In separate announcements, both Ricardo, a European automotive engineering firm, and Nissan recently announced that they are developing diesel engines that meet emissions standards that match the Toyota Prius. Does this mean that diesel vehicles are finally worthy of the "clean diesel" label?

Not quite yet, but apparently the time is coming closer. Neither company is saying when—or even if—Super Ultra Low Emission Vehicle (SULEV) diesels will enter production. California’s SULEV standard is an impressive goal, but the more immediate goal is for diesels to meet federal Tier 2, Bin 5 standard (T2B5).

Today, there is one diesel car and five diesel SUVs sold in the United States that meet the EPA’s less stringent Tier 2 Bin 8 (T2B8) emissions requirement. That means today’s diesels are still dirty enough to outlaw their sale in five states.

2007 Diesel Vehicles(sold in 45 states)

Mercedes-Benz E320 Bluetec
Mercedes-Benz R320 CDI 4matic
Mercedes-Benz ML320 CDI 4matic
Mercedes-Benz GL320 CDI 4matic
Jeep Grand Cherokee CRD
Volkswagen Touareg TDI

You’ll have to wait another year for cleaner diesel cars that meet Tier 2, Bin 5 (T2B5) standards. These models will be available for sale anywhere in the U.S.

2008 Diesel Vehicles – Announced (sold in 50 states)

Audi Q7 3.0 TDI
BMW 535d
Mercedes-Benz E320 Bluetec
Mercedes-Benz E320 Bluetec
Mercedes-Benz R320 CDI 4matic
Mercedes-Benz ML320 CDI 4matic
Mercedes-Benz GL320 CDI 4matic
Volkswagen Jetta TDI

Until the uncertain date when technology from Ricardo, Nissan, and others produce a diesel worthy of Mr. Clean, the T2B5 diesels will remain dirtier than the typical hybrid. The big issue is oxides of nitrogen (NOX)—gases which contribute to the formation of smog, particularly in cities. A T2B5 diesel in Los Angeles can emit as much NOX as three and-a-half Priuses. So while the new diesels are fuel efficient, they still pollute more, making them an environmental mixed bag.

***

> More Hybrid Cars News