WO2007003859A2

WO2007003859A2 - Method for evaluating a mixture of oil products and biofuels

Info

Publication number: WO2007003859A2
Application number: PCT/FR2006/050663
Authority: WO
Inventors: Michaël HADDAD; Karim Mokaddem; Jean-Pierre Goedgebuer
Original assignee: Peugeot Citroën Automobiles Sa.
Priority date: 2005-07-05
Filing date: 2006-07-03
Publication date: 2007-01-11
Also published as: WO2007003859A3; FR2888323A1; EP1899710A2; FR2888323B1

Abstract

The invention concerns a method for evaluating the biofuel concentration of a fuel consisting of a mixture of oil products and biofuels including the evaluation of the refractive index of the mixture by analyzing the reflection by the mixture of a light beam conveyed from a light source to the mixture by a waveguide.

Description

METHOD FOR EVALUATING A MIXTURE OF PETROLEUM PRODUCTS AND BIOFUELS

The present invention claims the priority of the French application 0552055 filed 05/07/2005 whose content (description, claims) is incorporated herein by reference

The present invention relates to the identification of the basic characteristics of a motor fuel, in particular the concentration of biofuel and petroleum products and the automatic adjustment of certain engine parameters according to the identification of these characteristics. .

Nowadays, motorists often have the choice between several fuels, especially between petroleum species, mainly based on hydrocarbons or "biofuels" which contain greater or lesser proportions of alcohol. Similarly, diesters can be substituted for fuels of the diesel type. In the remainder of this document, we will describe as petroleum products a fuel essentially obtained by refining a natural or synthetic hydrocarbon, as for example traditional fuels such as gasolines, unleaded gasolines and diesel, possibly enriched with certain additives as it is well known to those skilled in the art, and biofuels, products mostly from agriculture and alcohol-based (methanol or ethanol for example) or diesters.

The exclusive use of a biofuel for the engine power of a motor vehicle is possible but is generally not recommended given a certain degradation in performance. This is particularly the case of the cold start; when the outside temperature is below about 5 ° C. This explains in particular that in many countries only limited biofuel blends are marketed.

In countries where biofuels are available "pure", often at particularly attractive rates, motorists often opt for individual strategies, choosing for example to fill about a third of the tank with biofuel and two thirds remaining with petroleum products, and by seeking what they consider to be the best price / performance compromise given the planned route.

Obviously, this type of behavior does not adjust the best vehicles. However, by adjusting certain engine parameters such as in particular the amount of fuel injected at each engine time and / or ignition delay, it is possible to optimize the performance of the vehicle according to the fuel actually used. Since a mechanic's intervention after every visit to a gas station is out of the question, most vehicles are best tuned to the fuel mix usually used by the driver.

[Oooη Some manufacturers have for some time been proposing an auto tuning of the engine servo to a sensor placed in the exhaust system. This system assumes that the engine was able to start and is therefore not a solution for cold start. By the way, by definition this system can only correct after the fact a bad setting.

On modern vehicles, provided with control means controlled by an electronic board, such as an onboard computer, it would be possible to control this setting automatically from information on the nature of the fuel actually used.

For a true automaticity of this setting, it is also desirable that the system is actually able to determine itself the nature of the fuel available in the tank of the vehicle - which excludes any process involving for example a seizure by the driver of the basic information and / or the association with a measuring device which could be available for example in service stations and which could be interfaced with the electronic box of the vehicle.

Any material, regardless of its gaseous state, liquid or solid, can be characterized by its dielectric constant. The dielectric constant varies with the pressure, the temperature and in the case of a mixture with the relative concentration of each of its constituents. An accurate measurement of the dielectric constant a solution whose constituents are known can often be deduced from its exact composition.

A simple means for determining the dielectric constant of a fluid consists in measuring the value of the capacitance formed by two electrodes separated by a known thickness of the tested fluid. Of a very easy implementation in a laboratory, this method would require a major development of the vehicle and / or the establishment of a bypass circuit to perform the sampling of the fluid.

Another well-known approach is based on an optical method. Indeed, the dielectric constant is a characteristic quantity of the response of a material to an electric field. Light being an electromagnetic wave, its propagation through a material is affected by the value of the electrical constant of said material. The refractive index of a fluid is therefore an indirect measure of the dielectric constant. Furthermore, in the case of a mixture, the refractive index of the mixture at a value intermediate between those of the refractive indices of the individual constituents of the mixture, weighted by the fractions (volume, mass) of said constituents. In the case of a biofuel / hydrocarbon mixture, the problem is simplified to the extent that the nature of the constituents of the mixture - and therefore their respective refractive indices - is known.

It has been proposed to apply this optical approach to determine the composition of an alcohol / fuel mixture in a motor vehicle. European Patent Publication 0 441 056 in the name of Ford Motor Company Ltd thus discloses a device in which the tested fluid flows in a hemispherically shaped volume which redirects light from a light source to a detector. The amount of light received by the detector depends on the refractive index of the fluid, so that the composition of the fluid trapped in the hemisphere can be deduced. Such a system is very complex to implement.

According to US Pat. No. 5,015,091 to Mitsubishi Denki KK, the ethanol concentration of a fuel is determined using a prism filled with the tested fluid. The deviation of the light beam varies according to the refractive index of the fluid. This system is sensitive to mechanical constraints and there again, requires a modification of the fuel system to include prismatic optical access.

It would therefore be desirable to develop a simpler system, requiring no particular development of the vehicle and relatively robust.

According to a first aspect of the invention, this object is achieved by a method for evaluating the biofuel concentration of a fuel consisting of a mixture of petroleum products and biofuel comprising the evaluation of the index. refraction of the mixture by analyzing the reflection by mixing a light beam conveyed from a light source to the heart of the mixture by a waveguide.

Depending on the case, the evaluation of the refractive index may comprise a step of estimating the real value of this index or simply the variation of this index compared to that of a mixture consisting exclusively of biofuel. or petroleum products.

In a particularly simple embodiment of implementation, the waveguide may be constituted by an optical fiber.

The step of analyzing the reflected light beam is preferably performed by means of a detector after separation of the reflected beam.

In a preferred embodiment of the invention, the end of the waveguide immersed in the mixture is directly placed in the tank of a motor vehicle and the evaluation of the concentration is taken into account to adjust at least a motor operating parameter.

In another variant of the invention, the end of the guide is immersed in a mixing chamber and the conditions of formation of the mixture are regulated by a control loop taking into account in particular the operating conditions of the engine and the engine. 'index of the mixture.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, among which: FIG. 1 is a schematic diagram of the propagation of a non-polarized plane wave between two media of index R ₁ and n ₂ ;

Figure 2 is a diagram illustrating a device for implementing the method according to the invention;

FIG. 3 is a block diagram showing the paths of the light beams at the waveguide-mixing interface;

Figure 4 is a diagram illustrating a Y-junction according to the invention; and

Figure 5 is a block diagram illustrating the operation of the invention.

As is well known from the constitutive relationships in the context of Maxwell's general theory of electromagnetism, the optical information on the dielectric constant ε, of the material / is contained in the refractive index n _t the medium that in the case of a non-magnetic insulator is given by:

n, = _Λ jε

To optically measure the refractive index several strategies may be employed. If, as illustrated in FIG. 1, we call n ₂ the index of the medium that we are trying to measure and D ₁ the index of the reference medium, in accordance with Snell-Descartes' law on the refraction of light, for an unpolarized wave, the product of the index of refraction D ₁ by the sinus of the angle of incidence / of a ray in a first medium is equal to the product of the refractive index by the sinus of the angle of refraction t of a second medium, or:

U ₁ sin i = n ₂ sin t

Equivalent relationships can be written in the case of non-planar and / or polarized waves.

If the intensity of the reflected or refracted beams is measured at the interface of the medium whose index is to be measured, and if n is the ratio of the indices H ₁ and n ₂ ("= -), the reflection coefficients f1 and transmission Ten normal incidence

W ₁ for an unpolarized wave are given by:

From these equations, it follows that the shape of the curve giving the reflection coefficient at normal incidence as a function of the refractive index n ₂ to be determined is a parabola. The maximum sensitivity is obtained when the indices D ₁ and n ₂ are very different.

Various systems have been proposed that use the refractive beam deviation, proportional to the refractive index, for measuring this refractive index. These systems require optical access to the liquid whose characteristics are to be known as well as precise alignment and are, by their design, sensitive to shocks and vibrations which is disadvantageous in an automotive application.

This is not the case of the present invention which allows to measure the refractive index of a motor vehicle to deduce its physical characteristics in a non-intrusive manner, without having to modify the reservoir. The technique proposed in the invention, especially in its preferred variants is compact, robust and easily industrializable, which can be based in particular on semiconductor technologies well known in the world of telecommunications. It is very easy to integrate into a vehicle, without requiring modification of the latter.

The principle of the refractometer according to the invention is described in relation to Figure 2 which illustrates a first variant of the invention consisting essentially of a light source 1, a waveguide 2, one end of which is immersed in the fluid measured 3 placed in a chamber 4. This chamber may be constituted for example by the walls of the vehicle tank, with an optical fiber having by example an outer diameter (including sheath) of the order of 1 to 5 mm, bathed in this tank.

Although these means are not shown, the end of the dipped fiber dipped in the tank can be fixed to the bottom of the tank (preferably relatively flexible to cushion shocks) or slaved to a float if preferred avoid testing the bottom of the tank where impurities may eventually accumulate.

The light source 1 used is for example a light emitting diode (LED), preferably chosen because of its cost.

However, it is also possible to use a laser or other source that can be injected into a waveguide, including an optical fiber without too much loss. Since the phenomenon studied is non-resonant, the wavelength is of little importance but must be outside the absorption ranges of the liquid whose index is to be measured and, if possible, in a spectral domain where detectors Sensitive and low cost are available. The emission of light can be continuous or pulsed. This latter method is preferred because it makes it possible to synchronize the detection of the reflected beam with its emission, and consequently, to filter in a simple way a possible background noise. Moreover, certain light sources have a maximum power of emission in pulse mode which can be for example ten times greater than the power of emission in continuous. Using a pulse mode thus makes it possible to use an inexpensive but nevertheless powerful source, thus improving the quality of the measurement.

The waveguide is preferably an optical fiber, that is to say a means well suited in an environment subject to multiple sources of vibration such as an automobile.

In the device according to the invention, the refractive index of the waveguide corresponds to one of the two indices R ₁ and n ₂ , the second being the index of the mixture. To simplify the interpretation of the measurement, it is preferable that the refractive index of the waveguide be outside the range corresponding to a mixture of 100% petroleum product on the one hand and 100% of biofuel. somewhere else. The table below gives the refractive index of some common elements.

^* according to the type of plants used

It may be noted that the values given are merely indicative, and that in particular from one country to another, the fuels do not always have the same characteristics (and can have a variable quality over time or from one part of the territory to another). A waveguide having a refractive index of less than 1.33 or greater than 1.53 is therefore preferred.

According to another variant of the invention more particularly preferred, the index of the waveguide may be chosen to be identical (or at least very close) to the index of one of the components of the mixture. In other words, the device will be transparent when the mixture consists of 100% of this particular compound. Under these conditions, the response of the detector will be essentially linear, the mixture reflecting all the more light that it contains more of the compound whose refractive index is other. This will be the case for example for a waveguide having a refractive index close to 1, 42 or 1, 46 depending on whether the vehicle is a gasoline or diesel vehicle.

Note that if the waveguide is constituted by an optical fiber, it is easy to obtain an adjustment of this refractive index, for example by doping or choosing in an appropriate manner the ratio between the inside diameters ( core) and outer (sheath) of the fiber, any technique well known in the optical fiber industry.

It is also possible to choose a so-called multi-mode waveguide, in other words transmitting non-unidirectional light beams. The invention can thus be implemented by choosing an optical fiber with a relatively "thick" core, generally considered to be of inferior quality, particularly with regard to applications in telecommunications, and above all, the light beam need not be very fine and precise, as would be the case particularly with a relatively expensive source such as a source of laser beam.

The principle of the measurement based on the detection of the reflected beam, it goes without saying that the waveguide must be such that the reflected beam can be effectively returned. This distances the optical fibers having a bevelled end particularly to minimize reflections, while the waveguides having a cleaved face perpendicular to the general direction of the light beam are preferred. FIG. 3 shows the paths of the light beams at the interface of the waveguide and the mixture. In this figure, I ₀ denotes the intensity of the beam emitted by the light source towards the refractive index mixture n ₂ , I _T , the share of the transmitted light beam, I _R the reflected part and n ₁ the index of refraction of the optical fiber.

The system shown in Figure 2 further comprises a separation system 5 to access the reflected beam. This separator may be for example a separator plate, a separator cube or other equivalent means well known to optical specialists. In a more especially preferred variant, this separator is a junction of optical fibers X or preferably Y, the injection is preferably made by one of the two branches, as shown in Figure 4.

In the case of a Y junction, considered as two branches merging into a branch, the light beam is introduced by one of the two initial branches, joined the common branch, is reflected and the reflected beam is detected in the second branch. . This is illustrated in FIG. 3, in which E corresponds to the emitting light source, D to the detector and R to the reflecting medium. Advantageously, this junction Y will be such that the greater part of the reflected beam is directed towards the detector, for example 99% of the reflected beam being directed towards the detector and only the residual part, of the order of at most 1% continuous towards the light source. A junction X is also possible, with respect to the previous case an additional branch provided with a second detector serving as reference data.

In another variant of the invention, the device does not include a separator itself but an area in which the fiber is stripped (or at least is transparent to a light beam having a component not strictly parallel to the main direction If the fiber is multi-mode, the light beam propagates in part by a succession of bifurcations against the walls.With a "hole" in the fiber, opposite which is placed a detector, one can measure the amplitude of the "leakage" and deduce the amplitude of the reflected beam.This technique may require calibration, for example using a mixture having a refractive index identical to that of the waveguide so as to identify the "Leakage" of the emitted light beam.

Returning to the variant of the invention illustrated in Figure 2, it is noted that the device comprises a detector 6 for measuring the intensity of the reflected beam This detector is for example of the type photodiode, joulemeter etc.. The detector is associated with measurement and control electronics, not shown here. A device of the same type can be used for the optional detector 7, used to measure a reference intensity or to detect a failure of the lighting system.

In a particular variant of the invention, which can be implemented particularly when the light source is a laser source, the "detector" may in fact be constituted by observation means of the source. Indeed, in most optical systems, it is sought to minimize the reflection of the light beam, for example by cutting the end face of the optical fiber bevel so that the reflected ray is reoriented in a direction perpendicular to the direction the incident ray, because the reflection towards the source leads to a disturbance of the laser source. In this variant of the invention, one seeks in fact to take advantage of this disturbance to observe the reflection phenomenon. Such a variant has the advantage that it does not require a step of separation of the reflected beam. In another variant of the invention that is more particularly preferred, the selected optical fiber has an index close to the main component of the mixture, the intensity of the disturbance is then an indication of the "drift" of the index of the mixture. in other words, the intensity of the reflected beam.

An operating mode of the invention is described below with reference to Figure 5, in which the elements common with Figure 2 bear the same references. The light is injected into one of the arms 10 of the coupler 5, here a coupler Y. The light passes through the coupler and is guided in the branch 1 1 to the probe end immersed in the liquid which is to be measured the refractive index. At the interface between the fiber and the liquid, the light is reflected towards the inside of the fiber. The intensity of the reflected beam depends on the index of the liquid in which the fiber is dipped. The reflected beam is guided by the fiber and a portion exits through the branch 12 of the coupler 5 to be evaluated by a detector. From this measurement can be deduced the refractive index of the liquid. An "X" coupler can also be used to simultaneously measure a reference intensity with another detector.

Knowing all the parameters of the mixture except the one that we want to measure (the relative concentrations for example in the case of a mixture of biofuel and petroleum product temperature and chemical species data), if a single parameter evolves, a simple bijection makes it possible to access the information sought from the measurement of the reflected intensity and thus of the refractive index.

If more information is needed, an extension of the invention taking advantage of the chromatic dispersion in the liquid can be used. Any material has a refractive index that varies with wavelength. This variation is very strong in the vicinity of absorption resonances which are characteristic of the constituents of the mixture. However, even at wavelengths far from these resonances their influences are sensitive.

By using a spectrally resolved measurement, we can therefore characterize more finely the liquid probed. This diagnosis can be made easily by slightly modifying the invention described above. For example, one can simply multiplex several refractometers by ensuring that each transmitter operates at a different wavelength. By reconstructing the chromatic dispersion curve of the liquid there is thus additional information to analyze it. A simple means is for example to use a set of colored LEDs, with a barrel-type mechanism to select the desired color diode. Commercially available light emitting diodes may emit white light or colored light which we will consider to be "monochromatic" even though in practice the diodes emit on a wavelength spectrum but are relatively narrow in the case of colored diodes. Note that it is also possible to use diodes that emit in a color range varying according to the applied voltage, under these conditions, a single diode can be used by associating a means for applying a variable voltage.

In another variant of the invention, the light source is chosen such that it emits in a wide spectral range (again the light-emitting diodes constitute a relatively simple commercial implementation solution) associated with a set of detectors. placed downstream of an interference filter. For example, a 6DB coupler may be used, that is to say a coupler that breaks down the signal reflected into 4 signals carried by the 4 branches, each of which receives VA from the reflected intensity. One of the branches being used for the source, we will be able to equip each of the other 3 branches with an interference filter so as to detect the ray reflected in a given wavelength.

The interference filters will preferably be of the Bragg grating type, which have the advantage of being an integral part of the fiber, and therefore constitute robust systems.

The various variants described above can of course be combined if necessary.

From the description made above, those skilled in the art will not fail to note that the method according to the invention is implemented essentially via a single optical fiber of a few millimeters in diameter, immersed in the mixture to study. The design requires no alignment and is very robust mechanically. All the electronic part of signal processing can be possibly (but not necessarily) made in semiconductor technology and optical fiber, that is to say using low cost technologies, widely controlled and can be easily manufactured on a large scale.

Claims

claims

1. Method for evaluating the biofuel concentration of a fuel consisting of a mixture of petroleum products and biofuels comprising the evaluation of the refractive index of the mixture by the analysis of the reflection by mixing a light beam conveyed from a light source to the mixture of the mixture by a waveguide.

2. Method according to claim 1, further comprising a step of separating the reflected light beam.

3. Method according to claim 2, characterized in that the step of separating the reflected light beam is performed by means of a Y-junction.

4. Method according to one of the preceding claims, wherein the waveguide is an optical fiber.

5. Method according to claim 4, characterized in that the optical fiber is chosen such that its refractive index is outside the range of indices bounded by the index of a mixture containing exclusively biofuel and the index d a fluid of a mixture comprising exclusively petroleum products.

6. Method according to claim 5, characterized in that the optical fiber is chosen such that its refractive index is equal to that of one of the two terminals.

7. Method according to one of claims 4 to 6, characterized in that the end of the optical fiber in contact with the mixture has a cleaved face.

8. Method according to one of claims 4 to 7, characterized in that the fiber is multi mode.

9. The method of claim 8, characterized in that the fiber comprises a stripped portion and in that the detector is placed opposite this stripped portion.

10. Method according to one of the preceding claims wherein the light source is a laser source.

A method according to claim 10, characterized in that the disturbances of the laser source by the reflected light beam are observed for the detection of the reflected light beam.

12. Method according to one of claims 1 to 9, wherein the light source is a light emitting diode.

13. Method according to one of the preceding claims, wherein the light source is polychromatic.

14. The method of claim 12, characterized in that the light emitting diode emits in a narrow wavelength range so that the emitted light is not white.

15. Method according to one of the preceding claims, wherein the mixture is placed in the tank of a motor vehicle.

The method of claim 13 wherein the evaluation of the biofuel concentration is taken into consideration to adjust at least one engine operating parameter.