FILM EVAPORATOR BURNER ARRANGEMENT

Abstract

A film evaporator burner arrangement (1) is provided, having: a combustion chamber arrangement comprising a combustion chamber (2) for the conversion of a fuel-air mixture with the release of heat, which extends in the axial direction along a longitudinal axis (Z); a combustion air supply (5) for the supply of combustion air, which is configured such that the combustion air is supplied with a tangential flow component to at least one combustion air inlet (8) of the combustion chamber arrangement; a film evaporator surface (4) for evaporating liquid fuel originating from a fuel film (10), which is arranged at a rear wall (3) axially rearward of the combustion air inlet (8); and a fuel supply (9) for the supply of liquid fuel to the film evaporator surface (4).

Claims

1. A film evaporator burner arrangement comprising: a combustion chamber arrangement including a combustion chamber for reacting a fuel-air mixture with release of heat and which extends in an axial direction along a longitudinal axis; a combustion air feed supplying combustion air with a tangential flow component to the combustion chamber arrangement at at least one combustion air inlet; a film evaporator surface evaporating liquid fuel starting from a fuel film arranged on a rear wall axially to a rear of the combustion air inlet; and a fuel feed supplying liquid fuel to the film evaporator surface.

2. The film evaporator burner arrangement as claimed in claim 1, in which the combustion air is supplied from radially outside at the combustion air inlet.

3. The film evaporator burner arrangement as claimed in claim 1, wherein the film evaporator surface is free of porous, absorbent bodies.

4. The film evaporator burner arrangement as claimed in claim 1, wherein the film evaporator surface extends predominantly perpendicular to the longitudinal axis.

5. The film evaporator burner arrangement as claimed in claim 1, wherein the combustion air feed supplies the combustion air with the tangential flow component to the combustion chamber.

6. The film evaporator burner arrangement as claimed in claim 1, wherein the combustion chamber arrangement includes a pre-evaporation chamber arranged flow wise upstream of the combustion chamber for conditioning a fuel-air mixture prior to entry thereof into the combustion chamber.

7. The film evaporator burner arrangement as claimed in claim 6, wherein the pre-evaporation chamber is separated from the combustion chamber by a partition wall extending radially inwards from a side wall of the combustion chamber arrangement.

8. The film evaporator burner arrangement as claimed in claim 7, wherein the partition wall extends radially inwards and axially rearwards from the side wall.

9. The film evaporator burner arrangement as claimed in claim 6, wherein the pre-evaporation chamber has a smaller flow cross-section than the combustion chamber in a direction perpendicular to the longitudinal axis and the flow cross-section of the pre-evaporation chamber widens abruptly at a transition from the pre-evaporation chamber to the combustion chamber.

10. The film evaporator burner arrangement as claimed in claim 6, wherein the combustion air feed supplies the combustion air with the tangential flow component to the pre-evaporation chamber.

11. The film evaporator burner arrangement as claimed in claim 1, wherein the fuel feed supplies the fuel with a tangential direction component radially from outside to the film evaporator surface.

12. The film evaporator burner arrangement as claimed in claim 1, wherein the combustion chamber is free of constrictions or contractions over its axial extent.

13. A mobile heating appliance with a film evaporator burner arrangement as claimed in claim 1.

Description

[0021] Further advantages and further developments are revealed by the following description of exemplary embodiments made with reference to the appended drawings.

[0022] FIG. 1 is a schematic representation of a film evaporator burner arrangement according to a first embodiment.

[0023] FIG. 2 is a schematic representation of a swirl body for the combustion air feed according to the embodiment.

[0024] FIG. 3 is a schematic representation of a film evaporator burner arrangement according to a second embodiment.

[0025] FIG. 4 is a schematic representation of a film evaporator burner arrangement according to a third embodiment.

[0026] FIG. 5 is a schematic representation of a film evaporator burner arrangement according to a fourth embodiment.

[0027] FIG. 6 is a schematic representation of a first modification of the fourth embodiment.

[0028] FIG. 7 is a schematic representation of a second modification of the fourth embodiment.

[0029] FIG. 8 is a schematic representation of a third modification of the fourth embodiment.

FIRST EMBODIMENT

[0030] A film evaporator burner arrangement 1 according to a first embodiment is described in greater detail below with reference to FIG. 1 and FIG. 2. The film evaporator burner arrangement 1 is designed for a mobile heating appliance, in particular for a parking heating appliance or auxiliary heating appliance for a motor vehicle, which in particular comprises a heat exchanger (not shown) for transferring heat from the outflowing combustion waste gases to a medium to be heated. The medium to be heated may, for example in the case of a hot-air heater, take the form of air to be heated for a vehicle interior or, in the case of a liquid heater, take the form of a liquid to be heated in a liquid circuit of a vehicle, in particular cooling liquid. The heat exchanger may, in a manner known per se, be configured such that it surrounds the combustion chamber and/or a flame tube adjacent thereto substantially in the manner of a cup.

[0031] The mobile heating appliance further comprises, in a manner known per se, a fuel delivery device for delivering the liquid fuel, which may in particular take the form of diesel, gasoline, ethanol, or the like. The fuel delivery device may in particular take the form of a fuel metering pump. In addition, the mobile heating appliance comprises a combustion air delivery device for delivering the combustion air, which may in particular take the form of a blower, a control unit for controlling operation of the mobile heating appliance and further components necessary for operation, which are not described in any greater detail, in particular for example temperature sensors, etc.

[0032] The film evaporator burner arrangement 1 according to the first embodiment comprises a combustion chamber 2, which, in the example shown, is approximately cylindrical in shape and extends along a longitudinal axis Z. The combustion chamber 2 is bounded circumferentially by a peripheral side wall 21, which may for example be formed from a high-temperature resistant steel. A main direction of flow H in which combustion waste gases flow out from the combustion chamber 2 to the heat exchanger (not shown) extends substantially parallel to the longitudinal axis Z.

[0033] The combustion chamber arrangement 1 is closed at the rear by a rear wall 3, which is formed in the first embodiment by a rear wall of the combustion chamber 2. The rear wall 3 is formed on the side facing the combustion chamber 2 as a film evaporator surface 4 on which a film of the liquid fuel is distributed, starting from which evaporation of the liquid fuel takes place. Although the schematic representation of FIG. 1 shows a completely flat configuration of the rear wall 3, it is also possible, for example, to make the rear wall 3 convex or concave in the direction of the combustion chamber 2. In the embodiment shown, the film evaporator surface 4 takes the form of a substantially smooth metallic area; however, it is for example also possible to provide the film evaporator surface 4 with roughening or fine texturing, in order to improve distribution of the liquid fuel, wetting of the film evaporator surface 4 and fuel evaporation.

[0034] A combustion air feed 5 shown schematically in FIG. 1 is additionally provided, via which combustion air with a significant tangential flow component, i.e. strong swirl, is introduced into the combustion chamber 2. The combustion air feed 5 represented schematically in FIG.

[0035] 1 by arrows is in this case arranged in such a way that the combustion air is supplied to the combustion chamber 2 radially externally at the peripheral side wall 21 at a distance from the rear wall 3 of the combustion chamber arrangement 1 and thus at a distance from the film evaporator surface 4. The combustion air is thus introduced into the combustion chamber arrangement 1 with one flow component, i.e. strong swirl, extending in the circumferential direction and with one radially inwardly directed flow component, such that swirling flow around the longitudinal axis Z forms in the combustion chamber 2. To bring about this swirling flow, the combustion air feed 5 comprises a swirl body 6 with a plurality of air ducts or air blades, in order to impart the desired strong swirl to the combustion air.

[0036] FIG. 2 is a diagrammatic representation of a possible embodiment of the swirl body 6. The swirl body 6 depicted by way of example is substantially annular in shape and a plurality of combustion air ducts 7 are formed in the wall of the swirl body 6, via which combustion air may pass from the outside of the swirl body 6 to the inside of the swirl body 6. The combustion air is supplied to the combustion air ducts 7 on the outside of the swirl body 6 via a combustion air delivery device, as shown schematically by fat arrows, flows through the combustion air ducts 7 and enters the combustion chamber 2 on the inside of the swirl body 6 at combustion air inlets 8. Although the exemplary embodiment shown schematically depicts four such combustion air inlets 8, fewer than four, but at least one combustion air inlet 8, or more than four combustion air inlets 8 may also be provided. As a result of the curved shape of the combustion air ducts 7, which additionally taper inwards, the combustion air is provided with strong swirl and at the same time accelerated, as shown schematically in FIG. 2 by thin arrows.

[0037] The combustion air passing from the swirl body 6 into the combustion chamber 2 at the combustion air inlets 8 thus has a significant tangential direction component, i.e. strong swirl, and also at least one radially inwardly directed direction component. A fuel feed 9 is provided which opens into the side wall 21 to the rear of the combustion air inlets 8 with regard to the main direction of flow H. Via the fuel feed 9 liquid fuel, which may in particular take the form of gasoline, diesel, ethanol or the like, is supplied to the film evaporator surface 4 at the rear wall 3. Although FIG. 1 shows just one fuel line and one fuel outlet to the film evaporator surface 4 in the form of fuel feed 9, it is also possible, for example, to provide a plurality of fuel lines and/or a plurality of fuel outlets. In the exemplary embodiment, the liquid fuel is likewise fed radially inwards and with a tangential direction component, which is preferably in the same direction as the swirl of the supplied combustion air, something which may be achieved for example by corresponding orientation of the fuel outlet (or the fuel outlets).

[0038] As a result of the swirling flow of the combustion air formed in the combustion chamber 2, the fuel exiting the fuel feed 9 is distributed over the film evaporator surface 4 at the rear wall 3, such that a fuel film 10 forms there, starting from which the liquid fuel is evaporated or volatilized. The fuel film 10 is depicted schematically in FIG. 1 by a dashed line. As a result of the arrangement of the film evaporator surface 4 to the rear of the combustion air inlet 8 at which the strongly swirled combustion air is supplied, the fuel film 10 consisting of the liquid fuel spreads out due to small axial and large tangential flow components and the temperature input into the liquid fuel of the fuel film 10 may be adjusted in a very targeted manner.

[0039] Moreover, an ignition element 11 for starting the reaction of the fuel-air mixture is arranged in the combustion chamber 2, this being formed in the schematically depicted exemplary embodiment for example by a glow plug. Although, in the exemplary embodiment shown, the ignition element 11 projects from radially outside into the combustion chamber 2, other arrangements of the ignition element 11 are also possible, in particular the ignition element 11 may for example also project axially from behind through the rear wall 3 into the combustion chamber 2. When the film evaporator burner arrangement 1 is in operation, the fuel-air mixture is firstly ignited in the combustion chamber 2 by means of the ignition element 11, to start the reaction. Once a stable flame has formed in the combustion chamber 2, the ignition element 11 may then be switched off, for example, or be used in a manner known per se for example also as a flame detector for monitoring the flame. Although, in the exemplary embodiment depicted, the combustion chamber 2 is configured for reaction of the fuel-air mixture under flaming combustion, a refinement for reaction in a partially or fully catalytic reaction is for example in principle also possible.

[0040] The temperature established at the film evaporation surface 4 during operation of the film evaporator burner arrangement 1 is determined by the thermal energy introduced into the combustion chamber 2 by the flame. This thermal energy is here transferred by convection, via heat radiation and via thermal conduction in the material of the side wall 21. Through suitable geometric design and material selection, the optimum temperature for reliable evaporation of the liquid fuel during operation of the film evaporator burner arrangement 1 may be established. Experience shows that at very low temperatures below the initial boiling point of the fuel or at very high temperatures above the final boiling point, evaporation or volatilization is possible substantially without the formation of deposits. In addition, the thorough intermixing of the fuel film 10 results in the washing off of incipient deposits on the rear wall 3, so enabling operation of the film evaporator burner arrangement 1 at least substantially without deposits from the fuel.

[0041] As is depicted schematically in FIG. 1, the combustion chamber 2 is formed with an at least substantially free flow cross-section free of constrictions or contractions, so meaning that the flows of the gases in the combustion chamber 2 may be adjusted as desired.

[0042] A film evaporator burner arrangement 1 has thus been described which is structurally simple and inexpensive to produce. Since no additional porous evaporator element is provided, problems concomitant with such an evaporator element are reliably avoided. The robust configuration results in relatively low sensitivity with regard to component tolerances, which likewise has a positive effect on manufacturing costs. Reduced deposit formation and thus a long service life, low emissions and low sensitivity to coarse fuel impurities are also achieved. The useful evaporation area is variable, such that a large range of different heating powers can be provided and a large number of different liquid fuels may be used. Furthermore, the electrical power consumption needed for fuel feed is low and smoke and odor formation on start-up and burn-out of the film evaporator burner arrangement 1 is greatly reduced compared with evaporator burners with porous evaporator elements.

Second Embodiment

[0043] A second embodiment is described below with reference to FIG. 3. To avoid unnecessary repetition, in the description of the second embodiment the same reference signs as for the above-described first embodiment are used for the corresponding components of the film evaporator burner arrangement 100 according to the second embodiment. Moreover, only the differences from the above-described first embodiment will be described in greater detail below.

[0044] The film evaporator burner arrangement 100 according to the second embodiment depicted schematically in FIG. 3 differs from the above-described first embodiment in that, in addition to the combustion chamber 2, the combustion chamber arrangement also comprises a pre-evaporation chamber 12 arranged flow-wise upstream thereof for pre-processing the fuel-air mixture prior to entry thereof into the combustion chamber 2, as described in greater detail below. Furthermore, the rear wall 3 of the combustion chamber arrangement, on which the film evaporator surface 4 is formed, is not flat in the second embodiment but rather on the side facing the combustion chamber 2 is concave in shape, indeed substantially conical in shape in the specific example shown. In the second embodiment, the rear wall 3 of the combustion chamber arrangement and the film evaporator surface 4 are however not arranged in the combustion chamber 2, in which reaction of the fuel-air mixture proceeds with release of heat, but rather in the pre-evaporation chamber 12 arranged flow-wise upstream thereof, such that the rear wall 3 of the combustion chamber arrangement forms the rear wall of the pre-evaporation chamber 12. Furthermore, in the second embodiment the ignition element 11 is arranged in such a way that it projects axially through the rear wall 3 of the combustion chamber arrangement as far as into the combustion chamber 2. In an alternative, it is however also possible for example to arrange the ignition element 11 differently, in particular such that it projects radially from outside into the combustion chamber 2, as in the above-described first embodiment.

[0045] In the film evaporator burner arrangement 100 according to the second embodiment, the pre-evaporation chamber is separated from the combustion chamber 2 by a partition wall 13 projecting inwards from the peripheral side wall 21. In the schematically depicted exemplary embodiment, the partition wall 13 extends from the side wall 21 radially inwards and axially backwards with regard to the main direction of flow H. However, the partition wall 13 does not extend over the entire cross-section of the combustion chamber arrangement, but rather a central opening 14 is provided, via which the fuel-air mixture pre-processed in the pre-evaporation chamber 12 may pass from the pre-evaporation chamber 12 into the combustion chamber 2. In the example shown, the central opening 14 is arranged substantially coaxially with the longitudinal axis Z and has a substantially circular cross-section, but other shapes are in principle also possible. The partition wall 13 may for example be formed of the same material as the side wall 21, in particular high-temperature resistant steel.

[0046] Unlike in the first embodiment, in the film evaporator burner arrangement 100 according to the second embodiment the combustion air inlets 8, at which the combustion air exits with a tangential flow component and at least also a radial flow component from the swirl body 6, are however not arranged in the region of the combustion chamber 2 but rather in the region of the pre-evaporation chamber 12. Consequently, the combustion air with the tangential flow component is supplied from radially outside to the pre-evaporation chamber 12. In the second embodiment too, the film evaporator surface 4 is arranged to the rear of the combustion air inlets 8. Although FIG. 3 also schematically shows a plurality of combustion air inlets 8, the film evaporator burner arrangement 100 again comprises at least one combustion air inlet 8. The fuel feed 9 supplies the liquid fuel to the rear of the combustion air inlets 8 from radially outside to the film evaporator surface 4. At least the mouth of the fuel feed 9 is here preferably arranged in such a way that the liquid fuel is introduced with a tangential direction component which corresponds to the direction of swirl of the supplied combustion air.

[0047] As a result of the strong swirling of the combustion air supplied to the pre-evaporation chamber 12 and the surface forces between the rear wall 3 and the liquid fuel, the supplied liquid fuel is distributed at least partially radially at the film evaporator surface 4 to form a fuel film 10, as shown schematically by dashed lines in FIG. 3.

[0048] During operation of the film evaporator burner arrangement 100, the partition wall 13, which separates the pre-evaporation chamber 12 from the combustion chamber 2, heats up such that the fuel film 10 formed at the film evaporator surface 4 is heated and evaporated or volatilized mainly by way of heat radiation. The fuel-air mixture pre-processed in the pre-evaporation chamber 12 passes via the central opening 14 into the combustion chamber 2, in which it is reacted with release of heat, for example under flaming combustion. As a result of the strong swirl of the fuel-air mixture supplied via the opening 14 and the backflow thus established in the combustion chamber 2 in a central region about the longitudinal axis Z, the flame stabilizes itself in the combustion chamber 2. Since the combustion chamber 2 is configured with a substantially free flow cross-section, free of constrictions and contractions, advantageous flow conditions may form in the combustion chamber 2.

[0049] As a result of rear wall 3 tapering concavely or conically backwards together with the partition wall 13 extending radially inwards and axially backwards, the centrifugal forces acting on the fuel film 10 may be adjusted simply by way of selection of the precise shape of the rear wall 3, such that it may be ensured that the liquid fuel is neither distributed too quickly radially inwards at the film evaporator surface 4 nor does it remain too long in the radially outer region.

[0050] Preferably, heat exchange by way of thermal conduction between the combustion chamber 2 and the pre-evaporation chamber 12 may be minimized, which may be achieved in a technically simple manner for example by suitable selection of materials with low coefficients of thermal conductivity, smaller contact areas and structural barriers. This makes it possible to keep the rear wall 3 at low temperatures during operation of the film evaporator burner arrangement 100 and to heat and volatilize or evaporate the fuel film 10 predominantly by heat radiation.

[0051] With the axial arrangement of the ignition element 11 shown schematically in FIG. 3, it is furthermore possible, in particular if the ignition element 11 takes the form of a ceramic glow plug, to heat up the fuel film 10 evenly at the start of operation of the film evaporator burner arrangement 100.

[0052] In addition to the advantages already described in relation to the first embodiment, the refinement according to the second embodiment enables particularly low-emission operation due to the pre-processing of the fuel-air mixture in the pre-evaporation chamber 12 prior to entry into the combustion chamber 2.

Third Embodiment

[0053] A third embodiment is described below with reference to FIG. 4. To avoid unnecessary repetition, in the description of the third embodiment the same reference signs as for the above-described first embodiment are used for the corresponding components of the film evaporator burner arrangement 200 according to the third embodiment. Moreover, only the differences from the above-described first embodiment will be described in greater detail below.

[0054] The film evaporator burner arrangement 200 according to the third embodiment depicted schematically in FIG. 4 differs from the above-described first embodiment in that combustion air is not supplied to the combustion chamber arrangement radially from outside at the side wall 21, but rather the combustion air with the tangential flow component is supplied to the combustion chamber arrangement substantially in the axial direction. The film evaporator surface 4 is arranged at a set-back rear wall 3 of the combustion chamber arrangement.

[0055] Although it has been described in relation to each of the embodiments that all the combustion air is supplied via the swirl body 6, modifications are also possible in which only part of the combustion air is supplied via the swirl body and the remaining combustion air is supplied to the combustion chamber arrangement for example at another point.

Fourth Embodiment

[0056] A fourth embodiment is described below with reference to FIG. 5. To avoid unnecessary repetition, in the description of the fourth embodiment the same reference signs as for the above-described embodiments are used for the corresponding components of the film evaporator burner arrangement 300 according to the fourth embodiment. Moreover, only the differences are described in greater detail below.

[0057] In the fourth embodiment shown schematically in FIG. 5 too, the combustion chamber arrangement comprises not only the combustion chamber 2 but also a pre-evaporation chamber 12 arranged flow-wise upstream thereof for pre-processing the fuel-air mixture prior to entry thereof into the combustion chamber 2. In the fourth embodiment, the rear wall 3 of the combustion chamber arrangement and the film evaporator surface 4 are again arranged not in the combustion chamber 2 but in the pre-evaporation chamber 12 arranged flow-wise upstream thereof, such that the rear wall 3 of the combustion chamber arrangement forms the rear wall of the pre-evaporation chamber 12. Also in the fourth embodiment, the ignition element 11 is arranged, similarly to in the second embodiment, in such a way that it projects axially from the back into the pre-evaporation chamber 12.

[0058] In the fourth embodiment, the liquid fuel is supplied via the fuel feed 9 from radially outside to the rear wall 3 comprising the film evaporator surface 4. Also in the fourth embodiment, the fuel feed opens into the combustion chamber arrangement axially to the rear of the combustion air inlets 8. The combustion air inlets 8 are here arranged in such a way that the combustion air is supplied with strong swirl from radially outside into the pre-evaporation chamber 12.

[0059] As FIG. 5 shows, the pre-evaporation chamber 12 has a significantly smaller cross-section in the direction perpendicular to the longitudinal axis Z than the combustion chamber 2. In the case of a substantially cylindrical refinement with an approximately circular cross-section of the pre-evaporation chamber 12 and the combustion chamber 2, the ratio D/d of the diameter D of the combustion chamber 2 to the diameter d of the pre-evaporation chamber 12 lies in the range: 1.2<D/d<3.0, preferably 1.4<D/d<2.6. The transition from the pre-evaporation chamber 12 to the combustion chamber 2 takes the form of a neck portion, at which the cross-section widens abruptly in the main direction of flow H. Over the axial length of this neck portion, the flow conditions established may additionally be purposefully adjusted, wherein the axial length of the neck portion may also be selected in particular to be very short or the neck portion may also have substantially absolutely no axial extent.

[0060] During operation, the combustion air is supplied with strong swirl to the pre-evaporation chamber 12, which comprises the film evaporator surface 4 arranged to the rear of the combustion air inlets 8. In this way, good intermixing of the supplied combustion air with evaporating fuel takes place in the pre-evaporation chamber 12, to yield a fuel-air mixture which flows in the pre-evaporation chamber 12 with a high tangential flow component. Because of the significant widening of the flow cross-section at the point of transition from pre-evaporation chamber 12 to combustion chamber 2, significant radial widening of the swirl formed takes place, which is accompanied by a significant speed reduction in the axial direction, such that a recirculation region forms in the central region of the combustion chamber 2 close to the axis, in which recirculation region the gases flow contrary to the main direction of flow H. Furthermore, an axially symmetrical outer recirculation zone also forms in the radially outer region of the combustion chamber 2 directly downstream of the transition point. To achieve the described flow conditions, the combustion air is preferably introduced with swirl of such a strength that a swirl number S in the range of 0.4<S<1.4, preferably 0.5<S<1.1, is established at the transition from the pre-evaporation chamber 12 to the combustion chamber 2. In this way, very good flow stabilization is achieved, which during operation results in particular in reliable anchoring of the flame in the combustion chamber 2.

[0061] As a result of the described refinement of the combustion chamber arrangement in the fourth embodiment, pre-processing of the evaporated fuel with combustion air to yield an at least largely pre-mixed fuel-air mixture is achieved in a structurally very simple way, requiring only a little structural space in the axial direction, so resulting in good flow stabilization in the combustion chamber arrangement. In this manner, particularly low-pollutant combustion is achieved in the combustion chamber 2.

Modifications

[0062] The first modification of the fourth embodiment shown in FIG. 6 differs from the fourth embodiment shown in FIG. 5 in that the liquid fuel is not supplied from radially outside to the film evaporator surface 4 but rather in the center of the rear wall 3 in the axial direction. As a result of the arrangement of the film evaporator surface 4 axially to the rear of the combustion air inlet 8 and the strong swirl of the supplied combustion air, it is also possible in this case to achieve reliable fuel evaporation and intermixing to yield a fuel-air mixture.

[0063] The refinement according to the first modification furthermore differs from the above-described fourth embodiment in that the ignition element 11 does not project in the axial direction into the pre-evaporation chamber 12 but rather obliquely from the back and from radially outside into the pre-evaporation chamber 12.

[0064] Since the further features match the previously described fourth embodiment and the first modification also achieves the same advantages as described above, a new description will be omitted.

[0065] The second modification of the fourth embodiment shown in FIG. 7 differs from the fourth embodiment shown in FIG. 5 only in that the fuel feed 9 opens in the axial direction at the rear wall 3 of the pre-evaporation chamber 12 providing the film evaporator surface 4. In the second modification, the fuel feed 9 opens somewhat to the side of the longitudinal axis Z in the radial direction.

[0066] The third modification of the fourth embodiment shown in FIG. 8 differs from the second modification merely in the configuration of the transition from pre-evaporation chamber 12 to combustion chamber 2.

[0067] As FIG. 8 shows, although the flow cross-section at the transition from pre-evaporation chamber 12 to combustion chamber 2 in this case still widens very significantly, it does not do so quite so abruptly as it does in the fourth embodiment and the previously described modifications thereof. In the third modification specifically depicted, an approximately conical widening with a large opening angle is provided. Preferably, at least a double obtuse opening angle >90 is here provided.

[0068] In the fourth embodiment and the modifications thereof the individual structural features may also be combined with one another in different ways. It is for example possible to provide the structural configuration of the transition from pre-evaporation chamber 12 to combustion chamber 2 shown in the third modification also in the fourth embodiment or the first modification of the fourth embodiment.