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Tackling Diesel NOx Inside The Box

When low sulfur diesel fuel becomes available in the U.S. in October 2006, expect to see diesel cars offered here by all European manufacturers. And it looks like in some cases it might get done without the expense of NOx adsorbers or SCR aftertreatment.

The National Vehicle & Fuel Emissions Laboratory of EPA in Ann Arbor, Mich., and Ford Motor are now achieving Tier 2 Bin 5 emission regulations for NOx on an “engineout” basis. No NOx aftertreatment needed. EPA and Ford announced Phase II of their Cooperative Research and Development Agreement (CRADA), to further refine the technology and examine commercial viability, late last month.

While the EPA lab is also working on the very promising Homogeneous Charge Combustion Ignition technology (HCCI), this one involves a stratified charge TDI diesel fitted with EPA’s patented Clean Diesel Combustion (CDC) technology. The essential wisdom of CDC is limiting NOx generation during combustion by keeping the local peak temperatures of combustion below 3150 degrees F. According to David Haugen of EPA’s Lab, high rates of oxidizing nitrogen are avoided by managing oxidation of fuel in the diffusion flame region. That is done by operating at reduced global and local oxygen concentration.

The system uses substantially higher levels of EGR and throttles the fresh intake oxygen back from 21 percent to the 11 to 14 percent range. The EGR is cooled and it is tapped from the exhaust stream after the catalyzed diesel particulate filter. In earlier tests this combustion process promoted more smoke and PM emissions, but impressive strides have been made and smoke and PM have been reduced by more than half. It is believed that a PM filter and an oxidation catalyst will still be required for light vehicle applications to control PM, HC and CO.

The test engine is a modified 1.9L TDI diesel. EPA fits it with a new fuel injection system using Siemens and Sturman Industries technology, which employs a hydraulic intensifier to boost injection pressure. The tests are conducted using the 2006 low sulfur No. 2 diesel fuel.

Not normally thought to be a great promoter of diesel technology, EPA is squarely behind CDC. The diesel’s true benefits are fuel economy and big-time CO2 reduction, and both are extremely attractive to EPA. By keeping NOx in the box without aftertreatment, it’s suddenly a brighter day for diesel.

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