JPH0894526A - Method for measuring soot concentration - Google Patents

Abstract

PURPOSE: To provide a method for measuring the concentration of soot by a technique employing laser induced incandescence. CONSTITUTION: A beam-emitting part provided at one end of a measuring chamber illuminates a soot formation field with a pulse laser sheet beam 10 to raise the temperature of soot to near its evaporation point, a high-speed shutter camera 14 provided at the other end of the measuring chamber in such a way as to cross the direction of application of the pulse laser sheet beam 10 receives incandescence which the soot particles radiate, and the intensity of the pulse laser sheet beam 10 is in the range from 150 to 400MW/cm<2> , so that through the detection of the radiation the concentration of the soot is measured with high accuracy and efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soot concentration measuring method for efficiently and highly accurately measuring the concentration of soot in a soot generation field.

[0002]

2. Description of the Related Art As environmental problems have increased in recent years, reduction of nitrogen oxides (NOx) and particulate matter (PM) has been strongly demanded for diesel engines, for example. There is an urgent need to suppress the formation of soot, which is the main component of this particulate matter. In order to develop this soot reduction technology, information on phenomena relating to the generation and oxidation process of soot in the cylinder of a diesel engine is extremely useful. But in the non-stationary
In addition, it is very difficult to measure the soot distribution in a cylinder that has a complicated distribution.

Under such a circumstance, laser measurement such as the scattering method or the transmitted light attenuation method has hitherto been capable of instantaneously measuring high-resolution and wide-area soot distribution without disturbing the measurement field [("laser Study on Soot Formation in Unsteady Free Spray Flame by Sheet Scattering Method "
Ed.), 57, 543, No. 91-0639A (19
91). “Study on the structure of unsteady spray flame and soot formation by analysis of two-dimensional soot scattered light image”, Proc. 90-07
07A (1990). "Observation of Combustion in Direct Injection Diesel Engine by Laser Sheet Method", Proc. Of the 9th Joint Symposium of Internal Combustion Engine, 229. (1991).
SAE paper 831291 (1983). ]

However, in the conventional scattering method, since scattered light (laser sheet) is proportional to the sixth power of the particle diameter, only soot with a large particle diameter can be detected, but soot with a small particle diameter cannot be measured, and At the same time, there is a problem to be solved practically that an extra signal is generated from the droplets of the fuel contained at the same time, reflection from the wall surface, etc., and the S / N is bad. In addition, the conventional transmitted light attenuation method has a problem to be solved in practical use that the soot concentration distribution cannot be measured because only the integrated information in the optical path direction is used.

On the other hand, recently, a laser-induced incandescent method (hereinafter referred to as LII method) is known in which radiant heat obtained by irradiating soot particles with intense laser light is detected to measure soot distribution. This attracts attention because it has many advantages compared to other laser measurement methods.
SAE paper 831291 (1983). SAE Paper 920114 (1992). SAE paper 92
0115 (1992). SAE paper 932650
(1993). ]

These irradiate the soot particles with a powerful pulsed laser sheet and change the temperature of the particles to the soot evaporation temperature (about 45 ° C.).
The incandescent light (blackbody radiation) emitted by soot particles at this time is photographed with an ultra-high-speed shutter camera to visualize the volume concentration of soot particles in the laser sheet surface. This method is excellent in that a cross-sectional image can be obtained, that the signal intensity is almost proportional to the soot concentration, that it is not affected by fuel droplets, and that it is not affected by scattered light from the wall surface, etc. There is. On the other hand, the soot particles partially evaporate, so that repeated measurement in the same cycle is impossible, and the signal intensity is weak, so that it is easily affected by soot in the optical path.

When quantifying the soot concentration,
There are the following issues. (1) Correction of non-uniform laser intensity distribution (2) Correction of attenuation of laser intensity by soot cloud (3) Clarification of relationship between soot concentration and laser-induced incandescent signal (hereinafter referred to as LII signal) (4) Soot Correction of Attenuation of LII Signal Due to Cloud Also, there is no example of measuring the soot particle size in the above LII method, and empirically suggesting the saturation property of the LII signal, but the threshold value of the laser intensity at this time is obtained. Moreover, there are no examples confirmed by numerical simulation or the like.

By the way, in a diesel engine in which fuel is directly injected into a cylinder and burned, fuel droplets are unevenly distributed, resulting in a region where the fuel vapor concentration is high. for that reason,
It is considered that very high concentration of soot is locally present. Under such conditions, the application of the LII method to the quantitative measurement of the soot concentration in the cylinder of a diesel engine was earnestly studied. However, in the quantitative measurement of the soot concentration in the cylinder of a diesel engine, (2) the attenuation of the laser intensity by the soot of the incident laser light and (4) the attenuation of the LII signal by the soot existing between the measurement surface and the camera are performed. Has been found to be a big problem in practical use.

[0009]

Therefore, the inventors of the present invention have diligently studied, and in order to quantitatively measure the soot concentration, the obtained LII signal should be appropriately corrected with respect to the above (2) and (4). We have found that we need to do it. Then, the LII method was applied to a steady soot generation field having the same level of concentration as in the cylinder of a diesel engine, and the present invention was devised by conducting many studies and analyzes of attenuation correction methods for laser light and LII signals. The present invention has been made to solve the problems of the prior art, and to accurately and easily measure the soot concentration and the particle size of soot by accurately irradiating the soot generation field with laser sheet light. It is an object of the present invention to provide a soot concentration measuring method capable of producing a soot.

[0010]

The soot concentration measuring method of the present invention is such that a light emitting section provided at one end of a measurement chamber irradiates a pulse laser sheet on a soot generation field in the measurement chamber to raise the soot temperature to near an evaporation point. In addition, the incandescent light emitted by the soot particles in the soot generation field is received by the light receiving unit provided at the other end of the measurement chamber so as to intersect the pulse laser sheet irradiation direction of the light emitting unit, and the pulse laser It is characterized in that the soot concentration is measured by setting the strength of the sheet in the range of 150 MW / cm ² to 400 MW / cm ² and detecting the radiation intensity.

Further, the soot concentration measuring method of the present invention detects incandescent light signals of two or more different wavelengths which are dependent on the particle diameter of soot particles radiated by the detection unit and calculates the ratio of radiation intensity. It is characterized in that the particle diameter of soot is determined by the ratio to correct the attenuation of the signal light and the soot concentration is measured.

[0012]

According to the soot concentration measuring method (claim 1) of the present invention having the above-mentioned constitution, the temperature of soot particles rapidly rises with the irradiation of the pulse laser sheet from the light emitting part to the soot generation field. However, incandescent light is emitted. After a while,
Incandescent light decreases as the soot particles begin to evaporate and the particle size decreases. Then, the light receiving portion provided to intersect the irradiation direction of the pulsed laser sheet of the light emitting portion receives the incandescent light radiated by soot particles and measures the soot concentration efficiently and highly accurately by detecting the radiation intensity. can do.

Here, the simulation result of the change of the LII signal when the intensity of the pulsed laser sheet (hereinafter referred to as the laser intensity) is changed is shown in FIG. 1, and the experimental result is shown in FIG. When the laser intensity is relatively low, the LII signal increases as the laser intensity increases. This is mainly due to the temperature rise of the particles. When the laser intensity becomes higher, LI
The I signal saturates and eventually diminishes. This is because the particle size decreases due to the evaporation of soot despite the temperature rise of the particles, and the radiated light decreases together with the decrease in the absorption coefficient (FIG. 2). Due to such characteristics, the problems (2) and (4) can be solved. That is, the laser intensity is 150 MW / cm ² to 400 MW / cm ²
Is preferred.

As described above, when the laser intensity is, for example, 40 nm, if 400 MW / cm ² is used, the intensity at the peripheral portion of the laser sheet is reduced (150 M).
Even with W / cm ² ), the signal strength can be kept at the same level as the central part. Similarly, a laser that has been attenuated to some extent by soot clouds can also obtain a signal at the same level as before attenuation. As shown in FIG. 3, when a laser having an energy density of 344 MW / cm ² is used and the soot concentration is 10 ⁻⁵ g / cm ³ or less, a signal of 95% of the maximum intensity is obtained within an optical path length of 3.7 cm. Is obtained. This is an important advantage in measurement.For example, in the case of a signal having a characteristic proportional to the laser intensity such as the Mie scattering method, the effects of the laser intensity distribution and laser attenuation on the signal light must be corrected. However, when a signal light that is hardly affected by the laser intensity can be obtained like LII, these corrections become unnecessary, and the practically excellent effect that quantitative measurement of soot concentration can be performed efficiently and with high accuracy. Play.

Further, in the soot concentration measuring method of the present invention having the above-mentioned structure (claim 2), the incandescent light signal of two or more different wavelengths depending on the particle diameter of soot particles radiated is detected by the detecting section. The soot particle diameter is determined by the ratio of the radiant intensities, the attenuation of the signal light is corrected, and the soot concentration can be measured efficiently and highly accurately.

Here, FIG. 5 shows the change of the LII signal when the particle size is greatly changed. The LII signal increases as the particle size increases even at a constant concentration. Therefore, when the particle size changes greatly, particle size information is necessary to detect the concentration. The cause of the change in signal intensity is mainly the temperature change of the particles, as shown in FIG. Focusing on the fact that the wavelength distribution of blackbody radiation changes due to this temperature change, we examined whether or not information on the particle size could be obtained by taking the ratio of signal lights of two or more wavelengths. FIG. 6 shows the change in the ratio of the two wavelengths depending on the particle size. The particle size can be detected by selecting an appropriate wavelength within the range where the particle size is not too large.

Further, in FIG. 7, L when the particle size changes greatly
11 shows changes in the attenuation coefficient of the II signal. The attenuation coefficient changes depending on the particle size even at a constant concentration. This is mainly due to the change in the Mie damping coefficient due to the change in particle size. Even when performing multi-layer measurement for attenuation correction, if the soot particle size changes significantly, particle size information is necessary in addition to soot concentration information. Multicolor LII is also very effective in obtaining this information.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 8 and 9, the soot concentration measuring method of the present embodiment uses LI in the production field formed by the rich premix burner 1.
This is an example in which method I is applied. The main structure of the burner 1 is shown in FIG. Pressurized with nitrogen cylinder (gauge pressure 2.2 at)
m) The liquid fuel, benzene, is sealed in the tank and pumped. It is injected intermittently by an electronic fuel injection valve and evaporated by a micro heater installed inside the burner 1.
Further, the ribbon heater is configured to heat the burner wall to prevent the fuel droplets from adhering to the wall surface and preventing pseudo shrinkage. Then, the air heated up to about 450 degrees by the flame torch is introduced from two points on the bottom surface of the burner and mixed with the vaporized benzene. Due to such heating of the wall surface and the mixed air, the temperature of the premixed gas at the outlet of the burner 1 becomes about 180 degrees, so it is considered that the benzene fuel is completely vaporized (benzene boiling point: 80.1 degrees). ). In addition, a butane-air premixed flame is formed around the burner 1 to keep the benzene flame warm and stable. The soot concentration is changed by controlling the fuel injection amount (the number of injections of the fuel injection valve, the injection timing). The burner 1 is composed of a fuel, an air introduction part 2, a mixing part, a bead part, a honeycomb part 3 and an outer peripheral part 4.

The flame 11 is formed by inserting and arranging the wire mesh 5 behind the flame 11 in order to stabilize the flame 11. Further, in this embodiment, in order to suppress the entrainment of the surrounding air, the flame 1 is formed by the donut-shaped ring 6 having the same inner diameter as that of the flame 11.
With the configuration that surrounds 1, it is possible to realize further flame stabilization. This flame 11 emits a strong luminous flame,
A high concentration of soot is produced. In the measurement by the sheath type thermocouple (platinum-platinum rhodium, sheath diameter 1 mm), the temperature of the flame 11 is about 1400 [K] on the central axis.
The apparatus shown in Fig. 8 forms a soot generation field and uses the transmitted light attenuation method and C
T was combined to measure the concentration distribution of this production field. This distribution becomes Equations 1 and 2 when approximated by a plurality of straight lines.

[0020]

[Equation 1]

[0021]

[Equation 2]

Here, τ is 3. from the tip surface of the burner 1.
Laser light (10 mm) passing through the center of the burner 1 at a height of 3 mm.
64 nm). Therefore, the soot concentration distribution can be immediately calculated only by measuring the transmittance τ at this position. In this way, the present embodiment is configured by applying the LII method to the soot generation field whose concentration is already known. An outline of the LII device is shown in FIG. As the light source, the second harmonic of the Nd: YAG laser (wavelength: 532n
m). The laser beam 7 is formed by a cylindrical lens 8 and a convex lens 9 into a laser sheet light 10 having a width of 9.5 mm and a focal length of 0.5 mm. Further, this laser sheet light 10 has a slit 12 and a width of 2 mm.
The surface of which the soot concentration distribution was measured by the light rays of. Here, when the laser sheet light 10 is applied to the soot generation field as it is, the LII emission increases due to the particle size increase due to the aggregation of soot particles downstream of the flame 11, and the dynamic range at the measurement target position decreases. To do. Therefore, the slit 12 is used to narrow the laser width. And
The LII light 13 emitted from the soot is photographed by the high-speed shutter camera 14 from the direction perpendicular to the laser surface. Here, the shutter time is 20 [nsec] which is the shortest. In addition, the scattered light is removed and the S / N ratio to the bright flame light is increased.
In order to detect the LII light 13 on the short wavelength side where the ratio is improved,
2 full width at half maximum using two short wave pass filters
Signal light of 80 to 370 [nm] could be obtained. In the figure, reference numeral 15 is a detection unit.

Then, in this embodiment, a laser beam having various intensities was applied to a field where the soot concentration was fixed, and LII was irradiated.
Measure the change in light intensity. The laser intensity can be changed by the applied voltage of the oscillator (amplifier stage) of the laser. The LII signal intensity increased with the laser intensity, but at 150 MW / cm ² or more, the change in the LII signal was small and saturation was observed. Therefore, 150 MW / cm
It has been found that if an intensity of ² or more is ensured on the laser surface, no correction of the LII signal due to laser attenuation is necessary. In addition, by the numerical simulation of LII,
The change in the intensity of the LII signal was investigated. As a result, the soot temperature increases monotonically with the laser intensity, whereas the LI
The I signal has the same saturation as the experiment. It is speculated that when the laser light is too intense, the mass of soot that evaporates instantaneously increases, and the total soot particle surface area decreases, so that the emission amount of the LII signal decreases.

According to Lambert-Beer's law, the transmittance of the laser light with which the soot generation field is irradiated is given by Formula 3. By applying this, the signal attenuation correction is performed.

[0025]

[Equation 3]

However, I: signal intensity after being attenuated, IO: original signal intensity, D: particle size, Qext: efficiency factor, N: particle number density, 1: optical path length, c: constant, Cs : Since Qext / D in the soot concentration number 3 depends on the particle size D,
For correction, the particle size distribution of soot generation field is required.

In this embodiment, a soot generation field having a uniform distribution with a diameter of 100 nm (Qext = 0.65 at this time) and a thickness of 1 cm is assumed, and a laser beam (5
The transmittance at 32 nm) was calculated from Equation 3. However, Qex due to increase in soot temperature due to laser energy absorption
Changes in t and changes in particle size are not considered. Since the maximum energy density of the laser used in this example is 230 MW / cm ² , a critical value of 150 MW /
Can maintain cm ² . The soot concentration at this time is 1.0 x 10
^It becomes ^-5 g / cm ³ , and the correction of the laser intensity is unnecessary in the soot concentration field thinner than this.

Next, the multicolor LII method and the particle size determining method in this embodiment will be described. (A) The maximum temperature of soot particles that receive laser light depends on the soot particle diameter, and as shown in FIG. 5, the maximum temperature tends to increase as the particle diameter increases. This LII signal is a gray body radiation spectrum, but the spectrum of the LII signal differs due to the change in maximum temperature due to the difference in particle size. That is, a soot particle having a high maximum temperature and a large particle diameter has a spectrum having a higher peak in the ultraviolet region. When this is expressed by an equation, the equation 4 is obtained.

[0029]

[Equation 4]

Here, in the equation 4, a is a particle radius, T is a temperature, and kabs is an absorption coefficient. The (b) LII signal is proportional to the absorption coefficient, as shown in equation 4. Since this absorption coefficient depends on the wavelength and particle size, LI
The I signal depends on the wavelength and the particle size. Since the LII signal spectrum depends on the particle size for the reasons (a) and (b) above, the particle size can be measured by simultaneously detecting a plurality of wavelengths. The signal ratio of the two colors of LII light with respect to the particle diameter is actually obtained by simulation as shown in FIG. It can be seen that the signal ratio of any wavelength is a convex function, and the particle size can be obtained from the signal ratio obtained by the experiment based on FIG. However, since the particle diameter is binary in FIG. 6 because it has a divalent function, the true particle diameter can be specified by further obtaining the signal ratio of another wavelength.

Hereinafter, a specific example of the particle diameter in this embodiment will be described. In FIG. 6, when the signal ratio of 300/500 nm is 2.2 and the signal ratio of 350/500 nm is 1.85, the particle sizes obtained from FIG. 6 of 300/500 nm are 40 and 100 nm, and 350/500
The particle sizes obtained from FIG. 6 of 70 nm are 70 and 100 nm. Therefore, the particle size that simultaneously fills the three colors is 100 nm. That is, it is possible to determine only one particle size by simultaneously detecting signal lights having a plurality of (three or more colors) wavelengths.

[Brief description of drawings]

FIG. 1 is a diagram showing how the LII signal changes when the laser intensity is changed.

FIG. 2 is a diagram showing an example of LII simulation of the present embodiment.

FIG. 3 is a diagram showing an attenuation state of an LII signal according to the present embodiment.

FIG. 4 is a diagram showing a change situation of LII signal intensity with respect to laser intensity in a small range.

FIG. 5 is a diagram showing changes in the LII signal when the soot particle size changes significantly.

FIG. 6 is a diagram showing how the ratio of LII signals of two wavelengths changes with particle size.

FIG. 7 is a diagram showing changes in the attenuation coefficient of the LII signal when the soot particle size changes significantly.

FIG. 8 is a schematic diagram showing a main part of the apparatus according to the present embodiment.

FIG. 9 is a schematic diagram showing an apparatus of this example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Burner 2 Air introduction part 3 Honeycomb part 4 Outer peripheral part 5 Wire mesh 6 Donut ring 7 Laser beam 8 Cylindrical lens 9 Convex lens 10 Laser sheet light 11 Flame 12 Slit 13 LII light 14 High speed shutter camera 15 Detection part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinpei Miura, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor, Satoshi Watanabe, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation

Claims (2)

[Claims] 1. A light emitting section provided at one end of the measurement chamber raises the soot temperature of a pulsed laser sheet irradiating a soot generation field in the measurement chamber up to near an evaporation point, and the light emission section is provided at the other end of the measurement chamber. The incandescent light radiated by the soot particles in the soot generation field is received by the light receiving portion provided crossing the pulse laser sheet irradiation direction, and the intensity of the pulse laser sheet is 150 MW / cm ² to 400 MW /
A soot concentration measuring method, wherein the soot concentration is measured by detecting the radiation intensity within a range of cm ² . 2. A soot particle is radiated, and an incandescent light signal of two or more different wavelengths depending on the particle diameter of the soot is detected by a detection unit, and a ratio of radiation intensities is calculated to determine the particle diameter of soot. The soot concentration measuring method according to claim 1, wherein the soot concentration is measured by correcting the attenuation of the signal light.