[vteco]

I'm going to make someover-generalizations, so forgive me, but it does approximate a topic I've thought a lot about, and in fact experimented with over the last 20 years.

Here goes the generalizations...

Internal combustion engines for transportation (as opposed to stationary uses) benefit from a couple of things not often discussed.

The first is that they like fluid fuels (gasses and liquids). Why? because they can be made to flow through pipes. And because they can be more easily mixed with the oxygen in air. And it can be metered.

The ability to flow through pipes is handy for locating fuel storage (a tank) separate from the engine in a convenient location on the vehicle.

Solid fuels, on the other hand, are more difficult to mix with air, more difficult to store, more difficult to convey from storage, and tough to get inside an engine quickly. A piece of wood bouncing around in a cylinder doesn't make a pretty picture.

The second is that they like fuels of the highest energy density possible. When thinking of liquids and gasses as fuels, you could make a continuum from the least dense, hydrogen, through other gasses like methane and gaseous state propane, through the liquids like gasoline, diesel fuel, home heating oil, and jet fuels.

In an ideal world you'd want the densest fuel possible, because they are the most compact, and compactness is an advantage in a vehicle. Not necessarily in a stationary engine, but in anything mobile, the less space a fuel takes up the better.

It would be great if we could use a solid for transportation. They have lots of density, many are also renewable, but there is no good way to use them in an internal combustion engine.

.....sorry time for dinner. But you probably see where I'm going with this....