JPH0310908B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention is based on the Doppler frequency change of scattered light generated from a point where two laser beams are incident on a flowing fluid and where these two laser beams intersect. This invention relates to improvements to laser Doppler velocimeters that measure the flow velocity of fluids.

(Prior Art) An outline of a conventional laser Doppler current meter will be explained based on FIG. 3.

The laser Doppler current meter has an optical part 1 and a detection part 1.
3 and a signal processing section 14.

A single laser beam 3 emitted from a laser light source 2 is divided into a laser beam 5 that passes straight through the semi-transparent mirror 4 and a laser beam 6 that is refracted at right angles at a semi-transparent mirror 4. 7
reflected. Laser beam 5 and laser beam 6
are incident on the converging lens 8 in parallel, and the desired flow velocity measurement point 1 of the fluid 9 flowing by the converging lens 8
crossed at 0. Scattered light 11 generated by the intersection of the two laser beams 5 and 6 undergoes a Doppler frequency change due to scattered particles in the fluid 9 flowing at a certain speed at the flow velocity measurement point 10. Scattered light 11 that has undergone this Doppler frequency change
is condensed by a condensing lens 12. The above is the configuration of the optical section 1 of the laser Doppler current meter.

Next, the collected scattered light 11 is photoelectrically converted by the detection section 13, and the electrical signal is processed by the signal processing section 14 to display the flow velocity.

As mentioned above, in the laser Doppler anemometer, 2
It is necessary to intersect the main laser beams at the flow velocity measurement point.

(Problems to be Solved by the Invention) However, when measuring the flow velocity in a flow with a large temperature gradient or density gradient, such as in the combustion chamber of an internal combustion engine, the conventional laser Doppler flow meter described above has problems.
There was a problem with the change in refractive index.

That is, the temperature and density of the combustion gas fluctuate greatly in the flame field, and the refractive index accordingly fluctuates greatly spatially and temporally. Due to this variation in refractive index, the two incident linear laser beams are bent and do not intersect at the flow velocity measurement point, making measurement difficult.

The present invention has been made in view of the above circumstances,
The purpose is to provide a laser Doppler current meter that enables laser beams to intersect reliably near a flow velocity measurement point and to measure flow velocity even in a field where the refractive index of the fluid to be measured varies greatly.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a cylindrical lens is disposed at a position through which one of the two intersecting laser beams passes, and this cylindrical lens Accordingly, the laser beam is spread out in a fan shape and is made incident on the fluid, thereby ensuring that other laser beams intersect with the fan-shaped laser beam.

(Example) An example of the present invention will be described below in Figures 1 and 2.
This will be explained based on the diagram. The measurement target in this embodiment is the combustion gas 9 in the combustion chamber 22 of the internal combustion engine 21.
It is. 23 is a cylinder of the internal combustion engine 21, 24 is a piston, and the cylinder 23 is provided with a window 25 made of tempered glass through which the laser beams 5 and 6 enter and exit.

The laser Doppler current meter has an optical section 1 and a detection section 1.
3 and a signal processing section 14. A single laser beam 3 emitted from a laser light source 2 is divided into a laser beam 5 that passes straight through the semi-transparent mirror 4 and a laser beam 6 that is refracted at right angles at a semi-transparent mirror 4. It is reflected at 7. The laser beam 5 and the laser beam 6 both enter the converging lens 8 in parallel and are made to intersect by the converging lens 8 at a desired flow velocity measurement point 10 of the combustion gas 9 in the combustion chamber 22 of the internal combustion engine 21 .

The configuration up to this point is the same as that of the conventional laser Doppler current meter, and the present invention adds the configuration described below.

The temperature and density of the combustion gas 9 fluctuate due to the influence of the flame, and the refractive index fluctuates greatly both temporally and spatially. The present invention makes it possible to reliably intersect near the flow velocity measurement point 10 even if the refractive index in the optical path of the laser beams 5 and 6 that intersects in this way varies greatly and the course of the laser beams 5 and 6 is bent.

That is, in the present invention, a cylindrical lens 26 is disposed at a position through which one of the two intersecting laser beams 5 and 6 passes, and as shown in FIG. It spreads out and enters the combustion gas 9. Since one of the laser beams 6 is spread in this way, even if there is a fluctuation in the refractive index of the combustion gas 9, the laser beam 5
It becomes possible for the laser beam 6 and the laser beam 6 to intersect reliably near the flow velocity measurement point 10.

Scattered light 11 is generated by the intersection of the two laser beams 5 and 6. Then, the Doppler frequency changes due to scattering particles in the combustion gas 9 flowing at a certain speed at the flow rate measurement point 10. The scattered light 11 that has undergone this Doppler frequency change is transmitted to the condensing lens 1
The light is focused by 2. The above is the configuration of the optical section 1 of the laser Doppler current meter.

Next, the collected scattered light 11 is photoelectrically converted by the detection section 13, and the electrical signal is processed by the signal processing section 14 to display the flow velocity.

It goes without saying that the present invention is not limited to the embodiments described above. For example, the fluid to be measured is not limited to the combustion chamber of an internal combustion engine, but includes all objects in which large fluctuations in refractive index are a problem. Also, the laser beam 5 is spread out in a fan shape, and the other laser beam 6
It also involves measuring the flow velocity at multiple points in a short period of time by shaking the water.

(Effect of the invention) Even if the fluid to be measured has large fluctuations in refractive index, one of the two laser beams spreads out in a fan shape, so it can be ensured that the beams intersect at the flow velocity measurement point, allowing accurate flow velocity. measurement becomes possible.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, and Fig. 2 is a front view showing the measurement of the flow velocity of combustion gas in the combustion chamber of an internal combustion engine. FIG. 3, a plan view schematically showing the main parts, is a schematic diagram of a conventional laser Doppler current meter. 1: Laser Doppler current meter, 5, 6: Laser beam, 9: Fluid (combustion gas), 10: Flow velocity measurement point,
11: Scattered light, 13: Detection section, 14: Signal processing section, 26: Cylindrical lens.

Claims (1)

[Scope of Claims] 1. An optical section 1 that makes two intersecting laser beams 5 and 6 enter a flowing fluid 9 and intersect at a flow velocity measurement point 10, and detects scattered light 11 generated from the flow velocity measurement point 10. The fluid 9
In a laser Doppler current meter that measures the flow velocity of , one of the two intersecting laser beams 5 and 6 is spread into a fan shape at a position where one of the laser beams 6 passes and is made to enter the fluid 9. A laser Doppler current meter characterized by comprising a cylindrical lens 26.