BlueTEC is a trademark name used by Mercedes-Benz to describe its diesel engine exhaust treatment system. In order to keep up with the steadily evolving and increasingly demanding emissions laws of North America and Europe, the company has designed and released two versions of this system. Version one was released for the U.S. market in the form of the 2007 E320 BlueTEC sedan and was designed to utilize, the then newly introduced, Ultra Low Sulfur Diesel (ULSD). As a next step, Mercedes-Benz released the more sophisticated R, ML and GL 320 series BlueTECs with AdBlue injection diesels that meet America's demanding BIN 5 emissions standards and are on track to qualify for Europe's EU6 parameters.
BlueTEC and BlueTEC With AdBlue
The Mercedes-Benz BlueTEC system begins at the engine's combustion chamber with improved fuel burn characteristics that enhance efficiency, as well as minimize unburned fuel particles that would ordinarily have to be treated downstream. The BlueTEC engine architecture is built on CRD technology. While both systems use an oxidation catalyst (OxyCat) and a Diesel Particulate Filter (DPF) to banish unburned hydrocarbons (HC), carbon monoxide (CO) and particulates (soot), they differ in how they treat oxides of nitrogen (NOx).
Bluetec With Storage-Type Catalytic Reduction
This system uses a storage-type NOx catalytic converter to control oxides of nitrogen. With this design, NOx gasses produced under normal operation are trapped and temporarily held in the converter. At prescribed intervals, under the direction of the onboard computer, the fuel system delivers intermittent rich combustion phases. The entrained excess hydrocarbons from this dense mixture recombine with the trapped oxides of nitrogen inside the hot housing and break-up the NOx molecules. The resulting clean nitrogen gasses and water vapor are purged, leaving behind a clean converter with regenerated catalysts that are ready to accept the next wave of nitrogen oxides.
Bluetec With AdBlue Injection
Mercedes-Benz designed this process for their larger and heavier line of SUVs and their R-series crossover, following the logic that these vehicles already have a higher rate of fuel consumption and that they would be more economical using a system that does not rely on frequent fuel-consuming rich mixture events for NOx abatement. While the storage-type system does allow Mercedes to use a more-or-less out-of-the-box CRD engine, this Selective Catalytic Reduction (SCR) arrangement did require some changes to the engine design. Among those modifications: revised piston crowns for better fuel distribution and atomization, slightly reduced compression ratio and a more adaptive Variable Geometry Turbocharger (VGT) to a give smoother and flatter torque curve.
Whereas the storage device uses excess shots of rich fuel mixture to "burn-off" accumulated nitrogen oxides, this injection process relies on chemical conversion via a reaction between the AdBlue urea solution and the accumulated NOx molecules within the SCR converter. When AdBlue is injected into the hot exhaust steam, it is reduced to water and urea. At a temperature of about 400 degrees Fahrenheit (170 Celsius), the urea reforms into ammonia (NH3) which then reacts with NOx gasses in the converter to produce benign nitrogen gas and water vapor.
It's really a question of economics and practicality. Which of the two systems is applied to any particular vehicle depends primarily on the vehicle's intended use: Heavy, high fuel consumption SUVs that spend a good deal of time under load are best served by AdBlue injection. On the other hand, smaller fuel-efficient passenger cars that are, by and large, passenger moving cruisers, make optimal use of the NOx storage converter. Either way, the result with the Mercedes-Benz BlueTEC system is a considerable reduction in soot and pollutants.