EP0334779A1 - Method and apparatus to detect the nature of combustion gas with a view to optimize combustion and applications thereof - Google Patents

Abstract

The subject of the invention is devices intended for detecting the overall composition of gases obtained as a result of combustion, by means of a detector comprising a semiconductive film of metallic phthalocyanine which is deposited between two electrodes on an insulating plate and which is placed in contact with the combustion gases and maintained at a temperature above a specific threshold, for example above 40 DEG C, for a phthalocyanine of monoclinic copper, in order to make the phthalocyanine insensitive to the water vapour contained in the combustion gases. <IMAGE>

Description

The present invention relates to methods and devices for globally detecting the nature of the combustion gases with a view to optimizing the latter and applications of these devices.

Detectors are known comprising a layer of metallic phthalocyanine placed in contact with the gases resulting from a combustion, for example in contact with the fumes of a burner or the exhaust gases of an internal combustion engine to globally measure the nature and the proportions of the combustion gases.

The electrical resistance of the phthalocyanine layer which is a semiconductor varies with the nature and proportions of the combustion gases, which depends on the respective proportions of air and fuel which combine in combustion.

Such a detector emits an electrical signal which generally depends on the mixture of gases contained in the combustion gases and which can be used to indicate the ratio between the quantity of air and fuel and / or to optimize this ratio when the signal delivered by the detector is used in a control loop which regulates the amount of air or the amount of fuel.

US Patent 4,381,922 describes combustion detectors comprising an insulating plate, electrodes deposited on this plate and a thin layer of an amorphous or crystalline metallophthalocyanine deposited between said electrodes, which is composed of ferrous, ferric phthalocyanine particles , Nickel, cobalt or copper, which have been suspended in a liquid solvent taken from the group of carbon tetrachloride, ether and acetone to be applied in a thin layer.

This patent teaches in particular that a copper or iron phthalocyanine, which has been suspended for 24 hours in carbon tetrachloride or in a chlorinated solvent gives rise to a compound whose electrical resistance is ten times lower than that of the same metallic phthalocyanine not treated with carbon tetrachloride or with a chlorinated solvent.

This patent also teaches the use of detectors comprising a sensitive layer of copper phthalocyanine, treated with ether to control the proper functioning of a burner.

The resistance variation curve as a function of the excess combustion air passes through a fairly flat minimum in the vicinity of the stoichiometric proportions and the detector can be used to regulate the admission of air to the burner.

We also know that the conductivity of phthalocyanines is a function of the hygrometric degree of the atmosphere in contact with which they are placed and this property is used to build hygrometers based on phthalocyanines.

The electrical properties of phthalocyanines can be explained as follows. At room temperature and in the absence of gas absorbed at the surface, phthalocyanines are p-type semiconductors.

In the presence of gaseous molecules having an electron-capturing effect, which is the case for most of the oxygenated gases resulting from combustion such as oxygen or nitrogen, sulfur or carbon oxides, the formation of positive charge carriers is favored. Indeed, the transfer of an electron to a phthalocyanine molecule on which an oxygenated gas is adsorbed is facilitated by the electron capturing effect of the gas.

This property explains why phthalocyanines can be used to globally detect the nature of the combustion gases.

On the other hand, water vapor is an electron donor gas which reduces the conductivity of phthalocyanine. The positive charges are stabilized by water vapor and the number of positive carriers capable of ensuring conduction decreases.

For sufficient water vapor contents, the semiconductor can become n-type.

The action of water vapor or any other electron-donating gas manifests itself especially in the presence of an electron-absorbing gas previously absorbed. In this case, the adsorbed water vapor gradually destroys the electron-capturing effect of oxygen.

The gases produced by combustion, in particular by the combustion of hydrocarbons necessarily contain water vapor which results of the combination of hydrogen from hydrocarbons with oxygen from the air.

The brief description above shows that to use phthalocyanines to qualitatively or quantitatively detect the nature of the oxygenated gases resulting from combustion, it is necessary to eliminate or considerably reduce the effect of the water vapor contained in the gases, otherwise the presence of water vapor leads to variations in electrical resistance which do not correspond to the presence of oxygenated gases and which falsify the detection.

US Patent 4,381,922 teaches that, when a phthalocyanine-based detector is used to control a burner in order to regulate the ratio between the quantities of air and of fuels, the detector is placed in a cell heated to a temperature of 95 ° C, to avoid condensation on the combustion water detector by keeping the burner at a temperature above the dew point.

It is imperative that detectors based on phthalocyanines are kept at a temperature above the dew point. In fact, if conductive water condenses on the detector, the electrodes of the latter are short-circuited and the electrical signal between the electrodes does not depend on the nature of the combustion gases.

However, it is not enough to eliminate the condensation of water on the detector; it is also necessary to eliminate or considerably reduce the effect of the water vapor contained in the combustion gases which occurs even in the absence of condensation.

U.S. Patent 4,381,922 teaches that one of the problems encountered when using phthalocyanine detectors is their sensitivity to atmospheric humidity. He teaches one way to solve this problem which is to add silica gel or a finely ground molecular sieve saturated with water in a mixture of phthalocyanines and carbon tetrachloride used to make the detectors.

The silica gel or molecular sieve powder then acts as a buffer which regulates and stabilizes the reaction to humidity of the detectors.

FIG. 10 of this same U.S. patent shows that the logarithm of the resistance of a detector obtained by this method passes through a minimum for a value of the excess of combustion air close to the stoichiometry but this minimum is relatively flat.

This flattening of the resistance variation curve near the minimum is due, in particular to the addition of silica gel or a molecular sieve which fix the water and which cause the resistance variations due to a change in composition of gases are masked by the action of water on phthalocyanines.

This slow variation of the resistance on either side of the minimum is not favorable for good optimization of the combustion.

On the other hand, no burner achieves a truly perfect air-fuel mixture, that is to say completely homogeneous. It is therefore impossible to admit to the burner a mixture strictly corresponding to stoichiometry. To obtain optimal combustion, all burners must operate with an excess of air which can reach values of the order of 10% in unfavorable cases. The better the burner, the more the excess air will approach the stoichiometry.

The presence of molecular sieves or silica gel in phthalocyanine does not achieve this objective.

In fact, in this way, a water content is fixed in the preparation which flattens the minimum of the curve representing the logarithm of the resistance as a function of the excess air and no longer makes it possible to distinguish the optimum for operation.

On the other hand, it can be seen that the resistance values are substantially identical to + 3 and - 3% excess air.

This characteristic is very detrimental to an optimization of combustion because at - 3% (excess of negative air) the burner produces a lot of unburnt carbon monoxide and hydrocarbon, which causes significant pollution and involves the risk of explosion. .

An object of the present invention is to provide new means which make it possible to use phthalocyanine-based detectors to globally detect the nature of the combustion gases which contain water vapor by eliminating the effects of this water vapor on the resistance of said phthalocyanines, which new means have the advantage, compared to known means, that the curve which represents the resistance variations of the detector as a function of the excess combustion air has a very acute minimum peak which coincides with an excess of air corresponding to the combustion optimum of the burner considered.

A method according to the invention for globally detecting the nature of the gases produced by combustion comprises, in known manner, a detector comprising a layer of a metallic phthalocyanine placed between two electrodes which is arranged in the combustion gases and an electrical circuit which one connects to the electrodes between which an electrical signal is collected which varies as a function of the overall nature of the combustion gases, which itself varies as a function of the air / fuel ratio.

The objective of the invention is achieved by a process according to which curves of variation of the resistance of metallic phthalocyanine are plotted as a function of the inverse of the temperature thereof expressed in degrees Celsius for various hygrometric degrees of the gases , which curves have a point of convergence and said detector is maintained at a temperature above a minimum threshold, which may be slightly lower than the temperature corresponding to said point of convergence.

According to a preferred embodiment, the phthalocyanine is copper phthalocyanine and the temperature of the detector is maintained above a minimum threshold substantially equal to 40 ° C.

According to another embodiment, the phthalocyanine is cobalt phthalocyanine and the temperature of the detector is maintained at a minimum threshold substantially equal to 30 ° C.

According to a preferred embodiment, a detector according to the invention comprises, in a known manner, a plate made of an insulating material, on which are deposited two electrodes and a film of a metallic phthalocyanine connecting the two electrodes together.

In a preferred embodiment of a detector according to the invention, the insulating plate also carries electrical heating resistors which are connected to a voltage source.

Advantageously, the phthalocyanine film is obtained by applying to said support a thin layer of a suspension of metal phthalocyanine particles in a solvent taken from the group of carbon tetrachloride, ether or acetone, in which has dissolved a very small amount of a hydrophobic material, preferably a liquid or solid alkane whose molecules contain more than ten carbon atoms, for example paraffin oil.

The invention results in new detectors comprising a semiconductor layer of a metallic phthalocyanine connecting together two electrodes between which an electrical signal is collected which depends on the composition of the oxygenated gases resulting from combustion in contact with which the detector is placed and which does not depend on the water vapor content of said gases.

Most solid, liquid or gaseous fuels used in burners or in internal combustion engines contain hydrocarbons, the hydrogen of which combines with oxygen to give water vapor. Phthalocyanines are very sensitive to water vapor which modifies the semiconductor of phthalocyanines by passing it from a p type (electron recipient) to an n type (electron donor).

The method according to the invention, according to which the temperature of the point of convergence of the curves each representing the evolution of the resistance of a sample of a determined metallic phthalocyanine is determined, as a function of the inverse of the temperature expressed in degrees Celsius, when this phthalocyanine sample is placed in contact with a gaseous atmosphere having a determined hygrometric degree, and the detector made up of this phthalocyanine is kept at a temperature above a minimum threshold which is close to the temperature of said point of convergence and which can be slightly lower than this temperature, makes the detector insensitive to water vapor contained in the combustion gas and therefore to obtain an electrical signal representative of the composition of the combustion gases, which depends on the air / combustible.

Compared to the process described in US Pat. No. 4,381,922, according to which the phthalocyanine was mixed with silica gel or a molecular sieve saturated with water, in order to stabilize the reaction of phthalocyanine to humidity, the method according to the invention has the advantage that the phthalocyanine retains a high sensitivity to variations in the composition of the combustion gases and that the variation curve the resistance of phthalocyanine as a function of the excess air coefficient has a more acute minimum situated in the range of positive air excess coefficients and corresponding to the combustion burner optimum considered for a given load, that is to say for a given fuel flow. It therefore makes it possible to obtain a more precise regulation of combustion, that is to say to maintain the air / fuel ratio closer to the optimum of the burner.

Maintaining a temperature higher than that of the point of convergence makes it possible to avoid the influence of the water vapor contained in the combustion gases, while the US Pat. No. 4,381,922 teaches to place the detector in a cell heated to a temperature of 95 ° C to avoid condensation of water, which is a very different function. In fact, the water could simply have been trapped to prevent it from condensing on the detectors and causing a short circuit.

By keeping the temperature of the detector near or above the temperature of the point of convergence, the detector is made insensitive to the water vapor contained in the combustion gases, without seeking to avoid the condensation which does not occur if the temperature is higher than the dew point corresponding to the humidity of the combustion gases or if the partially condensed water is trapped.

The addition of a liquid or solid alkane in the solvent used to form a suspension of phthalocyanine particles also makes it possible to create around the phthalocyanine grains a hydrophobic film which effectively reduces the influence of water vapor on phthalocyanine.

• La figure 1 est un graphique qui représente les courbes d'évolution de la résistance d'un échantillon de phtalocyanine placé dans un gaz ayant un degré hygrométrique déterminé, en fonction de l'inverse de la température exprimée en degrés centigrades.
• La figure 2 représente le logarithme de la résistance (log R) en fonction du coefficient d'excès d'air exprimé en pourcentage (E%) pour un détecteur placé au contact des gaz d'une combustion qui brûle avec un excès d'air déterminé.
• La figure 3 est un graphique qui représente les variations de la teneur en oxyde de carbone et de la résistance d'un détecteur selon l'invention en fonction de la teneur en oxygène des fumées.
• La figure 4 est une représentation schématique d'un détecteur selon l'invention utilisé pour optimiser le fonctionnement d'un brûleur.
• La figure 5 représente un mode de réalisation d'un détecteur selon l'invention.
• La figure 6 représente schématiquement un détecteur selon l'invention utilisé pour optimiser un moteur à combustion interne.
• La figure 7 représente schématiquement une installation pour mesurer le pouvoir calorifique d'un gaz combustible utilisant un détecteur selon l'invention.

The following description refers to the appended drawings which represent, without any limiting character, exemplary embodiments of devices according to the invention and graphs showing the variations of the resistance of copper phthalocyanine as a function of the temperature and the hygrometric degree.

• FIG. 1 is a graph which represents the curves of evolution of the resistance of a phthalocyanine sample placed in a gas having a determined hygrometric degree, as a function of the inverse of the temperature expressed in degrees centigrade.
• FIG. 2 represents the logarithm of the resistance (log R) as a function of the excess air coefficient expressed as a percentage (E%) for a detector placed in contact with the gases of a combustion which burns with an excess of air determined.
• FIG. 3 is a graph which represents the variations in the carbon monoxide content and in the resistance of a detector according to the invention as a function of the oxygen content of the fumes.
• Figure 4 is a schematic representation of a detector according to the invention used to optimize the operation of a burner.
• FIG. 5 represents an embodiment of a detector according to the invention.
• FIG. 6 schematically represents a detector according to the invention used to optimize an internal combustion engine.
• FIG. 7 schematically represents an installation for measuring the calorific value of a combustible gas using a detector according to the invention.

FIG. 1 is a graph drawn up by the inventor which represents on the ordinate the resistance R expressed in ohms of a sample of copper phthalocyanine of type β and on the abscissa the inverse 1 / t of the temperature t ° of the sample expressed in degrees Celsius.

Phthalocyanine type β corresponds to the monoclinic crystallographic form.

This graph represents the resistance variation curves corresponding to different hygrometric degrees staggered between 10% and 70%. This graph shows that, for a determined hygrometric degree, the resistance varies linearly according to the inverse of the temperature and decreases when the temperature increases. It shows that the lines corresponding to different hygrometric degrees are concurrent at a point, called point P of convergence, which corresponds to a value of 1 / t of the order of 0.023, that is to say a temperature of the order of 44 ° C.

For values of 1 / t less than 0.023, that is to say for temperatures above 44 ° C, the lines are substantially confused, which shows that the resistance no longer depends on the humidity.

The present invention is a practical application of this discovery to detectors based on phthalocyanines intended to emit an electrical signal which indicates the nature of the combustion gases charged with water vapor without being influenced by this humidity.

This application consists in constantly maintaining the detector at a temperature higher than a value slightly lower than the temperature of the point of convergence P defined by the curves of FIG. 1.

For example, in the case of a β copper phthalocyanine, the temperature of the phthalocyanine is maintained above 40 ° C. The graph in FIG. 1 shows that for 1 / t <0.25, that is to say for t> 40 ° C., the variations in resistance due to variations in humidity of the order of 20% remain low and the electrical signal delivered by the detector is therefore disrupted to a negligible extent by the variations in humidity which are usually encountered.

Measurements of variation of the resistance as a function of the inverse of the temperature and the hygrometry carried out on a sample of phthalocyanine of cobalt monoclinic show that one also obtains straight lines which converge at a point which corresponds substantially to a temperature of 36 ° C and which are substantially confused for higher temperatures. In the case of a detector composed of cobalt phthalocyanine, the temperature of the detector is kept above approximately 30 ° C. and the effect of a change in the hygrometric degree of the combustion gases becomes negligible.

FIG. 2 is a graph which represents the variations of the logarithm of the resistance R plotted on the ordinates of a sample of phthalocyanine of copper, cobalt or iron, maintained at a temperature higher than that of the point of convergence as a function of the coefficient d 'excess air E plotted on the abscissa;

dans laquelle A est le débit d'air utilisée et Ast est le débit d'air correspondant à une combustion optimale, c'est-à-dire à des proportions stoechiométriques.It is recalled that to characterize the composition of the air-fuel mixture admitted to the burner, a parameter called "coefficient of excess air" E is used which is defined by the formula:

in which A is the air flow rate used and Ast is the air flow rate corresponding to optimal combustion, that is to say in stoichiometric proportions.

For total combustion for a perfect burner that cannot be achieved in practice; E = 0. In case of lack of air A is less than Ast and the coefficient E is negative.

FIG. 2 shows that the resistance of a detector composed of metallic phthalocyanine maintained at a temperature higher than a minimum determined according to the nature of the phthalocyanine and placed in contact with the gases of combustion decreases very rapidly when the excess of air increases in the zone corresponding to an air defect, passes through a minimum in the vicinity of optimal combustion, that is to say for slightly positive values depending on the burner and its load and increases again when the excess air increases.

FIG. 3 is a graph which represents values measured by means of a detector according to the invention in copper phthalocyanine, maintained at a temperature above 40 ° C. and placed in the fumes emitted by an industrial boiler burner, having a 9.3 MW power.

The dashed curve C1 represents the variations in the carbon monoxide (CO) content expressed in parts per million (ppm) as a function of the percentage of oxygen in the flue gases.

Curve C2 in solid lines represents the concomitant variations in the resistance expressed in mega-ohms of the detector. This graph shows that the resistance of the detector presents a very accentuated minimum for an excess of air of the order of 3% which corresponds to optimum combustion for which the carbon monoxide content reaches a value substantially zero.

The curves in FIGS. 2 and 3 show that a detector according to the invention placed in contact with the gases of combustion produces an electrical signal which varies very quickly as a function of the coefficient excess air. On the other hand, the signal does not vary or varies very little as a function of the hydrometric degree of the combustion gases.

This signal indicates the quality of combustion. It can be used, for example, to indicate whether a burner fitted to a boiler, an oven or any type of fireplace is operating in good conditions. In this case, it suffices to set a threshold higher than the minimum, to compare the signal emitted by the detector to this threshold and to trigger an alarm signal when this threshold is exceeded to warn the user that the burner is operating in bad conditions. conditions due to either a defect or an excess of air.

The signal delivered by a detector composed of metallic phthalocyanines placed in contact with the gases emitted by a combustion device, for example by a burner or by an internal combustion engine can also be used to automatically regulate the coefficient of excess air and to keep it around the optimal value corresponding to the minimum of the electrical resistance value.

FIG. 4 schematically represents an exemplary embodiment of a device according to the invention used to optimize the operation of a burner.

The reference 1 represents a combustion chamber, for example the hearth of a boiler, equipped with a burner 2 which is supplied with fuel, for example in liquid or gaseous hydrocarbons, by a line 3 which is connected to a source of food 5.

Line 3 may include a flow meter 4 for measuring the fuel flow. The burner 2 is supplied with combustion air through a pipe 7 connected to an air source, for example a fan. Line 7 may include a flow meter 8.

The combustion gases leave the chamber 1 through a pipe 10 commonly called smoke pipe. A pipe 12 is connected to said flue pipe and to the suction of a fan 13.

A chamber or enclosure 11 containing a detector 14 is placed in the path of the pipe 12, so that the detector 14 is constantly in contact with combustion gases which are renewed.

The detector 14 includes a semiconductor pad composed of a metallic phthalocyanine, the resistance of which varies as a function of the composition of the combustion gases and in particular, if no precautions were taken, of the water vapor contained in these gases.

The semiconductor pad is placed between two electrodes which are connected to a measuring device 15 which emits a signal which varies with the resistance of the detector 14.

This signal is used in a servo loop comprising for example an electrical circuit 16 which automatically controls an automatic adjustment means 18 of the air flow arriving at the burner via line 7 or of the fuel flow supplying the burner through line 3 .

The electrical circuit 16 can be an analog regulator with derivative action.

If the derivative is negative, this means an air fault and the regulator 16 then automatically increases the air flow or it reduces the fuel flow. If the derivative is positive, there is excess air and the regulator 16 automatically corrects. The electronic circuit 16 can also be a computer coupled to an analog to digital converter. In this case, the computer automatically reduces to the minimum the value of the resistance of the detector 14. For this, it controls the register 18 in one direction, for example that which increases the air flow and it compares the value of the resistance of the detector to a previous value.

If the resistance has increased, we move away from the minimum and the computer then controls a reduction in the air flow.

If the resistance has decreased, we go to the minimum and the computer continues to decrease the air flow until it obtains a resistance higher than the previous one.

FIG. 5 represents a preferred embodiment of the detector 14. This detector comprises an insulating support 25 which is for example a plate made of sintered alumina or of epoxy resin or of any rigid material, such as a plastic material coated with a film made of a copolymer of aromatic anhydride and aromatic diamine sold under the name "KAPTON". The material composing the wafer 25 has a very high resistivity for example greater than 10¹⁵Ω.cm, much greater than that of the phthalocyanine that makes up the active layer.

The plate 25 has an area of the order of cm².

The plate 25 carries two electrodes 26, 27 which for example have the shape of two combs whose teeth are parallel and interposed. The electrodes 26 and 27 can be deposited on the wafer by one of the techniques well known for the production of printed circuits.

On the wafer 25 provided with the two electrodes 26 and 27, a thin layer of metallic phthalocyanine is deposited which is preferably a phthalocyanine comprising a central ion Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺ or Ni²⁺.

The phthalocyanine layer can be applied directly above the electrodes or directly on the support 25.

According to a preferred embodiment, the electrodes 26 and 27 are first printed on the insulating support 25. A small quantity of phthalocyanine powder is mixed with a solvent which is taken from the group consisting of carbon tetrachloride, ether or acetone.

For example, 10 g of metallic phthalocyanine are mixed per liter of solvent. It is left to stand for approximately 24 hours. The mixture is stirred to form a homogeneous suspension and a thin layer of this suspension is applied to the support 25. It is left to dry for approximately two hours at a temperature of 150 ° C. to evaporate the solvent, then it is compressed under high pressure, for example a pressure of the order of 5.10⁷ Pa (500 bars). An electrical circuit is thus obtained between the electrodes which is constituted by a thin film composed of phthalocyanine particles having a resistance which varies between 10⁷ and 10⁹ ohms depending on the composition of the gases in contact with which the film is placed.

According to another embodiment, a thin film of metallic phthalocyanine is deposited on the insulating plate by evaporation under vacuum, that is to say by sublimation. This vacuum deposition is carried out for example by heating the phthalocyanine to a temperature of the order of 350 ° C., under a reduced pressure of the order of 0.1 Pas (10⁻³mbars).

In order to avoid the influence of water vapor on the detector 14, the latter is kept at a temperature constantly above a threshold determined according to the nature of the phthalocyanine used, for example a temperature above 40 ° C. for a copper phthalocyanine or higher than 30 ° C for a cobalt phthalocyanine.

One means of keeping the temperature of the detector above the desired threshold consists in providing the insulating board 25 with a heating resistor which may for example be a resistor printed on the back of the board and connected to a voltage source.

It is also possible to apply a layer of conductive lacquer paint to the back of the wafer or else to deposit a thin metallic film on the back of the wafers by sublimation.

Another means for keeping the temperature of the detector above a threshold consists in placing the detector 14 in a chamber 11 whose temperature is regulated so as never to fall below the fixed threshold.

In the application according to FIG. 3 where the detector 14 is placed on a pipe 12 connected to the flue pipe 10, it suffices to place the connection close enough to the hearth, where the gases are hot enough, so that the temperature of the gas passing through chamber 11 is always greater than the desired threshold.

If there is not enough hot gas, one can place in the chamber 11 a small electric radiator which sends on the detector 14 an infrared beam whose intensity is sufficient to maintain the temperature above the fixed threshold.

To reinforce the insensitivity of a phthalocyanine-based detector 14 to water vapor, another means consists in treating the phthalocyanine to block it on a p-type conductivity.

A method of preparing a detector 14 has been set out above in which a suspension of phthalocyanine particles is formed in a solvent which is preferably carbon tetrachloride.

In this case, a few grams / liter of a hydrophobic body is dissolved in this solvent, which is preferably a liquid or solid alkane, the molecules of which contain more than ten carbon atoms. For example, a few milliliters of a liquid alkane are added per liter of solvent.

When a film of this suspension is applied to the insulating plate 25, a thin layer of phthalocyanine particles is obtained after evaporation of the solvent, which are impregnated on the surface with an extremely thin film of a hydrophobic material, for example paraffin. The hydrophobic properties of this material prevent any adsorption of water, both in gaseous and liquid state by phthalocyanines. On the other hand, experience shows that this film does not prevent oxygen-accepting electron gases such as 0², NOx, SO₂, CO₂ from being adsorbed on the surface of phthalocyanines. As a result, the semi-conductivity of phthalocyanine remains blocked on the p type and the resistance at the terminals of the detector no longer depends on the water vapor present in the gases.

The consequences of this treatment are very important:
- only the electron sensing gases present in the combustion gases have an action on the electrical signal emitted by the detector.
- the detector resistance values are lower because the resistance increases with the adsorbed water content.

This is important because it is difficult to measure high resistance in an industrial environment.

The manufacture of detectors and the control of this manufacture are facilitated because the resistance of the detectors no longer depends on the humidity of the control room.

It overcomes changes in the percentage of relative humidity due to temperature variations and therefore partially overcomes the parasitic effect of temperature variations.

The responses obtained are more uniform from one combustion to another because the effect due to temperature variations is smaller and the minimum of the signal corresponds to the optimum of the burner considered.

FIG. 5 schematically represents an application of a detector based on metallic phthalocyanine to regulate the good combustion of an internal combustion engine. The figure shows a single cylinder 20, a piston 21 and the connecting rod 22 which connects the piston to crankshaft 22a. The elements corresponding to those of FIG. 3 are designated by the same references.

The reference 3 designates the fuel supply which is provided for example by an injector 23. The reference 10 represents the exhaust duct. The reference 24 represents a spark plug. The detector 14 is placed in a chamber 11 which is interposed on a duct 12 connected in bypass to the exhaust duct 10. The regulator 16 controls a means 18 for adjusting the air intake which is for example a motorized throttle valve placed in the intake duct.

As a variant, the regulator 16 can control the fuel injection pump.

FIG. 7 schematically represents an installation for measuring the calorific value of a combustible gas.

Fuel gas distributed by a network to subscribers is billed for a specified calorific value (PC).

FIG. 7 represents an installation allowing a subscriber to measure the real calorific power of the gas delivered to him.

Reference 28 represents a combustion chamber equipped with a small gas burner 29. Reference 30 represents a detector according to the invention based on metallic phthalocyanine which is placed in contact with the gases produced by combustion. The reference 31 represents a smoke rejection chimney.

The detector 30 is placed on a conduit connected in bypass to the chimney which leads to a suction device 32, for example a fan or a water pump.

The detector 30 is placed inside a thermally insulated chamber 33.

The electrical signal emitted by the detector 30 is sent to electronic circuits 34. The electronic circuits control an ignition electrode 35 of the burner and receive a signal from a flame detector 36 which is for example a photoelectric cell.

Reference 37 represents a bottle containing a standard combustible gas, for example methane. The outlet duct of the bottle 37 is equipped with a solenoid valve 37a.

The reference 38 represents a stop valve which is placed on a pipe 39 connected to the distribution network of a combustible gas for which it is desired to check the calorific value. The reference 38a is a solenoid valve. The reference 40 represents a filter. Reference 41 represents a heated chamber maintained at a constant temperature which is for example 45 ° C.

The gas pipe 39 passes through the chamber 40 and it includes, inside this chamber, a coil 41, a pressure regulator 42, a capillary tube 43 and a flow meter 44. The output of the flow meter is connected to the power supply in burner gas 29.

The reference 45 represents an air duct which is connected to a source of compressed air, for example to a compressor.

The pipe 45 is equipped with a stop valve 46, a solenoid valve 46a, a filter coupled to a pressure reducer 47 and a second filter called the coalescer filter 48.

The pipe 45 comprises, in the passage through the chamber 40, a coil 49, a mass flow meter 50 and an automatic valve 51 for regulating the air flow. The assembly formed by the mass flow meter 50 and the control valve 51 is connected to the electronic circuits 34. The air duct leaving the chamber 40 is connected to the air supply to the burner 29. The outlet of the bottle of standard gas 37 is connected in bypass on line 39.

The operation is as follows.

In a calibration phase, the burner is first operated by supplying it with standard gas and with air and the detector 30 automatically adjusts the position of the automatic valve 51 so that combustion is optimum, that is to say -to say that the air / fuel ratio is equal to the optimum combustion of the burner for the standard gas considered. Knowing the stoichiometric air / fuel ratio of the standard gas, we can thus calculate the deviation from the stoichiometry due to the burner and calibrate the installation.

Note the position of the automatic valve 51.

Once the calibration has been carried out, the burner 29 is supplied with an unknown fuel gas, for example the gas delivered by a network of distribution. The detector 30, in cooperation with the electronic circuits 34 and with the regulating valve 51, automatically regulates the air flow to the optimum value corresponding to the combustion optimum.

The position of the automatic valve 51 compared to the position it occupied during calibration, indicates the amount of air corresponding to the stoichiometric proportions for the gas to be controlled and makes it possible to calculate the lower calorific value of this gas.

Claims (15)

1. A method for globally detecting the nature of the combustion gases, according to which there is a detector in the combustion gas circuit comprising a layer of metallic phthalocyanine placed between two electrodes and an electrical signal is collected between said electrodes which varies according to the nature of the combustion gases, characterized in that curves of variations in the resistance of phthalocyanine are plotted as a function of the inverse of the temperature in degrees Celsius for various hygrometric degrees of the gases, which curves have a point of convergence and said detector is kept at a temperature above a minimum threshold, slightly lower than the temperature corresponding to said point of convergence, which makes the detector insensitive to water vapor. 2. Method according to claim 1, characterized in that the phthalocyanine is copper phthalocyanine, and the temperature of said detector is maintained above a threshold equal to approximately 40 ° C. 3. Method according to claim 1, characterized in that the phthalocyanine is cobalt phthalocyanine, and the temperature of said detector is maintained above a threshold equal to approximately 30 ° C. 4. Device for globally detecting the nature of the combustion gases of the type comprising a detector comprising a thin layer of a metallic phthalocyanine which is placed in contact with the combustion gases and which connects two electrodes between which an electrical signal which varies varies depending on the nature of the combustion gases and which passes through a minimum for an air / fuel ratio close to the optimum, characterized in that it comprises means for maintaining the temperature of said detector above a threshold, which is determined as a function of the nature of said phthalocyanine and which is slightly lower than the temperature of the point of convergence of the lines representing the variations in the resistance of said phthalocyanine as a function of the inverse of the temperature expressed in degrees Celsius for different hygrometric degrees. 5. Device according to claim 4 wherein said phthalocyanine is copper phthalocyanine, characterized in that it comprises means for maintaining the temperature of said copper phthalocyanine constantly above 40 ° C. 6. Device according to claim 4 wherein said phthalocyanine is cobalt phthalocyanine, characterized in that it comprises means for maintaining the temperature of said cobalt phthalocyanine constantly above 30 ° C. 7. Device according to any one of claims 4 to 6 of the type comprising a detector (14), consisting of a plate (25) of an insulating material on which are deposited two electrodes (26, 27) and a film of a metallic phthalocyanine connecting the two electrodes together, characterized in that said wafer further carries electrical heating resistors which are connected to a voltage source. 8. Device according to any one of claims 4 to 7, of the type in which said phthalocyanine film is obtained by applying to said support a thin layer of a suspension of metal phthalocyanine particles in a solvent taken from the group of tetrachloride of carbon, ether or acetone, characterized in that said film also contains a few grams per liter of a hydrophobic material dissolved in said solvent. 9. Device according to claim 8, characterized in that said hydrophobic material is a liquid or solid alkane whose molecules have a number of carbon atoms greater than 10. 10. Device according to claim 9, characterized in that said alkane is paraffin oil. 11. Method for manufacturing a detector intended for a device according to any one of claims 9 and 10, characterized in that:
- Dissolving in a solvent taken from the group of carbon tetrachloride, ether and acetone, a quantity of a liquid or solid alkane of the order of a few grams per liter of solvent;
a quantity of particles of a metallic phthalocyanine is then added to said solvent, of the order of 10 g per liter of solvent,
- Stirred to form a homogeneous suspension;
- applying a thin layer of said suspension between two electrodes (26, 27) placed on an insulating plate (25);
- And, after evaporation of the solvent, one obtains a phthalocyanine semiconductor film insensitive to the humidity of the gases. 12. Application of a device according to any one of claims 4 to 10 to a fuel burner to verify the proper functioning of said burner, characterized in that the electrical signal delivered by said phthalocyanine-based detector is compared with a determined threshold and an alarm signal is triggered when this threshold is exceeded. 13. Application of a device according to any one of claims 4 to 10 to a fuel burner (8), for automatically regulating the operation thereof, characterized in that said detector (14) is placed in a duct (12), in which flue gases emitted by said burner (8) circulate and the electrical signal emitted by said detector (14) is sent into a control loop (15, 16), which controls a shutter means automatic (18), which is placed on the supply pipe of said burner with combustion air (6) or with fuels (5) and which automatically regulates the air / fuel ratio, so that the signal emitted by said detector is minimum, which corresponds substantially to optimum combustion. 14. Application of a device according to any one of claims 4 to 10 to an internal combustion engine in order to automatically regulate the operation thereof, characterized in that said detector (14) is placed in a connected conduit in derivation on the exhaust duct (10) of said engine and the electrical signal emitted by said detector (14) is sent in a control loop (15, 16) which controls an automatic shutter means (18) which is placed in the air supply circuit (3) or in the fuel supply circuit (23) of said engine and which automatically adjusts the air / fuel ratio, so that said signal corresponds to optimum operation of said engine. 15. Application of a device according to any one of claims 4 to 10 for measuring the calorific value of a combustible gas, characterized in that said combustible gas and a known standard gas are successively burned in a burner ( 29) which is equipped with a metal phthalocyanine detector (30) which is placed in contact with the fumes emitted by said burner, which detector sends an electrical signal to electronic circuits (34), which control an automatic valve (51) placed on the duct (45) supplying said burner with combustion air and which automatically adjust the air / fuel gas ratio to a value corresponding to the optimum proportions, and the compared positions of said automatic valve (51) during the combustion of said fuel gas and that of said etlon gas make it possible to calculate the calorific value of said fuel gas.

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