Russelsheim, Germany - Opel is working on a compressed natural gas (CNG) hybrid drive system in cooperation with car parts supplier Bosch and the University of Stuttgart to combine a turbo engine with an electric motor.

A prototype based on an Astra Caravan and equipped with a start- stop-system achieved a carbon dioxide emission figure of just 90 grammes per kilometre, the car maker said.

The three-litre combustion engine has an output of 71 kW/97 hp. The electric motor supplied by Bosch add an additional 35 kW. Opel currently offers the Zafira CNG Turbo with an output of 150 hp and C02 emissions of 144 g/km. The Ampera, based on the Chevy Volt, is scheduled for European markets in 2011. It is fitted with both a combustion engine and electric motor. (dpa)