•
Technical Field
The present invention relates to a hydrogen flame ionization type exhaust gas
analyzer for measuring a concentration of a measurement target substance contained in the
5 exhaust gas discharged from an internal combustion engine such as an engine of, for example,
a vehicle and the like, or discharged from an external combustion engine such as a steam
turbine.
Background Art
10
As disclosed in Patent Literature I, a hydrogen flame ionization detector (FlO) of
this kind is intended to detect ion current caused at a time of introducing a sample gas such as
exhaust gas into hydrogen flame by a collector electrode to thereby measure a concentration
of hydrocarbon which is a measurement target substance contained in the sample gas based
15 on the ion current detected by the collector electrode. This hydrogen flame ionization
detector is used while it is provided on an exhaust gas flow path in which the exhaust gas
discharged from such as a vehicle.
Since hydrocarbon (for example, THC) contained in the exhaust gas is adhered to
20 and deposited on an inner surface of an exhaust gas flow path incorporating the hydrogen
flame ionization detector, an error component is to be contained in a concentration of
hydrocarbon obtained by the hydrogen flame ionization detector. Therefore, conventionally,
purge gas is supplied to the exhaust gas flow path and the hydrogen flame ionization detector
by a predetermined regular purge process to thereby remove the adhered and deposited
25 hydrocarbon.
2
However, in the case of performing a regular purge process as mentioned above, an
amount of the hydrocarbon adhered to the exhaust gas flow path and the hydrogen flame
ionization detector exceeds a permissible range in some cases even before performing a purge
process. Then, the measurement of a concentration of a measurement target substance is to
5 be performed remaining in a state of being incapable of addressing by such as a correction
until the regular purge process is started.
Meanwhile, there may be a case where an amount of hydrocarbon adhered to the
exhaust gas flow path and the hydrogen flame ionization detector is within a permissible
10 range even without performing the regular purge process. In that case, a purge process of
the exhaust gas flow path and the hydrogen flame ionization detector is to be performed as a
lapse of a predetermined maintenance period, and there arises a problem such that a
measurement should be necessarily stopped due to an unnecessary purge process.
15 Citation List
Patent Literature
Patent Literature 1: JP2007-205968A
e 20 Summary of Invention
Technical Problem
Therefore, the present invention has been made in order to solve the problems at a
stroke and its essential object is to be able to determine an appropriate purge time in a
25 hydrogen flame ionization type exhaust gas analyzer and an exhaust gas analyzing system
incorporating the hydrogen flame ionization type exhaust gas analyzer.
3
Solution to Problem
That is, a hydrogen flame ionization type exhaust gas analyzer according to the
5 present invention is adapted to measure a concentration of a measurement target substance
contained in the exhaust gas based on ion current that is generated upon introduction of the
exhaust gas into hydrogen flame. The hydrogen flame ionization type exhaust gas analyzer
is characterized by including: a collector electrode for capturing ions generated from the
exhaust gas by the hydrogen flame; an acquisition circuit electrically connected to the
10 collector electrode to acquire ion current caused by the ions captured by the collector
electrode; and an abnormality determining part for determining an abnormality in the case
where a difference between, a first output value outputted from the acquisition circuit in the
case where there flows no ion current caused by the exhaust gas to the collector electrode or a
first relevant value obtained from the first output value, and a second output value outputted
15 from the acquisition circuit in the case where gas of a known concentration of a measurement
target substance is introduced into the hydrogen flame or a second relevant value obtained
from the second output value, is equal to or larger than a predetermined value. It is noted
that the phrase "gas of a known concentration of a measurement target substance" implies a
concept including the zero gas which does not contain a measurement target substance in
20 addition to the gas containing a measurement target substance ofa predetermined quantity.
With this configuration, since the abnormality is determined in the case where a
difference between a first output value (or a first relevant value) outputted from the
acquisition circuit in the case where there flows no ion current caused by the exhaust gas to
25 the collector electrode and a second output value (or a second relevant value) outputted from
the acquisition circuit in the case where gas of a known concentration of a measurement
4
target substance is introduced into the hydrogen flame is equal to or larger than a
predetermined value, it becomes possible to determine an appropriate purge time. The first
output value (or first relevant value) outputted from the acquisition circuit in the case where
there flows no ion current caused by the exhaust gas to the collector electrode is, in other
5 words, a constant value irrespective of whether or not a measurement target substance
adheres to the exhaust gas flow path and the hydrogen flame ionization type exhaust gas
analyzer. Meanwhile, the second output value outputted from the acquisition circuit in the
case where gas of a known concentration of a measurement target substance is introduced
into the hydrogen flame is a value that increases in the case where the measurement target
10 substance adheres to the exhaust gas flow path and the hydrogen flame ionization type
exhaust gas analyzer. By taking a difference between these first and second output values, it
becomes possible to determine how much degree of the measurement target substance is
adhered to the exhaust gas flow path and the hydrogen flame ionization type exhaust gas
analyzer, and hence an appropriate purge time can be determined.
15
In this configuration, it is considered that a voltage value obtained by
current-to-voltage conversion of the first output value which is a current value, a digital
signal obtained by AID conversion of the first output value which is an analog signal, a value
obtained by subjecting a predetermined calculation process such as, e.g., a linearity correction e 20 to the first output value, or the like may be available, as the first relevant value. Also, the
second relevant value is the same as the first relevant value.
As the case where there flows no ion current caused by the exhaust gas to the
collector electrode, there may be considered two cases: case (I) where the exhaust gas is not
25 combusted by the hydrogen flame; and case (2) where a closed circuit for rendering current to
flow into the collector electrode is interrupted. That is, it is considered that the first output
5
value is outputted from the acquisition circuit in the case where the exhaust gas is not
combusted by the hydrogen flame or in the case where the closed circuit for rendering the
current to flow into the collector electrode is interrupted.
5 Here, as the case (1) where the exhaust gas is not combusted by the hydrogen flame,
there may be considered two cases: (a) where the hydrogen flame has been turned off; and (b)
where the exhaust gas is not introduced into the hydrogen flame. In the case of acquiring
the first output value in the case (a) where the hydrogen flame has been turned off, it is only
necessary to switch ignition (ON) / extinguishing (OFF) of the hydrogen flame. Also, in the
10 case of acquiring the first output value in the case (b) where the exhaust gas is not introduced
into the hydrogen flame, it is only necessary to switch introduction / stop of the exhaust gas
to the hydrogen flame. Thus, there is no need to make a modification to the conventional
configuration of the system. It is noted that, in the case (b), although there flows no ion
current caused by the exhaust gas, the ion current flows to the collector electrode only by
15 ignition of the hydrogen flame. Therefore, as the first output value, there may be used an
output value in the case where the ion current caused by ignition of the hydrogen flame flows
or may be used a value obtained by subtracting an output component caused by the ignition
ofthe hydrogen flame from the above-mentioned output value.
20 Further, in the case of acquiring the first output value in the case (2) where the
closed circuit for rendering the current to flow into the collector electrode is interrupted, a
switching time can be made faster compared to the case of switching ignition / extinguishing
of the hydrogen flame or switching introduction / stop of the exhaust gas, and it is also
possible to increase a degree of freedom of the switching timing thereof.
25
Furthermore, it is preferable that the hydrogen flame ionization type exhaust gas
6
analyzer includes a purge determining part for determining whether or not a purge output
value obtained by the acquisition circuit in the case where purge gas is rendered to flow into
an exhaust gas introduction path for introducing the exhaust gas into the hydrogen flame to
introduce the purge gas into the hydrogen flame or a relevant value obtained from the purge
5 output value, is smaller than a predetermined reference value. With this configuration, it is
possible to determine appropriate end timing of the purge process. Therefore, by combining
this merit with the above invention, it is possible to determine appropriate purge start timing
and to determine appropriate end timing of the purge process, and hence it becomes possible
to optimize the purge process in the hydrogen flame ionization type exhaust gas analyzer and
10 the system incorporating the analyzer.
Advantageous Effects of Invention
According to the present invention configured as described above, it becomes
15 possible to determine appropriate purge timing in the hydrogen flame ionization type exhaust
gas analyzer and the system incorporating the analyzer.
Brief Description of Drawings
-. 20 Fig. I is a schematic diagram showing a configuration of an exhaust gas analyzing
system including a hydrogen flame ionization type exhaust gas analyzer of the present
embodiment;
Fig. 2 is a schematic diagram showing a configuration of the hydrogen flame
ionization type exhaust gas analyzer of the same embodiment;
25 Fig. 3 is a block diagram showing a functional configuration of a computing device
ofthe same embodiment;
7
Fig. 4 is a flow chart showing a procedure of an abnormality determination and
purge processing ofthe same embodiment;
Fig. 5 is a schematic diagram showing a variation with time of an output value in the
hydrogen flame ionization type exhaust gas analyzer; and
5 Fig. 6 is a schematic diagram showing a configuration of a hydrogen flame
ionization type exhaust gas analyzer of a modified embodiment.
Description of Embodiments
10 The following describes one embodiment of a hydrogen flame ionization type
exhaust gas analyzer according to the present invention with reference to the accompanying
drawings.
As shown in Fig. 1, a hydrogen flame ionization type exhaust gas analyzer 1
15 (referred to as "FID meter 1" hereinafter) of the present embodiment is provided on an
exhaust gas flow path 100 with its one end connected to an introduction port 10I for
introducing exhaust gas exhausted from an engine E. The FlO meter 1 is adapted to
measure a concentration of hydrocarbon which is an organic compound as a measurement
target substance contained in the exhaust gas, based on ion current which is caused upon
20 introduction of the exhaust gas into the hydrogen flame. Further, a filter 102 and a suction
pump 103 etc. are provided on the exhaust gas flow path 100.
Specifically, as shown in Fig. 2, the FID meter 1 includes a combustion chamber
block (chimney) 2 having a combustion chamber S formed inside thereof and a nozzle 3 with
25 its distal end portion provided inside the combustion chamber S for injecting hydrogen flame
F. Further, a combustion gas supply path 4 for supplying the combustion gas to the nozzle 3
8
is connected to a proximal end portion of the nozzle 3. Further, an exhaust gas supply path
5 for supplying the exhaust gas from the exhaust gas flow path 100 together with the
combustion gas to the nozzle 3 is connected to the combustion gas supply path 4. In
addition, the FID meter 1 includes an auxiliary combustion gas supply path 6 for supplying
5 auxiliary combustion gas (i.e., air) to the combustion chamber S.
Moreover, the FID meter 1 includes: a collector electrode 7 which is provided
around the hydrogen flame F inside the combustion chamber S to capture the ions generated
from the exhaust gas by the hydrogen flame F; an acquisition circuit 8 which is electrically
10 connected to the collector electrode 7 to acquire the ion current which is caused upon capture
of the ions by the coIlector electrode 7; and a calculation device 9 which acquires an output
signal ofthe acquisition circuit 8 to calculate a concentration of hydrocarbon contained in the
exhaust gas.
15 The acquisition circuit 8 includes: a lead wire 81 which is connected to the collector
electrode 7; and an amplifier (operational amplifier) 82 which is connected to the lead wire
81 to amplify the ion current flowing through the collector electrode 7 and output the
amplified ion current. In this arrangement, a feedback resistor 83 is connected between a
minus-side input terminal and an output terminal ofthe amplifier 82. e 20
The calculation device 9 is configured of a general purpose or dedicated computer
including a CPU, an internal memory, an input/output interface, an NO converter, a display,
and the like. Specifically, as shown in Fig. 3, the calculation device 9 has a function as a
concentration calculation portion 91 calculating a concentration of hydrocarbon (in specific, a
25 THe concentration) contained in the exhaust gas based on the output signal outputted from
the acquisition circuit 8. It is noted here that a value of the output signal is proportional to
9
the concentration ofthe hydrocarbon contained in the exhaust gas.
Moreover, as shown in Fig. 3, the calculation device 9 has a function as an
abnormality determining part 92 determining whether or not a predetermined amount or more
5 ofthe hydrocarbon is adhered to the exhaust gas flow path 100 provided with the FlO meter I
and to the inside of the FlD meter 1 in an abnormal state. Fig. 4 is a flow chart showing an
example ofa procedure from the abnormality determining process to a purge process.
As shown in Fig. 5, the abnormality determining part 92 determines whether or not a
10 difference (S2 - Si) between, a first output value St outputted from the acquisition circuit 8 in
the case where there flows no ion current caused by the exhaust gas through the collector
electrode 7, and, a second output value S2 outputted from the acquisition circuit 8 in the case
where gas of a known concentration of hydrocarbon (for example, zero gas having a zero
concentration of hydrocarbon) is introduced into the hydrogen flame F, is equal to or larger
15 than a predetermined threshold value A. In specific, the abnormality determining part 92
acquires the output value outputted from the acquisition circuit 8 as the first output value SI
in the case where the exhaust gas is not combusted by the hydrogen flame F, i.e., in the case
where the hydrogen flame F is being off. In the present embodiment, the first output value
St and second output value S2 correspond to current signals (raw data) outputted from the
20 acquisition circuit 8 before correction and before conversion in concentration, respectively.
In this arrangement, the first output value St is, for example, an output value
outputted from the acquisition circuit 8 at a time of shipping products of the FlO meter I or
before starting a first measurement of the FID meter 1, and the first output value SI is a value
25 unique to the amplifier 82 of the acquisition circuit 8 and is a constant value regardless of
whether the hydrocarbon substance is adhered to the exhaust gas flow path 100 or the FlO
10
meter 1. Thus, the first output value 8\ is acquired at a time of shipping products or before
starting a first measurement of the FlO meter 1, and is recorded in a recording part set in such
as an internal memory or the abnormality determining part 92 of the calculation device 9. It
is noted that, although the first output value SI may be sequentially acquired to be recorded,
5 since it is outputted as a constant value in the case where the hydrogen flame F is turned off,
it is sufficient to acquire the first output value S, to be recorded once at a time of shipping
products or before starting a first measurement of the FID meter 1. Moreover, in the case
where the amplifier 82 of the acquisition circuit 8 is replaced due to such as a maintenance
thereof, the first output value S\ is updated to a first output value S\ unique to a substituted
10 new amplifier 82.
In addition, the second output value S2 is an output value which increases in
accordance with increase of an amount of the hydrocarbon adhered to the exhaust gas flow
path 100 and the FID meter 1. In the present embodiment, the second output value S2 is an
15 output value which is outputted from the acquisition circuit 8 in the case where measurement
of exhaust gas is not performed. For example, in the case where a zero calibration, span
calibration and measurement of exhaust gas of the FlO meter I are performed in this order,
the second output value S2 is an output value outputted from the acquisition circuit 8 in a
state that the zero calibration of the FlO meter 1 is under performance. That is, the
e 20 abnormality determining part 92 of the present embodiment does not perform an abnormality
determination at the time of measurement of exhaust gas but performs the abnormality
determination at the time of zero calibration. It is noted that, in the case where an output
value outputted from the acquisition circuit 8 during a measurement of exhaust gas is used as
the second output value S2, the output value acquired during the measurement of exhaust gas
25 results in containing an output component due to the hydrocarbon contained in the exhaust
gas together with an output component due to contamination of such as deposited
11
hydrocarbon other than that, it is impossible to take a correct target value by simply taking a
difference (S2 - S\) between the first output value S\ and the second output value S2. In the
present embodiment, although the second output value S2 is acquired in the case where the
zero gas is rendered to flow at the time of performing the zero calibration of the FlO meter 1,
5 it may be also acquired in the case where the zero gas is rendered to flow without performing
the zero calibration.
Then, in the case where the difference (S2 - S\) between the first output value Sl and
the second output value S2 is equal to or larger than the predetermined threshold value A, the
10 abnormality determining part 92 outputs an abnormality determination signal indicative of
the above abnormal state to an abnormality notification part 93.
This abnormality notification part 93 is configured by the calculation device 9 to be
intended to notify a user that the difference (S2 - S\) is equal to or larger than the
15 predetermined threshold value A, i.e., that a purge process of the exhaust gas flow path 100
and the FlO meter 1 is required to be performed. The abnormality notification part 93 of the
present embodiment is composed of a display control part performing a notification display
on a display of the calculation device 9. Thus, the user can know that it is time to perform a
purge process.
e 20
In this configuration, when the user presses a purge start button by such as seeing the
notification display, a purge start signal receiving part (not shown) receives a purge start
signal to thereby start a purge process by a purge process control part 94 which is configured
by the calculation device 9.
25
More specifically, the purge process control part 94 controls a purge gas mechanism
12
(not shown) which is configured of a purge gas supply path connected to the exhaust gas flow'
path 100, a purge gas pump and the like to thereby supply the purge gas to the exhaust gas
flow path 100 and the FID meter 1.
5 In this purge process, the calculation device 9 has a function as a purge determining
part 95 for appropriately determining purge end timing.
As shown in Fig. 5, in the case where the purge gas is rendered to flow through the
exhaust gas introduction path for introducing the exhaust gas into the hydrogen flame F to
10 thereby introduce the purge gas into the hydrogen flame F, the purge determining part 95
determines whether or not a purge output value Sp acquired from the acquisition circuit 8 is
smaller than a predetermined reference value B. In the case where the purge determining
part 95 determines that a difference (Sp - Si) between the purge output value Sp and the first
output value S, is smaller than the predetermined reference value B, the purge determining
15 part 95 outputs a corresponding determination signal to the purge process control part 94.
Upon acquisition of this determination signal, the purge process control part 94 renders the
purge process to be ended. It is noted that, in the case of strictly determining the purge end,
although it is desirable to compare the difference (Sp - Sl) between the purge output value Sp
and the first output value Si with the predetermined reference value B, it is configured in the
20 present embodiment to simply compare the purge output value Sp with the predetermined
reference value B.
According to the FlO meter I according to the present embodiment configured as
described above, since it is determined whether or not the difference (S2 - SI) between the
25 first output value S, outputted from the acquisition circuit 8 in the case where there flows no
ion current through the collector electrode 7 and the second output value S2 outputted from
13
5
10
the acquisition circuit 8 in the case where zero gas is introduced into the hydrogen flame F, is
equal to or larger than the predetermined threshold value A, it becomes possible to determine
appropriate purge timing.
In addition, the present invention should not be limited to the above embodiment.
For example, although the acquisition circuit outputs the ion current amplified by the
amplifier, the ion current before amplified by the amplifier may be used as the first output
value and the second output value.
In addition, the abnormality determining part may be configured to determine an
abnormality using a voltage value obtained by current-to-voltage converting the first output
value (current value) outputted from the acquisition circuit as a first relevant value and a
voltage value obtained by current-to-voltage converting the second output value (current
15 value) as a second relevant value and taking a difference between the first and second
relevant values to determine the abnormality based on the difference.
Moreover, the abnormality determining part may be configured to determine an
abnormality based on a difference between first and second relevant values before converting
20 to concentrations obtained by subjecting the first and second output values outputted from the
acquisition circuit to a predetermined calculation process such as a correction. Further,
digital values obtained by digitally converting the first and second output values may be used
as the first and second relevant values. In this case, the acquisition circuit includes an AID
conversion circuit.
25
Further, by converting the first output value to a first concentration value which is
14
used as a first relevant value and by converting the second output value to a second
concentration value which is used as a second relevant value, the abnormality determination
may be performed based on a difference between the first relevant value and the second
relevant value.
5
In this configuration, in the case of performing the zero calibration as in the above
embodiment, the second output value S2 is referenced as a zero point. Therefore, with a
configuration capable of setting the first output value SI as a minus concentration, by
converting the first output value S\ to a first concentration value which is used as a first
10 relevant value and by converting the second output value S2 to a second concentration value
which is used as a second relevant value, the abnormality determining part may determine an
abnormality based on the difference between the first relevant value and the second relevant
value.
15 Further, in the present embodiment, although the purge process is started upon
pressing of the purge start button by a user, the purge process may be automatically started in
the case where the abnormality determining part 92 determines an abnormality.
Moreover, in the present embodiment, although the abnormality determining part,
e 20 abnormality notification part, purge process control part and purge determining part are
configured by the calculation device, these functions may be implemented by at least one
control unit other than the calculation device. Also, these functions may be implemented in
either the calculation device or the other control unit.
25 In addition, in the present embodiment, although an output value of the acquisition
circuit 8 is used as the first output value in a state that the hydrogen flame F is being off (OFF
15
time), an output value of the acquisition circuit 8 may be used as the first output value in a
state that the hydrogen flame F is being ignited and the supply of the exhaust gas through the
nozzle is being stopped.
5 Furthermore, as shown in Fig. 6, the output value of the acquisition circuit 8 in the
case where the closed circuit for flowing the current through the collector electrode 7 is
interrupted, may be used as the first output value SI. In specific, it may be considered that,
an on/off switch 84 for interrupting the acquisition circuit 8 is provided in the acquisition
circuit 8 to be a closed circuit and in the case where the on/off switch 84 is opened, the output
10 value ofthe acquisition circuit 8 may be used as the first output value S\.
Further, in the present embodiment, although an output value obtained in the case
where the zero gas having a concentration of hydrocarbon being zero is rendered to flow is
used as the second output value, a value obtained by subtracting an output value caused by
15 hydrocarbon of the known concentration from an output value obtained in the case where gas
containing hydrocarbon of the known concentration is rendered to flow may be used as the
second output value. Further, an output value obtained in the case where the gas containing
the hydrocarbon of a known concentration may be used as the second output value.
e 20 Moreover, the abnormality determining part may be configured to determine an
abnormality without calculating a difference between the first and second output values in the
case where the second output value outputted from the acquisition circuit in the case of
introducing the gas of a known concentration of hydrocarbon into the hydrogen flame or the
second relevant value obtained from the second output value is equal to or larger than a
25 predetermined value. In this case, it may be considered that the predetermined value is set
in consideration ofthe first output value.
16
In addition, the present invention should not be limited to the above embodiment,
and various modifications are of course possible within the scope unless departing from the
intended spirit thereof.
5
Reference Signs List
... Hydrogen flame ionization type exhaust gas analyzer(FlO meter)
F Hydrogen flame
10 7 Collectorelectrode
8 Acquisition circuit
SI First output value
S2 .,. Secondoutput value
92 .,. Abnormality determining part
15 95 Purge determining part
Sp Purge output value
17

CLAIMS
WECLAIM:
1. A hydrogen flame ionization type exhaust gas analyzer (l) adapted to measure a
5 concentration of a measurement target substance contained in the exhaust gas based on ion
current that is generated upon introduction of the exhaust gas into hydrogen flame (F),
characterized by comprising:
a collector electrode (7) for capturing ions generated from the exhaust gas by the
hydrogen flame;
10 an acquisition circuit (8) electrically connected to the collector electrode to acquire
ion current caused by the ions captured by the collector electrode; and
an abnormality determining part (92) for determining an abnormality in the case
where a difference between, a first output value (SI) outputted from the acquisition circuit in
the case where there flows no ion current caused by the exhaust gas to the collector electrode
15 or a first relevant value obtained from the first output value, and a second output value (S2)
outputted from the acquisition circuit in the case where gas of a known concentration of a
measurement target substance is introduced into the hydrogen flame or a second relevant
value obtained from the second output value, is equal to or larger than a predetermined value.
20 2. The hydrogen flame ionization type exhaust gas analyzer as claimed in claim I,
wherein the first output value is outputted from the acquisition circuit in the case where the
exhaust gas is not combusted by the hydrogen flame.
3. The hydrogen flame ionization type exhaust gas analyzer as claimed in claim I,
25 wherein the first output value is outputted from the acquisition circuit in the case where a
closed circuit for supplying current to the collector electrode is interrupted.
18
4. The hydrogen flame ionization type exhaust gas analyzer as claimed in claim 1,
comprising a purge determining part (95) for determining whether or not a purge output value
(S») obtained by the acquisition circuit in the case where purge gas is rendered to flow into an
5 exhaust gas introduction path for introducing the exhaust gas into the hydrogen flame to
introduce the purge gas into the hydrogen flame or a relevant value obtained from the purge
output value is smaller than a predetermined reference value.