Why can't the 2015 Mazda 6 diesel work in the US?

Unfortunately, I think the issues of refining motor fuels from crude oil are misunderstood. It is not possible to produce only diesel or only gasoline fuel, both result from refining. It is possible to tilt the ratio and produce some more of one or the other, but there are limits as to how far the ratio can be moved. In Europe, the usage of diesel is about half, across all the countries (from info I saw some years back), but varying widely from country to country. In USA, the diesel percentage in passenger cars is much lower, somewhere around 3 or 5 percent. Of course, more diesel is used in USA for over-the-road trucking than in Europe (due to the much greater distances).

Pressure combustion has traditionally offered somewhat greater efficiencies (about a 15% advantage) for diesels. Attempts to utilize pressure combustion for gasoline cars has been problematic and not very successful. However, it seems that technology such as direct injection, variable valve timing, etc has achieved much of the advantage, so diesel engines may have less of an advantage than previously.

It is incorrect to say that diesel production requires more feedstock. Probably, the opposite is true, there are likely greater losses in cracking to get more gasoline (and also probably more energy input, also offsetting total energy efficiency). What is true to say is that there are limits as to the availability of either fuel, depending on refining ratios and overall demand. I am not a fuels producer insider, so I don't know where those limits lie and thus how many more diesel passenger cars could be accommodated with current refining plants and demand. Likely a (knowledgeable) person from the industry could answer this question relatively easily.

BioWillie will save the planet.

"we already use all the diesel we produce"

Oil companies would have to be pretty stupid to produce more diesel than we use.

"How is a car that cannot even emit less CO2 than a regular, non-hybrid gas car green?"

The diesel Mazda6 emits less CO2 (108 g/km -> 172 g/mile) than the gas Mazda6 (275 g/mile)

mazda uk -> /aboutmazda/news/technology/when-size-doesnt-matter-with-co2-emissions/

That's the problem with comparing apples to oranges - or Mazdas to Passats

Thanks Max. You make excellent points and give the story more of a balanced viewpoint.

The exception, Max, is high compression gasoline engines. These are very similar to diesel and thus achieve the same basic MPG per dollar spent on fuel. Even, as you say, driving at high speed or in a less than eco-friendly manner means good economy. I noted this in the Mazda6 SKYACTIV with iELOOP. The SKYACTIV system is running at a compression ratio between 13-14:1, depending on the engine size. Ford's EcoBoost runs at about a point lower, between 12 and 13. It's this compression that tends to remove much of the variability from fuel usage.

I will agree to the easier biofuel options diesel offers and have talked about that a lot. In addition, the glycerol byproduct of biodiesel can be made into bio-gasoline. Methanol is another oft-overlooked fuel.

You obviously don't know a whole lot about diesel. Do you realize that it requires MORE oil to make a gallon of diesel fuel than it does a gallon of gasoline? And that nearly all diesel cars do not allow biodiesel and will void warranties if you use it because of uncertainties about its cleanliness? It's time for you to drop your conspiracy theories and read up on some actual facts about fuels.

I compared the car that the story is about (the Mazda6) to the only diesel car in its category, the Passat. At the time of this story's publication VW didn't have any gasoline engines that sold well in the US. Their poor fuel economy compared to the leaders in the class could be one reason.

Please provide your specific examples of diesel cars that lead their size category in fuel economy. Maybe you can find some truck or sports/luxury examples where this imaginary 30% diesel advantage is true, but in the family car category the VW Jetta Diesel's engine has no edge over the Toyota Corolla LE Eco gasoline engine, or the Nissan Sentra's. These are the two sales leaders in that category. In the larger category that the Mazda 6 falls into the VW Passat Diesel has an EPA rating of 34 combined and the gasoline Mazda 6 rates 32 MPG. They have the same highway mileage. My examples are taken from fueleconomy.gov and are in the body of the story. The 30% number you cite is the diesel lobby's talking point. It is not based on any affordable cars for sale in the US market. I asked them.