@ Ashrak,
I've done a lot of research, and I disagree completely. While I will grant you that you will always get more power out of diesel than gasoline, it does NOT burn cleaner at all, least of all in the States because our diesel fuel standards suck. That will improve with some of the new fuel and diesel engine standards we finally got passed, but it still isn't as good as what is available in Europe already. Oh well, at least now they can hook up catalytic converters without the sulfur immediately poisoning them.
But to the point, you can run a hybrid on whatever fuel you want. If you want to run a hybrid on diesel, more power to you. The advantage of a hybrid is its ability to minimize the time that the engine is on and, when it is on, run it in a more efficient fashion than is possible in a system that does not have electric drive.
The biggest problem with diesel compression-ignition engines is that they...-it's a combination of things, really. Part of the reason a diesel engine is more powerful/energy efficient than a gasoline engine is that it burns hotter and with a higher compression ratio. They also don't throttle the air used to burn the fuel. Gasoline engines are controlled by deliberately lowering their pumping efficiency (throttling the air intake). Diesel engines are always operated wide open, pumping as much air into the cylinder as you can. Control is handled by fuel injection rate.* So, diesel engines are always running lean (more air present than needed for a complete burn). i.e., there is plenty of oxygen left over once the fuel is burned to react with nitrogen. The consequence of oxygen and high temperature is that the nitrogen chemistry takes off like a rocket. NOx emissions from diesel engines are horrible, and only new engines will be able to use catalytic converters to reduce the NOx down to something remotely acceptable. Not having seen such engines in action, I cannot speculate whether the emission reductions will be good, adequate, or hardly better than they are now.
But a diesel turbine-driven hybrid? Now that's something that might work pretty well, and I'd sure love to see one attempted. A turbine might be run lean enough to bring the flame temperature down so that nitrogen chemistry isn't as much of a problem. Higher residence times in turbines mean soot and HC emissions should also be reduced.
*I'm talking about conventional SI and CI engines here, not GDI or HCCI or any of the other interesting concepts that most of the industry has refused to adopt. I know there are plenty of alternative engine designs out there which use other control mechanisms.
