Tech Briefs
Zafira's new fuel cell unveiled at Geneva

GM says the Opel Zafira fuel-cell stack achieves full power nearly 12 times faster in freezing conditions than a similar design achieved recently.

The Opel Zafira exhibited at the Geneva Motor Show is a demonstration fuelcell vehicle based on GM's popular European passenger van. GM will use the vehicle to test global fuel-cell technology on the road this year. Six months ago, GM demonstrated a fuel-cell stack that at -20°C (-4°F) took over six minutes to achieve full power. The current generation fuel-cell stack now achieves significant power levels quicker at even lower temperatures. At -20°C (-4°F) full power is achieved in just 30 seconds and at -30°C (-22°F) just 60 seconds.

The fuel-cell stack is GM's seventh generation, with several more generations in development. GM claims its seventh-generation stack is 15% better in volumetric power density than the nearest competitor's fuel cell, developing more power in a head-to-head comparison than any automotive fuel cell known today. GM engineers are also focused on making the fuel cell affordable without sacrificing performance. Fuel-cell stacks under development target issues that drive cost, including component materials, design for manufacture, and precious-metal content.

Apart from water vapor, the Zafira produces no emissions. Its 55-kW (75-hp) three-phase ac traction motor is supplied with electrical energy from a fuel-cell unit operating on pure hydrogen. The Zafira is a road-going project capable of carrying five people and achieving a top speed of 140 km/h (87 mph). Its range is about 400 km (250 mi), and demonstrates one aspect of the experimental work for some 200 scientists and technicians at the German and U.S.-based Opel/GM Global Alternative Propulsion Center (GAPC).

Opel showed its first experimental vehicle powered by this technology at Geneva in 1997, and a second vehicle—based on the current Zafira—at the Paris Motor Show in 1998. Whereas both of these experimental vehicles converted methanol to hydrogen-rich gas in a reformer, the fuel-cell unit of the latest experimental vehicle obtains its energy directly from a special tank. At this year's North American International Auto Show, GM presented the Precept FCEV (fuel cell electric vehicle), which features an advanced, compact chemical hydride system for onboard hydrogen storage.

In the fuel-cell Zafira, the cylindrical hydrogen tank has a length of about 1 m (3.3 ft) and a diameter of 400 mm (16 in). It stores up to 75 L (20 gal) of liquid hydrogen fuel weighing only about 5 kg (11 lb) at a temperature of -253°C (-423°F). This low temperature is made possible by glass-fiber mat tank insulation, which has the same insulating properties as a layer of polystyrene several meters thick. The stainless steel tank is stowed under the second row of seats and the baggage compartment, and can withstand an acceleration force of up to 30 g. The second row of seats and the baggage area of the concept Zafira are 30 and 100 mm (1.2 and 3.9 in) higher than in the volume-production Zafira.

The fuel cells and the electric motor are situated under the front hood. The stack of fuel cell units assembled by the GAPC experts occupies an area of 590 x 270 x 500 mm (23.2 x 10.6 x 19.7 in). Its working principle is based on an electrochemical process in which hydrogen reacts with oxygen to produce direct electrical energy. The Zafira stack has a maximum output of 80 kW (107 hp), generated by the 195 single cells in the block at a process temperature of about 80°C (176°F).

Their electric current is supplied to a 55-kW (74-hp), three-phase, ac synchronous electric motor, which drives the front wheels through fixed-ratio gears. The complete unit has a mass of only 68 kg (150 lb). The motor's maximum torque of 251 N•m (185 lb•ft) is available all the time and accelerates the fuel-cell version of this compact van, with a mass of 1575 kg (3472 lb) compared with the standard Zafira's 1425 kg (3142 lb), from a standstill to 100 km/h (62 mph) in 16 seconds. The electric motor can reach performance peaks of 60 kW (82 hp) and a maximum torque of 305 N•m (225 lb•ft).

The development of fuel-cell technology fully suitable for everyday use is receiving additional impetus from strategic alliances with other OEMs and a number of mineral oil companies. The most important joint objectives include setting up the necessary infrastructure, the reduction of costs, and the development of lighter and more compact fuel-storage technology for the fuel of the future. This is, according to GAPC Co-Director Dr. Erhard Schubert, "most definitely hydrogen, because a propulsion system using hydrogen fuel cells has optimum efficiency, emits nothing but water vapor, runs practically noise-free, and offers at the same time a high degree of driving pleasure."

Jean L. Broge