27 September 2006

On October 15, 2006, Mercedes will launch the E 320 Bluetec model in the North American market. It will be the only model year 2007 diesel passenger car offered for sale in the USA. 2007 is the first year when all new light-duty vehicles in the United States must meet the more stringent Tier 2 emission standards, forcing the discontinuation of the few Tier 1 diesel models that were available through model year 2006. More manufacturers are expected to introduce Tier 2 compliant diesel car models in 2008 and 2009.

The new E 320 is powered by a 3 liter V6 engine developing 208 hp and 400 lb-ft (540 Nm) of torque. These power and torque figures are 20-40% and 30-50%, respectively, higher than those in a comparable gasoline engine, said Mercedes. The fuel consumption of the new E 320 is 6.7 l/100 km (35.1 mpg), which provides a driving range of 700 miles (about 1,200 km) between fill-ups.

The Mercedes Bluetec models come equipped with a diesel particulate filter to meet the Tier 2 PM emission standards.

While the marketing name “Bluetec” has been derived from the urea—called AdBlue in Europe—selective catalytic reduction (SCR) technology, two different NOx control options are introduced in the Bluetec line-up: a NOx adsorber catalyst (NAC) and urea-SCR. In the 2007 model year, the E 320 emission control system includes a close-coupled diesel oxidation catalyst (DOC), followed by the NAC converter, the diesel particulate filter, and an SCR catalyst. The NOx adsorber stores NOx emitted during lean operation, followed by regeneration at a rich exhaust condition, which is periodically achieved through an engine management strategy. Regeneration in diesel NAC catalysts is typically performed at a frequency on the order of 2 minutes, and lasts a few seconds. During the regeneration, the NAC catalyst produces some ammonia, which is stored in the downstream SCR catalyst, and used to further enhance NOx reduction through the SCR reaction.

The NAC+SCR system, which does not require urea injection, enabled Mercedes to achieve only Tier 2 Bin 8 emission levels. Thus, the E 320 will be available only in the 45 states that follow the federal emission standards (California and states that adopted California-style legislation require that vehicles be certified to the more stringent Tier 2 Bin 5 standard or better).

Urea/AdBlue SCR technology will be introduced in 2008 Bluetec M-, R- and GL-Class models, announced Mercedes. The urea injection technology will enable these vehicles to be certified to the Tier 2 Bin 5 standard, and be offered in all 50 states. The announcement implies that DaimlerChrysler has reached, or is about to reach, an agreement regarding the use of urea based systems with the US EPA, who had voiced concerns about the emission compliance when using SCR technology, and the urea distribution infrastructure.

The launch date of the 2007 E 320 model coincides with the availability of ultra low sulfur diesel (ULSD) fuel (15 ppm S) at the retail level in the United States and Canada. ULSD is required for both the catalytic particulate filter and NOx adsorber technologies.

Honda has recently announced it plans to develop a Tier 2 Bin 5 diesel by 2009 using the NAC+SCR technology without urea injection.

Source: DaimlerChrysler