Chevrolet will put a bi-fuel gasoline compressed natural gas (CNG) Chevy Impala on sale in the summer of 2014 as a 2015 model. The CNG-gasoline fueled Impala will solve the range limitation problem of CNG-only fueled cars, according to an announcement by GMC chairman and CEO Dan Akerson on the 40th anniversary of the OPEC oil embargo of 1973.
Akers released few details on the CNG-gasoline Impala. However, such vehicles are intended to run primarily on compressed natural gas, using gasoline as a “range extender,” much like the on-board gasoline engine is used to recharge the batteries of the Chevrolet Volt and forthcoming Cadillac ELR. Akerson’ statement didn’t, however, say which engine would be used.
Natural gas is burned in a GNG-fueled vehicle much like gasoline, but typically requires changes to allow the use of a gaseous as opposed to liquid fuel as well as the burning characteristics of both fuels. Natural gas—the same stuff that’s used to heat houses— is a cleaner-burning transportation fuel compared to petroleum products, and is significantly cheaper than gasoline at current prices. CNG vehicles typically have 20 percent fewer “greenhouse gas” emissions than gasoline-powered cars, according to the California Air Resources Board.
The CNG-fueled Chevrolet Impala won’t be the first such vehicle sold by GM to fleets as well as individual consumers. Chevrolet Silverado 2500 HD and GMC Sierra 2500 HD extended cab pickups went on sale in late 2012. Powered by a CNG-ready 6.0-liter V-8 that can switch seamlessly between compressed natural gas and gasoline, the full-size pickups are capable of a maximum range of 650 miles.
The compressed natural gas fuel systems of the Silverado and Sierra is installed by a General Motors supplier after coming off the GM assembly line, the completed vehicle delivered directly to the customer.
About the same time as GM, the Chrysler Group’s gasoline-CNG Ram 2500 pickup became available to retail customers in late 2012. Produced on the company’s pickup truck assembly line in Mexico, the natural gas-gasoline powertrain allows the boast that the “2012 Ram 2500 CNG is the only OEM-built compressed natural gas-powered pickup truck in North America.”
The Ram 2500 bi-fuel is powered by a 5.7-liter Hemi V-8 has both a compressed natural gas storage tank and a choice of eight- or 35-gallon gasoline fuel tanks. Further changes to make V-8 run on both fuels include redesigned cylinder heads, CNG-compatible valves and valve-seat materials, a second, CNG-specific fuel rail and set of injectors, new spark plugs and of course a new powertrain control modules.
A full-size pickup, however, has much easier packaging opportunities than the tighter confines of even a full-size sedan such as the Chevrolet Impala. The Impala will lose significant trunk space to accommodate the second tank, much as hybrid versions of existing models sacrifice cargo capacity to batteries.
On the other hand, CNG is significantly more energy dense than hydrogen, as used in the hydrogen-gasoline bi-fuel BMW H7 research vehicle. And instead of having to be manufactured like hydrogen, natural gas is abundant thanks to the current natural gas boom in the United States and Canada.
“We know that U.S. energy security won’t come from a one-off moonshot,” Akers said. “It will flow from our systematic investment in technology and innovation… our drive to get more from existing energy sources and renewables… our commitment to conservation… and it will be assured by fully and safely exploiting our shale gas reserves.”