kerosene vs liquefied petroleum gas

kerosene

noun
  • A thin colorless to straw-colored petroleum-based fuel heavier than gasoline/petrol or naptha but lighter than diesel, used primarily as jet fuel but also for heating and lighting in some remote or impoverished areas. 

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 kerosene and liquefied petroleum gas occurred in a corpus of books? (source: Google Ngram Viewer )