Auto Electronics

UNDER THE HOOD OF THE 2007 MERCEDES-BENZ E 320 BLUETEC

Due to launch in autumn 2006, the E 320 BlueTec hosts a clean V6 diesel engine that develops 155 kW (211 hp) with 540 Nm torque and has a fuel consumption of 6.7 l/100 km (35 mpg). BlueTec is Mercedes-Benz's name for a new generation of diesel emissions control technology. It has been used for diesel trucks in Europe, but will initially be introduced in the United States in passenger cars. The system takes advantage of the nationwide availability of low-sulfur diesel fuel with a maximum sulfur content of 15 ppm, required by U.S. law (instead of the previous upper limit of 500 ppm) to meet the stringent nitrogen oxide (NOx) requirements in the U.S. 50-state emissions standard.

To satisfy the U.S. and other countries' aggressive emissions standards, Mercedes-Benz engineers developed advanced technology in four areas that come together in the E 320. Starting with the engine itself, the electronic engine management system controls four valves per cylinder, a third-generation common rail direct injection using piezoelectric injectors, a turbocharger with variable nozzle turbine, and exhaust gas recirculation. Next, an oxidizing catalytic converter minimizes carbon monoxide (CO) and unburned hydrocarbons (HC) emissions.

After the oxidizing catalytic converter, a particulate filter reduces particulate emissions by as much as 98% — a level below the current EU 4 particulate limit of 0.025 g/km. Controlled adjustments to the engine management system modify the fuel injection, intake throttle, exhaust gas recirculation and boost pressure to eliminate clogging of the pores in the particulate filter.

BLUETEC SPECIFICS

BlueTec, the newest aspect of Mercedes' emission control techniques, reduces NOx. BlueTec has two methods to reduce the higher concentration of NOx produced by diesel engines: 1) a DeNOx storage catalytic converter, which is used in the E 320, and 2) a system to inject a reducing agent called AdBlue. The DeNOx storage catalytic converter on the E 320 mounts between the oxidizing catalytic converter and the particulate filter with a selective catalytic reduction (SCR) converter completing the exhaust-gas treatment.

Beyond the E 320 implementation of BlueTec, injecting AdBlue in a system with SCR reduces nitrogen oxide levels by up to 80%. At the 2006 North American International Auto Show, Mercedes-Benz exhibited a Vision GL 320 using this more sophisticated BlueTec approach. In addition, Mercedes-Benz engineers are developing the process for use as a standard system in passenger cars.

In the more advanced version of BlueTec, exhaust gases flow through the oxidizing catalytic converter to a particulate filter integrated into the same assembly. Next, a metering valve injects a precise amount of AdBlue into the exhaust stream at the right time during the engine's operation. The SCR provides the final treatment to the process. A separate tank houses the aqueous urea solution called AdBlue. Injecting AdBlue into the hot exhaust stream converts the mixture to ammonia, water vapor and nitrogen oxides. A subsequent reaction in the SCR reduces these components into nitrogen and water.

The system includes diagnostics to identify any problems in the BlueTec operation and to inform the driver of the amount of AdBlue remaining in the tank.

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