8. August 2001

Future propulsion system on show at Opel's stand at the IAA

"HydroGen3" Fuel Cell Study Moves Closer to Volume Production

Significant advances in the environmentally friendly Zafira-based project

Rüsselsheim. The new "HydroGen3" prototype from Opel and GM marks another milestone along the way to fitting passenger cars with an environmentally compatible, resource-sparing fuel cell propulsion system. Compared with its predecessors the drive train of the new fuel cell Zafira has been improved to allow optimum packaging of the individual components in the vehicle. Opel and GM's expertise in the field of fuel cell propulsion was underlined by the HydroGen1 (also powered by pure hydrogen) in high-temperature tests in the US state of Arizona, during which it set a total of 15 international records for fuel cell vehicles. Opel will be presenting the pioneering concept of the HydroGen3 fuel cell study to a broader public for the first time at the coming IAA Motor Show (September 13 - 23) in Frankfurt with the aid of a cut-away scale-model.

The development of the new HydroGen3, which, like its forerunners, is based on the successful Zafira compact van, is the responsibility of Opel and GM's joint Global Alternative Propulsion Center (GAPC) with sites in Mainz-Kastel in Germany and Warren and Rochester in the USA. In the coming months, several road-going prototypes of the five-seater fuel cell Zafira will undergo the same rigorous heat, cold, height and stamina trials that production vehicles are subjected to.

The primary aim of the HydroGen3 development was to improve the performance and day-to-day use of the propulsion system. As part of the project, some of the components that were necessary in the HydroGen1 were dispensed with altogether – a useful side-effect that has further reduced the weight of the vehicle towards the target of 1590 kilograms. The most prominent component the development team managed to do without in the HydroGen3 is the high-performance buffer battery. Previously this energy-storage unit had the job of dealing with performance peaks in the drive unit, but it has become superfluous now that the GAPC engineers have optimized the fuel cell system so dynamically that it can provide the required power immediately on its own. Not only has this saved nearly 100 kilograms in weight, it also has the advantage that the floor height of the load area in the hydrogen-powered Zafira is now the same as that of the production-line model, so that the full loading space of the Zafira in the five-seater arrangement is also available in HydroGen3.

The optimization of the architecture of the entire fuel cell system has meant that the water produced in the cells as a result of the reaction between the hydrogen and the oxygen is enough to cover the moisture requirements of the fuel cell membranes. This obviated the need for additional external humidifying components for the cells, creating yet more extra space and weight savings.

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, which is placed between the voltage transformer and the drive shaft, weighs only 92 kilograms. Apart from this, it can be mounted on the existing Zafira supports, which represents a further step towards production line capability. Yet another advance is the significant improvement in comfort to be found in HydroGen3 compared with its predecessor. An electrically operated air conditioner now provides the occupants with cool air on a hot day. The vehicle also features a complete diagnosis system to keep the driver informed of the status of all the systems.

The major advances made by the entire HydroGen project are also evident in a number of seemingly trivial details. For example, the tank filler coupling of the stainless steel tank (1 meter long, 40 centimeters in diameter), in which the hydrogen for the fuel cell Zafira is stored in liquid form at a temperature of -253°C, 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 trial "California Fuel Cell Partnership". The twin-walled tank has a capacity of 68 liters or 4.6 kilograms of hydrogen. Its interior is insulated against heat conduction by a high vacuum between the exterior and interior walls. Extra layers of thin aluminum foil provide added protection against heat radiation. This volume is sufficient to give HydroGen3 an operating radius of around 400 kilometers. The tank is positioned in front of the rear axle below the rear seat, which has been raised by 25 millimeters to accommodate it. The complete tank system (including valves, heat exchanger and supports) weighs 90 kilograms.

A look under the hood of the latest fuel cell Zafira reveals just how much progress has been made with Opel and GM's fuel cell technology since its beginnings some 30 years ago. Surrounded by heat exchangers and cooling water circuits, the first thing to strike the eye is the fuel cell stack, which has a much improved specific output compared with its predecessor. The stack -– after further development by the GAPC specialists – consists of a block of 200 fuel cells connected in series. With its dimensions of 472 x 251 x 496 millimeters (length x width x height) it is now significantly smaller than the fuel stack used in the HydroGen1 (590 x 270 x 500 millimeters). On the other hand, the power density of the fuel cell block – which operates at a pressure of 1.5 to 2.7 bar – has been increased. It is 1.60 kilowatt per liter or 0.94 kilowatt per kilogram compared with 1.10 kilowatt per liter or 0.47 kilowatt per kilogram with the HydroGen1. It has enabled the GAPC engineers to move another step closer to their goal of 2.0 kW per liter.

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 in this manner is converted by an electronic control element 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 Newton meters, and a maximum speed of 12,000 rpm, drives the front wheels via a planetary transmission with a gear ratio of 8.67:1. With this highly effective driveline, the fuel cell Zafira travels from 0 to 100 km/h in 16 sec, and has a top speed of 150 km/h. These statistics – like the details of the engineering and architecture on show at Opel's IAA stand – prove just how close Opel and GM's fuel cell vehicle now is to volume production.