Simply Hybrid > Vehicles > Mercedes E320
How Mercedes’ BlueTEC works, and the 2009 clean-diesel SUVs to come
What is BlueTec?
It’s 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 re-circulates 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.
NOx emissions are the trickiest to deal with. NOx forms in the first place as a result of burning atmospheric air, and every lean-burning engine generates NOx as the ratio of fuel to air in the combustion cycle decreases. Current approaches to trapping or destroying NOx emissions all use catalysts that are vulnerable to degradation in the presence of sulfur. That’s why it was necessary to put the whole country on a diet of ultra-low-sulfur fuel.
Mercedes uses two strategies to deal with NOx, one for cars and one for SUVs. The E320 BlueTec sedan, which we tested last year, 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. Mercedes says that the AdBlue system reduces NOx emissions by 80 percent.
Engine: 3.0 L 24-valve V6 Diesel
Power: 140 hp @3,800 rpm
Transmission Type: 7- speed automatic
Fuel tank “capacity / reserve: 21.1 / 2.4
Fuel: Ultra low sulfur diesel
Net Torque: 400 lb –ft @ 1,600-2,400
City / Hwy MPG: 23 32
Passengers: 5
