HydroGen3 Zafira-based fuel cell project is further developed and will be unveiled at the Frankfurt Motor Show.

Significant advances in the Zafira-based fuel cell project from Vauxhall and parent company General Motors will be unveiled at the Frankfurt International Motor Show next month.

With massive developments in the last two years on the HydroGen1 project, the new HydroGen3 prototype marks another milestone along the way to fitting passenger cars with environmentally compatible fuel cell propulsion.

Compared with its predecessor, the new prototype has shed substantial weight, dispensed with some components altogether, increased power output, improved range, and increased top speed to 93.5 mph.

Compared with its predecessors, the drive train of the new fuel cell Zafira has been modfied and reduced in size to allow for the components to fit more compactly into the vehicle which means more room for passengers.

Earlier this year in the heat of the Arizona desert, HydroGen1 (also powered by pure hydrogen) set 15 international records for fuel cell vehicles.

HydroGen3 development is carried out by Vauxhall/Opel and GM's joint Global Alternative Propulsion Centre (GAPC) based in Germany and the US.

Several road-going prototypes of the five-seater fuel cell Zafira will undergo the same rigorous heat, cold, height and stamina trials to which production vehicles are subjected.

The primary aim of the HydroGen3 development has been to improve the performance and day-to-day use of the propulsion system.

During the huge development stages, some of the components needed in HydroGen1 have been dispensed with altogether, among them the high-performance buffer battery. Previously this energy-storage unit dealt with performance peaks in the drive unit, but is superfluous now that the GAPC engineers have developed the fuel cell system so dynamically that it can provide the immediate power on its own.

This has saved nearly 100 kgs in weight, and allowed the floor height of the load area in the hydrogen-powered Zafira to be the same as that of the production-line model.

Now, HydroGen3 has the same full load space of the production Zafira in the five-seater arrangement.

Other recent developments in the fuel cell system mean that the water produced in the cells from the reaction between the hydrogen and the oxygen is enough to cover the moisture requirements of the fuel cell membranes, so additional external humidifying components for the cells are no longer necessary.

The electrical traction system has also undergone further development, and is now more compact. The complete module, comprising the DC/AC converter, electric motor, and transmission with park position and differential, is placed between the voltage transformer and the drive shaft, and weighs only 92 kilograms. There is electrically operated air conditioner and a complete diagnosis system.

Further major advances mean that the tank filler coupling of the stainless steel tank (one metre long, 40 centimeters in diameter), in which the hydrogen for the fuel cell Zafira is stored in liquid form at a temperature of -253C, is now much easier to connect.

The coupling is also compatible with the hydrogen fuel station at Munich airport and with the planned filling facility for the large-scale US trial entitled the "California Fuel Cell Partnership".

The twin-walled tank, in front of the rear axle below the rear seat, has a capacity of 68 litres or 4.6 kilograms of hydrogen, sufficient to give HydroGen3 an operating radius of around 250 miles. The fuel cell stack now consists of a block of 200 fuel cells connected in series. With dimensions of 472 x 251 x 496 mm (length x width x height) it is now significantly smaller than the fuel stack used in the HydroGen1 (590 x 270 x 500 mm.) The power density of the fuel cell block ? which operates at a pressure of 1.5 to 2.7 bar ? has been increased to 1.60 kilowatt per litre or 0.94 kilowatt per kilogram compared with 1.10 kilowatt per litre or 0.47 kilowatt per kilogram with HydroGen1. This has enabled the GAPC engineers to move another step closer to their goal of 2.0 kW per litre.

The stack on board HydroGen3 develops a constant power of 94 kW (previously 80 kW) and a peak of 129 kW (previously 120 kW). This environmentally compatible powerhouse, in which hydrogen and oxygen react electrochemically to form water at a temperature of 80 degrees Celsius, generates between 125 and 200 volts of electrical energy, depending on load conditions.

The direct current generated is converted into alternating current (250-380 volt) and fed to a 60 kW (82 hp) three-phase asynchronous motor. This unit, with its maximum torque of 215 Nm and maximum 12,000 rpm, drives the front wheels via a planetary transmission with a gear ratio of 8.67:1. It gives the fuel cell Zafira a 0-62mph time of 16 seconds and a 93.5 mph top speed.