FR2937083A1 - BURNER FOR THE REGENERATION OF INTERNAL COMBUSTION ENGINE PARTICLE FILTERS AND CATALYTIC SYSTEM TEMPERATURE AND EXHAUST LINE INTEGRATING SUCH A BURNER - Google Patents

Abstract

This burner, fed by a mixture of fuel and oxidizer, is intended to generate a flame and, consequently, heat, so as to heat at least one treatment element or an exhaust gas filtration element of an internal combustion engine . The burner comprises: ▪ a burner body (9) having a closed or partially closed end, and the opposite side to this end, an exhaust opening capable of being connected to a pipe for exhausting said exhaust gas; An electric ignition means (2) for said mixture; Means (5, 6) for injecting the fuel and the oxidant independently of one another in the burner body in contact with the electric ignition means (2) at a determined frequency, the frequency controlling said means being identical.

Description

BURNER FOR THE REGENERATION OF PARTICLE FILTERS OF INTERNAL COMBUSTION ENGINE AND THE REALIZATION Ely CATALYTIC SYSTEM TEMPERATURE AND EXHAUST LINE INTEGRATING SUCH A BURNER DOMAIN OF THE INVENTION

The present invention generally relates to a burner intended to ensure the regeneration of particle filters present in internal combustion engines, and more particularly to diesel engines, and in particular a micro-burner operating according to a very particular process which consists in feeding said burner of air and fuel by a pulsed flow, at a certain frequency, and directing the mixture on a hot ignition point. The objective is to obtain for each pulse a variable richness of the fuel / air mixture, so as to scan a range of wealth the widest possible and thus ensure the ignition of this mixture on this incandescent point. The latter can be constituted by a spark plug disposed on the path of said mixture.

In order to finalize the combustion of this combustible mixture after ignition, ceramic honeycombs or grids or even refractory metal fibers are arranged on the path of the combustion gases. Advantageously, these elements can be impregnated with a catalyst of the oxidizing type which favors the combustion of said mixture as soon as combustion starts at the burner. This burner is disposed upstream of a particle filter type assembly with the objective of carrying the filter media integrated in said filter at a temperature sufficient to burn the solid particles, such as the soot, retained on this filter, each time as necessary. This same process can also be used to reach the operating temperature of the catalysts more quickly on motor engines, with the aim of obtaining optimum conversion efficiency. In both cases the objective is to carry the particulate filter or the catalyst to its operating temperature by means of this burner, which can be arranged directly in the vicinity of the filter or the catalyst, without being forced to carry a whole assembly to this temperature. This arrangement allows rapid warm-up for low fuel consumption.

PRIOR STATE OF THE TECHNIQUE

The authorities have introduced increasingly stringent standards to force car manufacturers to develop engines that produce fewer and fewer emissions. Manufacturers are therefore striving to develop heat engines, especially diesel engines and lean-burn engines, with as little as possible of unburned particles.

To this end, in addition to the development of new engines with ever lower fuel consumption, special efforts have been made to develop new exhaust systems designed to reduce emissions of unburned gaseous pollutants and solid particles.

For example, automobile manufacturers have developed catalytic converters, usually made of a stainless steel casing, a thermal insulator and a honeycomb support impregnated with precious metals, such as platinum (Pt). or rhodium (Rh). Such catalysts can reduce emissions of polycyclic hydrocarbons and carbon monoxide (CO), and this, in a proportion of the order of 90%.

However, they have no effect on solid particle emissions. Thus, such catalysts do not provide significant improvement in emissions of diesel engines producing many solid particles.

However, the change in engine combustion is no longer sufficient to meet the discharge guidelines. This is why energetic processes and devices for filtering exhaust gases with regeneration of the filters by combustion are now unavoidable. Such a filtration makes it possible to reduce by more than 90% the total mass of particles emitted by diesel engines.

In known manner, the solid particles are generally trapped by a ceramic filtration cartridge, making up a particulate filter. To work well, a particulate filter requires regeneration to burn the carbon particles trapped in its filtering parts, mainly in the filter cartridge at regular intervals. The main difficulty relates to the start of the combustion of these retained carbon particles, the temperature of the exhaust gas of these diesel engines being much lower than lL. 550 ° / 600 ° C required for this combustion to take place.

Many processes have been implemented to ensure the combustion of these particles associating the catalytic effects of additive, or the production of NO2 from the nitrogen oxides present in the exhaust gas, or even by the implementation of in place of a diesel injection device on an oxidation catalyst arranged upstream of the particulate filter.

However, the major difficulty in ensuring the operation of such particulate filters lies in the possibility or not to achieve the oxidation and combustion phases of the solid particles retained by the filter cartridge. Indeed, on an urban route, the exhaust gas hardly reach a temperature sufficient to ensure the regular and / or complete combustion of the solid particles and thus regenerate the filter significantly limiting its clogging. Even processes using post-injection devices no longer provide in these severe conditions a satisfactory service.

In addition, the known post-injection methods work satisfactorily only if a minimum exhaust gas temperature of about 300 ° C is reached for at least 5% of the operating time. Consequently, the devices and processes implementing the post-injection of diesel into the exhaust gas upstream of an oxidation catalyst become insufficient when the temperature is too low.

Another disadvantage of these systems lies in the parasitic and polluting emissions of hydrocarbons generated during the injection phase, when the temperatures are too low, for example around 300 ° C.35 To achieve the combustion of the solid particles retained on the filter , the prior art also proposes to have a burner at the filter inlet and turn it on when the vehicle engine is stopped. However, this involves many disadvantages, among which may be mentioned the difficulty of controlling or even simply initiate combustion in the burner, the difficulty of thermally insulating the filter, the significant rise in the temperature of the burner during the phase combustion (beyond 1400 ° C) and the requirement to have a large filtration capacity to be able to provide a sufficiently long service, that is to say between two stops engine.

More recently burners have been proposed to completely overcome the operating conditions at low temperatures. However, none of them currently allows satisfactory operation for all operating conditions. In addition, these burners have some unacceptable defects, such as excessive size with often in this case an overconsumption of diesel fuel, the difficulty of operating satisfactorily when the engine is at full speed, the stability of the flame or a contribution in insufficient calories.

In addition, such burners have real difficulties to operate satisfactorily during normal operation of the engine, because of the difficulty of igniting the burner, the strong turbulence associated with the pulsed regimes prevailing in the exhaust line and therefore in the burner is particularly unstable combustion. Sophisticated flame arrestors must be incorporated to avoid the parasitic hydrocarbon emissions that would follow in the event of its extinguishment.

Such burners therefore require large and sophisticated systems, so expensive, to control these problems.

The object of the present invention is to provide a method and a device for burning solid particles from the internal combustion of a heat engine solving the disadvantages of the devices of the prior art.

The object of the invention is to obtain the increase of the temperature necessary for the complete combustion of the solid particles or soot deposited on the filter cartridge, while reducing as much as possible the portion of these calories which will be absorbed upstream of the particulate filter. by allowing a reduction of the volume of the materials used, such as the envelope and the volume of the catalyst.

Another object of the invention is to provide a method and a device for burning solid particles, avoiding any risk of accumulation of particles in the filter cartridge (clogging), and therefore any risk of inadvertent regeneration, whatever the operating conditions of the engine, in particular for urban transport applications.

Furthermore, the invention may advantageously be associated with the known means already used alone or in combination with other devices to begin to oxidize the soot contained in the exhaust gas from the lowest temperatures (100 ° C) and ensure complete combustion, whatever the operating conditions. The use of an additive in the fuel, or the deposition of catalyst on the filter media can further reduce the heating duration and intensity, and thus further reduce overconsumption.

Another object of the invention is to provide a micro-burner for the quantitative reduction, or even the elimination of soot contained in the exhaust gases of heat engines, this micro-burner opening directly on the surface of the filter media, and especially at its center. It has reduced dimensions, which makes it compact and easily integrated on the particulate filter / exhaust line of a motor vehicle.

Another object of the invention is to allow the regeneration of the filtering means implemented without causing an excessive increase in the temperature of the gases at the outlet of the filtration device, or significant overconsumption of fuel.

Furthermore, the purpose of the invention is to achieve a quantitative reduction, or even elimination, of the particles contained in the exhaust gases of an internal combustion engine, without having to use a very specific oxidation catalyst, such as for the post-injection, which allows the use of catalyst with low concentration of precious metals because only remains the oxidation function of the hydrocarbons and the residual carbon oxides to ensure there will be nothing more than the oxidation function of the hydrocarbons and carbon monoxide residual exhaust gases to ensure.

Another object of the invention is to provide a solution for the quantitative reduction, or even elimination of soot contained in the exhaust gas of an internal combustion engine, which is relatively inexpensive, reliable and flexible, and which delays the clogging of the engine as much as possible. filter or eliminating it, which ope is the load of the engine, without being affected by the possible presence of sulfur compounds, such as sulfur dioxide in the exhaust gas. The object of the invention thus makes it possible to use gas oils with a high sulfur content.

Finally, this micro-burner is advantageously used in combination with all the new catalytic processes used to meet the emissions imposed by the new standards, such as Euro 6. Indeed, to satisfy these emissions, it is necessary to combine catalysts reduction of nitrogen oxides by urea injection to particulate filters and ensure optimum operation of both functions, namely oxidation of unburned combustion and reduction of nitrogen oxides. Since these nitrogen oxide reduction catalysts (SCR) only operate at a minimum temperature of 200 ° C., the operation of the micro-burner as soon as the engine is started makes it possible to reach this temperature rapidly and to satisfy the levels more easily. emissions to be respected.

Still in the context of these new Euro 6 standards, it is also envisaged to associate oxidation catalysts with nitrogen oxide reduction catalysts. In doing so, and for the same purpose of rapidly attaining the operating temperatures of these catalysts at startup, the use of one or more micro-burners in accordance with the invention makes it possible to satisfy these standards.

SUMMARY OF THE INVENTION

The object of the invention therefore relates to a burner for heating at least one filter cartridge for exhaust gas of an internal combustion engine at a temperature above the oxidation temperature and / or the combustion temperature solid particles trapped in said filter cartridge, or to temperature a catalytic system, that is to say a treatment member of said exhaust gas.

This burner is fed with a mixture of fuel and oxidant, intended to generate a flame and corollary heat for heating said filter cartridge or said catalytic system. It comprises a burner body having a closed or partially closed end, and the opposite side to this end, an exhaust opening may be connected to a discharge pipe of said exhaust gas. It further comprises: an electric ignition means of said combustion / fuel mixture; means for injecting the fuel and the oxidant independently of one another into the body of the burner in contact with the electric ignition means at a determined frequency, the control frequency of said means being identical or different. .

In other words, the burner - object of the invention, comprises means for supplying it by a flow of air (oxidant) and pulsed fuel at a determined frequency, depending on the size of the burner and the flow rate air / fuel mixture, so as to automatically have in contact with the electric ignition means, a variable fuel richness. In doing so, the fuel richness of the oxidant / fuel mixture passes sensib.ement of pure air to a very rich fuel mixture at each flow pulse, the interest being to have permanently in contact with the electrical ignition means and during each phase a period during which the mixture has the right range of richness to ignite in contact with said electrical ignition means located on the path of the mixture.

In order to maintain a pulsating effect, the means providing the injection of oxidant (air) and fuel must be open at most 80% of the time, and preferably with a duration of between 10 and 50%. According to the invention, the control frequency of said oxidant and fuel injection means is between 0.5 and 30 hertz.

According to an advantageous characteristic of the invention, the flame resulting from the ignition fuel / oxidant leads to a refractory metal knit, suitable to promote the maintenance of the flame and further to optimize the quality of combustion.

According to another advantageous characteristic of the invention. a jacket made of quartz or glass-ceramic material is positioned in the body of the burner, also in order to optimize the quality of the combustion.

According to yet another advantageous characteristic of the invention, a buffer of metal fibers, advantageously coated with a catalyst (of platinum oxidation), is positioned in the body of the burner, in the vicinity of its discharge opening. palladium, or other metals used in this type of catalyst) or a honeycomb structure made of ceramic or retallic material, able to obtain a more homogeneous heat flow and an optimum quality of combustion, this honeycomb structure which can be in the same way impregnated with an oxidation catalyst

Advantageously, the means for injecting the fuel and the oxidant respectively consist of an injector and a solenoid valve.

In addition, the adjustment of the fuel and oxidant injection frequency is advantageously carried out by means of a computer, the frequency signal being of square shape.

This calculator controls the injection rates into fuel (gas oil) and into oxidant (air) as a function of the signals delivered by temperature sensors, one of them being located in the body of the burner and the second to the particle filter inlet, and a differential pressure sensor which measures the pressure difference between the inlet and the outlet of the particulate filter, and thus indicates the evolution of the pressure drop due to clogging. filter media of said fila-e by the solid particles.

This computer controls the opening of the solenoid valve ensuring the arrival of air at the right frequency, as well as the fuel injector, so that the air / diesel fuel mixture present at the ignition resistance at each phase of the frequency of the pulses leading to pass through a range of richness with good flammability.

This calculator manages the resistance of the electric ignition means, both during the preheating, and during the entire operating time, as well as the adjustment of the intensity of the electric current which supplies said resistance, so that that, in spite of the flame, the temperature of the filaments which constitute it does not become excessive, with the risk of resulting in its destruction.

The optimized range of fuel / fuel mixture richness, for which it lights up perfectly, varies from 0.6 (poor, with a 40% excess of oxidant) to 1.2 (rich, with a fuel excess of 20%). relative to the stoichiometric mixture).

According to one embodiment of the invention, the mixture c.e fuel and oxidant opens by means of a conduit in a pre-chamber, located upstream of the burner body, the electric ignition means of said mixture being positioned in the prechamber.

According to an advantageous embodiment of the invention, the burner further comprises one or more ceramic elements, in particular of honeycomb structure, or grids or refractory metal fibers, arranged at the outlet of the prechamber or on the the flame resulting from the contact between the oxidant / fuel mixture and the electric ignition means in the burner body.

According to another advantageous embodiment of the invention, the mixture of fuel and oxidant opens into the body of the burner by means of at least one duct in a direction substantially tangential to said burner body, so as to be able to print to said mixture a swirling motion within the burner body. In this case, the burner body is essentially cylindrical in shape.

In this configuration, it may furthermore comprise a second conduit for supplying the mixture of fuel and oxidant discharging into the burner body, also in a direction substantially tangential to the burner body, so that it can again print to said mixture a swirling motion within the burner body. This makes it possible to evenly distribute the mixture in the ignition zone.

This feed assembly provided with its ignition resistance, opens, or advantageously is contained in a blind cylindrical tube, equipped with a tangential secondary inlet of air or mixture, and containing ceramics or metal elements to promote the spread of combustion.

According to a particular embodiment of the invention, the burner body can form a straight cylinder placed horizontally, vertically, or inclined if necessary.

In addition, according to another particular form of the invention, the body of the burner may comprise a blind cylinder, substantially coaxial with said body, and open at its lower end, that is to say upstream of the flow of gases. 20, said cylinder having diametrically opposite side openings in the vicinity of its blind end, adapted to allow the exit at this level of said exhaust gas within the body of the burner by printing a tangential rotation movement.

In practice, the burner may furthermore comprise two or more concentric pipes, one for the supply of fuel mixed with air, the other or the others for the supply of air or gas. exhaust, the pipes being disposed upstream of the adductiol conduit of a mixture of fuel and oxidant opening into the burner body. Conveniently, the supply duct of a mixture of fuel and oxidant opening into the burner body may have a length determined so as to allow homogenization of melanie upstream of the connection to the burner body. Thus, the mixture becomes easier to ignite by the electric ignition means.

In practice, the burner may further comprise a second electric ignition means, also positioned within the burner body, these electric ignition means being constituted by conventional heating candles or electric arc candles. These candles represent an inexpensive and easy to assemble means for igniting the mixture.

According to the invention, the burner is disposed upstream of a particulate filter. However, it may be mounted as a bypass of the exhaust duct, or even within such a duct, or may be incorporated in the particulate filter.

When the burner is for example installed on a vehicle exhaust line, it can be controlled via the on-board computer. In practice, the oxidant may be air from a turbocharger member. This provides a suitable air flow and a homogeneous mixture with a high air speed for mixing.

In addition, the invention relates to an exhaust line of an internal combustion engine, comprising at least one inlet for the gases resulting from the internal combustion, at least one filter cartridge for trapping the solid particles contained therein. in the exhaust gas of said engine, and at least one exhaust port to the atmosphere of the gases, located downstream of the filter cartridge. According to the invention, this line comprises at least one burner as explained above. It also relates to an exhaust line of an internal combustion engine, comprising at least one inlet for the gases resulting from the internal combustion, at least one nitrogen oxide reduction catalyst or an oxidation catalyst, intended reducing pollutants NOx, HC, CO contained in said exhaust gas, and at least one exhaust port to the atmosphere of said gas downstream of said catalyst. According to the invention, this line comprises at least one burner as explained above. BRIEF DESCRIPTION OF THE FIGURES

The present invention will be better understood on reading the description which follows, made with reference to the drawings which show, in no way limiting, embodiments of the device associating a burner with a filtration system according to the invention and in which: Figure 1 is a schematic representation for illustrating the supply of air and diesel in the pre-chamber of the burner according to a first embodiment of the invention to obtain ignition of the mixture on an incandescent electrical resistance; Figure 2 is a schematic representation of a second embodiment of the invention, wherein the air / diesel mixture is projected on the resistor contained directly in the body of the burner; said burner is equipped with a tangential secondary air inlet which can even be used to introduce additional fuel; Figure 3 is a schematic representation illustrating the implantation of the micro-burner of the invention directly into the casing containing the catalyst system and filtration; FIG. 4 is a diagrammatic representation of another embodiment of the pre-chamber installation in the body of a burner according to the invention, illustrating the possibility of incorporating multiple inputs of the exhaust gas flow rate; Inlets opening tangentially into the burner body; FIG. 5 is a schematic representation of the implantation of this miniaturized burner in an exhaust line of gases from an internal combustion engine for heating a nitrogen oxide reduction catalyst or an oxidation catalyst. ; Figure 6a is a schematic representation of a third embodiment of the burner according to the invention, Figure 6b of which is a cross-sectional view; Figure 7 is a schematic representation illustrating another embodiment of the burner of the invention in the exhaust line; Figure 8 is a schematic representation of a variant of the third embodiment of the burner of the invention shown in Figures 6; Figures 9a and 9b are diagrammatic cross-sectional representations of the particulate filter contained in the exhaust line, respectively of square and circular section. 12 MODES FOR CARRYING OUT THE INVENTION

According to a first embodiment of the invention, more particularly described in connection with FIG. 1, the burner 9 comprises a prechamber 3 containing a spark plug 2 on which an air / fuel mixture is injected.

A computer 1 controls, based on the significant counter-pressure information of the clogging and exhaust temperature collected by sensors, respectively of temperature and pressure mounted on the exhaust line and the engine, the start of the burner. following the procedure described below.

A heating plug 2, preferably of the type with apparent turns, is supplied with electrical energy via the computer 1 during a preheating period, to bring to incandescence the filaments that constitute it. This resistance is contained in the prechamber 3, so as to force the air / diesel fuel mixture arriving via a feed tube 4 to bathe it completely and to ignite before being ejected towards the body of the burner 9.

The air flow, advantageously supplied with compressed air by a compressor, the turbocharger of the engine or the two associated, is admitted by a solenoid valve 5, also controlled by the computer 1 in the form of a square signal, of the pulsed type. at a frequency ranging from 0.5 hertz to 30 hertz, and whose opening percentage is proportional to the amount of diesel fuel injected. However, it must not exceed 80% of the time in terms of the opening of the solenoid valve, in order to preserve the effect of the pulsations.

The choice of frequency depends on the size of the burner. Thus for a burner designed to provide up to 20 KW (power typically required to equip an engine of the order of 60 KW), contained in a cylinder 45 mm in diameter and 120 30 mm long, good combustion results and flame stability are obtained for an injection frequency of air and fuel of 10 to 12 hertz.

For a larger burner used to supply up to 80 KW and contained in a cylinder 60 mm in diameter and 150 mm long, the best operation is obtained for a frequency of between 5 and 7 hertz. .

However, good results have been obtained by using different frequencies, respectively of air and fuel. Thus, good ignition qualities were observed by introducing air at a pulsating frequency of 5 Hertz, and gas oil at a pulse frequency of 0.5 Hertz. In the same way, good results have been obtained with an air pulse frequency close to 1 Hertz, and a gas pulsation frequency close to 10 Hertz.

The diesel fuel is fed from an injector 6, then conveyed by a capillary 7 to open into the feed tube 4. The opening of this injector 6 is driven by the computer 1 at the same frequency as the solenoid valve 5 or at a different frequency, its opening percentage being slaved to the target temperature targets, controlled by the temperature sensor 8 located in the burner body.

Thus, for start-up, the diesel fuel injection flow rate may represent only 5% of the nominal flow rate, or even less, this start-up flow rate being implemented for about twenty seconds so as to bring the entire body of the burner into operation. temperature.

Then the flow rate is gradually increased to the nominal step flow, after 20 and 40 seconds minimum, the nominal flow then being maintained as long as the temperature level at the inlet of the filter does not exceed 600 ° C.

Then, by an all or nothing proportional control system, the flow is automatically adjusted to be close to the set temperature. In fact, with respect to this setpoint temperature, two possibilities of regulating the gas oil flow rate can be implemented: either arbitrarily reduce the fuel flow rate (for example 30%), then restore the nominal flow rate when the temperature drops below this setpoint temperature, 30 ^ is, more sophisticatedly, begin to reduce the nominal flow rate of the fuel before reaching this setpoint temperature e-: reduce it more and more when approaching it, and conversely again increase this fuel flow when moving away from this setpoint temperature.

The prechamber 3 preferably opens laterally to the cylindrical body of the burner 9 partially shown in cross section.

To promote combustion, a ceramic honeycomb type 10 or a metal refractory steel grid is positioned in front of the outlet of this prechamber 3 (see Figure 3) Figure 3 shows the implantation of this burner schematically directly in the volume of a catalyst / particulate filter unit. This burner is arranged in the path of the exhaust gas, which arrives through the pipe 13 in a casing 14 containing a catalyst 15 and a particulate filter 16.

Upstream of the catalyst 15 are arranged a back pressure or differential pressure sensor 17, intended to measure the evolution of the clogging of the filter, as well as a second temperature sensor 308, for regulating the temperature at the inlet of the system. and to be able to act on the fuel flow, in order to give the computer 1 the information necessary for managing the ignition of the burner.

A perforated steel plate or similar device 18, that a lining of refractory metal fibers is advantageously disposed between the burner and the catalyst, so as to have a more homogeneous heat flow.

FIG. 2 represents a second embodiment in which the air / diesel mixture is in this case directly injected via line 4 onto the ignition resistor 2, disposed directly in the body of the burner 9 near the closed orifice of the cylindrical tube constituting said burner body 9. In this embodiment, there is shown a secondary inlet pipe 11, intended to allow the introduction of additional air, or an air / fuel mixture.

This secondary pipe 11 opens tangentially at 12 into the burner body. It can even be envisaged to inject secondary fuel with air 206, through a capillary tube 207 in this tube 11. In this configuration, it is not necessary to inject variable frequency pulsed air, since there is in the body of the burner a flame already stabilized by the main injection of air / diesel mixture introduced in a pulsed manner at low frequency. Ceramics in the form of a honeycomb or metal fibers 10 are arranged near the resistor 2 in the path of the flame, but at a sufficient distance so that it does not disturb the starting phase. In known manner, these ceramics or metal fibers promote the development of the flame. A temperature sensor 8 placed in the body of the burner 9, advantageously near the gas discharge outlet, is connected to the computer 1, to allow the control of the presence and ignition of the flame.

FIG. 4 represents another possibility of implantation of the antechamber 3 containing the resistor 2 with its arrival of air / diesel mixture 4. In this embodiment, the antechamber is disposed at the center of the burner body and opens into the ci at its closed end. In front of the outlet zone of said prechamber 3, a deflector 19 is positioned, the function of which is to extend the path of the flame and to distribute it over the entire periphery of the burner, in order to promote the contact of the flame with the ceramics. or metal fibers 10.

FIG. 4 also shows the possibility of introducing a part of the flow rate of the exhaust gases coming from the duct 13 via several pipes 111 which open tangentially at 112 into the body of the burner 9. the gases resulting from the combustion of the air / gas oil mixture are given a rotational movement and the rate of combustion is thus accelerated. By tangentially, we mean tangentially to a circular section of the burner body 9 transversely to the axis of revolution of the burner. Thus, even if said mixture is already ignited at this level of the burner, the propagation of said combustion is optimized throughout the length of said burner, and because of this tangential introduction, the combustion rate is accelerated significantly, typically on the order of one to two times the speed of sound.

The glow plug 2 may, for example, be of the incandescent type (ie of the type used on the chambers of diesel engines) However, this glow plug may also be of apparent resistance type, which allows direct contact of the fuel mixture with the incandescent filament.In any case, it is positioned to be intimately bathed by the mixture of fuel and oxidant.5 According to a characteristic of the invention, the oxidant is delivered by a solenoid valve 5 controlled by a signal of the pulsed type, and in particular square, which may have an adjustable opening frequency of 0.5 hertz to 30 hertz, the opening time being adjusted according to the amount of fuel injected.

In parallel, the fuel is injected by an electromagnetic injector 6 of the type used on fuel injection vehicles. The opening frequency of this injector can be exactly the same as that of the control of the air solenoid valve. However, we have seen previously that these frequencies could be different.

In doing so, we obtain synchronized variations in the richness of the mixture.

Given the variations in density, the heated candle, and generally the electric ignition means is bathed in clean air, then by air with more and more fuel, until the mixture ideal for burning. The proportion of air will then be reduced more and more to obtain a mixture too rich for which, theoretically, the flame should go out, but that is where the judicious choice of the opening control frequencies of the solenoid valve and the injector.

Indeed, at the moment when the flame should go out due to an excess of fuel in the mixture, a new wave of air arrives, inducing the activation of the flame and so on.

To start up this burner, when starting the fuel is always injected in a very small quantity for a few seconds, so that the released combustion energy puts the temperature of the ceramic or metal fibers arranged on the path of the flame, so as to obtain the cleanest and most complete combustion possible.

The thermocouple 8 disposed within the burner can also be used by the computer 1 for the ramp-up of the burner and the control of the quantity of fuel injected, the frequency being selected according to the size of the burner.

When the nominal power of the burner is reached, the temperature level detected by the temperature sensor 308 located just upstream of the particulate filter is taken into account by the computer 1 to adjust the fuel flow injected to regulate this temperature.

As soon as the burner starts, the supply of oxidant through the pipes 11, when the burner is provided with them, makes it possible to generate turbulence within the burner inherent to the centrifugal introduction movement of the oxidant, which contributes to improving the quality of the burner. combustion. Advantageously, even if the case where compressed air is available in unlimited quantity, it is advantageous to have several manifolds 111 to introduce a part of the exhaust gas, the temperature of these contributing to improve the quality of the combustion. The pipes 111 allow to introduce air or diesel engine exhaust that today on modern engines, contain at least 10% oxygen, and will therefore help to finish the combustion

Similarly, for high-power burners, it is advantageous as soon as the burner increases in power, to introduce additional fuel by the solenoid valve 206 and then the capillary 207 into the tubing 11, at which a aerosol mixed with the oxidizer.

Indeed, in order to burn large mixing rates to minimize the volume of the burner it is necessary to introduce said mixture with as much movement as possible and at the highest temperature: this is the desired goal when a large proportion of the mixture is injected into a well-formed and sufficiently energetic flame.

At the outlet of the prechamber within the burner, the ceramic elements, in particular made in a honeycomb structure, are arranged so as to be on the path of the flame and thus contribute to the improvement of combustion. These ceramic elements can be replaced by fibrous structures of refractory metal. In both cases, ceramics or metal fibrous structures may advantageously be impregnated with a catalytic deposition of the oxidizing type, this deposit promoting the quality of the combustion at startup. The ignition of the burner by the computer comprises the phases consisting of: electrically supplying the heating candle 2; after a predetermined time corresponding substantially to the time required for the heating candle 2 to reach a temperature of between 600 ° C. and 800 ° C., to inject into the pre-chamber 3 a pulsed mixing flow via the tubular duct 4, proceeding under the control of the computer, microinjections of diesel fuel through the capillary 7 by means of the injector 6, until the temperature sensor 8 detects a significant increase in temperature: it is this sensor that plays the role flame detection; for example the computer decides to stop the process if after 10 seconds, an increase of more than 20 ° C in the temperature in the burner chamber has not been measured; The flame in direct contact with the ceramic elements 10 reaches after a few seconds of operation a very high temperature favoring perfect combustion. The flame heats the ceramic to more than 1100 ° C, and it is then the high radiation caused by this temperature of the ceramic that increases the temperature of the mixture before combustion and accelerates its combustion; Then, at the same time, the gas oil flow rate and the air-tightness rate controlled by the computer 1 are increased in quantities and proportions such as the temperature of the exhaust gases, measured by the temperature sensor 308 at the inlet. the filter cartridge remains below 600 ° C, this temperature being controlled by the computer which also provides information on the operating conditions of the engine; to stop the combustion in the burner by a control of the computer, depending on the operating time, the measurement of the clogging by the pressure sensor 16.

According to the invention, it is intended to ensure proper operation and especially a correct start of the burner, whatever the operating conditions of the engine, including at full power, that is to say when prevailing in the burner conditions of extreme turbulence.

For this, the principle of injecting into a prechamber containing a heating candle, an oxidant / fuel mixture in a pulsed manner at a controlled frequency, allows in fact the passage into contact with the heating candle a mixture having a good flammability to each pulsation, and thus generates at each pulse a flame front which develops all the faster as the speed of introduction of gases is large. There can therefore be no interruption of the flame since it is permanently re-lit.

As indicated in the prior art, this micro-burner can be implemented in the same way as for the regeneration of particulate filters, whenever the emission requirements for pollutants impose an optimum efficiency of the catalysts used for the aftertreatment of the exhaust gases from the start of the engines.

FIG. 5 shows the implantation of this miniaturized burner to bring the exhaust gas 20 up to temperature as soon as the engine is started, in order to raise the operating temperature of this catalyst 21 controlled by the temperature sensor 508 very rapidly. .

Thus, the burner of the invention can advantageously be used upstream of a catalyst for reducing nitrogen oxides 21 by injecting ammonia or urea, since this can only occur at a minimum temperature of 180/190 ° C, that is to say that it is not possible to reduce the nitrogen oxides on this catalyst until this minimum temperature is reached.

In the same way, said burner can also be used upstream of an oxidation catalyst 21 based on precious metals, such as platinum or palladium, so that the temperature at which the catalyst comes effective is reached very quickly. These catalysts generally do not have to be effective until around 200 ° C.

The very small size of this burner 9 making it possible for example to place it directly in front of the catalyst, or even in the conduit for the arrival of the exhaust gases at the level of this catalyst, so that it becomes possible to bring the temperature to room temperature. catalyst in an extremely short time, typically a few seconds, compared to a duration of several minutes in the absence of this device.

FIGS. 6a and 6b show another embodiment of the burner according to the invention. The body of the burner 9 comprises a blind cylinder 30, substantially coaxial with said body, and open 34 at its lower end, that is to say upstream of the flow of the exhaust gases, so that a part of these penetrates into said cylinder. The latter has at least one and advantageously two diametrically opposite lateral openings 31 in the vicinity of its blind end, extending along a generatrix of said cylinder, and able to allow the exit at this level of said exhaust gases within the body of the cylinder. burner by printing a tangential rotation movement in the same direction as that initially generated by the injection means within the burner.

The fuel / oxidant mixture enters the vicinity of the base of the body of the burner 9 as for the previous embodiments, but the flame resulting from the passage of said mixture on the ignition means 2 leads directly to a refractory metal knit 32, typically made Inconel, suitable to promote the maintenance of the flame and further optimize the quality of combustion. In this case, this knit is positioned according to a torus, around the base of the cylinder 30. This torus is held in place by means of fastening lugs 33 extending radially from the outer wall of the cylinder. The constituent fibers of this metal knit may advantageously be coated with a nitrogen oxide reduction catalyst or an oxidation catalyst intended to reduce the NOx, HC, CO pollutants contained in the exhaust gas.

Advantageously, as has been described with reference to FIG. 2, an additional feed 11 of fuel / oxidant mixture is put in place, a tangential movement being printed on said mixture through the opening 35 formed laterally on the free end of said inlet 11 within the body of the burner.

Due to the presence or the openings or lateral slots 31 formed in the cylinder, and corollary of the passage through them of a portion of the exhaust gas, is optimized combustion of the flame of the fuel / oxidant mixture , the latter removing in the exhaust gas residual oxygen they systematically due to the incomplete combustion resulting from the cycle in the engine itself.

Advantageously, it also positions within the body of the burner at its downstream outlet, and more precisely along its inner side wall, a jacket 37 made of quartz or glass-ceramic material. The presence of this shirt promotes combustion at a higher temperature and therefore more complete.

FIG. 7 shows the implantation of the burner previously described in an exhaust line, for example of the type described in connection with FIG. 3. The exhaust duct containing the burner opens into a volume allowing to have a homogeneous flow, and then direct it to the inlet of the catalyst and the particulate filter.

There is shown in Figure 8 a variant of the burner of Figures 6a and 6b. It is based on the same principle. However, it incorporates within the body of the burner in the vicinity of its downstream outlet a buffer 36 consisting of metal fibers advantageously coated with a reduction of nitrogen oxide catalyst or an oxidation catalyst for reducing NOHC pollutants type , CO contained in the exhaust gas. The presence of such a buffer makes it possible to homogenize the heat flow at the exit of the burner, and consequently to improve combustion. This buffer could also be made of ceramic honeycomb type.

FIGS. 9a and 9b show a cross-sectional view of the particulate filter. This, whether of cylindrical or parallelepipedic shape defines a central pipe extending substantially coaxially with the axis of revolution of the burner described in connection with Figures 6 and 8. In doing so, the burner in question opens close immediate filter media contained in the filter, so as to directly heat it limitatively the central portion of said media. This being brought to the temperature sufficient to burn the carbon particles retained at said filter, and because of the energy resulting from this combustion, there is propagation of all the combustion throughout the volume of said filter.

In doing so, this device makes it possible to very substantially reduce the amount of fuel consumed for the regeneration operation, since it allows in a certain way to carry only a small part of the flow of the exhaust gases at the temperature necessary to start carbon combustion on the filter. This optimizes the quality of the exhaust gas filtration.

Claims (18)

REVENDICATIONS1. Burner fed with a mixture of fuel and oxidant, for generating a flame and, consequently, heat for heating at least one treatment element (21) or for filtering (16) the exhaust gases of a combustion engine internal, said burner comprising a burner body (9) having a closed or partially closed end, and the opposite side to this end, an exhaust opening adapted to be connected to a discharge pipe of said exhaust gas; characterized in that it further comprises: an electric ignition means (2) of said mixture; means (5, 6) for injecting the fuel and the oxidant independently of one another pulsed into the burner body in contact with the electric ignition means (2) at a specific frequency, the frequency controlling said means being the same or different. 2. Burner according to claim 1, characterized in that the control frequency of said means (5, 6) is between 0.5 and 30 Hz. 3. Burner according to claim 2, characterized in that the opening percentage of the means (5, 6) for respectively injecting the fuel and the oxidant is less than 80%, and preferably between 10 and 50%. 4. Burner according to one of claims 1 to 3, characterized in that it comprises a refractory metal knit (32) at which opens the flame resulting from ignition fuel / oxidant, adapted to promote the maintenance of the flame and further to optimize the quality of combustion. 5. Burner according to one of claims 1 to 4, characterized in that it comprises a jacket (37) made of quartz or vitreous ceramic material, positioned in the vicinity of its downstream outlet and along its inner wall, adapted to optimize the quality of combustion. 6. Burner according to one of claims 1 to 5, characterized in that it comprises in the vicinity of its discharge opening, a buffer (36) made of metal fibers, preferably coated with an oxidation catalyst, or ceramic honeycomb structure, also likely to be impregnated with an oxidation catalyst, said buffer being able to obtain a more homogeneous heat flow and an optimum quality of combustion. 7. Burner according to one of claims 1 to 6, characterized in that the means for injecting the fuel and the oxidant are respectively constituted by an injector (6) and a solenoid valve (5). 8. Burner according to one of claims 1 to 7, characterized in that the adjustment of the fuel injection and oxidant frequency is achieved by means of a computer (1), and in that the signal of the frequency is of cane. 9. Burner according to claim 8, characterized in that the computer (1) controls the injection rates of fuel and oxidant according to the signals delivered by temperature sensors, one of them being located in the burner body (9) and the second at the inlet of the particulate filter, and by a differential pressure sensor which measures the pressure difference between the inlet and the outlet of the particulate filter, and thus indicating the evolution of the loss of charge due to clogging of the filter media of said wire: re by the solid particles. Burner according to one of Claims 1 to 9, characterized in that the mixture of fuel and oxidant flows out via a pipe (4) into a pre-chamber (3) situated upstream of the burner body (9). , and in that the electric ignition means (2) of said mixture is positioned in the antechamber (3). Burner according to one of Claims 1 to 10, characterized in that it further comprises a ceramic element or elements (10), in particular a honeycomb structure, or refractory metal grids or fibers. , arranged at the outlet of the antechamber (3) or on the path of the flame resulting from the contact between the oxidant / fuel mixture and the electric ignition means (2) in the burner body. 12. Burner according to one of claims 1 to 11, characterized in that the mixture of fuel and oxidant opens into the body of the burner (9) by means of at least one conduit (7) in a substantially tangential direction said burner body (9) so as to be able to impart to said mixture a swirling movement within the burner body (9). 13. Burner according to claim 12, characterized in that it comprises a second conduit (11) for supplying the mixture of fuel and oxidant opening into the burner body (9) in a direction substantially tangential to the burner body ( 9) so as to be able to impart to said mixture a swirling movement within the burner body (9). 14. Burner according to one of claims 1 to 9, characterized in that it comprises a deflector (19), obstructing a substantial portion of the burner body (9). 15. Burner according to one of claims 1 to 14, characterized in that the oxidant is air from the turbocharger engine. 16. Burner according to one of claims 1 to 15, characterized in that a portion of the exhaust gas flows tangentially (111, 112) into the burner body, so as to impart to the gases resulting from the combustion of the mixture oxidizer / fuel a rotational movement and to accelerate the rate of combustion. 25 17. Exhaust line of an internal combustion engine, comprising at least one inlet for gases from said internal combustion, at least one filter cartridge (16) for trapping solid particles contained in said gas exhaust of said engine, and at least one exhaust port to the atmosphere of said gases located downstream of said filter cartridge (16), characterized in that it comprises at least one burner according to one of claims 1 to 16.15 18. Exhaust line of an internal combustion engine, comprising at least one inlet for gases from said internal combustion, at least one nitrogen oxide reduction catalyst (21) or an oxidation catalyst (21). ), intended to reduce pollutants NOx, HC. CO contained in said exhaust gas of said engine, and at least one exhaust port to the atmosphere of said gas located downstream of said catalyst (21), characterized in that it comprises at least one burner according to one of Claims 1 to 16.