TAMPA, FL. The reduced energy density of ultra low sulfur diesel fuel, compared with today’s low sulfur diesel, will negate the 2% fuel economy improvement demonstrated by Volvo Trucks North America’s (VTNA) EPA emissions-compliant ’07 diesel engines, said the OEM. However, the good news is that the new engines will post fuel economy numbers equal to ’02 models, VTNA said.

“The [ULSD] fuel we started getting in the lab looked a little thinner and lighter than what we were used to,” said Ed Saxman, product manager for Volvo powertrain. “At the start of our testing, though, we thought we’d be okay. But we found that ULSD has 1.5% less weight than regular fuel – it’s less dense because of the refinery process used to take out the sulfur. And that lower density affects fuel economy.”

Saxman pointed out that the U.S. market measures fuel by volume-- not weight—which will affect fuel economy for all diesel vehicles when retail outlets nationwide are required to convert from low sulfur diesel to ULSD on Oct. 15, 2006. “When you measure fuel in gallons, differences in energy density affect fuel economy numbers,” said Saxman. “If you measure by weight alone, in pounds, the energy content doesn’t shift.”