Comments dehada has made

diesel will -- and should -- have a place

This is an interesting post, but one that does not adequately address the complexity of the issue.

The Prius is indeed a remarkable achievement, and perhaps the most remarkable thing about it is how "unremarkable" it is: you just get in and drive, and while it won't win any awards for performance or fun, it goes down the road just fine and produces very low emissions at the tailpipe.

But to elevate the Prius (and by association, Toyota) to deity because it gets 45ish mpg and isn't a diesel takes the praise too far.  First of all, Toyota earns good CAFE credits for each model -- credits that can offset the poor performance of their much more profitable trucks and SUVs.  Not counting its Lexus devision, Toyota sells six SUV models in the US, (more than Chevrolet or Ford) and is just pulling the wraps off its latest "Sequoia," a monster that is finally comparable in its excesses to the much-derided full-size American utes.  From a business perspective, having the thrifty Prius to support sales of the thirsty Sequoia is great foresight, indeed.

It's also true that diesel produces more greenhouse gasses per gallon than gasoline, and this is because, on a volume basis, it packs more potential energy than a gallon of gas.  But even adjusted for the higher emissions intensity of the fuel, the efficiency of the high-compression Diesel cycle trumps that of the spark-ignition Otto, particularly in the types of driving where hybridization shows the biggest gains (idling and stop-and-go) and also in the types of driving where hybrids produce no advantage (sustained high speeds and towing).  Over-the-road trucks don't use diesel because it's macho, but because it is so much more efficient than gasoline.  Look no further than the geniuses at Toyota, who will soon be installing diesel engines into their US versions of the Tundra and Sequoia.  For many, many, years, they have sold diesels overseas.

The point about the climate effects of "carbon black" is particularly troublesome to me because you're the bold takeaway from your post portrays the science behind the issue in the same light as the well-documented science behind the climate effects of CO2.  Even calling the particulate matter from diesel engines "carbon black" is a term that, like "Dihydrogen Monoxide," sounds like something we should automatically reject.  Meanwhile, our understanding of particulate emissions is ever-evolving.  Most of the stuff comes from things like volcanoes, crop burning, cowpie stoves, barbeques, etc. instead of diesels.  Even gasoline engines, whose particulate emissions are now thought to be much, much greater than previously assumed - just in much smaller particles that could rise higher in the atmosphere than their diesel counterparts.

The pollution controls for diesels are finally coming into their own, now that we've cleaned up the dirty fuel that precluded them in the US until 2007.  It's true that some take an efficiency toll, but this is nothing like the huge hits gasoline engines took in the late 1970s when their emissions equipment became standard.  In fact, the latest engines from Volkswagen, Mercedes, BMW, and even the relative newcomer, Honda, will produce fewer particulates than gasoline engines, without any discernable fuel economy penalty.  Many of these cars will be much better suited to the type of highway driving many Americans do.  While we all wish our driving patterns were different, it does make sense to use the technology that is best for the task.  Give diesel emissions controls a chance to mature - just a decade after catalytic converters became standard on gas engines, their performance and cost penalties became negligible.

Finally, it's worth mentioning that diesel, by virtue of its much lower vapor pressure, has some inherent advantages over gasoline in evaporative emissions and safety.

None of this is to diminish the Prius, which is for many people an excellent choice, if they have to drive at all.  But to count among its strengths "it's not a diesel," and to credit that strength to a benevolent and forward-thinking auto company is a stretch.   If we're really serious about cutting the environmental impacts of human transportation, we'll have to combine massive paradigm shifts with a full suite of promising technologies.  The Prius alone won't do it: hybrids will join diesels, biofuels, lightweight materials, and a host of other promising technologies as parts of a complex solution to a complex problem.On Why hybrids beat diesels posted 1 year, 6 months ago 21 Responses