What are primary and secondary fuels? To which class of fuel do the following belong: coke, wood, petroleum, LPG?

Primary fuels - Fuels that directly produce heat on ignition are called primary fuels. They are
  raw fuels.

Examples are wood, coal, petroleum, natural gas, animal dung, etc.  

Secondary fuels  - Fuels that are processed and prepared from  primary fuelsare called
  secondary type of fuels. 

Examples are charcoal, coke, petrol, diesel, kerosene.