FR2852670A1 - Oil burner igniting process for heating fixture, involves activating ignition device on one segment of inflammation period, with lower electric power than on other segment of inflammation period - Google Patents

Abstract

The process involves generating an oil mist (3) and conducting the mist to an activated ignition device (14) having a spark gap (15), for an inflammation period, by an electric power supply (16) supplied by a voltage circuit (17). The inflammation period is subdivided into two segments. The ignition device (14) is activated on one segment, with a lower electric power than on the other segment. An independent claim is also included for an ignition device for a group of oil burners.

Description

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  The present invention relates to a method for igniting an oil burner, in which an oil mist is generated. and is led to an ignition device activated, for a period of ignition, by supplying electrical power. In addition, the invention relates to an ignition device intended for an oil burner group 10 and connected to an electrical supply device.

  Oil burners of the type under consideration are frequently used in heating installations. With a view to adapting to the heat demand, said burners are then actuated not continuously, but intermittently. As a rule, the burner is lit with an interval of a few minutes, then operates for a certain period of time, then is put out of operation again until a request for heat is indicated, for example until the temperature of a heating water has dropped below a predetermined value.

  The oil is atomized in order to light the burner. The oil, which then takes the form of an oil mist, is passed to an ignition device. The latter can, for example, be produced in the form of a spark sparker supplied with electrical energy, in such a way that sparks fly repeatedly. A variant of the ignition device takes the form of a "hot spot", that is to say an electrode which can be heated and which can be brought to a temperature high enough for the oil mist ignites there.

  The ignition process generates exhaust gases containing toxic substances, in particular NO, and O3. The content of such toxic substances in exhaust gases should be kept as low as possible.

  The ignition device is usually turned on when ventilation of a combustion chamber is initiated. This prior ventilation occurs, conventionally, in conjunction with the actuation of a pump. Said pump is driven by the same motor as that also driving the fan or the blower. It takes time to ventilate the combustion chamber beforehand. Although the pump has already supplied the necessary oil pressure, during this period, the solenoid valve remains closed until the completion of the preliminary ventilation. The ignition device continues to operate when said valve releases the oil supply. Said ignition device will ignite the oil mist after a relatively short period of time. The actuation of the ignition device is however continued, for reliability considerations, in order to prevent the flame from being extinguished for any reason.

  The object of the invention is to keep the nuisance imposed on the environment at the start-up stage as low as possible.

  According to the invention, in a method of the type mentioned in the introduction, this object is achieved by the fact that the ignition period is subdivided into at least two segments and the ignition device is actuated, on a subsequent segment of post-ignition, with lower electrical power than on a previous ignition segment over time.

  It has been found that the nuisance of the exhaust gases by NO, and of O 3 is correlated with the operation of the ignition device. As long as said ignition device operates, the nuisance of the exhaust gases by the aforementioned toxic gases is greater than without the operation of said device. However, due to the requirements of many burner manufacturers, it is not possible completely renounce actuation of the ignition device, also after the ignition of the oil mist. However, a reduction in the power of said ignition device contributes to the fact that the proportion of toxic substances contained in the exhaust gases is likewise reduced, which concerns, first of all, nitrogen oxides (NO) and l 'ozone (03).

  Consequently, when a lower electrical power is used on the post-ignition segment, a correspondingly lower proportion of toxic substances is also obtained. When the flame is extinguished during the post-ignition segment following the ignition segment, said flame will nevertheless be re-ignited.

  Thus, it is possible to operate the oil burner with practically the same reliability as before, while at the same time reducing the nuisance of the exhaust gases by toxic substances.

  The electrical power is preferably delivered, on the post-ignition segment, with a lower supply frequency than on the ignition segment. Decreasing the frequency is a relatively simple measure to decrease the electrical power. It is assumed that a certain percentage of toxic substances is generated during each ignition pulse, that is to say during each spark, so that a smaller number of sparks governs less than toxic substances. The feed frequency can be reduced in a simple way to a fraction, for example to half or to a third, by suppressing one pulse out of two or two pulses out of three among those responsible for generating the ignition sparks. This can be achieved relatively simply, using an electrical circuit.

  The electric power is preferably delivered, on the post-ignition segment, with a lower amplitude of current than on the ignition segment.

  This also represents a relatively simple measure to decrease electrical power. It is perfectly possible to combine the decrease in frequency with the decrease in the amplitude of the current.

  The electrical power is preferably maintained, on the post-ignition segment, at a value allowing an ignition of the oil mist with a predetermined reliability. Reliability can be chosen by the user, within certain limits. If one wishes to keep the nuisance imposed on the environment as small as possible, the electric power is reduced as much as possible. Post-ignition is desirable to back up the flame until the combustion chamber is warmed up and the operating conditions of the oil burner are optimal. In the presence of low electrical power, it is to be expected that the flame will remain unstable until the combustion chamber has been reheated.

  On the other hand, if one places value on the generation of a stable flame, one will select a higher probability with also, as a counterpart, a nuisance by the exhaust gases significantly greater following a power electric upper.

  There is preferably provided, at the start of the ignition period, a pre-ignition segment during which the ignition device is actuated with a lower power than during the ignition segment. As explained above, prior ventilation of the combustion chamber already takes place before the release of the oil itself. During this preliminary ventilation, the ignition device is put into operation in order to ensure that an ignition can take place directly, also in the presence of a possible oil leak arriving in the combustion chamber. Given, however, that ignition is fundamentally not necessary, per se, during the period of prior ventilation, i.e. on the pre-ignition segment, the electric actuation power of the ignition device can easily be reduced on this pre-ignition segment without degrading the operation of the oil burner. The reduction in electrical power also makes it possible to obtain a reduction in the nuisance by the exhaust gases.

  The electric power preferably corresponds, on the pre-ignition segment, to the electric power on the post-ignition segment. This keeps the respective complexity of fitting or connection modest. In principle, it is only imperative to be able to adjust two power stages, that is to say 5 sometimes a reduced power for the pre-ignition segment and the post-ignition segment, sometimes a higher power for the ignition segment. On said respective pre-ignition and post-ignition segments, the nuisance imposed on the environment is kept significantly lower than on the ignition segment.

  In a preferred structural arrangement, it is intended that the ignition segment 10 begins when oil is released in order to generate the oil mist. This moment can be firmly established in different ways. To mark the start of the ignition segment, the validation signal for the solenoid valve which releases oil to the nozzle can be used. In this case, it can be taken into account that the release of the oil and the generation of the oil mist itself are separated by a relatively short period of time, which is however sufficient to increase the electrical power of the device. to a sufficient extent.

  Preferably, the ignition segment is terminated when the presence of a flame is observed. The higher electrical power is no longer necessary at this instant. Only for reasons of reliability, the ignition device is then actuated with a reduced electrical power, in order to authorize a post-ignition in the event of inadvertent extinction of the flame.

  According to the invention, in an ignition device of the type mentioned in the introduction, the desired object is achieved by the fact that the supply device is equipped with a power adjustment system which can be activated during a start-up process.

  Thus, thanks to the power adjustment system, it is possible to actuate the ignition device with a higher electrical power, during predetermined segments of the ignition period, and with a lower electrical power during other segments. of the said period. The nuisance caused by the exhaust gases is kept modest when using a lower electrical power. As an overall consideration attests, the reduction in electrical power caused by the power adjustment system makes it possible to obtain a reduction in the nuisance caused by the exhaust gases.

  In this case, preferably, the power control system has a system for varying the ignition frequency. In this way, during the operation of the supply device, it is possible to modify the frequency with which the ignition device is supplied. When, for example, a spark gap is used, this influences the number of sparks produced in a predetermined unit of time. For example, one in two sparks or two in three sparks can be suppressed to decrease the frequency of ignition.

  Preferably, the power adjustment system is coupled to a signal assigned to the release of the oil, and increases the ignition power upon release of the oil. In this structural arrangement, as explained above, the increased electrical power is undoubtedly only used during the effective generation of an oil mist which is yet to be ignited.

  Preferably, the power adjustment system is coupled to a flame detector, and lowers the ignition power in the event of detection of a flame. The actuation of the ignition device with increased electrical energy 15 can then, concretely, be limited to the time range between the start of the generation of the oil mist and the appearance of a flame.

  The invention will now be described in more detail, by way of nonlimiting examples, with reference to the appended drawings in which: FIG. 1 is a schematic illustration of an oil burner group; FIG. 2 shows a temporal pattern of the supply of an ignition device; FIG. 3 illustrates a modified shape of the supply of electric power to an ignition device; and FIG. 4 represents another variant of the temporal pattern of the supply of an ignition device.

  FIG. 1 is a schematic illustration of an oil burner group 1, presenting a combustion chamber 2 in which an oil mist 3 is burned in order to heat, by means of a heat exchanger 4, the water, for example, necessary to operate a central heating installation. Exhaust gases generated during the combustion of the oil mist 3 are expelled into the surrounding atmosphere via an exhaust duct 5. This is the reason why one aims to keep the nuisance by toxic substances, in particular the nuisance by NO, and 1'03 caused by the exhaust gases evacuated via the conduit 5 as low as possible. .35 The nuisance from exhaust gases is, in itself, relatively modest during the normal combustion process. However, this nuisance increases at the start-up stage of the oil burner 1.

  The oil mist 3 is generated by a nozzle 6 supplied by a pump 7, via a conduit 8, with oil under a predetermined minimum operating pressure. Said minimum operating pressure is high enough for the oil to be atomized in the combustion chamber 2 with the necessary reliability and precision. On the conduit 8 is shown an electromagnetic valve 9 remaining closed until the pump 7 has developed the minimum operating pressure required. Said valve 9 releases the delivery of oil operating from the pump 10 7 to the nozzle 6. Said pump 7 takes the oil from a reservoir 10.

  A blower 1 1 equipped with a drive 12 supplies the combustion chamber 2 with the quantity of air required. The blower 1 1 and the drive 12 are illustrated only schematically. Said drive 12 also drives the pump 7 in many cases, which is evoked by a drive shaft 13 shown schematically.

  An ignition device 14 has a spark gap 15 in which, during a starting process, sparks fly out when said device 14 is supplied, by a device 16 for supplying electricity, with corresponding voltage pulses. The supply device 16 is supplied, by the voltage 17 of the network, with electrical energy having for example a frequency of 50 Hz.

  Fifty sparks per second are also produced under normal conditions. A control device 18 is provided for controlling the operation of the oil burner 1, in particular of the pump 7, of the blower 1 1 and of the electromagnetic valve 9, as well as of the ignition device 14.

  A flame detector 19 is provided for monitoring the presence of a flame in the combustion chamber 2. A connection has been illustrated between said detector 19 and the device 16 for the electrical supply of the ignition device 14.

  Of course, a corresponding connection between said detector 19 and the control device 18 is also possible, even conducive in many cases.

  At the present stage, an oil burner 1 operates in the manner described below.

  When, by means of thermometric probes or other sensors not shown, the control device 18 notices a demand for heat, it simultaneously activates the pump 7 and the blower 11. At the same time, it activates the electrical supply device 16 which in turn, by means of the ignition device 14, causes a series of sparks to burst out by means of the spark gap 15. During this period qualified as "prior ventilation" , the electromagnetic valve 9 remains closed. The combustion chamber 2 is supplied with fresh air following the operation of the blower 11 during the prior ventilation period.

  The electromagnetic valve 9 is opened at the end of the prior ventilation period. Pressurized oil reaches the nozzle 6, from which it leaves in the form of the oil mist 3. Said mist 3 is ignited by the sparks gushing from the spark gap 15. However, the operation of the ignition device 14 is continued until it is certain that the flame cannot disappear again in the combustion chamber 2. If this is the case, the oil mist 3 is immediately re-ignited by the sparks of the spark gap 15.

  An increased nuisance by the exhaust gases is generated as long as sparks fly out through the spark gap 15. In particular, the operation of the ignition device 14 itself generates nitrogen oxides (NO, ) and ozone (03). These substances are undesirable, but cannot be avoided at this stage in the context of oil burner systems.

  However, it turns out that the nuisance caused by the exhaust gases can be very considerably reduced by a slight modification made to the operation.

  Figure 2 aims to provide an explanation in this regard. FIG. 2 illustrates a period of ignition, that is to say the period of time between the activation of the ignition device, during a starting process, and the completion of the operation of said device. 'ignition.

  The ignition period is split into three segments, i.e. a pre-ignition segment a, an ignition segment _ and a post-ignition segment c.

  The illustration highlights electrical pulses delivered to the ignition device 14 by the power supply device 16. Each pulse generates a spark in the spark gap 15.

  It can be seen that the frequency of the pulses is much higher, on the ignition segment _, than on the pre-ignition segment a and the post-ignition segment c. The frequency of the pulses, and therefore of the sparks occurring on the spark gap 15, corresponds for example to the frequency of the voltage 17 of the network, that is to say at 50 Hz in Western Europe. On the pre-ignition segment a 35 and on the post-ignition segment _, on which no electrical power is basically necessary to ignite the oil mist 3, the ignition frequency corresponds to a fraction of the ignition frequency on the ignition segment b. For example, the frequency on said segments a and c corresponds only to 10 Hz, that is to say one fifth of the frequency on said segment _.

  It is obvious that the decrease in the frequency of ignition, on the pre-ignition segment a and on the post-ignition segment _, results in a reduction in the electric power delivered to the ignition device 14. This however also implies , to an equal extent, a reduction in the nuisance caused by the exhaust gases, given that a significantly lower number of sparks is generated, and that it is assumed that each spark contributes to the nuisance by the exhaust gas.

  During the pre-ignition segment a, corresponding essentially to the period of prior ventilation, an ignition of the oil mist 3 is not possible because the electromagnetic valve 9 is still closed. The generation 15 of sparks, via the spark gap 15, is not necessary per se in this case. However, the illustrated embodiment facilitates ordering.

  During the post-ignition segment _, the generation of sparks via spark gap 15 is only a preventive measure. This preventive measure is maintained due to the decrease in the frequency of inflammation. If necessary, the likelihood of an immediate re-ignition of the oil mist 3 is significantly reduced if the flame goes out in the combustion chamber 2 for any reason. However, as soon as a flame has been generated, smaller or less frequent ignition sparks are generally sufficient to rekindle it.

  Then, the ignition device 14 can be controlled, as a function of the release of the oil by the electromagnetic valve 9, so that the ignition segment b begins at the stage of opening of said valve 9. Being given that the control device 18 opens said valve 9, it can simultaneously issue a corresponding control instruction to the power supply device 16 or to said ignition device 14 proper. Of course, it is also possible to connect said ignition device 14 or said electrical supply device 16 to the valve 9 by means of a sensor indicating the switching state of said valve 9.

  The ignition segment can be terminated when a flame has been generated. This can be seen by the flame detector 19 which, for this purpose, is connected to the power supply device 16.

  The reduction in the ignition frequency can, for example, result from the fact that the electrical supply device 16 does not transmit, to the ignition device 14, certain predetermined pulses. It can be one pulse out of two, one pulse out of three or each nth pulse. As can be seen from FIG. 2, it is also possible to transmit only one pulse out of two, one pulse out of three or an nth pulse to said device 14.

  FIG. 3 shows a modified operating mode in which, on the pre-ignition segment a and on the post-ignition segment c, the reduction relates not only to the frequency of ignition delivered to the ignition device 14, but also to the amplitude of the supply voltage and, consequently, the amplitude of the current. This results in an even more marked reduction in the nuisance by the exhaust gases in the duct 5.

  FIG. 4 represents a third variant in which the electric power is regulated when a hot spot is supplied, for example a spark plug or an ignition electrode. Said hot spot is supplied by an increased electrical power, for example by an increased current intensity, only on the ignition segment _. The delivery of electric power undergoes a drastic decrease on the pre-ignition segment a and on the post-ignition segment c.

  As explained above, sensors can be used to control the electrical supply to the ignition device 14 via the electrical supply device 16. It is however also possible to integrate, in said electrical supply device 16 or in the control device 18, timers which control the electrical supply of said ignition device 14 according to a fixed time program. Said timers can be implemented as a separate unit, or as a unit integrated into the ignition device 14.

  The time processes illustrated in Figures 2 to 4 all lead to a decrease in the generation of nitrogen oxides and ozone, at the ignition stage, compared to a procedure in which the ignition power is kept constant throughout the period of inflammation.

  In addition, the modification of the power supply also results in an extension of the service life of the structural elements of the ignition circuit, and in a reduction in the power absorption of the oil burner group. It can even be expected to operate with a higher ignition power on the ignition segment _, in order to increase the probability of ignition, since this condition only occurs for a short period of time and exerts, this fact, a limited negative influence on the components of said burner 1.

  It goes without saying that many modifications can be made to the invention as described and shown, without going beyond its ambit. he

Claims (12)

-REVENDICATIONS1. Method of lighting an oil burner (1), in which a fog   oil (3) is generated and is led to an ignition device (14-15) activated, for a period of ignition, by supplying (16-17) with electric power, a process characterized in that the ignition period is subdivided into at least two segments (b, c) and the ignition device (14-15) is activated, during a subsequent post-ignition segment (c), with lower electrical power than during an ignition segment (b) earlier in time.   2. Method according to claim 1, characterized in that the electric power is delivered, on the post-ignition segment (c), with a lower supply frequency than on the ignition segment (b).   3. Method according to claim 1 or 2, characterized in that the electrical power is delivered, on the post-ignition segment (c), with a lower current amplitude than on the ignition segment (b ).   4. Method according to any one of claims 1 to 3, characterized in that the electric power is maintained, on the post-ignition segment (c), at a value allowing an ignition of the oil mist (3) with pre-established reliability.   5. Method according to any one of claims 1 to 4, characterized in that there is provided, at the start of the ignition period, a pre-ignition segment (a) during which the ignition device (1415) is operated with a lower power than on the ignition segment (b).   6. Method according to claim 5, characterized in that the electric power corresponds, on the pre-ignition segment (a), to the electric power on the post-ignition segment (c).   7. Method according to any one of claims 1 to 6, characterized in that the ignition segment (b) begins when oil is released in order to generate the oil mist (3).   8. Method according to any one of claims 1 to 7, characterized in that the ignition segment (b) is terminated when the presence of a flame is observed.   9. Ignition device intended for an oil burner group (1) and connected to an electrical supply device, ignition device characterized in that the supply device (16) is equipped with a power control system that can be activated during a starting process.   10. Device according to claim 9, characterized in that the power adjustment system has a system for varying the ignition frequency.   11. Device according to claim 9 or 10, characterized in that the power adjustment system is coupled to a signal assigned to the release of the oil, and increases the ignition power upon release of the oil. 'oil.   12. Device according to any one of claims 9 to 11, characterized in that the power adjustment system is coupled to a flame detector (19), and causes the ignition power to drop in the event of detection of a 10 flame.