Toni Said:

Is information like 'how to build a diesel engine' available online?

We Answered:

I don't want to discourage you but the skill and knowledge levels needed to make a diesel engine is very high. Just the knowledge to make the drawings of the various parts is significant. The skill to weld and machine the various parts is equally high.

Just one part, the fuel injector can be quite complex when you realize it must be timed to match the other movements of the engine.

You would be more likely to succeed if you opted for a ready built gasoline engine and then used methanol or coal gas as the fuel source