DE102013211483A1 - Gas storage system for gaseous fuels and method for operating a gas storage system - Google Patents

Abstract

The invention relates to a gas storage system (1) for gaseous fuels (A) and to a method for operating such a gas storage system (1), which comprises a storage vessel (2). The storage vessel (2) has a variable storage volume (3) for receiving and removing the fuel (A). A compression device (6) is also provided, which has a partition (7) which can be loaded on one side with a storage pressure (P) of the filled fuel (A). The compression device (6) is designed to increase a storage pressure (P) within the storage volume (3) that decreases when the fuel (A) filled into the storage volume (3) is removed. According to the invention, the compression device (6) can be preloaded by filling the fuel (A) into the storage volume (3). In addition, the partition (7) is designed to generate a reaction force (R) with respect to the storage pressure (P), the storage volume (3) being changeable by prestressing and / or releasing the compression device (6).

Description

The present invention relates to a gas storage system for gaseous fuels, in particular fuels for motor vehicles according to the preamble of claim 1 and a method for operating such a gas storage system for gaseous fuels according to claim 4.

For example, vehicles with gas internal combustion engines provide for the use of LPG, LNG, CNG or hydrogen. In particular, the gaseous fuels CNG and H2 generally have the problem of low volumetric energy density compared to liquid fuels. Since the space for the entrainment of fuels is also subject to volume limits, therefore, results in a limited and mostly relatively short range for gas-powered vehicles.

In addition, the low energy density of gaseous fuels requires a correspondingly large volume flow into the cylinder of the internal combustion engine. This in turn requires inlet nozzles with very large opening cross-sections as well as long inlet times and high gas pressures in order to achieve the required volume flow. However, the possible cross-sectional sizes of the openings and the times for the gas to be admitted into the cylinder are limited.

In particular, in combination with a direct injection (DI = Direct Injection), the maximum dimensions of the inlet nozzles already result from the remaining space. Any increase in the outer diameter of the inlet nozzles also has an effect on their maximum opening cross-section. The maximum enforceable volume flow would be limited by the maximum achievable opening cross-section, which - in addition to the Injektorventilhub - is determined directly by the maximum inner diameter and thus the maximum outer diameter of the injector. The injector outer diameter is severely limited by the combustion chamber size and geometry, as well as the required charge exchange valve cross sections and the installation space for the spark plug. Usual outer diameters of the injector tip are in the range of 7.0 to 8.0 mm. In addition, the minimum cross-section of the injector must not become so large that the smallest quantity metering - as required in idling mode - no longer functions robustly.

Another way to achieve the largest possible opening cross-section is to maximize the Düsennadelhubs, however, is limited by the dynamics of the actuator used. The maximum stroke of the nozzle needle within the inlet nozzle is very dependent on the drive technology used for this purpose. Further restrictions result from the achievable opening and closing times of the inlet nozzles. In this respect, the possibilities are limited by superficial enlargements of the inlet nozzles in order to achieve the required volume flow.

The closing times are particularly relevant for supercharged internal combustion engines with direct injection. These may be, for example, charged by a turbo or a compressor internal combustion engines. For these, for example for reasons of emission minimization, it is advantageous to not inject under full load at low speed before the inlet valve is closed. In this respect, it is first possible to use the already compressed state of the gaseous fuel. If an injection was made before closing the inlet valve, the gaseous fuel would have to be expanded back down to the required boost pressure, which is generally 1.0 to 2.5 bar absolute. Subsequently, a new compression would have to be done by the charging system. This would lead to increased requirements for the boost pressure. In addition, the benefits of direct injection would be eliminated and the engine would behave like a port fuel injection (PFI) in terms of boost pressure performance. This would result in a significant torque loss at low speeds.

The late onset of injection requires only a very limited time interval for the injection, especially at high speeds, as the injection time decreases proportionally as the speed increases. Even with full load requirement at low speeds, the injection windows are very limited, since just in turbo engines, which are often operated in this area with control times of large valve overlap, injection before admission would lead to very high emissions of unburned fuel. Reducing the charge cycle valve overlap to provide a prolonged injection time interval results in significant torque fall in full load, low speed operation.

In order to increase the flow of the fuel, the last possibility is to increase the gas pressure. Known CNG naturally aspirated engines are operated at a gas pressure of about 3.0 to 5.0 bar (absolute). In contrast, today's more demanding turbo engines require a gas pressure of about 7.0 to 9.0 bar. The prevailing in the gas tanks gas pressure is throttled for this purpose to the required operating pressure. The gas pressure for CNG tanks it is about 200 bar (at 15 ° C), whereas for gas tanks for H2 fueled vehicles it is up to 700 bar.

In order to reduce the injection times, the operating gas pressure for operation would have to be further increased. In this context, however, the gas tanks used can not be extended beyond the currently used gas pressure levels. Future CNG engines place high demands on the required operating pressure, which will range from 10 to 30 bar (absolute). As a result, the already considered to be critical range of such a vehicle operated even further reduced.

From the EP 1 333 168 A1 is an optimized method for operating a four-stroke internal combustion engine is known, which is supplied with natural gas. In the upper part-load range or in the full load range, the natural gas is injected for this purpose towards the end of the intake stroke or at the beginning of the compression stroke directly into the cylinder of the engine. The injection should occur in a crankshaft range of 210 ° and 90 ° before top dead center in order to improve the efficiency of the engine without raising the gas pressure provided from the gas tank.

The DE 10 2006 048 498 A1 shows a gas-powered internal combustion engine, in which the gaseous fuel is blown in a conventional manner in a combustion chamber of a cylinder of the internal combustion engine. For this purpose, at least one injector is provided, via which the gas is introduced from a gas tank into the combustion chamber. In this case, the gas pressure acting on the injector corresponds approximately to the pressure in the gas tank.

The US 5,454,408 A is focused on a compressed natural gas (CNG) storage and dispensing system. This has a variable volume, which is variable in dependence on the internal pressure. For this purpose, the at least one CNG tank is divided into two regions, which are separated from each other by an impermeable interface. To compensate for the decreasing pressure in the gas region of the tank when removing the gas, a hydraulic fluid can be pumped into the fluid region. In this way, located above the internal pressure of a gas tank to be filled filling pressure can be maintained or generated, for example, to fuel a gas-powered vehicle.

From the US 5,253,682 A is also a device for gas delivery is known which has a plurality of compressed gas cylinders. The compressed gas cylinders are used for the transport of gas and have a gas reservoir and a separate from the gas reservoir via a piston water reservoir. After filling the compressed gas cylinder with gas, the opposite water reservoir can be filled with water to move the piston against the gas reservoir.

Of the US 5,868,122 A is a device for providing a gaseous fuel, in particular to take CNG for an internal combustion engine of a vehicle with a reverse series connection. The device serves to supply the gas to the engine at high pressure. For this are several storage vessels 2 . 4 . 6 . 8th , a high-pressure accumulator 10 and a cache 12 and a plurality of valves V1, V2, V3, V4 provided. The internal combustion engine 56 is via the high-pressure accumulator 10 supplied with gas, wherein the high-pressure accumulator is coupled to the storage vessels. As soon as the pressure within the high-pressure accumulator falls below a predetermined value, this is transmitted via an amplifier 24 raised again. The amplifier is powered by a pump 26 operated, the amplifier is supplied via the storage vessels with the gas.

The known in the art systems for increasing the gas pressure all use devices that provide at least indirect coupling with the driven internal combustion engine. As a result, the energy required to drive these booster systems is ultimately absent in the energy balance of the engine being operated. This leads in particular to an increase in fuel consumption.

Against this background, the present invention has the object to provide a gas storage system for gaseous fuels and a method for operating such a gas storage system, which is improved despite improving the energy balance of the engine to be operated of the otherwise decreasing in the removal of the gaseous fuel storage pressure.

This object is achieved by a gas storage system for gaseous fuels with the features of claim 1 and by a method for operating such a gas storage system with the features of claim 4. Further, particularly advantageous embodiments of the invention disclose the respective subclaims.

It should be noted that the features listed individually in the following description can be combined with one another in any technically meaningful manner and show further embodiments of the invention. The description characterizes and specifies the Invention in particular in connection with the figures additionally.

According to the invention, the gas storage system comprises a storage vessel which has a variable storage volume for receiving and removing the gaseous fuel. The storage vessel may also be referred to as a gas tank, which is to be interpreted according to the male internal pressures of the gaseous fuel to be stored therein. Of course, any temperature fluctuations are taken into account. These can lead to a change in volume and thus to an additional load on the storage vessel. Furthermore, the respective safety regulations are to be considered, which are directed to such storage vessels.

Particularly preferably, the gas storage system is a mobile system. In other words, the gas storage system may in this case preferably be mounted in or on the vehicle of the internal combustion engine to be operated. In addition, the gas storage system is also suitable for stationary use, for example in connection with the storage of the gaseous fuel for a permanently installed gas tank system or filling station.

Furthermore, a compression device is provided in connection with the gas storage system according to the invention. The compression device is provided for and therefore adapted to increase a decreasing in the removal of the filled into the storage volume of fuel storage pressure within the storage volume. As previously explained, the storage pressure within the storage volume usually decreases as the gaseous fuel is removed. The compression device serves to provide a sufficiently high pressure of the fuel to generate the required volume flow even with increasing emptying of the storage volume.

The compression device has a with the storage pressure of the filled fuel on one side resilient partition. This partition stands with the filled gaseous fuel on one side in an at least partially planar contact.

Thus, the partition wall advantageously serves to allow the actual bias of the compression device. For this purpose, the compression device may be formed by means of the partition as a corresponding memory for potential energy. Said energy is in this case supplied during the filling operation of the storage volume on the pressurized gaseous fuel and accumulated.

According to the invention, the compression device is designed such that it can be prestressed by filling the gaseous fuel into the storage volume of the storage vessel. The partition wall is designed to generate a reaction force with respect to the accumulator pressure. The variable storage volume makes it possible to change the volume available for storing the gaseous fuel. According to the invention, the storage volume can be changed by pretensioning and / or relaxing the compression device.

The particular advantage lies in the design of the compression device. This invention provides a memory for potential energy. It acts as a mechanical energy storage, which requires no additional energy for the necessary pressure increase within the storage volume after its biasing. Consequently, the steady state energy available when filling the storage volume is used to bias the compression device above the gaseous fuel itself. This is possible since the filling of the fuel takes place with a pressure level above the maximum accumulator pressure. Said pressure energy is used at least in part for biasing the compression device during the filling process.

In this way, the necessary pressure increase is thus not actively generated during operation of the internal combustion engine, but results passive from the so-biased compression device. The result is a much better energy balance for the internal combustion engine. On the one hand, it can be operated for a longer time via the gaseous fuel entrained, for example, with sufficient pressure. On the other hand, the previously preloaded compression device does not require the internal combustion engine additional burdening energy to realize the necessary pressure increase.

The variable design of the storage volume requires that the Compression device is disposed within the storage vessel. Thus, when a partition wall is arranged, it can be arranged inside the storage vessel in order to structurally separate the compression device from the storage volume.

As a result, an extremely compact design of the gas storage is made possible in an advantageous manner. This is due to the fact that the gas storage system is formed purely outwardly of the storage vessel, wherein the required compression device is disposed within the storage vessel. Furthermore, this way the already existing and adapted to the respective requirements wall of the storage vessel can be used to include the compression device with. In addition to the resulting protection of the compression device can be arranged between the partition and the wall of the storage vessel so for example, a spring element or an enclosed compressible fluid cushion.

A preferred development of this partition provides that it is at least partially formed as an elastic membrane. Thus, said partition may have at least one elastic portion correspondingly yielding in response to the pressurization with the gaseous fuel during its filling. The displacement of this sub-area required for this happens against its respective restoring forces. Overall, the compression device is thus pretensioned via an elastic deformation of the membrane during the filling of the gaseous fuel.

The advantage of this embodiment lies in its extremely simple design, since this only a trained at least in a partial region as an elastic membrane partition wall is required. By their respective material properties and their dimensions, the required restoring forces of said membrane can be adjusted. The membrane is, for example, an area which is at least biaxially stretched and at the same time acts as a separating layer with respect to the gaseous fuel. The design as an elastic membrane also no further sealing measures are required to keep the gaseous fuel within the storage volume.

In a further advantageous embodiment, the partition may be coupled to a spring element. This embodiment is applicable as an alternative embodiment to the elastic membrane described above or as a supplement thereto. In principle, the partition wall can be loaded by the spring force of the spring element, which provides a mechanical energy store. In this way, the spring element via a change in position of the partition during the filling of the fuel is biased.

In the context of the invention, a change in position of the partition is considered as such, which results from a complete displacement of the same or else from an elastic deflection of one of its partial areas.

Thus, the partition may for example be formed as a rigid element which is variable in its position. This can be configured in the form of a piston, which is displaceable relative to a portion of the compression device. In this case, the displaceability takes place both against the spring force of the spring element and against the storage pressure of the gaseous fuel. The direction of the respective displacement depends on whether there is currently a filling process or a removal process of the gaseous fuel.

When filling the storage volume, the spring element is tensioned according to the pressure with which the gaseous fuel is introduced into the storage volume. The surface of the dividing wall which is to be acted upon by the accumulator pressure is to be dimensioned so that the force resulting from the surface pressure or the tension during filling is sufficient to prestress the spring element. Conversely, the spring constant of the spring element is to be sized so that it is sufficient to generate the necessary pressure in the removal of the gaseous fuel.

As a result, an almost unlimited stroke of the partition is made possible in an advantageous manner. This is to be seen in rigid design of the partition regardless of any elastic properties. In this way, even a small area loaded with the accumulator pressure is sufficient to enable a high compression of the gaseous fuel with a corresponding increase in pressure over a sufficiently long stroke.

In principle, the dividing wall can be designed such that its property as a mechanical energy store can only be called up when needed. Thus, for example, the change in shape and / or change in position of the partition during filling of the storage volume can be fixed such that the bias voltage of the compression device thus generated is first held. In this way, the filled gaseous fuel is not continuously charged by the restoring force of the partition. In this way, the resulting from the restoring forces of the partition wall pressure increase can be retrieved controlled within the storage volume. This can be done, for example, if the value falls below a preset value for the required accumulator pressure.

Moreover, the partition wall can also be displaced against a compressible fluid, which acts in the form of an enclosed pad from a side opposite the gaseous fuel side on the partition wall. In addition, a possible transmission ratio can be taken into account when forming the partition in the form of a displaceable piston. The translation is done then over different areas, which are each loaded with the storage pressure of the gaseous fuel or the aforementioned included pad.

The compression device may, for example, be arranged outside the storage vessel within the scope of the invention. In this case, it is connected to the storage vessel in such a way that the storage pressure in the storage volume of the storage vessel also bears against the compression device. The resulting advantage is seen in the full use of the storage vessel as a storage volume.

The subject part of the present invention shows a gas storage system for gaseous fuels with which, despite improving the energy balance of the internal combustion engine to be operated, the otherwise decreasing storage pressure during the removal of the gaseous fuel is increased. In a particularly advantageous manner, the energy surplus in the form of pressure present during filling is used for this purpose in order to bias the compression device. Without further energy consumption, the pressure-increasing effect of the compression device can then be used. In this way, a still existing proportion of gaseous fuel in the storage volume can be brought to a sufficiently high pressure level to be supplied to the internal combustion engine. As a result, the range of such operated vehicle is significantly increased.

The procedural part of the invention further shows a method for operating a gaseous fuel gas storage system as described above. The gas storage system has for this purpose a variable storage volume for receiving and removing the fuel. Furthermore, a compression device is provided, by means of which a storage pressure which decreases during the removal of the gaseous fuel charged into the storage volume can be increased within the storage volume if required. In this case, the compression device has a with the storage pressure of the filled fuel on one side resilient partition.

According to the invention, the compression device can be biased by the filling of the fuel in the storage volume. In this case, a reaction force with respect to the accumulator pressure can be generated via the dividing wall. Thus, the storage volume can be changed by the biasing and / or relaxing the compression device in an advantageous manner.

With a further advantageous measure it is provided that the partition wall is at least partially formed as an elastic membrane, so that the compression device can be biased by an elastic deformation of the membrane during the filling of the fuel.

As an additional or alternative advantageous measure, the partition may be coupled to a spring element. Said spring element can then be biased by a change in position of the partition during the filling of the fuel.

The advantages resulting from the aforementioned measures have already been sufficiently described in the context of the subject part of the present invention, so that reference is made to said statements at this point.

Further advantageous details and effects of the invention are explained in more detail below with reference to two embodiments shown in the following figures. Show it:

1 a schematic longitudinal section through an inventive gas storage system for gaseous fuels and

2 an alternative embodiment of the gas storage system according to the invention for gaseous fuels 1 in self-presentation.

1 schematically illustrates a gas storage system according to the invention 1 for gaseous fuels A dar. The gas storage system 1 includes a storage vessel 2 , Which in this case in a longitudinal section through the gas storage system 1 is shown through. With reference to the representation of 1 points the storage vessel 2 a storage volume located to the left in its interior 3 on. The storage volume 3 serves to receive and remove the gaseous fuel A. In the present case, the gaseous fuel A is within the storage volume 3 indicated.

The storage vessel 2 has an inlet nozzle 4 and an outlet nozzle 5 on. Both nozzles 4 . 5 are through the wall of the storage vessel 2 arranged through and connect the storage volume 3 with unspecified external peripherals. These are a filling station for the gaseous fuel, which via the inlet nozzle 4 enters the storage volume. Furthermore, this is an internal combustion engine, also not shown. This is done via the outlet nozzle 5 the gaseous fuel A is supplied.

Furthermore, a compression device 6 provided, which in this case within the storage vessel 2 is arranged. The compression device 6 is designed to take one in the removal of the in the storage volume 3 filled gaseous fuel A decreasing storage pressure P within the storage volume 3 to increase. For this purpose, the compression device 6 one relative to the storage vessel 2 movable partition 7 which is loaded on one side with the accumulator pressure P of the gaseous fuel A. In this way, the available storage volume 3 through a partial region of the wall of the storage vessel 2 and the partition is limited. Consequently, the storage volume 3 variable, the storage volume 3 by biasing and / or relaxing the compression device 6 is changeable.

On a side facing away from the gaseous fuel A side of the partition 7 is a spring element 8th arranged. The spring element 8th extends between said side of the partition 7 and a part of the wall of the storage vessel 2 in the area of the compression device 6 , In this way, the compression device 6 by filling the fuel A into the storage volume 3 prestressed. The reason for this is the filling of the storage volume 3 with the gaseous fuel A rising storage pressure P, which on one side of the partition 7 acts. By the arrangement of the spring element 8th is the dividing wall 7 is adapted to one of the presently compressed spring element 8th resulting reaction force R in the form of a back pressure against the accumulator pressure P to produce.

Out 2 goes an alternative embodiment of the gas storage system 1 out 1 out. For the realization of the compression device 6 is the dividing wall 7 Here, at least partially formed as an elastic membrane. In this respect, it lacks an additional spring element 8th so that the alternative compression device 6 via an elastic change in shape of the partition wall designed as a membrane 7 is biased during filling of the fuel A. Due to the elastic deformation of the partition wall formed as a membrane 7 is also a reaction force R generated, which results from the restoring forces of the elastic membrane.

LIST OF REFERENCE NUMBERS

1

Gas storage system

2

Storage vessel of 1

3

Storage volume of 2

4

Inlet nozzle in 2

5

Outlet nozzle in 2

6

compression device

7

Partition of 6

8th

Spring element of 6

A

Fuel, gaseous

P

Memory pressure in 3

R

reaction force

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1333168 A1 [0010]
• DE 102006048498 A1 [0011]
• US 5454408 A [0012]
• US 5253682 A [0013]
• US 5868122 A [0014]

Claims (6)

Gas storage system for gaseous fuels (A), comprising a storage vessel ( 2 ), which has a variable storage volume ( 3 ) for receiving and removing the fuel (A), wherein a compression device ( 6 ) is provided, which one with a storage pressure (P) of the filled fuel (A) unilaterally resilient partition ( 7 ) and is adapted to a in the removal of the in the storage volume ( 3 ) filled fuel (A) decreasing storage pressure (P) within the storage volume ( 3 ), characterized in that the compression device ( 6 ) by filling the fuel (A) into the storage volume ( 3 ) is biased and the partition ( 7 ) is adapted to generate a reaction force (R) with respect to the storage pressure (P), the storage volume ( 3 ) by biasing and / or relaxing the compression device ( 6 ) is changeable. Gas storage system according to claim 1, characterized in that the partition ( 7 ) is at least partially formed as an elastic membrane, wherein the compression device ( 6 ) can be prestressed via an elastic deformation of the membrane during the filling of the fuel (A). Gas storage system according to claim 1 or 2, characterized in that the partition ( 7 ) with a spring element ( 8th ), wherein the spring element ( 8th ) about a change in position of the partition ( 7 ) is preloaded during filling of the fuel (A). Method for operating a gas storage system ( 1 ) for gaseous fuels (A) in particular according to one of the preceding claims, comprising a storage vessel ( 2 ), which has a variable storage volume ( 3 ) for receiving and removing the fuel (A), wherein a compression device ( 6 ) with a with a storage pressure (P) of the filled fuel (A) unilaterally resilient partition ( 7 ) is provided, via which a in the removal of the in the storage volume ( 3 ) filled fuel (A) decreasing storage pressure (P) within the storage volume ( 3 ), characterized in that the compression device ( 6 ) by filling the fuel (A) into the storage volume ( 3 ) and over the partition ( 7 ) a reaction force (R) with respect to the accumulator pressure (P) is generated, the storage volume ( 3 ) by biasing and / or relaxing the compression device ( 6 ) is changed. Method according to claim 4, characterized in that the partition wall ( 7 ) is at least partially formed as an elastic membrane, wherein the compression device ( 6 ) is biased by an elastic deformation of the membrane during the filling of the fuel (A). Method according to claim 4 or 5, characterized in that the partition wall ( 7 ) with a spring element ( 8th ), wherein the spring element ( 8th ) about a change in position of the partition ( 7 ) is biased during filling of the fuel (A).

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