Combustion usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water. In the more general sense, combustion involves a reaction between any combustible material and an oxidizer to form an oxidized product. Combustion is an exothermic reaction , so it releases heat, but sometimes the reaction proceeds so slowly that a temperature change is not noticeable.
There are two types of combustion you are likely to encounter:
Complete Combustion : Also called "clean combustion", clean combustion is oxidation of a hydrocarbon the produces only carbon dioxide and water. An example of clean combustion is burning of candle wax, where the heat from the wick vaporizes wax (a hydrocarbon), which reacts with oxygen in air to release carbon dioxide and water. Ideally, all the wax burns so nothing remains once the candle is consumed. The water vapor and carbon dioxide dissipate into air.
Incomplete Combustion :Also called "dirty combustion", incomplete combustion is hydrocarbon oxidation that produces carbon monoxide and/or carbon (soot) in addition to carbon dioxide. An example of incomplete combustion would be burning coal, where a lot of soot and carbon monoxide is released. Many of the fossil fuels burning incompletely, releasing waste products.