Optimal space utilization through novel adaptive lightweight hydrogen tanks

These tanks are to be used for the newly designed hydrogen combustion engine for medium-duty commercial vehicles. IVW is working closely with project module partners, including Mercedes-Benz Special Trucks, Commercial Vehicle Cluster – Nutzfahrzeug GmbH, comlet Verteilte Systeme GmbH, HYDAC Process Technology GmbH, Institut für Oberflächen- und Schichtanalytik GmbH (IFOS), Photonik-Zentrum Kaiserslautern e. V. (PZKL), and Thomas Magnete GmbH.

Currently, the supply of hydrogen to the newly developed hydrogen combustion engine in the UNIMOG demonstrator, which has recently obtained road approval, is facilitated by four conventional Type-4 tanks. Initially, this research vehicle provides about 13 kg of H₂. The goal of WaVe project is to increase this H₂ capacity in the UNIMOG to about 28 kg, while maintaining the same space requirements on the vehicle. In the future, the lightweight tank modules developed by IVW will efficiently utilize the available space and provide the necessary quantity for regular operation. CFRP pressure vessels with plastic liners, ensuring sufficient resistance against H₂ permeation (so-called Type 4 tanks), represent the state-of-the-art technology for hydrogen storage nowadays. For the load-bearing structure of the vessel, carbon fibres are applied to the preformed liner using winding techniques. Common winding methods are efficient and suitable for industrial use, but they have significant geometric limitations. For instance, it is not readily possible to apply purely axial fibre layers due to the mandatory winding angle. Additionally, vessels smaller than about 200 mm in diameter cannot be produced in a production-ready process as the winding angle deviates significantly from the geodesic path, resulting in an overproportional increase in thickness in the dome area due to frequent wrapping of the boss area on a smaller surface.

For commercial vehicle technology, the use of purely axial fibre reinforcement has the potential to utilize the pressure vessel as an additional structural element (e.g., link, spar). This is precisely where the presented research project comes into play. A novel manufacturing process is being developed to create cylindrical pressure vessels with purely axial fibres and circumferentially applied fibres. These vessels possess maximum lightweight design qualities and can be manufactured with very thin diameters. The load transfer from the axial layers in the cylindrical section of the pressure vessel is achieved layer by layer using the patented “IVW load introduction” developed by IVW. This method allows for the proper integration of the metal dome regions to carry the load. In contrast to the conventional approach where a preformed “plastic bladder” is used as the liner, a metal or plastic tube can be utilized as a liner in this research. This tube can be easily adjusted for geometric changes, especially length variations.

An initial design variant (Figure 1, left) could not achieve the required burst pressure of 1575 bar for an operating pressure of 700 bar due to a leak in the overlap area between the liner and the dome region. Consequently, the design was extensively revised to generate higher circumferential layer pre-tension and increase the compression between the liner and the dome region (Figure 1, right). This is accomplished by using a patented conical clamping element in the interior (wedge connection). Additionally, an O-ring is used to enhance sealing. Initial prototypes have been manufactured and subjected to burst testing, reaching values up to 1660 bar.