U.S. patent application number 11/827708 was filed with the patent office on 2009-01-15 for flow diffuser for exhaust pipe.
This patent application is currently assigned to PACCAR Inc. Invention is credited to Paul J. Troxler.
Application Number | 20090014235 11/827708 |
Document ID | / |
Family ID | 40252171 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090014235 |
Kind Code |
A1 |
Troxler; Paul J. |
January 15, 2009 |
Flow diffuser for exhaust pipe
Abstract
A flow diffuser for vehicles of the type having an engine and an
exhaust pipe generally includes a substantially tubular body having
an outer surface and a first end configured for attachment to an
exhaust pipe. The flow diffuser further includes a diffusion
portion on the outer surface having a plurality of elongated
diffusion ports. Each elongated diffusion port has an average
length and an average width and a shape factor of less than about
0.7.
Inventors: |
Troxler; Paul J.;
(Bellingham, WA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE, SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
PACCAR Inc
Bellevue
WA
|
Family ID: |
40252171 |
Appl. No.: |
11/827708 |
Filed: |
July 13, 2007 |
Current U.S.
Class: |
181/228 |
Current CPC
Class: |
F01N 2470/04 20130101;
F01N 13/08 20130101 |
Class at
Publication: |
181/228 |
International
Class: |
F01N 7/08 20060101
F01N007/08 |
Claims
1. A flow diffuser for vehicles of the type having an engine and an
exhaust pipe, the flow diffuser comprising: (a) a substantially
tubular body having an outer surface and a first end configured for
attachment to an exhaust pipe; and (b) a diffusion portion on the
outer surface having a plurality of elongated diffusion ports, each
diffusion port having an average length and an average width and a
shape factor of less than about 0.7.
2. The flow diffuser of claim 1, wherein the spacing between
adjacent diffusion ports is at least equal to the average width of
the adjacent diffusion ports.
3. The flow diffuser of claim 1, wherein the spacing between
adjacent diffusion ports is at least equal to twice the average
width of the adjacent diffusion ports.
4. The flow diffuser of claim 1, wherein the spacing between
adjacent diffusion ports is at least equal to three times the
average width of the adjacent diffusion ports.
5. The flow diffuser of claim 1, wherein the plurality of elongated
diffusion ports are configured as a plurality of slots in the outer
surface.
6. The flow diffuser of claim 1, wherein the plurality of elongated
diffusion ports are configured as a plurality of channels extending
from the outer surface.
7. The flow diffuser of claim 1, further comprising a second end,
wherein the second end is a substantially closed end or a vented
end.
8. The flow diffuser of claim 6, wherein the diffusion portion
includes fluid passageways between the plurality of channels for
surrounding air.
9. The flow diffuser of claim 1, wherein the plurality of elongated
diffusion ports are configured to be oriented substantially
transverse with respect to a center longitudinal axis extending
through the tubular body.
10. The flow diffuser of claim 1, wherein the plurality of
elongated diffusion ports are configured to be oriented
substantially longitudinal with respect to a center longitudinal
axis extending through the tubular body.
11. The flow diffuser of claim 1, wherein each of the plurality of
elongated diffusion ports has a shape factor selected from the
group consisting of less than about 0.5, less than about 0.3, in
the range of about 0.1 to about 0.7, in the range of about 0.1 to
about 0.5, and in the range of about 0.1 to about 0.3.
12. The flow diffuser of claim 6, wherein each of the plurality of
channels has an exit port having a shape factor selected from the
group consisting of less than about 0.5, less than about 0.3, in
the range of about 0.1 to about 0.7, in the range of about 0.1 to
about 0.5, in the range of about 0.1 to about 0.3, and in the range
of about 0.02 to 0.2.
13. A flow diffuser for vehicles of the type having an engine and
an exhaust pipe, the flow diffuser comprising: (a) a substantially
tubular body having an outer surface and a first end configured for
attachment to an exhaust pipe; and (b) a diffusion portion on the
outer surface having a plurality of elongated slots having a
spacing between adjacent slots, wherein each elongated slot has an
average length and an average width and wherein the spacing between
adjacent slots is at least equal to the average width of the
slots.
14. The flow diffuser of claim 13, wherein the diffusion portion
includes a plurality of channels extending from the plurality of
slots.
15. The flow diffuser of claim 13, further comprising a second end,
wherein the second end is a substantially closed end.
16. The flow diffuser of claim 13, further comprising a second end,
wherein the second end is a vented end.
17. The flow diffuser of claim 14, wherein the diffusion portion
includes fluid passageways between the plurality of channels for
the passage of surrounding air.
18. The flow diffuser of claim 13, wherein the plurality of slots
are configured to be oriented substantially transverse with respect
to a center longitudinal axis extending through the tubular
body.
19. The flow diffuser of claim 13, wherein the plurality of slots
are configured to be oriented substantially longitudinal with
respect to a center longitudinal axis extending through the tubular
body.
20. A flow diffuser for vehicles of the type having an engine and
an exhaust pipe, the flow diffuser comprising: (a) a substantially
tubular body having an outer surface and a first end configured for
attachment to an exhaust pipe; and (b) a diffusion portion on the
outer surface having an elongated substantially serpentine slot
having a shape factor of less than about 0.7.
Description
BACKGROUND
[0001] New, more stringent emission limits for diesel engines
necessitate the use of exhaust after-treatment devices, such as
diesel particulate filters. Certain after-treatment devices include
a regeneration cycle. During the regeneration cycle, the
temperature of the exhaust gas plume may rise significantly above
acceptable temperatures normally experienced by exhaust systems
without such after-treatment devices. As an example, exhaust
systems without after-treatment devices typically discharge exhaust
gas at a temperature of around 650 degrees Kelvin. An exhaust
system having an after-treatment device that includes a
regeneration cycle may experience an exhaust gas plume temperature
exceeding 900 degrees Kelvin at its center core. Exhaust gas at
this high exit temperature creates a potentially hazardous
operating environment.
[0002] Thus, there exists a need for a flow diffuser for an exhaust
pipe for diffusing hot exhaust gas on exit from an exhaust
pipe.
SUMMARY
[0003] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
[0004] In accordance with one embodiment of the present disclosure,
a flow diffuser for vehicles of the type having an engine and an
exhaust pipe is provided. The flow diffuser generally includes a
substantially tubular body having an outer surface and a first end
configured for attachment to an exhaust pipe. The flow diffuser
further includes a diffusion portion on the outer surface having a
plurality of elongated diffusion ports. Each elongated diffusion
port has an average length and an average width and a shape factor
of less than about 0.7.
[0005] In accordance with another embodiment of the present
disclosure, a flow diffuser generally includes a diffusion portion
on the outer surface having a plurality of elongated slots having a
spacing between adjacent slots. Each elongated slot has an average
length and an average width. The spacing between adjacent slots is
at least equal to the average width of the slots.
[0006] In accordance with yet another embodiment of the present
disclosure, a flow diffuser generally includes a diffusion portion
on the outer surface having an elongated substantially serpentine
slot having a shape factor of less than about 0.7.
DESCRIPTION OF THE DRAWINGS
[0007] The patent or application file contains at least one figure
executed in color. Copies of this patent or patent application
publication with color figures will be provided by the Office upon
request and payment of the necessary fee.
[0008] The foregoing aspects and many of the attendant advantages
of this disclosure will become more readily appreciated by
reference to the following detailed description, when taken in
conjunction with the accompanying drawings, wherein:
[0009] FIG. 1 is a side view of a flow diffuser formed in
accordance with one embodiment of the present disclosure, showing
the flow diffuser coupled to a vehicle of the type having an engine
and an exhaust pipe;
[0010] FIG. 2 is a perspective view of the flow diffuser of FIG.
1;
[0011] FIGS. 3 and 4 are perspective views of flow diffusers for
exhaust pipes formed in accordance with other embodiments of the
present disclosure;
[0012] FIG. 5 is a comparison graph plotting exhaust gas exit
temperature versus the distance the exhaust gas has traveled from
the exit plane or surface for flow diffusers formed in accordance
with embodiments of the present disclosure and a standard exhaust
pipe not having a flow diffuser;
[0013] FIG. 6-9 are exit temperature section plots for the flow
diffuser of FIGS. 1 and 2;
[0014] FIGS. 10-13 are exit temperature section plots for the flow
diffuser of FIG. 3; and
[0015] FIGS. 14 and 15 are exit temperature section plots for a
standard exhaust pipe not having a flow diffuser.
DETAILED DESCRIPTION
[0016] A flow diffuser 20 constructed in accordance with one
embodiment of the present disclosure may be best understood by
referring to FIGS. 1 and 2. The flow diffuser 20 includes a
substantially tubular body 22 having an outer surface 24 and a
first end 26 configured for attachment to an exhaust pipe 12. The
flow diffuser 20 further includes a diffusion portion 28 on the
outer surface 24 having at least one diffusion port 30, wherein the
diffusion portion 28 has an optimized flow configuration. During
the operation of a vehicle, for example, the vehicle 10 shown in
the illustrated embodiment of FIG. 1, exhaust gas travels through
an exhaust pipe 12 and is diffused to the surrounding ambient air
by the flow diffuser 20.
[0017] Flow diffusers 20 of the present disclosure reduce
temperature and velocity profiles of hot exhaust gas plumes after
exiting an exhaust pipe to reduce the risk of danger associated
with hot exhaust pipe discharge. As discussed in greater detail
below, specifically, with reference to EXAMPLES 1-3, the flow
diffusers described herein reduce exhaust gas velocity, thereby
promoting ready mixing and diffusion of hot exhaust gas with cooler
surrounding ambient air. In that regard, the combined flow area of
the diffusion ports 30 is equal to or greater than the flow area of
the inlet or first end 26 to maintain or reduce exhaust gas
velocity at the diffusion ports 30 and prevent back pressure within
the flow diffuser 20. While fluid mixing with cooler ambient air
contributes more significantly to the overall heat dissipation
capabilities of the flow diffuser 20, some of the embodiments
described herein are also configured to promote heat dissipation
(for example, heat loss through the outer surface 24 of the flow
diffuser 20) prior to the exhaust gas exiting the flow diffuser 20,
as described in greater detail below.
[0018] Although illustrated and described in conjunction with
under-chassis exhaust pipes, other configurations, such as vertical
(i.e., stack) exhaust pipes, are also intended to be within the
scope of the present disclosure. It should be appreciated that the
first end 26 is an inlet, connectable to the exhaust pipe 12 (see
FIG. 1) by any means known to those having ordinary skill in the
art, including by an interference fit, welding, or any suitable
fastening devices, such as bolts, rivets, or other fasteners.
[0019] Referring to FIGS. 1 and 2, a flow diffuser 20 designed and
configured in accordance with various aspects of the present
disclosure is shown. In the illustrated embodiment of FIGS. 1 and
2, the diffusion ports 30 are shown as elongated slots on the outer
surface 24 of the substantially tubular body 22, the elongated
slots 30 each having an average length and an average width. The
elongated slots have an optimized relationship between slot
perimeter and slot area to promote rapid fluid mixing of the hot
exhaust gas with the surrounding ambient air. As described in
greater detail below with respect to the mixing principles of the
flow diffuser 20, an optimized perimeter to flow area relationship
provides for a smaller center core of hot exhaust gas in each of
the hot exhaust gas streams discharged from the slots 30 (compare
temperature section plots in FIGS. 6-9 for the flow diffuser 20 of
FIG. 2 and FIGS. 14 and 15 for a standard exhaust pipe 12 having a
circular cross-section). Therefore, the elongate slots promote
enhanced fluid mixing and temperature distribution for more rapid
heat dissipation of the hot exhaust gas streams. Alternate
embodiments of the flow diffuser having elongate, channeled
diffusion portions are described below with reference to FIGS. 3
and 4.
[0020] In the illustrated embodiment of FIG. 2, the perimeter to
flow area relationship or shape factor (a measure of compactness of
a shape, expressed mathematically as 4.pi.*area/(perimeter).sup.2)
of the slots 30 is less than about 0.7. For the most compact shape,
the circle, the shape factor is equal to 1.0. As a shape elongates,
the shape factor decreases, such that a square cross-section has a
shape factor of 0.785. An infinitely long and narrow shape has a
shape factor of 0. In another embodiment of the present disclosure,
the shape factor of the slots 30 is less than about 0.5. In another
embodiment of the present disclosure, the shape factor of the slots
30 is less than about 0.3. In yet another embodiment of the present
disclosure, the shape factor of the slots 30 is in the range of
about 0.1 to about 0.7. In yet another embodiment of the present
disclosure, the shape factor of the slots 30 is in the range of
about 0.1 to about 0.5. In yet another embodiment of the present
disclosure, the shape factor of the slots 30 is in the range of
about 0.1 to about 0.3.
[0021] The slots 30 are suitably spaced from one another to define
a spacing 48 between adjacent slots 30. In contrast with systems
not having adequate spacing between adjacent slots, for example,
baffled slot systems, the configurations of the present disclosure
provide increased mixing and cooling with cooler ambient air
residing in the spacing 48 between the slots 30. As a result of
this spacing 48, cooler ambient air is entrained into the exhaust
gas streams as they exit from the flow diffuser 20, as described in
greater detail below with respect to the mixing principles of the
flow diffuser 20. In addition, adequate spacing is required between
slots 30, so as to maintain the durability of the outer surface 24
between the slots 30. In that regard, if slots are too closely
spaced to one another, the slots are separated by only a thin
portion of the outer surface, for example, a thin piece of metal,
which creates a durability problem, because the hot exhaust gas may
burn through such a thin piece of metal over time.
[0022] In the illustrated embodiment, the spacing 48 adjacent each
of the slots 30 is at least as great as the average width of the
adjacent slots. In other embodiments, the spacing between slots may
be at least twice as great as the average width of the adjacent
slots. In other embodiments, the spacing between slots may be at
least three times the average width of the adjacent slots. In yet
other embodiments, the spacing between slots is one to five times
the average width of the slots.
[0023] Although the flow diffuser 20 is illustrated as having ten
equidistantly spaced slots 30 it should be apparent that the number
of slots is not intended to be limiting, so long as the combined
flow area of the slots 30 is equal to or greater than the flow area
at the first end 26, where the flow diffuser 20 is attached to an
exhaust pipe 12. As such, a flow diffuser 20 having more or fewer
than ten slots 30 is within the scope of the present disclosure. It
should be appreciated, however, that the number of slots may be
limited by design restrictions and/or the number of slots that can
be accommodated along the length of the flow diffuser 20. It should
further be appreciated that other diffusion portion configurations
are also within the scope of the present disclosure. For example,
in the illustrated embodiment, the slots 30 are alternatingly
offset by about half the average length of the adjacent slots.
[0024] It should be appreciated that the slots 30 may be aligned or
offset in any suitable configuration. It should further be
appreciated that the slots 30 may be configured to extend
transversely, longitudinally, or angled relative to a center
longitudinal axis extending through the substantially tubular body
22. In addition, the slots 30 may be configured in straight,
curved, and arcuate designs, including, as a nonlimiting example, a
substantially serpentine configuration. It should further be
appreciated that nonparallel, nonuniform, and nonequidistantly
spaced slots 30 are also within the scope of the present
disclosure.
[0025] As best seen in FIGS. 1 and 2, the slots 30 of the
illustrated embodiment are configured to extend on only a portion
of the outer surface 24 of the substantially tubular body 22 to
direct exhaust gas in one direction from the flow diffuser 20, for
example, away from areas of concern, such as the vehicle chassis,
wiring, or cab. It should be appreciated, however, that the slots
30 can be configured to extend around the entire outer surface 24
of the substantially tubular body 22, particularly in applications
where the direction of exhaust gas flow is not of concern, for
example, when the flow diffuser 20 is intended for use with a stack
exhaust pipe.
[0026] Referring to FIG. 2, the second end 50 of the flow diffuser
20 is capped in the illustrated embodiment to direct the exhaust
gas through the diffusion portion 28 of the flow diffuser 20.
However, it should be appreciated that other configurations, such
as a partially open second end or a vented second end, are within
the scope of the present disclosure. Venting of the flow diffuser
20 at the second end 50 may be a desirable configuration to
decrease the pressure at the second end 50 of the flow diffuser 20,
for example, to prevent back pressure, and/or to diffuse some fluid
flow through the second end 50.
[0027] The heat transfer and fluid mixing promoted by the flow
diffuser 20 of the illustrated embodiment of FIGS. 1 and 2 will now
be described in greater detail. When in use, heat dissipation of
hot exhaust gas is achieved through the flow diffuser 20 in at
least four ways: (1) by heat conduction; (2) by velocity reduction;
(3) by optimization of the shape factor of the slots 30; and (4) by
optimization of the spacing 48 between adjacent slots 30. As will
be described in greater detail below, velocity reduction, shape
factor optimization, and spacing optimization, in turn, result in
reduction of the center core of the hot exhaust gas streams exiting
the flow diffuser 20 to promote enhanced fluid mixing upon exit,
thereby resulting in more rapid heat dissipation of the exhaust gas
with the surrounding ambient air. As mentioned briefly above, fluid
mixing contributes more significantly to the overall heat
dissipation of the flow diffuser 20 than heat dissipation by
conduction (for example, heat loss through the outer surface 24 of
the flow diffuser 20).
[0028] First, heat is dissipated from the effective surface area of
the flow diffuser 20 to the surrounding ambient air. It should be
appreciated that wall thickness of the diffusion portion 28 and the
substantially tubular body 22, as well as the thermal resistivity
of the material from which the flow diffuser 20 is constructed,
contribute to the conductive cooling achieved by the flow diffuser
20, in accordance with the principles of heat transfer. It should
further be appreciated that additional cooling of the flow diffuser
20 surface may be achieved by convective cooling. For example, if
the vehicle 10 to which the flow diffuser 20 is attached is moving,
the fluid flow of the surrounding ambient air over the flow
diffuser 20 will further provide cooling to the flow diffuser
20.
[0029] Second, because the flow area of the diffusion portion 28
may be greater than the flow area at the inlet or first end 26 of
the flow diffuser 20, the velocity of the exhaust gas may decrease
as it exits the diffusion portion 28. Decreased exhaust gas
velocity allows for a decreased penetration distance of the jet
exhaust streams, which further allows for enhanced mixing of the
exhaust gas streams with the surrounding ambient air. In addition
to the mixing advantages described herein, increased flow area at
the diffusion portion 28 also helps decrease back pressure during
the vehicle exhaust stroke.
[0030] Third and fourth, optimization of the shape factor of the
slots 30 and the spacing 48 between adjacent slots 30 also promotes
increased mixing at the slots 30. With regard to the mixing
effects, it should be appreciated that exhaust gas generally has a
nonlaminar flow at a high velocity and, comparatively, the
surrounding ambient air generally has a substantially quieter flow
at a lower velocity. As the exhaust gas exits the separate slots
30, the slots 30 create a plurality of separate exhaust gas
streams. Although the velocities of the separate exhaust gas
streams decrease with increased flow area at the slots 30, the
exhaust gas still exits the slots 30 at a substantially higher
velocity than the surrounding ambient air.
[0031] When the exhaust gas streams exit the slots 30, the shearing
forces between the exhaust gas streams and the surrounding ambient
air create a frictional drag at their barriers. This frictional
drag creates a series of small vortices along the barriers of the
exhaust gas streams, and the circulation of the vortices promotes
mixing between the exiting streams and the surrounding ambient air
to aid in the diffusion of the exhaust gas. Such mixing aids in
significantly decreasing the temperature of the hot exhaust gas and
the penetration distance of hot exhaust gas streams discharging
from the slots 30. The more ambient air present at the barrier for
mixing, the greater the heat diffusion of the exhaust gas.
Therefore, the combination of slot 30 elongation for an increased
slot perimeter compared to flow area (i.e., shape factor closer to
0) and increased spacing 48 between adjacent slots 30 promotes
increased mixing of the exhaust gas with ambient air after exiting
the respective slots 30. In addition, if the vehicle 10 to which
the flow diffuser 20 is attached is moving, the fluid mixing may be
even more enhanced by the introduction of convective mixing
principles, described above.
[0032] FIG. 5 is a comparison line graph showing exit temperatures
for (1) the flow diffuser of FIG. 2, (2) a second embodiment having
a channeled diffusion portion described below with reference to
FIG. 3, and (3) a standard five-inch diameter exhaust pipe not
having a flow diffuser. All three systems were subjected to
simulated diesel particulate filter conditions of over 925 degrees
Kelvin and a mass flow rate of about 1 kg/sec. As seen in the
comparison graph, the exhaust gas exiting the flow diffuser 20 has
immediate heat dissipation from over 925 degrees Kelvin to less
than 600 degrees Kelvin within a lateral distance of less than 200
mm from the outer surface of the diffuser 20. Exhaust gas exiting
the flow diffuser 120 of the second embodiment, described below,
also has near immediate heat dissipation, from over 925 degrees
Kelvin to less than 600 degrees Kelvin within a lateral distance of
less than 300 mm from the exit plane of the diffusion channels 130.
The exhaust gas exiting the standard exhaust pipe, on the other
hand, has little to no heat dissipation from over 925 degrees
Kelvin to until the exhaust gas reaches a lateral distance of over
700 mm from the exit plane.
[0033] Still referring to the comparison graph in FIG. 5, the
exhaust gas exiting the standard exhaust pipe eventually reaches
about 600 degrees Kelvin after traveling about 1200 mm from the
exit plane, over six times further than the dissipated exhaust gas
from the flow diffuser 20 of the illustrated embodiment of FIGS. 1
and 2, and over four times further than the dissipated exhaust gas
from the flow diffuser 120 of the illustrated embodiment of FIG. 3.
Once the exhaust gas exiting the standard exhaust pipe begins to
dissipate, it also has more gradual heat dissipation after
traveling 700 mm from the exit plane than the exhaust gas exiting
the flow diffuser 20 has immediately upon reaching the exit plane,
as seen by comparing the cooling slopes of the three lines. For
further comparative analysis, see EXAMPLES 1-3 and FIGS. 6-15,
described below.
[0034] Now returning to FIGS. 3 and 4, flow diffusers formed in
accordance with other embodiments of the present disclosure will be
described in greater detail. The flow diffusers are substantially
identical in materials and operation as the previously described
embodiment, except for differences regarding the diffusion portions
of the flow diffusers, which will be described in greater detail
below.
[0035] For clarity in the ensuing descriptions, numeral references
of like elements of the flow diffuser 20 are similar, but are in
the 100 and 200 series, respectively, for the illustrated
embodiments of FIGS. 3 and 4.
[0036] Referring to FIG. 3, a flow diffuser 120 designed and
configured in accordance with various aspects of the present
disclosure is shown. In the illustrated embodiment of FIG. 3, the
diffusion ports 130 are shown as channels, as opposed to slots 30
in the illustrated embodiment of FIGS. 1 and 2. The channels 130
have root ends 132 located near the outer surface 124 of the
substantially tubular body 122, exit ports 134, and channel axes
136 extending between the root ends 132 and the exit ports 134. As
mentioned above, with reference to the previously described
embodiment, the fluid flow area from the diffusion ports 130 of
this second embodiment is equal to or greater than the flow area at
the inlet or first end 126 of the substantially tubular body 122 to
maintain or reduce exhaust gas velocity at the diffusion ports 130
and to prevent back pressure within the flow diffuser 120.
[0037] Similar to the previously described embodiment, the flow
diffuser 120 of the second embodiment also provides exhaust gas
diffusion; however, the flow diffuser 120 of the second embodiment
has exit ports 134 that are laterally spaced from the outer surface
124 of the tubular body 122. In this regard, the channels 130 of
the flow diffuser 120 can be used to laterally reposition the
exhaust exit ports 134 at a specific distance from the outer
surface 124 of the tubular body 122 to more effectively direct hot
exhaust gas away from areas of concern, such as the vehicle
chassis, wiring, or cab.
[0038] In the illustrated embodiment, the channels 130 preferably
increase in fluid flow area along the channel axes 136 to further
reduce exhaust gas velocity through the channels 130. In that
regard, the channels 130 each have first and second parallel
surfaces 138 and 140 and a channel width 142 that increases along
the channel axis 136 between the root end 132 and the exit port
134. Because the channel width 142 increases along the channel axis
136, the cross-sectional area of each channel 130 also increases
along the same direction to, respectively, increase the fluid flow
area of each channel 130 along the channel axis 136.
[0039] Similar to the previously described embodiment, the channels
130 of this second embodiment also have an optimized perimeter to
flow area relationship, or shape factor, at each exit port 134.
Like the previously described embodiment, the exit ports 134 may be
designed to have a shape factor of less than about 0.7. In another
embodiment, the shape factor at the exit ports 134 is less than
about 0.5. In another embodiment, the shape factor at the exit
ports 134 is less than about 0.3. In yet another embodiment, the
shape factor at the exit ports 134 is in the range of about 0.02
and 0.2.
[0040] Also similar to the previously described embodiment, the
channels 130 are suitably spaced from one another to define
spacings, shown as passageways 148 between adjacent channels 130.
The passageways 148 of the illustrated embodiment provide increased
conductive and convective cooling of exhaust gas within the
channels 130 with cooler ambient air residing in or passing through
the passageways 148. As a result of these passageways 148, cooler
ambient air may provide some convective cooling to the channels
130. This cooler ambient air residing in the passageways 148 also
is entrained into the exhaust gas streams exiting from the exit
ports 134. In the illustrated embodiment, the spacing between
channels 130 is at least as great as the average width 152 of the
adjacent channels 130. Like the previously described embodiments,
the spacing between channels 130 may be at least twice or three
times as great as the average width 152 of the adjacent channels
130, or anywhere from one to five times the spacing between
channels 130.
[0041] Like the previously described embodiment, it should be
apparent that the number and spacing of channels 130 in the flow
diffuser 120 is not intended to be limiting. In that regard, a flow
diffuser 120 having more or fewer than the five channels 130 shown
in FIG. 3 is within the scope of the present disclosure. It should
further be appreciated that other channel 130 configurations are
also within the scope of the present disclosure. As a nonlimiting
example, the configuration of the channels 130 may curve along the
width 152 or the channel axis 136. It should further be appreciated
that nonparallel, nonuniform, and nonequidistantly spaced channels
130 are also within the scope of the present disclosure.
[0042] The heat transfer and fluid mixing promoted by the flow
diffuser 120 of the illustrated embodiment of FIG. 3 will now be
described in greater detail. Like the previously described
embodiment, heat dissipation of the hot exhaust gas is achieved
through heat conduction, velocity reduction, optimization of the
shape factor of the channel 130 flow area, and optimization of the
spacing or passageways 148 between adjacent channels 130.
[0043] In addition to the heat transfer and fluid mixing described
above with reference to the previous embodiment, the illustrated
embodiment of FIG. 3 provides for additional conductive heat
transfer over the previously described embodiment. In that regard,
heat is dissipated from the effective surface area of the flow
diffuser 120 to the surrounding ambient air. Channels 130 having
increasing flow area along the channel axis 136 also have an
increasing effective surface area surrounding the flow area and,
correspondingly, increased heat conduction to the surrounding
ambient air. In addition to increasing the effective surface area
surrounding the flow area, the passageways 148 between the channels
130 allow ambient air to pass around the entirety of the effective
surface area of the channels 130 to increase conductive cooling. As
mentioned above, such cooling may be increased by convection, for
example, when the vehicle is in motion.
[0044] Turning now to FIG. 4, a flow diffuser 220 designed and
configured in accordance with other aspects of the present
disclosure is shown. In that regard, the flow diffuser 220 of the
illustrated embodiment of FIG. 4 includes a substantially
serpentine diffusion port 230. Similar to the flow diffuser 120
described above, the diffusion port 230 includes a channel that
increases in cross-sectional area along the channel axis 236 to
reduce exhaust gas flow temperature and velocity. In accordance
with a serpentine configuration, the channel 230 has first and
second undulating surfaces 238 and 240 that are spaced from one
another at a channel width 252 along the channel axis 236. The
first and second undulating surfaces 238 and 240 thus define a
substantially serpentine channel 242 along the channel axis 236,
best seen at the exit port 234. In that regard, the first and
second undulating surfaces 238 and 240 include a repeating series
of uniform peaks 244 and troughs 246 that are substantially
U-shaped in cross-section.
[0045] Along the channel axis 236, the flow area of the serpentine
channel 242 increases. Specifically, the height of the peaks 244
and troughs 246 increases along the channel axis from the root end
232 of the serpentine channel 242 to the exit port 234 of the
serpentine channel 242. In the illustrated embodiment of FIG. 4,
the root end 232 of the serpentine channel 242 is located near an
elongated slot on the outer surface 224 of the substantially
tubular body 222 of the flow diffuser 220. As the peaks 244 and
troughs 246 of the serpentine channel 242 increase, exterior
passageways 248 are formed for the passage of surrounding ambient
air at the exterior surfaces of the channel 230. As the height of
the peaks 244 and troughs 246 increases along the channel axis 236
from the root end 232 to the exit port 234, the depth of the
exterior spacings or passageways 248 likewise increases.
[0046] In the illustrated embodiment, the passageways 248 between
the peaks 244 and troughs 246 have an average width at least as
great as the average width 252 of the channel 230 at the exit port
234. In other embodiments, the passageways 248 between the peaks
244 and troughs 246 have an average width at least twice, three
times, or anywhere between one and five times as great as the
average width 252 of the adjacent channels 230 at their exit port
234. Moreover, in accordance with embodiments of the present
disclosure, the exit port 234 of the serpentine channel has a shape
factor of less than about 0.7, less than about 0.5, less than about
0.3, or in the range of about 0.02 to about 0.2.
[0047] It should be appreciated that in other embodiments in
accordance with the present disclosure, the serpentine channel may
include nonuniform peaks and troughs or a varying channel width 252
between first and second undulating surfaces 238 and 240. Moreover,
the serpentine pattern may include a repeating pattern of another
configuration than the U-shaped design illustrated herein. As
nonlimiting examples, the pattern may include V-shaped peaks and
troughs, as well as box-shaped peaks and troughs.
[0048] Like the previously described embodiments, heat dissipation
of the hot exhaust gas is achieved through heat conduction,
velocity reduction, optimization of the shape factor of the channel
230 flow area, and optimization of the passageways 248 between
adjacent peaks 244 and troughs 246. The peaks 244 and troughs 246
increase along the channel axis 236 from the root end 232 to the
exit port 234 to provide increased effective surface area along the
channel axis 236 for enhanced conductive and/or convective cooling.
As mentioned above, the depths of the exterior spacings or
passageways 248 likewise increase along the channel axis 236 to
increase conductive and convective heat transfer with the
surrounding ambient air. In addition, the velocity of the exhaust
gas decreases as the flow area of the channel 230 increases to
promote enhanced fluid mixing with the surrounding ambient air.
[0049] The heat transfer and fluid mixing promoted by the flow
diffuser embodiments described herein may be further understood by
referring to the exemplary temperature section plots of flow
diffusers under simulated use conditions, as described below in
EXAMPLES 1 and 2 and as seen in FIGS. 6-13, modeling mass flow,
inlet temperature, and exit port temperature of a diesel
particulate filter undergoing regeneration. For further comparative
analysis, exit temperature section plots for a standard five-inch,
straight exhaust pipe under the same exhaust gas exit conditions
are described below in EXAMPLE 3 and seen in FIGS. 14 and 15.
[0050] As best seen by comparing the temperature section plots of
FIGS. 6-13 for the flow diffusers embodiments 20 and 120 and FIGS.
14 and 15 for the standard exhaust pipe, the mixing effects of the
flow diffusers formed in accordance with embodiments of the present
disclosure are improved over the mixing effects of a standard
exhaust pipe as a result of the following: the combination of
decreased exhaust stream velocity, resulting in improved mixing at
the barrier; increased slot perimeter compared to flow area (i.e.,
a shape factor approaching 0), resulting in a reduced core in the
exhaust gas streams and an increased barrier for the flow area for
enhanced mixing; and a greater spacing area between adjacent exit
ports, resulting in a greater amount of ambient air at the barrier
of the exhaust gas streams for enhanced mixing with ambient
air.
EXAMPLE 1
Exhaust Temperature Section Plots for Flow Diffuser
[0051] The simulated exhaust gas exit conditions seen in FIGS. 6-9
for the illustrated flow diffuser 20 of FIG. 2 will now be
described in greater detail. FIG. 6 is a side, cross-section view
taken through the center of the diffusion ports or slots 30,
showing the exit temperature section plot of exhaust gas traveling
through the flow diffuser 20 of FIG. 2. This section plot shows
that hot exhaust gas travels through the exhaust pipe at about 940
degrees Kelvin. Heat from the exhaust gas begins to dissipate
immediately upon exiting the slots 30. Such dissipation continues
after exit, such that the exhaust gas temperatures drop to less
than about 650 degrees Kelvin within a distance of 155 mm from the
center longitudinal axis of the flow diffuser 20. (See also the
line graph of FIG. 5, described in greater detail above).
[0052] FIGS. 7-9 show temperature section plots at radial distances
of 50 mm, 100 mm, and 150 mm, respectively, from the exhaust pipe
outer surface at the diffusion ports 30 of the flow diffuser 20.
These section plots show that the hottest cores of the exhaust gas
streams diffuse from an exit temperature of 774.3 degrees Kelvin
(FIG. 7) to 593.6 degrees Kelvin (FIG. 9) within a distance of 100
mm--between the 50 mm radial distance point (FIG. 7) to the 150 mm
radial distance point (FIG. 9). In addition, by examining the
expanding and cooling cores of the exhaust gas streams in the
series of exit temperature section plots starting at FIG. 7 and
ending at FIG. 9, these section plots indicate that enhanced mixing
between the exhaust gas and the surrounding ambient air is
occurring, as a result of the spacing and design of the slots 30,
to significantly reduce the temperature of the exhaust gas.
EXAMPLE 2
Exhaust Temperature Section Plots for Flow Diffuser
[0053] The simulated exhaust gas exit conditions seen in FIGS.
10-13 of the illustrated flow diffuser 120 of FIG. 3 will now be
described in greater detail. FIG. 10 is a side view exit
temperature section plot of the flow diffuser 120 of FIG. 3. This
section plot shows that hot exhaust gas travels through the exhaust
pipe at about 940 degrees Kelvin. Heat from the exhaust gas begins
to dissipate immediately upon exiting the exit ports 134. Such
dissipation continues after exit, such that the exhaust gas
temperatures drop to less than 600 degrees Kelvin within a distance
of 300 mm of the exit ports 134. (See also the line graph of FIG.
5, described in greater detail above).
[0054] FIGS. 11-13 show temperature section plots at lateral
distances of 150 mm, 300 mm, and 450 mm, respectively, from the
exit plane at the exit ports 134 of the flow diffuser 120. These
section plots show that the hottest cores of the exhaust gas
streams diffuse from an exit temperature of 762.8 degrees Kelvin
(FIG. 11) to 552.4 degrees Kelvin (FIG. 13) within a distance of
300 mm--between the 150 mm lateral distance point (FIG. 11) to the
450 mm lateral distance point (FIG. 13). In addition, by examining
the expanding and cooling cores of the exhaust gas streams in the
series of exit temperature section plots starting at FIG. 11 and
ending at FIG. 13, these section plots indicate that mixing between
the exhaust gas and the surrounding ambient air is occurring to
reduce the temperature of the exhaust gas.
EXAMPLE 3
Exhaust Temperature Section Plots for Standard Exhaust Pipe
[0055] To illustrate the improved fluid mixing achieved with the
flow diffusers 20 and 120 as compared to a standard exhaust pipe,
FIGS. 14 and 15 are exit temperature section plots for an exhaust
pipe taken from a lateral cross-section of the exhaust gas after
exiting the device at lateral distances of 150 mm and 300 mm,
respectively, from the exit plane of the exhaust pipe. Under the
same conditions as the flow diffusers 20 and 120 were subjected to
above with reference to EXAMPLES 1 and 2 and FIGS. 6-13, hot
exhaust gas flows through the exhaust pipe at about 940 degrees
Kelvin. These section plots show that the hottest core of the
exhaust gas diffuses from 922.1 degrees Kelvin (FIG. 14) to only
920.9 degrees Kelvin (FIG. 15) within a distance of 150 mm--between
the 150 mm lateral distance point (FIG. 14) and the 300 mm lateral
distance point (FIG. 15).
[0056] By examining the limited expansion and mixing of the hottest
core of the exhaust gas stream in the series of exit temperature
section plots starting at FIG. 14 and ending at FIG. 15, these
section plots indicate that significantly less mixing between the
exhaust gas and the surrounding ambient air at the barrier is
occurring, as compared to the mixing achieved with the flow
diffusers 20 and 120, described above. Less mixing at the standard
exhaust pipe outlet is a result of the constant velocity of the
exhaust gas at the exhaust pipe inlet and outlet, as well as the
shape factor for a standard exhaust pipe having a circular
cross-section. Although the cross-sectional diameter of the hot
spot decreases in diameter with lateral distance from the exit
port, the hot spot remains a penetrating jet of hot exhaust gas,
even after traveling a lateral distance of 300 mm from the exit
port.
[0057] While illustrative embodiments have been illustrated and
described, it will be appreciated that various changes can be made
therein without departing from the spirit and scope of the
disclosure.
* * * * *