New Energy Carriers for Propulsion Systems – A Literature Review Study with a focus on confined spaces safety aspects

For decades, most road transport has relied on internal combustion engines powered by fossil fuels. In recent years, however, driven by the need to change the road transport energy source from fossil fuels to carbon free sources, alternative propulsion technologies (most notably battery-electric vehicles) have begun to play an increasingly prominent role. Although vehicles powered by so-called New Energy Carriers (NECs) still make up only a small share of the global fleet, their presence is expected to grow rapidly in the near term, driven by policy incentives and advances in fuel and powertrain technologies. Moreover, in certain specific applications such as airports and public transport, NEC vehicles fleets could be adopted sooner than in public road network traffic, creating environments in which NEC specific risks density and probability will be higher, thus requiring a specific approach in legislation, risk analysis and emergency management. This thesis presents an analysis of the current state of the art in NEC vehicles, based on a comprehensive review of scientific literature. The study focuses on emerging energy carriers, including electric systems, hydrogen, compressed or liquefied natural gas (CNG/LNG) and petroleum gas (LPG), with the aim of highlighting critical issues that are subject to scientific research, technological development and statistical investigation. Particular attention is given to safety aspects, especially in confined environments such as road tunnels and parking facilities, where operational risks may be amplified. The first 3 chapters provide a comprehensive overview of the main characteristics of the considered categories of NEC vehicles, at chapter 4 the current adoption of NEC vehicles in European Fleets of Light-Duty, Heavy-Duty and Public Transport Vehicles in terms shares distribution and recharging infrastructure development is provided as well. Safety aspect and hazard scenarios are discussed in chapters 5 and 6, reporting outcomes of several recent European research projects and providing a summary comparison at chapter 7. Emerged considerations about possible improvements in design of safety systems and safety measures are provided at chapter 8, while some examples of incidents involving NEC vehicles are reported at chapter 9.