Mazda hasn't exactly been clean about its future United States clean diesel plans - saying first it would concentrate on the technology before switching alliances to hybrids -- but the Japanese automaker revealed earlier this week that is seriously considering oil burners for the American market.

Seita Kanai, head of Mazd's research and development efforts, revealed to Automotive News on Tuesday that Mazda is currently testing its clean diesel technology on U.S. soil. Kanai failed to specify how many prototypes are currently roaming the streets of America.

However, Mazd's clean diesel technology has plenty of hurdles to overcome before it gets the green light for the U.S. market, namely adequate volume levels. "As an engineer, ideally I would want to introduce diesels, but I am not sure if it makes a business case," Kanai said. Mazda estimates that it would need a minimum of 10,000 U.S. diesel sales to make an adequate business case.

But Volkswagen U.S. diesel sales are quickly making a case for Mazda. VW is one of just a handful of automakers spearheading the U.S. diesel efforts, with the initial results proving to be very positive. Moreover, Mazda recently reveal the next-generation of its 2.2L diesel engine, promising 50 percent better fuel economy than the current mill.