Burner and device for monitoring a flame

p0001The invention concerns a burner apparatus according to the preamble of Patent Claim first

p0002For use in mobile leisure facilities, such as boats, mobile homes or caravans, heating the fuel (diesel or gasoline) or gas (LPG such as propane, butane, or mixtures thereof) are known, can be operated. Advantages of mobile gas heaters exist in the low-noise operation, low power consumption and a very low exhaust odor. For liquid fuel heaters should be reported as positive in that it can be powered by the same fuel that is present in greater quantity in the fuel tank for the drive of the recreational vehicle most. This eliminates the additional carrying of LPG cylinders. Due to the odors from the liquid fuels and the resulting exhaust gases but special precautions must be taken. It can be particularly problematic if the flame does not correctly or not burning in the burner apparatus, yet further fuel is supplied. The circumstances still hot burner then produces long strong smoke until finally the fuel supply is interrupted. The fumes and the associated odor but at a mobile heater in the leisure market only very briefly, about a few seconds acceptable, but not for an extended period.

p0003Various devices are known, with which the presence of a flame can be monitored in a burner. In particular, it is known to detect a flame by optical means. Alternatively, a change in temperature of the exhaust gas or the flame can be detected, can then be closed from a change in the flame behavior.

p0004From the <patcit id="pcit0001" dnum="DE10249872A1"><text>DE 102 49 872 A1</text></patcit> is a mobile combustion heater, in which a flame detector (flame sensor) and a glow element are performed at the start of combustion as an integral component. The flame sensor is located directly in the flame and therefore provides a very fast signal for flame detection. However, a disadvantage are the extremely high probe temperatures in the flame, and the fact that the sensor may be destroyed due to deposits in the combustion chamber or the signal quality is reduced due to deposits on the sensor and / or a resulting as a result of deposits displacement of the flame.

p0005In the <patcit id="pcit0002" dnum="DE29924803U1"><text>DE 299 24 803 U1</text></patcit> describes a flame detector in the form of a thermocouple which protrudes into the central region of the flame a burner powered heater. Again, there are the disadvantages described above.

p0006It is also known, ie placing a thermocouple in the exhaust line downstream of the flame. The slow response of the sensor is disadvantageous because the flame can not be visually monitored. The sensor is located in a built environment that is strongly heated by the exhaust gas. In addition, it is difficult for the sensor to distinguish between a change of load (reducing the heat output) and a flame failure, because both processes initially produce a signal of a similar nature and gradient. In both cases, the exhaust gas temperature decreases. A reliable differentiation is only after a longer measurement period (for example, five minutes) possible. Such a long period is, however - as stated above - because of the possibly associated formation of fumes and odors unacceptable.

p0007The invention is based on the object to provide a burner assembly having a reliable flame detection.

p0008The object is achieved by a burner device Claim 1. Advantageous further developments of the invention are specified in the dependent claims.

p0009A burner apparatus according to the invention, with a fuel supply for supplying fuel, a combustion air feed for feeding combustion air, in particular primary combustion air, a mixing area for forming a mixture of the fuel with the combustion air, one adjoining the mixing region combustion chamber, in which the mixture in the form of a flame to a waste gas is combustible and a sensing element for sensing a parameter that represents a criterion for the presence of the flame, characterized in that the measuring element upstream is arranged from the exhaust gas stream in a region having a caused by the combustion air excess oxygen and that the measuring element is held by a holder to which the combustion air is passed prior to reaching the flame.

p0010Accordingly, the burner device is supplied primary combustion air via the combustion air supply. There is the possibility that the flame also so-called secondary combustion air is supplied, but originates from the environment of the flame and is not enriched with fuel easily. The secondary combustion air can be characterized, for example, with the exhaust gas stream, so mix the reaction products generated by the flame. The primary combustion air, however, is specifically supplied to the burner device and accumulated in the mixing region with fuel (eg diesel or gasoline). The fuel is in this case in a suitable manner known per se - for example via a metal non-woven - is evaporated, so that it can be gas or vapor form out of the combustion air to the flame.

p0011The adjoining the mixing region combustion chamber must not spatially separated by structural measures from the mixing area. Rather, the combustion chamber results from the flow conditions, in particular by the flow rate of the combustion air and the exhaust gas. The combustion chamber surrounds the area in which the flame forms.

p0012The measuring element is used to detect a parameter, based on which the presence of the flame can be detected. This is for example - as well as from the state of the art - a temperature change, a certain brightness, when the flame is burning, or even the recognition of Ionisationsvorgängen that take place during combustion in the flame.

p0013According to the invention, however, the measuring element is not - placed in the exhaust stream, or in the middle of the flame, but upstream thereof - as in the prior art. In particular, the measuring element is arranged in a region in which an excess of oxygen is added, which is achieved by the primary combustion air. This may be the area in which the combustion air is supplied or a "start region" of the flame (flame root) in which an excess of oxygen is still given by the combustion air. The oxygen excess combustion air is reduced downstream in the flame, as the oxygen is greatly reduced by the hydrocarbons of the fuel. In this downstream region of the flame, however, the flame temperature is much higher, so that the measuring element should not be located there.

p0014Furthermore, the measuring element is held by a holder which is arranged such that the combustion air is guided past it before reaching the flame. The sensing element can be a stand-alone, held by a separate mounting device. Likewise, however, the sensing element may be integrated with the holder in a common component, such as a PT1000 temperature-measuring element to a flame sensor. therefore, only effective for the actual measurement range of a sensor is considered as the measuring element, for example a resistance element whose resistance value changes with temperature change. The surrounding Komponeten, (for example, the resistance) embed the sensing element, protect and maintain and take over the power supply and signal dissipation, the holder will be allocated.

p0015Thus, the bracket protrude into the region of the flame, in which the excess oxygen is given due to the combustion air. However, it must be ensured that at least a part of the bracket is arranged outside of the flame - and upstream of the flame - such that the still cold combustion air for cooling of the holder and with it - can also be used the measuring element - at least indirectly. In this way, it is possible that the measuring element is exposed to much lower temperatures, as is known in measuring elements from the prior art, which are positioned in the center of the flame or the hot exhaust area.

p0016At the measuring element and / or on the holder at least 30% of the combustion air can be led past. This means that at least 30% of the combustion air for cooling of the sensing element or the holder can be used. Here, the term of the combustion air is generally used and may comprise both primary and secondary combustion air. The measuring element or the holder can thus be cooled by both primary and secondary combustion air through. By providing at least 30% of the combustion air, it is ensured that the measuring element and the holder can be reliably cooled.

p0017The sensing element can be fully surrounded by the combustion air. In this case, the measuring element is held by the holder completely upstream of the flame in the combustion air flow.

p0018Likewise, the measuring element can be arranged in the range of an existing between the flame and the combustion air flammable limit, so that the measuring element can dip as partially in the flammable limit. In this field the required, caused by the combustion air excess oxygen is present. The flammable limit can be seen clearly with the naked eye, and identifies the area where the flame is produced and extends from the from the flame. The flame boundary is also called a flame root. In stable flow conditions and the position of the flame boundary will be relatively stable, while the downstream Flaming usually can have a higher variability of the flicker and lick of flame.

p0019The measuring element may be arranged such that a visual contact between the measuring element and the flame is provided. Due to the fact that the measuring element upstream of the exhaust gas stream and also of the major part of the flame - even completely upstream of the flame under certain circumstances - must be located, the measuring element is not flowed around by hot gas. Thus, a temperature measurement of the flame and the exhaust gas through convection is possible, but not mandatory. Instead, the resulting heat in the flame in the form of radiant heat must be captured. The radiant heat can then be detected particularly reliably if the required visual contact between the measuring element and the flame is.

p0020Here, the visual contact should be as large as possible, so that no disturbing elements such as shutters or gratings are arranged between the flame and the sensing element. The space between the measuring element and the part of the flame, the heat radiation to be detected, should therefore remain free of other components. It may be advantageous when starting a fictitious measuring cone with a cone angle of at least 60 ° to space virtually describes of the measuring element, which is to have no further components between the measuring element and flame.

p0021The amount recognized by the measuring element parameters can be selected from the group temperature, radiation, presence of gas ions.

p0022For detecting the temperature of the measuring element can be designed as a temperature-sensing element, such as PT1000 sensors (measuring range up to about 500 ° C). It is therefore not necessary to provide a special high-temperature sensor. Provided by the transmitted radiant heat at a high temperature, which, however, does not have to be above 600 ° C, is detected, this is evaluated as a criterion for the presence of the flame. However, if the temperature drops below a pre-definable value, it is concluded that no flame present. The fuel supply is then to interrupt.

p0023Alternatively, the measuring element may also be for detecting radiation, for example for optical detection of the brightness, to be thus formed of the emitted light from the flame. The light radiation can be in the visible region, but are also in the UV or infrared radiation. If the area around the measuring element is light, a flame must be. Thus, an optical detection of the flame is possible. Similarly, a flicker detector may be used that detects fluctuations in radiation in the visible, UV or IR range and deriving the presence of a flame.

p0024As a further alternative it is possible to form the sensing element as a ionisation sensor. The ionisation is able to detect ionisation in the flame, which occur during the combustion process. It is however provided that the sensor in the region of the flame is located, but in accordance with the above rules. According to the relevant for the measurement part of the ionisation probe (measuring element) is not positioned in the hot center of the flame, or even downstream of it, but in the cooler through the supply of combustion air initial region of the flame, where also the required excess oxygen is present.

p0025The sensing element provides a signal, which is evaluated by a not to be detailed, known control. If the controller detects that a flame is present, no control measures must be taken. Conversely, if the flame goes out or not formed for a predefined period of time during the starting process, the absence of the flame is detected and then detected by the controller through the sensing element. The controller can then take action, such as an interruption of fuel supply, to prevent odors or fumes. Likewise, giving off an audible or visual signal to the operator control, to alert him to the extinction of the flame.

p0026In the mixing region may be provided for vaporizing the liquid fuel, a nonwoven evaporator. The nonwoven evaporator, for example, an annular metal fleece, fuel is dropwise fed from one side. The generated in the combustion chamber heat of the flame, the metal web is heated so that the fuel is vaporized and conveyed by the pre-combustion air flowing. Here it mixes with the combustion air and is finally burnt in the flame.

p0027The combustion air supply may comprise a twisting device, to produce a swirl flow and thus a vortex-shaped flow of the combustion air as it enters the mixing region. By swirling flow of combustion air, the fuel is more reliably and uniformly mixed with the combustion air, resulting in improved combustion ensures.

p0028The measuring element with the holder can be "back" plugged z. B. of the flame and in so far introduced into the mixing zone or the combustion chamber, that the measuring element allows a direct measurement of Strahlunswärme the flame. The measuring element is thereby at least partially flows from the combustion air (fresh air) or even completely immersed, so that a targeted deflection of the flame is the measuring element away. The flow of combustion air can be formed concentrically to the measuring element, but also in the form of a "curtain".

p0029The sensing element has, depending on the installation depth and therefore penetration no or only minimal contact with the flammable limit and therefore can either measure the radiant heat of the flame on shortest distance, but without assuming the high flame temperatures, or can only with the very tip of the measuring element in the by the combustion air flow specifically shaped flame border plunge. The introduced in the measuring element and heat the circulated combustion air keep the sensing element in a thermal equilibrium. The sensing element can be placed with millimeter precision relative to the flame or the flame boundary, so that let the heat distribution in the measuring element and the support and therefore the absolute temperature of the measuring element optimally adjusted.

p0030Even with a load change of the burner device, the measured temperature at the sensor remains nearly constant. So is for example of a higher burner power, with greater radiation heat of the flame, a higher (cooling) flow through the combustion air against. The pressure acting on the measuring element and the support heating and cooling mechanism is therefore effective in opposite directions, so that the temperature level at the measuring element hardly changes.

p0031The excess oxygen at the measuring element ensures that no soot can affect the measurement result. The targeted flow around the sensing element with clean combustion air may also be formed using a protective sheath against other deposits.

p0032Since the holder is positioned in an area which is at least partially cooled by the combustion air, it is very easy, cables that need to be guided to the measuring element without holding particularly high temperature stress.

p0033The measuring element may be arranged at a position in which by shaping of the mixing section of the combustion chamber and a higher flow rate is achieved than downstream thereof. In particular, the flow rate of combustion air in this area may be higher than the subsequent flame propagation velocity. In this way it is ensured that the flame strikes back.

p0034With the aid of the bracket, it is possible to provide a physical contact of the measuring element, and thus a heat transition in a range which is located far away from the hot regions of the flame and the exhaust gas. For example, the holder may be secured to a rear wall of the burner, at the present by design much lower temperatures.

p0035These and other advantages and features of the invention will be explained in more detail by way of example with the aid of the accompanying figure. The single figure shows a cross section through an embodiment of the burner apparatus of the invention.

p0036The figure shows a simplified cross-sectional view of a burner apparatus of the invention. A combustion air supply 1 2 primary combustion air is supplied. In the field of combustion air supply 1 can serving as a twisting device twist scoops his 3 provided which provide the combustion air flow with a twist, so that the combustion air is 2 eddying out in a mixing area. 4

p0037In the mixing area 4, a fuel supply for supplying fuel is provided, which is exemplified by metal webs fifth The metal webs 5 can be annular and be placed in different areas. The positions shown in the figure therefore are merely illustrative.

p0038In the mixing area 4 of a slit wall 4a is provided. Through the slots 2 combustion air can also flow into the outer region and reach the outer metal fabric 5 as shown in the figure.

p0039The metal nonwoven fabric 5 is externally supplied fuel, which vaporizes in the metal nonwoven fifth The vaporized fuel is entrained by the swirling combustion air 2, so that the resulting mixture passes to a combustion chamber 6, which is enclosed by a flame tube. 7

p0040There is a flame 8 forms in a known manner. Upstream from the flame 8 can be seen a flame front or flame border 9, which is kept relatively stable by the prevailing flow conditions in the mixing zone 4 and the combustion chamber. 6 The flame border 9 represents the area at which the combustion process begins. There is by the incoming combustion air 2 before an excess of oxygen.

p0041In order to achieve a controlled combustion in the flame 8, an aperture 10 is further arranged in the flame pipe. 7 The resulting in the flame 8 gas is discharged upwards and can be, for example, fed to a heat exchanger, which may be part of a heater, for example a mobile deployable radiator for motor homes and caravans.

p0042In the area of ​​the aperture 10, so-called secondary combustion air can be supplied from the surroundings, which burns in the flame. 8

p0043In the interior of the mixing section 4, a flame sensor 11 is arranged so as to be relevant for the measurement the measuring element 12 as close as possible ranges to the flame 8, but without penetrating the flame eighth The measuring element 12 is thus located close to the flame boundary 9 in the inflow of the combustion air. 2

p0044The measuring element 12 is held by a belonging to the flame sensor 11 mount 13th The sensing element 12 and the holder 13 forming the flame sensor 11 as an integral component, which, for example, by a commercially available temperature sensor (PT1000) can be formed with a protective tube.

p0045The flame sensor 11 is attached via an attachment 14 to a torch back 15th From there, supply voltage and signal lines 16 can be led away.

p0046As shown by the arrow in the figure, flows around the combustion air 2 to the flame sensor 11, before it reaches the flame eighth Since the combustion air 2 comes from the environment, it is initially cold and thus cools the holder 13 and the measuring element 12. This is due to the measuring element 12 is a temperature which is considerably lower than the temperatures in the flame 8. The measuring element 12 registered only the resultant of the flame 8 radiant heat. However, the measuring element 12 does not come into contact with hot gases in the flame 8 or in the exhaust gas.

p0047In another, not shown embodiment of the invention, the flame sensor 11 may be formed by an ionization sensor. Since the ionization sensor relies on coming into contact with the resultant flame in the gas ions, the measuring element located on the tip of the flame sensor 11 must be positioned 12 in the flame. 8 It is sufficient here, the measuring element 12 to be placed in the area of ​​the flame boundary 9, where already combustion processes and thus ionization occur, however, an excess of oxygen is still given by the zoom flowing combustion air. 2

p0048Since the combustion air 2 at least cools the holder 13, the holder 13 serves as a heat sink for the measuring element 12, so that the measuring element 12, although disposed on the flame border 9 in the region of the flame roots, cooled, and a lower temperature is applied as in the flame 8 ,