Posted by: carboncreditsusa | November 29, 2008

“Hydrogen Fuel-Cell Vehicles”: VW Introduces Passat Lingyu Project At 2008 L.A. Auto Show


Having eschewed the idea of hydrogen fuel cells for years, Volkswagen now finds itself with three distinct fuel-cell projects, which it laid out at the recent Los Angeles Auto Show.

The first and most prestigious is the company’s high-temperature, phosphoric-acid fuel cell, which we’ve already written about in Telegraph Motoring (March 16, 2007). The drawbacks of a conventional water-based electrolyte fuel-cell are its boiling and freezing points. A fuel cell must run lower than 100°C or the water is boiled off as steam. Water management is also a problem as the gases tend to dry out the cell, which inhibits the path of the protons – the cell has to be fed with humid air to prevent it drying. In addition, the water has to be purged from the cell after each use, because in cold weather it can freeze and damage the cell. And the incoming air has to be carefully filtered: impurities can also damage the cell.

Phosphoric acid has similar electrolytic properties to water but a higher boiling point. The idea is that the stripped hydrogen protons use the molecules of phosphoric acid rather than water to transfer the charge across the cell. The benefits are that the phosphoric acid cell can withstand high temperatures and therefore requires less cooling, and because the gas doesn’t dry out the membrane, there’s no need for a humidifier, which saves weight, cost and space.

The trouble is, commercial phosphoric acid fuel cells need to operate at their peak 160°C – any lower and there’s a danger that the exhaust steam turns to water and leaches the acid out of the cell. The different thermal loading imposed by idling, shunting through traffic and full-speed operation means that automotive fuel cells operate at widely different temperatures so, up to now, phosphoric acid cells in cars have been a big no-no.

VW thinks it has invented a way of keeping the acid in the cell while allowing different thermal cycles. The trick is a secret coating on the electrodes that prevents the acid escaping. VW soaks the PBI (PolyBenzImidazole) fuel-cell membrane in phosphoric acid, which permeates the heat resistant, wafer-thin material. The membrane is then cut into shapes and sandwiched between coated carbon tiles. The whole assembly is then sealed between compressed carbon plates, which have etched surfaces to allow the inflow of hydrogen and oxygen. Everything is hand-assembled at present, with hydraulic presses applying 180psi to the whole cell stack before it is bolted together.

VW is talking about potential efficiency improvements in the order of 20 per cent over a water fuel cell, about a 33 per cent decrease in the size and weight of cooling requirements, the lack of a humidifier and reduced need for special air filtration because acid fuel cells are much more tolerant of impurities.

More startling are the power gains. VW has calculated that the cooling capacity of the Touareg research vehicle limits its conventional Ballard 900 series fuel cell to a maximum continuous speed of 87mph, which falls to just 30mph on a six per cent gradient. The equivalent figures if the Touareg used a phosphoric acid fuel cell are 120mph and 62mph.

But progress has been slow and although VW is promising a driving prototype by 2010, there was no sign of the high-temperature fuel cell when we were invited to drive the other big news project at the LA Auto Show last week. This was the fuel-cell powered Passat Lingyu, which has been developed in China as part of a joint research project between VW Group Research, Volkswagen Shanghai and Tongji University. There are currently more than 40 engineers working on the project.

Unlike the Ballard-equipped fuel-cell Touareg, which was provided for comparison purposes, the Passat Lingyu’s fuel-cell was developed entirely by the university and is the fourth generation unit to come out of Tongji. The unit produces 73.8bhp, which feeds a lithium-ion battery with a capacity of 8Ah at 376 volts, as well as the 118bhp/155lb ft electric motor that drives the front wheels. The 3.2kg of gaseous hydrogen fuel is stored on board at 5,000psi in a spun carbon-fibre tank.

While the Ballard-equipped Touareg whined around the route with so little drama it was possible to imagine it was a production car, the Passat Lingyu was slower and a lot more vocal. Its compressor was loudly whirring under the bonnet and the exhaust constantly spat water onto the road surface. Top speed for the 1.8-ton car is quoted at 87mph and the range is about 124 miles. In LA’s fast moving traffic, however, the acceleration wasn’t enough to keep up and the Passat bobbed and weaved like an underpowered ship in a storm.

On the plus side, the car was very well insulated and the driving experience was serene, without the snap acceleration that characterises most electric drivelines. The lithium-ion battery is used to augment the fuel cell during peak acceleration, although its power quickly ran out in sustaining foot-to-the-boards running and the Passat’s mini charge was over almost before it had begun.

You might wonder why VW doesn’t just give the university its Ballard-powered Touareg and let them get on with it, but that isn’t China’s way. It wants to develop the skills and knowledge base to make its own fuel-cell cars and VW is happy to nurture the talent rather than take over. General Motors found the same attitude when it tried to sell the Chinese government its fuel-cell knowledge a few years ago. The Chinese want help and co-operation, not turn-key solutions that keep them out of the intellectual property rights. Judging by this fuel-cell drive, they’re on their way, too.

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