GB2401930A

GB2401930A - A method and device for igniting an oil burner

Info

Publication number: GB2401930A
Application number: GB0405622A
Authority: GB
Inventors: Lars Andreasen; Aksel Sundwall
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 2003-03-19
Filing date: 2004-03-12
Publication date: 2004-11-24
Anticipated expiration: 2024-03-12
Also published as: SE528997C2; KR20040083363A; FR2852670B1; CN1550715A; SE0400671L; SE0400671D0; GB0405622D0; FR2852670A1; DE10312111A1; GB2401930B; ITTO20040184A1; DE10312111B4

Abstract

A method and device for igniting an oil burner 1, in which an oil mist 3 is produced and supplied by way of an ignition device 14,15 activated for an ignition period by being supplied with electrical power, wherein the ignition period is subdivided into at least two intervals, and the ignition device 14,15 is operated in a later post-ignition interval with a lower electrical power than in an earlier ignition interval. The ignition period may be subdivided into three intervals: a pre-ignition interval (a, figure 2), an ignition interval (b, figure 2) and a post-ignition interval (c, figure 2). Electrical power supplied in the post-ignition interval (c, figure 2) may be supplied at a lower supply frequency or lower current amplitude than in the ignition interval (b, figure 2). The electrical power in the post-ignition interval (c, figure 2) may be maintained at a value that ensures ignition of the oil mist 3 with a pre-determined degree of reliability. The ignition interval (b, figure 2) may begin when the oil mist 3 is released and end when a flame is detected.

Description

2401 930 O - 1 _e hod o g an oil burner and Ignition device for an otl

burn r a rangement 'this Invention relates to a method of igniting an oil burner, lo which an Old mist as produced and supplied by way of an ignition device that Is activated for an ignition period by being supplied with electrical power. The invention furthermore relates to an ignition device for an oil burner arrangement that is connected to an electrical supply arrangement.

Oils burners of the kind in question are frequently used in heating systems. In these systems, for reasons associated with adaptation to heat demand, the oil burners are operated not continuously but intermittently. Normally, the oil burner is ignited in an interval lasting several minutes, then runs for a certain time and is then switched off again, until a demand for heat is signalled, for example, the temperature of heating water has dropped below a predetermined value.

To ignite the oil burner, the oil is atomised. The oil then present in the form of an oil mist is admitted via the ignition device. The ignition device can be in the form, for example, of a spark gap, which is supplied with electrical energy in such a way that sparks repeatedly flash over. An alternative ignition device is a so-called "hot spot", that is, a treatable electrode, the temperature of which can be increased such that the oil mist thereon ignites.

O - 2 During the ignition process, exhaust gases occur, which contain noxious constituents, especially NOX and O3. The content of such noxious constituents in the exhaust gas should be kept as low as possible.

The ignition device is conventionally brought into operation when ventilation of a combustion chamber is started. This pre-ventilation usually commences together with the operation of a pump. The pump is driven by the same motor that drives also the fan or the blower. A certain time is required to pre-ventilate the combustion chamber. Although the pump has already produced the necessary oil pressure in this period, the electromagnetic valve remains closed until the pre- ventilation has finished.

The ignition device continues its operation when the electromagnetic valve releases the oil feed. After a relatively short time, the ignition device will ignite the oil mist. For reasons of reliability, however, operation of the ignition device is continued, in order to prevent the flame from extinguishing for any reason.

The invention is based on the problem of keeping environmental pollution as low as possible during start-up.

The present invention provides a method of igniting an oil burner, in which an oil mist is produced and supplied by way of an ignition device activated for an ignition period by being supplied with electrical power, wherein the ignition period IS subdivided into at least two intervals, and the ignition device IS operated in a later post-ignition interval with a lower electrical power than in an earlier ignition interval. O - 3

The above-mentioned problem IS solved in that the Ignition period is subdivided into the at least two intervals, and the Ignition device is operated in the later post-lgnltlon interval with the lower electrical power than in the earlier ignition interval.

It has been established that charging of the exhaust gas with NOX and Or is connected with the operation of the ignition device. Whlle the ignition device is working, charging of the exhaust gas with the said noxious gases is greater than when the ignition device is not operating.

Nevertheless, because of the requirements of many burner manufacturers, it is not possible to dispense with operation of the ignition device completely even after ignition of the oil mist. A reduction in the power of the ignition device is, however, a contributory factor to a reduction also in the proportion of pollutants in the exhaust gas, primarily in respect of oxides of nitrogen (NOX) and ozone (03). If, therefore, a lower electrical power is used in the post- ignition interval, then a proportionately lower content of pollutants is also produced. If the flame goes out in the post-ignition interval that follows the ignition interval, the flame will nevertheless be re-ignited. The oil burner can therefore be operated with virtually the same reliability as before, but the pollutant charge in the exhaust gas can be reduced.

Preferably, the electrical power in the post-ignition interval is supplied at a Lower supply frequency than in the ignition interval. Reduction in the frequency is a relatively simple measure to reduce the electrical power. O - 4

It is assumed that at each ignition pulse, that is, each spark, a certain proportion of pollutants occurs, consequently there will be fewer pollutants with fewer sparks. The supply frequenc-:y can be reduced in a simple manner to a friction, for example, to a half or a third, by blanking out every other pulse or two out of three pulses that are responsible for generating the ignition sparks.

This can be achieved relatively easily with an electrical circuit arrangement.

Preferably, the electrical power is supplied in the post-igoltion interval at a dower current amplitude than in the ignition interval. This too is a relatively simple measure to reduce the electrical power. The reduction in frequency can be combined perfectly well with the reduction in current amplitude.

Preferably, the electrical power in the post-ignition interval is kept at a value that allows ignition of the oil mist with a predetermined degree of reliability. The reliability can be chosen by the user within certain limits.

If it is desired to keep environmental pollution to the minimum, then the electrical power will be reduced as far as is possible. Post-ignition is desired in order to boost the flame until the combustion chamber has been heated and the operating conditions of the oil burner are virtually optimum. With low electrical power, one accepts that the flame will remain unstable, until the combustion chamber has been heated. If, on the other hand importance is attached to a stable flame production, then a higher probability will be chosen and, because of a higher electrical power in the O - 5 post-lgnition interval, a somewhat greater charging of the exhaust gas with pollutants will be tolerated.

Preferably, at the start of the ignition period, a pre- ignitlon Interval Is provided, during which the ignition device IS operated with lower power than in the ignition interval. As stated above, before the actual release of oil, a pre-ventilation of the combustion chamber already takes place. During this pre-ventilation, the ignition device IS brought into operation, to ensure that if there is any leakage of oil Into the combustion chamber an ignition can also take place Immediately. Since ignition per se is not really required during the pre- ventilation period, that is, in the pre-igntlon Interval, the electrical power for operating the igolDlon device in this pre-ignition interval can be reduced without problem without endangering the operation of the oil burner. Reducing the electrical power also reduces pollution of the exhaust gas.

Preferably, the electrical power in the pre-ignition interval corresponds to the electrical power in the post ignition interval. Thls keeps the degree of sophistication of apparatus and circuit engineering to a low level.

Basically, lt must be possible to set just two power stages, namely, first a reduced power for the pre-ignition interval and the post-ignition interval, and then a higher power for the ignition interval. In the preignition interval and in the post-ignition interval, environmental pollution is kept substantially lower than in the ignition interval.

In a preferred construction, the ignition interval is commenced when all for creating the oil mist is released. O - 6

This point lo time can be determined in different ways. The release signal for the electromagnetic valve to release oil to the nozzle can be used to start the ignition interval.

It is possible here to take into account the fact that the time between release of the oil and the actual creation of the oll mist is relatively short, but adequate for the electrical power of the ignition device to be increased sufficiently.

Preferably, the ignition interval is terminated when l0 the presence of a flame is established. At this point in time, the higher electrical power IS no longer necessary.

Only for reasons associated with reliability is the ignition device then operated with reduced electrical power, in order to enable the flame to be re-ignited if it should have become unintentionally extinguished.

The present invention also provides an ignition device for an oil burner arrangement connected to an electrical supply arrangement, wherein the supply arrangement comprises power adjustment means arranged to be activated during a start-up process.

The above-mentioned problem is solved in that the supply arrangement comprises the power-adjustment means, which is arranged to be activated during a start-up process.

Using the power-adustment means, it is therefore possible to admit a higher electrical power to the ignition device in predetermined intervals of the ignition period and, in other intervals of the ignition period, to admit a lower electrical power. When using a lower electrical power, pollution of the exhaust gas is kept low. Taking a O - 7 general view, by reducing the electrical power by way of the power-adjustment means, a reduction in pollution of the exhaust gas IS achieved.

It IS preferred here for the power-adjustment means to comprise a device for changing the ignition frequency. The frequency with which the ignition device is supplied can therefore be changed during operation of the supply arrangement. This has an influence, for example, when using a spark gap, on the number of sparks that are produced within a predetermined unit of time. For example, every other spark, or two out of three sparks can be omitted in order to reduce the ignition frequency.

Preferably, the power-adustment means is coupled with a signal for oil release and increases the ignition power on release of the oil. As stated above, with this construction one is sure that the increased electrical power will be used only when an oil mist still to be ignited is actually being produced.

Preferably, the power-adjustment means is coupled with a flame sensor and reduces the ignition power when a flame is detected. Operation of the ignition device with increased electrical energy can then be limited essentially to the period between the start of production of the oil mist and the appearance of a flame.

Ways of carrying out the invention will now be described, by way of example only, with reference to the accompanying drawings, In Welch: Fig. 1 is a schematic representation of an oil O - 8 burner arrangement) Flg. 2 shows the characteristics as a function of time of the supply of an ignition device; Flg. 3 shows a modified response of the electrical power supply of an ignition device; and Flg. 4 shows another modification of the characteristics as a function of time of the supply of an ignition device.

Referring to the drawings, Fig. 1 shows schematically an oil burner arrangement 1, having a combustion chamber 2, in which an oil mist 3 IS combusted in order, by way of a heat exchanger 9, to heat water that is required, for example, for operation of a central heating system. Exhaust gases generated when the oil mist 2 is combusted are expelled into the ambient atmosphere via an exhaust gas pipe 5. For that reason, efforts are made to keep the charge of pollutants in the exhaust gas discharged through the exhaust gas pipe 5 as small as possible, especially pollution with NOX and O3. During the normal combustion process, the exhaust gas pollution can be kept small, but the exhaust gas pollution increases when the oil burner arrangement 1 is started up.

The oil mist 3 is created by a nozzle 6, which is supplied from a pump 7, by way of a line 8, with oil under a predetermined minimum operating pressure. The minimum on - 9 operating pressure is sufficiently great for the oil to be atomised with the required reliability and fineness into the combustion chamber 2. An electromagnetic valve 9 is arranged in the line 8 and remains closed until the pump 7 has built up the required minimum operating pressure. The electromagnetic valve 9 releases the oil supply from the pump 7 to the nozzle 6. The pump 7 takes the oil from a tank 10.

A fan 1l with a drive 12 admits the required amount of air to the combustion chamber 2. The fan 11 and the drive 12 are shown merely schematically. Optionally, the drive 12 can also be arranged to drive the pump 7, which is indicated by a schematically shown drive shaft 13.

An ignition device 14 has a spark gap 15, across which sparks flash during a start-up process when the ignition device 14 is supplied with suitable voltage pulses from an electrical supply device 16. The supply device 16 is fed from the mains voltage 17 with electrical energy, for example at a frequency of 50 Hz. Normally, this then produces 50 sparks per second. A control device 18 is provided to control the operation of the oil burner arrangement 1, in particular the pump 7, the fan 11 and the electromagnetic valve 9 and also the ignition device 14.

A flame sensor 19 is provided in order to monitor the presence of a flame in the combustion chamber 2. A connection from the flame sensor 19 to the electrical supply device 16 of the ignition device 14 is shown. A corresponding connection between the flame sensor 19 and the control device 18 is also possible, of course, and in many O - 10 cases IS also beneficial.

The oll burner arrangement 1 as described so far operates as follows: When the control device determines, via temperature sensors c>r other sensors, not shown, that there IS a requirement for heat, it sets the pump 7 and the fan 11 simultaneously in operation. At the same time, the electrical supply device 16 is activated, which in its turn, via the ignition device 14, allows a series of sparks to flash across the spark gap 15. In this so-called "pre- ventilation time", the electromagnetic valve remains closed.

Through operation of the fan 11 in the pre-ventilation time, the combustion chamber 2 is supplied with fresh air.

At the end of the pre-ventilation time, the electromagnetic valve 9 is opened. Oil under pressure reaches the nozzle 6 and emerges therefrom in the form of an oil mist 3. The oil mist 3 is ignited by the sparks flashing across the spark gap 15. Operation of the ignition device 14 is continued, however, until one is sure that the flame in the combustion chamber 2 cannot go out again. If the flame does go out, the oil mist 3 is immediately re- ignlted by the sparks of the spark gap 15.

While sparks flash across the spark gap 15, increased exhaust gas pollution is produced. Oxides of nitrogen (NOx) and ozone (Ox) in particular are produced by the operation of the ignition device 14 itself. These substances are undesirable, yet currently, in connection with oil burner systems, cannot be avoided. o

The exhaust gas pollution is, according to the invention, quite considerably reduced through a slight but highly significant modification of the above-described operation.

This will he explained with reference to Fig. 2. Fig. 2 shows an ignition period, that is, the period from start up of the ignition device during a starting process to termination of the operation of the ignition device.

The ignition period is subdivided loto three intervals, namely, a preignition interval a, an ignition interval b, and a post-ignition interval c.

Electrical pulses are shown, which are supplied from the electrical supply device 16 to the ignition device 14.

Each pulse produces a spark at the spark gap 15.

It can be seen that in the ignition interval b the frequency of the pulses is substantially greater than in the pre-ignition interval a and in the post-ignition interval c.

For example, the frequency of the pulses, and hence of the sparks at the spark gap 15, corresponds to the frequency of the mains voltage 17, that is, in Western Europe 50 Hz. In the pre-ignition interval a and in the post-ignition interval c, in which basically no electrical power is required to ignite the oil mist 3, the ignition frequency corresponds to a fraction of the ignition frequency in the ignition interval b. For example, the frequency in the pre- ignition interval a and in the post-ignition interval c is merely 10 Hz, that is, a fifth of the frequency in the ignition interval b.

O - 12 It follows that the electrical power that is supplied to the igniter- device 14 is reduced by the reduction in the ignition frequency of the pre-ignition interval a and in the post-ignition interval c. The exhaust gas pollution is also reduced, however, to the same degree, because correspondingly fewer sparks flash over and it is assumed that each spark contributes to exhaust gas pollution.

In the pre-ignition interval a, which corresponds substantially to the pre-ventilation time, ignition of the oil mist 3 is not possible, because the electromagnetic valve 9 is stilt closed. In this case, production of sparks across the spark gap 15 as such is unnecessary. The embodiment illustrated does make control easier, however.

In the post-ignition interval c, production of sparks across the spark gap]5 is merely a precautionary measure.

By reducing the ignition frequency, this precautionary measure is retained. Nevertheless, the probability is reduced somewhat that the oil mist 23 will be re-ignited immediately if the flame in the combustion chamber 2 should be extinguished for any reason. If the flame has already existed once, however, generally speaking relatively small or less frequent ignition sparks will be sufficient to re- ignite it.

The ignition device 14 can now be controlled in dependence on the release of oil by the electromagnetic valve 9 in such a way that the ignition interval b commences when the electromagr-etic valve 9 is opened. Since the control device 18 opens the electromagnetic valve 9, it can simultaneously send a corresponding command to the O - 13 electrical supply device 16 or to the Ignition device 19 itself. Of course, J.t is also possible for the ignition device 14 or the electrical supply device 16 to be connected to a sensor on the electromagnetic valve 9, which indicates the circuit state of the electromagnetic valve 9.

The Ignition Interval b can be terminated when a flame is produced. This can be established by way of the flame sensor 19, which for that purpose is connected to the electrical supply device 16.

The reduction in ignition frequency can be effected, for example, In that the electrical supply device 16 does not relay predetermined pulses to the ignition device 14.

This can be every other pulse, every third pulse, or every no pulse. It is also possible to allow only every other pulse, every third pulse, every nth pulse through to the ignition device 14, as is clear from Fig. 2.

Fig. 3 shows a modified procedure in which, in the pre- ignition interval a and in the post-ignition interval c, not only is the ignition frequency to the ignition device 14 reduced, but also the amplitude of the supply voltage and hence along with that the amplitude of the current. This leads to an even further reduction in the exhaust gas pollution In the exhaust gas pipe 5.

Fig. 4 shows a third alternative, in which the electrical power- during supply of a "hot spot", for example a glow plug or hot electrode, is controlled. The hot spot is supplied with increased electrical power, for example, an Increased current Intensity, only in the ignition interval b. In the pre-ignition interval a and in the post-ignition O - 14 interval c the supply of electrical power is drastically reduced.

As stated above, sensors can be used for control of the electrical supply to the ignition device 14 by way of the electrical supply device 16. Alternatively, it is possible to incorporate tinters into the electrical supply device 16 or into the control device 18, which control the electrical supply of the lgnlDlon device 14 in accordance with a fixed time program. The timers can be in the form of a separate unit or an integrated unit of the ignition device 14.

The time sequences described illustrated in Figs 2 to 4 all result ire a reduction in the production of oxides of nitrogen and ozone, compared with a procedure in which the ignition power is maintained at a constant level for the entire ignition period.

furthermore, the change in power supply also leads to an increase in the service life of the system elements in the ignition circuit and to a reduction in the power consumption of the oil burner arrangement. Provision can even be made for the ignition power to be greater during the ignition interval b, in order to increase the probability of ignition, since this condition occurs only for a short period of time and hence has a limited adverse effect on the components of the oll burner arrangement 1.

Claims

C L A I M S: 1. A method of igniting an oil burner, in which an oil mist

is produced and supplied by way of an ignition device activated for an ignition period by being supplied with electrical power, wherein the ignition period is subdivided into at least two intervals, and the ignition device IS operateci in a later post-ignition interval with a lower electrical power than in an earlier ignition interval.
2. A method as claimed in claim 1, wherein the electrical power in the post-ignition Interval is supplied at a lower supply frequency than In the ignition interval.
3. A method as claimed in claim 1 or 2, wherein the electrical power is supplied in the post-ignition interval at a lower current amplitude than in the ignition interval.
4. A method as claimed in any one of claims 1 to 3, wherein the electrical power in the post-ignition interval is maintained at a value that allows ignition of the oil mist with a predetermined degree of reliability.
5. A method as claimed in any one of claims 1 to 4, wherein at the start, of the ignition period a pre-ignition interval is provided, during which the ignition device is operated with a lower power than in the ignition interval.
6. A method as claimed in claim 5, wherein the electrical power in the pre-ignltion interval corresponds to the electrical power in the postignition interval.
7. A method as claimed in one of claims 1 to 6, wherein the ignition interval is commenced when oil for creating the all mist is released. - 16
8. A method as claimed in one of claims 1 to 7, wherein the Ignition interval is terminated when the presence of a flame is established.
9. A method of igniting an oil burner, the method being substantially as herein described with reference to and as illustrated by Flqures 1 and 2 of the accompanying drawings.
10. A method as claimed in claim 9, the method being modified substantially as herein described with reference to and as illustrated by Figure 3 of the accompanying drawings.
11. A method as claimed in claim 9, the method being modified substantially as herein described with reference to and as illustrated by Figure 4 of the accompanying drawings.
12. An ignition device for an oil burner arrangement connected to an electrical supply arrangement, wherein the supply arrangement comprises power adjustment means arranged to be activated during a start-up process.
13. An ignition device according to claim 12, wherein the poweradjustment means comprises means for changing the ignition frequency.
14. An ignition device according to claim 12 or 13, wherein the poweradustment means is coupled to a signal for oil release and increases the ignition power on release of the oil.
15. An Ignition device according to any one of claims 12 to 14, wherein the power-adjustment means is coupled to a flame sensor and reduces the ignition power when a flame is detected.
l6. An ignition device for an oil burner arrangement, - 17 the device being substantially as herein described with reference to and as illustrated by Figures 1 and 2 of the accompanying drawings.
17. A device as claimed in claim 16, the device being modified substantially as herein described with reference to and as illustrated by Figure 3 of the accompanying drawings.
18. A device as claimed in claim 16, the device being modified substantially as herein described with reference to and as illustrated by Figure 4 of the accompanying drawings.