EP1574782B1 - Vaporizing Burner, in particular for a Car Heater - Google Patents

Description

The present invention relates to an evaporator burner, in particular for a vehicle heater, comprising a combustor housing providing a combustion chamber with a peripheral wall and a bottom wall according to the preamble of claim 1.

In such evaporator burners, an air / fuel mixture to be combusted in the combustion chamber is produced by evaporation of the initially liquid supplied fuel. The evaporation may be assisted by providing a porous evaporator medium to the inside of the combustor casing, through which porous evaporator medium the feed fuel is first distributed over a larger surface area and then evaporated towards the combustor. In order to support this evaporation, it is also known to assign a heating device to the porous evaporator medium, in order to be able to provide sufficient heat, in particular in the startup phase, in order to be able to convert even heavy-boiling or hardly evaporating fuels into the vapor phase in sufficient quantity. The ignition of the air / fuel mixture generated in the combustion chamber is effected by an ignition element, generally a Glühzündstift, which is arranged in the region of the porous evaporator medium and extends into the combustion chamber to produce locally very high temperatures.

There are several problems with such evaporator burners. In principle, such evaporator burners should be able to be used in conjunction with a wide variety of liquid fuels, for example gasoline, diesel or even biodiesel. However, these fuels sometimes have a very different boiling behavior or different boiling temperatures, so that with low-boiling fuels there is a risk that they are already before being introduced into the porous Evaporating medium, for example, begin to boil in a Brennstoffzuführleitung and thus the Abdampfverhalten is adversely affected. High-boiling fuels can lead to the problem that a supersaturation of the porous evaporator medium takes place, with the risk that due to the insufficient evaporation, a fuel sump in the region of the combustion chamber is formed, which can lead to deposits. Excessive heating of such an evaporator burner, in particular in the area of the fuel supply and in the area of the combustion air supply, may adversely affect the feed behavior, with the risk that unfavorable combustion conditions arise and thus, in particular, also the ignition behavior is impaired or the combustion can not proceed with the required emission of pollutants.

The DE 40 36 147 A1 discloses an evaporator burner according to the preamble of claim 1. This evaporator burner is constructed in the region of a combustion chamber housing providing a combustion chamber with a double-walled peripheral wall having an inner wall and an outer wall. In this built-up with the inner wall and the outer wall peripheral combustion air inlet openings are provided, through which the air required for combustion from a combustion chamber housing in the region of its peripheral wall annular space is introduced into the combustion chamber.

It is the object of the present invention to provide a well usable in connection with various fuels evaporator burner, which has both an improved starting behavior, as well as an improved combustion behavior.

According to a first aspect of the present invention, this object is achieved by an evaporator burner, in particular for a vehicle heater, according to claim 1.

Due to the at least partially double-walled design of the combustion chamber housing with provision of a gap between the two walls of a very good thermal insulation of that space is achieved in a very compact and stable structure in which arise during combustion very high temperatures. Through this improved insulation, both the combustion air supply and the Fuel supply take place at thermally much cheaper conditions. Also, the heat provided in the region of the combustion chamber can be used better for starting or also for supporting a suitable combustion. By providing the intermediate space between the outer wall and the inner wall, it is further possible to adapt the insulation behavior of such a combustion chamber housing to the requirements by filling this intermediate space with suitably insulating materials. Thus, the gap may be filled, for example, with air or with another thermally even better insulating gas or possibly also with a thermally insulating solid.

According to a further very advantageous aspect it can be provided that the inner wall is formed of metal material. By designing the inner wall of metal material ensures that in the combustion chamber immediately enclosing component, namely the component also providing the inner wall, a very good thermal conduction takes place, so that the heat generated during combustion in an optimal manner and also where it can be used for fuel evaporation. However, due to the provision of the outer wall and the space between the inner wall and the outer wall is still provided for a sufficient thermal foreclosure to the environment out.

In a very simple design embodiment, it may be provided that the combustion chamber housing has an inner housing with a peripheral wall and bottom wall providing the inner wall, and an outer housing with a peripheral wall and bottom wall providing the outer wall.

As already explained at the beginning, in order to support the fuel evaporation in such an evaporator burner, a porous evaporator medium can be provided, preferably in the region of the bottom wall.

In order to be able to obtain a sufficient fuel evaporation especially in the case of hard-evaporating fuels, in particular in the starting phase at comparatively low ambient temperatures, a heating device can be assigned to the porous evaporator medium.

In an advantageous development of the evaporator burner according to the invention, a fuel receiving nozzle extending further away from the combustion chamber can be provided further in the region of the bottom wall. The porous evaporator medium may extend into this fuel receiving stub and a fuel supply line may be provided for introducing fuel into the porous evaporator medium provided in the fuel stub. If it is further provided that the fuel supply takes place in a region of the porous evaporator medium which can not be heated by the heating device, the fuel is introduced into the porous evaporator medium at a comparatively low temperature. Thus, premature boiling of low-boiling fuels in the region of the fuel feed line is prevented, and the substantially cold introduction of the liquid fuel into the porous evaporator medium achieves a significantly better homogenization of the fuel flow with pulsed fuel feed.

In order to obtain a uniform as possible fuel evaporation in the combustion chamber, the fuel receiving nozzle may further be provided in a central region of the bottom wall. The centered arrangement of the Brennstoffaufnahemstutzens can take place via the provided there porous evaporator medium and taking advantage of the capillary action a very uniform distribution on the other used for Brennstoffabdampfung area of the porous evaporator medium.

Furthermore, an ignition device can be provided in the fuel intake nozzle.

According to a further aspect of the present invention, a part of the combustion air introduction openings may have an air introduction projection projecting in the direction of the combustion chamber and surrounding the respective opening.

By providing the Lufteinleitvorsprünge in the range of at least a portion of the combustion air inlet openings is prevented in the region of such openings or the openings having these walls, accumulating fuel enters the openings, these clogged and there leads to deposits. This danger is particularly present in heavy boiling or difficult to evaporate fuels, which can emerge in the above-mentioned and occurring in unfavorable conditions supersaturation of the porous evaporator medium in liquid form from this and can then accumulate at the wall bounding the combustion chamber.

The preceding embodiment is particularly advantageous when at least a portion of the combustion air inlet openings is provided in the peripheral wall, if in the region of the bottom wall, a porous evaporator medium is provided and if at least at the bottom wall near-positioned combustion air inlet openings each an air inlet projection is provided. In this way it is ensured that, especially in the area in which the risk of leakage of liquid fuel is comparatively high, the accumulation of the fuel in those openings in which the air is to be introduced into the combustion chamber, is avoided.

To provide such Luftteinleitvorsprünge may be provided in particular in double-walled design of the combustion chamber housing on the outer wall in the direction of the combustion chamber and through an opening in the inner wall extending therethrough Lufteinleitstutzen.

The present invention will be described in detail below with reference to the accompanying drawing which shows a partial longitudinal sectional view of an evaporator burner designed in accordance with the invention.

In the figure, an evaporator burner is generally designated 10. This evaporator burner has a substantially cup-shaped combustion chamber housing 12. This combustion chamber housing 12 defines with its pot-like shape a combustion chamber 14, which is open on one axial side - axially with respect to a longitudinal center axis L of the evaporator burner - via a so-called flame diaphragm 16 to a flame tube 18. About the formed in the flame tube 18 Ausbrandstrecke the combustion gases flow toward a heat exchanger assembly to transfer heat there to a medium to be heated.

It can be seen in the figure that the combustion chamber housing 12 is basically designed with a peripheral wall 22 and a bottom wall 24. In particular, the combustion chamber housing 12 with its cup-shaped and the peripheral wall 22 and the bottom wall 24 comprehensive design of two also for each cup-shaped housing parts 26, 28 constructed. In this case, the housing part 26 forms an inner housing part, and the housing part 28 forms an outer housing part. Each of these housing parts in turn has a circumferential wall 30 and 32 and a bottom wall 34 and 36, respectively. In the region of its axially free end, the peripheral wall 32 of the outer housing 28 rests on the peripheral wall 30 of the inner housing 26 and is fixedly connected thereto, for example, by soldering, welding or gluing. The peripheral wall 30 of the inner housing 26 is guided radially inward in the region of this free end and thus also provides the flame cover 16 ready.

In the area of the circumferential wall 22, a plurality of air inlet openings 38 are provided, via which the combustion chamber 14, which is supplied in an annular manner around a combustion chamber housing 12, can enter the combustion chamber 14, for example, by a side channel blower. In order to provide between the inner housing part 26 and the outer housing part 28 recognizable in the Fig. Clearance 42, the outer housing part 28 in its peripheral wall 32 where each combustion air inlet opening 38 is to be formed, inward, ie in the direction of Combustion chamber 14, formed to form a respective Luftteinleitstutzen 44. These Lufteinleitstutzen 44 on the peripheral wall 32 of the outer housing part 28 extend in openings 47 on the peripheral wall 30 of the inner housing part 26 and form with these a substantially tight seal to the gap 42 out.

It can be seen in Fig. Further, that at the bottom wall 24 near combustion air inlet openings 38, the Luftteinleitstutzen are dimensioned such that they project beyond the inner surface of the peripheral wall 30 of the inner housing part in the direction of the combustion chamber and thus form a respective Lufteinleitvorsrpung 46.

In the bottom wall 24 of the combustion chamber housing 12 and the bottom walls 34, 36 of the inner housing part 26 and the outer housing part 28 an opening is in each case in a central, ie the longitudinal center axis L close range formed. In this opening of the bottom wall 36 of the outer housing part 28 a, for example, pot-like ausgestalteter fuel receiving nozzle 48 is inserted, and indeed so that it extends to the bottom wall 34 of the inner housing part 26 and, for example, abuts against this. The substantially extending in the direction of the combustion chamber 14 away In order to be able to provide a tight closure of the intermediate space 42 here as well, the fuel receiving connection 48 is preferably connected both to the bottom wall 34 and to the bottom wall 36, for example by soldering, welding, gluing or in some other way.

In the region of the bottom wall 24 of the combustion chamber housing 12, a surface-configured porous evaporator medium 50 is provided. This porous, for example, braid, knitted fabric, ceramic foam or other porous material provided porous evaporator medium 50 preferably covers substantially the entire bottom wall 24 and is in its radially inner, ie the longitudinal center axis L near range, out with a hose-like projection 52 in the fuel receiving port 48, and although preferably up to a bottom wall 54 thereof. At this bottom wall 54, an ignition member 56 is further supported, for example, a Glühzündstift which extends along the fuel receiving nozzle 48 and the hose-like projection 52 of the porous Verdampermediums 50 in the direction of the combustion chamber 14 out. The end region of the ignition element 56 protrudes a small distance into the combustion chamber 14. In or near this end region, the ignition element is provided, for example, with an incandescent filament or the like in order to be able to generate high temperatures locally in this region.

In the fuel receiving port 48, a ring-like channel 58 is further formed, which is covered by the hose-like projection 52 of the porous evaporator medium 50 and in which a fuel supply line 60 opens. The initially liquid fuel passes via line 60 into this annular channel 58, is pre-distributed in this and received in the hose-like projection 52 of the porous evaporator medium 50. Via this hose-like projection 52, the liquid fuel then passes into the region of the porous evaporator medium 50 facing the combustion chamber 14, using the capillary action present due to the porosity.

The porous evaporator medium 50 is also associated with a generally designated 62 heater. In the example shown, this comprises two radially staggered and electrically energizable heating elements 64, 66, each spirally or helically embedded in a good thermally conductive material 68, 70 between the bottom wall 34 of the inner housing part 26 and the near the bottom wall 34 area extensively spread of the porous evaporator medium 50 run. Between these two radially staggered heating elements 64, 66 an annular insulation 72 is provided. This is for example provided by a ceramic ring or a ring made of other thermally well insulating material, but may also be formed by an air gap. Also, the fuel receiving port 48 is preferably formed of thermally good insulating material, such as zirconium oxide (ZrO ₂ ) and / or PTFE. In this way it is achieved that even upon energization of the heater 62 and concomitant heating of the porous evaporator medium 50 in its combustion chamber 14 opposite area a heat transfer to the fuel receiving nozzle 48 and thus a heat transfer to the hose-like projection 52 of the porous evaporator medium 50 is largely excluded. By energizing the heater 62 so primarily that fuel is heated and thus assisted in its evaporation, which is in the combustion chamber 14 facing surface area of the porous evaporator medium 50 is present, while fuel still in the conduit 60, in the channel 58th or in the hose-like projection 52, is substantially not heated.

The two heating elements 64, 66 are controlled separately from each other, so that depending on the heat demand only one of the heating elements or both can be energized to provide even under the influence of ambient temperature and taking into account the fuel to be evaporated, the appropriate amount of heat, especially in the startup phase the evaporator burner 10 is required to the ignitable air / fuel mixture to create.

With an evaporator burner 10, as described above with regard to its structural design, various advantages in operation are achieved. First, a very good thermal insulation of that volume region, which is heated by the running combustion or the excitation of the heater, can be obtained to the environment by the double-walled design of the combustion chamber. The consequence of this is that the heat present in the region of the combustion chamber can be used efficiently, in particular in order to evaporate heavily evaporating fuels to a sufficient degree, so that a liquid accumulation of unvaporized fuel can be avoided. In particular, the gap between the outer wall and the inner wall of the double-walled configuration of the combustion chamber housing, which can be filled with a suitable thermally insulating material, also contributes to this purpose. This material may be, for example, air, but may also be another, even better thermally insulating gas or a thermally insulating solid material. Further contributes to the improved thermal insulation in that the fuel receiving nozzle is also formed from thermally well insulating material, so that in particular in the field of fuel supply no risk of too early evaporation of the fuel is given.

A further advantage of the double-walled embodiment is that, in particular, the inner housing part can be formed from metal, that is, for example, from cast material or from a sheet metal material, as well as, of course, the outer housing part, and nevertheless a suitable thermal insulation can be obtained. Above all, the provision of the inner housing part of metal material, that is, a thermally highly conductive material, has the advantage that the resulting heat during combustion in the combustion chamber 14 is very evenly distributed over this inner housing part and well directed towards the evaporator medium, so that in Combustion operation an improved Brennstoffabdampfung can be obtained, which is particularly advantageous when used with heavy evaporating fuels.

Another advantage of the arrangement according to the invention is that the fuel supply takes place in the region of the fuel intake nozzle in a region which is shielded with respect to the running in the combustion chamber combustion and also with respect to the heating of the evaporator medium by the electrically operable heater. That the fuel is introduced into the porous evaporator medium in a comparatively cool region, with the result that a better homogenization of the generally pulsating fuel can be achieved in the delivery or forwarding in the direction of the combustion chamber. That is, the protruding into the fuel receiving nozzle portion of the United steamer fleece, which of course also separated from the remaining portion, but can be arranged in contact with this, is used essentially for fuel transfer, but not for Brennstoffabdampfung. Especially in the start phase, the fuel evaporation will take place mainly in that area in which the porous evaporator medium covers the heating device, whereby, due to the two-stage configuration of this heating device, especially in the start phase, it is possible to proceed in such a way that initially only in the vicinity of the ignition element lying area is heated, the porous evaporator medium, especially in order to create the most efficient use of electrical energy an atmosphere that is favorable for the ignition. For this purpose, it is also advantageous that the ignition element still engages with its free end region in the combustion chamber and, above all, can be heated by excitation in this free end region, so that the ignition can take place there. Nevertheless, an impairment of the flow conditions in the combustion air is largely avoided by the centered positioning of the ignition and the only short projection into the combustion chamber.

Another particular advantage of the evaporator burner according to the invention in that, above all, the combustion air inlet openings which are close to the porous evaporator medium are formed with a projection or projection with respect to the inner surface of the combustion chamber housing. The risk that occurs by excessive Brennstoffheranförderung or possibly too bad Brennstoffabdampfung in liquid form from the porous evaporator medium escaping fuel when accumulating on the peripheral wall in these openings, can thus be avoided. The openings thus remain open to the air inflow especially in the region near the porous evaporator medium or the bottom wall and are not blocked by fuel deposits, coking or the like.

It should finally be pointed out that, of course, the evaporator burner shown in the figure can be varied in different areas. Thus, it is possible to extend the porous evaporator medium in the region of the peripheral wall and provide, for example, on the bottom wall a centrally arranged and substantially projecting into the combustion chamber projecting combustion air inlet nozzle with inlet slots for the combustion air. In this case, the fuel receiving nozzle could then be moved from its centric positioning radially outward into the still existing annular region of the bottom wall. It is also obvious that suitable materials can be selected for the various components. For example, the thermally conductive material 68 or 70 of the electric heater 62 may be a good heat conductive ceramic material.

Claims (13)

1. Evaporation burner, in particular for a vehicle heating device, comprising a combustion chamber housing (12) providing a combustion chamber (14), with a circumferential wall (22) and a bottom wall (24), said combustion chamber housing (12) being formed at least partly double-walled in the region of the circumferential wall (22) with an inner wall (30) and an outer wall (32), combustion air inlet openings (38) being provided in the region of the circumferential wall (22) for inserting combustion air from a space (40) surrounding the combustion chamber housing (12) ring-like into the combustion chamber (14),
   characterized by an intermediate space (42) being formed between the inner wall (30) and the outer wall (32) of the circumferential wall (22) and by air inlet connections (44) which extend into openings (47) in the inner wall (30) being formed in the region of the combustion air inlet openings (38) at the outer wall (32) for providing a tight sealing of the intermediate space (42).
2. Evaporation burner according to claim 1,
   characterized by the inner wall (30, 34) being made of a metal material.
3. Evaporation burner according to claim 1 or 2,
   characterized by the combustion chamber housing (12) comprising an inner housing (26) with a circumferential wall (30) and a bottom wall (34) providing the inner wall (30, 34) as well as an outer housing (28) with a circumferential wall (32) and a bottom wall (36) providing the outer wall (32, 36).
4. Evaporation burner according to any one of claims 1 to 3,
   characterized by a porous evaporator medium (50, 52) being provided in the region of the bottom wall (24) of the combustion chamber housing (12).
5. Evaporation burner according to claim 4,
   characterized by a heating device (62) being associated to the porous evaporator medium (50, 52).
6. Evaporation burner according to any one of claims 1 to 5,
   characterized by a fuel uptake connection (48) extending away from the combustion chamber (14) being provided in the region of the bottom wall (24).
7. Evaporation burner according to claim 6,
   characterized by the porous evaporator medium (50, 52) extending into said fuel uptake connection (48).
8. Evaporation burner according to claim 7,
   characterized by a fuel supply line (60) being provided for inserting fuel into the porous evaporator medium (50) provided inside said fuel uptake connection (48).
9. Evaporation burner according to claim 5 and any one of claims 7 or 8,
   characterized by the fuel supply being realized in a region (52) of the porous evaporator medium (50, 52) which can substantially not be heated by the heating device (62).
10. Evaporation burner according to one of claims 6 to 9,
    characterized by said fuel uptake connection (48) being provided in a central area of the bottom wall (24).
11. Evaporation burner according to one of claims 6 to 10,
    characterized by an ignition element (56) being provided in said fuel uptake connection (48).
12. Evaporation burner according to one of claims 1 to 11,
    characterized in that at least in part of the combustion air inlet openings (38) an air inlet projection (46) is provided, projecting towards the combustion chamber (14) and surrounding the respective opening (38), and by an air inlet connection (44) provided at the outer wall (32) extending towards the combustion chamber (14) and through an opening (47) in the inner wall (30) for providing an air inlet projection (46).
13. Evaporation burner according to claim 12,
    characterized by at least part of the combustion air inlet openings (38) being provided in the circumferential wall (22), by a porous evaporator medium (50, 52) being provided in the region of the bottom wall (24) and by at least one air inlet projection (46) being provided at the bottom wall (24) near the positioned combustion air inlet openings (38).

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