A Design Methodology for Hydrogen Fuel Powered City Vehicles in Rear Impact Collisions

With the overwhelming reliance on fossil fuels, alternative fuel vehicles are beginning to emerge in the market. Battery electric vehicles are largely inferior to conventional fuel vehicles, as a result of the poor energy density (storage capacity) of current battery technology. Hydrogen technology may be a stepping-stone to a viable alternative fuel vehicle. The Microcab vehicle, considered in this study, is based on the hydrogen technology and has been designed using M1 criteria with front and side crash protection in mind. The hydrogen fuel tank is however located in the rear floor area, hence its structural integrity after rear crash needs to be considered despite the lack of relevant legislative requirements. The research presented proposes a design methodology for hydrogen fuel tanks protection in rear impact accidents using Computer Aided Engineering (CAE) analysis. A generic rear impact safety load case, involving a rigid 1500kg barrier travelling at 30mph, is proposed to mimic a plausible rear city impact, allowing a structural assessment of the vehicle via explicit crash dynamics simulation and understanding the risks of tank rupture. The initial CAE studies suggested that the Microcab backup structure needed improvements for the rear impact. Following initial studies a link was established between the stability of the structure and its sequential crush for robustness in the rear impact load case. This discovery was the underpinning for the improvements of the Microcab rear impact structural integrity. The new design assessment method established the creation of adequate load paths in the structure, support for the envisaged crash loads, and the fulfilment of the hydrogen tank and structural integrity targets. This design process has the potential to be improved in the future by parameterising the dimension and masses of bullet vehicles to reflect a large variety of possible rear end accidents as part of the design process to ensure that hydrogen fuel tanks remain intact.