Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR REACTING FUEL AND AIR TO PRODUCE A REFORMATE
Field of the Invention
This invention relates to a system for reacting fuel and air
to produce 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.
Background of the Invention
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 tempera-
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ture, possibly C02, H20 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 k = 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 possi-
ble 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 sup-
plied. For example, the mixture has an air ratio of k = 0.4.
The partial oxidation is exothermal, so that an undesired
heating of the reformer can occur in a problematic way. Fur-
thermore, the partial oxidation tends to lead to an increased
formation of soot. To avoid the formation of soot, the air
ratio k 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 in-
side the reformer further gas treatment steps are effected,
and downstream of the partial oxidation there can in particu-
lar be provided a methanization.
A commonly used fuel cell system for instance is a PEM system
(PEM = Proton Exchange Membrane), which can typically be op-
erated 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.
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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.
Summary of the Invention
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.
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The invention is a system for reacting fuel and air to produce
a reformate, comprising a reformer which has a reaction space;
a nozzle for supplying a fuel and 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, wherein 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
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the objective to introduce the gaseous medium into the annular
space at a low speed, to accelerate the same therein and intro-
duce 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
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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 out-
let.
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 out-
let.
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 re-
quired to deliver the mixture of liquid and gaseous medium
into the nozzle outlet. In another advantageous embodiment it
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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 re-
former 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 re-
alized as bore extending at an angle with respect to the noz-
zle axis. For the proper positioning, the glow plug then must
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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.
Brief Description of the Drawings
The invention will now be explained by way of example by means
of preferred embodiments with reference to the accompanying
drawings, in which:
Fig. 1 shows a schematic block circuit diagram of a system in
which the present invention can be used;
Fig. 2 shows a partial longitudinal section of an embodiment
of a nozzle for use in a system in accordance with the
invention; and
Fig. 3 shows a cross-sectional view of the annular space of
the swirl chamber of the nozzle as shown in Fig.
2.
Detailed Description of the Drawings
In the following description of the drawings, the same or
comparable components are designated by the same reference
numerals.
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Fig. 1 shows a schematic block circuit diagram of a system in
which the present invention can be used. Via a pump 240, fuel
216 is supplied to a reformer 214. Furthermore, air 218 is
supplied to the reformer 214 via a blower 242. Via a valve
means 222, the reformate 220 produced in the reformer 214
reaches the anode 224 of a fuel cell 212. Via a blower 226,
cathode supply air 228 is supplied to the cathode 230 of the
fuel cell 212. The fuel cell 212 produces electric energy
210. The anode waste gas 234 and the cathode waste air 236
are supplied to a burner 232. Reformate can likewise be sup-
plied to the burner 232 via the valve means 222. In a heat
exchanger 238, the thermal energy produced in the burner 232
can be supplied to the cathode waste air 228, so that the
same is preheated. Waste gas 250 flows out of the heat ex-
changer 238.
The system illustrated in connection with the Figures de-
scribed below can be used for supplying a fuel/air mixture to
the reformer 214.
The low-pressure atomizer which in Figure 2 is generally des-
ignated with the reference numeral 10 comprises a two-fluid
nozzle 11 inserted in the wall 12 of a reformer. In detail,
the two-fluid nozzle 11 includes a solid cylindrical base
body 13, which from the rear side is inserted flush into a
cylindrical blind-hole bore 27 of the wall 12. The relatively
thin-walled wall portion 12A of the wall 12, which defines
the blind-hole bore 27, is interrupted by a cylindrical aper-
ture 28. On the right-hand side in Figure 2, which corre-
sponds to the exit of the two-fluid nozzle 11 into the re-
former, the base body 13 has a recess 16 which defines the
outer edge of a narrowing spiral channel 19.
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
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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 en-
trance 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 noz-
zle 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 Figure 2) of the cylindrical part 17 and
the end plate 21 a gap space 22 is left, which due to the end
face of the cylindrical part 17 has a circular shape and
merges with the spiral channel 19 over its entire periphery.
The spiral channel 19 and the gap space 22 together form the
swirl chamber of the two-fluid nozzle 11.
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 co-
axially 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 pro-
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vided, 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 condi-
tions. 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 me-
dium 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 chan-
nel 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.
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The features of the invention disclosed in the above descrip-
tion, in the drawings and in the claims can be essential for
the realization of the invention both individually and in any
combination.
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List of reference numerals
low-pressure atomizer
11 two-fluid nozzle
12 wall
12A wall portion
13 base body
14 central longitudinal axis
recess
16 recess
17 cylindrical part
18 entrance channel
19 spiral channel
parting rib
21 end plate
22 gap space
23 nozzle bore
24 supply conduit
bore
26 bore
27 blind-hole bore
28 aperture (in 12)
64 glow plug
210 electric power
212 fuel cell
214 reformer
216 fuel
218 air
220 reformate
222 valve means
224 anode
226 blower
228 cathode supply air
230 cathode
232 burner
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234 anode waste gas
236 cathode waste air
238 heat exchanger
240 pump
242 blower
250 waste gas
