You can try chemical cleaners, if the crud is "light" they might help.
Usually, grit is needed to remove the dirt, and oxidized layer(s).
What type/size of grit you need to use depends on how nice you want the metal to look.
Larger/coarser grit will give you a rough and somewhat shiny look, finer grit will give it a more polished, mirror like finish.
A wire wheel on a grinder will "clean" the metal, but give it a rough look, while using metal polish with a cloth wheel will also clean the metal, but leave it much smoother.
All personal choice.
PS. a sandblaster will work well, and fast, but it won't be shiny...