The two areas of major difference between the less stringent EPA Tier 2 Bin 8 (which becomes the uppermost level permissible at the end of 2006) and Bin 5 are in NO_x and PM emissions. Getting from Bin 8 to Bin 5 (and CA LEV compliance) requires a 64% further reduction in NO_x and a 50% further reduction in PM emissions.

The ever-tightening requirements on multiple criteria have pushed automakers to explore a range of different systems and solutions.

BLUETEC is both an umbrella term that includes different emissions aftertreatment technologies and applications of technologies to solve the basic problem of emissions reduction as well as a descriptor applied to the various solutions of reducing oxides of nitrogen underneath the larger BLUETEC banner.

The design of each BLUETEC system depends upon the operating characteristics which must be considered in achieving the Bin 5/LEV target required for 50-state sales.

Each BLUETEC system performs the same combination of processes:

1. Reduce carbon monoxide (CO) and hydrocarbons (HC). This is currently done with oxidizing catalytic converters (Diesel Oxidation Catalysts—DOC).

2. Reduce particulate matter (PM) with a particulate filter, either as a separate element or integrated with one of the other BLUETEC elements.

3. Reduce NO_x. This is a problematic area for all manufacturers, and one in which Mercedes is opting for two approaches. The first is a newly developed NO_x adsorber, a catalytic device that converts NO_x to nitrogen. The other is a urea-based injection system (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.

These operate in conjunction with in-engine reduction of emissions via improved engine management, enhanced high-pressure common-rail fuel injection systems, and turbocharging with exhaust gas recirculation.

E320 BLUETEC Emissions System with DeNOx catalyst.	VISION GL320 BLUETEC Emissions System with AdBlue injection system.
Click each diagram to enlarge.

For the E320, due to be released in the US later this year, DaimlerChrysler implemented the DeNO_x adsorber. The EPA tested an earlier prototype of this car, along with light-duty diesels from several other manufacturers, between April 2002 and October 2003 (results reported in the SAE paper referenced below).

The testing results of the prototype E320 show the early capabilities of the system, and also highlight advances DaimlerChrysler engineers have made over the last few years in fuel efficiency while maintaining emissions control. During the test process, the E320 delivered about 31 mpg—as announced, the E320 BLUETEC promises 35 mpg.

The system on the concept VISION GL BLUETEC full-size SUV, which is the same as applied on the concept Jeep BLUETEC, uses the AdBlue injection system for more robust NO_x reduction. Without the AdBlue system, Mercedes would have only complied with Bin 8, according to Prof. Herbert Kohler, Head of the Vehicle Body and Drive Systems Directorate and DaimlerChrysler Environmental Officer. In other words, it wouldn’t have met the 50-state goal.

The urea-based selective catalytic reduction systems, in which the injection of the AdBlue urea solution into the pre-cleaned exhaust gas releases ammonia (NH₃), causing the nitrogen oxides to be converted into nitrogen (and water) in a downstream catalytic converter, is currently the most effective established aftertreatment technique for NO_x reduction, and is looked to by many truck manufacturers as the solution for their commercial diesels.

The problem with these systems, according to some—notably the EPA itself—is the requirement to replenish the tank of the aqueous urea solution. No AdBlue, no NO_x reduction.

DaimlerChrysler has been lobbying the EPA for several years to change the agency’s mind on the use of urea injection systems.

The AdBlue tank (normally hidden with a liftable cover) in the Jeep BLUETEC concept.

The company counters that since an average of around 0.1 liters per 100 km (2,352.15 mpg of AdBlue or 1 to 3 percent of diesel consumption) is all that is required, the tank can be designed so that it only needs to be refilled when service staff are carrying out regular, scheduled maintenance. In other words, take it out of the hands of the drivers.

The company has a large base of operating experience from which to speak on this area, having delivered more than 10,000 AdBlue-based commercial diesel vehicles in Europe over the past number of years.

Outlook for diesel. DaimlerChrysler is becoming increasingly bullish about the prospects for diesel in the US, given the rising concerns about fuel economy here combined with apparently ongoing customer demand for size and performance.

J.D. Power and Associates forecasts that the market share for diesel passenger cars in the US, which currently stands at around 3.4%, will quadruple by the year 2015. Mercedes-Benz is convinced that once BLUETEC technology has established itself, this forecast will appear conservative rather than optimistic.

Accordingly, the Mercedes group will share the technology with the Chrysler group, as evidence by the Jeep prototype. The pace of that, and the pace of the overall BLUETEC diesel rollout in the US, will depend to a great extent on the customer reaction to the E320s when they hit showrooms in the fall.

This may, over the next several years, contribute to altering the competitive landscape for improved fuel-efficiency, with clean diesel cars becoming poised to occupy the territory currently being scoped out by many hybrid implementations—fuel economy improvements of some 20–30% over comparable current gasoline platforms—with a lower-cost solution than hybrids.

Mercedes’s GL BLUETEC full-size SUV, for example, is projected to offer fuel economy of 26 mpg US; the upcoming Chevy Tahoe Hybrid 25 mpg.

The diesels are simpler, more reliable [than hybrids]. I can say this as someone who is on both sides of the position.

—Prof. Herbert Kohler, (referring to DaimlerChrysler’s ongoing hybrid powertrain development with GM and BMW)

In 2004, Margo Oge, Head of the Office of Transportation and Air Quality at the US Environmental Protection Agency (EPA) noted that:

If we had a light duty vehicle population that was one third diesels, that could save up to 1.4 million barrels of oil per day in the US, the amount of oil the US currently imports from Saudi Arabia. If we made these vehicles diesel hybrids, the oil savings would about double or up to 2 times the amount of oil Saudi Arabia ships to the US every day.

DaimlerChrysler appears very interested in developing that combination (diesel hybrids)—assuming it sees the demand with its BLUETEC vehicles.

Resources:

• SAE Paper 2004-01-1791: Progress in the Development of Tier 2 Light-Duty Diesel Vehicles

• EPA: Urea SCR Certification & Compliance Considerations