CARB Softens Stance on Diesels

The California Air Resources Board, which seemed intent on banning the diesel engine from the face of the earth, appears to be re-evaluating its position.

In July, California Gov. Gray Davis signed legislation to reduce carbon dioxide emissions from cars in an effort to curb global warming.

Highly efficient diesels could play a major role in helping auto makers to significantly improve fuel economy — and reduce carbon dioxide emissions — if only they can meet upcoming regulations that strictly limit oxides of nitrogen (NOx) and particulate (soot) tailpipe emissions — the Achilles heel of compression ignition engines.

Until recently, it was believed diesels couldn't meet the new standards, which begin in 2007.

Toyota Motor Corp.'s upcoming new diesel engine and advanced exhaust aftertreatment may be one reason why CARB is said to be rethinking its stand on diesel technology.

Toyota announced more than two years ago it had developed an advanced aftertreatment system for diesel exhaust that continuously reduces NOx and particulate matter by more than 80%.

At that time, Toyota said the new diesel aftertreatment system would reach the market in 2003.

If that forecast remains valid, the engine will appear soon, probably for a production vehicle sold in Europe, where the needed low-sulfur diesel fuel is available.

The system cannot be used in the U.S. because low-sulfur diesel fuel is not mandated for nationwide supply until 2006.

A Toyota source says the auto maker's new diesel engine recently was tested at an Environmental Protection Agency laboratory in Ann Arbor, MI, using diesel fuel with a sulfur content of just six parts per million.

Toyota says the function of its “revolutionary DPNR diesel particulate and NOx reduction system” employs a simple catalytic converter and common rail diesel fuel supply system.

It adds: “During lean operation, particulate matter is oxidized by active oxygen released by the NOx storage function and by excess oxygen in the exhaust.

“Then, during momentary stoichiometric operation, PM is also oxidized by active oxygen released” from NOx reduction.

Unknown is whether Toyota has made further, yet-unannounced advances with its diesel technology, and how this may influence the company's plans for marketing diesel-powered vehicles.