MONTVALE, N.J. – There is a
wave of diesel-powered vehicles coming to
America despite the price premium
on diesel fuel, and Mercedes-Benz has been leading the movement with its
50-state-legal “clean diesels” featuring BlueTec technology that mark the
culmination of years of scientific research, powertrain engineering, and market
preparation, according to www.consumerreports.org. The resulting BlueTec
diesels burn cleaner than most gasoline engines and exhibit superior fuel
economy at the same time.
This
month, Mercedes announced that it would offer a clean-diesel option for three
of its 2009-model SUVs: the midsized ML- and R-Class, and the big GL-Class. All
will use the same 210-hp, 3.2L diesel V-6. Mercedes has estimated that the
GL320 BlueTec will record an average of 24 mpg, some 20 to 40 percent better
than a comparable gasoline engine. It should also be able to travel 600 miles
on a single tank of fuel.
Honda,
Nissan, and Toyota are all developing
clean-diesel technology, but the Mercedes BlueTec system is the first practical
mass-market application available in the United States.
BlueTec is
the proprietary name for a series of engine technologies, filters, and
catalysts that result in low emissions and high fuel economy. It starts with a
high-pressure common-rail turbo direct injection diesel engine. “Common rail”
refers to the method for injecting precisely the right amount of fuel directly
into each cylinder at exactly the right moment. The turbocharger boosts
horsepower, and the system recirculates the exhaust gas that powers it in order
to consume any unburned fuel.
When
exhaust gas leaves the engine, a multi-phase treatment process begins. By their
nature, diesels tend to produce high levels of carbon monoxide, oxides of
nitrogen known collectively as NOx, and particulate matter, also known as soot.
Oxidation catalysts minimize the carbon monoxide and further reduce unburned
hydrocarbons. A maintenance-free particulate filter, or soot trap, then reduces
soot to nearly undetectable levels.
Mercedes
uses two strategies to deal with NOx, one for cars and one for SUVs. The E320
BlueTec sedan, attacks NOx with a storage catalyst and a second catalyst called
SRC (Selective Catalytic Reduction). Periodically the engine runs rich for a
little while, which cleanly purges the NOx storage catalyst. For heavier vehicles,
such as SUVs, Mercedes has adopted a urea-injection system called AdBlue.
That’s because the NOx trap technology used in cars would require too-frequent
purging and thus reduce fuel economy.
The
AdBlue system uses the SRC catalyst and a tank of liquid urea, which is misted
into the exhaust stream. When the urea comes in contact with the hot exhaust
gas, it releases ammonia, which in turn reacts with NOx and emerges as harmless
nitrogen and water. The urea supply is said to be good for 10,000 miles, so it
only needs to be refilled at the vehicle’s normal service intervals. The AdBlue
system reduces NOx emissions by 80 percent, according to Mercedes.
The
Mercedes-Benz BlueTec SUVs are slated to go on sale this fall as 2009 models.
