Patent Application
20050271993
This invention relates to a system for reacting fuel and air to a reformate, comprising a reformer which has a reaction space, a nozzle for supplying a fuel/air mixture to the reaction space, at least one supply conduit for supplying fuel to the nozzle, and at least one entrance channel for supplying air to the nozzle.
Generic systems are used for converting chemical energy into electric energy. For this purpose, fuel and air, preferably in the form of a fuel/air mixture, are supplied to the reformer. Inside the reformer, the fuel then is reacted with the atmospheric oxygen, preferably by performing the process of partial oxidation.
The reformate thus produced then is supplied to a fuel cell or a fuel cell stack, respectively, electric energy being released due to the controlled reaction of hydrogen, as part of the reformate, and oxygen.
As has already been mentioned, the reformer can be designed such that the process of partial oxidation is performed to produce reformate. In this case, when using diesel as fuel, it is particularly useful to perform preliminary reactions prior to the partial oxidation. In this way, long-chain diesel molecules can be converted to shorter-chain molecules with a “cold flame”, which ultimately promotes the operation of the reformer. In general, a gas mixture is supplied to the reaction zone of the reformer, which gas mixture is converted to H2 and CO. Another constituent of the reformate is N2 from the air and, in dependence on the air ratio and the temperature, possibly CO2, H2O and CH4. In normal operation, the fuel mass flow is controlled corresponding to the required power, and the air mass flow is controlled to obtain an air ratio in the range of λ=0.4. The reforming reaction can be monitored by different sensors, for instance temperature sensors and gas sensors.
Beside the process of partial oxidation it is likewise possible to perform an autothermal reforming. In contrast to the autothermal reforming, the process of partial oxidation is effected in that a substoichiometric amount of oxygen is supplied. For example, the mixture has an air ratio of λ=0.4. The partial oxidation is exothermal, so that an undesired heating of the reformer can occur in a problematic way. Furthermore, the partial oxidation tends to lead to an increased formation of soot. To avoid the formation of soot, the air ratio λ can be chosen smaller. This is achieved in that part of the oxygen used for the oxidation is provided by steam. Since the oxidation with steam is endothermal, it is possible to adjust the proportion of fuel, oxygen and steam such that on the whole neither heat is released nor heat is consumed. The autothermal reforming thus achieved therefore eliminates the problems of the formation of soot and of an undesired overheating of the reformer.
It is likewise possible that subsequent to the oxidation inside the reformer further gas treatment steps are effected, and downstream of the partial oxidation there can in particular be provided a methanization.
A commonly used fuel cell system for instance is a PEM system (PEM=Proton Exchange Membrane), which can typically be operated at operating temperatures between room temperature and about 100° C. Due to the low operating temperatures, this type of fuel cell frequently is used for mobile applications, for instance in motor vehicles.
Furthermore, high-temperature fuel cells are known, so-called SOFC systems (SOFC=Solid Oxide Fuel Cell). These systems operate for instance in a temperature range of about 800° C., a solid electrolyte (solid oxide) being able to perform the transport of oxygen ions. The advantage of such high-temperature fuel cells as compared to PEM systems in particular consists in the ruggedness with respect to mechanical and chemical loads.
As field of application for fuel cells in conjunction with the generic systems not only stationary applications are considered, but also applications in the field of motor vehicles, for instance as auxiliary power unit (APU).
For a reliable operation of the reformer it is important to supply the fuel or the fuel/air mixture, respectively, to the reaction space of the reformer in a suitable way. For instance, a good mixing of fuel and air and a good distribution of the fuel/air mixture in the reaction space of the reformer are advantageous for the operation of the reformer. Within the scope of the present disclosure reference is always made to a fuel/air mixture when mentioning substances which have to be or have been introduced into the reaction space of the reformer. However, the substances introduced are not restricted to a mixture of fuel and air. Rather, other substances can also be introduced in addition, such as steam in the case of autothermal reforming. In so far, the term fuel/air mixture should be understood in this general form.
It is the object underlying the invention to provide a system for reacting fuel and air to a reformate, which has advantageous properties as regards the introduction of the fuel/air mixture into a reaction space of a reformer.
This object is solved with the features of the independent claims.
Advantageous embodiments and developments of the invention are indicated in the dependent claims.
The invention is based on the generic system in that the nozzle has a swirl chamber into which at least one supply conduit for supplying fuel opens substantially axially centrally and the at least one entrance channel opens substantially tangentially and from which exits a nozzle outlet, and that the swirl chamber comprises a narrowing spiral channel, into which opens the entrance channel for the gaseous medium, and a gap space axially contiguous thereto in the direction toward the nozzle outlet, into which opens the supply conduit for supplying fuel and from which exits the nozzle outlet. The arrangement of the invention thus provides that the entrance channel for the air or the gaseous medium in general opens into the annular space, while the supply for fuel, i.e. the liquid medium in general, opens into the gap space. The same in turn opens into the nozzle outlet and via its peripheral edge merges with the annular space or communicates with the same. Thus, the annular space performs the function of a turbulence chamber, into which the gaseous medium is introduced through a relatively large bore at least substantially tangentially at a relatively large distance from the central longitudinal axis of the swirl chamber. From the turbulence chamber or the spiral channel, respectively, the gaseous medium is introduced into a chamber with small axial extension. In the present case, this chamber is referred to as gap space. The small axial extension is chosen to be able to ensure a rather low pressure loss. An essential aspect of the system of the invention, in which there is provided a swirl chamber composed of a spiral channel and a gap space, relates to the maintenance of the spin with the objective to introduce the gaseous medium into the annular space at a low speed, to accelerate the same therein and introduce the same into the gap space at a high speed. At the axial outlet thereof, which in the present case is also referred to as nozzle outlet, a negative pressure thereby is provided such that the liquid medium axially flowing through the gap space is nebulized. The rheological design of the spiral channel can be effected according to the usual aspects of the design of deflectors for centrifugal fans, which are well known in the prior art.
The system in accordance with the invention in particular has an advantageous design in that one end wall of the spiral channel, i.e. the inner wall or the outer wall, is formed in a circular cylindrical shape, and the other end wall of the spiral channel is formed in a spiral shape. In this way, the spiral channel can be manufactured in two parts from a milled part provided with the spiral shape and a cylindrical part centrally inserted into the same.
Particularly preferably, the entrance channel for the liquid medium is arranged coaxially with respect to the nozzle outlet.
In particular, the liquid medium thus is centrally fed into the gap space in alignment with the central longitudinal axis of the swirl chamber through a small bore and on the side of the gap space directly opposite said bore is discharged through another larger bore; the same forms the nozzle outlet.
In this connection it is particularly preferable that the nozzle outlet is defined by a nozzle bore in an end plate of the gap space of the swirl chamber.
The edge of the nozzle outlet bore on the side of the gap space can be rounded, in order to minimize the pressure required to deliver the mixture of liquid and gaseous medium into the nozzle outlet. In another advantageous embodiment it is possible that this edge can be bevelled or can also be sharp-edged for the same purpose.
In a particularly advantageous way, the system in accordance with the invention is constituted such that the axial length of the nozzle outlet is 0.05 mm to 1 mm, in particular 0.1 mm to 0.5 mm.
Particularly preferably, means are provided so that secondary air can flow into the reaction space. In this connection, the air entering the reaction space through the nozzle, i.e. the air present in the fuel/air mixture, can be referred to as primary air. The secondary air advantageously is delivered through secondary air bores in the housing of the reaction space. Dividing the air into primary air and secondary air can be useful for providing a rich, readily ignitable mixture at the outlet of the nozzle. This is useful in particular during the starting operation of the system, as here the reformer advantageously operates in the manner of a burner.
Advantageously, the invention is developed in that the nozzle has means for holding a glow plug. The position of the glow plug with respect to the nozzle is an important parameter with regard to a good starting behavior of the reformer. In prior art devices, the glow plug generally was held by the reformer housing, so that this could lead to variations in position with respect to the nozzle. Due to the property of the inventive nozzle that the nozzle itself has means for holding the glow plug, such tolerances can be excluded. The glow plug always has the same position with respect to the nozzle.
In another preferred embodiment of the present invention it is provided that the means for holding the glow plug are realized as bore extending at an angle with respect to the nozzle axis. For the proper positioning, the glow plug then must merely be introduced into the bore. A stop at the glow plug and/or inside the bore ensures that the glow plug is guided into its optimum position with respect to the nozzle.
The invention is based on the knowledge that by means of a swirl chamber composed of a spiral channel and a gap space a particularly advantageous maintenance of the spin can be obtained. As a result, the gaseous medium, i.e. in particular the air, can be introduced into the annular space at a low speed, can be accelerated in the same, and from the same can then be introduced into the gap space at a high speed. In this way, a negative pressure is provided at the outlet of the gap space such that the liquid medium flowing through the gap space, i.e. in particular the fuel, is atomized or nebulized, respectively.
The invention will now be explained by way of example by means of preferred embodiments with reference to the accompanying drawings, in which:
In the following description of the drawings, the same or comparable components are designated by the same reference numerals.
The system illustrated in connection with the Figures described below can be used for supplying a fuel/air mixture to the reformer 214.
The low-pressure atomizer which in
Inside the spiral channel 19, coaxially with respect to the base body 13, a cylindrical recess 15 in the shape of a blind hole is provided, which has a larger axial extension than the spiral channel 19. Into the recess 15, a solid cylindrical part 17 is tightly inserted with a close fit, which protrudes from said recess axially extending into the spiral channel 19 and defines the inner contour thereof. The spiral channel 19 forms part of the swirl chamber of the two-fluid nozzle 11. An entrance channel 18 for a gaseous medium tangentially opens into the same. The entrance channel 18 continuously merges with the spiral channel 19 at the widest point thereof. With its narrowest point, the spiral channel 19 ends on the inside after about 360 degrees at the level of the entrance channel 18, separated from the same by a parting rib 20. At its front end (nozzle outlet end), the blind-hole bore 27 is closed almost completely by an end plate 21 and is merely interrupted by a central nozzle bore forming the nozzle outlet 23. The axial extension of the solid cylindrical part 17 is chosen such that between the front end face (the right-hand face in
The nozzle bore forming the nozzle outlet 23 is formed in alignment with the central longitudinal axis 14 in the end plate 21.
The two-fluid nozzle 11 also comprises a supply conduit 24 for a liquid medium, in particular fuel, which is traversed by a bore 25 of the solid cylindrical part 17 extending coaxially with respect to the central longitudinal axis 14 and which is received flush in an extension of the bore 25. The same is incorporated in the cylindrical part 17 proceeding from the rear side, and it extends along about half the axial length of the cylindrical part 17. Adjoining this bore in the cylindrical part 17 a bore 26 of smaller diameter is provided, which opens into the gap space 22. The axial extension of the gap space 22 is comparatively small with regard to a rather low pressure loss.
The base body 13 of the two-fluid nozzle 11 can additionally have a bore (not shown) extending at an angle with respect to the central longitudinal axis. For this purpose, either the base body 13 can have a diameter larger than shown or the spiral channel 19 can be arranged with less space required. Such bore (not shown) then can receive a glow plug (not shown), so that the position of the glow plug (not shown) with respect to the nozzle bore 23 then can be defined almost without any tolerance.
The operation of the low-pressure atomizer 10 is as follows. Via the entrance channel 18, gaseous medium, in particular air, is fed into the spiral channel 19 of the swirl chamber, and this air flows through this spiral channel into the gap space 22 of the swirl chamber under uniform pressure conditions. Via the bore 26, liquid medium, in particular fuel, is fed into the gap space 22, and this fuel is discharged from the opposed nozzle outlet 23 by the pressurized gaseous medium and thereby torn into fine droplets.
If it is desired, for instance, that fuel be introduced with a flow rate of 500 g/h, typical dimensions of the two-fluid nozzle 11 are as follows: The distance of the entrance channel 18 from the central longitudinal axis 14 is about 8 mm, and the free cross-section is about 4 mm. The axial extension of the gap space 22 is about 0.65 mm. The diameter of the nozzle bore forming the nozzle outlet 23 is about 2 mm, and its length is 0.05 mm to 1 mm (maximum length about 0.5 mm to 1 mm). With a two-fluid nozzle 11 of such dimensions, the minimum pressure required for atomizing the liquid medium is 30 mbar.
The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for the realization of the invention both individually and in any combination.
This application claims the benefit of International Application PCT/EP02/02192, filed on Feb. 28, 2002, which claims benefit of German Application DE10117875.1, filed on Apr. 10, 2001, which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP02/02192 | 2/28/2002 | WO | 6/1/2005 |
