An increasing number of automakers are betting on diesel as the next hot seller among green car buyers.  Diesel engines have won increasing media attention this year as a diesel-powered BMW won the World Green Car of the Year award at the New York Auto Show, and another bested a Toyota Prius in a mileage challenge.  Still, it isn’t yet clear whether Americans buy the argument for diesel.

A report on Slate has been generating a lot of discussion in auto forums about the environmental impact of diesel engines compared to that of convention gasoline-powered engines.  The report notes that diesel is “simpler to refine than gasoline,” but that “making it requires more crude oil per gallon.  The end result is a fuel that boasts much greater energy density than gasoline, which explains why diesel cars get up to 40 percent more miles per gallon than their petrol counterparts,” but “the higher energy density also means that burning a gallon of diesel emits more greenhouse gases than burning a gallon of gasoline—about 15 percent more, to be specific.”  Diesel engines also emit more particulate pollution, although new technologies like Mercedes’ Bluetec system help neutralize the impact of those emissions.  The report concludes that gasoline is not “necessarily more eco-friendly than diesel—the two fuels just have different pluses and minuses.” 

The Slate piece leans heavily on an earlier Union of Concerned Scientists report that concluded, “Gasoline vehicles are more cost-effective than diesel for reducing oil use and lowering global warming pollution.”  That report, however, was released before Bluetec and similar technologies were released for sale in the U.S.

Automobile magazine’s Tech Talk blog is concerned about the impact of the Slate report. 

“All things being equal, a gallon of diesel will get you farther down the road than a gallon of regular gas,” Automobile says, but the Slate report “has surfaced to change that perception.” Automobile concludes, “It looks like diesels may receive another setback if consumers start worrying about greenhouse gas emissions and how much oil it takes to produce a gallon of fuel.”

The Slate report spotlights biodiesel as “the wild card here,” noting that it “can drastically reduce a diesel vehicle's tailpipe emissions.”  You can brew your own biodiesel at home.  Florida ABC affiliate WMBB-TV interviews a man who does just that.  Tim Dutrow claims “He saves up to $70 a month on fuel,” and that his biodiesel brewing set-up “paid for itself in six months.” 

Home biodiesel brewing may, however, lead to an oddball new crime wave: grease theft.  California’s San Jose Mercury News carries a report this morning of a man “arrested Wednesday on suspicion of stealing grease after police said he siphoned it from a storage tank at a Morgan Hill Burger King.”  Police believe the man intended to convert the grease into biodiesel, estimating that “a full tank would have been worth $6,750.”

Ironically, yesterday while the argument about diesel’s green credibility was raging, the EPA announced a new grant program aimed at helping cities and school districts shift their bus fleets to biodiesel (press release here).