There were actually plenty of rotary diesels made (the one above powered tanks) but aexcorp is right, they aren’t very practical. They would certainly never pass emissions, as the gasoline ones barely do right now, and the compression pressure needed for light-off is monstrous, so you need a beastly starter motor and a ton of noise and rattle to get it going. Diesel motors are indeed extremely reliable, run cooler, don’t have spark plugs to change and provide ungodly amounts of torque. However, they don’t accelerate well (mass in the pistons) and they clatter like crazy when you engine-brake, which is why you will almost always find them with an automatic transmission.

US Diesels need a urea tank because our diesel sucks; it is very poor quality compared to Europe and our refineries do not want to be retrofitted to refine it to that degree; they are still pissed about low-sulfur diesel and are passing that cost along to the consumer, which is why (along with taxes) diesel is so expensive. It is worth it to note that the price of diesel does NOT fluctuate seasonally and dip up and down like gas does, so over a long cycle you most likely come out ahead.

The real villain here is California, which hates trucks and thus has produced quite a few rules (such as NoX emissions levels that are nearly impossible to reach) that prevent the spread of diesel passenger cars as a side-effect of busting the nuts of truck nuts.

The one really nice thing about diesels is that you can turbocharge the shit out of them, as diesel has extremely predictable light-off and the cylinders and heads are heavily reinforced. Thus, Fiat produces a 50 MPG 1.4 liter (yes, that is the displacement of four soda cans) turbo diesel that puts out 189hp and 220lbs/torque, and the entire motor would fit in the footwell of the average passenger seat.

Oh, and Volkswagens suck.

As for people, such as RaineMan, stating that Diesel isn’t reliable, than please, tell me where you found that gem, because as far as I know, all trucks in the US use diesel and yet they have generally much less issues (especially taking mileage driven into account) than unleaded cars.

Diesels don’t have spark plugs so that’s one less thing to worry about. The blocks for diesels are heavier (and heavier duty) because of higher compression ratio and more energetic combustion. The realest problem (no longer really an issue, but used to be) was running a diesel engine when it’s really cold.

Now I do agree that having a tank of urea that needs to be refilled is silly, but not all manufacturers have decided to go that route, many, such as VW, Audi and several of the other German companies that teamed up, just store the NOx in the catalytic converter until it gets burned off. And voila!, nothing to refill!

If you go to the middle east, north Africa and eastern Europe, you’ll find that there are plenty of diesels that make it to 150k miles without major incidents, and you should see the abuse they take (both in terms of fuel quality and driving).

Lastly, tell me which car, while providing the same driving feel (tones of torque at low RPM, great pickup) will match the 30 city and 41 highway (very conservative as many people seem to be getting more like 50 on the highway) that the Jetta TDI gets? There really aren’t many, if any, cars that get close to that, most that have high mpg run of shitty 4 bangers with no pickup and painfully slow acceleration, which is not an option for most of us here…

Now don’t get me wrong, diesel isn’t that amazing, and even if Audi proved that it’s possible to make great sports cars with diesel, and even win Le Man many times in a row with them, few mass-market cars with diesel engines are really nice to drive. BMW has one though…

The US charges higher taxes on diesel, which partially explains the price difference at the pump, but the rest has more to do with refineries not making it in large enough quantities, not sure the precise reason though…

I think Mazda did smartest move of all manufacturers. The cost of developing small diesel is less then development of hybrid and much less then future maintenance of the hybrid. Except in US & Japan (total population about 500 millions people) diesel is very popular with the rest of the civilized world (much more then 500 million people, as a matter of fact EU alone is 500 millions). The hybrid have its place in the market place, but diesel already has a bigger slice. There is nothing precluding Mazda to stick diesel into hybrid, if they choose to add another dimension.

Should be able to shave a couple hundred pounds off an 6+ passenger vehicle with little effort.

DB9;-)

PS. Overall, the lowest total impact to the environment from production to recycle… and there ain’t no refuting that!;-)