Crossing Diesels with Plug-In Hybrids: Good or Bad Idea?

Volvo V70_PHEV_dieselDiesels and hybrid-electric cars have often been posed as competitors racing to capture the green-automotive market. Diesels are more popular in Europe, while hybrids are more popular in the United States. Both have their advantages and disadvantages: diesels can get impressive fuel economy without complicated drivetrains (providing a cost advantage over hybrids today), while plug-in hybrids bundled with a renewable energy-powered grid can be even cleaner.

But now, it looks like these competitors are coming together. Volvo Car Corp. announced Friday that it plans to bring a diesel plug-in hybrid to the market by 2012. The news comes after Peugeot earlier this month unveiled a diesel PHEV minicar that it plans to bring to the market next year, and BMW also showed off a sporty diesel PHEV concept car at the Frankfurt auto show. While companies have been tinkering with the concept for some time, it looks like diesel PHEVs are finally starting to gain some traction.

It’s an exciting idea. First of all, diesel fuel packs 10-20 percent more energy per gallon than gasoline, according to Fusel, a site that advocates running diesel engines on vegetable oil. That higher energy content, combined with some engine advantages, means modern diesel cars can get about 40 percent more miles per gallon than their gasoline counterparts, according to the site.

With that kind of diesel fuel economy, it means the new crop of clean diesels, such as the Volkswagen Jetta TDI, achieves similar fuel economy to hybrids like the Toyota Prius without a complex drivetrain, according to AutoblogGreen. On top of that, advocates say diesels are more fun to drive, because they deliver more torque. Perhaps the most important factor to consumers: diesels often cost less than hybrids. According to an Edmunds comparison earlier this year, the 2009 Jetta TDI cost $22,890, compared with $28,933 for the Prius. And plug-in hybrids are expected to cost even more.

But diesels also emit more particulates than gasoline, and while new technologies have enabled companies to meet strict U.S. standards for particulates, those technologies cost money. Diesels also have an image problem. In the United States, many people still think of diesel as the “loud, smoke-belching beast” they remember from the 1970s, as this article puts it, even though they have changed dramatically.

A marriage of diesel and plug-in hybrid technology could produce a wonder child that brings out the best of both technologies, boosting fuel economies to their highest levels yet while avoiding the range issues of pure electric vehicles. An electric motor could help diesels easily meet even the strictest potential particulate standards being considered today, while a diesel engine could boost the fuel economy of a PHEV.

But some think that the match could also produce a monster. Adding the technologies together could result in an even more complex drivetrain that ends up being far more expensive than its worth. And it could still have trouble winning diesel converts in the United States. We’ll be waiting with our fingers crossed to see what automakers produce. What do you think?

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