CompositesWorld
Issue link: https://cw.epubxp.com/i/450689
FEBRUARY 2015 24 CompositesWorld WORK IN PROGRESS » Most of the world's automakers are scrambling to increase fuel efciency and/or reduce greenhouse-gas emissions ahead of tough regulations that are phasing in between now and 2025. Toward that end, these OEMs are reducing vehicle mass and exploring alternative powertrains options (see "Learn More," p. 26). One of the most intriguing of the latter is the fuel cell. Although major technical and logistical hurdles must be cleared before we see widespread deployment, fuel-cell vehicle (FCVs) are under development or already in road testing. Fuel-cell electric powetrains are of great interest because the only combustion byproducts of their two most common fuels — hydrogen (H 2 ) and compressed-natural gas (CNG) — are water and heat, making zero-emissions vehicles (ZEVs) possible. One of the biggest hurdles is H 2 fuel storage. H 2 has been handled safely by industry for decades and can be produced locally, nearly anywhere, from diverse inputs (biomass, coal, geothermal, hydro- electric, nuclear, solar, wind, electrolysis of water, or even CNG). Tis fexibility is highly benefcial from a cost, energy security and lifecycle analysis standpoint. But this extremely light gas (14-times lighter than air) has three times more energy density by weight but far less energy by volume than conventional liquid petroleum fuels. Further, the hydrogen molecule is the world's smallest, so perme- ation resistance of storage containers becomes a real concern, lest fuel leak out. It's very difcult, therefore, to package H 2 in the small spaces available in most cars in sufcient quantity to duplicate the 500 km-per-tank driving range of today's petrol-powered cars, espe- cially when the goal is to do this without boosting vehicle mass. Although there are alternatives (see "H 2 storage methods," on p. 17), the most practical and least costly onboard H 2 storage method is as a compressed gas at working pressures of 20-70 MPa in tanks that must test out to a burst strength of twice their rated pressure. Storage challenges Today, four types of pressure vessel are available for H 2 storage (see "Learn More"). Type I (all-steel) containers are heavy and bulky. Type II tanks (steel or aluminum liners hoop-wound with carbon fber/epoxy) are lighter but cost more. Each is capable of up to 30 MPa working pressures and used for bulk transport or stationary gas storage at refueling stations. Similar to Type II tanks, but fully wound with carbon/epoxy composite, Type III tanks are even lighter but more costly, withstand higher working pressures (to 82.5 MPa, with aluminum liners) and are primarily used for H 2 or CNG storage on commercial trucks. Type IV tanks feature either high- density polyethylene (HDPE) or rubber liners fully overwrapped with carbon fber/epoxy. Te lightest but most costly, they ofer performance similar to Type III tanks. Unfortunately, certain metals and metal alloys tend to absorb H 2 , leading to embrittlement that reduces tank durability. And hybrid- material tanks are prone to fatigue at the mixed-material interface, which can limit useful life. Further, the epoxy matrix, a thermoset, complicates end-of-life reclamation, an added headache for auto- makers selling into the European Union. Generally, then, available tanks deliver insufcient weight-to-cost beneft, store too little fuel for adequate driving range, are difcult to recycle and/or lack sufcient durability for mass use on automobiles. Building a better tank In 2010, a multi-partner, multi-year research program called Low Cost, Durable Termoplastic Hydrogen Storage Tanks, or DuraStor, was formed to address these problems by investigating a drop-in replacement for Type IV tanks. Partially funded by Innovate UK (Swindon, Wiltshire, UK), DuraStor ended in early 2014, but a UK-only program called Hydrogen – Optimisation of Storage and Transfer (HOST) picked up where DuraStor left of in mid-2014, funded in part by the UK Technology Strategy Board, with the same By Peggy Malnati / Contributing Writer UK consortiums address durability, weight, cost of high-pressure tanks for hydrogen fuel-cell-powered vehicles. Thermoplastic composite pressure vessels for FCVs Thermoplastic Composite Pressure Vessels The U.K-based DuraStor and followup HOST consortiums were mobilized to fnd a safe and efcient way to store enough hydrogen or natural gas under high pressure to give fuel-cell-powered electric vehicles the equivalent driving range ofered by conventional liquid petroleum fuels and internal combustion engines. Thermoplastic composites have provided a likely solution. Preliminary testing on this carbon fber/ acetal tape-wound vessel (shown here partially and fully wound) indicates the completed vessel meets or exceeds all requirements. Source | DuraStor Consortium