Natural Gas VW Up! Tops Energy Efficiency Rating

Volkswagen AG says the natural gas-powered version of its Up! minicar emits only 79 g/km of carbon dioxide on the European test cycle.

Dubbed the Eco Up, the little four-seater went on sale in Europe earlier this month. VW, which unveiled a production version at the Geneva auto show in March, describes the car as the world's most efficient NG-fueled vehicle.

The Eco Up is powered by a variant of the 1.0-liter three-cylinder gasoline engine VW developed for the standard Up. When fueled with natural gas, the aluminum powerplant produces 50 kW (67 hp) and 90 Nm (66 lb-ft) of torque. The car needs more than 16 seconds to reach 100 kph (62 mph) and can eventually reach a top speed of 164 kph (102 mph), according to the company.

Two under-floor tanks with combined NG capacity of 71 liters give the car a range of 380 km (236 miles). VW says the car also can run on bio-methane.

The car is fitted with a 10-liter gasoline reserve tank that can be tapped to extend range by 220 km (137 miles). The engine uses gasoline for startups at temperatures below -10 C (+14 F). The powerplant also burns gasoline briefly after the NG tanks are filled until it can determine the quality of the gas and adjust engine mapping accordingly.

Among the modifications made to the base Up engine to accommodate NG are a lower compression ratio (10.5:1 from 11.5:1), higher-voltage sparkplugs, reconfigured camshafts, reformulated catalytic converters and a switch to tougher materials for the valves, guides and seats. The engine controller's duties have been expanded to include managing the fuel system's gas pressure regulator.