Hydrogen is very attractive as an alternative to fossil fuelsas it can be combined with oxygen in a fuel cell to produce electrical energyheat and water.
Unlike burning fossil fuelsthere is no carbon dioxidecarbon monoxideoxides of nitrogen or sulphuror particulates. If the hydrogen is electrolysed from water using electricity that has been generated using a ‘clean’ source – such as windwavetidal or solar energy – then it is very environmentally-friendly.
The fuel cell concept has existed since the mid-nineteenth century but it was only in the second half of the twentieth century that fuel cell research led to units being produced commerciallyalbeit in small numbers. Nowwith record oil prices and concerns over global warmingfuel cell development has reached a point where there are units available for a variety of applicationsfrom automobiles to lighthouses (see panel).
Given the prevalence of automobilestheir combined fuel consumption and their contribution to global warmingit is only to be expected that a substantial amount of research is being undertaken into hydrogen fuel cells for automotive applications. Honda was the first carmaker to put a fuel cell car on the road with regular customersdelivering the Honda FCX to fleet users in the USA and Japan in 2002. The company has now unveiled a fuel cell vehicle that delivers superior environmental performance and is said to be fun to driveknown as the FCX Clarity (Fig.1)which is due to be available in the summer of 2008. Startup and acceleration times are claimed to be comparable to those of a similarly sized car with a 2.4-litre internal combustion engine.
Honda’s engineers set out to design a car with components optimised to give an enjoyable driving experience. One result of this was the V Flow Honda FC Stackwhich is a lightweightcompacthigh-output fuel cell stack. Compared to the 2005 FCX stack designthe V Flow FC Stack features an entirely new cell structure that achieves a higher output of 100kWsmaller size and lower weightwith a 50percent improvement in output per unit volume volumeand a 67percent increase in output per unit mass. Because the new stack uses a vertical flow of hydrogen and oxygen instead of the more conventional horizontal flowwater drains away more easilypower generation is more stable and the stack’s size and weight are reduced (Fig.2). Another feature of the stack is wave-shaped flow channels that improve hydrogen and air diffusionthereby helping to improve the electricity generation performance.
To complement the hydrogen fuel cell stack and provide additional power for accelerationthe FCX Clarity has a compacthigh-efficiency lithium ion battery to store electricity from regenerative braking.
The engineers also made the fuel cell systemdrive motorhydrogen storage and other powertrain components more compactand took advantage of the fuel cell vehicle’s layout possibilities to create a revolutionary new platform with a low centre of gravity for sportystable driving performance. The fuel cell stack is housed in the central tunnelthe battery is under the rear seat and the hydrogen fuel tank is located between the rear wheels.
Automotive fuel cells
Daimler AG is also investing heavily in fuel cell vehicles. In November 2007 the company announced that it was taking a 50.1 per cent stake in the Automotive Fuel Cell Co-operationa company founded specifically for developing fuel cell applications in the automotive sector. The two other companies involved are Ford Motor Company and Ballard Power Systems. Dr Thomas Weberthe member of the board of management of Daimler AG with responsibility for group researchas well as for development within Mercedes-Benz Carsstated: "At Daimlerwe have identified the future fields of activity and key technologies for zero-emission mobilityand we invest specifically in expanding our competencies in these fields. Our majority stake in Automotive Fuel Cell Co-operation is the next consequent step in this direction."
Professor Dr Herbert Kohlervice president with responsibility for advanced vehicle and powertrain engineering within group research as well as being the chief environmental officer of the Daimler Groupadded: "With the newly founded companywe pursue the aim of strengthening our leading position in fuel cell development and going full steam ahead in our preparations for the large-scale production of fuel cell cars."
Following successful low-temperature trials held in Sweden using a fuel cell-powered Mercedes-BenzB-Classthe company reports that it isindeedon target to commence small-series production of the B-Class F-Cell model in early 2010 (Fig.3).
Honda and Daimler are two of the world’s mainstream automotive manufacturers that are taking hydrogen power seriouslyand there are plenty of others too – such as BMWFordGeneral MotorsPeugeot Citroën and Volkswagen. But hydrogen fuel cell technology is not restricted to just major manufacturers. OSCar Automotivewhich is owned by RiverSimplehas initiated two collaborative projects involving industry and academia to demonstrate the viability of hydrogen fuel cell cars using currently available technology. These projects are delivering two concept cars: LIFECara hydrogen fuel cell sports car developed with the Morgan Car CompanyLinde and QinetiQ (Fig.4); and Hyrbana lightweight city car. Both projects involve research teams at Cranfield and Oxford Universities. The LIFECar prototype was unveiled at the Geneva Motor Show in March 2008 and RiverSimple’s Hyrban city car is due to be revealed in the autumn of 2008.
RiverSimple says the LIFECar (lightweight integrated fuel-efficient car) summarises the company’s three key design principles: whole-system designenergy efficiency and resource minimisation (Fig.5). Hugo Spowersthe founder of OSCar Automotive and managing partner at RiverSimplesought to demonstrate with the LIFECar project that significant gains in fuel efficiency could be achieved with readily available technology – though the state of the art is advancing rapidly (see panel). In order for this project to take placeand with the support of the Morgan Motor Companyhe formed the LIFECar consortium with Cranfield UniversityLindeOxford University and QinetiQ; together they received financial support from BERR (the UK Government’s Department for EnterpriseBusiness and Regulatory Reform) for the project that had a budget of less than £2million (around US$3.9million or
The LIFECar combines a hydrogen fuel cell with a bank of ultracapacitors – rather than batteries – such that cruise and acceleration requirements are decoupled and resolved in a highly optimised fashion. By combining these technologies with a lightweight structurethe LIFECar is intended to achieve a combination of performancecost-effectiveness and fuel efficiency.
To keep the weight down to the target of 650kgthe LIFECar’s design uses technologies that Morgan currently employs in its Aero8including bonded aluminium and laminated wood. For the hydrogen fuel tankcarbon fibre is wound around a drum.
Oxford University undertook the design of the electric motorswhich are reported to be 92–94percent efficient across their operating range. Four motors are usedall mounted inboard to minimise the unsprung weight and help to improve the car’s ride and handling. Drive to each wheel is via a small gearbox (Fig.6).
Crucial to the success of the vehicle will be the PEM (polymer electrolyte membrane) fuel cell stackand this has been provided by QinetiQ to meet the specific needs of the LIFECar. Consisting of four 6kW sub-stacksthe complete fuel cell achieves a quoted efficiency of 45percent. Furthermorethe regenerative brakes are said to enable up to 50percent of the kinetic energy to be converted to electricitywhereas the norm for regenerative braking is typically around 10percent. Cranfield University developed the management systems for the vehiclefuel cellultracapacitorsmotor/generators and hydraulic brakes – which are employed at low speeds.
Hydrogen fuel cells clearly offer a number of potential advantages over conventional internal combustion engines burning fossil fuelsbut there remains the issue of refuelling unless onboard hydrogen generation (sometimes called hydrogen-on-demand) is employed. For the LIFECar projectLinde provided the hydrogen refuelling expertise.
Another company with experience in hydrogen refuelling is Air Products. In April 2008 Air Products commissioned a Series100 fuelling station at the University of Birmingham’s Department of Chemical Engineeringwhere research projects are being carried out to ascertain the viability of hydrogen in transport applications (Fig.7). Engineers from the University will be comparing five hydrogen-powered vehicles with the University’s own fleet of petroldiesel and pure electric vehicles so that they can learn more about their efficiency and performance. The researchers will determine how these vehicles need to be adapted in order to make hydrogen an attractive and cost-effective option as a future fuel. Five Microcabs have been purchased for the purposes of the research; these weigh 500kghave a maximum speed of 64km/h (40mph) and a range of approximately 160km (100miles).
As a direct result of this research it is hoped that the public sector will start to buy into these new technologiesproviding support to companies in the supply chain that are moving from the technology demonstration phase into the early stages of commercialisation.
The Series 100 station has been specially designed by Air Products to meet the fuelling needs of the first hydrogen vechicles to appear on the roads. It comprises an intergrated compressionhydrogen storage and dispensing systemand is optimised to fuel up to approximately six vehicles a day. The hydrogensupplied bt Green Gasesis produced by 'green' meansresulting in a considerable reduction in greenhouse gas emissions when compared with conventionally produced hydrgen.
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