U.S. patent application number 14/515992 was filed with the patent office on 2016-04-21 for differential fueling between donor and non-donor cylinders in engines.
The applicant listed for this patent is General Electric Company. Invention is credited to Jennifer Lynn Jackson, Adam Edgar Klingbeil, Thomas Michael Lavertu.
Application Number | 20160108873 14/515992 |
Document ID | / |
Family ID | 55638086 |
Filed Date | 2016-04-21 |
United States Patent
Application |
20160108873 |
Kind Code |
A1 |
Jackson; Jennifer Lynn ; et
al. |
April 21, 2016 |
DIFFERENTIAL FUELING BETWEEN DONOR AND NON-DONOR CYLINDERS IN
ENGINES
Abstract
A method of controlling an engine includes injecting a first
fuel and a second fuel to each of a donor cylinder group and a
non-donor cylinder group of the engine. The method also includes
injecting a higher fraction of the first fuel into the donor
cylinder group in comparison to the first fuel being injected into
the non-donor cylinder group. Further, the method includes
injecting a lower fraction of the second fuel into the donor
cylinder group in comparison to the second fuel being injected into
the non-donor cylinder group. Furthermore, the method includes
recirculating an exhaust emission from the donor cylinder group to
the non-donor cylinder group and the donor cylinder group and
combusting a mixture of air, the first fuel, the second fuel and
the exhaust emission from the donor cylinder group in both the
donor cylinder group and the non-donor cylinder group.
Inventors: |
Jackson; Jennifer Lynn;
(Troy, NY) ; Klingbeil; Adam Edgar; (Ballston
Lake, NY) ; Lavertu; Thomas Michael; (Clifton Park,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
55638086 |
Appl. No.: |
14/515992 |
Filed: |
October 16, 2014 |
Current U.S.
Class: |
123/445 |
Current CPC
Class: |
F02D 19/0647 20130101;
Y02T 10/30 20130101; F02B 29/0412 20130101; F02D 41/34 20130101;
F02M 26/22 20160201; F02M 43/00 20130101; F02M 26/43 20160201; F02D
19/0694 20130101; F02D 19/081 20130101; F02D 41/0027 20130101; F02D
41/0025 20130101; F02D 41/0082 20130101; Y02T 10/36 20130101; F02D
41/40 20130101 |
International
Class: |
F02M 43/00 20060101
F02M043/00 |
Claims
1. A method of controlling an engine, comprising: injecting a first
fuel and a second each of a donor cylinder group and a non-donor
cylinder group of the engine; injecting a higher fraction of the
first fuel into the donor cylinder group in comparison to the first
fuel being injected into the non-donor cylinder group; injecting a
lower fraction of the second fuel into the donor cylinder group in
comparison to the second fuel being injected into the non-donor
cylinder group; recirculating an exhaust emission from the donor
cylinder group to the non-donor cylinder group and the donor
cylinder group; and combusting a mixture of air, the first fuel,
the second fuel and the exhaust emission front the donor cylinder
group in both the donor cylinder group and the non-donor cylinder
group.
2. The method of claim 1, wherein the first fuel comprises a diesel
fuel.
3. The method of claim 1, wherein the second fuel comprises at
least one of natural gas, nitrogen, hydrogen, syngas, gasoline,
ethanol, carbon monoxide, propane, biogas, liquid petroleum gas
(LPG).
4. The method of claim 1, wherein a quantity of the first fuel
injected into the donor cylinder group is about forty percent of
total fuel combusted in the donor cylinder group.
5. The method of claim 1, wherein a quantity of the first fuel
injected into the non donor cylinder group is about twenty percent
of total fuel combusted in the non-donor cylinder group.
6. The method of claim 1, further comprising operating a first
direct injector and a second port injector in the donor cylinder
group at an optimal first fuel injection timing so as to obtain
higher substitution rate of the first fuel as compared to a
substitution rate of the first fuel in the non-donor cylinder
group.
7. The method of claim 6, wherein the operation of the donor
cylinder group at the optimal first fuel injection timing is
carried out by a controller.
8. The method of claim 7, further comprising generating emissions
from the donor cylinder group having increased amounts of carbon
monoxide.
9. The method of claim 8, further comprising recirculating the
emissions having increased amounts of carbon monoxide from the
donor cylinder group to the non-donor cylinder group and the donor
cylinder group for further oxidizing the carbon monoxide.
10. The method of claim 1, further comprising feeding the first
fuel directly to the donor cylinder group and the non-donor
cylinder group and the second fuel via port injectors disposed in
intake passages of the donor cylinder group and the non-donor
cylinder group.
11. A system comprising: an engine comprising: a donor cylinder
group coupled to an intake manifold; wherein the take manifold is
configured to feed a flow of air to the donor cylinder group; a
non-donor cylinder group coupled to the intake manifold and an
exhaust manifold; wherein the intake manifold is further configured
to feed air to the non-donor cylinder group; a first direct
injector disposed in each cylinder of the donor cylinder group
configured to inject a first fuel from a first fuel source and a
second port injector disposed in each of a plurality of first
intake passages configured to inject a second fuel from a second
fuel source; a third direct injector disposed in each cylinder of
the non-donor cylinder group configured to inject the first fuel
from the first fuel source and a fourth port injector disposed in
each of a plurality of second intake passages for injecting the
second fuel from the second fuel source; an exhaust channel
extending from the donor cylinder group to the intake manifold for
recirculating an exhaust emission from the at least one donor
cylinder to the at least one donor, and non-donor cylinders via the
intake manifold; and a controller configured to, during a single
engine cycle, operate the first direct injector, the second port
injector, the third injector and the fourth port injector such that
there is a higher fraction of injection of the first fuel into the
donor cylinder group in comparison to the first fuel being injected
into the non-donor cylinder group and a lower fraction of injection
of the second fuel into the donor cylinder group comparison to the
second fuel being injected into the non-donor cylinder group.
12. The system of claim 11, wherein the first fuel comprises a
diesel fuel.
13. The system of claim 11, wherein the second fuel comprises at
least one of natural gas, nitrogen, hydrogen, syngas, gasoline,
ethanol, carbon monoxide, propane, biogas, liquid petroleum gas
(LPG).
14. The system of claim 11, wherein a quantity of the first fuel
injected into the donor cylinder group is about 40 percent of total
fuel combusted in the donor cylinder group.
15. The system of claim 11, wherein a quantity of the first fuel
injected into the non donor cylinder group is about 20 percent of
total fuel combusted in the non-donor cylinder group.
16. The system of claim 11, wherein the controller operates the
first direct injector and the second port injector in the donor
cylinder group at an optimal first fuel injection timing so as to
obtain higher substitution rate of the first fuel as compared to
substitution rate of the first fuel in the non-donor cylinder
group.
17. The system of claim 11, further comprising a two-staged
turbocharger having a plurality of compressors and a plurality of
turbines.
18. A method of controlling an engine, comprising: injecting a
first fuel and a second fuel to each of a donor cylinder soup anal
a non-donor cylinder group of the engine; injecting a lower
fraction of the first fuel into the nor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group; injecting a higher fraction of the second fuel into
the donor cylinder group in comparison to the second fuel being
injected into the non-donor cylinder group; combusting a mixture of
air, the first fuel, the second fuel in the donor cylinder group
and the non-donor cylinder group and an exhaust emission from the
donor cylinder group; operating the donor cylinder group, during
low power or low temperature conditions, at an optimal first fuel
injection timing so as to obtain higher substitution rate of the
first fuel as compared to a substitution rate of the first fuel in
the non-donor cylinder group causing generation of emissions from
the donor cylinder group having increased amounts of carbon
monoxide; and recirculating the exhaust emission from the donor
cylinder group to the non-donor cylinder group and the donor
cylinder group for oxidizing the increased amounts of carbon
monoxide.
19. The method of claim 18, wherein the first fuel comprises a
diesel fuel.
20. The method of claim 18, wherein the second fuel comprises at
least one of natural gas, nitrogen, hydrogen, syngas, gasoline,
ethanol, carbon monoxide, propane, biogas, liquid petroleum gas
(LPG).
Description
BACKGROUND
[0001] The present technology relates generally to dual fuel
engines and, in particular, to methods and systems for a dual fuel
engine having differential fuelling between donor and non-cylinders
operating with exhaust gas recirculation (EGR).
[0002] Generally, a dual-fuel engine is an alternative internal
combustion engine designed to run on more than one fuel each stored
in separate vessels. Dual fuel engines are known for various
applications, such as generator sets, engine-driven compressors,
engine driven pumps, machine, off-highway trucks and others. Such
engines are capable of burning varying proportions of the resulting
blend of fuels in the combustion chamber and the fuel injection or
spark timing may be adjusted according to the blend of fuels in the
combustion chamber. The operation of such engines by substitution
of a certain amount of heavy fuel, such as diesel, with a lighter
fuel, such as natural gas, biogas, liquid petroleum gas (LPG) or
other types of fuel that may be more readily available and cost
effective, makes them more effective to operate. However, such
engines having donor cylinders operate at higher exhaust pressure
for the donor cylinders, resulting in increased exhaust gas
residuals, potentially causing knock in the donor cylinders, Also,
the increased exhaust gas residuals limit substitution rate in the
dual fuel engines since lighter fuels such as natural gas are
susceptible to knock. Further, the exhaust emissions generally
include pollutants such as carbon oxides (e.g., carbon monoxide),
nitrogen oxides (NOx), sulfur oxides (SOX), and particulate matter
(PM). The amount and relative proportion of these pollutants varies
according to the fuel-air mixture, compression ratio, injection
timing, environmental conditions (e.g., atmospheric pressure,
temperature, etc.), and so forth,
[0003] There is therefore a desire for an improved system and anal
method for engines operating on more than one fuel.
BRIEF DESCRIPTION
[0004] In accordance with an example of the present technology, a
method of controlling an engine includes injecting a first fuel and
a second fuel to each of a donor cylinder group and a non-donor
cylinder group of the engine. The method also includes injecting a
higher fraction of the first fuel into the donor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group. Further, the method includes injecting a lower
fraction of the second fuel into the donor cylinder group in
comparison to the second fuel being injected into the non-donor
cylinder group. Furthermore, the method includes recirculating an
exhaust emission from the donor cylinder group to the non-donor
cylinder group and the donor cylinder group and combusting a
mixture of air, the first fuel, the second fuel and the exhaust
emission from the donor cylinder group in both the donor cylinder
group and the non-donor cylinder group.
[0005] In accordance with an example of the technology, a system
for controlling an engine is provided. The engine includes a donor
cylinder group coupled to an intake manifold. The intake manifold
is configured to feed a flow to the donor cylinder group. The
engine also includes a non-donor cylinder group coupled to the
intake manifold and an exhaust manifold, wherein the intake
manifold is further configured to feed air to the non-donor
cylinder group. The system further includes an exhaust channel
extending from the donor cylinder group to the intake manifold for
recirculating an exhaust emission from the at least one donor
cylinder to the at least one donor, and non-donor cylinders via the
intake manifold. Furthermore, the system includes a first direct
injector disposed in each cylinder of the donor cylinder group
configured to inject a first fuel from a first fuel source and a
second port injector disposed in each of a plurality of first
intake passages configured to inject a second fuel from a second
fuel source. The system includes a third direct injector disposed
in each cylinder of the non-donor cylinder group configured to
inject the first fuel from the first fuel source and a fourth port
injector disposed in each of a plurality of second intake passages
for injecting the second fuel from the second fuel source. The
system also includes a controller configured to, during a single
engine cycle, operate the first direct injector, the second port
injector, the third injector and the fourth port injector such that
there is a higher fraction of injection of the first fuel into the
donor cylinder group in comparison to the first fuel being injected
into the non-donor cylinder group and a lower fraction of injection
of the second fuel into the donor cylinder group in comparison to
the second fuel being injected into the non-donor cylinder group
while maintaining a similar fuel energy in each of the
cylinders.
[0006] In accordance with an example of the technology, a method of
controlling an engine includes injecting a first fuel and a second
fuel to each of a donor cylinder group and a non-donor cylinder
group of the engine. The method also includes injecting a lower
fraction of the first fuel into the donor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group. Further, the method includes injecting a higher
fraction of the second fuel into the donor cylinder group in
comparison to the second fuel being injected into the non-donor
cylinder group. Furthermore, the method includes combusting a
mixture of air, the first fuel, the second fuel in the donor
cylinder group and the non-donor cylinder group and an exhaust
emission from the donor cylinder group. The method includes
operating the donor cylinder group, during low power or low ambient
temperature conditions, at an optimal first fuel injection timing
so as to obtain higher substitution rate of the first fuel as
compared to a substitution rate of the first fuel in the non-donor
cylinder group causing generation of emissions from the donor
cylinder group having increased amounts of carbon monoxide and
recirculating the exhaust emission from the donor cylinder group to
the non-donor cylinder group and the donor cylinder group for
oxidizing the increased amounts of carbon monoxide.
DRAWINGS
[0007] These and other features, aspects, and advantages of the
present technology 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:
[0008] FIG. 1 schematically shows a system for controlling a
dual-fuel engine in accordance with an example of the present
technology;
[0009] FIG. 2 is a flow chart of a method of controlling an engine
in accordance with an example of the present technology;
[0010] FIG. 3 is a flow chart of a method of controlling an engine
in accordance with embodiment of the present invention.
DETAILED DESCRIPTION
[0011] When introducing elements of various embodiments of the
present technology, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements. Any examples of operating parameters are not
exclusive of other parameters of the disclosed examples.
[0012] FIG. 1 schematically shows a system 10 for controlling a
dual-fuel engine 12 in accordance with an example of the present
technology. The dual-fuel engine 12 includes a donor cylinder group
14 having multiple donor cylinders coupled to an intake manifold 16
that is configured to feed a flow of air to the donor cylinder
group. The dual-fuel engine 12 also includes a non-donor cylinder
group 18 coupled to the intake manifold 16 and an exhaust manifold
20. The intake manifold 16 is further configured to feed air to the
non-donor cylinder group 18. The dual fuel engine 12 also includes
an exhaust channel 22 extending from the donor cylinder group 14 to
the intake manifold 16 for recirculating an exhaust emission in an
exhaust gas recirculation (EGR) loop 17 from the donor cylinders to
both donor cylinders 14, and non-donor cylinders 18 via the intake
manifold 16.
[0013] Further each cylinder of the donor cylinder group 14
includes a first direct injector 24 that injects a first fuel 28
from a first fuel source 32. The system 10 also includes a second
port injector 26 disposed in each of a plurality of first intake
passages 27 configured to inject a second fuel 30 from a second
fuel source 34. Similarly, each cylinder of the non-donor cylinder
group 18 includes a third direct injector 36 and a fourth port
injector 38. The third direct injector 36 injects the first fuel 28
from the first fuel source 32, while the fourth port injector 38
disposed in each of a plurality of second intake passages 39,
injects the second fuel 30 from the second fuel source 34. in one
embodiment, the first fuel 28 includes a diesel fuel. The second
fuel 30 may include at least one of natural gas, nitrogen,
hydrogen, syngas, gasoline, ethanol, carbon monoxide, propane,
biogas, liquid petroleum gas (LPG).
[0014] Furthermore, the system 10 includes a two-staged
turbocharger 40 configured to provide compressed air to the dual
fuel engine 12 through the intake manifold 16. The two-staged
turbocharger 40 includes a first stage turbocharger 42 that
includes a low pressure compressor 44 and a low pressure turbine
46. The two-staged turbocharger 40 also includes a second stage
turbocharger 48 having a high pressure compressor 50 and a high
pressure turbine 52. As shown in FIG. 1, the low pressure
compressor 44, the high pressure compressor 50 and the intake
manifold 16 are in fluid communication with each other. Ambient air
is routed through the low pressure compressor 44 and the high
pressure compressor 50 for sufficient compression prior to being
directed into the intake manifold 16. The flow of air is cooled in
two stages in an intercooler 54 located between the compressors 44,
50 and in an aftercooler 56 located between the high pressure
compressor 50 and the intake manifold 16. The exhaust emissions in
the exhaust gas recirculation loop 17 are also cooled in an EGR
cooler 58 prior to being directed into the intake manifold 16. In
one embodiment, each of the intercooler 54, aftercooler 56 and the
EGR cooler 58 is a heat exchanger that may utilize a fluid for
extracting heat thereby cooling the flow of air and exhaust
emissions flowing through each of the cooler. The exhaust emissions
flowing out of the non-donor cylinder group 18 through the exhaust
manifold 20 are routed through the high pressure turbine 52 and the
low pressure turbine 46 prior to being released out of the system
10. As shown in FIG. 1, the high pressure turbine 52 and the low
pressure turbine 46 are driven by the force of the exhaust
emissions and in turn drive the high pressure compressor 50 and the
low pressure compressor 42 respectively. In one embodiment, the
system 10 includes a high pressure turbine (HPT) bypass line 60
having a valve 62 that may be operated to route the exhaust
emissions directly through the low pressure turbine 46 bypassing
the high pressure turbine 52. In another embodiment, the system 10
also includes a valve 64 located in a fluid line connecting the EGR
loop 17 and the exhaust manifold 20 for controlling flow of exhaust
emissions in the EGR loop 17. In a non-limiting example, the system
10 may include a single staged turbocharger (not shown) configured
to provide compressed air to the dual fuel engine 12 through the
intake manifold 16.
[0015] The system 10 also includes a controller 66 e.g., an
electronic control unit (ECU), coupled to various sensors and
components throughout the system 10. As shown, the controller 66
includes electrical connections 68, 70, 72 and 74 that are coupled
with fuel lines that supply the first fuel 28 and second fuel 30 to
the donor cylinder group 14 and the non-donor cylinder group 18.
Thus, the controller 66 is configured to, during a single engine
cycle, operate the first direct injector 24 and the second port
injector 26, the third injector 36 and the fourth port injector 38
in each of the donor cylinder group 14 and the non-donor cylinder
group 18 respectively, such that there is a higher fraction of
injection of the first fuel into the donor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group and a lower fraction of injection of the second fuel
into the donor cylinder group in comparison to the second fuel
being injected into the non-donor cylinder group. This operation of
differential fueling reduces the risk of knock in the donor
cylinder group 14 while maintaining a required power output. In one
non-limiting example, a quantity of the first fuel injected into
the donor cylinder group 14 is about 40 percent of a total fuel
combusted in the donor cylinder group 14, while a quantity of the
first fuel injected into the non-donor cylinder group 18 is about
20 percent of a total fuel combusted in the non-donor cylinder
group 18. This allows more consumption of the second fuel 30 and
thereby, resulting in economical operation of the dual fuel engine
12. This operation of differential fueling is carried out during
high load or high ambient temperature conditions. The dual fuel
engine 12 is also configured to operate such that the quantity of
the first fuel injected into the donor cylinder group 14 may vary
from about one percent to about 100 percent.
[0016] Moreover, in one embodiment, during low power load
conditions or low ambient temperature conditions, the controller 66
is configured to operate the first direct injector 24 and the
second port injector 26 in the donor cylinder group 14 at an
optimal first fuel injection timing so as to obtain higher
substitution rate of the first fuel 28 as compared to substitution
rate of the first fuel 28 in the non-donor cylinder group 18.
Further, the terms `substitution rate` to each cylinder in the
donor cylinder group may be defined as a ratio of second fuel 30
supply by injector 26 to a total fuel supply by injectors 24, 26.
This causes generation of emissions from the donor cylinder group
with increased amounts of carbon monoxide. The recirculation of the
emissions having increased amounts of carbon monoxide from the
donor cylinder group 14 to the non-donor cylinder group 18 and the
donor cylinder group 14 for further oxidizing the carbon monoxide.
It is to be noted that operating the injectors 24, 26 at optimal
first fuel injection timing so as to obtain high substitution rate
of the first fuel 28 per the second fuel 30 in each cylinder of the
donor cylinder group 14 is carried out at low power or low ambient
temperature conditions. In another embodiment, at low power or low
ambient temperature conditions, each non-donor cylinder of the
non-donor cylinder group 18 may be operated at lower substitution
rate in order to control emissions, while donor cylinder group 14
may be operated at high substitution rate. It is to be understood
that the terms `substitution rate` to each cylinder in the
non-donor cylinder group may be defined as a ratio of second fuel
30 supply by injector 38 to a total fuel supply by injectors 36,
38.
[0017] FIG. 2 is a flow chart 100 of a method of controlling an
engine in accordance with embodiment of the present invention. At
step 102, the method includes injecting a first fuel and a second
fuel to each of a donor cylinder group and a non-donor cylinder
group of the engine. In one example, the first fuel includes a
diesel fuel. Non-limiting examples of the second fuel includes
natural gas, nitrogen, hydrogen, syngas, gasoline, ethanol, carbon
monoxide, propane, biogas, liquid petroleum gas (LPG) and mixtures
thereof. At step 104, the method includes injecting a higher
fraction of the first fuel into the donor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group. In one embodiment, a quantity of the first fuel
injected into the donor cylinder group is about 40 percent of total
fuel combusted in the donor cylinder group. Further, at step 106,
the method includes injecting a lower fraction of the second fuel
into the donor cylinder group in comparison to the second fuel
being injected into the non-donor cylinder group. In one
embodiment, a quantity of the first fuel injected into the
non-donor cylinder group is about 20 percent of total fuel
combusted in the non-donor cylinder group. Furthermore, at step
108, the method includes recirculating an exhaust emission from the
donor cylinder group to the non-donor cylinder group and the donor
cylinder group. At step 110, the method includes combusting a
mixture of air, the first fuel, the second fuel and the exhaust
emission from the donor cylinder group in both the donor cylinder
group and the non-donor cylinder group.
[0018] FIG. 3 is a flow chart 200 of a method of controlling an
engine in accordance with embodiment of the present invention. At
step 202, the method includes injecting a first fuel and a second
fuel to each of a donor cylinder group and a non-donor cylinder
group of the engine. In one example, the first fuel includes a
diesel fuel. Non-limiting examples of the second fuel includes
natural gas, nitrogen, hydrogen, syngas, gasoline, ethanol, carbon
monoxide, propane, biogas, liquid petroleum gas (LPG) and mixtures
thereof. At step 204, the method includes injecting a lower
fraction of the first fuel into the donor cylinder group in
comparison to the first fuel being injected into the non-donor
cylinder group. In one embodiment, a quantity of the first fuel
injected into the donor cylinder group is about 40 percent of total
fuel combusted in the donor cylinder group. Further, at step 206,
the method includes injecting a higher fraction of the second fuel
into the donor cylinder group in comparison to the second fuel
being injected into the non-donor cylinder group. In one
embodiment, a quantity of the first fuel injected into the
non-donor cylinder group is about 20 percent of total fuel
combusted in the non-donor cylinder group. Furthermore, at step
208, the method includes combusting a mixture of air, the first
fuel, the second fuel in the donor cylinder group and the non-donor
cylinder group and an exhaust emission from the donor cylinder
group. At step 210, the method includes operating the donor
cylinder group, during low power or low temperature conditions, at
an optimal first fuel injection timing so as to obtain higher
substitution rate of the first fuel as compared to a substitution
rate of the first fuel in the non-donor cylinder group causing
generation of emissions from the donor cylinder group having
increased amounts of carbon monoxide. This operation of the donor
cylinder group at the optimal first fuel injection timing is
carried out by a controller that controls the first direct injector
and the second port injector in the donor cylinder group such that
there is the optimal first fuel injection timing for obtaining high
substitution rate of the first fuel as compared to the substitution
rate of the first fuel in the non-donor cylinder group. At step
212, the method includes recirculating an exhaust emission from the
donor cylinder group to the non-donor cylinder group and the donor
cylinder group for oxidizing the increased amounts of carbon
monoxide.
[0019] Advantageously, the present invention enables the
development of a dual fuel engine operating with the exhaust gas
recirculation loop that meets low emissions requirements. The
present invention also allows operation with high second fuel
substitution, resulting in increased use of second fuel such as
natural gas and thereby reducing operational expenses of the dual
fuel engines or the reciprocating engines.
[0020] Furthermore, the skilled artisan will recognize the
interchangeability of various features from different examples.
Similarly, the various methods and features described, as well as
other known equivalents for each such method and feature, can be
mixed and matched by one of ordinary skill in this art to construct
additional systems and techniques in accordance with principles of
this disclosure. Of course, it is to be understood that not
necessarily all such objects or advantages described above may be
achieved in accordance with any particular example. Thus, for
example, those skilled in the art will recognize that the systems
and techniques described herein may be embodied or carried out in a
manner that achieves or improves one advantage or group of
advantages as taught herein without necessarily achieving other
objects or advantages as may be taught or suggested herein.
[0021] While only certain features of the technology have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
claimed inventions.
* * * * *