Clean diesel. No, it's not an oxymoron anymore--it's a term that'll be bandied around frequently as more diesels are introduced. So what exactly is a clean diesel engine?
Clean diesel is a combo: take a diesel engine with advanced CRD fuel delivery and add a diesel particulate filter and selective catalytic reduction exhaust scrubbing technology that takes advantage of the 15 ppm sulfur content of ultra low sulfur diesel (ULSD). Package it all up for a clean diesel that is aimed at meeting increasingly strict diesel emissions legislation.
The pluses: not only do clean diesels offer sparkling emissions, particulate matter (soot) is reduced 95 percent or more (over standard diesels), and there's also a substantial reduction in oxides of nitrogen (NOx) and sulfur. Clean diesels also generate more power and have increased fuel economy since the fuel is burned more efficiently and completely (as compared to conventional diesel engines). The cons: clean diesel engines are compatible only with ULSD fuel and biodiesel/ULSD blends. While widely available, not all stations carry it. Double check that pump label--otherwise only one or two tankfuls of regular diesel fuel can seriously damage the particulate filter.