That explains why Mazda USA is also reportedly looking at using the Sky-D in both the CX-9 and Mazda6. The Ford-derived 3.7-liter V-6 used in both vehicles is expensive and will require future investment to meet long-term fuel consumption and emissions targets. While the 3.7 is currently the sole engine available in the CX-9, total sales of the three-row crossover totaled just over 21,000 units last year. And although the V-6 is available in the Mazda6, it accounted for just 18 percent of the 35,000 cars sold last year. The thinking is the Sky-D could possibly replace the V-6 altogether, ensuring the diesel engine has the volume it needs to make a solid business case.

The good news, say Mazda USA insiders, is that German premium brands -- Audi, BMW, and Mercedes, along with Volkswagen -- seem to be doing the heavy lifting to change consumer perceptions about diesel in North America. About half of all Audi Q7 SUVs and A3 hatches now sold in the U.S. are diesels, for example. Diesels accounted for almost 4 percent of total Mercedes-Benz sales in the U.S. last year, 17 percent of BMW X5 sales, and about 20 percent of total VW sales. While diesel will never reach the market penetration of Europe for a whole bunch of reasons, there is clear evidence a growing band of American consumers are enthusiastically taking to the technology.

With Ford having reduced its stake in Mazda to just over 13 percent (and relying more on its European product development teams for small car technology for the North American market), Mazda is now less able to join Ford research and development programs. And it's simply not big enough or wealthy enough to develop by itself a broad portfolio of powertrain alternatives that meet future emissions and fuel economy targets in the medium term. So it has a tough decision to make. Linking Mazda to proven technology used by premium European automakers -- i.e., diesel -- instead of attempting to follow Toyota and Honda down the hybrid route seems like a smart move.

But is it the right bet? Would you by a four-cylinder diesel Mazda instead of a V-6?