|The E320 BLUETEC. Click to enlarge.
When the Mercedes E320 BLUETEC hits salesrooms shortly, it will be as a 45-state compliant vehicle, not a 50-state vehicle. (Earlier post.)
BLUETEC is DaimlerChrysler’s modular emissions aftertreatment architecture that provides the potential for 50-state compliance—i.e, meeting EPA Tier 2 Bin 5 emissions levels, which map to California LEV II levels.
To tackle the difficult NOx target, DaimlerChrysler has currently defined two technology approaches.
The E320 BLUETEC, first of the family to arrive in the US, uses a newly developed NOx adsorber, a catalytic device that converts NOx to nitrogen. Subsequent family members are slated to use urea-based injection system for NOx reduction (using an aqueous urea solution called AdBlue, the genesis of the BLUETEC name).
Both are combined with Selective Catalytic Reduction systems, which, while in principle are the same, differ in application design based on vehicle parameters and emissions targets. (Earlier post.)
|Emission Bins and the results of 2004 testing of an E320 prototype. Close, but no Bin 5. Click to enlarge.
Although the E320 BLUETEC comes “quite close” to Tier 2 Bin 5 NOx levels, according to a DaimlerChrysler spokesperson, “the urea SCR system will be necessary” for full 50-state compliance.
Tests by the EPA in 2004 of a E320 prototype indicated that the aftertreatment system came in at just beneath 0.06 g/mi of NOx; the Tier 2 Bin 5 target is 0.05 NOx g/mi. (See graph at right.)
The EPA has yet to sign off on urea-SCR systems for light-duty vehicles, partly due to concerns on enforcement. It is clear, however, that urea-SCR is going to be necessary to support a full 50-state rollout of most clean diesel vehicles. The EPA said at the recent DEER 2006 conference that it would soon provide guidance to manufacturers on urea-SCR systems for light-duty vehicles.
SAE Paper 2004-01-1791: Progress in the Development of Tier 2 Light-Duty Diesel Vehicles