JP6277938B2 - Gas analyzer - Google Patents

Description

  The present invention relates to a gas analyzer that measures specific gas amount information (density / partial pressure / concentration) in a gas by using laser absorption spectroscopy, and more particularly, in a vacuum region, a flue, or a combustion process in a semiconductor manufacturing apparatus. The present invention relates to a gas analyzer that measures specific gas amount information such as inside a measurement target gas (intake and exhaust) of an internal combustion engine (engine), in a flow path of a fuel cell, and a global warming gas.

  Conventionally, in order to measure hydrocarbon (Hydro Carbon) concentration (hereinafter referred to as “component concentration”) contained in exhaust gas from an internal combustion engine such as an engine, the FID (Frame Ionization Detector) method or NDIR (Non-Dispersive Infrared) 2. Description of the Related Art An exhaust gas analyzer using a measurement method called “Red” method is known.

  Further, as one method for measuring the oxygen concentration in a gas, absorption spectroscopy using the fact that oxygen molecules absorb only light in a specific wavelength region (for example, 761 nm) is known. Since this absorption spectroscopy allows non-contact measurement with the measurement target gas, the oxygen concentration in the measurement target gas can be measured without disturbing the measurement target gas field, and the response is extremely short. It can be measured in time.

  Among such absorption spectroscopy, in particular, “tunable wavelength semiconductor laser absorption spectroscopy” using a tunable semiconductor laser (laser element) as a light source can be realized with a simple apparatus configuration. For example, in a gas analyzer using “wavelength tunable semiconductor laser absorption spectroscopy”, an incident optical window and an output optical window formed in a pipe are connected to a pipe in which a measurement target gas flows in a predetermined direction. It is common to add a wavelength tunable semiconductor laser and a light detection sensor (light receiving unit) provided to face each other so that an optical path (optical path length l) is formed across the pipe (for example, Patent Document 1).

According to such a gas analyzer, laser light (measurement light) of a predetermined wavelength oscillated from a wavelength tunable semiconductor laser is laser-shielded by the shielding action of oxygen molecules present in the measurement target gas in the process of passing through the pipe. Light with respect to the amount of laser light oscillated from the wavelength tunable semiconductor laser by utilizing the fact that the amount of light incident on the light detection sensor is reduced corresponding to the concentration of oxygen molecules in the gas to be measured. The concentration of oxygen molecules is calculated by measuring the amount of laser light incident on the detection sensor. FIG. 5 is a graph showing an example of an absorption spectrum obtained by the gas analyzer. The vertical axis is the received light intensity I, and the horizontal axis is the frequency ν. Note that I ₀ (ν) (reference line) is the light reception intensity when oxygen molecules are not absorbed at the frequency ν, and is derived by creating an approximate expression based on the light reception intensity I of the non-absorption wavelength. . In the figure, the solid line represents I ₀ (ν), and the alternate long and short dash line represents I (ν).

  Here, an example of a calculation process using the absorption spectrum shown in FIG. 5 will be described. From Lambert-Beer's law, the following formula (1) holds.

Here, I ₀ (ν) is the light intensity when oxygen molecules are not absorbed at the frequency ν, I (ν) is the transmitted light intensity at the frequency ν, c (mol / cm ³ ) is the number density of oxygen molecules, l (cm) is the length of the optical path passing through the gas to be measured, S (T) (cm ⁻¹ / (mol / cm ⁻² )) is a function of temperature T at a predetermined absorption line intensity, and f (ν) is Absorption profile function.
FIG. 6 is a graph (absorbance curve) in which the vertical axis is −log ₁₀ (I (ν ₀ ) / I ₀ (ν ₀ )) and the horizontal axis is frequency ν.

  At this time, when the total pressure p of the measurement target gas is atmospheric pressure, the absorption profile function f (ν) is represented by the Lorentz profile of the following formula (2).

Note that ν ₀ is the center frequency of the absorption peak, and ν _L is the Lorentz width (full width at half maximum) of the absorption peak.
Substituting equation (2) into equation (1) yields equation (3) below.

Therefore, the transmitted light intensity I (ν ₀ ) at the center frequency ν ₀ is expressed by the following formula (4).

Therefore, if the temperature T and the light intensity changes I (ν) and I ₀ (ν) can be obtained, the number density c of oxygen molecules can be calculated using the equation (4).

Next, FIG. 7 is a schematic configuration diagram showing an example of a gas analyzer using wavelength tunable semiconductor laser absorption spectroscopy. One direction horizontal to the ground is defined as an X direction, a direction horizontal to the ground and perpendicular to the X direction is defined as a Y direction, and a direction perpendicular to the X direction and the Y direction is defined as a Z direction.
The gas analyzer 101 includes a light source unit 10, a light receiving unit 20, a gas temperature sensor 32 that measures a temperature T, and a control unit 140 that includes a microcomputer or a PC.

  Such a gas analyzer 101 is used to measure the number density (specific gas amount information) c of oxygen molecules (specific gas) in the measurement target gas existing in the combustion chamber of the engine (internal combustion engine) 50. The engine 50 includes a cylinder (cylinder) 51, a piston 52 slidable in the Z direction and the -Z direction within the cylinder 51, a crankshaft (not shown) coupled to the piston 52 via a connecting rod 53, ECU60.

The intake port and the exhaust port are formed in the head of the cylinder 51, and the intake port and the exhaust port communicate with the combustion chamber. The intake port is connected to the intake passage 54, and an intake valve 56 for opening and closing the intake port with respect to the combustion chamber is provided between the intake port and the combustion chamber. The exhaust port is connected to the exhaust passage 55, and an exhaust valve 57 for opening and closing the exhaust port with respect to the combustion chamber is provided between the exhaust port and the combustion chamber.
Although not shown, the combustion chamber is provided with an injector for injecting fuel into the combustion chamber, an ignition plug for igniting the air-fuel mixture in the combustion chamber, and the like.

  The ECU 60 is provided in the vicinity of the crankshaft and receives information from various sensors such as a rotation sensor that detects the crank position and crank angular velocity as measurement information, and controls the fuel injection amount and ignition timing of the engine 50.

  According to such an engine 50, an intake process is performed in which intake gas from the intake passage 54 is drawn into the combustion chamber via the intake valve 56 as the piston 52 descends. After the intake process, the intake valve 56 is closed, and a compression process is performed in which the air-fuel mixture in which fuel is injected into the intake air is compressed in the combustion chamber by the rise of the piston 52 that has reached bottom dead center. When the piston 52 rises to near the top dead center, a combustion process is performed by ignition of the air-fuel mixture at a predetermined timing. Then, when the piston 52 lowered by the combustion pressure rises again, the exhaust valve 57 is opened, and an exhaust process is performed in which the combustion gas in the combustion chamber is discharged as exhaust gas through the exhaust valve 57 to the exhaust passage 55. Is called. A series of four processes including the intake process, the compression process, the combustion process, and the exhaust process constitute one cycle.

On the side wall of the cylinder 51, a lens 35 serving as an entrance optical window, and a lens 36 serving as an exit optical window disposed facing the lens (incident optical window) 35 with a distance l in the −X direction. Is formed.
A gas temperature sensor 32 is installed in the combustion chamber, and measures the temperature T of the measurement target gas at predetermined time intervals. As such a gas temperature sensor 32, for example, a thermocouple, a platinum resistance temperature detector, a thermistor, or the like is used.

  The light source unit 10 includes a semiconductor laser (for example, a distributed feedback (DFB) semiconductor laser diode for optical communication) 11, a lens 13, and a D / A converter 12. The laser light from the semiconductor laser 11 enters the combustion chamber in the −X direction from the lens 35 via the lens 13 and the optical fiber 33, and is irradiated to the measurement target gas existing in the combustion chamber. It is like that.

  Further, when such a light source unit 10 is used for continuous monitoring of the number density c of oxygen molecules, PI control is performed so that the temperature of the semiconductor laser 11 becomes a set temperature (constant) by the Peltier module, and the semiconductor laser 11 The drive current value applied to the semiconductor laser 11 is changed at a predetermined cycle. Specifically, by applying a drive current value having a sawtooth shape, laser light having a predetermined wavelength range (sweep width) is supplied at a predetermined cycle. It oscillates from. FIG. 8 is a conceptual diagram showing the relationship between the drive current value and the oscillation wavelength of the laser beam, and FIG. 8A is a waveform diagram of the drive current value applied to the semiconductor laser 11, and FIG. These are waveform diagrams of the oscillation wavelength of laser light oscillated from the semiconductor laser 11 to which the drive current value is applied. The waveform and set temperature of the drive current value as shown in FIG. 8A are input by the user or stored in advance at the start of continuous monitoring, and are output from the control unit 140 to the light source unit 10 as a control signal. It is like that.

The light receiving unit 20 may be anything that can convert light intensity into an electric signal, and for example, a photodiode 21 is used. The photodiode 21 is arranged so as to receive the laser beam emitted from the lens 36 in the −X direction outside the combustion chamber via the optical fiber 34 and the lens 23, and the laser beam that has passed through the measurement target gas. The intensity I (ν) is received. Then, the control unit 140 calculates I ₀ (ν) and I (ν) by acquiring the intensity I (ν) of the laser light from the photodiode 21 via the A / D converter 22 in each cycle. It is like that.

The control unit 140 includes a CPU 141 and a memory (data storage unit) 142. Further, the functions processed by the CPU 141 will be described as a block. The laser control unit 41a that controls the light source unit 10, the acquisition unit 41b that acquires the intensity I _n (ν) of the laser light, and the non-absorption wavelength in each period n A reference line creation unit 41c for creating an intensity change I _0n (ν) by creating an approximate expression based on the intensity I _n (ν) of the laser beam, and a number density using the formula (4) in each period n and a calculation unit 41f for calculating a c _n.

JP 2010-237075 A

However, the gas analyzer 101, such as described above, when calculating the number density c _n of the oxygen gas to be measured in the gas in the combustion chamber, the temperature T and pressure p in the combustion chamber to change dynamically during the cycle As a result, the absorption peak (absorption line) of oxygen gas also changes greatly, and it is difficult to control the drive current value (sweep width) applied to the semiconductor laser 11.

Furthermore, when the absorption line width of the oxygen gas absorption peak widens and decreases, especially when the absorption line width broadens (becomes broader) than the sweep width, the intensity change of the measurement light in the predetermined wavelength range of the nth period In some cases, the intensity change I _0n (ν) cannot be created from I _n (ν). FIG. 9 is a graph showing an example of an absorption spectrum obtained by the gas analyzer 101. The vertical axis is the received light intensity I, and the horizontal axis is the frequency ν. In the figure, the solid line indicates I ₀ (ν), and the alternate long and short dash line indicates I (ν).

The applicant has, when calculating the number density c _n of the oxygen gas to be measured in the gas in the combustion chamber, was studied how to create strength in the n-th cycle change I _0n the _([nu) accurately.
First, in the compression process, there is no gas in and out of the combustion chamber, and even if the gas is compressed, the oxygen gas concentration does not change because all the gas in the combustion chamber is compressed. If the oxygen gas concentration does not change, even if the shape of the absorbance curve changes, the area value D _n of the absorption line changes only with the temperature T.

Next, when the shape of the absorption line is atmospheric pressure or higher, the temperature T immediately after the end of the intake process does not change greatly using the fact that it is governed by the Lorentz function as described above. In a situation where the absorption line is relatively sharp at atmospheric pressure, the area value D _n of the absorption line can be accurately calculated.
Therefore, the absorption line area values D _mn , D _{m (n + 1)} ,... _Are measured after completion of the intake process in the m-th cycle, and the absorption line area values D _mn , D _{m (n + 1)} ,. _Are the reference lines I _0mn (ν), I _{0m (n + 1)} (ν) until they change by about 10% compared to the reference area value (when the compression rate is low and the absorption line is sharp in the first half of the compression process), The average of... Was taken, and the average was used as the reference line for the process in which the absorption line in the latter half of the mth cycle compression process and the combustion process was broad and the reference line I _0n (ν) could not be created.

That is, the gas analyzer of the present invention includes a light source unit having a laser element that irradiates measurement light to a measurement target gas in a cylinder of an internal combustion engine, and a light receiving unit that receives the intensity of the measurement light that has passed through the measurement target gas A laser control unit that oscillates measurement light in a predetermined wavelength range from the laser element at a predetermined period, and an intensity change I _n (ν) of the measurement light in the predetermined wavelength range of the nth period received by the light receiving unit. Then, an intensity change I _0n (ν) of measurement light in a predetermined wavelength range of the nth period when no absorption of the specific gas is received, an absorption peak of the specific gas of the nth period is detected, and the measurement target gas A gas analyzer including a calculation unit that calculates specific gas amount information therein, wherein the internal combustion engine performs an intake process, a compression process, a combustion process, and an exhaust process in a predetermined cycle in this order, After the intake process of the mth cycle Predetermined wavelength range of the period of the measurement light intensity variation _{I mn (ν), I m} (n + 1) (ν), area value of the absorption peak of the specific gas in _{··· D mn, D m (n} + 1), · An area value calculation unit for calculating, and area change amounts ΔD _mn , ΔD _{m (n + 1)} , which are differences between the area values D _mn , D _{m (n + 1)} ,... And the reference area value D _m ′ , _{Are calculated} , and intensity changes I _0mn (ν), I _{0m (n + 1)} (ν), which are created in a period in which the area change amounts ΔD _mn , ΔD _{m (n + 1) ,.} A representative reference line creating unit that creates a representative light intensity change I _0m ′ (ν) of the m-th cycle by averaging , and the arithmetic unit is configured to perform the compression process or the combustion process of the m-th cycle. the (n + a) in the cycle, the (n + a) the intensity change of the predetermined wavelength range of the measurement light cycle I _{n + a) (ν)} and by using the representative light intensity variation I _0m '(ν), and to detect the absorption peak of a specific gas in the (n + a) cycle.

Here, the “predetermined period” is an arbitrary time determined by a measurer or the like. For example, in order to oscillate measurement light in a predetermined wavelength range from the laser element, the frequency becomes, for example, several tens Hz to several tens kHz. Can be mentioned. “A” is a natural number and is a period in which the absorption line becomes broad.
The “predetermined cycle” is an arbitrary time determined by a measurer or the like, and at least three cycles are executed in one cycle.
Further, the “specific gas” is an arbitrary component determined by a measurer, for example, oxygen, water vapor, carbon dioxide, carbon monoxide, or the like.

As described above, according to the gas analyzer of the present invention, the reference line calculated at the time of the most recent intake process or compression process is used even in a situation where the absorption curve is broad and a reference line cannot be created. Thus, the specific gas amount information can be accurately calculated. Further, even easier broad absorption curve buried in the noise, the area value D _mn of absorption lines are dependent on the temperature T, is rapidly by utilizing the fact that no change, in the fitting area value D _mn of absorption lines It can be used as an evaluation parameter.

In the present invention, the representative reference line creation unit includes area change amounts ΔD _mn , ΔD _{m (n + 1)} , which are differences between the area values D _mn , D _{m (n + 1)} ,... And the reference area value D _m ′. _{Are calculated} , and intensity changes I _0mn (ν), I _{0m (n + 1)} (ν), which are created in a period in which the area change amounts ΔD _mn , ΔD _{m (n + 1) ,.} by averaging ..., and so as to create a representative light intensity variation I _0m '(ν).

Here, the “reference area value D _m ′” is an arbitrary value determined by a measurer or the like, for example, an area value D _mn of a cycle n immediately after the end of the intake process.

The schematic block diagram which shows an example of the gas analyzer of this invention. The graph which shows an example of the absorption spectrum obtained with the gas analyzer of FIG. The flowchart explaining the measuring method using the gas analyzer of this invention. The schematic block diagram which shows another example of the gas analyzer of this invention. The graph which shows an example of the absorption spectrum obtained with the general gas analyzer. A graph in which the vertical axis is −log ₁₀ (I (ν ₀ ) / I ₀ (ν ₀ )) and the horizontal axis is frequency ν. The schematic block diagram which shows the gas analyzer by wavelength tunable semiconductor laser absorption spectroscopy. The conceptual diagram which shows the relationship between a drive current value and the oscillation wavelength of a laser beam. The graph which shows an example of the absorption spectrum obtained with the gas analyzer of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention.

FIG. 1 is a schematic configuration diagram showing an example of a gas analyzer of the present invention. Moreover, FIG. 2 is a graph which shows an example of the absorption spectrum obtained with the gas analyzer of this invention. In addition, the same code | symbol is attached | subjected about the thing similar to the conventional gas analyzer 101 mentioned above.
The gas analyzer 1 includes a light source unit 10, a light receiving unit 20, a gas temperature sensor 32 that measures a temperature T, and a control unit 40 that includes a microcomputer or a PC.

The control unit 40 includes a CPU 41 and a memory (data storage unit) 42. Further, the function processed by the CPU 41 will be described as a block. The laser control unit 41a that controls the light source unit 10, the acquisition unit 41b that acquires the intensity I _n (ν) of the laser light, and the non-absorption wavelength in each period n A reference line creation unit 41c that creates an intensity change I _0n (ν) by creating an approximate expression based on the intensity I _n (ν) of the laser beam, and an area value D _n of the absorption peak of oxygen gas are calculated. calculating an area value calculating section 41d, a representative reference line creating unit 41e for creating a representative light intensity variation I _{0 m} of the m cycles' ([nu), the number density c _n using equation (4) in each period n And an arithmetic unit 41f. Further, the memory 42 has an area value storage area 42a for storing the area value D _n and storing the threshold value A (10% of the reference area value).

The area value calculation unit 41d uses the intensity change I _mn (ν) and the intensity change I _0mn (ν) of the measurement light in the predetermined wavelength range of the nth cycle immediately after the end of the m-th cycle intake process, to calculate the nth The oxygen gas absorption peak at the period intensity change I _mn (ν) is detected, and the area value D _mn of the oxygen gas absorption peak is calculated and stored in the area value storage area 42a. In addition, the area value calculation unit 41d performs control to store the area value _Dmn of the nth cycle immediately after the end of the intake process in the mth cycle in the area value storage area 42a as the reference area value _Dm '.

Specifically, first, the intensity change I _mn (ν) of the laser light in a predetermined wavelength range of the nth cycle immediately after the end of the m-th cycle intake process acquired by the acquisition unit 41b, and the reference line creation unit 41c Using the generated intensity change I _0mn (ν), an absorption peak of oxygen gas in the intensity change I _mn (ν) of the laser light in the n-th cycle of the m-th cycle is detected, and the absorption peak of this oxygen gas is detected. The area value D _mn is calculated and stored in the area value storage area 42a. Then, the area value _Dmn of the nth period immediately after the end of the intake process in the mth cycle is stored in the area value storage area 42a as the reference area value _Dm ′. Next, the intensity change I _{m (n + 1)} (ν) of the laser beam in the predetermined wavelength range of the (n + 1) -th cycle of the m-th cycle acquired by the acquisition unit 41 b and the intensity change generated by the reference line creation unit 41 c I _{0m (n + 1)} (ν) is used to detect the absorption peak of the oxygen gas in the intensity change I _{m (n + 1)} (ν) of the laser beam in the (n + 1) period of the m-th cycle. The absorption peak area value _{Dm (n + 1)} is calculated and stored in the area value storage area 42a. In this way, the area values D _mn , D _{m (n + 1)} ,..., D _{(m + 1) n} , D _{(m + 1) (n + 1)} ,... Are calculated and stored in the area value storage area 42a. At the same time, the reference area values D _m ′, D _{(m + 1)} ′,... Are stored in the area value storage area 42a.

In the m-th cycle, the representative reference line creation unit 41e is configured such that area change amounts ΔD _mn , ΔD _{m (n + 1)} , which are differences between the area values D _mn , D _{m (n + 1)} ,... And the reference area value D _m ′. _{Are calculated,} and the intensity change I _0mn (ν), I created in a cycle in which the area change amounts ΔD _mn , ΔD _{m (n + 1)} ,..., ΔD _{m (n + a−1)} are within the threshold A. Control is performed to create the representative light intensity change I _0m ′ (ν) by averaging _{0 m (n + 1)} (ν),..., I _{0m (n + a−1)} (ν).
For example, first, an area change amount ΔD _mn that is a difference between the area value D _mn and the reference area value D _m ′ is calculated, and it is determined whether or not the area change amount ΔD _m is within the threshold A. If the area change amount ΔD _m is within the threshold A, an area change amount ΔD _{m (n + 1)} that is a difference between the area value D _{m (n + 1)} and the reference area value D _m ′ is calculated, and the area change amount is calculated. It is determined whether or not ΔD _m is within the threshold A. In this way, the area change amounts ΔD _mn , ΔD _{m (n + 1)} ,... Are calculated until the area change amount ΔD _{m (n + a)} exceeds the threshold A. Thereafter, intensity changes I _0mn (ν), I _{0m (n + 1)} created at a period of ΔD _mn , ΔD _{m (n + 1)} ,..., ΔD _{m (n + a−1)} within the threshold A. (Ν),..., I _{0m (n + a−1)} (ν) is averaged to create a representative light intensity change I _0m ′ (ν).

The calculation unit 41f uses the intensity change I _mn (ν) and the intensity change I _0m (ν) of the laser light in the predetermined wavelength range of the n-th cycle until the (n + a−1) -th cycle of the m-th cycle. , While detecting the absorption peak of the oxygen gas in the nth period and obtaining the number density c _mn using the equation (4), the laser in the predetermined wavelength range of the nth period from the (n + a) period of the mth cycle The absorption peak of the oxygen gas in the nth period is detected using the light intensity change I _mn (ν) and the representative light intensity change I _0m ′ (ν), and the number density c _mn is calculated using equation (4). To get control.

Here, an example of a method of using the gas analyzer 1 will be described. Figure 3 is a flow chart for explaining a measuring method of measuring the number density c _n.
First, in the process of step S101, the cycle parameter m = 1 (cycle start) and the cycle count parameter n = 1 (intake process start) are set.

Next, in the process of step S <b> 102, the laser control unit 41 a outputs a control signal to the light source unit 10.
Next, in the process of step S103, the acquisition unit 41b acquires the intensity I _mn (ν) of the laser light, and the reference line creation unit 41c is based on the intensity I _mn (ν) of the laser light having a non-absorption wavelength. Thus, the intensity change I _0mn (ν) is created by creating an approximate expression.
Next, in the process of step S104, the computing unit 41f uses the intensity change I _mn (ν) and the intensity change I _0mn (ν) of the laser light in the predetermined wavelength range of the nth period, The absorption peak of oxygen gas is detected, and the number density c _mn is obtained using equation (4).

Next, in the process of step S105, it is determined whether n = 11 (compression process start). If it is determined that n is not 11, the process returns to step S103 after setting n = n + 1 in the process of step S106.
On the other hand, when it is determined that n = 11, in the process of step S107, the acquisition unit 41b acquires the intensity I _mn (ν) of the laser beam, and the reference line generation unit 41c receives the laser beam having a non-absorption wavelength. An intensity change I _0mn (ν) is created by creating an approximate expression on the basis of the intensity I _mn (ν).

Next, in the process of step S108, the calculation unit 41f uses the intensity change I _mn (ν) and the intensity change I _0mn (ν) of the laser beam in the predetermined wavelength range of the nth period to calculate the nth period. The absorption peak of oxygen gas is detected, and the number density c _mn is obtained using equation (4). The area value calculation unit 41d then stores by calculating the area value D _mn of the absorption peak of the oxygen gas to the area value storage area 42a.
Next, in the process of step S109, the representative reference line creation unit 41e calculates an area change amount ΔD _mn that is a difference between the area value D _mn and the reference area value D _m ′.

Next, in the process of step S110, it is determined whether or not ΔD _mn ≦ A. When it is determined that ΔD _mn ≦ A, after setting n = n + 1 in the process of step S111, the process returns to the process of step S107.
On the other hand, when it is determined that ΔD _mn ≦ A is not satisfied, in the process of step S112, the representative reference line creation unit 41e determines that the area change amounts ΔD _mn , ΔD _{m (n + 1)} ,..., ΔD _{m (n + a−1)} By _averaging the intensity changes I _0mn (ν), I _{0m (n + 1)} (ν),..., I _{0m (n + a−1)} (ν) created in a cycle that is within the threshold A, the representative light intensity Create the change I _0mn '(ν).

Next, in the process of step S113, the acquisition unit 41b acquires the intensity I _mn (ν) of the laser light.
Next, in the process of step S114, the calculation unit 41f uses the intensity change I _mn (ν) of the laser light in the predetermined wavelength range of the nth period and the representative light intensity change I _0m ′ (ν) to An absorption peak of oxygen gas having an n period is detected, and the number density c _mn is obtained using the equation (4).

Next, in the process of step S115, it is determined whether n = 31 (exhaust process start). If it is determined that n is not 31, the process returns to step S112 after setting n = n + 1 in the process of step S116.
On the other hand, when it is determined that n = 31, in the process of step S117, the acquisition unit 41b acquires the intensity I _mn (ν) of the laser beam, and the reference line generation unit 41c receives the laser beam having a non-absorption wavelength. An intensity change I _0mn (ν) is created by creating an approximate expression on the basis of the intensity I _mn (ν).

Next, in the processing of step S118, the calculation unit 41f uses the intensity change I _mn (ν) and the intensity change I _0mn (ν) of the laser beam in the predetermined wavelength range of the n-th cycle, The absorption peak of oxygen gas is detected, and the number density c _mn is obtained using equation (4).
Next, in the process of step S119, it is determined whether n = 40 (exhaust process end). If it is determined that n = 40 is not satisfied, in step S120, after n = n + 1, the process returns to step S117.
On the other hand, when it is determined that n = 40, in the process of step S121, after n = 1 and m = m + 1, the process returns to step S103.

As described above, according to the gas analyzer 1 of the present invention, even when the absorption curve is broad and a reference line cannot be created, the reference line calculated at the time of the most recent intake process or compression process is used. it is, it is possible to accurately calculate the number density c _n.

<Other embodiments>
In the gas analyzer 1 described above, on the side wall of the cylinder 51, a lens (incident optical window) 35 and a lens (exit) disposed opposite to the lens (incident optical window) 35 with a distance l in the −X direction. However, instead of this, a lens 35 is formed on the side wall of the cylinder 51, and within the cylinder 51, a distance l / It is good also as a structure in which the reflecting mirror 236 which arrange | positions facing 2 is formed. FIG. 4 is a schematic configuration diagram showing a gas analyzer 1 ′ which is an embodiment in the case where the reflecting mirror 236 is arranged in the gas analyzer 1 of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used for a gas analyzer that measures specific gas amount information in a gas by using laser absorption spectroscopy.

DESCRIPTION OF SYMBOLS 1 Gas analyzer 10 Light source part 11 Laser element 20 Light-receiving part 32 Gas temperature sensor 41a Laser control part 41d Area value calculation part 41e Representative reference line preparation part 41f Calculation part 50 Engine (internal combustion engine)

Claims (1)

A light source unit having a laser element that irradiates measurement light to a measurement target gas in a cylinder of an internal combustion engine;
A light receiving unit that receives the intensity of the measurement light that has passed through the measurement target gas;
A laser controller that oscillates measurement light in a predetermined wavelength range from the laser element at a predetermined period;
Using the intensity change I _n (ν) of the measurement light in the predetermined wavelength range in the nth period received by the light receiving unit, the measurement light in the predetermined wavelength range in the nth period when the specific gas is not absorbed. A gas analyzer comprising: an intensity change I _0n (ν); an absorption peak of a specific gas having an n-th period; and a calculation unit that calculates specific gas amount information in the measurement target gas,
The internal combustion engine performs an intake process, a compression process, a combustion process, and an exhaust process in this order in a predetermined cycle,
Area value D _mn of the absorption peak of a specific gas in intensity change I _mn (ν), I _{m (n + 1)} (ν),... , D _{m (n + 1)} ,...
The area value _{D mn, D m (n +} 1), the area change amount which is the difference between ... and the reference area value _{D m 'ΔD mn, ΔD m} (n + 1), was calculated.., Area change amount [Delta] D _{By averaging} the intensity changes I _0mn (ν), I _{0m (n + 1)} (ν),... created in a cycle in which _mn , ΔD _{m (n + 1) ,.} A representative reference line creation unit for creating a representative light intensity change I _0m ′ (ν) of
In the (n + a) period in the compression process or combustion process of the m-th cycle, the calculation unit calculates the intensity change I _{(n + a)} (ν) of the measurement light in the predetermined wavelength range in the (n + a) period and the representative light intensity change. A gas analyzer characterized by detecting an absorption peak of a specific gas in the (n + a) period using I _0m ′ (ν).

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