Researchers in Zurich, Switzerland, are attempting to put a new wrinkle in the automotive hybrid tapestry by matching an internal-combustion engine with compressed air instead of battery-electric assist. According to Lino Guzzella, team leader and Professor of Thermotronics at ETH (Eidgenossische Technische Hochschule, aka the Swiss Federal Institute of Technology), this new combo powerplant can provide nearly 80 percent of the overall fuel efficiency benefits realized by a conventional gas-electric alternative but at a fraction of the incremental cost. The prototype currently being evaluated in the ETH labs has shown an 18-24 percent increase in economy on the European Test Cycle. It's reportedly capable of up to a 50 percent gain when operating in an urban traffic environment where the gasoline engine can more readily replenish the supply of compressed air.

The mechanical formula for the ETH hybrid is a familiar one that matches decreased displacement with a supplemental force-feeding circuit. Here, the engine's cylinder count has been halved from four to two, which cuts both weight and associated pumping losses. To compensate for that reduction, it's fitted with a high-efficiency turbocharger that brings power levels up to what's required to deal with real-world traffic. Supplementing that output is compressed air from the on-board tank, which passes through an electronically controlled valve to restart the engine from stops or supplement output after a gear change.

Guzzella reports that a number of automakers have expressed interest in the ETH gas-air hybrid design, which he sees as a particularly attractive and clean but cost-effective alternative for vehicles being manufactured for sale in developing countries. Research and results of the ETH program, as well as papers on pneumatic hybrid work currently being undertaken by other organizations, will be presented in April at the 2009 SAE World Congress in Detroit.

Photo: P. Ruegg/ ETH Zurich

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