Environmentally-friendly mobility powered by natural gas
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Unlike other gas-powered vehicles in its class, the Zafira CNG features the 'monovalent plus' operating mode, which combines the advantages of the monovalent and bivalent systems. Four large-capacity CNG tanks provide an operating range of up to 350 kilometres in the natural-gas operating mode, and there is an extra spare petrol tank installed between the gas tanks. Its capacity of only 14 litres is so small that the Zafira CNG can be classed as a monovalent vehicle. In emergencies, the petrol provides an additional operating range of about 150 km – enough to bridge supply gaps in the natural-gas filling station network.
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Concept
In keeping with the general trend, the problem of accommodating the gas container and components without encroaching on the load space, which is always a problem when a car is modified to run on natural gas, has been solved in the Zafira CNG by means of an underfloor tank. The entire fuel-tank system, consisting of four natural-gas cylinders and the above-mentioned petrol tank, was divided into two separate groups – one in front and one behind the rear axle. For additional crash safety the two systems are mounted in safety cages made of high-strength special steel tube.
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Project handling
Bertrandt Rüsselsheim’s project work began in November 2000 with the collection of data on CNG components such as the tank unit, its plastic covers and the tubular frame from a prototype car ready for service. Package investigations of the bodyshell, floor pan assembly and chassis were followed by detailed designs for the structural components of the exhaust system and its fastenings, the fuel pipe systems, the tank filler neck and various engine parts.
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The inlet manifold flange, for example, can be considered a central engine component. It is the link between the induction pipes and the cylinder head, and is the point where fuel delivery takes place. For natural-gas vehicles, a natural-gas injection system therefore had to be added to the existing fuel-injection system.
The integration of new injector nozzle seats proved problematic. Because their intended position collided with an existing water duct, the duct had to be repositioned. In the initial prototype parts, the cast canal was eliminated so that the coolant was re-routed by means of a fabric hose, but for package reasons, this solution had to be modified for series production. The water duct was integrated into the cast part again at a different position. This also called for revision of the remaining connecting points and openings. The new design had to take into account the need to machine the new casting on the same machines as the original production parts for petrol-engined vehicles.
Examination of the structural components mainly extended to dimensional stability and a functional check on the prototype car. In addition to design tasks, we were also responsible for data management and the final release process for all the components.
Our entire team worked on the design over the full project period through to production launch in January 2002. The follow-up Astra CNG project shows that we have acquired expertise in the promising alternative fuel systems market segment, which we can apply effectively for the benefit of our customers. |
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