JP2994859B2 - Gas temperature measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas temperature measuring method using a laser-induced fluorescence method.

[0002]

2. Description of the Related Art FIG. 3 shows a transition process between energy levels in a laser-induced fluorescence method (hereinafter abbreviated as "LIF"). In the LIF, a wavelength of a laser beam corresponding to a difference in electron energy between gas molecules is selected as incident light, and the gas molecules are excited to a higher electronic level by absorption of the incident light. Following the absorption of the incident light, the gas molecules return to a stable ground level through radiation and collision processes. The light observed at this time is fluorescence.

FIG. 4 shows a configuration of an experimental apparatus for measuring gas temperature using a general LIF. In FIG. 2A, the laser light emitted from the excitation pulse laser 1 is split by the beam splitter 3a, and the two dye lasers 2a and 2b are oscillated and output as laser lights having two different wavelengths. 2
The laser light is oscillated at a fixed time interval (several tens of μS), is aligned coaxially by the beam splitter 3b, is formed into a sheet by the beam expander 4, and is incident on the measurement field. You.

[0004] Fluorescence induced by each laser beam is converted into lenses 5a and 5b as shown in FIG.
And are imaged and measured by the CCD cameras 6a and 6b. At this time, the CCD camera 6a
Since lines 7a and 7b for synchronizing laser oscillation and imaging are provided from the dye laser 2b to the CCD camera 6b, the ratio of the fluorescence intensity measured by the CCD cameras 6a and 6b is obtained. The gas temperature at the measurement site is determined.

[0005]

However, there is a condition that the above experimental apparatus can be applied only in a low pressure field of about 0.1 atm or less.
That is, since the collision process in the LIF is a non-radiative process, it is necessary to quantitatively estimate the process due to the collision in order to measure the temperature using the LIF, but this process exists in the measurement field. This is because it is generally difficult to measure the collision quantitatively because it depends on the chemical species concentration.

There is a saturation fluorescence method as a measuring method for removing the influence of collision, but a laser beam having a very high energy is required, which is not practical. Therefore, it was impossible to measure the gas temperature in a wide temperature and pressure range with the conventional technology.

The present invention has been made in view of the above circumstances, and has as its object to measure a wide temperature and pressure range within the energy range of existing laser light without being affected by collision. It is to provide a possible gas temperature measurement method.

[0008]

That is, the present invention relates to a gas temperature measuring method using an LIF, wherein an upper rotational level excited by a measurement molecule existing in a measurement field is equal to a lower vibration level. Two absorption lines having different wavelengths are selected, and the same two wavelengths of laser light are irradiated at regular time intervals, and the intensity of the fluorescence emitted from the measurement site is measured in synchronization with the irradiation time. The gas temperature of the measurement field is determined by taking the ratio of the intensities.Because the upper electron rotation levels are equal, the effect of the collision on each fluorescent ray becomes the same, and as a result, the relative collision By removing the influence, even within the energy range of the existing laser light, measurement can be performed in a wide temperature and pressure range without being affected by the collision.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. Since the configuration of the experimental apparatus itself is basically the same as that shown in FIG. 4, the same parts are denoted by the same reference numerals and description thereof will be omitted.

FIG. 1 shows the laser-induced process. Two absorption lines having the same upper rotational level excited by the measurement gas molecules existing in the measurement field and different lower vibration levels, for example, 0H 308.97 nm and 314.6
Select 9 nm. Then, laser beams having the same two wavelengths as the selected two absorption lines are irradiated to the measurement field at regular time intervals, and the intensity of fluorescence emitted from the measurement field is measured in synchronization with the irradiation timing.

In this way, since the upper electron rotational levels are equal, the effect of collision on each fluorescent ray is the same, which means that the assignment of emitting fluorescence is equal, and as a result, it is relatively The effect of the collision has been removed. Therefore, the measured 2
If the gas temperature of the measurement field is determined by taking the ratio of the two fluorescence intensities, it is possible to measure over a wide temperature and pressure range without being affected by collisions even within the energy range of the existing laser light. is there.

Further, since different lower vibration levels are used, it is possible to increase the energy difference between the two lower vibration levels to be excited, and to measure the temperature with high accuracy.

FIG. 2 shows the relationship between the ratio of the fluorescence intensity and the temperature. The ratio "B / A" of the fluorescence intensity A of the first laser beam and the fluorescence intensity B of the second laser beam depends on the temperature. Exists, and the temperature is determined by the intensity ratio “B / A”.

By adopting the above-mentioned method, since it is not affected by pressure in principle, it is possible to measure the temperature in a high pressure field. The temperature inside the apparatus or the like can be measured at points or planes.

[0015]

As described above, according to the present invention, the LI
In the gas temperature measurement method using F, two absorption lines having the same upper rotational level of electrons excited by the measurement molecules existing in the measurement field and different lower vibration levels are selected, and the same two absorption lines are selected. Laser light of two wavelengths is irradiated at regular time intervals, the intensity of the fluorescence emitted at the measurement site is measured in synchronization with the irradiation time, and the gas temperature at the measurement site is determined by taking the ratio of the two fluorescence intensities. As a result, since the upper electron rotation levels are equal, the effect of the collision on each fluorescent beam is the same, and as a result, the effect of the collision is relatively eliminated and the effect of the collision is within the energy range of the existing laser beam. It is possible to provide a gas temperature measurement method capable of performing measurement in a wide temperature and pressure range without receiving the gas.

[Brief description of the drawings]

FIG. 1 is a diagram showing a laser induction process according to one embodiment of the present invention.

FIG. 2 is a view showing the relationship between the ratio of the fluorescence intensity and the temperature according to the embodiment.

FIG. 3 is a diagram showing a conventional gas temperature measurement method using an LIF.

FIG. 4 is a diagram showing a configuration of an experimental apparatus for measuring gas temperature using a conventional LIF.

[Explanation of Symbols] 1 ... pulse laser for excitation, 2a, 2b ... dye laser, 3
a, 3b: beam splitter, 4: beam expander, 5a, 5b: lens, 6a, 6b: CCD camera.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-30628 (JP, A) JP-A-53-67481 (JP, A) JP-A-60-107535 (JP, A) JP-A-62 175648 (JP, A) JP-A-64-57720 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01K 11/20

Claims (1)

(57) [Claims] A gas temperature measurement method using a laser-induced fluorescence (LIF) method, wherein two higher-order rotational levels of electrons excited by measurement molecules existing in a measurement field and different lower-order vibration levels are provided. And irradiates the same two wavelengths of laser light at regular time intervals, measures the intensity of the fluorescent light emitted at the measurement site in synchronization with the irradiation time, and takes the ratio of the two fluorescent light intensities. Determining the gas temperature of the measurement site by using the method.