Gas analyzer

Abstract

A gas analyzer is provided, capable of measuring specific gas amount information within a measurement target gas in which pressure varies greatly. The gas analyzer includes a calculation member for calculating specific gas amount information of the nth cycle, a gas pressure change amount calculation unit for calculating an amount of gas pressure change at each time, and a correction signal creation member for generating a time changing, corrected light intensity at each wavelength , by performing a fitting process using the time-changing intensity over a long time period in a time zone in which the amount of gas pressure change is small but using the time-changing intensity over a short time period in a time zone in which the amount of gas pressure change is large. The calculation member generates a light intensity change of the measurement light in the predetermined wavelength range of 1 to 2 of the nth cycle by using the time changing, corrected light intensity at each wavelength , and calculates the specified gas amount information for the nth cycle.

Claims

1. A gas analyzer comprising: a light source member for irradiating measurement light at predetermined time intervals in a predetermined wavelength range of 1 to 2 to a target gas for measurement in an object for measurement; a light receiving member for receiving a light intensity I of the measurement light having passed through the measurement target gas; a calculation member for calculating specific gas amount information in n cycles, using a light intensity change I.sub.n() of the measurement light in the predetermined wavelength range of 1 to 2 of the nth cycle; a pressure sensor for detecting a gas pressure P of the measurement target gas; a gas pressure change amount calculation member for generating a time-changing P(t) of the gas pressure P and for calculating an amount of gas pressure change P(t) at each time t; an acquisition signal generating member for generating a time-changing I.sub.(t) of the light intensity at each wavelength ; and a correction signal creation member for generating a time-changing i.sub.(t) of a corrected light intensity at each wavelength , by performing a fitting process using the time-changing I.sub.(t) over a long time interval in a time zone in which the amount of gas pressure change P(t) is small but using the time-changing I.sub.(t) over a short time interval in a time zone in which the amount of gas pressure change P(t) is large, wherein the calculation member generates a light intensity change i.sub.n() of the measurement light in the predetermined wavelength range of 1 to 2 of the nth cycle by using the time-changing i.sub.(t) of the corrected light intensity at each wavelength , and calculates the specified gas amount information for the nth cycle.

2. The gas analyzer according to claim 1, wherein the light source member comprises: a laser element; and a laser control member for oscillating the measurement light in the predetermined wavelength range 1 to 2 from the laser element at a constant period n.

3. The gas analyzer according to claim 2, wherein the object to be measured includes an internal combustion engine that performs an intake step, a compression step, a combustion step, and an exhaust step in a predetermined cycle.

4. The gas analyzer according to claim 1, wherein the object to be measured includes an internal combustion engine that performs an intake step, a compression step, a combustion step, and an exhaust step in a predetermined cycle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic configuration drawing showing an embodiment of a gas analyzer of the present invention.

(2) FIG. 2 is a graph showing an example of temporal changes in gas pressure and light intensity.

(3) FIG. 3 is a graph showing an example of temporal change of the corrected light intensity superimposed on the graph of FIG. 2.

(4) FIG. 4 is a graph showing an example of an absorption spectrum obtained by a conventional gas analyzer.

(5) FIG. 5 is a schematic configuration drawing showing an example of a gas analyzer using wavelength tunable semiconductor laser absorption spectroscopy.

(6) FIGS. 6a and 6b are conceptual drawings showing relationships between a drive current value and an oscillation wavelength of a laser beam, respectively.

DETAILED DESCRIPTION OF THE INVENTION

(7) Hereinafter, embodiments and examples of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments and examples described below, and appropriate variations, modifications, and additions are included within the scope not deviating from the concept of the present invention.

(8) FIG. 1 is a schematic configuration drawing showing an embodiment of a gas analyzer of the present invention. The same reference numerals are given to the same components as those of the above-described conventional gas analyzer 101. The gas analyzer 1 includes a light source unit 10, a light receiving unit 20, a gas temperature sensor (not shown) for measuring temperature T, a pressure sensor 32 for measuring pressure P, and a control unit 40 in a microcomputer or a PC.

(9) The gas analyzer 1 of the present invention is used for measuring a number density (specific gas quantity information), Cn, of oxygen molecules (specific gas) in the measurement target gas existing in the combustion chamber of an engine 50 (internal combustion engine). The engine 50 includes a cylinder 51, a piston 52 slidable in both the Z direction and the Z direction in the cylinder 51, a crankshaft (not shown) connected to the piston 52 via a connecting rod 53, and an ECU 60 that controls the amount of fuel injection, ignition timing, and so forth.

(10) 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 an intake passage 54, and between the intake port and the combustion chamber, an intake valve 56 for opening and closing the intake port with respect to the combustion chamber is provided. The exhaust port is connected to an 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 abbreviated, the combustion chamber is provided with an injector for injecting fuel into the combustion chamber and a spark plug for igniting an air-fuel mixture in the combustion chamber, and the like.

(11) According to the engine 50, an intake process in which the intake gas from the intake passage 54 is drawn into the combustion chamber via the intake valve 56, is performed together with the descent of the piston 52. After the intake process, the intake valve 56 closes, and the piston 52 reaches the bottom dead center to raise the piston 52 so that the compression process is performed in which the fuel injected into the intake air is compressed in the combustion chamber. When the piston 52 rises to near the top dead center, the combustion process is performed by ignition against the air-fuel mixture at a predetermined timing. When the piston 52 descends because the combustion pressure rises again, the exhaust valve 57 is opened, and the exhaust process is performed in which the combustion gas in the combustion chamber is exhausted to the exhaust passage 55 as exhaust gas via the exhaust valve 57. A series of four processesthe intake process, the compression process, the combustion process, and the exhaust processconstitutes one cycle.

(12) On the side wall of the cylinder 51, there are formed a lens 35 serving as an incident optical window and a lens 36 which is an exit optical window opposed to the lens 35 with a distance 1 in the X direction.

(13) Further, a pressure sensor 32 is installed in the combustion chamber and measures pressure P of the measurement target gas at predetermined time intervals and outputs it to the control unit 40 via the A/D converter 31.

(14) The control unit 40 includes a CPU 41 and a memory 42 (data storage unit). Further, the function to be processed by the CPU 41 will be described in a block form. A laser control unit 41a controls the light source unit 10; a light intensity acquisition unit 41b acquires intensity I of the laser light; a pressure acquisition unit 41c acquires pressure P; a gas pressure change amount calculation unit 41d calculates an amount of gas pressure change P(t); an acquired signal generation unit 41e generates a light intensity, time-changing I(t), at a wavelength ; a correction signal generation unit 41f generates a corrected light intensity, time-changing i(t), at a wavelength ; and a calculation unit 41g calculates a number density Cn for the nth cycle.

(15) The gas pressure change amount calculation unit 41d performs control to create time-changing P(t) of the gas pressure based on the pressure P acquired by the pressure acquisition unit 41c. Then, the gas pressure change amount calculation unit 41d performs control to calculate a gas pressure change P(t) at each time t by differentiating the time changing P(t) of the gas pressure.

(16) The acquired signal creation unit 41e performs control to create time-changing I.sub.(t) of the light intensity at each wavelength in a predetermined wavelength range of 1 to 2. For example, it creates time-changing LAO of the light intensity at the wavelength 1, time-changing I.sub.A(t) of the light intensity at the wavelength A, . . . , and time-changing I.sub.2(t) of the light intensity at the wavelength 2, where 1<A<2.

(17) FIG. 2 shows an example of the time-changing P(t) of the gas pressure created by the gas pressure change amount calculation unit 41d and the time changing I.sub.(t), of the light intensity created by the acquired signal generating unit 41e, shown in parallel. The time-changing I.sub.A(t) of the light intensity at the wavelength A is indicated by solid line, and the time-changing P(t) of the gas pressure is indicated by dotted line.

(18) The correction signal generation unit 41f determines a fitting range W based on the amount of gas pressure change P(t) at each time t and performs a fitting process using the time-changing I.sub.(t) of the light intensity in the fitting range W to perform control to create a time-changing i.sub.(t) of the corrected light intensity at each wavelength . For example, by substituting the amount of gas pressure change P(t) into the following equation (2), the fitting range W1 over the time zone t1 is determined, and then the fitting range W2 over the time zone t2 is determined, and in that manner, the fitting range W over each time zone is determined.
W=/(P(t))+(2)

(19) Here, and are constants.

(20) With respect to the light intensity, the time-changing I.sub.1(t), at the wavelength 1, a fitting process is performed using a quadratic function in the fitting range W1 over the time zone t1, and a fitting process is performed using a quadratic function in the fitting range W2 over the time zone t2 and in that manner, fitting process is performed using each quadratic function in each fitting range W over each time zone t. In this way, time-changing i.sub.1(t) of the corrected light intensity is created.

(21) Also, with respect to the time-changing, I.sub.A(t), of the light intensity at the wavelength A, a fitting process is performed using a quadratic function in the fitting range W1 over the time zone t1, and a fitting process is performed using a quadratic function in the fitting range W2 over the time zone t2, and in that manner, the fitting process is performed using each quadratic function in each fitting range W over each time zone t. Thus, time-changing i.sub.A(t) of the corrected light intensity is created. FIG. 3 is a graph in which an example (dashed line) of the time-changing i.sub.A(t) of the corrected light intensity at the wavelength A is superimposed on the graph of FIG. 2.

(22) In this way, over the time zone in which the amount of gas pressure change P(t) is small, the fitting process is performed with the time-changing I.sub.(t) of the fitting range W over a long time interval, while the time zone in which the amount of gas pressure change P(t) is large, the fitting process is performed with the time-changing I.sub.(t) of the fitting range W over a short time interval, so that the time-changing i.sub.(t) of the corrected light intensity at each wavelength in the predetermined wavelength range of 1 to 2 is created.

(23) The calculation unit 41g creates an intensity change i.sub.0n() by creating an approximate expression based on the intensity i.sub.n() of the laser light of the non-absorptive wavelength in each cycle n, and performs control to calculate the number density Cn of n cycles using equation (1).

(24) As described above, according to the gas analyzer 1 of the present invention, by setting the fitting range, W, and by using the amount of gas pressure change P(t) for counting, the fitting range W related to the periodic change by the influence of the interference noise can be appropriately selected. As a result, the number density Cn can be accurately calculated in the measurement target gas in which the pressure P changes greatly.

OTHER EMBODIMENTS

(25) (1) In the gas analyzer 1 described above, the light source section 10 is provided with the DFB semiconductor laser diode 11, but it can also be a configuration with having a short wavelength laser, a white light source, a super luminescent diode light source or the like.

(26) (2) In the gas analyzer 1 described above, a configuration was indicated where the fitting range W is determined by substituting the amount of gas pressure change P(t) into equation (2), but it is also possible to have a configuration that uses another method with a fitting range over a long time interval in a time zone where the amount of gas pressure change P(t) is small, and with a fitting range over a short time interval in a time zone where the amount of gas pressure change P(t) is large.

(27) (3) In the gas analyzer 1 described above, the fitting process is performed using a quadratic function, but it is also possible to adopt a configuration in which the fitting process is performed using another method.

INDUSTRIAL APPLICABILITY

(28) The present invention can be applied to a gas analyzer or the like for measuring information on specific gas amount in a gas.

EXPLANATION OF SIGN

(29) 1 Gas analyzer 10 Light source section 20 light receiving section 32 Pressure sensor 41 a laser controller 41 d gas pressure change amount calculation unit 41 e Acquisition signal creation unit 41 f correction signal creation unit 41 g calculation unit 50 Engine (Measurement object)