My diesel engine can burn coal

[Hardlec]

If I select a diesel engine, I must either used an enormous number of funnels of induced boilers to get top engine efficiently.  
A diesel engine should have boilers greyed out.  They are not needed.  
Engine efficiency should be 100% with any funnel.
It is possible to select coal as a fuel for a diesel engine. Only oil should be allowed as a fuel for Diesels.