Pressure reducer for enabling the use of polymer pipes for thermal pressure relief devices of hydrogen-operated vehicles

Abstract

The invention relates to a pressure-reducing system for a high-pressure tank (10), in particular for a high-pressure tank (10) of a motor vehicle, in which high-pressure tank (10) a fluid is stored under positive pressure, wherein the high-pressure tank (10) has an outlet (9) for relieving the pressure, wherein the high-pressure tank (10) is fluidically connected via the outlet (9) to a thermal pressure relief device (20) through which the fluid flows in the flow direction (x) when pressure is being relieved. According to the invention, a pressure reducer (1) for reducing the pressure when relieving the high-pressure tank (10) of pressure is provided in the thermal pressure relief device (20).

Description

[0001] Pressure reducer to enable the use of polymer pipes for thermal pressure relief devices of hydrogen-powered vehicles

[0002] The invention relates to a pressure reduction system for a high-pressure tank according to the preamble of claim 1.

[0003] In vehicles powered by hydrogen or natural gas, for example, high-pressure tanks are used for fuel storage. Pressures of several hundred bar, such as 700 bar in the passenger car segment, are typical for such high-pressure tanks.

[0004] For safety reasons, the high-pressure tanks are equipped with a thermal pressure relief device, which is usually a pipe system or relief pipe that empties the high-pressure tanks in the event of a vehicle fire.

[0005] Relief pipes or thermal pressure relief devices that are directly coupled to a high-pressure hydrogen tank are already known from the prior art. These are typically stainless steel pipes, which exhibit relatively high mechanical strength and can therefore withstand increased pressure conditions when the fuel flows out. Depending on the system design, the line pressure can reach approximately 80-95% of the tank pressure when the thermal pressure relief device is activated and the hydrogen flows from the high-pressure tank into the pipeline.

[0006] The disadvantage here is that the stainless steel pipes are relatively heavy and also expensive to produce.

[0007] The aim of the invention is to overcome these and other disadvantages of the prior art and to create an improved pressure reduction system for high-pressure tanks in hydrogen-powered motor vehicles, which is constructed cost-effectively using simple means and at the same time has a low dead weight.

[0008] Main features of the invention are defined in the characterizing part of claim 1. Embodiments are the subject of claims 2 to 10.

[0009] In a pressure reduction system for a high-pressure tank, in particular for a high-pressure tank of a motor vehicle, in which high-pressure tank a fluid is stored under excess pressure, wherein the high-pressure tank has an outlet for relief, wherein the high-pressure tank is fluidly connected via the outlet to a thermal pressure relief device through which the fluid flows in the flow direction upon relief, according to the invention a pressure reducer is provided in the thermal pressure relief device for reducing the pressure upon relief of the high-pressure tank.

[0010] The invention achieves this objective surprisingly simply by using an additional pressure reducer within the thermal pressure relief device. The pressure reducer reduces the pressure in the thermal pressure relief device, allowing it to be manufactured from a significantly cheaper and lighter plastic, particularly a polymer material. Thus, the present invention provides a system for venting high-pressure tanks that ensures low pipe pressure during pressure relief.

[0011] The pressure reducer is preferably a throttle valve, wherein the throttle valve has a throttle opening. The pressure is effectively reduced due to the throttle valve at the outlet of the high-pressure tank and within the thermal pressure relief device downstream or in the direction of flow. It is particularly preferred that the throttle valve be designed as a ring throttle. This represents a cost-effective design variant and thus further reduces overall manufacturing costs. Alternatively, other inexpensively manufactured throttle geometries, such as a simple perforated plate, would also be conceivable.

[0012] Preferably, the throttle opening is smaller in diameter than the outlet and the thermal pressure relief device. This effectively reduces the total pressure in the system and increases entropy. At the same time, the throttle reduces the static pressure in the thermal pressure relief device downstream or in the direction of flow.

[0013] According to a further embodiment of the invention, the throttle valve is arranged indirectly at the outlet of the high-pressure tank and within the thermal pressure relief device. Due to the distance between the outlet and the throttle, excessive pressure peaks advantageously do not occur during the outflow in the area of ​​the outlet or at the pipe inlet of the thermal pressure relief device.

[0014] According to a preferred embodiment, the invention provides that the thermal pressure relief device is designed as a relief pipe, wherein the outlet has a diameter corresponding to a pipe diameter of the thermal pressure relief device. This ensures a uniform mass flow rate when flowing through the relief pipe. Due to the throttle valve, the density of the fuel is reduced when flowing through the relief pipe. To compensate for this reduction in density, the diameter of the outlet or the relief pipe is generally larger than in known solutions from the prior art, thereby achieving a sufficient mass flow rate despite the throttling.

[0015] According to another preferred embodiment, the thermal pressure relief device is designed as a polymer tube. Polymer tubes are particularly cost-effective to manufacture and, at the same time, very lightweight compared to stainless steel tubes. The polymer tube can be manufactured, for example, using a simple injection molding process.

[0016] According to an important embodiment, the invention provides that the pressure reducer accelerates the flow at the outlet to supersonic speeds. Due to the acceleration of the fluid or fuel into the supersonic range, an effective pressure reduction can be achieved downstream or in the direction of flow in the thermal pressure relief device.

[0017] The pressure reducer is preferably a Laval nozzle, wherein the Laval nozzle has a convergent section and a divergent section. The Laval nozzle is preferably arranged between the outlet and the thermal pressure relief device, wherein the convergent section of the Laval nozzle is arranged directly and immediately at the outlet of the high-pressure tank. The arrangement of the Laval nozzle allows the static pressure to be reduced without lowering the total pressure in the system. The flowing out fuel is accelerated to supersonic speed with the help of the Laval nozzle at the outlet of the high-pressure tank or at the pipe inlet of the thermal pressure relief device. Further acceleration to supersonic flow, i.e. to Mach numbers > 1, can take place in the divergent section of the Laval nozzle.Since the static pressure decreases with increasing Mach number, this leads to a significant pressure reduction in the thermal pressure relief device while maintaining a constant total pressure, meaning that acceleration occurs essentially isentropic. Due to this interaction, the diameter of the thermal pressure relief device or the relief tube can be smaller than that of the throttle design. Preferably, the flow throughout the relief tube remains supersonic, even if it decreases due to frictional forces.

[0018] In a preferred embodiment, the Laval nozzle has a reduced throat diameter, with the convergent section of the Laval nozzle transitioning into the divergent section immediately after reaching the throat diameter. Alternatively, the convergent section of the Laval nozzle can also transition smoothly into the divergent section and have a slight axial extension in the region of the throat diameter.

[0019] In the Laval nozzle design, the outlet preferably has a diameter that is smaller than the pipe diameter of the thermal pressure relief device. The Laval nozzle preferably has a circular or elliptical cross-sectional area over its entire length. The narrowest cross-section of the Laval nozzle preferably corresponds to the throat diameter, with the flow reaching the speed of sound at the throat diameter and being accelerated into the supersonic range in the divergent section. Further features, details, and advantages of the invention emerge from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. In the drawings:

[0020] Fig. 1a is a schematic view of a high-pressure tank with a thermal relief pipe of the prior art;

[0021] Fig. 1b is a schematic view of an inventive

[0022] pressure reduction system;

[0023] Fig. 1c is a schematic view of another embodiment of a pressure reduction system according to the invention

[0024] Fig. 1a shows a high-pressure tank 10 in which hydrogen can be stored under high pressure. The high-pressure tank 10 is coupled to a thermal pressure relief device 20 on an outlet side. The thermal pressure relief device 20 is designed as a relief pipe and has a pipe diameter D. When the high-pressure tank 10 is relieved, the fuel flows into the thermal pressure relief device 20 in the flow direction (x). This arrangement corresponds to the prior art.

[0025] Fig. 1b is a schematic representation of a pressure reduction system for hydrogen-powered motor vehicles with at least one high-pressure tank 10 in which fuel is stored under excess pressure. The high-pressure tank 10 has an outlet 9 for pressure relief, via which the high-pressure tank 10 is fluidly connected to a thermal pressure relief device 20.

[0026] The thermal pressure relief device 20 is designed as a relief pipe. During relief, the fuel flows through the relief pipe in the flow direction x. The outlet 9 has a diameter D1 that corresponds to a pipe diameter of the thermal pressure relief device 20 or the relief pipe.

[0027] A pressure reducer 1 is arranged at the outlet 9 within the relief pipe. In the embodiment shown, the pressure reducer 1 is designed as a throttle valve 7 and has a throttle opening 8. This is, in particular, an annular throttle. Fig. 1c schematically shows another embodiment of the invention. In Fig. 1c, a Laval nozzle 5 is arranged instead of the throttle valve 7 from Fig. 1b, whereby the thermal pressure relief device is also designed as a relief pipe in this embodiment.

[0028] The Laval nozzle 5 has a convergent section 2 and a divergent section 6. The Laval nozzle 5 is arranged between the outlet 9 and the thermal pressure relief device 20 or a constant section of the relief pipe. The convergent section 2 of the Laval nozzle 5 is arranged directly and immediately at the outlet 9 of the high-pressure tank 10.

[0029] The Laval nozzle 5 further has a throat diameter 3, with the convergent section 2 of the Laval nozzle 5 transitioning into the divergent section 6 immediately after reaching the throat diameter 3. The outlet 9 has a diameter D2 that is smaller than a pipe diameter D3 of the relief pipe or the thermal pressure relief device 20. The throat diameter 3 has the smallest cross-section or diameter of the Laval nozzle 5.

[0030] The pressure reduction system according to the invention can generally relate to high-pressure vessels and thermal pressure relief devices. In particular, the invention relates to hydrogen-powered vehicles, which typically have a high-pressure tank filled with hydrogen under excess pressure. Due to the increased risk of explosion and fire in the event of accidents or the like, the invention is used in particular for venting such high-pressure tanks. In principle, however, the pressure reduction system can also be implemented in a stationary high-pressure vessel with a thermal pressure relief device.

[0031] All features and advantages arising from the claims, the description, and the drawings, including structural details, spatial arrangements, and method steps, may be essential to the invention both individually and in a wide variety of combinations. Reference symbols list

[0032] D Diameter (standard) 5 Laval nozzle

[0033] D1 Diameter Outlet 6 Divergent Section

[0034] (Throttle) 7 Throttle valve

[0035] D2 Diameter outlet (Laval) 8 Throttle opening

[0036] D3 Diameter relief pipe 9 Outlet

[0037] (Laval) 10 High pressure tank x Flow direction 20 Thermal

[0038] Pressure relief device

[0039] 1 pressure reducer

[0040] 2 convergent section

[0041] 3 neck diameters (Laval)

Claims

Claims: Pressure reduction system for a high-pressure tank (10), in particular for a high-pressure tank (10) of a motor vehicle, in which the high-pressure tank (10) stores a fluid under overpressure, wherein the high-pressure tank (10) has an outlet (9) for pressure relief, wherein the high-pressure tank (10) is fluidly connected via the outlet (9) to a thermal pressure relief device (20), through which the fluid flows in the flow direction (x) during pressure relief, characterized in that a pressure reducer (1) is provided in the thermal pressure relief device (20) for reducing the pressure when the high-pressure tank (10) is relieved. Pressure reduction system according to claim 1, characterized in that the pressure reducer (1) is a throttle valve (7), wherein the throttle valve (7) has a throttle opening (8) and is in particular designed as a ring throttle.Pressure reduction system according to claim 2, characterized in that the thermal pressure relief device (20) is designed as a relief pipe, wherein the outlet (9) has a diameter (D1) corresponding to the pipe diameter of the thermal pressure relief device (20). Pressure reduction system according to claims 2 to 3, characterized in that the throttle opening (8) has a smaller diameter than the outlet (9) and the thermal pressure relief device (20). Pressure reduction system according to claim 2, characterized in that the throttle valve (7) is arranged indirectly at the outlet (9) of the high-pressure tank (10) and within the thermal pressure relief device (20). Pressure reduction system according to claim 1, characterized in that the pressure reducer (1) accelerates the flow to supersonic speed.Pressure reduction system according to claim 6, characterized in that the pressure reducer (1) is a Laval nozzle (5), wherein the Laval nozzle (5) has a convergent section (2) and a divergent section (6). Pressure reduction system according to claim 7, characterized in that the Laval nozzle (5) is arranged between the outlet (9) and the thermal pressure relief device (20), wherein the convergent section (2) the Laval nozzle (5) is arranged directly and immediately at the outlet (9) of the high-pressure tank (10). Pressure reduction system according to claim 7, characterized in that the Laval nozzle (5) has a neck diameter (3), wherein the convergent section (2) of the Laval nozzle (5) extends immediately after reaching the neck diameter. (3) transitions into the divergent section (6). Pressure reduction system according to claim 7, characterized in that the thermal pressure relief device (20) is designed as a relief pipe, wherein the outlet (9) has a diameter (D2) that is smaller than a pipe diameter (D3) of the thermal pressure relief device (20).

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