I don't know anything about "fashion" when it comes to cars. I can't figure out why the Hummer 2 is selling at all, for instance. But here is my $.02 as a mechanical engineer.

Diesel has some advantages, but as others have said the reason for the price difference in Europe is due to taxes. In the US, diesel is about the same cost as gasoline.

Diesel's have quite a few disadvantages:

- Much more expensive to build (29 or 30:1 compression ratio means a stronger and heavier engine is required).
- Much less power than an equivalent gasoline engine
- Extremely difficult to start in very low temperatures
- Fuel non-volitile at very, very low temperatures
- Requires a very large oil sump due to combustion contaminants
- Noiser than gasoline engines
- "Dirtier" than gasoline engines (not only in particulate pollution, they just get physically very dirty)

They have a couple of nice advantages:

- Much more efficient than gasoline engines (due to the higher comresson ratio. There is an upper limit on Rc for gas engines because the fuel detonates. The compression ratio determines a displacement engine's efficiency.)
- Tend to last much longer than gasoline engines because they are more heavily built and run at lower RPMS and lower temperatures
- The energy density of the fuel, per unit volume, is higher for diesel (more range on your fuel tank)
- Generally huge torque at low engine speed, which is great for pulling vehicles

Diesel doesn't solve any ecological, political or financial issues for the world. It's just another way of refining oil. Hydrogen is probably the near-term "answer", but you need to make electricity to make hydrogen, which, at least in North America, is over 90% coal generated. If we can ever figure out how to make non-hydrocarbon electricity on a large scale (hyrdo doesn't do this), then hydrogen represents a great way of transporting the engergy.

Airplanes are a bigger issue. The energy density of hydrogen is quite low, so what do the airplanes run when the oil is gone?

Jim