JP2012052880A - Fuel property measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost fuel property measurement device that can be installed on a motor vehicle, a motor cycle, a small-sized marine vessel and any other vehicles with an internal combustion engine.SOLUTION: The fuel property measurement device, using a plurality of low-cost near-infrared LED sources L, L, Lhaving a wide emission wavelength width, makes the LED sources substantially function as a light source with a narrow emission wavelength width by combining the LED sources with a diffraction grating 7, and reduces the cost required for detectors, which are more expensive than light sources in near-infrared applications, by reducing light receiving elements of the detector 7 to a single type. As the detection method substantially has a narrow wavelength width, a plurality of components of mixed fuel can be separated and measured.

Description

  The present invention relates to a fuel property measuring apparatus for detecting and measuring a composition of a mixed fuel that can be mounted on an automobile, a motorcycle, a small ship, or the like having an internal combustion engine.

  In recent years, mixed fuels in which alcohol such as ethanol is mixed with gasoline have been used as automobile fuels in response to problems such as soaring crude oil prices and global warming. Gasoline and alcohol differ in calorific value and vaporization characteristics, and optimum combustion conditions differ depending on these ratios. Therefore, in vehicles using mixed fuel (FFV), the mixture ratio of the components in the fuel used is measured or estimated so that it can correspond to various mixture ratios, and the fuel injection amount, ignition timing, etc. of the engine accordingly. It is necessary to change the control.

In a fuel property detection device mounted on an automobile or the like, the following is required in order to measure the concentrations of various components contained in the mixed fuel.
-The response is fast.
-The components of the mixed fuel can be accurately separated and quantified.
・ It must be inexpensive.
-Be resistant to temperature changes.
-Be resistant to vibration.
・ It must be compact.

  Conventionally, various methods have been proposed for measuring the concentrations of various components contained in the mixed fuel. For example, Patent Document 1 discloses a technique for irradiating a mixed fuel with near-infrared light having a predetermined wavelength near 1600 nm and measuring the alcohol concentration based on the absorbance obtained from the detection signal of the transmitted light. Yes. Since the absorption wavelength band of alcohol exists in the wavelength range near 1600 nm, the higher the alcohol concentration, the higher the absorbance. Therefore, if a map showing the relationship between the absorbance and the alcohol concentration is created in advance, the alcohol concentration can be immediately calculated by simply irradiating the mixed fuel with light and detecting the transmitted light (that is, the response is fast).

  In addition, when analyzing by using light absorption with respect to mixed fuel, the light of a near infrared region is generally used like patent document 1. FIG. This is due to the following reason. Infrared light absorbs components contained in the mixed fuel too strongly (absorption coefficient is too large), so it is necessary to dilute the mixed fuel. In contrast to infrared light, visible light is not absorbed by alcohol or hydrocarbon (because the absorption coefficient is too small) and cannot be used for analysis. In contrast, near-infrared light has an intermediate absorption coefficient, and the transmitted light is measured with an optical path length of about several millimeters (the length of the optical path where the absorption is received) without diluting the mixed fuel. Can do. For this reason, light in the near-infrared region between the infrared region and the visible region is used for practical analysis that does not require dilution of the sample.

  However, the method of Patent Document 1 has the following problems. Alcohol often contains water, and the absorption wavelength band of water is close to the absorption wavelength band of alcohol. In addition, light with a wavelength around 1600 nm is weakly absorbed by hydrocarbons (gasoline). For this reason, it is difficult to accurately separate and quantify gasoline, alcohol, and water only by using light of one wavelength as in Patent Document 1. Therefore, when light absorption is used to measure the properties of the mixed fuel, it is necessary to measure light absorption with respect to light having a plurality of wavelengths.

JP 2008-157728 A

  When measuring the absorption of multi-wavelength light in the measurement of the properties of the mixed fuel, the mixed fuel is irradiated with continuous light from a single continuous light source, and the transmitted light is dispersed with a diffraction grating, and then a plurality of light receiving elements (for example, It is conceivable to use a configuration in which a photodiode) is detected in parallel by an array type detector arranged in one dimension. This configuration has the advantage that it has no moving parts and is resistant to vibration, and can simultaneously measure multi-wavelength light.

  However, a silicon array detector available at low cost has high sensitivity in the visible region, but cannot detect light in the near infrared region. Although an array type detector for the near infrared region other than silicon is available, it is very expensive, and is not suitable for an inexpensive apparatus mounted on an automobile or the like.

  On the other hand, a configuration in which the light receiving element of the detector is single (that is, an array detector is not used) is also conceivable. In this case, single-wavelength light with different wavelengths is emitted from a plurality of single-color (single-wavelength) light sources toward this single light-receiving element, and light is absorbed by the mixed fuel between the single-color light source and the light-receiving element (detector). It becomes the composition that it is made to do. In this configuration, since the light receiving element is single, the cost for the detector can be reduced. However, a monochromatic light source (for example, a laser light source) that can irradiate a single wavelength light having a sufficiently narrow wavelength width is expensive, and it is necessary to prepare as many as the required number of wavelengths. Cost becomes high.

  The problem to be solved by the present invention is to provide a fuel property measuring apparatus suitable for in-vehicle use and capable of satisfying the above various requirements.

The fuel property measuring apparatus according to the present invention, which has been made to solve the above problems,
A plurality of near-infrared light sources having predetermined wavelength widths arranged at different positions;
A diffraction grating that diffracts light of a specific wavelength in a common direction from among the light emitted from the plurality of light sources,
A single light receiving portion for receiving each light diffracted in the common direction by the diffraction grating;
A measurement cell provided on an optical path between the light source and the light receiving unit for containing fuel to be measured;
Calculation means for calculating the concentration of each component contained in the fuel based on the degree of absorption of light from each light source obtained from the detection signal of the light receiving unit;
It is characterized by having.

  The light of a specific wavelength diffracted from each light source through the diffraction grating in a common direction (the direction of the light receiving unit) corresponds to the absorption wavelength band of the component to be detected included in the fuel. There are different wavelengths for each light source.

  In the fuel property measuring apparatus according to the present invention, since light of a specific wavelength is diffracted from the light of each light source toward the light receiving unit using a diffraction grating, the wavelength narrower than the wavelength width of the light emitted by each light source Light having a width can be incident on the light receiving unit. Further, by providing slits at the light emission position of each light source and the light incident position of the light receiving unit, it is possible to extract light having a narrower wavelength width. Therefore, the emission wavelength width of each light source may be wide. For example, an inexpensive near infrared LED having an emission wavelength width of about 100 nm can be used as the light source, and the cost of the apparatus can be further reduced.

  When the measurement cell is provided between the diffraction grating and the light receiving unit, the light of a specific wavelength of each light source passes through a common optical path. Therefore, the measurement cell may be disposed on this optical path. On the other hand, when the measurement cell is provided between each light source and the diffraction grating, the optical path is different for each light source. Therefore, it is necessary to dispose the measurement cell so as to straddle each optical path.

  The fuel property measuring apparatus according to the present invention is configured by combining the advantages of the conventional method using a single light source and the method using a single light receiving element. By adopting such a configuration, it is possible to reduce the number of near-infrared light-receiving elements, which has been a cause of high costs, and to produce inexpensive near-infrared LEDs with a light emission wavelength width of about 100 nm as a light source. Therefore, the fuel property measuring device can be provided at low cost. In addition, since there is one light receiving section, variation in absorbance measurement error for each wavelength due to temperature change is reduced, and as a result, separation and quantification can be performed more accurately than before (that is, stronger against temperature change). It becomes possible.

Absorption spectrum of each component typically contained in a mixed fuel. The figure which shows the chromatic dispersion and wavelength resolution in each light source position of a present Example. The figure which shows the optical system of one Example of the fuel property measuring apparatus which concerns on this invention. The functional block diagram of the fuel property measuring apparatus of a present Example. The table | surface which shows the result of the numerical simulation by the fuel measuring apparatus of a present Example. The figure which shows the optical system of the modification of the fuel property measuring apparatus which concerns on this invention.

  FIG. 1 shows absorption spectra of ethanol, water, and straight chain hydrocarbons (heptane and hexane) that are generally contained in a mixed fuel. In addition, the absorption spectrum of FIG. 1 is a thing when optical path lengths other than water are 10 mm, and the optical path length of water is 2 mm.

  When the components of ethanol, water, and straight chain hydrocarbons having the absorption spectrum shown in FIG. 1 are separated using a plurality of light sources, three monochromatic light sources that generally generate monochromatic lights of 1550 nm, 1450 nm, and 1200 nm, respectively. Is used. 1450 nm and 1200 nm are the wavelengths of water and linear hydrocarbon absorption peaks, respectively, but 1550 nm is slightly deviated from the absorption peak of ethanol near 1580 nm. This is because the absorption peak of benzene is around 1630 nm and is not affected by this.

  In FIG. 1, the three wavelengths (1550 nm, 1450 nm, and 1200 nm) to be used are indicated by bar lines. However, if an LED light source having a full width at half maximum of about 100 nm, for example, is used as it is instead of a monochromatic light source, the light emission is as follows. Since the base width spreads in the range of about 200 nm as shown in FIG. 2 centering on this vertical bar, it is not sufficient to separate the steep absorption spectrum of FIG. In order to perform these separations, it is necessary to reduce the full width at half maximum to about 20 nm (40 nm for the base width). The fuel property measuring apparatus according to the present invention described below realizes an effective reduction effect of the light source wavelength width.

FIG. 3 shows an optical system of an embodiment of the fuel property measuring apparatus according to the present invention. In this embodiment, an in-plane arrangement is used in which each light source and detector are arranged on the same horizontal plane.
The fuel property measuring apparatus of this embodiment is a three-wavelength measuring system using three light sources L ₁ , L ₂ , and L ₃ , and each light source has a center wavelength of 1550 nm, 1450 nm, 1200 nm, and a full width at half maximum of about 100 nm. Use an LED light source.

The light emitted from the light sources L ₁ , L ₂ and L ₃ is first incident on the diffraction grating 2. The diffraction grating 2, respectively specific extracting light of a wavelength "narrowing the wavelength width" function from the light source L _1, L _2, L _3, from the light source L _1, L _2, L _3, which are arranged at different positions And a function as an “optical mixer” for directing the irradiated light toward the single detector 7. The function of “narrowing the wavelength width” of the diffraction grating 2 will be described later. For example, when a diffraction grating 2 having a number of grooves of 1000 / mm is used, the half-wavelengths of the light sources L ₁ , L ₂ , and L ₃ are used. Even if the total width is about 100 nm, it can be reduced to about 30 nm. Further, because of the function as the “optical mixer” of the diffraction grating 2, even if the three light sources L ₁ , L ₂ , and L ₃ are separated from each other by several mm, the diffraction grating 2 is directed toward the detector 7. You can follow a common optical path. With the above function, light having a specific wavelength among the incident lights from the light sources L ₁ , L ₂ and L ₃ is diffracted by the diffraction grating 2 toward the detector 7 and collected by the lens 3. The mixed fuel 6 introduced into the flow cell 5 is irradiated.

The flow cell 5 is a tube having a diameter of about 5 mm provided with a window 4 on the optical path between the lens 3 and the detector 7, and light from the light sources L ₁ , L ₂ , L ₃ is transmitted from the flow cell 5. After irradiating the mixed fuel 6 introduced into the tube and receiving absorption of each component contained in the mixed fuel 6, the transmitted light reaches the detector 7, and a single light receiving element (light receiving) of the detector 7 is received. Part)), the transmitted light intensity is measured. Here, the transmitted light intensity representing the degree of absorption is converted into absorbance (logarithm of the reciprocal of the transmittance) that is directly proportional to the concentration of each component of the sample, and then divided into the concentration of each component.

  As the light receiving element of the detector 7, a Ge (germanium) diode having sensitivity in a wavelength range of 1200 nm to 1700 nm can be preferably used. Further, although it is somewhat expensive, an InGaAs (indium gallium arsenide) diode may be used. In any case, in the present invention, since the light receiving element can be made single, the cost of the apparatus can be greatly reduced.

Each of the above optical elements, the flow cell 5 and the like are all fixed to the housing 1 having a light shielding function, and have no movable parts, so that they are resistant to vibrations and external impacts. In addition, the size of the device is about 3 cm in length and width, and it is small enough to be mounted on a car.
As in this example, the use of a planar diffraction grating in which divergent light is incident on the planar diffraction grating instead of parallel light has been known for a long time as Monk-Gilleyson mounting, and is often used for simple spectrometers. Has been. Also in this example, Monk / Gillison mounting was used to reduce the size of the apparatus.

As the light sources L ₁ , L ₂ , and L ₃ , it is desirable to use a light source having a narrow wavelength width such as a semiconductor laser. However, since a semiconductor laser is very expensive, an inexpensive fuel property measuring device mounted on an automobile or the like. Is not appropriate. Therefore, in this embodiment, a near-infrared LED having a full width at half maximum of about 100 nm is used as the light source, and the same width is used for the light emission position of each of the light sources L ₁ , L ₂ , and L _{3 and} the light incident position of the detector 7. Slit 8 (to be precise, the effective width of the slit including the magnification is the same since the incident / exit magnification is not 1), and the opening of the slit 8 on the detector 7 side is the focal position of the lens 3. I made it. Although only the diffraction grating 2 can extract light having a narrow wavelength width from the light sources L ₁ , L ₂ , and L ₃ , it is possible to extract light having a narrower wavelength width by using the slit 8 as follows. It becomes.

が成り立つ。ここで、Lは回折格子から光源までの距離、dは回折格子の溝間隔、θは回折格子の法線と回折格子からみた注目する光源の方向とのなす角度である。L=25mm, d=0.001mm,θ=38度の場合で(1)式を計算すると、δλ=1nm に対して、δｘは0.032mm、100nmあたりなら3.2mmとなる。すなわち図２のように、中心波長が1450nmの光源Ｌ₂の位置を0mm（原点）とすれば、1550nmの光源Ｌ₁は+3.2mmの位置に、1200nmの光源Ｌ₃を-7.1mm（マイナス側では計算上分散が250nm×3.2mm/100nm=8mmより少し小さくなる）の位置に置くことになる。ここでスリット幅を0.5mmにすると、光源の光の半値全幅は16nm（分散の計算：100/3.2×0.5）となるため、各光源において実質的に利用される波長幅は図２の三角形のようになり、もとの波長幅を十分狭くすることができる。なお、図２では参考のために、中心波長が1300nmの光源を使う場合の位置（-4.3mm）も記載した。 For example, assuming that the diffraction grating has a number of grooves of 1000 / mm (groove spacing 0.001 mm), and the distance between the diffraction grating 2 and the light sources L ₁ , L ₂ , L ₃ is 25 mm, the diffraction grating lines on the light source I calculated the variance. As is well known in the design of spectrometers, an equation for linear dispersion (in this case, the proportional relationship between the lateral movement distance δx of the light source and the change in wavelength δλ),

Holds. Here, L is a distance from the diffraction grating to the light source, d is a groove interval of the diffraction grating, and θ is an angle formed between the normal line of the diffraction grating and the direction of the light source to be observed as viewed from the diffraction grating. When equation (1) is calculated when L = 25 mm, d = 0.001 mm, and θ = 38 degrees, Δx is 0.032 mm for Δλ = 1 nm and 3.2 mm for 100 nm. That is, as shown in FIG. 2, if the position of the light source L ₂ having a center wavelength of 1450 nm is 0 mm (origin), the light source L ₁ of 1550 nm is at the position of +3.2 mm and the light source L ₃ of 1200 nm is −7.1 mm (minus). On the side, the dispersion is calculated at a position where the dispersion is slightly smaller than 250 nm × 3.2 mm / 100 nm = 8 mm). If the slit width is 0.5 mm, the full width at half maximum of the light from the light source is 16 nm (dispersion calculation: 100 / 3.2 × 0.5). Thus, the original wavelength width can be made sufficiently narrow. For reference, FIG. 2 also shows the position (−4.3 mm) when a light source having a center wavelength of 1300 nm is used.

  As the value of linear dispersion is reduced from 38 degrees to 0 degrees, the value of 3.2 mm per 100 nm becomes as small as about 2.5 mm, and the value of linear dispersion also changes with the number of grooves in the diffraction grating. Since the horizontal size of the light source is about 2 mm to 3 mm, the typical example in FIG. 2 is that the distance between the three light sources does not collide with each other if the diffraction grating of this level is used. It shows that it can be accommodated in the right size without too much. In addition, since it is possible to make LED chips as light sources exclusively (about 1mm), the L value in Fig. 2 is halved and the overall size is reduced to about half. Miniaturization is also possible.

By using such a configuration, the fuel property measuring apparatus of this embodiment has the following effects.
(1) The response is fast due to the combination of LED and photodiode.
(2) Even if an inexpensive near-infrared LED having a wide wavelength width is used, the full width at half maximum of the wavelength can be narrowed by the action of the diffraction grating and the slit. Then, by comparing the absorption wavelength of infrared light having a narrow half-value width, each component in the mixed fuel can be accurately measured.
(3) Since only one photodiode needs to be used for the detector, the cost of expensive photodiodes can be reduced in the near infrared region.
(4) LEDs, diffraction gratings, and photodiodes are resistant to temperature changes because their characteristics change little with temperature. Further, since there is only one photodiode, it is possible to reduce variation in absorbance measurement error for each wavelength due to temperature change, and as a result, it is possible to calculate the concentration of each component more accurately than in the past. .
(5) Since there are no moving parts, it is strong against vibration and is robust.
(6) Each size is about 3cm in length and width or less, and is compact.

FIG. 4 shows a functional block diagram of the fuel property measuring apparatus of the present embodiment. As shown in this figure, in the fuel property measuring apparatus of the present embodiment, in addition to the optical measurement system shown in FIG. 3, a light source lighting circuit 20 that switches lighting of the light sources L ₁ , L ₂ , L ₃ at high speed, and a detection Included in the mixed fuel 6 based on the signal processing unit 21 that performs various signal processing such as amplification of the detection signal of the detector 7 and conversion from an analog signal to a digital signal, and the absorbance of light from each light source obtained from the detection signal The light source lighting circuit 20, the signal processing unit 21, and the control unit 23 that controls the calculation unit 22 are included.

The light from each light source sequentially switched by the light source lighting circuit 20 is detected by the detector 7 after being absorbed by the mixed fuel 6 in the flow cell 5, and is acquired by the signal processing unit 21 in a time division manner. . Then, the calculation unit 22 calculates the absorbance for each light source, and calculates the concentration of each component contained in the mixed fuel 6 by the multiwavelength calculation described below. In this embodiment, a period for detecting a dark signal is provided in which none of the light sources L ₁ , L ₂ , and L ₃ is lit when the light source is switched by the light source lighting circuit 20, and the light sources L ₁ , L ₁ , A value obtained by subtracting the detection signal obtained during the dark signal period from the detection signal obtained during the period during which each of L ₂ and L ₃ is lit is used as the detection signal for each light source.

なお、上式ではuの寄与が十分小さいものとしてuに関する項を除いている。そのため、式(1)は実際には近似式であるが、簡単のため等式で表すことにする。
さらに濃度の総和が1であることから、次式が得られる。

式(1)及び(2)を行列を用いて表すと、

となる。ここで、式(3)の係数行列の逆行列を両辺に掛けると次式が成立する。

式(4)の逆行列は、h_ijが既知であれば予め求めておくことができる。そのため、吸光度の測定値a₁, a₂, a₃が得られれば、式(4)より、x₁, x₂, x₃及びuの濃度が即座に算出される。 <Example of multi-wavelength calculation>
For example, the calculation unit 22 performs the following calculation.
x ₁ , x ₂ , x ₃ are the concentrations of alcohol, straight chain hydrocarbons, and water contained in the mixed fuel, u is the concentration of other components (such as benzene), and the sum of the concentrations is 1 And In addition, the measured absorbance values obtained for the light sources L ₁ , L ₂ , and L ₃ are a ₁ , a ₂ , and a ₃ , and h _ij is the light source L _j when x _i = 1. The absorbance obtained as described above. At this time, the following simultaneous equations hold.

In the above equation, the term relating to u is excluded on the assumption that the contribution of u is sufficiently small. Therefore, equation (1) is actually an approximate equation, but will be expressed as an equation for simplicity.
Further, since the sum of the concentrations is 1, the following equation is obtained.

When Expressions (1) and (2) are expressed using a matrix,

It becomes. Here, when the inverse matrix of the coefficient matrix of Expression (3) is multiplied on both sides, the following expression is established.

The inverse matrix of Equation (4) can be obtained in advance if h _ij is known. Therefore, if the absorbance measurement values a ₁ , a ₂ , and a ₃ are obtained, the concentrations of x ₁ , x ₂ , x _3, and u are immediately calculated from the equation (4).

The result of the simulation calculation using the absorbance h _ij of each component obtained from the graph of FIG. 1 is shown in the table of FIG. This table shows the calculated values and set values by Equation (4) when x ₁ (ethanol concentration), x ₂ (average concentration of heptane and hexane), and x ₃ (water concentration) are changed. Is a comparison. In this numerical simulation, u is the concentration of benzene only.

  From the table in Fig. 5, the ethanol error is not likely to occur no matter how the set values of each component are changed, and the error is about 1% at the maximum (the rightmost column in the second row from the top) with sufficient accuracy. It can be seen that the ethanol concentration can be measured. On the other hand, regarding the error of straight chain hydrocarbons (heptane and hexane), the leftmost column in the third row from the top had the largest error, which was 3.4%. This is due to the fact that the concentration of benzene is 0.8 even though benzene contribution is not corrected in equation (4), but each concentration is still measured with sufficiently high accuracy.

FIG. 6 shows a modification of the fuel property measuring apparatus of the present embodiment. This modification is an example using an off-plane arrangement in which the light sources L ₁ , L ₂ , L ₃ and the detector 7 are not on the same horizontal plane. In the example of FIG. 6, light emitted from the light sources L ₁ , L ₂ , and L ₃ is incident on the diffraction grating 2 from an obliquely downward angle and is emitted obliquely upward. In the apparatus of this modification, the degree of freedom in design can be made higher than in the in-plane arrangement in which the light source and the detector are arranged on the same horizontal plane shown in FIG.

  It should be noted that any of the above-described embodiments is an example of the present invention, and it is obvious that modifications, corrections, additions, and the like as appropriate within the scope of the present invention are included in the scope of the claims of the present application. For example, in the above embodiment, a three-wavelength measurement system using three light sources is shown, but a four-wavelength measurement system further provided with a light source corresponding to the absorption wavelength band of benzene can be used. Further, it can be easily expanded to a larger number of light sources. Furthermore, by further narrowing the groove interval of the diffraction grating 2 and the slit width of the slit 8, a light source having a wider wavelength width can be used, or the effective wavelength width of the light source can be further narrowed.

1 ... housing 2 ... diffraction grating 3 ... lens 4 ... window 5 ... flow cell 6 ... mixed fuel 7 ... detector 8 ... slit 20 ... light source lighting circuit 21 ... signal processor 22 ... computing unit 23 ... controller L _1, L ₂ , L ₃ ... Light source

Claims (5)

A plurality of near-infrared light sources having predetermined wavelength widths arranged at different positions;
A diffraction grating that diffracts light of a specific wavelength in a common direction from among the light emitted from the plurality of light sources,
A single light receiving portion for receiving each light diffracted in the common direction by the diffraction grating;
A measurement cell provided on an optical path between the light source and the light receiving unit for containing fuel to be measured;
Calculation means for calculating the concentration of each component contained in the fuel based on the degree of absorption of light from each light source obtained from the detection signal of the light receiving unit;
A fuel property measuring apparatus comprising:   2. The fuel property measuring apparatus according to claim 1, wherein the light source is a light emitting diode that emits light having a wavelength of 700 nm to 3000 nm.   3. The fuel property measuring apparatus according to claim 1, wherein the light emission has a full width at half maximum of 40 nm to 200 nm.   The fuel property measuring device according to any one of claims 1 to 3, wherein slits are arranged at each of an emission position of light in the light source and an incident position of light in the light receiving unit.   The fuel property measuring device according to any one of claims 1 to 4, wherein the concentration of chain hydrocarbon or aromatic hydrocarbon, the concentration of alcohol, and the concentration of water are measured from the fuel. .

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