For some reason it won't load coal into trains. I tried several different fuels and found:

Will load: solid fuel, rocket fuel, nuclear fuel
Won't load: coal, wood, small poles, wooden chests

As further experimentation I built an inserter that constantly removed the fuel from the requester chest, never letting it get high enough to trigger. For coal the train was build anyway. For solid fuel it was not.

The only pattern I can see is the working fuels modify top speed and acceleration. I have no idea why that would have an effect though.

I do have a number of other mods installed but none are major overhauls and they don't modify coal or solid fuel.

I did a little more digging and it seems coal exists under both game.entity_prototypes and game.item_prototypes while solid-fuel only exists under item_prototypes. This causes the elseif's at control.lua 180 and 202 to skip over it. Changing those to a regular if seems to do the trick.

Hi, I still have this problem with coal.
Rhamphoryncus, could you please explain what modification you did ?
it says "if game.item_prototypes[name].fuel_category == "chemical"".
What should I change ?
Tks