By 2010, all diesels sold in the U.S. will have to meet Tier 2 Bin 5 emissions levels, the same standards as their gas-powered counterparts. Even though we're used to talking about diesels as green machines, they still have the issue of nitrous oxide (NOx) emissions with which they need to overcome.

As a result, the Environmental Protection Agency is looking to publish urea guidelines as early as October of this year. Over the past few years, urea injection has been considered the cheapest effective way of scrubbing NOx emissions from diesel tailpipes. Because urea requires driver involvement (it needs to be refilled), the guidelines will address penalties to ensure urea tanks never go empty. Margo Oge, director of the EPA's Office of Transportation and Air Quality, said that one possibility would be to disable the engine. Another is to lock the fuel filler door until there's urea in the urea tank. Auto manufacturers are notably opposed to these types of restrictions citing safety issues. However, Oge says that the EPA can't allow cars that don't meet emissions standards to be driven. Once the guidelines are published, the automakers will have a an opportunity to petition for changes.

It will be interesting to see if Honda really can develop a clean diesel that won't require urea or a costly NOx trap. The Mercedes E320 BLUETEC which was unveiled at the 2006 New York Auto Show uses Adblue, a water-based urea solution, and can travel roughly 11,000 miles before its 6.8 gallon Adblue tank needs to be replenished.

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[Source: AutoWeek]

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