U.S. patent application number 11/418938 was filed with the patent office on 2007-11-08 for reformer temperature control with leading temperature estimation.
This patent application is currently assigned to Eaton Corporation. Invention is credited to Johannes Walter Reuter.
Application Number | 20070256407 11/418938 |
Document ID | / |
Family ID | 38535368 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256407 |
Kind Code |
A1 |
Reuter; Johannes Walter |
November 8, 2007 |
Reformer temperature control with leading temperature
estimation
Abstract
One concept relates to a method of controlling fuel reforming
within an internal combustion engine exhaust line. Fuel injections
are controlled using a predicted temperature, the predicted
temperature being a temperature that would occur at some point in
the future if predetermined assumptions are met. Preferably, the
prediction is made using a model that includes terms for
hydrocarbon storage and subsequent reaction within the reformer.
The method improves reformer temperature control, particularly over
periods during which the fuel supply to the reformer is pulsed. The
scope of the invention also includes methods wherein a temperature
is not specifically predicted, provided the control method takes
into account hydrocarbon storage and subsequent reaction.
Inventors: |
Reuter; Johannes Walter;
(Ypsilanti, MI) |
Correspondence
Address: |
PAUL V. KELLER, LLC
4585 LIBERTY RD.
SOUTH EUCLID
OH
44121
US
|
Assignee: |
Eaton Corporation
Cleveland
OH
|
Family ID: |
38535368 |
Appl. No.: |
11/418938 |
Filed: |
May 5, 2006 |
Current U.S.
Class: |
60/286 ; 60/295;
60/301 |
Current CPC
Class: |
F01N 3/208 20130101;
F01N 9/005 20130101; Y02A 50/2325 20180101; F02D 41/028 20130101;
Y02T 10/24 20130101; Y02T 10/47 20130101; F01N 3/0253 20130101;
F01N 2570/12 20130101; F02D 2041/1433 20130101; F01N 13/0097
20140603; Y02T 10/12 20130101; F01N 2250/14 20130101; Y02T 10/40
20130101; Y02A 50/20 20180101; F01N 3/2073 20130101; F01N 2250/02
20130101; F01N 2570/18 20130101; F01N 2240/30 20130101; F01N 3/106
20130101; F01N 11/005 20130101; F01N 2250/12 20130101; F01N 2610/03
20130101; F01N 3/0885 20130101; F02D 41/0275 20130101; F02D
2200/0804 20130101 |
Class at
Publication: |
060/286 ;
060/295; 060/301 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/10 20060101 F01N003/10 |
Claims
1. A method of fuel reforming within an internal combustion engine
exhaust line, comprising: injecting fuel into the exhaust line
upstream of a fuel reformer; measuring a temperature within the
exhaust line; predicting a temperature based in part on the
measured temperature; and controlling the fuel injection using the
predicted temperature; wherein the predicted temperature is a
temperature that would occur at some point in the future if
predetermined assumptions are met.
2. The method of claim 1, wherein controlling the fuel injection
using the predicted temperature comprises temporarily discontinuing
the fuel injection if the predicted temperature meets or exceeds a
critical value.
3. The method of claim 1, wherein injecting fuel into the exhaust
line upstream of the fuel reformer comprises: injecting fuel at
rate that produces a sub-stoichiometric concentration of fuel in
the exhaust line to heat the fuel reformer to a temperature
suitable for producing reformate; and subsequently injecting fuel
at a higher rate to produce a super-stoichiometric concentration of
fuel in the exhaust line in order to produce reformate.
4. The method of claim 1, wherein the temperature prediction is
based in part on a model.
5. The method of claim 4, wherein the fuel is injected in pulses
and the model predicts the availability within the reformer of a
portion of the injected fuel in periods between temporally adjacent
fuel pulses.
6. The method of claim 4, wherein the model takes into account fuel
storage within the fuel reformer and subsequent reaction of the
stored fuel.
7. The method of claim 4, wherein the model predicts the reformer
will heat in periods following the termination of fuel injection
due to reactions of previously injected fuel within the
reformer.
8. The method of claim 4, wherein the model predicts that some of
the injected fuel will absorb within the fuel reformer without
immediately reacting, but will subsequently react.
9. An exhaust treatment system comprising a controller, wherein the
controller implements the method of claim 1.
10. A vehicle comprising the exhaust treatment system, of claim
9.
11. A method of controlling the temperature of a fuel reformer,
comprising: using a model to predict a temperature associated with
the reformer; and using the predicted temperature in a temperature
control algorithm; wherein the temperature prediction takes into
account hydrocarbon storage and subsequent reaction.
12. The method of claim 11, wherein the fuel reformer is configured
within an exhaust line upstream of a lean NOx trap.
13. The method of claim 12, wherein fuel is injected into the
exhaust line in pulses during a regeneration of the lean NOx
trap.
14. The method of claim 11, wherein the model predicts the reformer
temperature using dynamics that are faster than the actual dynamics
are expected to be.
15. A method of controlling the temperature of a fuel reformer,
comprising: predicting future reformer temperatures; and using the
predicted future reformer temperatures in a feedback control loop;
wherein the predictions take into account hydrocarbon storage and
subsequent availability for reaction.
16. The method of claim 15, wherein the fuel reformer is configured
within an exhaust line upstream of a lean NOx trap.
17. The method of claim 15, wherein fuel is injected into the
exhaust line in pulses during a regeneration of the lean NOx
trap.
18. A method of reforming within an internal combustion engine
exhaust line, comprising: injecting hydrocarbons into the exhaust
line upstream of a reformer; estimating hydrocarbon storage by the
reformer; controlling the reformer temperature based in part on the
hydrocarbon storage estimate.
19. The method of claim 18, wherein the fuel reformer is configured
within an exhaust line upstream of a lean NOx trap.
20. The method of claim 18, wherein fuel is injected into the
exhaust line in pulses during a regeneration of the lean NOx
trap.
21. The method of claim 18, wherein the hydrocarbon storage
estimate is used in a thermal model of the reformer.
22. The method of claim 21, wherein the model is applied with
accelerated dynamics.
23. The method of claim 18, controlling the reformer temperature
based in part on the hydrocarbon storage estimate comprises
temporarily terminating the hydrocarbon injection if the estimated
amount of hydrocarbon stored is too high.
24. The method of claim 18, wherein injecting hydrocarbons into the
exhaust line upstream of a reformer comprises: injecting
hydrocarbons at rate that produces a sub-stoichiometric
concentration of hydrocarbons in the exhaust line to heat the fuel
reformer to a temperature suitable for producing reformate; and
subsequently injecting hydrocarbons at a higher rate to produce a
super-stoichiometric concentration of fuel in the exhaust line in
order to produce reformate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to pollution control systems
and methods for diesel and lean burn gasoline engines.
BACKGROUND
[0002] NO.sub.x emissions from diesel engines are an environmental
problem. Several countries, including the United States, have long
had regulations pending that will limit NO.sub.x emissions from
trucks and other diesel-powered vehicles. Manufacturers and
researchers have put considerable effort toward meeting those
regulations.
[0003] In gasoline powered vehicles that use stoichiometric
fuel-air mixtures, three-way catalysts have been shown to control
NO.sub.x emissions. In diesel-powered vehicles, which use
compression ignition, the exhaust is generally too oxygen-rich for
three-way catalysts to be effective.
[0004] Several solutions have been proposed for controlling NOx
emissions from diesel-powered vehicles. One set of approaches
focuses on the engine. Techniques such as exhaust gas recirculation
and partially homogenizing fuel-air mixtures are helpful, but these
techniques alone will not eliminate NOx emissions. Another set of
approaches remove NOx from the vehicle exhaust. These include the
use of lean-burn NO.sub.x catalysts, selective catalytic reduction
(SCR), and lean NO.sub.x traps (LNTs).
[0005] Lean-burn NOx catalysts promote the reduction of NO.sub.x
under oxygen-rich conditions. Reduction of NOx in an oxidizing
atmosphere is difficult. It has proven challenging to find a
lean-burn NO.sub.x catalyst that has the required activity,
durability, and operating temperature range. Lean-burn NO.sub.x
catalysts also tend to be hydrothermally unstable. A noticeable
loss of activity occurs after relatively little use. Lean-burn NOx
catalysts typically employ a zeolite wash coat, which is thought to
provide a reducing microenvironment. The introduction of a
reductant, such as diesel fuel, into the exhaust is generally
required and introduces a fuel economy penalty of 3% or more.
Currently, peak NOx conversion efficiencies for lean-burn NOx
catalysts are unacceptably low.
[0006] SCR generally refers to selective catalytic reduction of NOx
by ammonia. The reaction takes place even in an oxidizing
environment. The NOx can be temporarily stored in an absorbent or
ammonia can be fed continuously into the exhaust. SCR can achieve
high levels of NOx reduction, but there is a disadvantage in the
lack of infrastructure for distributing ammonia or a suitable
precursor. Another concern relates to the possible release of
ammonia into the environment.
[0007] LNTs are devices that adsorb NOx under lean exhaust
conditions and reduce and release the adsorbed NOx under rich
condition. A LNT generally includes a NOx absorbent and a catalyst.
The absorbent is typically an alkaline earth oxide absorbent, such
as BaCO.sub.3 and the catalyst is typically a precious metal, such
as Pt or Ru. In lean exhaust, the catalyst speeds oxidizing
reactions that lead to NOx adsorption. In a reducing environment,
the catalyst activates reactions by which adsorbed NOx is reduced
and desorbed. In a typical operating protocol, a reducing
environment will be created within the exhaust from time-to-time to
regenerate (denitrate) the LNT.
[0008] A LNT can produce ammonia during denitration. Accordingly,
it has been proposed to combine a LNT and an ammonia SCR catalyst
into one system. Ammonia produced by the LNT during regeneration is
captured by the SCR catalyst for subsequent use in reducing NOx,
thereby improving conversion efficiency over a stand-alone LNT with
no increase in fuel penalty or precious metal usage. U.S. Pat. No.
6,732,507 describes such a system. U.S. Pat. Pub. No. 2004/0076565
describes such systems wherein both components are contained within
a single shell or disbursed over one substrate. WO 2004/090296
describes such a system wherein there is an inline reformer
upstream of the LNT and the SCR catalyst.
[0009] Creating a reducing environment for LNT regeneration
involves eliminating most of the oxygen from the exhaust and
providing a reducing agent. Except where the engine can be run
stoichiometric or rich, a portion of the reductant reacts within
the exhaust to consume oxygen. The amount of oxygen to be removed
by reaction with reductant can be reduced in various ways. If the
engine is equipped with an intake air throttle, the throttle can be
used. The transmission gear ratio can be changed to shift the
engine to an operating point that produces equal power but contains
less oxygen. However, at least in the case of a diesel engine, it
is generally necessary to eliminate some of the oxygen in the
exhaust by combustion or reforming reactions with reductant that is
injected into the exhaust.
[0010] Reductant can be injected into the exhaust by the engine or
a separate fuel injection device. For example, the engine can
inject extra fuel into the exhaust within one or more cylinders
prior to expelling the exhaust. Alternatively, or in addition,
reductant can be injected into the exhaust downstream of the
engine.
[0011] The reactions between reductant and oxygen can take place in
the LNT, although it is generally preferred for the reactions to
occur in a catalyst upstream of the LNT, whereby the heat of
reaction does not cause large temperature increase within the LNT
at every regeneration.
[0012] In addition to accumulating NOx, LNTs accumulate SOx. SOx is
the combustion product of sulfur present in ordinarily fuel. Even
with reduced sulfur fuels, the amount of SOx produced by combustion
is significant. SOx adsorbs more strongly than NOx and necessitates
a more stringent, though less frequent, regeneration. Desulfation
requires elevated temperatures as well as a reducing atmosphere.
The temperature of the exhaust can be elevated by engine measures,
particularly in the case of a lean-burn gasoline engine, however,
at least in the case of a diesel engine, it is often necessary to
provide additional heat. Typically, this heat is provided through
the same types of reactions as used to remove excess oxygen from
the exhaust. The temperature of the LNT is generally controlled
during desulfation, as the temperatures required for desulfation
are generally close to those at which the LNT catalyst undergoes
thermal deactivation.
[0013] U.S. Pat. No. 6,832,473 describes a system wherein the
reductant is reformate produced outside the exhaust stream and
injected into the exhaust as needed. During desulfations, the
reformate is injected upstream of an oxidation catalyst. Heat
generated by combustion of the reformate over the oxidation
catalyst is carried by the exhaust to the LNT and raises the LNT to
desulfations temperatures.
[0014] U.S. Pat. Pub. No. 2003/0101713 describes an exhaust
treatment system with a fuel reformer placed in the exhaust line
upstream of a LNT. The reformer includes both oxidation and
reforming catalysts. The reformer both removes excess oxygen and
converts the diesel fuel reductant into more reactive reformate.
For desulfations, heat produced by the reformer is used to raise
the LNT to desulfations temperatures.
[0015] U.S. Pat. Pub. No. 2003/0101713 describes a case in which
endothermic reactions dominate and the reformer tends to cool when
hydrocarbons are injected at a rate that produces a desired
concentration of reformate. Between pulses that produce reformate,
fuel is injected at a reduced rate whereby exothermic reactions
dominate and the reformer heats.
[0016] In spite of advances, there continues to be a long felt need
for an affordable and reliable exhaust treatment system that is
durable, has a manageable operating cost (including fuel penalty),
and is practical for reducing NOx emissions from diesel engines to
a satisfactory extent in the sense of meeting U.S. Environmental
Protection Agency (EPA) regulations effective in 2010 and other
such regulations.
SUMMARY
[0017] One of the inventor's concepts relates to a method of
controlling fuel reforming within an internal combustion engine
exhaust line. A reformer is supplied with fuel injected into the
exhaust upstream of the reformer. The fuel injections are
controlled using a predicted temperature that is a temperature that
would occur at some point in the future if predetermined
assumptions are met. In general, the predicted temperature is based
in part on a temperature measurement. In a preferred embodiment,
the prediction is made using a model that includes terms for
hydrocarbon storage and subsequent reaction within the reformer.
The method improves reformer temperature control, particularly over
periods where the fuel supply to the reformer is pulsed.
[0018] A further concept relates to a method of controlling a
temperature of a fuel reformer. The method comprises using a model
to predict a temperature associated with the reformer and using the
predicted temperature in a temperature control algorithm. According
to the concept, the temperature prediction is made taking into
account the effects of hydrocarbon storage and subsequent reaction,
which can result in heating of the reformer following the
termination of fuel injection.
[0019] A closely related concept is a method of controlling the
temperature of a fuel reformer comprising predicting a future
reformer temperature. The predicted future temperature is used in a
feedback control loop. The predictions take into account the
effects of hydrocarbon storage and subsequent reaction.
[0020] A further concept relates to a method of reforming within an
internal combustion engine exhaust line. Hydrocarbons are injected
into the exhaust line upstream of a reformer. The amount of
hydrocarbon adsorbed in the reformer is estimated and the reformer
temperature is controlled based in part on that estimate.
[0021] The primary purpose of this summary has been to present
certain of the inventors' concepts in a simplified form to
facilitate understanding of the more detailed description that
follows. This summary is not a comprehensive description of every
one of the inventor's concepts or every combination of the
inventor's concepts that can be considered "invention". Other
concepts of the inventor will be conveyed to one of ordinary skill
in the art by the following detailed description together with the
drawings. The specifics disclosed herein may be generalized,
narrowed, and combined in various ways with the ultimate statement
of what the inventor claim as his invention being reserved for the
claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic illustration of an exemplary exhaust
treatment system to which the inventor's concepts can be
applied.
[0023] FIG. 2 is a schematic illustration of another exemplary
exhaust treatment system to which the inventor's concepts can be
applied.
[0024] FIG. 3 is a flow chart of a computational procedure
conceived by the inventor.
[0025] FIG. 4 is a schematic illustration of control architecture
in which some of the inventor's concepts can be applied.
[0026] FIG. 5 is a flow chart of a desulfation method in which some
of the inventor's concepts can be applied.
DETAILED DESCRIPTION
[0027] FIG. 1 provides a schematic illustration of an exemplary
power generation system 5 in which various concepts of the inventor
can be implemented. The system 5 comprises an engine 9, a
transmission 8, and an exhaust aftertreatment system 7. The exhaust
aftertreatment system 7 includes a controller 10, a fuel injector
11, a lean NOx catalyst 15, a reformer 12, a lean NOx-trap (LNT)
13, an ammonia-SCR catalyst 14, a diesel particulate filter (DPF)
16, and a clean-up catalyst 17. The controller 10 receives data
from several sources; including temperature sensors 20 and 21 and
NOx sensors 22 and 23. The controller 10 may be an engine control
unit (ECU) that also controls the transmission 8 and the exhaust
aftertreatment system 7 or may include several control units that
collectively perform these functions.
[0028] The exhaust from the engine 9 generally contains products of
lean combustion including NOx, particulates, and some oxygen
(typically 5-15%). The lean-NOx catalyst 15 removes a portion of
the NOx from the exhaust using reductants, typically hydrocarbons
that form part of the exhaust or hydrocarbon that have been stored
by the lean-NOx catalyst 15. The DPF 16 removes particulates.
During lean operation (a lean phase), the LNT 13 adsorbs a second
portion of the NOx. The ammonia-SCR catalyst 14 may have ammonia
stored from a previous regeneration of the LNT 13 (a rich phase).
If the ammonia-SCR catalyst 14 contains stored ammonia, it removes
a third portion of the NOx from the lean exhaust. The clean-up
catalyst 17 may serve to oxidize CO and unburned hydrocarbons.
[0029] FIG. 2 provides another exemplary system 25 in which various
concepts of the inventor can be implemented. The system 25 contains
many of the same components as the system 5, although it does not
include the lean NOx catalyst 15 or the cleanup oxidation catalyst
17. Another difference is that in the system 25 the DPF 16 is
placed between the reformer 12 and the LNT 13. In this
configuration, the DPF 16 may serve to protect the LNT 13 from high
temperatures during denitrations by providing a thermal buffer
between the reformer 12 and the LNT 13. Reducing the number and/or
magnitude of temperature excursions experienced by the LNT 13 may
extend its life.
[0030] From time-to-time, the LNT 13 must be regenerated to remove
accumulated NOx (denitrated). Denitration may involve first heating
the reformer 12 to an operational temperature by injecting fuel at
a sub-stoichiometric rate with respect to the oxygen in the exhaust
whereby the injected fuel reacts in the reformer 12 in an excess of
oxygen. An operational temperature for the reformer 12 depends on
the reformer design. Once the reformer 12 is sufficiently heated,
denitration may proceed by injecting fuel at a super-stoichiometric
rate whereby the reformer 12 consumes most of the oxygen in the
exhaust while producing reformate. Reformate thus produced reduces
NOx adsorbed in the LNT 13. Some of this NOx is reduced to
NH.sub.3, most of which is captured by the ammonia-SCR catalyst 14
and used to reduce NOx during a subsequent lean phase. The clean-up
catalyst 17 oxidizes unused reductants and unadsorbed NH.sub.3
using stored oxygen or residual oxygen remaining in the exhaust
during the rich phases. During regeneration, the lean-NOx catalyst
15 may store reductant for later use.
[0031] From time-to-time, the LNT 13 must also be regenerated to
remove accumulated sulfur compounds (desulfated). Desulfation may
involve heating the reformer 12 to an operational temperature,
heating the LNT 13 to a desulfating temperature, and providing the
heated LNT 13 with a reducing atmosphere. Desulfating temperatures
vary, but are typically in the range from about 500 to about
800.degree. C., more typically in the range from about 650 to about
750.degree. C. Below a minimum temperature, desulfation is very
slow. Above a maximum temperature, the LNT 13 may be damaged.
[0032] During these operations, the temperature of the reformer 12
is affected by several factors. These factors may include, for
example, exothermic reactions by which oxygen is consumed,
endothermic reactions by which reformate is produced, convective
heat transfer into the reformer 12 by the exhaust feeding the
reformer 12, convective heat transfer out of the reformer 12 by
exhaust exiting the reformer 12, and the thermal mass of the
reformer 12.
[0033] In certain modes of operation, the balance of these factors
has a tendency to overheat the reformer 12. For example, during
desulfation only a small amount of reformate production may be
desired and the heat released by exothermic reactions that remove
excess oxygen from the exhaust may be far in excess of the heat
taken up by endothermic reforming reactions and the heat taken up
by the exhaust passing through the reformer 12. Also, during
periods of high exhaust oxygen concentration, the characteristics
of the reformer 12 may be such that the reformer 12 cannot be
operated efficiently, or not at all, at the high fueling rates
required for auto-thermal reforming. In either of these cases where
the reformer 12 has a tendency to overheat, periods of fuel
injection may need to be limited. In between periods of fuel
injection, the reformer 12 will cool. Once the reformer 12 has
cooled to a sufficient degree, fuel injection can be resumed. This
results in pulsed operation.
[0034] When the reformer 12 is on the verge of overheating, it may
be possible to cool the reformer 12 by increasing the fuel
injection rate. Increasing the fuel injection rate will sometimes
cool the reformer 12 by increasing the ratio of endothermic to
exothermic reactions. Such an operation is within the scope of the
inventor's concepts; however, in some situations increasing the
fuel injection rate may be undesirable or ineffective. For example,
increasing the fuel injection rate may be undesirable if it
produces more reformate than can be effectively used by the exhaust
aftertreatment system; increasing the fuel injection rate may be
undesirable if it would push the reformer 12 into a regime where it
does not operate effectively; and increasing the fuel injection
rate may be undesirable if it ultimately increases the likelihood
of overheating due to the hydrocarbon adsorption phenomena
discussed herein. Therefore, it is generally preferred that fuel
injection be discontinued when the reformer 12 is almost at a point
where it will overheat.
[0035] In order to determine when overheating is imminent, the
inventor contemplates using a model that takes into account
hydrocarbon storage. A preferred model comprises a thermal model,
which is a model based in part on an energy conservation equation.
A thermal model can be zero, one, two, or three-dimensional,
although a zero-dimensional lumped parameter model will generally
suffice.
[0036] A lumped parameter model generally includes at least a term
for heat convection into the model system, a term for heat
convection out of the model system, a term for heat taken up by the
reformer 12, and a term for heat generated by chemical reaction.
Heat losses to the surrounding can also be considered, but
generally have a small effect.
[0037] Preferably, the model tracks hydrocarbon storage within the
reformer 12 and eventual reaction of a portion of that stored
hydrocarbon in the reformer 12. In one embodiment, hydrocarbon
storage takes place when the reformer 12 is supplied with a rich
feed and reaction of previously stored hydrocarbon takes place when
the reformer 12 is supplied with a lean feed. By modeling
hydrocarbon storage during rich phases and subsequent reaction of a
portion of that hydrocarbon during lean phases, the model predicts
availability within the reformer 12 of a portion of the injected
fuel in periods between temporally adjacent fuel pulses. Temporally
adjacent pulses are two periods of continuous fuel injection
separated in time by one period during which no fuel is
injected.
[0038] The heat convection rate into the reformer 12 is the
production of the exhaust specific heat, the exhaust temperature,
and the exhaust mass flow rate. The exhaust mass flow rate can be
measured or estimated, for example using an intake air flow rate
measurements, an engine fuel flow rate measurement, or simply with
data available from the engine control unit (ECU). The temperature
of the exhaust entering the reformer 12 can be measured or
determined from the operating point of the engine 9, for
example.
[0039] The heat convection rate out of the reformer 12 depends on
the temperature of the exhaust leaving the reformer 12. That
temperature can be measured. Where the temperature of the reformer
12 is measured, the reformer exhaust gas temperature can be
approximated as equal to the reformer temperature.
[0040] The chemical reactions in the fuel reformer 12 can be
modeled as a combination of the three following reactions: 0.684
CH.sub.1.85+O.sub.2.fwdarw.0.684 CO.sub.2+0.632 H.sub.2O (1) 0.316
CH.sub.1.85+0.316 H.sub.2O.fwdarw.0.316 CO+0.608 H.sub.2 (2) 0.316
CO+0.316 H.sub.2O.fwdarw.0.316 CO.sub.2+0.316 H.sub.2 (3) wherein
CH.sub.1.85 represents an exemplary reductant, such as a diesel
fuel, with a 1.85 ratio between carbon and hydrogen. Reaction (1)
is exothermic complete combustion by which oxygen is consumed.
Reaction (2) is endothermic steam reforming, which results in
reformate production. Reaction (3) is the water-gas shift
reaction.
[0041] In a preferred embodiment, Reaction (1) is assumed to
proceed at a rate and to an extent dependent on temperature, oxygen
availability when fuel is in excess, fuel availability when oxygen
is in excess, but independently of Reaction (2). The oxygen
availability depends at least on the oxygen flow rate into the
reformer 12. If the reformer 12 has a significant oxygen storage
capacity, then it may be desirable to includes terms for the rates
of oxygen adsorption and desorption. The oxygen concentration of
the exhaust flowing into the reformer 12 can also be measured or
estimated using data available from the ECU. While a significant
temperature gradient generally exists within the reformer 12, the
purposes of the invention can generally be achieved using a single
average temperature for the reformer 12.
[0042] In the preferred embodiment, Reaction (2) is considered to
proceed to an extent dependent on the availability of fuel after
the effect of Reaction (1). Reaction (3) is considered third, and
has the least impact on a thermal model. Reaction kinetics,
adsorption rates, and desorption rates depend on reactor geometry
and composition and are best determined experimentally for a
particular system.
[0043] FIG. 3 is a flow chart of an exemplary computational
procedure 50 for modeling the temperature of the reformer 12. This
procedure is implemented in finite time steps. Two instances of the
procedure may be used at one time. The first instance may track the
actual process. The second instance may be used to look forward in
time and make predictions to determine how much the temperature
could increase if fuel injection were to cease and excess oxygen
were to become available.
[0044] At the start of procedure 50, certain values are
initialized. These typically include the amount of stored
hydrocarbon and the reformer temperature. After initialization, the
process begins with operation 51.
[0045] Operation 51 accounts for Reaction (1). The reaction is
treated as proceeding to the fullest extent of the available
reagents, the extent therefore being determined by the limiting
reagent, whether that be fuel or oxygen. An amount of heat is added
to the reformer 12 based on the extent of Reaction (1) and the size
of the time step. The amounts of fuel and oxygen for purposes of
the following steps are reduced in accordance with the extent of
Reaction (1).
[0046] Operation 52 accounts for Reaction (2). Reaction (2) is
assumed not to proceed at all if there is excess oxygen and all the
fuel is considered to have been consumed by Reaction (1). Where
there is fuel remaining after Reaction (1), then Reaction (2)
proceeds to some extent. Unlike Reaction (1), the inventor has
found that Reaction (2) should not be assumed to proceed to the
extent of available reagents. Rather, Reaction (2) is preferably
modeled with a limited efficiency. Typical efficiencies may be from
about 0.35 to about 0.7 based on the stoichiometry, with values in
the range from about 0.45 to about 0.55 having been used in the
inventor's work. It is recognized, however, that the best values to
use will depend on the particular reformer to which the model is
applied and the system in which the reformer is used. Moreover, the
efficiency depends on factors including, without limitation, the
reactor temperature and the exhaust flow rate, although the
inventor does not consider it generally necessary to take these
factors into account. Heat is removed from the reformer 12 in
accordance with the extent of Reaction (2).
[0047] Operation 53 accounts for Reaction (3). In the preferred
embodiment, Reaction (3) is assumed to proceed to equilibrium based
on the exhaust composition following accounting for Reactions (1)
and (2). Heat is added to the reformer 12 in accordance with the
extent of Reaction (3).
[0048] Operation 54 determines whether there is excess oxygen
following Reactions (1)-(3). In general, there will be excess
oxygen if the reformer is supplied with fuel at below the
stoichiometric rate with respect to the exhaust and there will not
be excess oxygen if the fuel is supplied at a stoichiometric or
higher rate. If there is excess oxygen, the process 50 proceeds
with Operation 55. If there is not, the process 50 proceeds with
Operation 58.
[0049] Taking the case of excess oxygen, Operation 55 accounts for
the release of stored fuel. The release rate may be assumed to be a
stoichiometric rate in proportion to the excess oxygen as long as
stored fuel is available. Other assumptions may also be used,
although the stoichiometric rate assumption is preferred.
[0050] Operation 56 accounts for the heat released by reaction of
the released fuel. The extent of reaction may be assumed to be
stoichiometric with respect to the amount of excess oxygen. The
term release is used in a broad sense: the fuel may react without
physically moving from its stored location. Operation 57 is a
place-holder to account for slip of released fuel. In the
inventor's preferred embodiment, there is no fuel slip under
conditions of excess oxygen.
[0051] Taking the case of excess fuel, Operation 58 determines the
amount of the excess fuel that is stored. In one model, the fuel
storage amount is a fraction of the fuel that is in liquid form.
For example, it may be assumed that about 90% of the excess fuel is
in liquid form and that about 45% of this liquid fuel becomes
stored on the surfaces of the reformer 12. It should be understood
that the inventor's concepts have a largely empirical basis and are
independent of the actual mechanism of fuel storage. The actual
mechanism may be, for example, physical absorption or chemical
adsorption. Whatever the actual mechanism, the inventor has found
it can be sufficient to assume that the fuel storage rate is a
fixed fraction of excess fuel flow rate. The remaining portion of
the excess fuel that is not stored in the reformer 12 is considered
to slip from the reformer 12 and is tracked in Operation 59 for use
in the management of downstream devices.
[0052] Operation 60 adds or removes heat from the reformer 12 based
on convective heat transfer: the net heat added to or taken up by
the exhaust passing through the reformer 12. Operation 61 advances
a clock in preparation for the next iteration of the process 50. If
the process 50 is being applied to determine a peak predicted
temperature of the reformer 12, the iterations may cease when the
amount of stored fuel in the reformer 12 is reduced to zero or when
the temperature of the reformer 12 begins to decline.
[0053] FIG. 4 provides a schematic of an exemplary control
architecture 100 that can be used to control both the temperature
of the reformer 12 and the temperature of the LNT 13. The control
architecture 100 includes inner and outer loop controls and uses a
model of the reformer 12 that tracks hydrocarbon storage and
subsequent release.
[0054] The LNT temperature controller 102 is activated by a
desulfation scheduler/controller 101 that applies any appropriate
criteria to determine when to initiate a desulfation process. The
LNT temperature controller 102 considers a LNT temperature provided
by a state estimator 103. It is preferred to use an observer or
state estimator to determine the LNT temperature, because the LNT
temperature responds comparatively slowly to controllable
parameters. If some form of prediction is not used, there is a risk
of the LNT temperature exceeding an intended limit. An
extrapolation based on the current measured temperature, its rate
of change, and an estimate of the temperature measurement delay is
generally sufficient. However, a model of the LNT 13 can be used.
Such a model preferably takes into account reactions of
hydrocarbons slipping from the reformer 12. These hydrocarbons can
react with residual oxygen in the exhaust or with oxygen stored in
the LNT 13. When there is no oxygen in the exhaust, some
hydrocarbons may become stored in the LNT 13 and subsequently react
when oxygen becomes available. These processes can be modeled as
they are for the reformer 12.
[0055] The output of the LNT temperature controller 102 is
instructions for the reformer controller 106. The instructions may
simply be instructions for the reformer 12 to switch between active
and inactive modes. During the active mode, the reformer 12 is
heated to a temperature suitable for reformate production and
controlled to produce reformate subject to not overheating the
reformer 12. During an inactive mode, the reformer 12 is generally
"off", meaning there is no reductant injection and the reformer 12
is allowed to cool freely.
[0056] When the reformer 12 is to be active, the reformer
controller 106 regulates the reformer temperature at least by
issuing commands to the injection controller 107. The injection
influences the state of the reformer 12, which is illustrated by
block 108 in the exemplary control architecture. A state includes
all properties of the reformer, including its temperature, the
composition of the exhaust entering it, and the composition of the
exhaust leaving it. The temperature portion of the reformer state
108 is estimated by the reformer temperature estimator 105, and
used to provide feedback for the reformer temperature controller
106. Accordingly, steps 105-108 comprise the inner loop of the
control process 100.
[0057] The reformer state 108 influences the LNT state 109. The
temperature portion of the LNT state 109 is temperature estimated
by the LNT temperature state estimator 103 to provide a temperature
estimate that is used by the LNT temperature control 102 in an
outer control loop.
[0058] FIG. 5 illustrates a desulfation control process 200
consistent with the control architecture 100. The process 200
begins with operation 201, determining whether desulfation is
required. The determination may be made in any suitable fashion.
For example, desulfation may be scheduled periodically, e.g., after
every 30 hours of operation. Alternatively, the need for
desulfation can be determined based on system performance, e.g.,
based on the activity of the LNT 13 following an extensive
denitration or based on the frequency with which denitration is
required having increased to an excessive degree.
[0059] The desulfation process begins with operation 202, warming
the reformer 12. The reformer 12 can be heated in any suitable
fashion. In this example, the reformer 12 is heated by injecting
fuel at a rate that keeps the exhaust at or below a stoichiometric
fuel to oxygen ratio. Substantially all the fuel thereby combusts
in the reformer 12 to produce heat with essentially no reformate
production.
[0060] The LNT 13 heats while the reformer 12 is heating, however,
after the reformer 12 is fully heated, the LNT 13 may still require
further heating. If necessary, at or below stoichiometric operation
may be extended to adequately heat the LNT 13. In one example, the
LNT 13 is heated to a temperature of at least about 450.degree. C.
prior to commencing rich operation.
[0061] Once the warm-up phase is complete, operation 203 begins.
The fuel injection rate at this stage may be controlled to give a
targeted reformate production rate. Where the controller 10 can
throttle the engine air intake or select the transmission gear
ratio, these control parameters can be selected to facilitate the
efficient production and/or usage of the reformate.
[0062] Operation 204 determines whether the reformer 12 is
overheating. Preferably, this determination is made on the basis of
a predicted temperature wherein a predicted temperature is a
temperature that will or could occur at a future time. In other
words, a predicted temperature is a temperature that would occur at
some point in the future if predetermined assumptions are met.
Predetermined means that the assumptions are made first and the
temperature predicted second, based on the assumptions. As used
herein, the term prediction does not include an estimate of a
current temperature based on past information, which will be
referred to herein as an estimate to avoid confusion. Also, the
term "predicted future temperature" may be used to explicitly
distinguish an estimate of a current temperature. The main purpose
of using a prediction herein is to account for the effect of
hydrocarbon storage and subsequent reaction. The prediction is
therefore preferably made on the basis of a model that takes into
account this phenomenon.
[0063] A prediction of the type described herein is typically made
using a measured temperature and a predicted or possible
temperature increase. A possible temperature increase could be made
on the basis of the assumption that the fuel dosing will stop in
the next instant and thereafter an excess of oxygen will become
available for combustion of stored hydrocarbons. The model may look
ahead over some finite interval of time to determine the value at
which the temperature will peak.
[0064] Some of the inventor's concepts can be implemented without
attempting to accurately predict a temperature. For example, a
temperature at which the reformer 12 is determined to be on the
verge of overheating can be set as a function that decreases with
increasing hydrocarbon storage amount. As a more specific example,
it can be assumed that the reformer 12 will heat after fuel cut-off
by an amount that is proportional the amount of stored fuel. The
amount of heating can be used as the amount by which the limit
temperature is reduced.
[0065] Another approach contemplated by the inventor is to make an
effective prediction through the mechanics by which a temperature
estimate is formed. For example, one method of forming a
temperature estimate is Kalman filtering. In Kalman filtering, a
temperature estimate is made on the basis of a blended average of a
measured temperature and a model-based estimate of the current
temperature based on a past system state. The Kalman filter
estimate can be converted to a prediction by using artificial
values to form the model-based estimate whereby the model-based
estimate is no longer intended to accurately estimate a current
temperature. For example, the Kalman filter can be given
accelerated dynamics. Accelerating the dynamics typically involves
reducing a term reflecting the heat capacity of the reformer. The
model prediction may also depart from an approximation of actual
conditions by assuming the presence of excess oxygen not thought to
be present under current conditions.
[0066] When the reformer 12 is on the verge of overheating,
operation 205 shuts off the fuel injection. In operation 206, the
process 200 waits while the reformer 12 cools. The length of the
waiting period can be determined in any suitable fashion. In one
example, operation 206 lasts until the reformer 12 has cooled to a
target temperature. In another example, there is a fixed period
between each fuel pulse. In a further example, the length of the
period is selected dynamically by the controller as part of a
process of optimizing the amount of reformate production per unit
fuel injected.
[0067] Operation 207 determines whether the LNT 13 is getting too
hot. A temperature prediction is preferably used in making this
determination as the LNT 13 may heat considerably following the
termination of fuel injection. If the LNT is getting too hot,
operation 208 terminates the fuel injection. Terminating the fuel
injection may comprise issuing instructions to the inner loop
control. If the LNT is not getting too hot, the process continues
with Operation 210, which checks whether desulfation is complete.
Fuel injection continues in Operation 203 if fuel injection is not
complete and terminates in Operation 211 if desulfation is
complete.
[0068] Operation 209 is another waiting operation. In one example,
this comprises waiting until the LNT 13 has cooled to a target
temperature. Preferably, however, there is a fixed period between
phases of active fuel injection on the longer time scale determined
by the outer loop controls.
[0069] Following operation 209, the reformer 12 is heated again in
operation 202. If the reformer 12 is of the type that must be
heated to operate effectively, heating is generally necessary
following a period of no fuel injection during which the LNT 13 is
allowed to cool. The periods of no fuel injection to cool the
reformer 12 are generally shorter and are normally selected to
avoid having to reheat the reformer 12 to a temperature suitable
for producing reformate. After the longer periods of no fuel
injection to cool the LNT 13, the reformer 12 is generally too cool
to effectively produce reformate without a heating period. Such a
heating period generally comprises fuel injection at a
sub-stoichiometric rate with respect to the exhaust oxygen
content.
[0070] While the engine 9 is preferably a compression ignition
diesel engine, the various concepts of the invention are applicable
to power generation systems with lean-burn gasoline engines or any
other type of engine that produces an oxygen rich, NOx-containing
exhaust. For purposes of the present disclosure, NOx consists of NO
and NO.sub.2.
[0071] The transmission 8 can be any suitable type of automatic
transmission. The transmission 8 can be a conventional transmission
such as a counter-shaft type mechanical transmission, but is
preferably a CVT. A CVT can provide a much larger selection of
operating points than a conventional transmission and generally
also provides a broader range of torque multipliers. In general, a
CVT will also avoid or minimize interruptions in power transmission
during shifting. Examples of CVT systems include hydrostatic
transmissions; rolling contact traction drives; overrunning clutch
designs; electrics; multispeed gear boxes with slipping clutches;
and V-belt traction drives. A CVT may involve power splitting and
may also include a multi-step transmission.
[0072] A preferred CVT provides a wide range of torque
multiplication ratios, reduces the need for shifting in comparison
to a conventional transmission, and subjects the CVT to only a
fraction of the peak torque levels produced by the engine. This can
be achieved using a step-down gear set to reduce the torque passing
through the CVT. Torque from the CVT passes through a step-up gear
set that restores the torque. The CVT is further protected by
splitting the torque from the engine, and recombining the torque in
a planetary gear set. The planetary gear set mixes or combines a
direct torque element transmitted from the engine through a stepped
automatic transmission with a torque element from a CVT, such as a
band-type CVT. The combination provides an overall CVT in which
only a portion of the torque passes through the band-type CVT.
[0073] The fuel injector 11 can be of any suitable type.
Preferably, it provides the fuel in an atomized or vaporized spray.
The fuel may be injected at the pressure provided by a fuel pump
for the engine 9. Preferably, however, the fuel passes through a
pressure intensifier operating on hydraulic principles to at least
double the fuel pressure from that provided by the fuel pump to
provide the fuel at a pressure of at least about 4 bar.
[0074] The lean-NOx catalyst 15 can be either an HC-SCR catalyst, a
CO-SCR catalyst, or a H.sub.2-SCR catalyst. Examples of HC-SCR
catalysts include transitional metals loaded on refractory oxides
or exchanged into zeolites. Examples of transition metals include
copper, chromium, iron, cobalt, nickel, cadmium, silver, gold,
iridium, platinum and manganese, and mixtures thereof. Exemplary of
refractory oxides include alumina, zirconia, silica-alumina, and
titania. Useful zeolites include ZSM-5, Y zeolites, Mordenite, and
Ferrerite. Preferred zeolites have Si:Al ratios greater than about
5, optionally greater than about 20. Specific examples of
zeolite-based HC-SCR catalysts include Cu-ZSM-5, Fe-ZSM-5, and
Co-ZSM-5. A CeO.sub.2 coating may reduce water and SO.sub.2
deactivation of these catalysts. Cu/ZSM-5 is effective in the
temperature range from about 300 to about 450.degree. C. Specific
examples of refractory oxide-based catalysts include
alumina-supported silver. Two or more catalysts can be combined to
extend the effective temperature window.
[0075] Where a hydrocarbon-storing function is desired, zeolites
can be effective. U.S. Pat. No. 6,202,407 describes HC-SCR
catalysts that have a hydrocarbon storing function. The catalysts
are amphoteric metal oxides. The metal oxides are amphoteric in the
sense of showing reactivity with both acids and bases. Specific
examples include gamma-alumina, Ga.sub.2O.sub.3, and ZrO.sub.2.
Precious metals are optional. Where precious metals are used, the
less expensive precious metals such as Cu, Ni, or Sn can be used
instead of Pt, Pd, or Rh.
[0076] In the present disclosure, the term hydrocarbon is inclusive
of all species consisting essentially of hydrogen and carbon atoms,
however, a HC-SCR catalyst does not need to show activity with
respect to every hydrocarbon molecule. For example, some HC-SCR
catalysts will be better adapted to utilizing short-chain
hydrocarbons and HC-SCR catalysts in general are not expected to
show substantial activity with respect to CH.sub.4.
[0077] Examples of CO-SCR catalysts include precious metals on
refractory oxide supports. Specific examples include Rh on a
CeO.sub.2--ZrO.sub.2 support and Cu and/or Fe ZrO.sub.2
support.
[0078] Examples of H.sub.2-SCR catalysts also include precious
metals on refractory oxide supports. Specific examples include Pt
supported on mixed LaMnO.sub.3, CeO.sub.2, and MnO.sub.2, Pt
supported on mixed ZiO.sub.2 and TiO.sub.2, Ru supported on MgO,
and Ru supported on Al.sub.2O.sub.3.
[0079] The lean-NOx catalyst 15 can be positioned differently from
illustrated in FIG. 1. In one embodiment, the lean NOx catalyst 15
is upstream of the fuel injector 11. In another embodiment the lean
NOx catalyst is downstream of the reformer 12, whereby the lean NOx
catalyst 15 can use reformer products as reductants. In a further
embodiment, the lean NOx catalyst 15 is well downstream of the LNT
13, whereby the lean NOx catalyst 15 can be protected from high
temperatures associated with desulfating the LNT 13.
[0080] A fuel reformer is a device that converts heavier fuels into
lighter compounds without fully combusting the fuel. A fuel
reformer can be a catalytic reformer or a plasma reformer.
Preferably, the reformer 12 is a partial oxidation catalytic
reformer. A partial oxidation catalytic reformer comprises a
reformer catalyst. Examples of reformer catalysts include precious
metals, such as Pt, Pd, or Ru, and oxides of Al, Mg, and Ni, the
later group being typically combined with one or more of CaO,
K.sub.2O, and a rare earth metal such as Ce to increase activity. A
reformer is preferably small in size as compared to an oxidation
catalyst or a three-way catalyst designed to perform its primary
functions at temperatures below 500.degree. C. A partial oxidation
catalytic reformer is generally operative at temperatures from
about 600 to about 1100.degree. C. A preferred reformer has a low
thermal mass and a low catalyst loading as compared to a device
designed to produce reformate at exhaust gas temperatures.
[0081] The NOx absorber-catalyst 13 can comprise any suitable
NOx-adsorbing material. Examples of NOx adsorbing materials include
oxides, carbonates, and hydroxides of alkaline earth metals such as
Mg, Ca, Sr, and Be or alkali metals such as K or Ce. Further
examples of NOx-adsorbing materials include molecular sieves, such
as zeolites, alumina, silica, and activated carbon. Still further
examples include metal phosphates, such as phosphates of titanium
and zirconium. Generally, the NOx-adsorbing material is an alkaline
earth oxide. The absorbent is typically combined with a binder and
either formed into a self-supporting structure or applied as a
coating over an inert substrate.
[0082] The LNT 13 also comprises a catalyst for the reduction of
NOx in a reducing environment. The catalyst can be, for example,
one or more precious metals, such as Au, Ag, and Cu, group VIII
metals, such as Pt, Pd, Ru, Ni, and Co, Cr, Mo, or K. A typical
catalyst includes Pt and Rh, although it may be desirable to reduce
or eliminate the Rh to favor the production of NH.sub.3 over
N.sub.2. Precious metal catalysts also facilitate the absorbent
function of alkaline earth oxide absorbers.
[0083] Absorbents and catalysts according to the present invention
are generally adapted for use in vehicle exhaust systems. Vehicle
exhaust systems create restriction on weight, dimensions, and
durability. For example, a NOx absorbent bed for a vehicle exhaust
systems must be reasonably resistant to degradation under the
vibrations encountered during vehicle operation.
[0084] An absorbent bed or catalyst brick can have any suitable
structure. Examples of suitable structures may include monoliths,
packed beds, and layered screening. A packed bed is preferably
formed into a cohesive mass by sintering the particles or adhering
them with a binder. When the bed has an absorbent function,
preferably any thick walls, large particles, or thick coatings have
a macro-porous structure facilitating access to micro-pores where
adsorption occurs. A macro-porous structure can be developed by
forming the walls, particles, or coatings from small particles of
adsorbant sintered together or held together with a binder.
[0085] The ammonia-SCR catalyst 14 is a catalyst effective to
catalyze reactions between NOx and NH.sub.3 to reduce NOx to
N.sub.2 in lean exhaust. Examples of SCR catalysts include oxides
of metals such as Cu, Zn, V, Cr, Al, Ti, Mn, Co, Fe, Ni, Pd, Pt,
Rh, Rd, Mo, W, and Ce, zeolites, such as ZSM-5 or ZSM-11,
substituted with metal ions such as cations of Cu, Co, Ag, Zn, or
Pt, and activated carbon. Preferably, the ammonia-SCR catalyst 14
is designed to tolerate temperatures required to desulfate the LNT
13.
[0086] The particulate filter 16 can have any suitable structure.
Examples of suitable structures include monolithic wall flow
filters, which are typically made from ceramics, especially
cordierite or SiC, blocks of ceramic foams, monolith-like
structures of porous sintered metals or metal-foams, and wound,
knit, or braided structures of temperature resistant fibers, such
as ceramic or metallic fibers. Typical pore sizes for the filter
elements are about 10 .mu.m or less. Optionally, one or more of the
reformer 12, the LNT 13, the lean-NOx catalyst 15, or the
ammonia-SCR catalyst 14 is integrated as a coating or within the
structure of the DPF 16.
[0087] The DPF 16 is regenerated to remove accumulated soot. The
DPF 16 can be of the type that is regenerated continuously or
intermittently. For intermittent regeneration, the DPF 16 is
heated, using a reformer 12 for example. The DPF 16 is heated to a
temperature at which accumulated soot combusts with O.sub.2. This
temperature can be lowered by providing the DPF 16 with a suitable
catalyst. After the DPF 16 is heated, soot is combusted in an
oxygen rich environment.
[0088] For continuous regeneration, the DPF 16 may be provided with
a catalyst that promotes combustion of soot by both NO.sub.2 and
O.sub.2. Examples of catalysts that promote the oxidation of soot
by both NO.sub.2 and O.sub.2 include oxides of Ce, Zr, La, Y, and
Nd. To completely eliminate the need for intermittent regeneration,
it may be necessary to provide an additional oxidation catalyst to
promote the oxidation of NO to NO.sub.2 and thereby provide
sufficient NO.sub.2 to combust soot as quickly as it accumulates.
Where regeneration is continuous, the DPF 16 is suitably placed
upstream of the reformer 12. Where the DPF 16 is not continuously
regenerated, it is generally positioned as illustrated downstream
of the reformer 12. An advantage of the position illustrated in
FIG. 2 is that the DPF 16 buffers the temperature between the
reformer 12 and the LNT 13.
[0089] The clean-up catalyst 17 is preferably functional to oxidize
unburned hydrocarbons from the engine 9, unused reductants, and any
H.sub.2S released from the NOx absorber-catalyst 13 and not
oxidized by the ammonia-SCR catalyst 15. Any suitable oxidation
catalyst can be used. A typical oxidation catalyst is a precious
metal, such as platinum. To allow the clean-up catalyst 17 to
function under rich conditions, the catalyst may include an
oxygen-storing component, such as ceria. Removal of H.sub.2S, where
required, may be facilitated by one or more additional components
such as NiO, Fe.sub.2O.sub.3, MnO.sub.2, CoO, and CrO.sub.2.
[0090] The invention as delineated by the following claims has been
shown and/or described in terms of certain concepts, components,
and features. While a particular component or feature may have been
disclosed herein with respect to only one of several concepts or
examples or in both broad and narrow terms, the components or
features in their broad or narrow conceptions may be combined with
one or more other components or features in their broad or narrow
conceptions wherein such a combination would be recognized as
logical by one of ordinary skill in the art. Also, this one
specification may describe more than one invention and the
following claims do not necessarily encompass every concept,
aspect, embodiment, or example described herein.
* * * * *