Diesels will dominate the battle to improve fuel economy and air quality until fuel cells emerge, but gasoline-electrical hybrids also have an interim role.
That's the conclusion reached by a panel of auto industry researchers at the Society of Automotive Engineers World Congress in Detroit earlier this month.
Gasoline-electric hybrids such as the Honda Civic and Toyota Prius offer excellent economy in city driving. But they have expensive and complex powertrains, and fuel economy gains on the highway are negligible, panelists said.
Diesels are simpler, offer great low-speed performance and deliver higher fuel economy in city and highway driving. Diesels currently on sale in the USA emit far more pollution than future US regulations allow.
But European technology under development should enable diesels to meet the toughest standards on the books, the USA's so-called Tier 2 emission levels, which make no distinction between gasoline and diesel engines. And low-sulfur fuel scheduled to arrive in 2006 will help lower diesel emissions.
By 2009, when Tier 2 laws are fully phased in, US diesels must not emit more than 0.043 grams per kilometer (0.07 grams per mile) of nitrogen oxides.
European-market diesels such as the Peugeot 607 already can meet the 2009 standard. But the Volkswagen Jetta, New Beetle and Golf sold in the USA now emit more than 10 times that amount.
"There is hope," said Tom Cackette, chief deputy executive officer of the California Air Resources Board. Citing the Peugeot 607 sold in Europe, Cackette said automakers can meet the most stringent regulations on the books. The Peugeot uses a NOx absorber in the exhaust system to reduce emissions to 0.037 grams per kilometer (0.06 grams per mile) and a particulate trap to collect soot before it leaves the exhaust.
A Toyota Avensis test vehicle also meets the Tier 2 standards.
Panelist Brian Fitzgerald of Siemens VDO Automotive said diesel engines will need more powerful computers with the ability to diagnose and continually recalibrate.
Kevin DeHart, vice president of diesel fuel systems for Robert Bosch, said consumers will choose diesels over hybrids once they compare performance and price.
Said DeHart: "Diesel is the best interim solution until fuel cells arrive around 2020."