conjunction with FIG. 5.
[0080] Referring again to FIG. 1, as will be appreciated, in some embodiments of the
invention, the power generation system 100 may also be employed in mobile applications, where
a vehicle employing the power generation system 100 may stay in or transit through multiple
regions. Moreover, different regions may also have different emission regulatory limits for a
given contaminant. Accordingly, it may be advantageous to control the emission amount in the
gas stream 10 based on the location-specific emission regulatory limit.
[0081] Accordingly, in some embodiments of the invention, the power generation system 100
may also include a global positioning system (GPS) sensor 126. The GPS sensor 126 may be
communicatively coupled to the engine controller 108. More particularly, the GPS sensor 126
may be communicatively coupled to the engine controller 108. The GPS sensor 126 may
determine location coordinates of the power generation system 100. In one embodiment of the
invention, the GPS sensor 126 may determine the location coordinates of the power generation
system 100 at a regular interval of time. In another embodiment of the invention, the GPS sensor
126 may determine the location coordinates of the power generation system 100 at random or
irregular intervals of time. In yet another embodiment of the invention, the GPS sensor 126 may
determine the location coordinates of the power generation system 100 on a request from the
processor 110.
[0082] In one embodiment of the invention, once the location coordinates of the power
generation system 100 are determined, the location coordinates may be communicated by the
GPS sensor 126 to the processor 110. The processor 110 may then store the received location
coordinates into the memory 112. In another embodiment of the invention, once the location
coordinates of the power generation system 100 is determined, the location coordinates may be
stored in the memory 112 by the GPS sensor 126.
[0083] In some embodiments of the invention, the processor 110 may utilize the location
coordinates determined by the GPS sensor 126 to determine the emission regulatory limit at step
212 of the method 200. FIG. 5 illustrates the details of the step 212 of FIG. 2. More
particularly, FIG. 5 depicts a flowchart illustrating a method 500 for determining the emission
regulatory limit, in accordance with one embodiment of the invention. As illustrated in FIG. 5,
in some embodiments of the invention, the method 500 may include steps 502 and 504. Steps
502 and 504 may be performed by the processor 110 when one or more of the processorexecutable
routines are executed by the processor 110. In a non-limiting example, one or more
of the steps 502 and 504 may contribute to one or more of the acts performed, when one or more
of the processor-executable routines are executed by the processor 110.
[0084] In some embodiments of the invention, the method 500 includes, at step 502,
determining a region of operation of the power generation system 100 based at least on the
location coordinates determined by the GPS sensor 126. The processor 110 may reference the
emission data look-up table to determine the region of operation. The processor 110 may
determine the region of operation corresponding to the location coordinates from the emission
data look-up table. For example, in order to determine the region of operation, the processor 110
may perform a check to determine whether the determined location coordinates belong to a
certain set of location coordinates stored in the emission data look-up table. If a set of location
coordinates that includes the determined location coordinates is identified, the processor 110
may select a region corresponding to the identified set of location coordinates from the emission
data look-up table as the region of operation of the power generation system 100.
[0085] Further, in some embodiments of the invention, the method 500 includes, at step 504,
determining an emission regulatory limit based on the region of operation of the power
generation system 100. The processor 110 may reference the emission data look-up table to
determine the emission regulatory limit. For example, for the determined region of operation,
the processor 110 may select an emission regulation norm for the given contaminant from the
emission data look-up table.
[0086] The systems and methods according to some embodiments of the invention aid in
reducing the emission amount in the exhaust gas stream emitted from the power generation
system 100 such that the emission amount is maintained below the emission regulatory limit.
Accordingly, environmental hazards that may have caused due to such emissions is limited. As a
result, the systems and methods described herein may help achieve a greener environment.
[0087] Moreover, in some embodiments of the invention, the systems and methods described
herein may also aid in maintaining the operation of the power generation system 100 at
substantially close to the stoichiometric condition by way of adjusting the actual value of the
engine operating parameter while achieving reduced levels of contaminants in the exhaust gas
stream. In addition, when the power generation system 100 may be used in the mobile
application, the emission regulatory limit for a given region may be referenced by the processor
110 while determining the estimated value of the engine parameter. Accordingly, the emissions
may be controlled such that the emission amount in the gas stream 10 may be maintained below
the emission regulatory limit for an instantaneous region of operation of the power generation
system 100.
[0088] The present invention has been described in terms of some specific embodiments of
the invention. They are intended for illustration only, and should not be construed as being
limiting in any way. Thus, it should be understood that modifications can be made thereto,
which are within the scope of the invention and the appended claims.
[0089] It will be appreciated that variants of the above disclosed and other features and
functions, or alternatives thereof, may be combined to create many other different systems or
applications. Different implementations of the systems and methods may perform some or all of
the steps described herein in different orders, parallel, or substantially concurrently. Various
unanticipated alternatives, modifications, variations, or improvements therein may be
subsequently made by those skilled in the art and are also intended to be encompassed by the
following claims.