Trends: GM Natural Gas Vehicles

Just because General Motors stopped selling natural gas vehicles (NGVs) in North America a number of years ago doesn’t mean the automaker has abandoned the development and sale of these clean fuel vehicles. Over the years GM’s Opel division in Germany has built more than 58,000 NGVs. This makes Opel the second largest producer of such vehicles in Europe where NGV sales are booming. Over 75,000 NGVs have been sold in the five largest European CNG markets (Germany, Italy, Sweden, Austria, and Switzerland) in the first nine months of 2008. Some 82,000 CNG vehicles were sold in 2007.

In 2001, Opel pioneered its compressed natural gas (CNG) engines with its innovative ‘monovalent plus’ technology. Monovalent plus is between a monovalent (or mono-fuel) NVG that runs only on natural gas and bivalent (or bi-fuel) NVGs that can use both natural gas and gasoline. Opel’s monovalent plus engines features dual sequential injection banks, one for gas and one for gasoline. Bivalent engines use common injectors for both fuels. There are also special pistons for the higher combustion ratios needed as well as special valves, valve guides, and valve seats designed for natural gas combustion.

Today, Opel sells two CNG vehicles, the Zafira 1.6 CNG ecoFLEX minivan and the Combo 1.6 CNG ecoFLEX high roof van. About 26 percent of all CNG vehicles sold in Europe in the first nine months of 2008 were compact vans. They are very popular with taxi and commercial fleets as well as with families. The 94 horsepower (69 kilowatt) 1.6-liter engine can run on natural gas, biogas, or any mixture of the two, as well as gasoline. Biomethane or biogas produced from organic waste materials is growing in popularity in Europe.

CNG is stored beneath the floor in four high-pressure gas tanks located around the rear axle, thus interior space and function are not affected. The Zafira features a Flex7 seating system so the interior can be quickly converted from a seven-seater to a two-seater without complicated procedures to remove the seats. There is also a 3.7 gallon (14 liter) gasoline tank that allows driving should CNG not be available. The CNG Zafira has a combined fuel operating range of more than 310 miles (500 kilometers).

Opel has now launched a more powerful CNG fueled Zafira with a 1.6 liter engine equipped with a turbocharger. The new Zafira 1.6 CNG Turbo has an output of 150 horsepower (112 kilowatts) and maximum torque of 210 newton-meters (155 lbs-ft). With a 60 percent increase in horsepower and a top speed of 124 mph (200 km/hr), the turbocharged version produces only 6 grams/kilometer more CO2 emissions – 144 g/km versus 160 g/km – compared to the naturally aspirated version. Total range is 322 miles (520 kilometers), with a 229 mile (370 kilometer) driving range available on CNG and a 93 mile (150 kilometer) range on gasoline.

According to General Motors, CNG vehicles produce almost no soot particles, 20 percent less CO2 than a comparable gasoline model, and an up to 80 percent less other harmful emissions. They are also cheaper to operate – about 50 percent lower than a comparable car running on gasoline – primarily because of favorable tax policies for NGVs in Europe.