17 October 2007

Mercedes-Benz USA (MBUSA) unveiled a version of its E320 Bluetec diesel sedan that will immediately be available in limited numbers to California customers through a special limited mileage lease program. It is the first time in more than a decade that diesel cars are available in California.

Beginning October 15, MBUSA offers its E320 Bluetec to customers under a two-year/24,000 mile lease program. The E320 Bluetec is lease-priced on a par with its gasoline sibling, the E350, in spite of the higher cost of the diesel engine and aftertreatment system compared to the gasoline version.

“We hope California has shed its anti-diesel reputation by certifying this vehicle as the first diesel passenger car to meet the most stringent smog emission standards in the world,” said Tom Cackette, executive director of the California Air Resources Board (ARB).

The E320 Bluetec was launched in October 2006. It was certified as a Tier 2 Bin 8 vehicle (NOx = 0.20 g/mi), and available in the 45 states that follow federal emission standards. In California and in states that adopted California-style legislation, diesel cars must meet emission standards equivalent to at least Tier 2 Bin 5 (NOx = 0.07 g/mi).

The emission control system in the 2007 E320 Bluetec includes a close-coupled diesel oxidation catalyst, followed by a NOx adsorber catalyst, a diesel particulate filter, and an SCR catalyst (without urea injection). 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. During regeneration, the NOx adsorber produces some ammonia, which is stored in the downstream SCR catalyst, and used to further enhance NOx reduction through the SCR reaction.

One of the major issues with NOx adsorber technology is thermal durability, as the NOx storage capacity and conversion efficiency of the device deteriorate due to exposure to high temperatures (such as during desulfation). The mileage limit in the California lease program is an indication that the NOx adsorber-based E320 could meet Bin 5 emission requirements over the 24,000 mile period, but not over the vehicle full useful life of 120,000 miles.

The California lease program will function as a bridge to begin phasing in 50-state Bluetec vehicles nationwide starting in 2008, said MBUSA. In January 2008, the special lease program will be extended to other states which require California emissions. Later in 2008, Mercedes will introduce its M-, R- and GL-Class vehicles which will use SCR technology with urea (AdBlue) injection for NOx control to fully comply with Tier 2 Bin 5 emission standards.

Source: Mercedes-Benz