【Haichuan Explores the World】How are vehicle hydrogen tanks capable of withstanding 700 atmospheres of pressure made?
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Shared from the internet: The hydrogen storage tank, which serves as the core component for storing fuel in hydrogen fuel cells, is just like the fuel tank in traditional internal combustion engines – it is an essential device for supplying the fuel (hydrogen) to the fuel cells. Of course, since the hydrogen currently in use is in a high-pressure gaseous state, its production process is much more complex than that of traditional fuel tanks. Next, let’s first get a brief understanding of the basic classifications and manufacturing processes of hydrogen cylinders
Hydrogen cylinders are classified by generation into Type I, Type II, Type III, and Type IV cylinders.
It is classified into Category A and Category B based on pressure type. 35MPa is Class A ； 70MPa is Class B. (Due to different pressures, the methods for conducting tests and verification also vary.) Type I and Type II tanks are primarily made of pressure-resistant steel; Type II tanks incorporate a fiber-resin composite coating on top of the structure used in Type I tanks. They are still used in some fixed installations, such as fixed fuel cell power systems or other applications that require hydrogen storage. Due to their long history of development and highly mature manufacturing processes, we will not go into further detail here. Next, we will briefly introduce Type III bottles and Type IV bottles. Type III cylinders: Since fuel cells are used as mobile power sources (such as fuel cell vehicles, ships, aircraft, etc.), there is a greater demand for lighter hydrogen supply systems, which led to the development of Type III cylinders. While the weight of the product has been reduced, the manufacturing cost has increased compared to types I and II in order to maintain performance. Based on the schematic diagram of its appearance, Type III bottles use an aluminum inner liner, with the entire bottle body covered in a fiber and resin composite material. The wrapping pattern is either polar laying or spiral laying. Type III bottles can meet the pressure requirements of fuel cell vehicles, and are divided into Category A with 35 MPa and Category B with 70 MPa. Currently, the hydrogen tanks used in domestic fuel cell vehicles are typically the more mature Type A and Type B III tanks.
Type IV bottle: The Type IV bottle was developed to achieve further lightweighting and lower costs. The liner of Type IV bottles is made of polymer plastic, making them lighter in weight than the aluminum liners of Type III bottles; the entire bottle body is covered with a fiber-resin composite material. The wrap uses a combination of polar laying and spiral laying. It should be specifically noted that to achieve a better seal, type IV cylinders have a metal fitting at their hydrogen outlet (which represents a technical challenge). In terms of wall thickness, Type IV bottles are slightly thinner than Type III bottles. The gas storage pressure is the same as that of Type III cylinders. At present, there are no commercially viable Type IV bottles available in China; all such bottles in the country are still in the research and development or pilot production stage. Almost all companies that produce Type III bottles are actively advancing the research, development, and prototyping of Type IV bottles in order to enable their timely industrialization.
Currently, the industry landscape is such that Type A 35MPa Class III bottles have mature production processes and ample manufacturing capacity, while Type B 70MPa bottles are also generally available for use. Type IV bottles of categories A and B are basically in the research and development and trial production stages. Regarding standards, the group standard for \"Plastic-lined carbon fiber fully wound gas cylinders for compressed hydrogen in vehicles\" (which specifies requirements for 70 MPa and Type IV cylinders) was issued and put into effect on October 8, 2020. Regarding manufacturing, in accordance with the safety technical specifications for gas cylinders: first of all, we need to create a gas cylinder. The first step is to carry out design based on standards, taking into account possible failure modes as well as potential material cracking and other issues ； Secondly, this design document must be evaluated by a qualified testing institution before it can be put into use. Samples must be developed based on this design document, and those samples must undergo formal tests conducted by a qualified testing institution before they can be manufactured on a large scale.