U.S. patent application number 12/511132 was filed with the patent office on 2011-02-03 for exhaust aftertreatment system with heated device.
This patent application is currently assigned to International Engine Intellectual Property Company, LLC. Invention is credited to Gregory A. Griffin, Vadim Strots.
Application Number | 20110023461 12/511132 |
Document ID | / |
Family ID | 42938556 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110023461 |
Kind Code |
A1 |
Strots; Vadim ; et
al. |
February 3, 2011 |
EXHAUST AFTERTREATMENT SYSTEM WITH HEATED DEVICE
Abstract
An exhaust aftertreatment system (10) for a vehicle having an
engine (14) includes a fluid passageway (20) extending from the
engine to an ambient (18) for fluidly communicating exhaust gas
(F), and a NOx reduction catalyst (28) disposed on the fluid
passageway and downstream of the engine. An injector (34) is
disposed downstream of the engine (14) and upstream of the NOx
reduction catalyst (28) on the fluid passageway (20) for injecting
a reductant (36) into the fluid passageway. A heated mesh device
(44) is disposed on the fluid passageway downstream of the injector
(34) and upstream of the NOx reduction catalyst (28). The reductant
(36) that is injected from the injector (34) impinges on the heated
mesh device (44).
Inventors: |
Strots; Vadim; (Forest Park,
IL) ; Griffin; Gregory A.; (Glendale Heights,
IL) |
Correspondence
Address: |
INTERNATIONAL ENGINE INTELLECTUAL PROPERTY COMPANY
4201 WINFIELD ROAD, P.O. BOX 1488
WARRENVILLE
IL
60555
US
|
Assignee: |
International Engine Intellectual
Property Company, LLC
Warrenville
IL
|
Family ID: |
42938556 |
Appl. No.: |
12/511132 |
Filed: |
July 29, 2009 |
Current U.S.
Class: |
60/286 ;
60/301 |
Current CPC
Class: |
F01N 2240/40 20130101;
B01F 5/0473 20130101; F01N 2610/102 20130101; F01N 2240/16
20130101; Y02T 10/24 20130101; B01F 3/04049 20130101; F01N 3/2066
20130101; Y02T 10/12 20130101; B01F 5/0694 20130101; Y02A 50/20
20180101; F01N 2610/02 20130101; B01F 15/066 20130101; Y02A 50/2325
20180101 |
Class at
Publication: |
60/286 ;
60/301 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/10 20060101 F01N003/10 |
Claims
1) An exhaust aftertreatment system for a vehicle having an engine,
the aftertreatment system comprising: a fluid passageway extending
from the engine to an ambient for fluidly communicating exhaust
gas; a NOx reduction catalyst disposed on the fluid passageway
downstream of the engine; an injector disposed downstream of the
engine and upstream of the NOx reduction catalyst on the fluid
passageway for injecting a reductant into the fluid passageway; and
a heated mesh device disposed on the fluid passageway downstream of
the injector and upstream of the NOx reduction catalyst, wherein
the reductant injected from the injector impinges on the heated
mesh device.
2) The exhaust aftertreatment system of claim 1 further comprising
a heater that maintains a minimum temperature of the heated mesh
device at a predetermined temperature.
3) The exhaust aftertreatment system of claim 2 further comprising
a sensor that senses the temperature of the heated mesh device and
communicates the temperature to a control system.
4) The exhaust aftertreatment system of claim 3 wherein when the
temperature of the heated mesh device is below the predetermined
temperature, the control system actuates the heater to heat the
heated mesh device.
5) The exhaust aftertreatment system of claim 2 wherein the
predetermined temperature is about 200-degrees Celsius.
6) The exhaust aftertreatment system of claim 2 wherein the heater
electrically heats the heated mesh device.
7) The exhaust aftertreatment system of claim 1 wherein the heated
mesh device comprises a wire mesh portion that permits the flow of
exhaust gas therethrough.
8) The exhaust aftertreatment system of claim 7 wherein the heated
mesh device further comprises a support ring that axially encloses
the wire mesh portion.
9) The exhaust aftertreatment system of claim 7 wherein the wire
mesh is at least partially coated with a urea hydrolysis
catalyst.
10) The exhaust aftertreatment system of claim 1 wherein the fluid
passageway is defined by a reductant pipe extending between a
diesel oxidation catalyst and the NOx reduction catalyst, wherein
the heated mesh device is attached to an interior surface of the
reductant pipe.
11) A method of evaporating a reductant in an aftertreatment system
of an engine, the method comprising: providing a fluid passageway
from the engine to an ambient; injecting a reductant into the fluid
passageway with an injector; impinging the reductant onto a mesh
device downstream of the injector on the fluid passageway; and
heating the mesh device to a predetermined minimum temperature.
12) The method of claim 11 further comprising the steps of sensing
the temperature of the mesh device with a sensor.
13) The method of claim 12 further comprising the steps of
communicating the temperature to a control system, wherein if the
temperature is below the predetermined minimum temperature, the
control system actuates a heater to heat the mesh device.
14) The method of claim 11 further comprising the step of at least
partially coating the mesh device with a urea hydrolysis
catalyst.
15) The method of claim 11 wherein the fluid passageway is defined
by a reductant pipe, and further comprising the step of brazing the
mesh device to the reductant pipe.
16) A mesh device for an SCR system of an engine having a reductant
pipe with an interior surface, the mesh device comprising: a wire
mesh portion that permits a flow of exhaust gas therethrough; a
support ring that at least partially axially encloses the wire mesh
portion, wherein the support ring is configured for attachment to
the interior surface of the reductant pipe; and a heater for
heating the wire mesh portion.
17) The mesh device of claim 16 wherein the wire mesh portion is at
least partially coated with a urea hydrolysis catalyst.
18) The mesh device of claim 16 wherein the mesh device is made of
chromium, iron, nickel, and carbon.
19) The mesh device of claim 16 wherein the wire mesh portion is a
grid.
20) The mesh device of claim 16 wherein the mesh device is heated
electrically.
Description
BACKGROUND
[0001] Embodiments described herein relate to a system, method and
device for evaporating liquid reductant injected into a gas stream.
More specifically, embodiments described herein relate to a system,
method and device for evaporating an emission reductant, such as
urea, into an exhaust gas stream of an aftertreatment system of a
vehicle, such as an SCR system.
[0002] Diesel engine combustion results in the formation of
nitrogen oxides (NOx) in the exhaust gas. Typically, urea selective
catalytic reduction systems (urea SCR systems) are used to reduce
NOx from engines. Urea SCR systems rely on injection of aqueous
urea solution, which is injected into the exhaust line of a vehicle
upstream of an SCR catalyst. In the SCR catalyst, the NOx is
reduced by ammonia, and the emission from the catalyst is N.sub.2,
H.sub.2O and CO.sub.2.
[0003] For efficient performance, the emission reductant, for
example urea for SCR systems, must be injected into the engine
exhaust gas, evaporized and decomposed before reaching the inlet of
the aftertreatment catalyst. The characteristic time of the
evaporation of the reductant depends on the physical properties of
the reductant, the injection characteristics, and the energy of the
exhaust gas. The heat required for evaporating most reductants is
high. For example, a urea solution is injected into the system at
an ambient temperature and typically needs to be heated above
150.degree. C. or 200.degree. C. to evaporate the water and to
decompose the remaining urea into ammonia and isocyanic acid.
[0004] When the urea or other reductant is sprayed into the system,
the exhaust gas velocity is high, and the exhaust gas stream
carries the large droplets at a high velocity to the catalyst. As a
result, the characteristic time of the reductant evaporation can be
larger than the travel time to the catalyst. If the evaporation and
the decomposition are not complete, the SCR catalyst performance is
reduced due to insufficient availability of reductant.
[0005] Additionally, if the urea solution is not evaporated and
decomposed before hitting an inner surface of the exhaust gas pipe,
which is at a cooler temperature due to it being exposed to the
ambient, the urea solution will remain liquid and will not
decompose. Further, the urea can form a solid deposit on the inner
surface of the exhaust gas pipe.
[0006] To facilitate evaporation and decomposition of the
reductant, a mixer may be installed in front of the SCR catalyst.
Additionally, the reductant injector may be placed as far away as
possible upstream of the SCR catalyst. However, without
sufficiently high exhaust temperatures, poor evaporation and
decomposition of the urea solution can occur, and solid deposits
can form on the mixer and the walls of the exhaust system. Solid
urea deposition can decrease the flow area of the exhaust pipe,
resulting in an increased pressure drop and higher exhaust gas
velocity in the pipe, which can in turn, result in urea deposition
at the downstream catalyst. Eventually, the solid deposits can lead
to clogging of the exhaust system, and reduced NOx conversion
efficiency.
SUMMARY OF THE INVENTION
[0007] An exhaust aftertreatment system for a vehicle having an
engine includes a fluid passageway extending from the engine to an
ambient for fluidly communicating exhaust gas, and a NOx reduction
catalyst disposed on the fluid passageway and downstream of the
engine. An injector is disposed downstream of the engine and
upstream of the NOx reduction catalyst on the fluid passageway for
injecting a reductant into the fluid passageway. A heated mesh
device is disposed on the fluid passageway downstream of the
injector and upstream of the NOx reduction catalyst. The reductant
that is injected from the injector impinges on the heated mesh
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic of an exhaust aftertreatment system
having a heated mesh device located downstream of an injector and
upstream of a NOx reduction catalyst.
[0009] FIG. 2 is a front elevation view of the mesh device of FIG.
1.
DETAILED DESCRIPTION
[0010] Referring now to FIGS. 1 and 2, an SCR system (or other
exhaust aftertreatment system), is indicated generally at 10, and
has an exhaust pipe assembly 12 extending from an engine 14 to an
outlet 16, such as the outlet to an ambient 18. The exhaust pipe
assembly 12 forms a fluid passageway 20 for the flow of exhaust gas
F from the engine 14 to the ambient 18. A first portion 22 of the
exhaust pipe assembly 12 extends from the engine 14 to a diesel
oxidation catalyst/diesel particulate filter 24 (DOC/DPF). A
reductant pipe 26 of the exhaust pipe assembly 12 extends from the
DOC/DPF 24 to a NOx reduction catalyst 28, such as a selective
catalytic reduction catalyst (SCR catalyst). A third portion 30 of
the exhaust pipe 12 assembly extends from the SCR catalyst 28 to
the outlet 16. It is possible that the SCR system 10 of FIG. 1 can
have other configurations, for example, the reductant pipe 26 can
be placed between the DOC and the SCR catalyst 28, followed by a
DPF, or the reductant pipe 26 can be installed between the DOC and
a substrate that combines the functions of the SCR catalyst and the
DPF, among other configurations.
[0011] Mounted on a mounting boss 32 on the reductant pipe 26
between the DOC/DPF 24 and the SCR catalyst 28 is an injector 34
for spraying a reductant 36, such as a urea solution, into the flow
of exhaust gas F. The injector 34 can be mounted externally to the
reductant pipe 26, with a nozzle 38 of the injector 34 being
located at or in fluid communication with an interior surface 40 of
the reductant pipe 26 such that the sprayed urea or other reductant
36 is in fluid communication with the fluid passageway 20 and the
flow of exhaust gas F. The urea solution 36 is stored in a tank
(not shown) and pumped to the injector 34 with a pump (not shown)
for injection into the reductant pipe 26.
[0012] After being emitted from the engine 14 and flowing through
the DOC/DPF 24, the exhaust gas F flows through the reductant pipe
26 of the exhaust pipe assembly 12 where the injector 34 injects
urea 36 into the exhaust gas flow. The urea 36 is injected
generally at an ambient temperature, and typically needs to be
heated above at least 200-degrees Celsius to be evaporized and
decomposed in the exhaust gas F before reaching an inlet 42 of the
SCR catalyst 28. The urea 36 is heated by the energy of the exhaust
gas F emitted from the engine 14. However, the characteristic time
of the urea or other reductant 36 evaporation may still be larger
than the travel time to the catalyst 28, and solid deposits can
form on the interior surface 40 of the reductant pipe 26, on the
SCR catalyst 28, and on any other components downstream of the
injector 34 on the SCR system 10.
[0013] Downstream of the injector 34, a heated mesh device 44 is
mounted inside the reductant pipe 26 and is configured to receive
all or substantially all of the flow of the exhaust gas F through
the heated mesh device. The heated mesh device 44 includes a wire
mesh portion 46 that permits the flow of exhaust gas F
therethrough, without creating a substantial backpressure upstream
of the heated mesh device. It is possible that the wire mesh
portion 46 is a grid, a plurality of grids, or other shape that is
capable of permitting the flow of exhaust gas F therethrough
without creating a substantial backpressure, and that is capable of
being heated to temperatures sufficient to evaporate and decompose
the urea or other reductant solution 36.
[0014] The heated mesh device 44 may include a support ring 48 that
at least partially axially encloses the wire mesh portion 46, where
the support ring is attached to the interior surface 40 of the
reductant pipe 26, or alternatively, the heated mesh device may be
directly attached to the reductant pipe. The heated mesh device 44
may be generally cylindrical or disk-shaped, however other shapes
are possible.
[0015] The heated mesh device 44 is mounted in the aftertreatment
system 10 upstream of the SCR catalyst 28, and can be mounted by
brazing the heated mesh device 44 to the reductant pipe 26, or can
be mechanically attached to the reductant pipe, for example with a
rib stop or with retainer rings. It is also possible that the
heated mesh device 44 is attached to a pipe that is attached to the
reductant pipe 26, so that the heated mesh device and the attached
pipe are attached to two portions of the reductant pipe.
Alternatively, the heated mesh device 44 may be located between two
portions of the reductant pipe 26 without a separate attached pipe.
The reductant pipe 26 and the wire mesh device 44 fluidly
communicate exhaust flow F from the DOC/DPF 24 to the SCR catalyst
28 without the loss of exhaust gas between the DOC/DPF and the SCR
catalyst.
[0016] The heated mesh device 44 is positioned downstream of the
injector 34 such that the spray of urea 36 impinges on the heated
mesh device, which minimizes or avoids the urea contacting and or
crystallizing at the interior surface 40 of the exhaust pipe
assembly 12. The urea 36 decomposes on the heated mesh device 44
and the heated mesh device distributes ammonia to the SCR catalyst
28. The heated mesh device 44 can be partially or entirely coated
with TiO.sub.2 or other suitable material serving as a hydrolysis
catalyst that hydrolyzes HNCO into ammonia. A stationary mixer 50
may be located downstream of the heated mesh device 44 and upstream
of the SCR catalyst 28.
[0017] The flow of exhaust gas F through the heated mesh device 44
is a winding path through the wire mesh portion 46, which provides
increased surface area over the wire mesh to transfer heat from the
mesh device to the exhaust gas. The wire mesh material may be
crimped at angles of about 10 to 30-degrees, however other angles
are possible. Additionally, a crimp height and a crimp distance of
the material can be varied. The crimp pattern of the wire mesh
material can be in a herringbone pattern, a 10-degree straight
pattern, and a 30-degree straight pattern, however other crimp
patterns are possible.
[0018] The material of the heated mesh device 44 may include
varying amounts chromium, aluminum, iron, nickel, and carbon,
although other materials are possible. In one example material,
there is about 18-20% Chromium, 68-74% Iron, 8-12% Nickel, and
0.08% Carbon. In another example material, there is about 24-26%
Chromium, 48-55% Iron, 19-22% Nickel, and 0.08% Carbon. In a third
example, there is about 22% Chromium, 4.8% Aluminum, and 73.2%
Iron. The melting point of the material may be about 1400 or
1500-degrees Celsius, with a maximum operating temperature of the
heated mesh device being about 900 to 1300-degrees Celsius. The
density of the material may be about 7.25 to 8.1 g/cm.sup.3,
however other densities are possible. The electric resistivity may
be about 0.72 to 1.35 .mu.ohm-m at 20-degrees Celsius, however
other amounts of resistivity are possible. Further, the material
may have a coefficient of thermal expansion from about 11 to 17
.mu.m/m K, thermal conductivity of about 11 to 16.2 W/m K, and a
specific heat of about 0.46 to 0.5 kJ/kg K.
[0019] A sensor 52 senses the temperature of the heated mesh device
44 and communicates the temperature to a control system 54. When
the temperature of the heated mesh device 44 is below a
predetermined minimum temperature, for example 200-degrees Celsius,
the control system 54 actuates a heater 56 to heat the heated mesh
device 44, such as by electrically heating. Electrically heating
the heated mesh device 44 provides a fast heating response time.
Alternatively, the heater may be a coolant heater 56, where heated
coolant can be used to transfer heat to the heated mesh device 44.
The coolant can be routed through or near high temperature
components, for example the exhaust system, where the coolant is
heated, and then the coolant is routed to the mesh device 44. It is
possible that the heated mesh device 44 is insulated so as not to
impact other portions of the vehicle.
[0020] A power source 58 provides power to the heater 56 to heat
the heated mesh device 44. The heater 56 maintains the heated mesh
device 44 above the predetermined temperature. It is possible that
the predetermined temperature can be variable, and that the heater
56 can be both automatically actuated and manually actuated.
[0021] When the injector 34 sprays the urea or other reductant
solution 36 towards the heated mesh device 44, the urea solution is
minimized or prevented from hitting the colder exhaust pipe
assembly 12 (which is surrounded by ambient air), and instead
contacts the wire mesh portion 46. Since the wire mesh portion 46
of the heated mesh device 44 is heated to a minimum predetermined
temperature, for example at least 200 degrees Celsius, the urea
solution 36 can continue to evaporate. Additionally, since the urea
solution 36 does not contact the exhaust pipe assembly 12, the pipe
can be made of less expensive steel or other less-corrosion
resistant materials.
[0022] The temperature of the urea or other reductant solution 36
is increased due to contact with the mesh, which improves
evaporation. The lifetime of the urea droplet becomes shorter due
to the contact with the mesh device 44. The result is that there is
improved evaporation of the urea or other reductant 36, improved
efficiency of the SCR system 10, reduced solid urea buildup, and
reduced corrosion of the exhaust pipe assembly 12. With the
increased efficiency in the SCR system 10, the distance between the
injector 34 and the SCR catalyst 28 may be decreased.
* * * * *