Reducing U.S. dependence on imported oil and cutting the amount of emissions spewed into the atmosphere are desirable goals. There are numerous ways to pursue these goals, and GM is working on several of the most promising.
Reducing fuel consumption is the name of the game. Not by moving to increasingly smaller vehicles, but by making the larger vehicles businesses and individuals require more fuel efficient.
One easily obtainable alternative to petroleum-based gasoline is E-85 ethanol-based fuel. E-85 stands for fuel that is 85-percent ethanol and 15-percent gasoline. Currently, the GM 5.3L V-8 is E-85 compatible, and it lives in the engine bays of a host of truck and car models. Vehicles that can run on E-85 as well as gasoline are called Flexible-Fuel Vehicles (FFVs) and usually carry a badge indicating this capability.
Most ethanol used in E-85 today in the U.S. is derived from corn, but new technologies are being developed to produce ethanol from biomass waste material.
E-85 fuel has a higher octane than gasoline, so vehicles can be tuned for better performance on it. The downside is that it has lower energy content, so actual fuel mileage is reduced.
The major automakers, including GM, have committed to adding more than 1 million FFVs to the nation’s fleet in 2007 alone. In a report to President Bush, they explained that if all these vehicles were running on E-85, more than 3.6 billion gallons of gasoline would be displaced each year.
Another technology that uses the country’s vast agricultural reserves is biodiesel. Biodiesel fuel replaces a portion of the petroleum products used in diesel fuel with vegetable oil, made from plant byproducts. Biodiesel is rated by the percentage of vegetable oil mixed into the final fuel. Biodiesel B-5 is 5-percent biodiesel; biodiesel B-20 is 20-percent biodiesel. If all diesel vehicles on the road today used B-5, it would displace 1.85 billion gallons of petroleum each year; 7.4 billion gallons if B-20 were used.
Current GM light trucks with the 6.6L Duramax engine are certified for B-5, and certification for B-20 is underway. A 4.5L version of the Duramax is under development for the 2009 model-year, and diesel passenger car engines are also in development.
The Two-Mode Hybrid
In conjunction with other manufacturers, GM is developing a two-mode hybrid system. This new powertrain will appear first on the 2008-model Tahoe and Yukon SUVs. GM says, “With the addition of the light-duty two-mode full hybrid propulsion system, the Chevrolet Tahoe and GMC Yukon two-mode hybrids will deliver a 25-percent improvement in fuel economy.
The Vortec V-8-powered two-mode hybrid is expected to deliver a composite fuel efficiency improvement of 25 percent when combined with GM’s active fuel management cylinder deactivation technology.” The two-mode system is essentially an electrically variable transmission with two hybrid-drive modes. It will reduce fuel consumption at highway speeds much more effectively than available single-mode systems and achieve up to a 25-percent improvement in composite fuel economy in full-size truck applications.
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