The engines of today may operate along familiar principals to the internal combustion engines of yesteryear but their efficiency and cleanliness is almost beyond comparison thanks to advances in technology.

Like all automakers Mercedes-Benz has put millions into developing engines to meet ever stricter emissions regulations all around the world and has made huge improvements in fuel efficiency, but its latest generation of 'BlueDirect' engines may not be available in the United States as the sulphur content in U.S. gasoline is too high.

The new lean-burn 4- and 6-cylinder gasoline engines are unable to function as intended when sulphur concentration in the fuel is too high. U.S. sulphur concentration sits between 80 and 95 parts per million and the new engines require a concentration of lower than 50 ppm. The higher concentrations damage the trap that captures nitrogen oxides from the exhaust gases.

Levels of NOx are higher in lean burn engines, and the special trap is designed to capture the excess NOx where it can then be burned off. Mercedes-Benz can sell the more efficient motors - which offer improvements of up to 10 percent - in Europe where sulphur levels are near zero.

The new Mercedes engines offer significant improvements in fuel efficiency. At the bottom of the line a new 1.8 liter turbocharged 4-cylinder debuts in the C-Class with 201 horsepower and 229 lb-ft of torque, that makes 24 mpg combined, a 15 percent improvement over the C300 it replaces.

At the top, a new bi-turbo 4.6L V8 in the CL550 Coupe makes 15mpg city and 23mpg highway, avoiding the gas guzzler tax.

It's good to see that manufacturers are bringing down emissions as a whole even if governments around the world concentrate more on carbon dioxide. The EPA is currently reviewing the impact of sulphur levels in gasoline, so we may yet see the most efficient Mercedes engines making an appearance.

[Wards Auto]