Delphi is developing on-board diesel fuel reformer technology to improve NO_x reduction systems, helping diesels meet future Euro VI and EPA Tier II-Bin 5 emissions standards without compromising cost, fuel-efficiency and engine performance.

There are several approaches to reducing NO_x in exhaust. One is to use a urea-based selective reduction catalyst that requires the presence of a reducing agent such as AdBlue. This is the approach licensed by Mitsubishi Fuso from Nissan Diesel (earlier post) and used by DaimlerChrysler among many other global auto and truck makers. 

An alternative approach is the use of a NO_x adsorber or NO_x trap that frequently needs to be regenerated. Some systems use diesel fuel directly as the regenerating agent.

Unlike catalysts, which continuously convert NO_x to N₂, NO_x adsorbers are materials which store NO_x under lean conditions and release and catalytically reduce the stored NOx under rich conditions.

This process can perform well at high exhaust temperatures, but historically has demonstrated poor performance at lower exhaust temperatures. Low exhaust temperatures represent a large portion of vehicle operating time, particularly for medium- and light-duty diesel vehicles (including cars and SUVs) used in cities.

The on-board diesel fuel reformer uses air to convert diesel fuel into a hydrogen-rich reformate during a catalytic partial-oxidation process. The reformate is used to regenerate and to desulfate NO_x adsorbers. The reformate is also used for diesel particulate filter regeneration.

The reformate-assisted NO_x adsorber regeneration appears to be especially effective at exhaust temperatures below 250 ºC, where the use of diesel fuel as a reductant faces serious challenges.

We all agree that diesel has enormous potential worldwide. Of all the current fuel and propulsion alternatives, diesel holds the best near-term promise. However, it imperative to develop a cost-effective emission solution that helps maintain the diesel engine as a leader in fuel economy and performance.

Dr. Jean Botti, Delphi Powertrain Systems

Cost is they key here, given that emissions targets must be met and fuel economy must improve (for cost and emissions reasons). There are numerous approaches to emissions reductions, and there are other vendors tackling the on-board reforming of fuel to the hydrogen and CO-rich reformate gas.

Delphi is developing its system to be adaptable to a wide variety of vehicle architectures and optimized to help diesels compete with gasoline-electric hybrids in the US market. Delphi is targeting its reforming technology to be available in the marketplace when 100% compliance to Tier2 Bin5 fleet average begins in 2009.

Resources:

• ArvinMeritor: A Fast Start-up On-Board Fuel Reformer for NOx Adsorber Regeneration and Desulfation

• NO_x Adsorbers for Diesel Applications: General Considerations and Operational Issues