Claims:1. A method for controlling an air-fuel ratio (AFR) in a power generation system having an engine, comprising:
determining an estimated oxygen content in an exhaust gas stream to be emitted from the power generation system based on a target oxygen content using an engine model or an engine look-up table;
determining a measured oxygen content in the exhaust gas stream to be emitted from the power generation system;
determining a difference between the estimated oxygen content and the measured oxygen content; and
adjusting at least one flow control device in the power generation system based on the target oxygen content and the difference between the estimated oxygen content and the measured oxygen content to control the AFR.

2. The method of claim 1, wherein the engine model or the engine look-up table is representative of a relationship among one or more of an engine speed, an engine power, a flow-rate of the exhaust gas stream, a manifold air pressure, a manifold air temperature, an age of the engine, an age of an oxygen sensor used for sensing oxygen content in the exhaust gas stream, and one or more fuel quality parameters.

3. The method of claim 2, further comprising generating an electric signal by the oxygen sensor disposed in a flow path of the exhaust gas stream in the power generation system, wherein the measured oxygen content is determined based on the electric signal.

4. The method of claim 1, further comprising filtering the measured oxygen content prior to determining the difference, wherein filtering the measured oxygen content comprises limiting a bandwidth of the measured oxygen content using a first band pass filter.

5. The method of claim 1, further comprising filtering the difference to generate the filtered difference, wherein filtering the difference comprises limiting a bandwidth of the difference using a second band pass filter.

6. The method of claim 5, wherein the at least one flow control device is controlled based on the target oxygen content and the filtered difference to control the AFR.

7. The method of claim 1, further comprising determining the target oxygen content in the exhaust gas stream to be emitted from the power generation system based on an engine operating parameter using a look-up table or a physics based model, wherein the engine operating parameter comprises an engine load, an engine speed, actual value of the AFR, an ambient temperature, an ambient pressure, an altitude, one or more fuel quality parameters, a manifold air pressure, a manifold air temperature, an emission level, knock and/or misfire boundaries, a fuel type, a turbocharger speed, or combinations thereof.

8. The method of claim 7, wherein adjusting the at least one flow control device comprises determining a first estimated opening of the at least one flow control device based on the target oxygen content and the engine operating parameter using a feed-forward model, wherein the feed-forward model is representative of a relationship between the engine operating parameter and the first estimated opening of the at least one flow control device.

9. The method of claim 8, wherein adjusting the at least one flow control device further comprises determining a second estimated opening of the at least one flow control device based on the difference between the estimated oxygen content and the measured oxygen content.

10. The method of claim 9, wherein adjusting the at least one flow control device further comprises determining a third estimated opening of the at least one flow control device based on one or both of the first estimated opening and the second estimated opening.

11. The method of claim 10, wherein the third estimated opening is a sum of the first estimated opening and the second estimated opening.

12. The method of claim 10, wherein adjusting the at least one flow control device further comprises communicating a signal to the at least one flow control device such that an actual open position of the at least one flow control device is set based on the third estimated opening.

13. A power generation system, comprising:
an engine;
at least one flow control device in flow communication with the engine; and
an engine controller operatively coupled to the at least one flow control device, comprising:
one or more processors configured to:
determine an estimated oxygen content in an exhaust gas stream to be emitted from the power generation system based on a target oxygen content using an engine model or an engine look-up table;
determine a measured oxygen content in the exhaust gas stream to be emitted from the power generation system;
determine a difference between the estimated oxygen content and the measured oxygen content; and
adjust the at least one flow control device in the power generation system based on the target oxygen content and the difference between the estimated oxygen content and the measured oxygen content to control an air-fuel ratio (AFR).

14. The power generation system of claim 13, wherein the engine is a dual-fuel engine.

15. The power generation system of claim 13, wherein the at least one flow control device comprises an air control valve, a compressor recirculation valve, a waste gate valve, a turbocharger, or combinations thereof.

16. The power generation system of claim 13, further comprising an oxygen sensor disposed in a flow path of the exhaust gas stream in the power generation system and configured to generate an electric signal indicative of an actual oxygen content in the exhaust gas stream, wherein the measured oxygen content is determined based on the electric signal generated by the oxygen sensor.

17. The power generation system of claim 13, wherein the engine model or the engine look-up table is representative of a relationship among one or more of an engine speed, an engine power, a flow-rate of the exhaust gas stream, a manifold air pressure, a manifold air temperature, an age of the engine, an age of a sensor used for sensing an actual oxygen content in the exhaust gas stream, and one or more fuel quality parameters.

18. The power generation system of claim 13, wherein the one or more processors are further configured to filter the measured oxygen content prior to determining the difference by limiting a bandwidth of the measured oxygen content using a first band pass filter.

19. The power generation system of claim 13, wherein the one or more processors are further configured to filter the difference to generate the filtered difference by limiting a bandwidth of the difference using a second band pass filter.

20. The power generation system of claim 13, wherein the one or more processors are further configured to determine the target oxygen content in the exhaust gas stream to be emitted from the power generation system based on an engine operating parameter using a look-up table or a physics based model, and wherein the engine operating parameter comprises an engine load, an engine speed, actual value of the AFR, an ambient temperature, an ambient pressure, an altitude, one or more fuel quality parameters, a manifold air pressure, a manifold air temperature, a fuel type, a turbocharger speed, or combinations thereof.

21. An engine controller for controlling an air-fuel ratio (AFR) in a power generation system having an engine, comprising:
one or more processors configured to:
determine an estimated oxygen content in an exhaust gas stream to be emitted from the power generation system based on a target oxygen content using an engine model or an engine look-up table;
determine a measured oxygen content in the exhaust gas stream to be emitted from the power generation system;
determine a difference between the estimated oxygen content and the measured oxygen content; and
adjust at least one flow control device in the power generation system based on the target oxygen content and the difference between the estimated oxygen content and the measured oxygen content to control the AFR.
, Description:BACKGROUND
[0001] Embodiments of the present technique relate to power generation systems.
More particularly, embodiments of the present technique relate to methods and
systems for controlling an air-fuel ratio (AFR) in the power generation systems.
[0002] Combustion engines such as internal combustion (IC) engines are used in a
wide range of applications. Typically, a mixture of fuel(s) and air is combusted in
the IC engine for generating a mechanical power. Generally, disproportionate air
available in such mixture leads to problems including, but not limited to misfire and
knock. If the IC engine is subjected to the misfire because of an inaccurate AFR of
the mixture, there may remain some unburnt fuel(s) in the exhaust gas from the
power generation system. Presence of such unburned fuel in the exhaust gas
sometime leads to fire in the exhaust manifold, thereby adversely affecting the
performance and reliability of the power generation system. Additionally, the
insufficient air in the mixture leads to an improper combustion in the IC engine.
Such improper combustion may result in violation of emission norms of a given
region. Therefore, it is desirable to maintain the AFR to a desired level in order to
mitigate or minimize some of the problems discussed hereinabove.
[0003] Typically, the AFR is controlled using feedback methods based on oxygen
content present in the exhaust gas emitted from the power generation system. The
oxygen content is typically measured using an oxygen sensor. Consequently,
response time for taking a control action for correcting the AFR is highly dependent
on a time response of the oxygen sensor. In general, the oxygen sensor has a dead
time (i.e., a time delay in start of the detection of change in the oxygen content) and a
slow time response. Due to this time delay and slow response time associated with
the oxygen sensor, when measurements of the oxygen content are performed using
281474-1
3
the oxygen sensor, the measurements of the oxygen content are slower, which results
in subsequent control action that is inadequate to control the AFR in a desirable
manner.
[0004] Sometimes, computer model based feed-forward techniques are used for
controlling the AFR. Though these computer model based feed-forward techniques
provide faster control action to maintain the AFR at the desired set-point, however,
these techniques suffer from model inaccuracies. Further, these techniques may also
be undesirably influenced by aging of the IC engine and/or the oxygen sensor.
BRIEF DESCRIPTION
[0005] One embodiment is directed to a method for controlling an air-fuel ratio
(AFR) in a power generation system having an engine. The method includes
determining an estimated oxygen content in an exhaust gas stream to be emitted from
the power generation system based on a target oxygen content using an engine model
or an engine look-up table. The method further includes determining a measured
oxygen content in the exhaust gas stream to be emitted from the power generation
system. Furthermore, the method includes determining a difference between the
estimated oxygen content and the measured oxygen content. Moreover, the method
also includes adjusting at least one flow control device in the power generation
system based on the target oxygen content and the difference between the estimated
oxygen content and the measured oxygen content to control the AFR.
[0006] Another embodiment is directed to a power generation system. The power
generation system includes an engine and at least one flow control device in flow
communication with the engine. The power generation system further incudes an
engine controller operatively coupled to the at least one flow control device. The
engine controller includes one or more processors configured to determine an
estimated oxygen content in an exhaust gas stream to be emitted from the power
generation system based on a target oxygen content using an engine model or an
281474-1
4
engine look-up table. The one or more processors are further configured to
determine a measured oxygen content in the exhaust gas stream to be emitted from
the power generation system. Furthermore, one or more processors are configured
determine a difference between the estimated oxygen content and the measured
oxygen content. Moreover, one or more processors are configured to adjust at least
one flow control device in the power generation system based on the target oxygen
content and the difference between the estimated oxygen content and the measured
oxygen content to control the AFR.
[0007] Yet another embodiment is directed to an engine controller for controlling
an air-fuel ratio (AFR) in a power generation system having an engine. The engine
controller includes one or more processors configured to determine an estimated
oxygen content in an exhaust gas stream to be emitted from the power generation
system based on a target oxygen content using an engine model or an engine look-up
table. The one or more processors are further configured to determine a measured
oxygen content in the exhaust gas stream to be emitted from the power generation
system. Furthermore, one or more processors are configured determine a difference
between the estimated oxygen content and the measured oxygen content. Moreover,
one or more processors are configured to adjust at least one flow control device in the
power generation system based on the target oxygen content and the difference
between the estimated oxygen content and the measured oxygen content to control
the AFR.
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:
281474-1
5
[0009] FIG. 1 is a diagrammatical illustration of a power generation system, in
accordance with aspects of the present technique;
[0010] FIG. 2 depicts a flowchart illustrating a method for controlling an air-fuel
ratio (AFR) in the power generation system of FIG. 1, in accordance with aspects of
the present technique;
[0011] FIG. 3 depicts a flowchart illustrating a method for controlling an air-fuel
ratio (AFR) in the power generation system of FIG. 1, in accordance with another
aspect of the present technique; and
[0012] FIG. 4 depicts a flowchart illustrating a method for adjusting at least one
flow control device, in accordance with another aspect of the present technique.
DETAILED DESCRIPTION
[0013] The specification may be best understood with reference to the detailed
figures and description set forth herein. Various embodiments 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.
[0014] 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.
281474-1
6
[0015] 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.
[0016] 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.
[0017] In certain embodiments, a power generation system includes an engine and
at least one flow control device in flow communication with the engine. The power
generation system further incudes an engine controller operatively coupled to the at
least one flow control device. The engine controller includes one or more processors
configured to determine an estimated oxygen content in an exhaust gas stream to be
emitted from the power generation system based on a target oxygen content using an
engine model or an engine look-up table. The one or more processors are further
configured to determine a measured oxygen content in the exhaust gas stream to be
emitted from the power generation system. Furthermore, one or more processors are
configured determine a difference between the estimated oxygen content and the
measured oxygen content. Moreover, one or more processors are configured to
281474-1
7
adjust at least one flow control device in the power generation system based on the
target oxygen content and the difference between the estimated oxygen content and
the measured oxygen content to control the AFR.
[0018] FIG. 1 is a diagrammatical illustration of a power generation system 100,
in accordance with aspects of the present specification. As illustrated in FIG. 1, in
certain embodiments, the power generation system 100 may include a combustion
engine 102, an intake manifold 104, an exhaust manifold 106, a turbocharger 108, an
after-cooler 110, and an engine controller 112. Additionally, in some embodiments,
the power generation system 100 may include one or more of a waste gate valve 114,
an air control valve 118 (sometimes also referred to as a shut-off valve), and a
compressor recirculation valve 120 (alternatively also referred to as a bleeding
valve). Moreover, the power generation system 100 may also include an oxygen
sensor 124. The engine controller 112 may be operably coupled to the combustion
engine 102, the oxygen sensor 124, and one or more of the waste gate valve 114, the
air control valve 118, and the compressor recirculation valve 120.
[0019] In some embodiments, the combustion engine 102 may be an internal
combustion (IC) engine. For example, the combustion engine 102 may be a singlefuel
engine or a multi-fuel engine such as a dual-fuel engine. Moreover, the
combustion engine 102 may include one or more cylinders (not shown in FIG. 1).
Each cylinder of the one or more cylinders may include a combustion chamber, a
piston, and a crankshaft mechanically coupled to the piston. Further, each cylinder
may be in fluid communication with the intake manifold 104 for receiving a
pressurized air stream 10 (or a pressurized air-fuel mixture) for combustion in the
cylinder. Additionally, each cylinder may be in fluid communication with the
exhaust manifold 106 for removing combustion residues from the cylinder, where the
combustion residues may be in the form of an exhaust gas stream 20 which may be
exited from the power generation system 100 as an exhaust gas stream 60.
281474-1
8
[0020] In some embodiments, the turbocharger 108 may be coupled between the
exhaust manifold 106 and the intake manifold 104 in a fluid communication
relationship. The turbocharger 108 may include a compressor 125 and a turbine 126
mechanically, coupled to each other via a shaft 128. At least a portion (for example,
a turbine stream 40) of the exhaust gas stream 20 may drive (for example, rotate) the
turbine 126 which in-turn may drive the compressor 125 via the shaft 128. In
operation, the compressor 125 may pressurize an intake air stream 30 to generate the
pressurized air stream 10.
[0021] In certain embodiments, the pressurized air stream 10 generated by the
turbocharger 108 may optionally be passed through the after-cooler 110. The aftercooler
110 may be disposed downstream of the turbocharger 108 and upstream of the
throttle valve 111. More particularly, the after-cooler 110 may be in fluid
communication with an output of the compressor 125 of the turbocharger 108. In a
non-limiting example, the after-cooler 110 may be coupled between the compressor
output and the throttle valve 111 in a fluid communication relationship. The aftercooler
110 may include cooling systems including, but not limited to, cooling fluids,
fans, or other heat exchangers, the cooling systems aid in reducing the temperature of
the pressurized air stream 10 generated by the compressor 125.
[0022] In the embodiment of FIG. 1, the power generation system 100 is shown as
having a single turbocharger 108 for ease of illustration. However, use of a plurality
of turbochargers 108 is also envisioned. In such a configuration, one or more
intercoolers such as the after-cooler 110 may be disposed between two turbochargers
108.
[0023] The pressurized air stream 10 may be supplied to the intake manifold 104.
In one embodiment, the supply of the pressurized air stream 10 to the intake manifold
104 may be controlled via the throttle valve 111. As depicted in FIG. 1, the throttle
valve 111 may be disposed in a fluid path between the turbocharger 108 (more
281474-1
9
particularly, a compressor output) and the intake manifold 104. In the presently
contemplated configuration, the throttle valve 111 is disposed downstream of the
after-cooler 110. The throttle valve 111 may be controlled by the engine controller
112 to control the supply of the pressurized air stream 10 (or the air-fuel mixture) to
the intake manifold 104.
[0024] In some embodiments, the combustion engine 102 may also include one or
more fuel injectors (not shown in FIG. 1) to inject one or more fuels directly into a
combustion chamber of a cylinder. Injection of the one or more fuels into the
combustion engine 102 may be controlled by the engine controller 112 by controlling
the one or more fuel injectors. Furthermore, the injection of the pressurized air
stream 10 into the combustion engine 102 may be controlled by the engine controller
112 by controlling an intake valve (not shown in FIG. 1) operatively coupled to the
intake manifold 104. Moreover, in some embodiments, the injection of the
pressurized air stream 10 may also be controlled by controlling the turbocharger 108.
For example, the turbocharger 108 may be a variable-geometry turbocharger (VGT)
that is controllable to vary gas swirl angle and a cross sectional area of the
turbocharger 108 to achieve desired pressure of the air stream 10. More particularly,
in some embodiments, the VGT may be controlled by appropriately varying an angle
of at least one blade of one or both of the compressor 125 and the turbine 126.
[0025] However, in certain embodiments, instead of injecting the one or more
fuels in the combustion chamber, the one or more fuels may be injected into the
intake manifold 104 (for example, using a carburetor) that is located upstream of the
combustion chamber. Accordingly, in these embodiments, the air-fuel mixture may
be created in the intake manifold 104. The injection of the air-fuel mixture into the
combustion engine 102 may be controlled by the engine controller 112 by controlling
the intake valve. Accordingly, in such a configuration, the pre-mixed air-fuel
mixture may enter into the combustion chamber for combustion. In an alternative
281474-1
10
embodiment, while one or more of these fuels may be directly injected into the
cylinder of the combustion engine 102, other fuels may be injected into the intake
manifold 104.
[0026] In some embodiments, the air-fuel mixture may be combusted in the
combustion chamber using a spark-ignition technique. For example, in such a
configuration, a source of spark (e.g., one or more spark plugs) may be provided in
the combustion chamber for generating spark sufficient to combust the air-fuel
mixture. In some other embodiments, the air-fuel mixture may be combusted in the
combustion chamber along with a pilot fuel (e.g., diesel) using a compressionignition
technique. For example, in such a configuration, with the movement of the
piston, the available air-fuel mixture may be compressed such that the temperature of
the air-fuel mixture becomes sufficient to aid the combustion upon injection of the
pilot fuel.
[0027] In response to the combustion of the fuel(s) in the combustion engine 102,
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 certain
embodiments, 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. In some embodiments, the crankshaft may be rotated at a fixed or
substantially fixed speed. In some other embodiments, the crankshaft may be rotated
at a variable speed. The combustion residues or by-products of the combustion may
be discharged from the combustion engine 102 in the form of the exhaust gas stream
20, which is discharged via the exhaust manifold 106.
[0028] As previously noted, at least a portion of the exhaust gas stream 20 is
utilized to power the turbocharger 108. To that end, in some embodiments, the
power generation system 100 may optionally employ the waste gate valve 114 to
281474-1
11
control an operation of the turbocharger 108. The waste gate valve 114 may be in
fluid communication with the exhaust manifold 106 and an exhaust pipe 130. The
waste gate valve 114 may be controlled such that at least a portion (hereinafter
referred to as “a bypass exhaust stream 50”) of the exhaust gas stream 20 bypasses
the turbocharger 108 and enters into the exhaust pipe 130. In some embodiments, the
output of the turbocharger 108 may be inversely proportional to an amount of the
bypass exhaust stream 50. In some embodiments, the output of the turbocharger 108
may be referred to as an air stream percentage compression, an intake air stream
compression ratio, or a rotational speed of the turbine 126. Accordingly, the output
of the turbocharger 108 may be controlled by controlling the amount of the bypass
exhaust stream 50. In some embodiments, when the waste gate valve 114 is not
employed, almost all of the exhaust gas stream 20 may pass though the turbine 126
of the turbocharger 108 and eventually exit the power generation system 100 via the
exhaust pipe 130.
[0029] Additionally, in one embodiment, the air control valve 118 may be
disposed upstream of the compressor 125 of the turbocharger 108. The air control
valve 118 may be controlled by the engine controller 112 to control an amount of the
ambient air entering into the compressor 125. Further, the compressor recirculation
valve 120 may be coupled across the compressor 125 in fluid communication
relationship. In a non-limiting example, the compressor recirculation valve 120 may
be disposed such that, during its open condition, the compressor recirculation valve
120 allows a flow of at least a portion of the pressurized air stream 10 from
downstream of the compressor 125 to the upstream of the compressor 125, thereby
bypassing the compressor 125.
[0030] For ensuring stable operation of the power generation system 100, in some
embodiments, it may be desirable to maintain an air-fuel ratio (AFR) of the
combustion products (e.g., the mixture of the pressurized air stream 10 and the
281474-1
12
fuel(s) to be combusted in the combustion chamber) in the power generation system
100. In some embodiments, the engine controller 112 may be configured to control
the AFR in the power generation system 100. The engine controller 112 may include
one or more processors, such as, a processor 132. The processor 132 may include a
specially programmed general purpose computer, a microprocessor, a digital signal
processor, and a microcontroller. Examples of the processor 132 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 132 may be a single-core processor or a multi-core processor.
The processor 132 may also include, or, comprise electrically coupled thereto, one or
more input/output ports.
[0031] The engine controller 112 may further include a memory 134 accessible by
the processor 132. In one embodiment, the memory 134 may be integrated into the
processor 132. In another embodiment, the memory 134 may be external to the
processor 132 and electrically coupled to the processor 132, as depicted in FIG. 1.
The memory 134 may be a non-transitory computer-readable media. The nontransitory
computer-readable media may include tangible, computer-readable media,
including, without limitation, non-transitory computer storage devices. The nontransitory
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 134 include a dynamic random
access memory (DRAM) device, a static random access memory (SRAM) device,
and a flash memory.
281474-1
13
[0032] In some embodiments, the memory 134 may store processor-executable
routines that are executable by the processor 132. 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, by
executing one or more of the processor-executable routines, the processor 132 may
be configured to control the AFR in the power generation system 100.
[0033] The processor-executable routines, when executed by the processor 132,
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 some embodiments,
the acts to be performed may include steps illustrated in flowcharts of FIGs. 2-4.
FIG. 2 depicts a flowchart 200 illustrating a method for controlling the AFR in the
power generation system 100 of FIG. 1. As illustrated in FIG. 2, in some
embodiments, the method may include steps 202-212. The processor is configured to
perform acts indicated by the steps 202-212 of the method of flowchart 200.
[0034] In some embodiments, the method, at step 202, includes determining a
target oxygen content in the exhaust gas stream 60 that is to be emitted from the
power generation system 100. The target oxygen content may be indicative of a
desired level of the oxygen content (in mole or molar percent) for a given value of an
engine operating parameter. Non-limiting examples of the engine operating
parameter may include an engine load, an engine speed, actual value of the AFR, an
ambient temperature, an ambient pressure, an altitude, one or more fuel quality
parameters, a manifold air pressure, a manifold air temperature, a fuel type, a
turbocharger speed, an emission level, knock and/or misfire boundaries, or
combinations thereof. The emission level may include one or more of a nitrogen
oxide (NOx) emission level, a carbon monoxide (CO) emission level, and a
particulate matter (PM) emission level. One or more of these engine operating
parameters may be determined using various sensors. Alternatively, or additionally,
281474-1
14
the one or more of the engine operating parameters may be determined using various
physics or mathematical models.
[0035] In one embodiment, the target oxygen content in the exhaust gas stream 60
is determined based on the engine operating parameter using a look-up table or a
physics based model. The first look-up table or a first physics based model is
representative of the relationship between the target oxygen content and values of the
engine operating parameter. In a non-limiting example, the first look-up table may
include values of the target oxygen content with respect to different values of a target
engine speed, target torque (e.g., engine load), knock and/or misfire boundaries,
and/or one or more of a target NOx emission level, a target CO emission level, and a
target PM emission level.
[0036] Further, at step 204, an estimated oxygen content in an exhaust gas stream
to be emitted from the power generation system is determined based on the target
oxygen content using an engine model or an engine look-up table. In some
embodiments, the engine model or the engine look-up table is representative of a
relationship between the estimated oxygen content and one or more of an engine
speed, an engine power, a flow-rate of the exhaust gas stream, a manifold air
pressure, a manifold air temperature, an age of the engine, an age of an oxygen
sensor used for sensing oxygen content in the exhaust gas stream, and one or more
fuel quality parameters. By way of a non-limiting example, the fuel quality
parameters may include 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, 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 134.
281474-1
15
[0037] In a non-limiting example, the estimated oxygen content may be
determined using one or more transfer functions based on a transfer delay. For
example, the transfer delay may be representative of fluid flow delay, delays
experienced by the oxygen sensor 128 and computation delays by the processor 132.
In some embodiments, the fluid flow delay may be indicative of a time duration for
the air-fuel mixture to combust in the combustion chamber and exited from the
exhaust pipe 130 as the exhaust gas stream 60. The transfer function may be
representative of which engine’s behavior at a given operating point of the engine
operating parameters.
[0038] Further, an electric signal may be generated by the oxygen sensor 124
disposed in the flow path of the exhaust gas stream 60, as indicated by step 206. In
some embodiments, one or more properties of the electric signal generated by the
oxygen sensor 124 are indicative of an amount of the oxygen content (in mol or
molar percent) in the exhaust gas stream 60. For example, amplitude, frequency,
and/or phase of the electric signal are indicative of the actual oxygen content (in mol
or molar percent) in the exhaust gas stream 60.
[0039] Furthermore, at step 208, a measured oxygen content in the exhaust gas
stream 60 is determined. In one embodiment, the measured oxygen content in the
exhaust gas stream 60 is determined based on the electric signal that may be
generated by the oxygen sensor 124. More particularly, the measured oxygen
content in the exhaust gas stream 60 is determined based on amplitude, frequency,
and/or phase of the electric signal. In a non-limiting example, based on the electric
signal generated and received by the processor 132, values of one or more of the
amplitude, frequency, and/or phase of the electric signal are determined by the
processor 132. Thereafter, the processor 132 may determine the measured oxygen
based on the determined value of one or more of the amplitude, frequency, and/or
phase of the electric signal.
281474-1
16
[0040] In some alternative embodiments, the measured oxygen content may be
determined by the processor 132 based on a parameter, such as but not limited to, the
manifold air pressure. In some embodiments, the manifold air pressure may be
determined by the processor 132 based on signals generated by one or more sensors
(not shown), such as, a pressure sensor disposed in the intake manifold 104. For
example, the MAP may be applied to a filter such as a Kalman or extended Kalman
filter to determine the measured oxygen content.
[0041] Moreover, at step 210, in some embodiments, a difference between the
estimated oxygen content (determined at step 204) and the measured oxygen content
(determined at step 208) is determined. In one embodiment, the measured oxygen
content may be subtracted from the estimated oxygen content by the processor 132 to
determine the difference. In another embodiment, the estimated oxygen content may
be subtracted from the measured oxygen content by the processor 132 to determine
the difference. In certain embodiments, the measured oxygen content may be higher
or lower than the estimated oxygen content. Accordingly, a lower of the measured
oxygen content and the estimated oxygen content may be subtracted from the other
oxygen content to determine the different between the measured and estimated
oxygen contents.
[0042] Additionally, at step 212, at least one flow control device in the power
generation system may be adjusted based on the target oxygen content (determined at
step 202) and the difference (determined at step 210) to control the AFR. The flow
control device may include the waste gate valve 114, the air control valve 118, the
compressor recirculation valve 120, the turbocharger 108, or combinations thereof.
In some embodiments, an operation of the flow control device at a desired open
position aids in maintaining the AFR at the desired value. Further details of
adjusting the at least one flow control device are described in detail with regard to
FIG. 4.
281474-1
17
[0043] FIG. 3 depicts a flowchart 300 illustrating a method for controlling the
AFR in the power generation system of FIG. 1, in accordance with another aspect of
the present technique. In some embodiments, the processor 132 of FIG. 1 is
configured to carry out steps 302-316 illustrated in the flowchart 300 of FIG. 3. It is
to be noted that steps 302, 304, 306, and 308, are similar to steps 202, 204, 206, and
208, respectively, of FIG. 2. Accordingly, at step 302, a desirable target oxygen
content in an exhaust gas stream 60 to be emitted is determined. At step 304, an
estimated oxygen content in an exhaust gas stream 60 to be emitted from the power
generation system is determined based on the target oxygen content using an engine
model or an engine look-up table. At step 306, an electric signal may be generated
by the oxygen sensor 124 disposed in the flow path of the exhaust gas stream 60.
Further, at step 308, a measured oxygen content in the exhaust gas stream 60 is
determined.
[0044] In some embodiments, once the measured oxygen content in the exhaust
gas stream 60 is determined at step 308, the measured oxygen content may be filtered
at step 310 to generate the filtered measured oxygen content. The filtering of the
measured oxygen content at step 310 may include limiting a bandwidth of the
measured oxygen content using a first band pass filter. Non-limiting examples of the
first band pass filter may include a digital filter, a wavelet based filter, or a Fourier
transform based filter. In certain embodiments the functionalities of the first band
pass filter may be implemented using the processor, such as the processor 132 of
FIG. 1.
[0045] Further, at step 312, a difference between the estimated oxygen content
(determined at step 304) and the filtered measured oxygen content (determined at
step 310) is determined. In one embodiment, a difference between the filtered
measured oxygen content and the estimated oxygen content may be determined by
the processor 132.
281474-1
18
[0046] Further, the difference between the estimated oxygen content and the
filtered measured oxygen content may also be filtered at step 314 to generate a
filtered difference. The filtering of the difference at step 314 may include limiting a
bandwidth of the difference between the estimated oxygen content and the filtered
measured oxygen using a second band pass filter. Non-limiting examples of the
second band pass filter may include a digital filter, a wavelet based filter, or a Fourier
transform based filter. In certain embodiments, the functionalities of the second band
pass filter may be carried out by the processor 132.
[0047] In some embodiments, one or both of the first filter and the second filter
may be static filters. For example, cut-off limits of the static filter may remain same
irrespective of engine operating parameter. In some embodiments, one or both of the
first filter and the second filter may be dynamic filters. For example, cut-off limits of
the dynamic filter may vary depending on the engine operating parameter.
[0048] Additionally, at step 316, the at least one flow control device in the power
generation system may be adjusted based on the target oxygen content (determined at
step 302) and the filtered difference (determined at step 314) between the estimated
oxygen content and the filtered measured oxygen content to control the AFR. In
some embodiments, an operation of the flow control device at a desired open position
by controlling the at least one flow control device at step 316 aids in maintaining the
AFR at the desired value. Further details of adjusting the at least one flow control
device is described in detail in conjunction with, FIG. 4.
[0049] FIG. 4 depicts a flowchart 400 illustrating a method for adjusting the at
least one flow control device, in accordance with another aspect of the present
technique. In some embodiments, a processor, such as the processor 132 of FIG. 1,
may be configured to carry out steps 402-408 illustrated in the flowchart 400 of FIG.
4.
281474-1
19
[0050] At step 402, a first estimated opening of the at least one flow control
device is determined based on the target oxygen content (determined at step 202 or
302 of FIGs. 2 and 3, respectively) and the engine operating parameter using a feedforward
model, hereinafter referred to as, a second model, or a second look-up table.
As previously noted, the non-limiting examples of the engine operating parameter
may include the engine load, the engine speed, the actual value of the AFR, the
ambient temperature, the ambient pressure, the altitude, the one or more fuel quality
parameters, the manifold air pressure, the manifold air temperature, the fuel type, the
turbocharger speed, or combinations thereof. Moreover, in some embodiments, the
second model or the second look-up table is representative of a relationship between
the first estimated opening and the target oxygen content and engine operating
parameter. In a non-limiting example, following equations may represent, at least
partially, the second model that is used to determine the first estimated opening at the
step 402.
????????
?????? ?? ????????2??????, ????????????, ????????1??????????????, ????????????, ????????2????????????????
Eqn. 1
?????????? ?????????????????? ?????????????????????????? ?? ????????????
??????, ??????????
????????????????, ??????????
??????????????????
Eqn. 2
[0051] For example, Eqn. 1 may be used to first determine a desired air content
(W??????
??????) based on the target oxygen content in the exhaust gas stream 60 (XO2??????),
mass flow rates of one or more fuels (W??????????, W??????????), and Hydrogen-Carbon ratios of
the one or more fuels (????????1??????????????, ????????2??????????????). Thereafter, for example, for a
given flow control device (??????1), the first estimated opening may be determined
based on the desired air content (????????
?????? determined using the Eqn. 1), a pressure at
an inlet of the flow control device (??????????
????????????????), and a temperature at an inlet or
an outlet of the flow control device (??????????
????????????????). In non-limiting examples, the
281474-1
20
pressure at an inlet of the flow control device (??????1) may be representative of the
pressure of the air stream 30 (when ??????1 is the turbo charger), the pressure of the
pressurized air stream 10 (when ??????1 is the compressor recirculation valve 120), or
the pressure of the exhaust gas stream 50 (when ??????1 is the waste gate valve 114).
[0052] Furthermore, at step 404, a second estimated opening of the at least one
flow control device is determined based on the difference determined at step 210 (or
the filtered difference determined at 312) between the estimated oxygen content and
the measured oxygen content determined at step 208 (or the filtered measured
oxygen content determined at step 310). In one embodiment, the processor 132 may
maintain a third model or a third look-up table is representative of the relationship
between the second estimated opening and the difference determined at step 210 (or
the filtered difference determined at 312). In a non-limiting example, the third model
may be implemented using a proportional-integral-derivative controller (PID
controller), and lead and/or lag compensator(s).
[0053] Thereafter, at step 406, a third estimated opening of the at least one flow
control device is determined based on one or both of the first estimated opening and
the second estimated opening. In a non-limiting example, the third estimated
opening is equivalent to sum of the first estimated opening and the second estimated
opening.
[0054] Additionally, to control the actual value of the AFR, a signal (or
command) may be communicated to the at least one flow control device such that an
actual open position of the at least one flow control device is set based on the third
estimated opening, as indicated by step 408. In some embodiments, the processor
132 may generate the signal (or command) based on the third estimated opening
determined at step 406. The generated signal is indicative of a desired open position
of the at least one flow control device. As previously noted, the open position of the
at least one flow control device may control an amount of air and/or fuel for
281474-1
21
combustion into the combustion engine 102, thereby resulting into desired AFR of
the air-fuel mixture.
[0055] The methods and engine controller according to some embodiments, aid in
controlling the AFR in the power generation system 100. More particularly, the
methods and engine controller according to some embodiments provides faster and
substantially accurate control of the AFR. As will be appreciated, such faster and
substantially accurate control of the AFR results in reduced misfire and knock
occurrences. Consequently, the efficiency and reliability of the power generation
system 100 may be improved. Further, the improved control of the AFR results in
reduced overall emission from the power generation system 100.
[0056] 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.