Note: Descriptions are shown in the official language in which they were submitted.
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Internal Combustion Engine Aftertreatment Heating Loop
Cross-Reference to Related Applications
[0001] This application claims the benefit of benefit of priority to U.S.
Provisional
Application Number 62/424,914 filed on November 21, 2016, the disclosure of
which is
incorporated by reference herein.
Background of the Invention
[0002] The first portion of the background relates to the challenges of engine
aftertreatment system operation at low exhaust temperatures. One of the
findings
from the blended aftertreatment system (BATS) program in North Carolina was
that
exhaust gas temperatures where the Urea is injected and vaporized needs to be
220 C for
early stage dissociation, but the overall SCR system and bulk exhaust gas
temps could be
cooler in the 165 C range and the SCR system still had good NOx reduction
efficiency at low
loads and air flows.
[0003] While the BATS solution was good for passenger locomotives that had
both a
large prime mover and a smaller generator that ran at higher loads and exhaust
temperatures, it did not offer a solution to the majority of locomotives that
only had a
single large prime mover. These large medium speed engines were very efficient
and spent
considerable times at idle and low loads, where exhaust temperatures would be
below the
220 C needed to vaporize and process a mixture of UREA liquid and exhaust gas.
[0004] For locomotive engines operating with natural gas as the primary
fuel, this low
temperature operation also hinders the use of an oxidizing catalyst (OC) which
is needed to
reduce carbon monoxide (CO) emissions and help reduce non-methane hydrocarbon
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(NMHC) emissions, two of the EPA-mandated criteria emissions that are
generated in
higher quantities when a diesel engine is converted to natural gas. The
temperature range
for making an OC efficiently reduce CO and start reducing NMHC is the same
200+ Celsius
that is needed for effective SCR operation.
[0005] A similar problem but at a different range of temperatures is
becoming apparent
with the introduction of heavy duty natural gas engines that operate at very
lean air fuel
ratios in order to both increase thermal efficiency and lower NOx emissions.
In the
emissions regulations for on-road applications, there is not an exception for
methane
emissions and therefor total hydrocarbons (HC) need to be reduced. Methane has
a very
high ignition temperature over 500 C and therefore an OC needs to be at a
temperature
greater than 400 C before it is effectively oxidizing methane, which makes up
a majority of
the challenging HC emissions from a high efficiency lean burn engine.
[0006] What would help solve the above problems is an effective solution to
increase
engine out exhaust temperatures on these engines with a minimal penalty in
extra fuel
consumption and complexity.
Brief Summary of the invention
[0007] Instead of second engine operating at a higher exhaust temperature
to make up
for the low main engine exhaust temperature as in the first BATS system, there
could be a
separate exhaust gas heating loop where urea is mixed with a portion of the
main engine
exhaust. In this loop, the urea is vaporized if needed and the dissociation
process is started.
If the hot exhaust gasses in this loop are not hot enough at some operating
conditions, they
could be locally heated with the injection of fuel that is burned across a
small oxidizing
catalyst. Typical aftertreatment systems on heavy duty engines dose all of the
exhaust
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gases with raw fuel and or UREA. What is novel in this case is that a portion
of the total
exhaust gas flow is removed and locally heated to the appropriate temperature
before
dosing with fuel or UREA. This separate external exhaust gas loop will be
called the heating
loop.
[0008] This system is not specific to just SCR systems that require UREA
dosing. It
would work for any exhaust aftertreatment system that is challenged to reduce
emissions
at low exhaust temperatures, including an OC by itself or in series with an
SCR.
[0009] The first challenge of a heating loop would be to induce the correct
portion of the
total exhaust gas mass to go through the separate loop. The simplest technique
would be to
use the main exhaust gasses kinetic energy to drive the portion of exhaust gas
through the
loop. In the main exhaust pipe, an inlet could be facing into the exhaust flow
using ram air
pressure to drive exhaust into the loop. Where the heated loop gasses are
reintroduced
back into the main exhaust flow, the outlet could be directed in the direction
of the main
exhaust gas flow causing a low pressure region at the loop exit and further
increasing the
flow of exhaust gases drawn into and through the heating loop.
[0010] In a preferred embodiment, the ram inlet and lower exit pressure
would
generate all of the heating loop flow that is required. Any additional flow
that is not moved
by these pressure differences that is needed could be generated in a simple
fashion using
an air amplifier similar to that disclosed in US4046492. Compressed air is a
readily
available source to drive an air amplifier. Trucks, locomotives, busses and
many other
heavy-duty engine applications typically have compressed air supplies to
operate the air
brakes on the vehicle. Air amplifiers (a type of jet pump) are simple and low
maintenance.
The only moving part would be an air flow control mechanism, typically a
solenoid that is
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controlling reasonably low pressure (likely 100-150p5i) and near ambient
temperature air.
Further, the pressurized air flow to the air amplifier can be manipulated by
using more
than one solenoid to control the pressurized air flow or pulsing one or more
solenoids at
varying duty cycles to vary the amount of additional exhaust gases that the
air amplifier
draws into the heating loop.
[0011] On
turbo engines, the exhaust back pressure upstream of the turbine can be used
as a source of pressurized air to drive the air amplifier operating at the
near ambient
pressure that the exhaust gasses going through the aftertreatment are
operating at. As
most turbochargers operate with a wastegate slightly open at higher loads,
bypassing the
turbine with some exhaust gas to drive a air amplifier in the heating loop
should have no or
very little effect on engine efficiency. Compressed air from the turbine would
be at a lower
pressure than typical compressed air from and air brake compressor so it will
operate at a
lower mass amplification ratio. Also turbine back pressure varies with engine
load and is
negligible at idle. The turbo pressure variation with engine load will vary in
the same
direction as the requirement for the air amplifier to induce exhaust gas flow.
Like the
airbrake compressed air supply system, the preturbine pressurized exhaust gas
supply
flow or pressure could be manipulated with a valve that controls flow rate.
Because valves
that operate at these high temperatures can be problematic, in a preferred
embodiment the
pressurized exhaust gas supply would be controlled by a fixed orifice with no
moving parts.
[00010] If there is a benefit to having the orifice larger at lower exhaust
temperatures,
one variation could be an orifice that varies with temperature using the
premise of thermal
expansion. This could be with a bimetallic spring that when heated moves into
position to
restrict the orifice. While technically a moving part, a bimetallic spring
system could be
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designed that had no rubbing parts such as a bearing that over time would wear
and
change its characteristics. The preferred embodiment would have the flow
control orifice
be the actual jet nozzle where the compressed exhaust gas is mixed with the
heating loop
exhaust gases.
[0012] In some air amplifiers, the fixed orifice is actually a continuous
radial gap
between two radial faces of almost touching parts. In the case of the Nex Flow
Air Products
Corp part number 30003TS this gap is set to .004 inch and is adjustable by
turning the
threaded body parts in relation to each other. These two parts could be
designed in such a
way that this gap was closed up at higher temperatures that would correspond
to higher
engine loads and higher turbine boost pressure. If one part was made from
stainless steel
and one from carbon steel, the stainless part would grow in length 1.5 times
that of the
steel part thereby changing the gap distance.
[0013] In a natural gas fueled engine using a heating loop, if natural gas
fuel is being
injected into the heating loop to add temperature, the natural gas injector
could also be
used to drive an air amplifier. This would have the secondary benefit of also
helping to
evenly mix the air and fuel if the air amplifier has a continuous radial gap
for an orifice like
the Nex Flow PN 30003TS.
[0014] A natural gas-powered air amplifier would both improve mixing and
get the
benefit of recycling the energy used to compress the natural gas, it likely
will still need an
additional compressed air powered air amplifier to both increase and control
the amount
of exhaust gas flowing through the heating loop.
[0015] Now that there is an adequate and controlled amount of exhaust gas
flowing
through the heating loop, a system needs to be implemented to raise its
temperature. This
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additional heat will typically be provided by combusting injected fuel and
excess oxygen in
the exhaust gases across an OC mounted inside the dosing loop flow path.
Compared to an
open flame burner, combusting the fuel across a catalyst will minimize the
amount of
criteria emissions added to the total exhaust flow when this extra fuel
combusted.
[0016] If or when the exhaust temperature entering the dosing loop is not
hot enough to
ignite the injected fuel when it reaches the dosing loop OC, an additional
system will be
needed to temporarily provide extra heat to the exhaust gas flow until the OC
is at a high
enough temperature to light off and insure continuous catalytic combustion of
the injected
fuel. A simple way of doing this is with an electric exhaust heater similar to
a Watlow ECO
Heat unit. This electric heater could be used for both diesel injection or
natural gas
injection. The electric heater is more likely to be effective with diesel fuel
injection because
of diesel fuels much lower light off temperature at the OC.
[0017] Instead of an electric heater when using natural gas, a conventional
burner with
a flame holder and ignition system could be used to drive the OC temperature
up to that
needed for light off and continuous catalytic combustion. The supply pressure
of natural
gas to the natural gas injector could be manipulated to control the heat rate
of both the
preheater and the catalytic combustion system. The flame holder system should
only need
an ignition source to start combustions. One method to switch from combustion
at the
flame holder to combustion at the catalyst system is to temporarily turn off
the natural gas
supply to the heating loop and keep it off long enough to extinguish the flame
at the flame
holder but then turn the natural gas fuel back on soon enough that the OC is
still hot
enough to light off and maintain continuous catalytic combustion.
[0018] Various embodiments of the above described system will be effective
for engines
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that only need an OC. For systems that will use an SCR the system is the same
up to the OC
that combusts the added fuel for heating up the exhaust gases. After the OC is
where the
UREA would be injected and then there would need to be a length of straight
and well
insulated ducting to give the UREA time to mix with the hot exhaust gases and
start
decomposing into ammonia before the mixture of ammonia and exhaust gas from
the
heating loop mixes with the bulk of the exhaust gases in the main exhaust
system on its
way to the SCR unit.
[0019] For an aftertreatment system that only has an OC, the heating loop
system
should not need to increase flow capacity at higher loads as the main engine
exhaust
temperature should become high enough to keep the after treatment operating,
in this case
the air amplifiers and fuel injection for the heating loop can be turned off.
[0020] On the other hand, for an SCR system, the systems exhaust gas mass
flow and
heating capacity will need to increase as the required amount of UREA
increases. This
makes the turbocharged engine slightly easier for an SCR application as the
exhaust back
pressure being used to drive an air amplifier requires less energy than
suppling
compressed air from an engine driven compressor to drive the increasing
amounts of
exhaust gas through the heating loop.
[0021] Exhaust gas heating can also be used in the main exhaust system. As
high
efficiency engines are able to operate at lower and lower exhaust
temperatures, two
problems are becoming apparent. First the exhaust temperatures are getting so
low that at
moderate loads it is not high enough to oxidize any of the methane that isn't
burned in the
main chamber. Also these lower temperatures make it a challenge to drive the
turbo
charger. Putting an OC upstream of the turbocharger has been investigated in
prior art but
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at the time found not practical. What would be an improvement over a heating
loop as
proposed above could be a pre-turbine and after treatment system. The
preferred
embodiment would be a natural gas engine with a pre turbine after treatment
system that
has both OC substrates and SCR substrates. This could have a heating system in
front of the
first OC substrate, then a UREA injection system, then a second heater, then a
final OC
before the exhaust gases reach the turbocharger. In this case the extra fuel
needed to
increase the exhaust temperature enough to burn off the methane and the
oxidized
methane that originally left the engine cylinder without being burned would
now provide
energy to the turbo charger turbine. The reason that a heater after the SCR is
needed is
that the light off temperature for methane in the final OC is higher than the
temperature
that the SCR should be operating at.
[0022] To add further benefit to this system, the turbocharger could be
electrified. This
will greatly accelerate engine response and increase engine efficiency by
eliminating the
need for a waste gate and capturing as much energy as possible with the
exhaust turbine.
For more efficiency a second electrically driven compressor can be used in
series with the
turbocharger.
[0023] For gaseous fuels the heaters in this system could use a burner at
first until the
OC substrates reach light off temperature and then turn off the gas supply
momentarily to
extinguish the burner flame so that the combustion then starts up again and
continues in
the OC downstream of that burner.
Description of the Drawings
[0024] Fig. 1 is a side view of a turbocharged engine with an
aftertreatment system
including a heating loop.
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[0025] Fig. 2 is a side view of a normally aspirated engine with an
aftertreatment
system including a heating loop.
[0026] Fig. 3 is a preferred embodiment for a turbocharged diesel engine
with an SCR
aftertreatment system.
[0027] Fig. 4 is a block diagram of a control system with its sensors and
valves.
Detailed Description
[0028] To facilitate an understanding of the present disclosure, a number
of terms and
phrases are defined below:
[0029] Blended Aftertreatment System (BATS): As described in US 9,752,481,
incorporated herein by reference, a BATS system reduces the NOx emissions from
the
mixed exhaust of two engines in a single larger SCR assembly using only one
UREA
injection point into the exhaust of the smaller engine.
[0030] Gaseous Fuel: The predominant gaseous fuel used in internal
combustion
engines is natural gas consisting mostly of methane, but with minor
modifications these
engines could consume any gaseous fuel including but not limited to propane,
natural gas
and hydrogen. In this document the term natural gas and gaseous fuel are used
interchangeably.
[0031] Hydrocarbon (HC): Emissions resulting from incomplete combustion of
fuel and
engine lube oil.
[0032] Main Charge: The air fuel mixture in the main combustion chamber
space
between the piston top and the cylinder head. If an opposed piston engine,
this would be
the space between the opposed piston faces.
[0033] Particulate Matter (PM): Particulate matter is a criteria pollution
emitted from
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many sources. In this document we will commonly refer to it simply as PM. It
could include
both diesel soot PM that is considered toxic in California or the type of PM
created by the
consumption and combustion of lube oil from an engine. While still considered
PM as a
criteria emission, the PM from lube oil consumption is considered less toxic
than diesel
soot.
[0034] Reductant: In active NOx reductions systems like a Selective
Catalytic Reduction
(SCR) system, a reductant is mixed with the hot exhaust gases and is
chemically processed
by the catalyst system along with the exhaust gasses to reduce NOx emissions
to N2 and
water. Diesel Exhaust Fluid (DEF) is currently the most common reductant for
SCR systems
in mobile applications. DEF is actually a mixture of 32.5% UREA and 67.5%
water. Once
injected into the engine the DEF is first vaporized, and then the UREA
crystals are
decomposed into ammonia and CO2 molecules. It is the ammonia particles that
the SCR
catalyst uses to reduce NOx into N2 and water. SCR systems can be used on heat
engines
burning any kind of fuel so the DEF term can be misleading, in Germany DEF
falls under the
trademark AdBlue. DEF is also frequently called UREA for short. In some
instances
ammonia gas is extracted from some other system and injected directly into the
exhaust
flow as a gas before the exhaust and ammonia mixture reaches the SCR
catalysts.
Throughout this document the reductant injected into any aftertreatment device
that
actively reduces NOx will typically be referred to as UREA. In addition the
term SCR will be
used to identify any active NOx reduction system that uses a reductant.
[0035] FIG. 1 is a side view of a turbocharged medium speed engine with a
heating loop.
Exhaust Manifold 3 is on top of engine 1 and routes pressurized exhaust gases
into
turbocharger 2. Main exhaust duct 4 routes the exhaust gases from turbocharger
2 into
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aftertreatement 5. After the exhaust gases are treated in aftertreatment 5
they exit the
engine system through main exhaust outlet 20. Aftertreatment 5 may contain OC
substrates, SCR substrates or a combination of both. If an aftertreatment 5
system contains
both types of substrates it is controlled in the same manner as a system with
only SCR
substrates.
[0036] Heating
loop inlet 6 extracts a portion of exhaust gases from main exhaust duct 4
and directs it through heater loop 7. Once the portion of exhaust gases have
been processed
through all the devices along heater loop piping 7 they are then injected back
into the main
exhaust duct 4 through heater loop exit 8. Air amplifier EP 10 will be fed
pressurized
exhaust gas sourced from exhaust manifold 3 to assist drawing more exhaust gas
into
heater loop piping 7. Air Amplifier CA 11 is driven by compressed air from an
external
source somewhere in the vehicle. This could be supplied by an engine driven
air
compressor that supplies air to the air brake system. If the vehicle doesn't
already have an
air compressor is could be supplied by the compressor in turbo 3, although
this would be
less efficient as turbo 3 boost pressure is likely 1/4 that of the air brake
system and will
require 4 times as much air mass to be as effective and all of this air will
need to be heated
by adding more heat energy into the heating loop 7. Electric preheater 12 is
used to
increase the temperature of the portion of exhaust gases to a point that the
OC 15 will light
off and burn the fuel and lean exhaust gas mixture. Electric preheater 12
would typically
only be used with a fuel other than methane that has a lower ignition
temperature, diesel
fuel would be the most appropriate fuel for use with electric preheater 12.
Fuel injector 13
is used to inject fuel into the heating loop 7. This is most likely the same
fuel used to power
engine 1, it could be a liquid hydrocarbon fuel such as diesel or any gaseous
fuel. In the case
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of pressurized gaseous fuels, fuel injector 13 may also act as an air
amplifier that is
powered by the pressurized gaseous fuel. Fuel burner 14 is used typically for
gaseous fuels
like methane that have very high ignition temperatures that are not reasonable
for use of
an electric preheater 12. Fuel burner 14 will likely incorporate a flame
holder and ignition
system to start combustion. OC 15 is where flameless combustion will occur
once the
heating loop 7 is at operating temperature. Temperature sensor 16 is the
parameter that a
control system will monitor to determine the system status and determine when
to inject
fuel, how much fuel to inject and when to transition from fuel burner 14 to OC
15 to
catalytically burn the injected fuel at the highest efficiency at lowest
emissions. Gaseous
fuel can be injected at any time, but diesel fuel should only be injected
after the portion of
exhaust gas flow has been preheated by electric preheater 12 to a threshold
temperature
that will cause light off of OC 15. After light off, the temperature sensor 16
will monitor the
exit temperature of OC 15 and that temperature will be used to determine if
more or less
fuel should be injected by fuel injector 13 to achieve the target temperature
in the heating
loop 7.
[0037] For an aftertreatment 5 unit that only has an OC substrate, the
temperature
sensor 16 will be the last device that heating loop 7 is equipped with and the
now heated
portion of exhaust gases would be then injected through heating loop exit 8
back into the
main exhaust duct 4.
[0038] For an aftertreatment 5 unit that does have an SCR substrate,
additional
components will be added to heating loop 7. UREA injector 17 is used to inject
UREA into
heating loop 7. Temperature sensor 19 will be used to measure the temperature
of the
portion of exhaust gas that was first heated and then cooled by injecting UREA
into it. With
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an SCR function temperature sensor 19 becomes the parameter that is used to
determine
fuel flow through fuel injector 13 to maintain a target temperature at the
exit of heating
loop 7. In some embodiments, if a temperature sensor 19 is installed, the
temperature
sensor 16 after OC 15 can be eliminated.
[0039] Recent research has indicated that decomposition of UREA is assisted
by being
passed through a catalyst at high temperature. In a conventional SCR system,
when the air
and UREA mixture gets to the SCR substrates, the UREA is typically only 50% of
the way
through the decomposition process and the remaining decomposition to ammonia
occurs
as the exhaust gas and decomposing UREA move along the flow length of the
substrate.
This lowers the overall effectiveness of the substrate. If all of the UREA had
been
decomposed to ammonia before the exhaust gases started passing through the SCR
substrate, it would have a higher NOx reduction efficiency and would be able
to operate at
lower temperatures. OC 18 is used to increase the amount of decomposition of
the mixture
of UREA and heated exhaust gases before they exit the heating loop 7 on their
way to the
SCR substrates inside of aftertreatment 5.
[0040] Fig. 2 is a side view of a normally aspirated medium speed engine
with a heating
loop. Figure 2 has all the same components and functionality as Figure 1
except that turbo
main exhaust duct 4' connects exhaust manifold 3 directly to aftertreatment 5
and turbo 3
and the exhaust pressure driven air amplifier EP 10 have been deleted. Because
air
amplifier EP 10 has been deleted, the compressed air driven air amplifier CA
11 may have
to provide more motive force to induce enough exhaust gas flow through heating
loop 7
[0041] Fig. 3 is the preferred embodiment of a medium speed turbocharged
diesel
engine with and SCR aftertreatment system and simplified heating loop. Exhaust
Manifold 3
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is on top of engine 1 and routes pressurized exhaust gases into turbocharger
2. Main
exhaust duct 4 routes the exhaust gases from turbocharger 2 into
aftertreatement 5. After
the exhaust gases are treated in aftertreatment 5 they exit the engine system
through main
exhaust outlet 20.
[0042] Heating loop inlet 6 extracts a portion of exhaust gases from main
exhaust duct 4
and directs it through heater loop 7. Once the portion of exhaust gases have
been processed
through all the devices along heater loop piping 7 they are then injected back
into the main
exhaust duct 4 through heater loop exit 8. Air amplifier EP 10 will be fed
pressurized
exhaust gas sourced from exhaust manifold 3 to assist drawing more exhaust gas
into
heater loop piping 7. Electric preheater 12 is used to increase the
temperature of the
portion of exhaust gases to a point that the OC 15 will light off and burn the
diesel fuel and
lean exhaust gas mixture. Fuel injector 13 is used to inject diesel fuel into
the heating loop
7. OC 15 is where flameless combustion will occur once the heating loop 7 is
at operating
temperature. Temperature sensor 19 is the parameter that a control system will
monitor to
determine the system status and determine when to inject fuel and how much
fuel to inject.
Diesel fuel should only be injected after the portion of exhaust gas flow has
been preheated
by electric preheater 12 to a threshold temperature that will cause light off
of OC 15. After
light off temperature sensor 19 will monitor the exit temperature of OC 15 and
that
temperature will be used to determine if more or less fuel should be injected
by fuel
injector13 to achieve the target temperature in the heating loop 7. Once OC 15
is at
temperature and catalytically combusting the injected fuel, electric preheater
12 can be
turned down or off.
[0043] After temperature sensor 19 has determined that the heating loop 7
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temperature is hot enough, UREA injector 17 is used to inject UREA into
heating loop 7. As
more UREA is injected through injector 17, temperature sensor 19 will detect a
dropping
temperature in heating loop 7 and the control system will command more fuel be
injected
through injector 13 to bring the heating loop exhaust gas exit temperature
back up to its
target temperature.
[0044] Fig. 4 is a bock diagram of a simplified control system for a
heating loop 7.
Controller unit 30 is electrically connected to various sensors and control
valves. Temp
sensor 31 will read the exhaust exit temperature from heating loop 7 and
depending on its
control mode with control the amount of fuel flowing through injector 3. This
fuel flow can
be controlled by valve 32 which could be an on or off solenoid valve that is
modulated to
control the flow rate of fuel to injector 13 or this control valve 32 could be
an integral part
of injector 13. Control solenoide 33 will control the flow of electricity to
electric preheater
12 if the system is so equipped. This electric current flow could be
controlled by several
different electrical devices ranging from a simple switch to a PWM controlled
transistor
module.
[0045] Control valve 34 regulates the supply of compressed air to an air
amplifier CA 11
if the system is so equipped. It may be a simple on off valve with one
setting, it can also be
PWM controlled to linearly regulate flow.
[0046] Control valve 35 will control UREA flow to UREA injector 17. This
could be a
solenoid valve that modulates flow or a pumping system of some sort that
provides a
metered amount of UREA.
[0047] Controller 30 may have its own table of engine operating parameters,
but it most
likely will be in communication with a master controller that will send it
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information and updated operating parameters such as heating loop 7 target
exhaust
temperature. Any of these control valves or solenoids could be physically
integrated into
control 30 without changing its functionality. Controller unit 30 itself could
be integrated
into another controller that controls other devices and even the entire engine
system or
vehicle.
[0048] It should be noted that various changes and modifications to the
presently
preferred embodiments described herein will be apparent to those skilled in
the art. Such
changes and modifications may be made without departing from the spirit and
scope of the
present invention and without diminishing its attendant advantages.
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