U.S. patent application number 12/122685 was filed with the patent office on 2009-11-19 for thermal stability for exhaust emissions treatment materials.
This patent application is currently assigned to The ITB Group Ltd.. Invention is credited to Joel Kopinsky.
Application Number | 20090282813 12/122685 |
Document ID | / |
Family ID | 41314829 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090282813 |
Kind Code |
A1 |
Kopinsky; Joel |
November 19, 2009 |
Thermal Stability for Exhaust Emissions Treatment Materials
Abstract
A storage vessel for emission control liquids such as aqueous
solutions of urea is equipped with phase change materials that are
calibrated to help maintain the liquid within a proper temperature
range. Multiple phase change materials having phase transition
temperatures of fifty to seventy degrees Celsius and seventy to one
hundred degrees Celsius provide staged high-temperature stability
for the urea solutions. Phase change materials can be included that
also provide low temperature stability by changing from liquids to
solids when freezing of the aqueous solution is threatened.
Containers of phase change materials are applied to the interior or
exterior surfaces of the storage vessel. Alternatively the storage
vessel is included within and surrounded by a housing that forms an
annular space with the storage vessel, and phase change materials
are installed within the annular space. A method for using the
storage vessel in an emissions control system also is
presented.
Inventors: |
Kopinsky; Joel; (Farmington
Hills, MI) |
Correspondence
Address: |
GLENN S. ARENDSEN
8556 ISLAND BLVD
GROSSE LLE
MI
48138
US
|
Assignee: |
The ITB Group Ltd.
Novi
MI
|
Family ID: |
41314829 |
Appl. No.: |
12/122685 |
Filed: |
May 17, 2008 |
Current U.S.
Class: |
60/286 ;
220/592.01; 423/239.1; 60/299 |
Current CPC
Class: |
Y02T 10/12 20130101;
F01N 13/16 20130101; F01N 2610/02 20130101; F01N 3/2066 20130101;
F01N 2610/1406 20130101; F01N 2610/14 20130101; Y02T 10/24
20130101 |
Class at
Publication: |
60/286 ;
423/239.1; 220/592.01; 60/299 |
International
Class: |
F01N 3/20 20060101
F01N003/20; B65D 81/18 20060101 B65D081/18 |
Claims
1. A storage vessel with improved thermal stability for liquids
used to reduce engine exhaust emissions comprising an inlet for
admitting a liquid into the storage vessel, an outlet for providing
liquid to exhaust emissions equipment of the engine, and phase
change material in heat transfer relationship with the liquid, said
phase change material being calibrated with a phase transition
temperature within an identified temperature range to exchange its
heat of fusion with the liquid and thereby stabilize the
temperature of the liquid within the identified temperature
range.
2. The storage vessel of claim 1 in which the phase change material
is calibrated to undergo a phase change and absorb thermal energy
when the temperature of the liquid increases above the phase
transition temperature of the phase change material.
3. The storage vessel of claim 2 in which the liquid is an aqueous
solution of urea and the phase change material is calibrated with a
phase transition temperature within a range of fifty to one hundred
degrees Celsius.
4. The storage vessel of claim 3 in which the phase change material
is high-temperature phase change material, said high-temperature
phase change material being calibrated with a phase transition
temperature within a range of seventy to one hundred degrees
Celsius.
5. The storage vessel of claim 4 comprising low-temperature phase
change material in heat transfer relationship with the liquid, said
low-temperature phase change material being calibrated with a phase
transition temperature within a range of fifty to seventy degrees
Celsius.
6. The storage vessel of claim 5 comprising additional phase change
material in heat transfer relationship with the liquid, said
additional phase change material being calibrated with a phase
transition temperature within a range of zero to minus ten degrees
Celsius to release thermal energy when the temperature of the
liquid is within the range of zero to minus ten degrees
Celsius.
7. The storage vessel of claim 1 comprising a sealed container
positioned on an interior surface of the storage vessel and in heat
transfer relationship with the liquid, said sealed container
containing said phase change material, said phase change material
being calibrated with a phase transition temperature within a range
of fifty to one hundred degrees Celsius to absorb thermal
energy.
8. The storage vessel of claim 1 comprising a first sealed
container in heat transfer relationship with the liquid, said
sealed container containing said phase change material, said phase
change material being calibrated with a phase transition
temperature within a range of seventy to one hundred degrees
Celsius to absorb thermal energy, and a second sealed container in
heat transfer relationship with the liquid, said second sealed
container containing phase change material calibrated with a phase
transition temperature within a range of fifty to seventy degrees
Celsius to absorb thermal energy.
9. The storage vessel of claim 1 in which the phase change material
is calibrated with a phase transition temperature within a range of
zero to minus ten degrees Celsius to release thermal energy when
the temperature of the liquid is within the range of zero to minus
ten degrees Celsius.
10. A storage vessel with improved thermal stability for liquids
used to reduce engine exhaust emissions comprising an inlet for
admitting a liquid into the storage vessel, an outlet for providing
liquid to exhaust emissions equipment of the engine, an outer
housing surrounding the storage vessel and forming an annular space
with the storage vessel, and phase change material installed in the
annular space and in heat transfer relationship with the
liquid.
11. The storage vessel of claim 10 in which the liquid is an
aqueous solution of urea and the phase change material is
calibrated with a phase transition temperature within a range of
fifty to one hundred degrees Celsius to absorb thermal energy when
the temperature of the liquid is within a range of fifty to one
hundred degrees Celsius.
12. The storage vessel of claim 11 comprising a partition that
extends through the annular space and divides the annular space
into more than one compartment, each of said compartments being
suitable for containing phase change material.
13. The storage vessel of claim 12 in which one compartment
contains phase change material calibrated with a phase transition
temperature within a range of fifty to one hundred degrees Celsius
to undergo a phase change and absorb thermal energy when the
temperature of the liquid is within a range of fifty to seventy
degrees Celsius, and another compartment contains phase change
material calibrated with a phase transition temperature within a
range of seventy to one hundred degrees Celsius to absorb thermal
energy when the temperature of the liquid is within a range of
seventy to one hundred degrees Celsius.
14. The storage vessel of claim 13 comprising additional phase
change material is calibrated with a phase transition temperature
within the range of zero to minus ten degrees Celsius to release
thermal energy when the temperature of the liquid is within the
range of zero to minus ten degrees Celsius.
15. A method for injecting an exhaust treatment liquid into engine
exhaust gases generated by an engine and having an exhaust conduit
for conducting the exhaust gases to a catalytic unit comprising
providing a storage vessel for the exhaust treatment liquid,
introducing exhaust treatment liquid into the storage vessel,
stabilizing the exhaust treatment liquid with phase change material
being calibrated with a phase transition temperature within an
identified temperature range to exchange its heat of fusion with
the liquid and thereby stabilize the temperature of the liquid
within the identified temperature range, and conducting the exhaust
treatment liquid to the engine emissions gases.
16. The method of claim 15 comprising calibrating the phase change
material with a phase transition temperature of seventy to one
hundred degrees Celsius to undergo a phase change and absorb
thermal energy when the temperature of the exhaust treatment liquid
within the storage vessel is seventy to one hundred degrees
Celsius.
17. The method of claim 16 comprising placing second phase change
material within the storage vessel and in heat transfer
relationship with the exhaust treatment liquid, and calibrating
said second phase change material with a phase transition
temperature of fifty to seventy degrees Celsius to undergo a phase
change and absorb thermal energy when the temperature of the
exhaust treatment liquid within the storage vessel is fifty to
seventy degrees Celsius.
18. The method of claim 17 in which dosing equipment for spraying
exhaust treatment liquid into the engine exhaust gases is located
in the exhaust conduit upstream of the catalyst, and comprising
transporting extra exhaust treatment liquid to the dosing
equipment, returning excess exhaust treatment liquid to the storage
vessel via a return line, and stabilizing the temperature of the
returning exhaust treatment liquid within the return line with
phase change material.
19. The method of claim 15 in which dosing equipment for spraying
exhaust treatment liquid into the engine exhaust gases is located
in the exhaust conduit upstream of the catalyst, and comprising
transporting extra exhaust treatment liquid to the dosing
equipment, returning excess exhaust treatment liquid to the storage
vessel via a return line, and stabilizing the temperature of the
returning exhaust treatment liquid within the return line with
phase change material.
20. The method of claim 15 comprising calibrating the phase change
material to undergo a phase change and release thermal energy when
the temperature of the exhaust treatment liquid is zero to minus
ten degrees Celsius.
Description
FIELD OF THE INVENTION
[0001] This invention provides improved thermal stability for
liquids used to reduce exhaust emissions particularly of nitrogen
oxides in exhaust gases from diesel engines and lean-burn
engines.
BACKGROUND OF THE INVENTION
[0002] Diesel engines produce exhaust emissions of oxides of
nitrogen (NOx) that must meet new federal and state standards.
Reducing these oxides to acceptable levels requires Selective
Catalytic Reduction (SCR), which consists of injecting a strong
reducing agent into the exhaust stream ahead of the SCR catalyst.
The reducing agent and the catalytic action combine under
controlled conditions to reduce NOx emissions to acceptable
levels.
[0003] Ammonia has come to the forefront as the reducing agent of
choice, but transporting and using ammonia creates new health and
safety issues of its own, especially when one considers that trucks
and many cars would be carrying a supply of ammonia on board. The
art turned to making up an aqueous solution of urea that is quite
safe, and the solution can be hydrolyzed simply by injecting it
into an exhaust stream having a suitable temperature that will
convert the urea into ammonia, or by passing the solution over a
catalyst just prior to injection into the exhaust stream. This
minimizes health and safety risks as only minimal amounts of
ammonia are present at any particular time.
[0004] Aqueous solutions of thirty-two percent urea by weight, the
more common concentration, freeze at minus eleven degrees Celsius,
a winter temperature not uncommon in the United States and many
other nations and frequently encountered by trucks and other
vehicles. Additionally an aqueous urea solution begins to decompose
at temperatures above fifty degrees Celsius. Decomposition is
hastened by temperatures of ninety to one hundred degrees Celsius,
and the nozzle or nozzles used to inject the solution into the
exhaust stream can be exposed to temperatures well above this range
and can become clogged and plugged by decomposing solution.
[0005] The art proposes several solutions to preventing
decomposition of the solution within the injection nozzle. In U.S.
Pat. No. 5,884,475, Hoffman et al. present a high pressure air
system that blows any remaining solution out of the nozzle and its
lines when the engine is shut down. In U.S. Pat. Nos. 5,976,475 and
6,063,350, Peter-Hoblyn et al. and Tarabulski et al. respectively
present re-circulating systems that pump excess aqueous solution of
urea to the dosing unit nozzle and return the excess to the storage
vessel, thereby using the re-circulated solution to help cool the
temperature of the solution within the nozzle.
[0006] Tarabulski et al. also propose an electrical heater in the
storage vessel that is activated by a control system when
environmental temperatures could result in freezing, but the supply
of electrical energy for a truck that is stopped for any length of
time is finite and maintaining a considerable volume of the
solution above freezing can use too much electrical energy.
Accordingly Hoffman et al. propose enabling the main portion of the
solution to freeze while maintaining a small amount in a heating
mechanism that can be thawed and ready for injection soon after a
cold start. Patent publication 2007/0157602A provides a different
structure that achieves a similar result.
[0007] These systems require bulky hardware new to diesel powered
vehicles. Packaging the new hardware offers limited options such as
squeezing hardware into the engine compartment where it would be
subjected to elevated temperatures, mounting it behind the cab of
the truck where it would be exposed to the fluctuating environment,
or installing the urea storage vessel within the existing fuel tank
of the vehicle. Minimizing the lengths of the lines that deliver
treatment liquid to the exhaust system also is desirable, which
suggests packaging hardware proximately to the engine exhaust
system where the treating liquid could be exposed to elevated
temperatures or to a cold environment. Complex control systems also
are required to heat or cool the treating liquid as necessary.
SUMMARY OF THE INVENTION
[0008] This invention represents a different approach to
maintaining the thermal stability of aqueous solutions of urea in
emission control systems. The invention provides a great deal of
flexibility in regard to the different locations of the required
additional hardware and can be used in conjunction with systems of
the prior art.
[0009] The invention provides a storage vessel that comprises an
inlet for admitting a liquid into the storage vessel, an outlet for
providing liquid to exhaust emissions equipment of the engine, and
phase change material in heat transfer relationship with the
liquid, said phase change material being calibrated to exchange its
heat of fusion with the liquid and thereby stabilize the
temperature of the liquid within an identified temperature
range.
[0010] The phase change material can be calibrated to undergo a
phase change and either absorb or release thermal energy, its heat
of fusion, when the temperature of the liquid increases above, or
decreases below, selected temperatures. Phase change materials
(PCMs) are chemical formulations that transform from one phase,
from the solid phase to the liquid phase or the reverse from the
liquid phase to the solid phase, upon exposure to the phase
transition temperature (PTT) of the formulation. During
transformation the phase change material absorbs or releases its
fusion energy and in this invention transfers that energy to its
surroundings, thereby helping to stabilize temperatures of nearby
materials. By selecting and calibrating PCMs that are liquids at
normal operating temperatures and have a phase transition
temperature at lower temperatures, the PCM will yield up its heat
of fusion and can be used to reduce and minimize temperature
decreases.
[0011] Phase change material preferably is installed within one or
more sealed containers positioned on the inner surfaces or the
bottom of the storage vessel where the container and the PCM it
contains contacts and is in a heat transfer relationship with the
liquid within the storage vessel. The container usually is at least
partially submerged in the liquid to achieve good heat transfer
characteristics with the liquid. An alternative installation
suitable for aftermarket use applies the containers to the exterior
surfaces of the storage vessel. Adding multiple containers with
PCMs having the same or differing PTTs provides additional
effectiveness and flexibility.
[0012] Aqueous solutions of urea preferably are used as the
treating liquid, and to help maintain the temperature of the
solution within a desired range one or more containers of PCMs
installed in the storage vessel has a phase transition temperature
of less than one hundred degrees Celsius, at which temperature
severe decomposition of urea solutions can occur. PCMs calibrated
with PTTs of seventy to one hundred degrees Celsius can be
installed to help with elevated temperatures. PCMs calibrated
within a lower temperature range of fifty to seventy degrees
Celsius can be used separately or in conjunction with PCMs
calibrated with higher PTTs to provide staged thermal stability.
Containers can have special surface features, both internally and
externally, to enhance heat transfer characteristics with the PCMs
and the treating solution.
[0013] A special embodiment provides a storage vessel that combines
the foregoing structures by comprising multiple phase change
materials, one that is calibrated with a phase transition
temperature above a selected temperature to absorb thermal energy
when the temperature of the liquid rises above the selected
temperature, and another phase change material that is calibrated
with a phase transition temperature below a selected temperature to
release thermal energy when the temperature of the liquid falls
below the selected temperature. This embodiment provides increased
stability by maintaining the liquid within a prescribed temperature
range.
[0014] An alternate structure of a storage vessel that provides
enhanced thermal stability for the liquid it contains comprises an
inner storage vessel for receiving and dispensing the liquid, a
larger outer housing surrounding and encasing the inner storage
vessel and forming an annular space between the outer housing and
the inner vessel, and phase change materials within the annular
space and in heat transfer relationship with the liquid. The phase
change material can be calibrated with a phase transition
temperature at a selected temperature to change phase and thereby
absorb thermal energy when the temperature of the liquid increases
beyond a selected temperature, or change phase to release thermal
energy when the temperature of the liquid decreases below a
selected temperature, or both.
[0015] Substantially filling the annular space with PCM enables the
use of additional PCM, and the annular space offers opportunities
for PCMs with differing phase transition temperatures to provide
staged thermal stability of the liquid for multiple ranges of high
temperature control and also for control of low temperatures.
[0016] When using this invention with the re-circulating systems
taught by Hoblyn et al. and Tarabulski et al., the lines that
return aqueous solution heated in the dosing unit nozzle can be
packaged within phase change materials calibrated to absorb thermal
energy when the aqueous solution is above a desired temperature
range. Similarly the lines that deliver aqueous solution to the
dosing unit nozzle can be packaged within phase change materials
calibrated to either deliver thermal energy to, or absorb thermal
energy from, the aqueous solution as required by the system.
[0017] The invention also provides a method for injecting a
stabilized exhaust treatment liquid into engine exhaust emissions
equipment. The method comprises providing a storage vessel for the
exhaust treatment liquid, introducing exhaust treatment liquid into
the storage vessel, stabilizing the exhaust treatment liquid with
phase change material being calibrated to undergo a phase change
and absorb thermal energy when the temperature of the exhaust
treatment liquid increases above a specified temperature, when the
temperature of the liquid decreases below a specified temperature,
or both, and conducting the exhaust treatment liquid to the engine
emissions equipment.
[0018] Calibrating the phase change material in the method with a
phase transition temperature within a range of seventy to one
hundred degrees Celsius to undergo a phase change and absorb
thermal energy when the temperature of the exhaust treatment liquid
within the storage vessel is within the range of seventy to one
hundred degrees Celsius provides high-temperature control. Staged
control can be achieved in the method by placing second phase
change material within the storage vessel and in heat transfer
relationship with the exhaust treatment liquid, and calibrating
said second phase change material to undergo a phase change and
absorb thermal energy when the temperature of the exhaust treatment
liquid within the storage vessel is fifty to seventy degrees
Celsius.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a sectional view of a storage vessel of this
invention that has two containers of phase change material
installed on the inside surfaces of the storage vessel.
[0020] FIG. 2 is a perspective of a container of phase change
material ready for installation in the storage vessel of FIG.
1.
[0021] FIG. 3 is a top view of the storage vessel of FIG. 1.
[0022] FIG. 4 is a top view of a storage vessel similar to that of
FIG. 1 but with containers of phase change material installed on
the outer surfaces of the storage vessel.
[0023] FIG. 5 is a sectional view of an alternate structure in
which an inner storage vessel is surrounded by an outer housing to
form one or more annular spaces for phase change material.
[0024] FIG. 6 is a sectional view of the storage vessel of FIG. 5
that shows a horizontal partition within the annular space.
[0025] FIG. 7 is a top view of the storage vessel of FIG. 5 that
shows a vertical partition within the annular space.
[0026] FIG. 8 is a schematic of an exhaust emissions system that
includes a storage vessel of this invention.
[0027] FIG. 9 is a sectional of a return line, also applicable to a
delivery line, for an exhaust emissions system of this
invention.
DETAILED DESCRIPTION
[0028] Referring to FIGS. 1, 2, and 3, a storage vessel 10
comprises a cylindrical body 12 and a sealable cap 14 that fits on
top of and seals body 12. An inlet 16 in cap 12 enables adding an
aqueous solution of urea 17 to storage vessel 10 and an outlet pipe
18 extends through cap 14 and into body 12, terminating near the
bottom of body 12. Outlet pipe 18 includes a liquid pump 19 for
pumping the aqueous solution out of the storage vessel. Storage
vessel 10 and cap 14 can be made of a variety of materials
including stainless steel and polymeric materials such as high
density polyethylene.
[0029] Heating elements, powered for example by electrical energy
from a vehicle battery, and cooling equipment, powered for example
by AC systems of the vehicle, along with temperature sensors and
other control equipment, can be added to storage vessel 10 as
needed. These are taught by the prior art and are not included in
the drawings of this invention.
[0030] Applying attention to FIG. 2, the Figure shows a container
20 that has a curved shape and conforms to the cylindrical walls of
body 12. An opening 22 enables adding phase change material 24 to
container 20 and closing opening 24 seals the phase change material
24 within container 20. As shown in FIGS. 1 and 3, containers 20a
and 20b are attached to the inner walls of body 12 where container
20a contains phase change material 24a and container 20b contains
phase change material 24b. Phase change materials 24a and 24b are
in heat transfer relationship with the aqueous solution of urea
17.
[0031] Typically excessive heating of the solution is of major
concern, and phase change materials 24a and 24b are calibrated to
help maintain the temperature of the solution below its
decomposition temperature but within its operating range.
Accordingly phase change material 24a in container 20a is
calibrated with a phase transition temperature within a temperature
range of fifty to seventy degrees Celsius. As solution temperature
approaches this range, phase change material 24a transforms from
solid to liquid and absorbs its heat of fusion from the aqueous
solution, thereby passively and effectively helping to maintain the
solution below its deterioration temperature and within the desired
range.
[0032] Staged control is obtained by calibrating phase change
material 24b with a phase transition temperature within a higher
temperature range of seventy to one hundred degrees Celsius to
transform from solid to liquid within this higher temperature
range. During extended operations, as the temperature of the
aqueous solution absorbs additional thermal energy, phase change
material 24b also transforms to help maintain the temperature of
the aqueous solution below its deterioration temperature.
Additional containers of phase change material can be installed
within storage vessel 10 and with phase change materials also
calibrated to transform at temperatures within the desired
operating range and below severe decomposition temperatures of
aqueous solution 17.
[0033] In other installations where cooling harmful to use of the
aqueous solution can occur, containers 24 can contain phase change
material 24 calibrated with a phase transition temperature of zero
to minus ten degrees Celsius at which material 24 transitions from
liquid to solid and yields up its heat of fusion, thereby
transferring heat to the aqueous solution and helping to prevent
freezing.
[0034] FIG. 4 is a construction similar to that of FIGS. 1-3 but
with containers 20c and 20d of phase change materials installed on
the outer surfaces of storage vessel 10. This construction is
suited to aftermarket applications in which the exterior of a
previously installed storage vessel is readily accessible.
[0035] Turning to the structure of FIG. 5, an outer housing 30 and
a cap 32 surround an inner storage vessel 34 and form an annular
space 36 with the walls of vessel 34. Inner storage vessel 34
contains an exhaust gas treating liquid like aqueous urea solution
17 and annular space 36 is filled with phase change material 24
which is in heat transfer relationship with aqueous urea solution
17. The structure of FIG. 5 operates like the operations of FIGS.
1, 2, and 3 as described above.
[0036] As shown in FIG. 6, annular space 36 of FIG. 4 can be
divided horizontally by a partition 38 to enable installing one
phase change material 40 in the resulting lower compartment 42 and
another phase change material 44 having a different phase
transition temperature in the upper compartment 46. The phase
change materials can complement each other with each helping to
control rising temperatures but at differing phase transition
temperatures as described above, or one can help control rising
temperatures while the other helps control falling temperatures. In
an alternative shown in FIG. 7, annular space 36 is divided
vertically by a partition 50 into separate compartments for phase
change materials that can have different PTTs as described.
[0037] Turning to the system of FIG. 8, a diesel engine 60 has an
exhaust conduit 62 that delivers engine exhaust to a Selective
Catalyst Reduction (SCR) unit 64. Downstream of SCR unit 64
typically are additional exhaust treatment devices 66 and a muffler
68.
[0038] An aqueous urea injection system indicated generally by 70
comprises an aqueous urea storage vessel 72 equipped with phase
change material and having the structure as described above for any
of FIGS. 1-7. Inlet 16 enables adding a treating liquid such as
aqueous urea into vessel 72 and outlet pipe 18 enables pumping the
liquid via delivery line 73 to a dosing unit 74 located in exhaust
conduit 62 and upstream of SCR unit 64. A return line 76 enables
returning excess liquid to storage vessel 72.
[0039] A urea solution is introduced into storage vessel 72 via
inlet 16 and a pump internal to vessel 72 pumps the urea solution
to dosing unit 74 which sprays the solution into exhaust conduit 62
upstream of SCR unit 64. Considerable mixing occurs inherently and
the urea converts to ammonia that SCR unit 64 uses to materially
reduce the amount of NOx in the engine exhaust. A control system
and appropriate valves and sensors that are necessary to make the
system operate properly and reliably are taught by the art.
[0040] FIG. 9 shows an added feature of the system in which return
line 76 is encased in a cylindrical container 80 that surrounds
line 76 and forms a cylindrical annular space 82 with line 76.
Phase change material 84 having a phase transition temperature that
typically is calibrated to absorb thermal energy at a temperature
of less than one hundred degrees Celsius is installed in annular
space 82. As heated aqueous solution returns from dosing unit 74
via return line 76 to vessel 72, phase change material 84 undergoes
a phase change and thereby helps to maintain thermal stability.
Similarly, delivery line 73 can be encased in a container of phase
change material that is calibrated with a phase change material
having a phase transition temperature suited to the needs of the
system.
[0041] A variety of suitable phase change materials are taught by
the art. Hydrated inorganic salts suitable for use are disclosed in
Hammond U.S. Pat. No. 5,785,884, Lane et al. U.S. Pat. No.
4,585,572, and Lane et al. U.S. Pat. No. 4,613,444, and in the
literature along with many paraffins, polyethylene glycols, and
additional organic compounds. As guidelines, lithium nitrate
trihydrate has a phase transition temperature of 29.9 degrees
Celsius and a heat of fusion of three hundred joules per gram., and
heptadecane has a phase transition temperature of 21.7 degrees
Celsius and a heat of fusion of two hundred thirteen joules per
gram. These and many other compounds can be modified chemically to
adjust the phase transition temperature by procedures known to the
art and modest quantities would handle considerable thermal energy
in a typical storage vessel of this invention.
[0042] The treating liquid can be made up of any of several
formulations of urea, including ammonium carbonate, ammonium
bicarbonate, ammonium carbamate, ammonium cyanate, ammonhium salts
of inorganic and organic acids, ammelide, or ammeline. Typically a
relatively inexpensive commercial urea is used. Aqueous solutions
of urea can be used up to solubility limits and selection of the
concentration depends on temperature control and other factors,
with thirty-five percent urea being typical.
[0043] As noted above, packaging the bulky equipment of the
required exhaust emissions control system for treating NOx in
trucks and other vehicles is a major challenge. This invention
offers considerable flexibility in that phase change material can
be calibrated to undergo a phase change and absorb thermal energy
when the temperature of the liquid increases above a calibrated
temperature, or can be calibrated to undergo a phase change and
release thermal energy when the temperature of the liquid decreases
below a calibrated temperature. Multiple containers with both of
these phase change materials also can be used for improved thermal
stability. The invention operates passively and does not need
additional control equipment.
* * * * *