autogas vs liquefied petroleum gas

autogas

noun
  • Liquefied Petroleum Gas (LPG) 

  • Automotive gasoline suitable for use in piston-engined gasoline-powered aircraft. 

liquefied petroleum gas

noun
  • A mixture of propane and butane with traces of some other gases, which is kept in a liquid state at high pressure in metal bottles, and used as a source of gas for cooking, heating and as a fuel in internal combustion engines in vehicles. 

How often have the words autogas and liquefied petroleum gas occurred in a corpus of books? (source: Google Ngram Viewer )