1. TITLE OF THE INVENTION: DILUTION GAS MIXING UNIT AND
10 EXHAUST GAS ANALYSIS SYSTEM
2. APPLICANT
i) Name: HORIBA, Ltd.
ii) Nationality: Japan
15 iii) Address: 2, Miyanohigashi-cho, Kisshoin, Minami-ku, Kyoto-shi, Kyoto
601-8510, Japan
3. PREAMBLE TO THE DESCRIPTION
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
20 INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:
2
Technical Field
[0001]
The present invention relates to a dilution gas mixing unit and an exhaust gas
analysis system.
5 Background Art
[0002]
A conventional exhaust gas analysis system includes an exhaust gas
introduction pipe into which an exhaust gas is introduced, and a dilution gas supply pipe
connected to the exhaust gas introduction pipe to supply a dilution gas (Patent Literature
10 1). With this configuration, the exhaust gas is analyzed by collecting a mixed gas
obtained by diluting the exhaust gas with a dilution gas, collecting the dilution gas, and
for example, subtracting the concentration of a component to be measured contained in
the collected dilution gas from the concentration of the component to be measured
contained in the collected mixed gas as a background value.
15 [0003]
In recent years, the concentration of various components contained in the
exhaust gas has been reduced, and compared to before it is necessary to lower a dilution
ratio in order to ensure the analysis accuracy for the exhaust gas.
[0004]
20 However, when the dilution ratio is lowered in the exhaust gas analysis
system described above, a dilution gas flow rate is lowered. Therefore, for example, in a
case where an exhaust gas flow rate rapidly fluctuates due to the rotation control of an
engine, a problem may occur wherein a part of the diluted exhaust gas (mixed gas)
flows up to the dilution gas supply pipe, and a component contained in the mixed gas
25 affects background measurement.
Citation List
3
Patent Literature
[0005]
Patent Literature 1: JP 2010-139340 A
Summary of Invention
5 Technical Problem
[0006]
Therefore, a main object of the present invention is to reduce the influence of
the blowing-up of the mixed gas on the background measurement even when the
dilution ratio is lowered and the dilution gas flow rate drops.
10 Solution to Problem
[0007]
That is, a dilution gas mixing unit according to the present invention is a
dilution gas mixing unit that is used in an exhaust gas analysis system for analyzing a
mixed gas obtained by diluting an exhaust gas with a dilution gas, and mixes the
15 dilution gas with the exhaust gas, and the dilution gas mixing unit includes: a dilution
gas supply pipe that is connected to an exhaust gas introduction pipe into which the
exhaust gas is introduced, and supplies a dilution gas to the exhaust gas introduction
pipe; a dilution gas sampling unit that is provided in the dilution gas supply pipe and
collects the dilution gas; and a backflow prevention member provided closer to the
20 exhaust gas introduction pipe than the dilution gas sampling unit in the dilution gas
supply pipe to prevent the mixed gas from flowing backward in the dilution gas supply
pipe.
[0008]
According to the dilution gas mixing unit configured as described above,
25 since the backflow prevention member is provided closer to the exhaust gas
introduction pipe than the dilution gas sampling unit in the dilution gas supply pipe,
4
even if a dilution ratio is lowered and a flow rate of the dilution gas drops, and as a
result, part of the mixed gas blows up into the dilution gas supply pipe, the mixed gas
collides with the backflow prevention member and is pushed back by the dilution gas,
and is less likely to flow backward through the dilution gas supply pipe. As a result, it is
5 possible to make it difficult for the blown-up mixed gas to reach the dilution gas
sampling unit, and it is possible to reduce the influence of the mixed gas on the
background measurement.
[0009]
When the mixed gas blows up, the mixed gas tends to flow along an inner
10 peripheral surface of the dilution gas supply pipe. In view of this, it is preferable that the
backflow prevention member includes a through hole through which the dilution gas
passes, and is provided along the inner peripheral surface of the dilution gas supply pipe.
In this case, since the backflow prevention member is provided along the
inner peripheral surface of the dilution gas supply pipe, the blown-up mixed gas can
15 more reliably collide with the backflow prevention member.
[0010]
As a specific aspect of the backflow prevention member, an orifice plate can
be exemplified.
[0011]
20 When the above-mentioned orifice plate with one through hole is used, the
dilution gas passing through the through hole is less likely to go around to a back side of
the orifice plate, and the dilution gas stagnates on the back side. This stagnation is
particularly noticeable when the dilution gas flow rate is in a low flow rate range.
As a result, on a downstream side of the orifice plate, the dilution gas that has
25 passed through the through hole flows without delay in a central part in the dilution gas
supply pipe, while the dilution gas stagnates in the vicinity of the inner peripheral
5
surface in the dilution gas supply pipe, and due to this, the uniformity of an exhaust gas
component contained in the mixed gas is reduced, and consequently the reproducibility
of an analysis result is reduced.
Note that, by expanding the through hole, a region on the back side of the
5 orifice plate is narrowed, and the dilution gas is less likely to stagnate, but in this case,
the backflow prevention effect by the orifice plate is impaired.
[0012]
Therefore, in order to improve the uniformity of the exhaust gas component
contained in the mixed gas while securing the backflow prevention effect, the backflow
10 prevention member is preferably a porous orifice plate provided with a large number of
the through holes.
With such a configuration, since the dilution gas is straightened by a large
number of the through holes, the dilution gas can be caused to flow smoothly on the
downstream side of the porous orifice plate. This makes it possible to improve the
15 uniformity of the exhaust gas component contained in the mixed gas while securing the
backflow prevention effect.
[0013]
As the through hole of the porous orifice plate is made smaller, the flow
velocity of the diluted exhaust gas passing through the through hole increases, so that
20 the backflow prevention effect can be improved, but in the analysis specification in
which the flow rate of the dilution gas is large, a pressure loss may become too large to
use.
Therefore, it is preferable that a plurality of the porous orifice plates are
provided along a flow direction of the dilution gas in the dilution gas supply pipe.
25 In this case, by using the plurality of porous orifice plates having different
through hole sizes, it is possible to appropriately adjust the backflow prevention effect
6
and the pressure loss according to various analysis specifications having different
dilution gas flow rates.
[0014]
As a more specific embodiment, it is preferable that the through holes of the
5 porous orifice plates on the downstream side are smaller than the through holes of the
porous orifice plates on an upstream side.
[0015]
In order to sample the dilution gas flowing toward the through hole of the
backflow prevention member, it is preferable that the dilution gas sampling unit
10 includes an introduction port disposed so as to be positioned in the through hole of the
backflow prevention member as viewed from a pipe axis direction in the dilution gas
supply pipe, or so as to be positioned inside more than half of an inner diameter from a
pipe axis of the dilution gas supply pipe, with the pipe axis being a center.
[0016]
15 The introduction port preferably faces the upstream side of the dilution gas.
In this case, as compared with a case where the introduction port faces, for
example, the downstream side or the side of the dilution gas, it is possible to make it
difficult for the mixed gas in a case where the blow-up occurs to reach the introduction
port while collecting the dilution gas without difficulty.
20 [0017]
Considering the influence on the exhaust gas analysis due to the provision of
the backflow prevention member, the pressure loss of the dilution gas supply pipe
provided with the backflow prevention member is preferably less than 250 Pa.
[0018]
25 Furthermore, an exhaust gas analysis system according to the present
invention includes: a mixed gas flow pipe through which the mixed gas flows; a mixed
7
gas sampling unit that is provided in the mixed gas flow pipe and collects the mixed
gas; a constant flow rate mechanism that sets a flow rate of the mixed gas to a constant
flow rate; a gas analyzer that analyzes a predetermined component to be measured
contained in the collected dilution gas and the collected mixed gas; and a dilution gas
5 mixing unit mentioned above.
Also in the exhaust gas analysis system configured as described above, the
same operational effects as those of the above-described dilution gas mixing unit can be
achieved.
Advantageous Effects of Invention
10 [0019]
According to the present invention configured as described above, even in a
case where the dilution ratio is lowered and the dilution gas flow rate drops, it is
possible to reduce the influence of the blowing-up of the mixed gas on the background
measurement.
15 Brief Description of Drawings
[0020]
FIG. 1 is a schematic diagram illustrating an overall configuration of an
exhaust gas analysis system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of a dilution gas
20 mixing unit of the embodiment.
FIG. 3 is experimental data illustrating an effect of a backflow prevention
member of the embodiment.
FIG. 4 is a schematic diagram illustrating a configuration of a backflow
prevention member of another embodiment.
25 FIG. 5 is a schematic diagram illustrating a configuration of a backflow
prevention member of another embodiment.
8
FIG. 6 is a schematic diagram illustrating a configuration of a backflow
prevention member of another embodiment.
FIG. 7 is a schematic diagram illustrating a configuration of a dilution gas
mixing unit of another embodiment.
5 Reference Signs List
[0021]
100 exhaust gas analysis system
X dilution gas mixing unit
21 exhaust gas introduction pipe
10 3H dilution gas supply pipe
250 dilution gas sampling unit
P introduction port
5 backflow prevention member
5a through hole
15 Description of Embodiments
[0022]
Hereinafter, an embodiment of an exhaust gas analysis system using a dilution
gas mixing unit according to the present invention will be described with reference to
the drawings.
20 [0023]
An exhaust gas analysis system 100 according to the present embodiment is
of a dilution sampling type, and dilutes an exhaust gas collected from a test vehicle 200
with dilution air as a dilution gas to perform concentration measurement. Hereinafter, in
the present embodiment, an exhaust gas analysis system with a constant volume dilution
25 sampling method will be described in which an entire amount of exhaust gas is sampled
and diluted with dilution air to have a constant known flow rate.
9
Note that examples of the test vehicle 200 include an engine vehicle, a hybrid
vehicle, and a fuel cell vehicle.
[0024]
Specifically, as illustrated in FIG. 1, this includes a constant volume sampling
5 device 2 that introduces the entire amount of exhaust gas and dilution air into the device,
controls a total flow rate of the exhaust gas and the dilution air so as to be constant, and
collects a part of the diluted exhaust gas (hereinafter, it is referred to as a mixed gas.) in
a collection bag at a constant flow rate, a dilution air purification device 3 that removes
impurities in the atmosphere and supplies the purified dilution air to the constant
10 volume sampling device 2, and a gas analyzer 4 that analyzes the concentration of a
predetermined component (for example, HC, CO, H2O, N2O, or the like) in the mixed
gas collected by the collection bag of the constant volume sampling device 2.
[0025]
The constant volume sampling device 2 includes an exhaust gas introduction
15 pipe 21 connected to an exhaust pipe 200H of the test vehicle 200 mounted on a chassis
dynamometer 300, a dilution gas supply pipe 3H connected to the exhaust gas
introduction pipe 21 and supplying a dilution gas, a mixed gas flow pipe 23 provided
with a constant flow rate mechanism 231 for setting a flow rate of the mixed gas to a
constant flow rate, a mixed gas collection line 24 for collecting the mixed gas flowing
20 through the mixed gas flow pipe 23, and a dilution gas collection line 25 for collecting
dilution air flowing through the dilution gas supply pipe 3H. Furthermore, a cyclone 22
for removing dust contained in the mixed gas may be provided downstream of the
exhaust gas introduction pipe 21. Note that the constant volume sampling device 2 does
not necessarily sample the exhaust gas of the test vehicle 200 mounted on the chassis
25 dynamometer 3, and may sample, for example, an exhaust gas from an engine
connected to an engine dynamometer or an exhaust gas from a power train connected to
10
one or a plurality of dynamometers.
[0026]
The constant flow rate mechanism 231 includes a Venturi tube 231a provided
on the mixed gas flow pipe 23 and a turboblower 231b provided downstream of the
5 Venturi tube 231a.
[0027]
The mixed gas collection line 24 includes a mixed gas sampling unit 240 in
the mixed gas flow pipe 23, a mixed gas collection pipe 241 having one end connected
to the mixed gas sampling unit, a mixed gas collection pump 242 provided on the mixed
10 gas collection pipe 241, and a mixed gas bag 243 that stores the mixed gas collected by
the mixed gas collection pump 242. Note that the mixed gas collection pipe 241 is
provided on an upstream side of the constant flow rate mechanism 231.
[0028]
Furthermore, the dilution gas collection line 25 includes a dilution gas
15 sampling unit 250 provided in the dilution gas supply pipe 3H, a dilution gas collection
pipe 251 connected to the dilution gas sampling unit 250, a dilution gas collection pump
252 provided on the dilution gas collection pipe 251, and a dilution gas bag 253 that
stores dilution air collected by the dilution gas collection pump 252.
[0029]
20 Then, so-called bag measurement is performed by the gas analyzer 4 using the
mixed gas bag 243 of the mixed gas collection line 24 and the dilution gas bag 253 of
the dilution gas collection line 25.
[0030]
The dilution air purification device 3 purifies dilution air from the atmosphere,
25 and removes at least any of CO, HC, NOx, and N2O in the dilution air in order to
stabilize a low concentration of a background in exhaust gas analysis. Furthermore, in
11
the dilution air purification device 3, a method of removing CO, HC, NO, N2O, and the
like is to convert CO, HC, NO, and N2O in the dilution air into CO2, H2O, N2, and NO2,
and to adsorb NO2 generated by oxidation of NO and N2O with an NOX adsorbent.
[0031]
5 Here, the exhaust gas analysis system 100 of the present embodiment has a
feature in a region surrounded by a broken line in FIG. 1, and specifically has a feature
in a dilution gas mixing unit X in which the exhaust gas and the dilution gas are mixed.
Therefore, this dilution gas mixing unit will be described in detail below.
[0032]
10 As illustrated in FIGS. 1 and 2, the dilution gas mixing unit X of the present
embodiment includes at least the above-mentioned dilution gas supply pipe 3H and the
dilution gas sampling unit 250 provided in the dilution gas supply pipe 3H, and also
includes at least a part of the exhaust gas introduction pipe 21.
[0033]
15 The dilution gas sampling unit 250 of the present embodiment is provided in
the dilution gas supply pipe 3H and has an introduction port P facing an upstream side
of the dilution gas.
[0034]
More specifically, the introduction port P is disposed such that a pipe axis L of
20 the dilution gas supply pipe 3H passes through the introduction port. Here, the
introduction port is disposed such that the pipe axis L passes through a center of the
introduction port P or the vicinity thereof.
[0035]
Furthermore, the introduction port P of this embodiment is provided at a
25 position closer to an upstream opening 3Ha of the dilution gas supply pipe 3H than the
exhaust gas introduction pipe 21 in a pipe axis direction of the dilution gas supply pipe
12
3H.
[0036]
Note that the introduction port P mentioned above may face a downstream
side of the dilution gas, may face a side (a radial direction of the dilution gas supply
5 pipe 3H), or may be provided at a position closer to the exhaust gas introduction pipe 21
than the upstream opening 3Ha of the dilution gas supply pipe 3H.
[0037]
However, the dilution gas mixing unit X further includes a backflow
prevention member 5 provided closer to the exhaust gas introduction pipe 21 than the
10 dilution gas sampling unit 250 in the dilution gas supply pipe 3H to prevent the mixed
gas from flowing backward through the dilution gas supply pipe 3H.
[0038]
The backflow prevention member 5 has a through hole 5a through which the
dilution gas passes. The backflow prevention member 5 of the present embodiment is,
15 for example, an annular member having a flat plate shape, and is specifically an orifice
plate. In this embodiment, the introduction port P of the dilution gas sampling unit 200
mentioned above is disposed inside the through hole 5a of the backflow prevention
member 5. Note that a size of the through hole 5a is such that a pressure loss of the
dilution gas flowing through the dilution gas supply pipe 3H does not affect the analysis
20 accuracy of the exhaust gas analysis, and specifically, the pressure loss in the dilution
gas supply pipe 3H provided with the backflow prevention member 5 is less than 250 Pa.
[0039]
The backflow prevention member 5 is provided along an inner peripheral
surface of the dilution gas supply pipe 3H, in other words, at least a part of an outer
25 peripheral surface of the backflow prevention member 5 is in contact with at least a part
of the inner peripheral surface of the dilution gas supply pipe 3H.

WE CLAIM:
1. A dilution gas mixing unit used in an exhaust gas analysis system that
analyzes a mixed gas obtained by diluting an exhaust gas with a dilution gas, the
5 dilution gas mixing unit mixing the dilution gas with the exhaust gas, the dilution gas
mixing unit comprising:
a dilution gas supply pipe connected to an exhaust gas introduction pipe into
which the exhaust gas is introduced, the dilution gas supply pipe supplying a dilution
gas to the exhaust gas introduction pipe;
10 a dilution gas sampling unit that is provided in the dilution gas supply pipe
and collects the dilution gas; and
a backflow prevention member provided closer to the exhaust gas
introduction pipe than the dilution gas sampling unit in the dilution gas supply pipe to
prevent the mixed gas from flowing back in the dilution gas supply pipe.
15 2. The dilution gas mixing unit as claimed in claim 1, wherein the backflow
prevention member includes a through hole through which the dilution gas passes, and
is provided along an inner peripheral surface of the dilution gas supply pipe.
3. The dilution gas mixing unit as claimed in claim 1 or 2, wherein the backflow
prevention member is an orifice plate.
20 4. The dilution gas mixing unit as claimed in claim 2 or 3, wherein the backflow
prevention member is a porous orifice plate provided with a large number of the through
holes.
5. The dilution gas mixing unit as claimed in claim 4, wherein a plurality of the
porous orifice plates are provided along a flow direction of the dilution gas in the
25 dilution gas supply pipe.
6. The dilution gas mixing unit as claimed in claim 5, wherein the through holes
21
of the porous orifice plates on a downstream side are smaller than the through holes of
the porous orifice plates on an upstream side.
7. The dilution gas mixing unit as claimed in any one of claims 2 to 6, wherein
the dilution gas sampling unit includes an introduction port disposed so as to be
5 positioned in the through hole of the backflow prevention member as viewed from a
pipe axis direction in the dilution gas supply pipe, or so as to be positioned inside more
than half of an inner diameter from a pipe axis of the diluent gas supply pipe, with the
pipe axis being a center.
8. The dilution gas mixing unit as claimed in claim 7, wherein the introduction
10 port faces the upstream side of the dilution gas.
9. The dilution gas mixing unit as claimed in any one of claims 1 to 8, wherein a
pressure loss of the dilution gas supply pipe provided with the backflow prevention
member is less than 250 Pa.
10. An exhaust gas analysis system comprising:
15 a mixed gas flow pipe through which the mixed gas flows;
a mixed gas sampling unit that is provided in the mixed gas flow pipe and
collects the mixed gas;
a constant flow rate mechanism that sets a flow rate of the mixed gas to a
constant flow rate;
20 a gas analyzer that analyzes a predetermined component to be measured
contained in the collected dilution gas and the collected mixed gas; and
a dilution gas mixing unit according to any one of 1 to 9.