oil burner vs steam generator

oil burner

noun
  • A heating device which burns fuel oil; an oil furnace. 

  • A machine that uses oil as its fuel. 

  • A device whose operation causes apparent combustion of lubricating oil. 

steam generator

noun
  • a type of boiler fitted in a diesel locomotive or another rail vehicle, which provided steam heating in steam-heated passenger trains that had previously been hauled by steam locomotives. 

How often have the words oil burner and steam generator occurred in a corpus of books? (source: Google Ngram Viewer )