What Happens During A Combustion Reaction?

Fuel + Oxygen ---> carbon dioxide + water

Burning is called combustion.

The most common combustion reaction occurs when a carbon compound reacts with oxygen to produce carbon dioxide and water.  This is called pure or complete combustion.  When you have incomplete combustion, other products form such as carbon (soot) or carbon monoxide.  

--Source:  Mallaney's Chemistry Lab Manual