EP1275901B1 - Vaporizing burner - Google Patents

Description

The present invention relates to an evaporator burner according to the preamble of claim 1, as used for example in heaters in motor vehicles application.

The WO 98/49494 discloses an evaporator burner in which a porous evaporator medium, for example nonwoven material, is arranged in the bottom region of a combustion chamber. In this porous evaporator medium, liquid fuel is passed to distribute this by capillary action in the porous evaporator medium. At the side facing the combustion chamber, the fuel vaporizes, so that an ignitable or combustible mixture is formed in the region of the combustion chamber by accumulation of fuel vapor and combustion air. Furthermore, a heating device is provided, which comprises a Glühzündstift projecting into the region of the combustion chamber. By heating the Glühzündstifts such a high temperature is generated in the environment that ignites the present in this area ignitable mixture and then propagates combustion in the combustion chamber.

Furthermore, from the DE 32 33 319 A1 an evaporator burner is known in which in the bottom region of a combustion chamber, in turn, a porous medium is provided for the distribution and evaporation of fuel. On the side of the porous medium exposed to the combustion chamber, a heating device designed in the manner of a heating coil is provided, which in the region of the porous medium, when energized, can generate the temperatures required for ignition which are in the region of approximately 1100 ° C.

Such known from the prior art evaporator burners have the disadvantage that they take up a relatively long time to reach a high heat output, which is significantly longer than the time required for example by Druckzerstäuberbrennern, Luftzerstäuberbrennern or Ultraschallzerstäuberbrennern. One significant reason is that the flame produced by the ignition also removes energy for evaporating further fuel, which prevents the rapid propagation of flames in the combustion chamber, especially at low outside temperatures and large component masses with comparatively good heat conduction. This disadvantage of the evaporator burner, which is in principle of interest due to its cost-effective construction, is less of an advantage when used, for example, in auxiliary heaters. Here, the spontaneous generation of relatively high temperatures is not a priority. However, this is different when such a burner is used as additional heater, which is particularly effective when cold starting an engine at low ambient temperatures. Here it is necessary that a very high heating power of the auxiliary heater can be provided in a very short time to reduce the emission of such a heated drive unit, especially in the startup phase.

An evaporator burner according to the preamble of claim 1 is known from JP 63017305 A known. In this known embodiment of an evaporator burner, a porous, wick-like evaporator element is provided at a bottom region of an evaporator housing enclosing a combustion chamber. On its side facing the combustion chamber, this evaporator element can deliver fuel vapor into the combustion chamber. The fuel is supplied via a fuel line adjacent to the side of this evaporator medium which faces away from the combustion chamber. Furthermore, a heating conductor is provided on the side facing away from the combustion chamber side of the porous evaporator medium, which can heat up by its contact with the evaporator medium and thus contribute to increased Brennstoffabdampfung.

From the US 4,365,952 A An evaporator burner is known in which a porous evaporator medium is immersed in an area remote from a combustion chamber in the liquid fuel and thus absorbs this by its suction. By capillary action of this liquid fuel passes in the inner volume region of the porous evaporator medium in that region thereof, which is within a combustion chamber. In this area, the porous evaporator medium is annular and encloses a tubular heater. As a result of its direct contact with the rear side, that is to say the side of the evaporator medium which is remote from the combustion chamber, it is heated and thus the evaporation efficiency is increased.

It is the object of the present invention to develop an evaporator burner of the generic type so that with improved protection for the evaporation assisting heater efficient Brennstoffabdampfung is obtained.

According to the present invention, an evaporator burner is provided for achieving this object, comprising an evaporator medium for feeding fuel vapor into a combustion chamber, a first heating device comprising at least one ignition heating element protruding into the combustion chamber for igniting fuel vapor present in the combustion chamber and at least its heating region a second heater comprising at least one of the evaporator medium for influencing Evaporation heater associated with its vaporization characteristic.

In order not to expose the at least one evaporation heating element, which is used only for preheating the fuel to be evaporated, to the relatively high temperatures prevailing in the combustion chamber, the at least one evaporation heating element is arranged on a side of the evaporator medium facing away from the combustion chamber. A further improved protection of the evaporation heating element against excessively high temperatures is achieved in that the evaporator medium is provided on an evaporator medium carrier and that the at least one evaporation heating element is provided on a side facing away from the evaporator medium side of the evaporator medium carrier.

The present invention is characterized in that it provides separate heating devices for igniting, on the one hand, and for evaporating the liquid-supplied fuel, on the other hand. These can each be optimally adapted to the requirements imposed on them with regard to the temperatures to be generated by these and the required heating capacities. By preheating the fuel to be evaporated, the evaporation rate is increased, while still avoiding that heat energy is withdrawn from the flame in the spreading. The flame propagation in the starting phase of such an evaporator burner runs much faster, so that ultimately the full load operation is achieved much faster than with the known from the prior art evaporator burners.

Preferably, in the evaporator burner according to the invention, a fuel feed channel arrangement is also provided for introducing liquid fuel into the evaporator medium. In order to obtain an approximately uniform combustion characteristic over the entire combustion chamber, it is proposed that the fuel feed channel arrangement is designed to distribute the liquid fuel over the evaporator medium. This can be achieved, for example, by virtue of the fact that the fuel feed channel arrangement has at least one annular channel region and / or at least one radial channel region extending radially from a fuel feed line in the evaporator medium or / and an evaporator medium carrier.

Furthermore, in order to provide the mixture that can be ignited in the combustion chamber, the inventive evaporator burner preferably has an air feed channel arrangement for feeding air to be combusted with the fuel vapor into the combustion chamber. For this purpose, it can be provided, for example, that the air supply duct arrangement has at least one air inlet opening open towards the combustion chamber in a wall delimiting the combustion chamber.

In order to promote together with the fuel vapor exiting from the evaporator medium at the same time the combustion air required for ignition in that space in which the ignition occurs, it is proposed that the Luftzuführkanalanordnung has at least one open to the evaporator medium air inlet opening. For this purpose, it can further be provided that the air supply duct arrangement has at least one air supply duct region which passes through the evaporator medium.

Since an essential parameter influencing the rapid propagation of the flame is the heat dissipation occurring in the region of an evaporator burner, according to a further advantageous aspect of the present invention Invention in that the at least one evaporation heating element and the evaporator medium are provided on an evaporator medium carrier formed of ceramic material, for improved thermal insulation and thus a further acceleration of the flame propagation are provided.

The evaporator medium may comprise porous material which may be designed to be multi-layered in order to obtain the fastest possible diffusion of the liquid fuel in the evaporator medium itself and then to evaporate the dispersed liquid fuel. For example, nonwoven material can be used here.

A general problem that occurs in the operation of evaporator burners, on the one hand, the required high variability of burner performance. Here, for example, a ratio of maximum to minimum burner power of at least 4: 1 is required. On the other hand, such evaporator burners should be able to be operated with a large number of different fuels or with fuels of different quality. Here, for example, in addition to the applicability of conventional diesel fuel, of course, the usability of winter diesel or Arctic diesel required. Also gaining increasingly natively based fuels, such as produced from rapeseed oil biodiesel, so generally obtained by transesterification of oils fatty acid methyl ester fuels, in importance. The consequence of the use of often unspecified fuels, especially in connection with the high variability of the burner output, is the risk of deposits formed in the combustion in that region in which the combustion takes place, ie in particular in the region of the combustion chamber or that region. where the evaporation of the basically liquid fuel takes place. One reason for this is, among other things, that the evaporation does not always take place under optimal conditions, such as optimal evaporation temperature and optimum oxygen supply. The formation of deposits, which are generally regenerable, So are flammable deposits, the impairment of the operating characteristics of such an evaporator burner whereby, among other things, the maximum service life can be limited.

According to a further aspect of the present invention, an evaporator burner preferably has a cleaning arrangement for removing deposits which deposit in the region of the combustion chamber in the combustion mode.

By providing the cleaning arrangement, it can be ensured that the deposits or impurities generated or precipitated in the region of the combustion chamber are removed again, so that the evaporator burner can again be operated with improved efficiency.

Since the deposits formed during combustion, as already stated, are generally combustible themselves, according to a further aspect of the present invention, it may be provided that the cleaning arrangement comprises a heating arrangement, by means of which in the region of the combustion chamber one or above a combustion temperature of Deposits lying temperature can be generated.

Since, as already stated above, especially the region in which the evaporation takes place is critical with respect to the deposition of deposits, it is preferably provided according to a further aspect of the present invention that the heating arrangement for generating the lying in the region or above the combustion temperature Temperature is formed at least in the region of the evaporator medium.

In particular, if a separate heating device is provided for the evaporator medium, it can be provided according to a further aspect of the present invention that this heating device also the forms to be used for cleaning heating assembly. Depending on whether a normal evaporation operation or a burn-off operation is then provided for cleaning, this heating device can then be operated with different heating power in order accordingly to generate different temperatures suitable for the different operating phases.

According to a further aspect, the present invention relates to a method for cleaning an evaporator burner, as described above, in which method by activating a heating arrangement heats deposits on a wall surrounding the combustion chamber to a temperature in the range of or above the burning temperature of the deposits and be burned down.

It is then preferably provided that the cleaning process is carried out when the heating burner is not in a heating operating state. Since, in the normal heating operating state, the interaction of different system components ensures that fuel and oxygen are input in a combustion-suitable ratio, this measure according to the invention can ensure that oxygen which, per se, does not burn off during a heating operating state phase would be required for the normal combustion of the injected or vaporized fuel is used to burn off the deposits and thus is no longer available for combustion. An impairment of normal operation can thus be avoided.

Preferably, according to the present invention, it is provided that the cleaning process is carried out subsequent to a heating operating state phase of the heating burner. The advantage of this measure is that following a normal heating operating state, the various system components are already heated, so that the burning of the Impurities or deposits required heating power can be reduced accordingly.

In order to ensure over a longer service life that the operating characteristics of a heating burner are impaired as little as possible by deposits that form, it can further be provided that the method is carried out after a predetermined operating time of the heating burner. In this case, it is thus possible to proceed in such a way that it is possible to monitor how long, possibly since the last cleaning, the heating device has been operated. If a certain maximum number of operating hours is reached here, the cleaning process according to the invention is carried out again.

In carrying out this cleaning method, the heating arrangement can then be activated with a duty cycle of less than one. The advantage of this measure is that one can regulate the heating power in a simple manner by the clocked driving of the heater, without being dependent on the available supply voltage or to be essentially limited by this.

In the operation of evaporator burners, it is important to recognize whether a metering pumping device which introduces the fuel into the combustion chamber operates in the correct manner, or whether fuel is present in the evaporator burner in order to correctly start the combustion. This is for example from the DE 198 59 319 A1 a procedure is known in which the excitation current of the metering pump is monitored and based on the evaluation of this flow through the metering pump electric current is closed, whether it works correctly or not. However, it is difficult to detect, for example, defects that may not be present in the metering pump itself, but occur only in the connection area between the metering pump and the combustion chamber. Furthermore, this monitoring process due to the manufacturing tolerances occurring in the production of metering pumps very expensive and can be used only with comparatively low precision.

In order to be able to conclude with an evaporator burner with increased precision on whether it is supplied in a correct manner with fuel, according to a further aspect of the present invention, this has a drive device by which the heating power of at least the second heater is adjustable, wherein a Monitoring module monitors the heating power and / or the required heating power of the second heater and detects based on the monitoring result, the presence of a fuel evaporation.

In this case, the present invention takes advantage of the fact that in the evaporation of fuel due to the energy required for evaporation and extracted from the environment in the transition from a state in which there is no evaporation to a state in which evaporation is present to maintain the same Temperature, the performance of the evaporation assisting heater must be increased. Otherwise, a cooling down of that area would occur in which the evaporation takes place. This change in the drive characteristic for this heater utilizes the present invention to detect when the transition to the vaporization state occurs.

Further, according to the present invention, it may be provided that the evaporation heating element comprises an electrically operated heating element with increasing electrical resistance as the temperature increases.

The present invention further relates to a method for monitoring the fuel supply to an evaporator burner according to the invention. In the method, based on the heating power of the heater and / or a change in the heating power of the heater and / or a required change in the heating power of the heater determines whether a fuel evaporation is present in the combustion chamber of the evaporator burner.

Here, for example, it is possible to proceed in such a way that the presence of fuel vaporization is detected when the heating power increasing during operation of the heating device and / or the required higher heating power are required.

Since it is particularly important when commissioning an evaporator burner to recognize when vaporized fuel is available to subsequently trigger further procedures, it is proposed according to a further aspect of the invention that in an ignition operation of the evaporator burner in a first phase of operation, the heater is operated at a higher, preferably in the range of maximum heating power lying in a subsequent second phase of operation, the heater with reduced, preferably decreasing heating power and in a further subsequent third phase of operation, the heater is operated with increased again, preferably increasing heating power, at or after transition to the third phase of operation is detected on the presence of fuel vaporization. In this case, it can then be further provided that, if it is detected on the presence of fuel vaporization, a heating device assisting the ignition of the vaporized fuel is activated.

When an evaporator burner is disabled, such as by deactivating a combustion assist heater and adjusting the fuel supply can take place, it is advantageous to ensure that remaining fuel residues are completely ejected in the evaporator burner. This can preferably be done by activating a heating device supporting the evaporation and by evaporating off the remaining fuel. Due to the above-described physical effect that energy is required to produce the fuel evaporation, which is provided by corresponding excitation of the associated heater, according to the present invention may further be provided that when the heating power or the required heating power of the evaporation supporting heater decreases, it is recognized that no more fuel for evaporation is available. This is again due to the fact that, if no further fuel is available, no heat of evaporation must be made available any more, so that the heating power to be provided by the corresponding heating device can be reduced to maintain a predetermined temperature. This reduction of the heating power or the required heating power can be used as a decision criterion.

Fig. 1

eine Explosionsansicht der wesentlichen Komponenten eines Verdampferbrenners gemäß einer ersten Ausgestaltungsform der vorliegenden Erfindung;

Fig. 2

eine Längsschnittansicht des in Fig. 1 dargestellten Verdampferbrenners;

Fig. 3

eine Zusammenbauansicht der die verschiedenen Heizeinrichtungen umfassenden Baugruppen des in Fig. 1 dargestellten Verdampferbrenners;

Fig. 4

eine Explosionsansicht einer alternativen Ausgestaltungsart der die beiden Heizeinrichtungen umfassenden Baugruppe des in Fig. 1 dargestellten Verdampferbrenners;

Fig. 5

die in Fig. 4 dargestellte Baugruppe im Zusammenbau;

Fig. 6

eine Explosionsansicht der wesentlichen Komponenten eines Verdampferbrenners gemäß einer alternativen Ausgestaltungsart der vorliegenden Erfindung;

Fig. 7

eine Längsschnittansicht des Verdampferbrenners der Fig. 6, geschnitten in einer eine Längsmittelachse des Verdampferbrenners nicht enthaltenden Ebene;

Fig. 8

eine Schnittansicht des in Fig. 6 dargestellten Verdampferbrenners, geschnitten in einer die Längsmittelachse enthaltenden Ebene;

Fig. 9

die die verschiedenen Heizeinrichtungen des Verdampferbrenners der Fig. 6 aufweisende Baugruppe im Zusammenbau;

Fig. 10

die beiden beim Verdampferbrenner der Fig. 6 eingesetzten Heizeinrichtungen;

Fig. 11

eine alternative Ausgestaltungsart der zum Verdampfen des Brennstoffs und zum Verteilen desselben eingesetzten Heizeinrichtung;

Fig. 12

eine Explosionsansicht der die beiden Heizeinrichtungen des Verdampferbrenners der Fig. 6 aufweisenden Baugruppe gemäß einer alternativen Ausgestaltungsart;

Fig. 13

eine Explosionsansicht einer die beiden Heizeinrichtungen und das Verdampfermedium aufweisenden Baugruppe gemäßeiner alternativen Ausgestaltungsart;

Fig. 14

die bei der Ausgestaltungsart gemäß Fig. 13 vorgesehenen Verdampfermediumträger;

Fig. 15

eine Schnittansicht der in den Fig. 13 und 14 dargestellten Baugruppe;

Fig. 16

eine Abwandlung der in den Fig. 13 - 15 dargestellten Baugruppe in perspektivischer Rückansicht.

The present invention will be described below in detail with reference to the accompanying drawings by way of preferred embodiments. It shows:

Fig. 1

an exploded view of the essential components of an evaporator burner according to a first embodiment of the present invention;

Fig. 2

a longitudinal sectional view of the evaporator burner shown in Figure 1;

Fig. 3

an assembly view of the various heaters comprehensive assemblies of the evaporator burner shown in Figure 1;

Fig. 4

an exploded view of an alternative embodiment of the assembly comprising the two heaters of the evaporator burner shown in Figure 1;

Fig. 5

the assembly shown in Figure 4 in the assembly.

Fig. 6

an exploded view of the essential components of an evaporator burner according to an alternative embodiment of the present invention;

Fig. 7

a longitudinal sectional view of the evaporator burner of Figure 6, cut in a longitudinal center axis of the evaporator burner not containing plane.

Fig. 8

a sectional view of the evaporator burner shown in Figure 6, cut in a plane containing the longitudinal center axis.

Fig. 9

the assembly comprising the various heaters of the evaporator burner of Figure 6;

Fig. 10

the two heaters used in the evaporator burner of Figure 6;

Fig. 11

an alternative embodiment of the used for vaporizing the fuel and distributing the same used heater;

Fig. 12

an exploded view of the two heaters of the evaporator burner of Figure 6 having assembly according to an alternative Ausgestaltungsart;

Fig. 13

an exploded view of an assembly having the two heaters and the evaporator medium according to an alternative embodiment;

Fig. 14

the provided in the embodiment of Figure 13 Evaporatormediumträger;

Fig. 15

a sectional view of the assembly shown in Figures 13 and 14;

Fig. 16

a modification of the assembly shown in FIGS. 13-15 in a perspective rear view.

A first embodiment of an evaporator burner 10 according to the invention is shown in FIGS. 1-5. The evaporator burner 10 comprises an air duct housing 12, which is shown only partially, as well as a burner housing 16 which defines it and essentially a longitudinal center axis L of the evaporator burner 10, as indicated schematically by arrows P ₁ in FIG supplied in an air supply area 18 of the air guide housing 12 combustion air. Also, the combustion exhaust gases via a discharge region 20 of the air guide housing 12, as indicated by an arrow P ₂ , discharged from the area of the evaporator burner 10. Insofar as the combustion air supply or the removal of the combustion products are relevant to the present invention, will be discussed in more detail below. Otherwise, it should be noted that the supply of combustion air or the discharge of the resulting exhaust gases during combustion can be carried out in a conventional manner.

In the burner housing 16, a flame tube 22 extending along the longitudinal central axis L of the evaporator burner 10 is provided. The flame tube 22, similar to the burner housing 16 in its axially open region, on the air guide housing 12, namely a front housing plate 24 thereof, set. At its end region 26 remote from the housing plate 24, the flame tube 22 is axially open, so that, as indicated by the arrow P ₃ , the exhaust gases resulting during combustion flow into an annular space region 28 formed between the flame tube 22 and the burner housing 16 can. The housing plate 24 has in its lower region a slot-like, approximately over an angular range of 180 ° curved extending outlet opening 30. The flame tube 22 is positioned on the housing plate 24 such that this outlet opening 30 is located outside of the space enclosed by the flame tube 22 space area and thus a Connection between the annular space 28 and the discharge area 20 of the air guide housing 12 manufactures.

In the space area enclosed by the flame tube 22, a pot-shaped evaporator medium carrier 32 is attached to the housing plate 24 on the same side as the flame tube 22. In the space area enclosed by the evaporator medium carrier 32, the evaporator medium, generally designated 34, is arranged, which in the illustrated example comprises two layers 36, 38 of nonwoven material. In this case, the nonwoven material layer 36 is formed, for example, with finer pore structure than the nonwoven material layer 38. At the substantially cylindrical wall portion 40 of the evaporator medium carrier 32 includes a ring-shaped, constructed for example of sheet metal combustion chamber wall part 42 at. In its end region remote from the evaporator medium carrier 32, this has an annular flame diaphragm 44 with a central passage opening.

It can be seen above all in FIG. 1 that a plurality of slot-like and curved air inlet openings 46 are provided on the housing plate 24. The air inlet openings 46 are - in relation to the longitudinal central axis L - in a radial region between the flame tube 22 and the evaporator medium carrier 32. As indicated by the arrows P ₁ in Fig. 2, the combustion air can enter via these air inlet openings 46 in an annular space 48, which is formed between the flame tube 22 and the evaporator medium carrier 32 and the adjoining the evaporator medium carrier 32 region of the Brennkammerwandungsteils 42. This annular space 48 is closed axially by the widening contour of the combustion chamber wall part 42, which then rests against the inner circumference of the flame tube 22. In its adjoining the evaporator medium carrier 32, approximately cylindrically shaped region, the Brennkammerwandungsteil 42 has a plurality of circumferentially successive and, for example, axially offset air passage openings 50. The air which has reached the annular space 48 via the air inlet openings 46 can thus flow through these air passage openings 50 into the combustion chamber 52 enclosed by the combustion chamber wall part 42 into a region which lies close to the surface of the evaporator medium 34.

In a central, i. the longitudinal central axis L near region, the bottom portion 54 of the evaporator medium carrier 32 has an opening into which a fuel supply line 56 opens. The fuel supply line 56 terminates before the evaporator medium 34, i. the nonwoven material layer 36 which approaches the bottom region 54. The fuel supplied via the fuel line 56 thus enters the nonwoven material layer 36 in this central region. In order to obtain a uniform distribution over the entire radial region, a disc-like deflecting element 58 can be provided between the two nonwoven material layers 36, 38, which permits the fuel to pass directly axially from the nonwoven material layer 36 into the nonwoven material layer 38 in the longitudinal central axis L prevents near area. It is thus achieved here a forced deflection radially outward. In order to further promote this flow radially outward, as can be seen in FIG. 1, radially outwardly extending groove-like channels 60 may be provided in the bottom region 54 of the evaporator medium carrier 32 so that, bypassing the nonwoven material layer 36, further flow paths are radial are available outside.

At a radial distance from the longitudinal center line L, openings 62, 64, 66, 68 are provided in the housing plate 24, the bottom region 54 of the evaporator medium carrier 32 and the two nonwoven material layers 36, 38. This passes through a Glühzündstift 70 so that it protrudes with its provided for providing the ignition temperatures end portion in the combustion chamber 52.

At the bottom region 54 of the evaporator medium carrier 32, an evaporation heating element 72 comprising, for example, a heating wire is provided on the side facing away from the evaporator medium 34 in a recessed region 88. It is understood that both the Glühzündstift 70 and the Verdampfungsheizelement 72 are supplied by appropriate line contacting with electrical energy to heat them by energization.

The evaporator burner 10 described above with reference to FIGS. 1 to 3 with regard to its constructional structure therefore has two heaters which are designed separately from one another and can also be operated independently of one another. A first of these comprises the Glühzündstift 70, while the second heater comprises the Verdampfungsheizelement 72. In order to obtain the maximum heating power as quickly as possible with such an inventive evaporator burner 10, ie to obtain the state of complete combustion in the combustion chamber 52 as quickly as possible, the evaporator burner 10 can be operated in particular in the starting state such that by energizing the evaporating heating element 72, the evaporator medium carrier 32 and thus also the carried on this evaporator medium 34 are heated. In this case, a heating to a temperature in the range of 400 ° C take place, so that a significant increase in the evaporation rate of the due to capillary action in the evaporator medium 34 distributed fuel is obtained. By energizing the Glühzündstiftes 70 a temperature of about 1100 ° C is set in the vicinity thereof, which is sufficient to ignite the mixture produced by fuel evaporation on the one hand and combustion air supply on the other hand in the combustion chamber 52, in particular in the near the evaporator medium 34 area thereof. Since no heat has to be removed from the flame which occurs when ignition occurs for further fuel evaporation, the heat required for this purpose is essentially supplied by the evaporation heating element 72 and, moreover, by increased evaporation of Fuel distributed over the entire region of the combustion chamber 52 is a very readily ignitable mixture, a very rapid flame propagation over the entire region of the combustion chamber will occur. However, this means that due to the very rapid development of the maximum combustion in the combustion chamber 52, the entire evaporator burner 10 is brought into the operating state of maximum heat output very quickly.

It has been shown that in the evaporative heating element 72 electrical powers of about 100 W are advantageous in order to obtain the advantageous for evaporation temperatures of up to about 400 ° C. For ignition, an electrical power in the range of about 60 W is advantageous in the range of Glühzündstiftes to reach the temperatures of 1,100 ° C there.

The control of the two heaters, ie the Glühzündstiftes 70 and the Verdampfungsheizelementes 72, can be adapted to the respective operating state or external parameters. Thus, at very low ambient temperatures in the area of the evaporation heating element 72, a higher heating capacity may be required. If the evaporator burner 10 is to be operated in the auxiliary heating mode, that is to say an operating mode in which an extremely rapid flame propagation is not absolutely necessary, the excitation of the evaporating heating element 72 can be completely dispensed with, which contributes to the saving of electrical energy. Whether such an evaporator burner 10 is to be operated in the auxiliary heating mode or in the auxiliary heater mode can be recognized, for example, by means of various signals present in the control system of a vehicle, such as a signal supplied by the generator, which is only delivered when the drive unit, ie the internal combustion engine , running.

Another important aspect for achieving a fast flame propagation is the thermal insulation of the components which heat up during combustion. It is therefore advantageous, for example, for the evaporator medium carrier 32 shown in the embodiment according to FIGS. 1-3 to be made of thermally highly insulating material, such as e.g. Ceramic material to provide. Since, as can be seen in particular in FIGS. 2 and 3, the evaporation heating element 72 provided on the rear side of the bottom region 54 is arranged in a region 88 of reduced wall thickness of the bottom region 54, nevertheless a comparatively good heat transfer to the evaporator medium 34 is achieved in this region , Of course, it is also possible to provide the combustion chamber wall part 42 of ceramic material or, if appropriate, to form it integrally with the evaporator medium support 32 as well. Alternatively, the combustion chamber wall part 42 may be constructed, for example, as a precision casting or as a sheet metal part. For example, it is also possible to provide the evaporation heating element on the evaporator medium 32 on the side at which it also the nonwoven material layer 36, i. the evaporator medium 34 carries. It creates a very good thermal contact in this way.

A modification of the embodiment shown in FIGS. 1 to 3, in particular in the region of the evaporator medium carrier 32, is shown in FIGS. 4 and 5. It can be seen here that several air passage openings 74 are provided distributed in the circumferential direction in the wall region 40 of the pot-shaped evaporator medium carrier 32. These are thus in an axial region which is covered by the evaporator medium 34. The air passage openings 74 open into the evaporator medium 34 in their radially inner regions. The combustion air supplied via the air passage openings 74 from the annular space 48 thus first flows through the evaporator medium 34 where it is heated together with the fuel accumulated in the evaporator medium 34 and then exits from the evaporator medium 34 together with the evaporating fuel into the combustion chamber 52. It is thus promoted the generation of a readily ignitable mixture of vaporized fuel and combustion air, so that according to an advantageous variant, the air passage openings 74 are preferably used for supplying ignition air. The then used or required air in the normal combustion state continues to be supplied mainly by the above-mentioned air passage openings 50. However, it should be noted that with appropriate design and number of air passage openings 74, which feed air directly into the porous evaporator medium 34, if necessary, can be dispensed with the not in the evaporator medium 34, but directly into the combustion chamber 52 opening air passage openings 50. It should also be noted that, of course, in the bottom region 54 of the evaporator medium carrier 32 through openings may be present, via which combustion air, which is preferably then used in the ignition process by improved mixing with the vaporized fuel, is supplied. In order to obtain in this way an increased supply of combustion air into the combustion chamber 52, it can be thought that in alignment with the then to be provided in the bottom region 54 passage openings 34 corresponding passages can be provided in the evaporator medium.

It should be noted here that, regardless of whether the combustion air supply via the bottom region 54 of the evaporator medium carrier 32, the wall portion 40 of the evaporator medium carrier 32, ie in the porous evaporator medium 34, or the air passage openings 50 in the combustion chamber wall 42, by appropriate shaping, design, Number and distribution of the intended air passage openings an influence on the air flow behavior and thus the combustion behavior can be taken. In particular, by appropriate design or arrangement and shaping of the arranged in different areas air passage openings a Division in the ignition air on the one hand, so for example by the evaporator medium 32 through or very close to this supplied air, and combustion air, so generally in the region of the combustion chamber 52 introduced air, obtained. In particular, the air flowing along various wall regions delimiting the combustion chamber also ensures that they are cooled, and at the same time this air is preheated.

An alternative embodiment of an evaporator burner according to the invention is shown in Figs. 6-10. The basic structure of the evaporator burner 10 with regard to the provision of the air guide region 12 and the evaporator housing 16 corresponds to the structure described above. A clear difference, however, is that now to the flame tube 22 concentrically a radially inner air supply pipe 80 is provided. This receives in an axially open end region, in which an example formed with spiral surfaces Luftverwirbelungsanordnung 82, as indicated by arrows P ₄ , the externally supplied combustion air, directs them in a central region in the axial direction and outputs the air over a plurality of provided in the other end portion air passage slots 84 radially outwardly and possibly also in the axial direction, as indicated by the arrow P ₅ in Fig. 8, in the combustion chamber 52 formed substantially between this Luftzuführrohr 80 and the flame tube 22 a. So here it forms the flame tube 22 a combustion chamber 52 radially outward limiting component. The combustion gases flow, as in the embodiment described above, via the annular space 28 to the opening 30 in the housing plate 24 and from there to the example shown in Fig. 7, in which the flame tube is not shown, shown discharge area 20. The evaporator medium carrier 32 is , as seen especially in Fig. 6 and 10, formed like a ring segment. The two nonwoven material layers 36, 38 of the evaporator medium 34 are of annular design and point in the interruption region of the Evaporator medium carrier 32, the openings 66, 68. In the assembled state, the evaporator medium carrier 32 with the nonwoven material layers 36, 38 carried thereon is arranged surrounding the air supply tube 80 in the bottom region of the combustion chamber 52 so that the nonwoven material layer 38 is again exposed to the combustion chamber 52.

In the surface in contact with the nonwoven material layer 36, the evaporator medium carrier 32 has a groove-like annular channel 86 that is axially open towards the nonwoven material layer 36. In these, the fuel line 56 opens, so that the supplied via the fuel line 56 fuel can be distributed through the channel 86 in the circumferential direction over the entire ring-shaped non-woven material layers 36, 38.

At the axial side remote from the nonwoven material layer 36, the evaporator medium carrier 32 again has a depression 88, in which the evaporation heating element 72, for example formed in turn by a heating coil or comprising such a heating coil, is positioned.

On the housing plate 24, the Glühzündstift 70 is carried in such a trained use area 90 such that it passes through its intended high temperatures range the interrupted region of the evaporator medium carrier 32 and the openings 66, 68 in the nonwoven material layers 36, 38, in one with respect to the longitudinal center line L in the example shown skewed configuration. The free end region of the Glühzündstifts 70 is thus positioned near the area in which when energizing the Verdampfungsheizelementes 72 a comparatively large amount of fuel passes through evaporation in the combustion chamber 52.

Also in this embodiment, therefore, the above-described advantages can be obtained by suitable interaction of the two heaters.

In addition to the supply of the air to be provided for combustion via the slots 84, it is also possible, via a visible in Figs. 6 and 9 through opening 92 in the housing plate 24 for ignition preferably then used air directly into the area of Glühzündstifts 70 to promote. This air, which is supplied via the passage opening 92, can reach the openings 66, 68 of the nonwoven material layers 36, 38 via these openings and then into the combustion chamber 52 directly into the region in which the surroundings of the Glühzündstifs 70 in the recessed area of the evaporator medium carrier 32 Combustion will occur.

An alternative type of fuel supply in this embodiment of an evaporator burner is shown in Fig. 11. It can be seen here that the fuel is not fed via the fuel line 56 in the axial direction in the channel 86, but approximately into a circumferential center region of this channel 86 is introduced from radially outside. Due to the introduction into the circumferential center region of this channel 86, an even better distribution of the supplied fuel can be achieved. It should be noted that in Fig. 11, a circumferentially uninterrupted annular evaporator medium carrier 32 is provided. Here, as will be described below, provision can be made for the appropriate positioning of the Glühzündstifts 70 by other positioning of Glühzündstifts 70 or by providing a passage opening, not shown in FIG. 11 for this in the evaporator medium carrier 32.

Another alternative variant of the fuel supply is shown in FIG. 12. It can be seen here that the fuel line 56 is in the groove-like open channel 86 extends into or extends along it. In the region lying in the channel 86, the fuel line 56 has openings 94, via which the fuel can then escape and enter the nonwoven material layer 36. The approximately ring-like distribution of the fuel shown in the variants according to FIGS. 6 to 12 is advantageous, in particular in the case of pulsed fuel supply. By suitable selection of the dimension of the openings 94 or the mutual distance of the same, an influence on the distribution characteristic can be taken here. For example, it is possible to provide circumferentially distributed apertures 94 with varying dimension or spacing.

Further, it can be seen in Fig. 12 that on the housing plate 24 here spacer ribs 96 are provided which reduce the contact area between the evaporator medium carrier 32 and the housing plate 24 to minimize the heat transfer. Also in this embodiment or in the embodiments described above, the annular-shaped evaporator medium carrier 32 is preferably formed of ceramic material or other poorly heat-conductive material.

Another embodiment of an assembly comprising the two heaters or the evaporator medium is shown in FIGS. 13 to 15. The construction corresponds approximately to the structure with central fuel supply described above with reference to FIGS. 1-5. One recognizes here an approximately disc-shaped evaporator medium carrier 32, in the central region of which the fuel line 56 discharges. At the side which carries the nonwoven material layer 36, the evaporator medium carrier 32 has the groove-like channels 60 which extend in a star shape radially outward from the junction region of the fuel line 56. The supplied fuel is distributed over the surface of the nonwoven material layer 36 at the rear side of the nonwoven material layer 36.

The embodiment variant shown in FIGS. 13-15 can form a preassembled subassembly, ie the evaporator medium carrier 32, which comprises, for example, multi-layer porous evaporator medium 34 and the two heating devices, that is to say the glow plug pin 70 and the evaporative heating element 72. This assembly can then be integrated in a particularly simple manner in the further manufacturing process of an evaporator burner according to the invention.

A modification of such an assembly is shown in FIG. It can be seen here that the Glühzündstift 70 is not integrated into this assembly, but from radially outside - with respect to the longitudinal center line L - in the region of this assembly, ie in the region of the porous evaporator medium 34 projects and with its free end at a small distance is positioned to this.

It should be noted that, of course, the various aspects presented above in the various embodiments can be arbitrarily combined with each other. Thus, it is of course possible that in all embodiments via the evaporator medium 34 carrying region of the evaporator medium carrier 32 through openings provided therein and possibly also provided in the porous evaporator medium 34 through openings air is fed into the combustion chamber, preferably in the vicinity of that area in which the heatable for ignition end of the Glühzündstifts 70 is located. Furthermore, in all embodiments it is possible either to supply the fuel in the axial direction and to distribute it, for example, by radial channels, or to feed it from radially outside and then to distribute it via annular channels and possibly also radially extending channels. Furthermore, it is possible to detect the combustion air which can be seen in FIG. 1 via the combustion-chamber wall part 42 from radially outside and the supply of the combustion air recognizable in FIG. 6 to combine the air supply tube 80 from radially inside, ie to provide these two modules at the same time. All of these embodiments then make use of the essential inventive teaching to provide a first heater, which is formed by their special Ausgestaltungsart and also by their heating power to comparatively high temperatures for igniting the air / fuel mixture in the combustion chamber in a localized area to create. A second heating means, by heating the medium which contributes to the distribution as well as the evaporation of the fuel, ensures that there is a high rate of evaporation independent of the flame formation of the fuel, which promotes quicker ignition and better flame spread over the fuel entire combustion chamber has the consequence. After the ignition has taken place and, for example, the heating element comprising the evaporation heating element has been switched off and then the Glühzündstift is no longer energized, there is a normal combustion, in which the introduced into the combustion chamber mixture of vaporized fuel and air is burned.

Previously, an evaporator burner has been described in which by providing the evaporative heating element 72, especially at the beginning of an operating phase, increased fuel evaporation and hence faster provision of a readily ignitable and combustible mixture of fuel vapor and air can be provided. A problem with such evaporator burners is that they should generally be applicable to a wide variety of fuels and beyond should have a comparatively large Brennerleistungssprektrum. Here a ratio of maximum to minimum burner power can be around 4: 1. These two aspects ensure that often inconvenient combustion conditions can not be set. The result of this are deposits which occur more frequently in the region of the evaporator medium 34. There are often not the necessary for optimal combustion Conditions, in particular with regard to the temperature and the oxygen supply ago. According to the present invention, by appropriate design of the evaporation heating element, it is ensured that the deposits which form in the combustion mode and which themselves are combustible again are removed at certain points in time. The procedure is such that for the evaporation heating element, a heating element is provided which can generate temperatures that lead to the burning of the deposits. These are temperatures of at least 600 ° C. If such a high temperature is generated by appropriate energization of the evaporation heating element 72, the coke-like deposits are ignited and burnt. To assist in this, the blower with which the combustion air is conveyed into the combustion chamber 52 during normal combustion operation can also be put into operation. In this way, the oxygen required for the burning off of the deposits can be provided in sufficient quantity.

As used for such purposes heating elements so-called Mantelheizleiter have proven. These include a resistor embedded in ceramic powder resistance wire. The ceramic powder and this resistance wire are pressed into a heat-resistant steel tube. The essential advantage of this arrangement is that it is electrically non-conductive and thus there is no danger of a short circuit even when producing so-called coke bridges. Furthermore, it is very heat resistant and optimally adaptable to other components due to their good deformability.

The heating of the evaporation heating element 72 to such high temperatures that deposits which are also burned in the region of the combustion chamber 52, in particular in the region of the evaporator medium 34, can be carried out at certain times, for example by monitoring the total operating time of the evaporator burner 10. It can be provided in this way more or less periodically be that the entire evaporator burner is brought back into a state in which this can perform a correct combustion operation. Since, during normal combustion operation, the oxygen provided is needed to combust the vaporized fuel, and thus substantially no oxygen is available to burn deposits, it is preferable, according to the present invention, to carry out the burning of the deposits at one time in which the evaporator burner 10 is not in an operating state in which evaporated fuel is burned. Here, the procedure is preferably such that the combustion of the deposits is subsequently carried out on such an operating phase. The advantage is that in this state, various components of the evaporator burner 10 are relatively warm. Thus, the electric power required to perform the burn-off is somewhat lowered.

In order to be able to use the evaporation heating element 72 in a simple manner either for a normal evaporation operation or for burning off deposits, this is preferably controlled in a clocked manner with a duty cycle different from one. Depending on whether lower temperatures are to be obtained in the evaporation operation or higher temperatures are to be obtained in the burn-off, the duty cycle can be adjusted accordingly. In this way, it is further ensured that the operation of the evaporation heating element 72 becomes substantially independent of the supply voltage. Just the setting of the heating intervals allows easy adjustment of the heating power.

Another advantage of performing a cleaning operation in this phase of operation is that, generally after the shutdown of an auxiliary heater or auxiliary heater, the internal combustion engine of a vehicle and the cooling water supplied thereto are at operating temperature and thus also by stopping the auxiliary heater, the load on the supply voltage is reduced. Also, in this phase of operation, in general, the seat heating, the rear and windscreen heating will no longer be in operation.

With the procedure according to the invention for cleaning an evaporator burner, the service life of such an aggregate can be significantly increased. Experiments have shown that even a doubling of the service life can be achieved. It should be pointed out that, of course, the cleaning arrangement 100 formed or comprising substantially the evaporation heating element 72 in the illustrated example can also comprise a separate heating element, which is especially suitable for carrying out cleaning operations. The evaporation heating element, on the one hand, and this heating element specially provided for the cleaning operation, on the other hand, can then each be optimally adapted to their operating requirements.

In evaporator burners of the type described above, the metering pump, via which the fuel is introduced into the combustion chamber 52 or conveyed to the evaporator medium 34, is generally monitored for its operation. For example, the coil current of the metering pump can be evaluated and it can be concluded if necessary, whether the metering pump is working properly or not. However, if, for example, there is a liquid leak in the region between the metering pump and the combustion chamber, this can only be partially recognized from the current signal curve of a metering pump coil. In particular, a very precise evaluation of this current waveform would require very expensive electronics. According to the present invention, therefore, it is intended to obtain information about whether or not fuel is introduced into the combustion chamber 52 by including the evaporation heating element. This will be described below.

In detecting the fuel supply, the present invention takes advantage of a particular temperature-resistance relationship of the evaporative heating element 72 provided in the bottom portion of the combustion chamber 52. This is provided in accordance with the principles of the present invention as a so-called PTC element. That is, the evaporation heating element 72 to be energized has an electrical resistance which increases with increasing temperature and correspondingly decreases with decreasing temperature. If the evaporator medium 34 is now to be heated to a temperature suitable for evaporation, for example in the range of 400 ° C., by means of such an evaporation heating element, the evaporation heating element 72 is energized by means of a drive device (not shown). It is preferably done in a clocked manner, i. with a certain duty cycle, a voltage is applied to the evaporative heater 72. For temperature detection, information can be stored, for example, in the drive device, which reproduces the relationship between the electrical resistance and thus the electric current flowing at a predetermined voltage and the temperature in the region of the evaporation heating element 72. If it is determined that the current flow is approaching a current flow expected for the desired temperature, then the heating power can be gradually reduced by shortening the intervals during which the voltage is applied, i. it also reduces the duty cycle. Upon reaching the desired temperature, ie reaching a current associated with this temperature, then the Verdampfungsheizelement 72 can be operated with a power that essentially only serves to keep the constant temperature.

If fuel is then conducted into the combustion chamber 52 or the evaporator medium 34 by excitation of a metering pump and the fuel evaporates due to the comparatively high temperature prevailing there, energy is required for this. This energy is extracted from the environment in the form of heat energy. It therefore occurs initially still kept constant heating power cooling in the region of the evaporator medium 34 and then in the region of the Verdampfungsheizelements 72. This cooling is reflected in a correspondingly decreasing electrical resistance and therefore at a constant voltage an increase in the current noticeable. The drive device then tries to keep the required evaporation temperature constant by increasing the heat output, ie, by renewing the voltage pulse duration, to provide a correspondingly increased heating power.

It can therefore be seen that when the evaporation starts at a heating power that is initially kept constant, a change in the current flowing through the evaporation heating element 72 will occur. This change or control or control measures based on this change can be used as an indicator that the evaporation has begun. It can then be generated for example in the driving device indicating the beginning of the evaporation signal. Then, for example, the ignition can be triggered by energizing the Glühzündstifts 70.

If such an evaporator burner, for example, when in a vehicle, the provision of additional heat is no longer required, stopped, so is to reduce the Abschaltemissionen in a similar manner. After the basic switching off of the evaporator burner 10, for example by switching off the metering pump, the evaporation heating element 72 is first energized further. The fuel still present in the evaporator medium 34 or the supply line provided for this purpose continues to evaporate, so that care is taken at first to keep the heating power constant so that essentially no liquid fuel remains in the evaporator burner 10 itself. If the entire fuel is then vaporized, no additional heat energy is needed to transfer more fuel into the vapor phase.

This means that when initially not actively changed heating by increasing the temperature, the electrical resistance increases and the Verdampfunsgheizelement 72 by flowing electrical current decreases. This recognizes the drive device. Based on the detected decrease in the electrical current, it can now be recognized that substantially no fuel is left to evaporate, so that now also the energization of the evaporation heating element 72 can be adjusted. Here, for example, it is possible to proceed in such a way that the change in the electrical current is observed. If there is no change, it can be concluded that no more fuel is available and therefore the thermal conditions have not changed. Furthermore, it is possible for the drive device in a control process to attempt to set the heating power in such a way that the temperature is kept constant. Only then, if no changes in the heating power are required, then the operation of the Verdampfungsheizelements 72 can be adjusted, since this is an indication that no more fuel residues to be evaporated are available.

The procedure according to the invention, in which it can be easily recognized by taking advantage of the electrical characteristics of the evaporation heating element, whether a fuel supply takes place, i. Whether fuel is vaporized or not, different operating phases can be optimally matched to each other without the need for additional design measures and thus induced costs. In addition to the already possible electrical monitoring of the operability of a fuel delivery system, such as e.g. a dosing pump, so can also take place a hydraulic monitoring, which can be closed with a correspondingly precise evaluation by the required amount of heat in the fuel evaporation amount, which fuel has been introduced or evaporated.

Claims (27)

1. An evaporative burner, comprising:

   - an evaporative medium (34) for feeding fuel vapour into a combustion chamber (52),

   - a first heating device (70), comprising at least one ignition heating element (70) for igniting fuel vapour present in the combustion chamber (52),

   - a second heating device (72), comprising at least one evaporative heating element (72) associated with the evaporative medium (34) so as to influence its evaporation characteristic, wherein

   the at least one evaporative heating element (72) is arranged on a side of the evaporative medium (34) remote from the combustion chamber (52), characterised in that
   the evaporative medium (34) is provided on an evaporative medium support (32), and in that the at least one evaporative heating element (72) is provided on a side of the evaporative medium carrier (32) remote from the evaporative medium (34).
2. An evaporative burner according to Claim 1, characterised by a fuel supply channel assembly (60;86,56) for introducing liquid fuel into the evaporative medium (34).
3. An evaporative burner according to Claim 2, characterised in that the fuel supply channel assembly (60; 86,56) is designed to distribute the liquid fuel over the evaporative medium (34).
4. An evaporative burner according to Claim 3, characterised in that the fuel supply channel assembly (60; 86, 56) has at least one annular channel region (86,56) and/or at least one radial channel region (60) extending substantially radially from a fuel supply duct (56) in the evaporative medium (34) and/or in an evaporative medium support (32).
5. An evaporative burner according to any one of Claims 1 to 4, characterised by an air supply channel assembly for feeding air to be combusted with fuel vapour into the combustion chamber (52).
6. An evaporative burner according to Claim 5, characterised in that the air supply channel assembly has in a wall bounding the combustion chamber (52) at least one air-inlet opening (50;84,92) open towards the combustion chamber (52).
7. An evaporative burner according to Claim 5 or 6, characterised in that the air supply channel assembly has at least one air-inlet opening (74) open towards the evaporative medium (34).
8. An evaporative burner according to any one of Claims 5 to 7, characterised in that the air supply channel assembly has at least one air supply channel region (92,66,68) which passes through the evaporative medium (34).
9. An evaporative burner according to any one of Claims 1 to 8, characterised in that the at least one evaporative heating element (72) and the evaporative medium (34) are provided on an evaporative medium support (32) formed from ceramic material.
10. An evaporative burner according to any one of Claims 1 to 9, characterised in that the evaporative medium (34) preferably comprises porous material arranged in a plurality of layers.
11. An evaporative burner according to any one of Claims 1 to 10, characterised in that the evaporative medium (34) comprises non-woven material (36,38).
12. An evaporative burner according to any one of Claims 1 to 11, characterised by a cleaning assembly (100) for removing deposits which are deposited in the vicinity of the combustion chamber (52) during combustion operation.
13. An evaporative burner according to Claim 12, characterised in that the cleaning assembly (100) comprises a heating assembly (72) by means of which a temperature in the region of or above a burning-off temperature of the deposits can be generated in the vicinity of the combustion chamber (52).
14. An evaporative burner according to Claim 13, characterised in that the heating assembly (72) for generating the temperature in the region of or above the burning-off temperature is provided at least in the vicinity of the evaporative medium (34).
15. An evaporative burner according to Claim 14, characterised in that the heating assembly (72) comprises the second heating device (72).
16. A method of cleaning an evaporative burner according to any one of Claims 13 to 15, in which method by activating the heating assembly (72) deposits on a wall surrounding the combustion chamber (52) are heated to a temperature in the region of or above a burning-off temperature of the deposits, whereupon the deposits are burnt off.
17. A method according to Claim 16, characterised in that the method is carried out when the heating burner is not in a heating operation condition.
18. A method according to Claim 17, characterised in that the method is carried out following a heating operation condition phase of the heating burner.
19. A method according to Claim 16 to 18, characterised in that the method is carried out after a predetermined operating time of the heating burner.
20. A method according to any one of Claims 16 to 19, characterised in that when carrying out the method the heating assembly (72) is activated with a mark/space ratio of less than unity.
21. An evaporative burner according to any one of Claims 1 to 15, characterised by an activating device by which the heating output of at least the second heating device (72) is adjustable, wherein a monitoring module monitors the heating output and/or the required heating output of the second heating device (72) and detects the presence of fuel evaporation, depending on the result of monitoring.
22. An evaporative burner according to any one of Claims 1 to 15 and 21, characterised in that the evaporative heating element (72) comprises an electrically operated heating element having an electrical resistance which increases with rising temperature.
23. A method of monitoring the fuel supply to an evaporative burner, according to any one of Claims 1 to 15 or 21 or 22, in which method, depending on the heating output of the heating device (72) and/or a change in the heating output of the heating device (72) and/or a required change in the heating output of the heating device (72), it is determined whether the evaporation of fuel is present in the combustion chamber (52) of the evaporative burner (10).
24. A method according to Claim 23, characterised in that with increasing heating output and/or required higher heating output during operation of the heating device (72) the presence of fuel evaporation is detected.
25. A method according to Claim 23 or 24, characterised in that, during an ignition process of the evaporative burner, in a first operating phase the heating device (72) is operated at higher heating output preferably in the region of a maximum heating output, in a subsequent, second operating phase the heating device (72) is operated at reduced, preferably decreasing heating output and in a further subsequent, third operating phase the heating device (72) is operated at once more increased, preferably rising heating output, wherein the presence of fuel evaporation is detected at or after the transition into the third operating phase.
26. A method according to any one of Claims 23 to 25, characterised in that when the presence of fuel evaporation is detected a heating device (72) is activated which assists the ignition of the evaporated fuel.
27. A method according to any one of Claims 23 to 26, characterised in that, in an operating phase in which the combustion operation of the evaporative burner is adjusted, the heating device (72) assisting the evaporation will be activated or is activated, and in that depending on a reduction in the heating output it is detected that fuel evaporation is no longer present.

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