combustion vs upturn

combustion

noun
  • A process wherein a fuel is combined with oxygen, usually at high temperature, releasing heat. 

  • A process whereby two chemicals are combined to produce heat. 

  • The act or process of burning. 

  • Violent agitation, tumult. 

upturn

noun
  • an upward turn or trend, especially in business activity or profit 

verb
  • to turn (something) up or over 

How often have the words combustion and upturn occurred in a corpus of books? (source: Google Ngram Viewer )