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

[0002] Vehicles powered by hydrogen or natural gas, for example, use high-pressure tanks for fuel storage. Pressures of several hundred bar, such as 700 bar in passenger cars, are typical for these high-pressure tanks.

[0003] For safety reasons, the high-pressure tanks are equipped with a thermal pressure relief device, which is usually a pipe system or a relief pipe that empties the high-pressure tanks in the event of a vehicle fire.

[0004] Pressure relief pipes or thermal pressure relief devices directly coupled to a high-pressure hydrogen tank are already known in the prior art. These are typically stainless steel pipes, which exhibit relatively high mechanical strength and can therefore withstand the increased pressure conditions during fuel discharge. Depending on the system design, the line pressure reaches up to approximately 80-95% of the tank pressure when the thermal pressure relief device is activated and hydrogen flows from the high-pressure tank into the pipeline.

[0005] A disadvantage here is that the stainless steel pipes are relatively heavy and also expensive to manufacture. DE102019125184A1 describes a known pressure reduction system.

[0006] 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 cost-effectively constructed using simple means and at the same time has a low weight. The main features of the invention are specified in the characterizing part of claim 1.

[0007] The embodiments are the subject of claims 2 to 3.

[0008] In a pressure reduction system for a high-pressure tank, in particular for a high-pressure tank of a motor vehicle, in which a fluid is stored under overpressure in the high-pressure tank, 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 direction of flow when relieved, a pressure reducer is provided in the thermal pressure relief device according to the invention for reducing the pressure when the high-pressure tank is relieved.

[0009] The invention solves the present problem surprisingly simply by using an additional pressure reducer within the thermal pressure relief device. The pressure reducer lowers the pressure in the thermal pressure relief device, allowing it to be manufactured from a significantly cheaper and lighter plastic, in particular a polymer material. Thus, the present invention provides a system for venting high-pressure tanks that ensures a low pipe pressure during the relief process.

[0010] According to an embodiment not part of the invention, the pressure reducer is a throttle valve, wherein the throttle valve has a throttle opening. Due to the throttle valve, the pressure is effectively reduced downstream, or in the flow direction, at the outlet of the high-pressure tank and within the thermal pressure relief device. 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 the overall manufacturing costs. Alternatively, other inexpensive throttle geometries, such as a simple perforated sheet, would also be conceivable.

[0011] Preferably, the throttle opening has a smaller diameter than the outlet and the thermal pressure relief device. This achieves an effective reduction of the total pressure in the system or an increase in entropy. At the same time, the throttle reduces the static pressure downstream in the thermal pressure relief device, i.e., in the direction of flow.

[0012] In another embodiment, 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, no excessive pressure peaks advantageously occur during outflow in the area of ​​the outlet or at the pipe inlet of the thermal pressure relief device.

[0013] In a preferred embodiment, the thermal pressure relief device is designed as a relief pipe, the outlet having a diameter corresponding to the pipe diameter of the thermal pressure relief device. This ensures a uniform mass flow rate as the fuel flows through the relief pipe. Due to the throttle valve, the density of the fuel decreases as it flows 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 prior art solutions, thereby achieving a sufficient mass flow rate despite the throttling.

[0014] In 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 produced, for example, using a simple injection molding process. The invention provides that the pressure reducer accelerates the flow at the outlet to supersonic speed. Due to the acceleration of the fluid or fuel into the supersonic range, an effective pressure reduction downstream, or in the direction of flow, can be achieved in the thermal pressure relief device.

[0015] The pressure reducer is a Laval nozzle, which has a convergent section and a divergent section. According to the invention, the Laval nozzle is arranged between the outlet and the thermal pressure relief device, with the convergent section of the Laval nozzle being located 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 outgoing fuel is accelerated to supersonic speed by 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 occur 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 the total pressure remains constant; that is, the acceleration is essentially isentropic. Due to this interaction, the diameter of the thermal pressure relief device or the relief tube can be smaller than in a throttle design. Preferably, the flow remains supersonic throughout the entire relief tube, even though it decreases due to frictional forces.

[0016] In a preferred embodiment, the Laval nozzle has a reduced neck diameter, wherein the convergent section of the Laval nozzle transitions directly into the divergent section upon reaching the neck diameter. Alternatively, the convergent section of the Laval nozzle can also transition smoothly into the divergent section and exhibit a slight axial extension in the region of the neck diameter.

[0017] In the Laval nozzle design, the outlet preferably has a diameter smaller than the pipe diameter of the thermal pressure relief device. The Laval nozzle preferably has a circular or elliptical cross-sectional area along its entire length. Preferably, the narrowest cross-section of the Laval nozzle corresponds to the neck diameter, with the flow reaching the speed of sound at the neck diameter and accelerating into the supersonic range in the divergent section.

[0018] Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. The drawings show: Fig. 1a a schematic view of a high-pressure tank with a thermal relief pipe from the prior art; Fig. 1b a schematic view of a pressure reducing system not belonging to the invention; Fig. 1c a schematic view of a further embodiment of a pressure reducing system according to the invention.

[0019] Fig. 1aFigure 1 shows a high-pressure tank 10 in which hydrogen can be stored under high pressure. The high-pressure tank 10 is coupled at one outlet end to a thermal pressure relief device 20. 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 in the flow direction (x) into the thermal pressure relief device 20. The arrangement is state of the art.

[0020] Fig. 1b Figure 1 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 overpressure. 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.

[0021] 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 the pipe diameter of the thermal pressure relief device 20 or the relief pipe.

[0022] A pressure reducer 1 is arranged inside the relief pipe at outlet 9. In the illustrated embodiment, the pressure reducer 1 is designed as a throttle valve 7 and has a throttle opening 8. This is, in particular, a ring throttle valve.

[0023] Fig. 1c schematically shows another embodiment of the invention. Fig. 1c is a Laval nozzle 5 instead of the throttle valve 7 Fig. 1b arranged, wherein the thermal pressure relief device is also designed as a relief pipe in this embodiment.

[0024] 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 located directly and immediately at the outlet 9 of the high-pressure tank 10.

[0025] The Laval nozzle 5 further comprises a neck diameter 3, wherein the convergent section 2 of the Laval nozzle 5 transitions directly into the divergent section 6 after reaching the neck diameter 3. The outlet 9 has a diameter D2, which is smaller than the pipe diameter D3 of the relief pipe or the thermal pressure relief device 20. The neck diameter 3 has the smallest cross-section or diameter of the Laval nozzle 5.

[0026] The pressure reduction system according to the invention can generally relate to high-pressure tanks 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 overpressure. Due to the increased risk of explosion and fire in accidents or the like, the invention is used especially for venting such high-pressure tanks. However, the pressure reduction system can also be implemented in a stationary high-pressure tank with a thermal pressure relief device. Reference symbol list

[0027] D Diameter (standard) 5 Laval nozzle D1 Outlet diameter (throttle) 6 divergent section 7 Throttle valve D2 Outlet diameter (Laval) 8 Throttle opening D3 Diameter of relief pipe (Laval) 9 Outlet 10 High-pressure tank x Flow direction 20 Thermal pressure relief device 1 Pressure reducer 2 convergent section 3 Neck diameter (Laval)

Claims

1. Pressure-reducing system for a high-pressure tank (10), in particular for a high-pressure tank (10) of a motor vehicle, wherein the pressure-reducing system comprises an outlet of a high-pressure tank and a thermal pressure-relief device, 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 by way of the outlet (9) to a thermal pressure relief device (20) through which the fluid flows in the flow direction (x) when the pressure is relieved, wherein a pressure reducer (1) for reducing the pressure when relieving the pressure of the high-pressure tank (10) is provided in the thermal pressure relief device (20), characterized in that the pressure reducer (1) is a Laval nozzle (5) which accelerates the flow to supersonic speed, wherein the Laval nozzle (5) has a convergent portion (2) and a divergent portion (6), wherein the Laval nozzle (5) is disposed between the outlet (9) and the thermal pressure relief device (20), wherein the convergent portion (2) of the Laval nozzle (5) is disposed directly and immediately on the outlet (9) of the high-pressure tank (10).

2. Pressure-reducing system according to Claim 1, characterized in that the Laval nozzle (5) has a neck diameter (3), wherein the convergent portion (2) of the Laval nozzle (5) transitions into the divergent portion (6) immediately after the neck diameter (3) has been reached.

3. Pressure-reducing system according to one of the preceding claims, characterized in that the thermal pressure relief device (20) is designed as a relief pipe, wherein the outlet (9) has a diameter (D2) which is designed to be smaller than a pipe diameter (D3) of the thermal pressure relief device (20).

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