During an incomplete combustion, instead of Carbon Dioxide, Carbon Monoxide and Carbon are produced as well.
Basic Equation for an incomplete combustion
hydrocarbon + oxygen à carbon monoxide + carbon + water
- Key reason for incomplete combustion is due to insufficient supply of oxygen available to react with the hydrocarbons. As partial combustion occurs, hydrogen will still react and oxide to form water vapor. However due to the shortage of oxygen, carbon monoxide or carbon in the form of soot is produced instead.
2C14 H30 + 33O2 → Heat Energy + 4C + 12CO + 12CO2 + 30H2O
Diesel+ Oxygen → Energy+Carbon(Soot)+ Carbon Monoxide+ Carbon Dioxide+ Water Vapour
C14 H30 +11O2 → Heat Energy + 7C +7CO + 15H2O
Diesel + Oxygen → Energy + Carbon(Soot) + Carbon Monoxide + Water Vapour
The chemical equation above demonstrates the 2 different outcomes of incomplete and partial combustion where one still manage to produce carbon dioxide along with soot and carbon monoxide whereas for the second equation only demonstrates soot and carbon monoxide as by products. Carbon particles are usually seem as soot or smoke.
Reference from: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/crudeoil/hydrocarbonsrev1.shtml