Abstract:
A fuel duct system for supplying fuel to a combustion chamber, in particular a vehicle heating device, comprises duct section, elongate in the flow direction (L), and also a heating element in the duct section with its length direction oriented substantially in the flow direction (L), for flow therearound of the fuel moving in the duct section.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates to a fuel duct system for supplying fuel to a combustion chamber, in particular in a vehicle heating device.  
         TECHNICAL FIELD  
         [0004]    In heating devices, such as are often used in vehicles as auxiliary heaters independently of the engine, because of their preferred use in low external temperatures, care has to be taken that the fuel introduced into the combustion chamber has a given minimum temperature. This minimum temperature is necessary on the one hand to ensure reliable ignition and clean combustion, and on the other hand to be able to carry out a suitable atomization when the fuel is introduced through an atomizer nozzle. With insufficient or uneven atomization, there exists the danger that ignition does not take place, or begins very slowly, or else, with successful ignition, the combustion is performed with excessive pollutant emission.  
           [0005]    In order to deal with the problem of too low a fuel temperature, it is known, for example, to heat the component, known as a nozzle pipe, bearing the said atomizer nozzle by means of a heating cartridge. By heating the nozzle pipe, the fuel flowing through the duct section formed therein is also heated. However, the problem here is that the process of heating by only indirect heating is comparatively sluggish, and thus in general cannot respond to temperature changes of the fuel in an appropriate time. Furthermore, there are considerable heat losses, since the heat is also transferred to other structural components from the nozzle pipe, which is in general made of metal, such as brass, having good thermal conductivity.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention has as its object to provide a fuel duct system, for supplying fuel to a combustion chamber, which can make sure of a rapid heating of the fuel conducted to a combustion chamber to temperatures suitable for reliable combustion.  
           [0007]    According to the present invention, this object is attained by a fuel duct system for supplying fuel to a combustion chamber, in particular in a vehicle heating device, including a duct section which is elongate in the flow direction and also a heating element in the duct section with its length direction oriented substantially in the flow direction, so that the fuel moving substantially in the flow direction in the duct section flows around the said heating element.  
           [0008]    By means of the direct integration of the heating element into a duct section itself, the fuel conducted to the combustion chamber flows around the heating element and is heated without the interposition of any housing component or the like. In this manner, the heating of the fuel can respond markedly more rapidly to changing temperature conditions, and the transfer of heat to other system components, which per se are not to be heated, or must not be heated, can be markedly reduced. Based on the fact that the fuel to be heated flows around the heating element in its length direction, a relatively long heating region is made available even with a comparatively small constructional size, so that even at very low external temperatures and correspondingly low fuel temperatures, this fuel can be heated to a suitable temperature while being conducted to the combustion chamber.  
           [0009]    In order to be able to contact in a simple manner the heating element integrated into the duct section, it is proposed that the duct section is made open in one end region, and is closed by a closure element having connections for the heating element.  
           [0010]    In order to prevent, as far as possible, direct heat transfer between the heating element and the duct section, or the component having this duct section, a supporting element arrangement can be provided by means of which the heating element is supported in the duct section, at a spacing from its inner surface. Here the supporting element arrangement can have at least two supporting elements. The connections provided in the closure element can be brought into electrically conducting connection with the heating element by means of these two supporting elements. It can be recognized that the supporting elements of the supporting element arrangements are to be selected according to two boundary conditions. On the one hand, they are to have as low as possible a thermal conductivity, in order to minimize the heat transfer from the heating element to the inner surface of the duct section. On the other hand, they are to have as low as possible an electrical resistance, in order to minimize electrical supply losses. It is advantageous, particularly as regards the minimization of electrical losses, if the supporting elements of the supporting element arrangement are constituted to extend on oppositely oriented side surfaces of the heating element. In this manner, it is made possible to contact the heating element over its length, uniformly and also over as large a surface as possible.  
           [0011]    The fuel duct system according to the invention can furthermore be characterized by an outlet duct leading from a first end region of the duct section to the combustion chamber and an inlet duct opening at a spacing from a second end region thereof, with the supporting element arrangement together with the duct section delimiting a flow path region leading to the second end region. It is ensured in this manner that above all the fuel supply can take place so that the previously mentioned electrical contacting of the heating element can occur without problems, and without thereby shortening that flow path region in which a heating of the fuel can take place.  
           [0012]    The duct section can, as already stated, lead to a fuel atomizer nozzle and can be provided with an inlet duct and/or an outlet duct in a pump housing portion.  
           [0013]    An embodiment which is particularly advantageous as regards rapidity of control and the minimization of energy losses provides that the heating element is a PTC heating element. This means that the heating element has a resistance/temperature characteristic such that with rising temperature the resistance also rises. As a consequence, when fuel flowing along the heating element has a higher temperature, the heat input into the fuel is smaller, and thus the heating element itself will also have a higher temperature. Because of the electrical resistance which is then also higher, the electric current decreases and with it, the electrical power converted into heat. With a suitable choice of the already mentioned resistance/temperature characteristic, a self-regulation can be provided here, making the intervention of external control systems superfluous. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The present invention is described hereinafter with reference to the accompanying drawings.  
         [0015]    [0015]FIG. 1 shows a perspective view of a fuel duct system according to the invention, shown partially cut away;  
         [0016]    [0016]FIG. 2 shows a longitudinal section of a system, sectioned along a line II-II in FIG. 1;  
         [0017]    [0017]FIG. 3 shows a cross sectional view of the system shown in FIG. 1, sectioned along a line III-III in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    A fuel duct system according to the invention is denoted in general by  10  in the drawings. The fuel duct system  10  is substantially accommodated in a housing component denoted generally by  12 , or is constituted integrally with this. The housing component  12  can be, for example, an end closure portion of a pump housing of a fuel pump.  
         [0019]    An elongate neck  14  forms a duct section  16 . An opening  18  like a blind hole is constituted in the duct section  16 . This opening  18  is open in an end region  20 . In a further end region  22  there opens an outlet opening  24  which is substantially orthogonal to the length direction of the opening  18 . A fastening section  26  is formed on the neck  14  in the region of the outlet opening  24 , and has a threaded member  30  screwed into it, supporting an atomizer nozzle  28 . A liquid-tight connection between the neck  14  of the housing portion  12  and the threaded portion  30  is obtained by means of a sealing element  32  like an O-ring.  
         [0020]    An inlet opening  34 , via which fuel forwarded by the pump (not shown) can flow into the opening  18  in the neck  14 , opens into a region in the opening  18  remote from the end region  20 . The fuel forwarded to the atomizer nozzle  28  thus flows successively through the inlet opening  34 , the opening  18 , and also the outlet opening  24  and, aligned with this, an opening  36  in the threaded portion  30 .  
         [0021]    A heating element  38  is inserted into the opening  18  or the duct section  16  having this. In can be seen in FIGS. 1 and 2 that this heating element  38 , cuboidal in the example shown, is oriented with its length direction along a longitudinal axis L of the opening  18 . In order to keep the heating element  38  positioned in the duct section  16  so that the heating element  38  is not in direct contact with an inner surface  40  of the duct section  16  surrounding the opening  18 , a supporting element arrangement  46  is provided, having two supporting elements  42 ,  44 . The two supporting elements  42 ,  44 , of substantially like construction and which can for example be bent from sheet metal, have a region  52  or  54  acting on a respective side surface  48  or  50  of the heating element  38  and likewise made substantially flat in conformity with the planar constitution of the sides  48 ,  50  of the heating element  38 , and also curved regions  56 ,  58  or  60 ,  62  in conformity with the curved shape of the inner surface  40 . By their own elasticity, the supporting elements  42 ,  44  keep the heating element  38  under prestress in its positioning in the opening  18 . In order to be able to obtain here a stable positioning over the whole length of the heating element  38 , the two supporting elements  42 ,  44  preferably extend substantially along the whole length of the heating element  38 .  
         [0022]    The opening  18  is closed at its end region  20  by a closure element  64 . In order to achieve a liquid-tight closure, a sealing element  66  of the O-ring kind is provided between the closure element  64  and the neck  14 . A retaining ring  70  engaging over the closure element  64  and a radial projection  68  of the neck  14  maintains fixed cohesion. Two electrical contacts  72 ,  74  are provided in the closure element  64 . When the closure element  64  is mounted on the neck  14 , these contacts  72 ,  74  engage in the two supporting elements  42 ,  44  and are in contact with these, for example at contacting sections  76 ,  78 , which are bent down from respective regions  56 ,  62  contacting the internal surface  40 , and which extend further from the regions  56 ,  62  to the regions  52 ,  54 . The electrical contacting of the heating element  38  provided in the opening  18  thus takes place by means of the contacts  72 ,  74  of the closure element  64  and the supporting elements  42 ,  44  provided on its two long sides  48 ,  50  and contacting the heating element  38 . In order to keep the electrical contact resistance as small as possible, it is advantageous to provide as large as possible a contact surface between the heating element  38  and the regions  52 ,  54  of the supporting elements  42 ,  44 . The sides  48 ,  50  of the heating element  38  can here be contacted substantially over the whole surface, as shown in FIG. 3. This full-surface contact however has the result that on the one hand the fuel to be heated cannot directly flow around the heating element  38  in these regions, and that on the other hand a comparatively good heat transfer to the supporting elements  42 ,  44  can take place due to this full-surface contact. To reach a compromise between these conflicting contact requirements, it is for example possible to form, by stamping out, plural tongue-like sections in the regions  52 ,  54  of the supporting elements  42 ,  44 , distributed along the length of the heating element  38 , and to bend these out onto the heating element  38 , so that the heating element  38  is then contacted by plural such tongues at plural regions distributed over the sides  48 ,  50 , but is otherwise left free for the fuel to flow around. The size of these contact tongues can be chosen so that an optimal compromise is obtained between good electrical contact on the one hand and the smallest possible heat transfer contact on the other hand.  
         [0023]    It can be seen in FIGS. 1 and 3 that the fuel supplied via the inlet opening  34  is first conducted through a flow path  80  in the direction of the end region  20  of the opening  18 . This flow path  80  is substantially formed by a groove  82  provided in the neck  14 , extending along the opening  18  to the end region  20 , and closed toward the opening  18  by the region  62  of the supporting element  44  otherwise adjoining the inner surface  40 . In this manner it is made sure that the fuel introduced through the inlet opening  34  is compelled to first reach the end region  20  and, beginning from this end region  20 , to then flow around the heating element  38  along its whole length in the duct section  16 . It is thus also ensured by the comparatively compact constructional size of the duct system  10  shown that as efficient as possible a heat transfer is provided from the heating element  38  to the fuel to be heated and to then reach the atomizer nozzle  28  when heated.  
         [0024]    By the embodiment of the duct system  10  according to the invention, it is made sure that the heat transferred to the fuel is directly given up to this, without any housing components first having to be heated also. This makes possible a markedly more rapid response to temperature changes by means of correspondingly adapted flow around the heating element  38  and moreover reduces the heat losses. The rapid response to temperature changes and the very efficient utilization of the electrical energy required for heating can be further improved by constituting the heating element  38  as a PTC element. PTC heating elements have a heating characteristic such that, with increasing heating of the same, their electrical resistance also increases in a defined manner, and thus with, for example, a constant applied voltage and hence decreasing current, the heating power also decreases. With a suitable choice of the resistance temperature characteristic of such a heating element, it is possible to provide the heating element  38  with its own temperature regulation by means of this characteristic alone, thus requiring no external intervention and in particular no provision of additional temperature sensors to determine the temperature of the supplied fuel.  
         [0025]    The duct system  10  according to the invention makes possible, with a minimization of the electrical power consumption and a minimization of the heat losses which occur, a very rapid heating of the fuel which is then directly supplied to an atomizer nozzle. In this manner, the atomization characteristic of the atomizer nozzle  28  can be optimized in conformity with the temperatures of the fuel supplied. Furthermore, there results therefrom a markedly better combustion characteristic of the fuel introduced into a combustion chamber. The time required to start combustion can be markedly reduced by the use of the duct system according to the invention. The pollutant emission can also be reduced due to the optimized combustion. Furthermore, the embodiment of the duct system according to the invention provides, with the advantages conferred by this duct system, a comparatively simple construction in which, in spite of the complete integration of a heating element into a duct section, an electrical contact arrangement is possible which is simple to produce. Above all, the incorporation of the system according to the invention into an otherwise already existing housing portion, which is preferably constructed, because of the thermal loading which may occur, of temperature-resistant plastic, such as e.g. polyphenylene sulfide (PPS), makes possible a very cost-effective and easily produced construction.