Answer:
Complete combustion takes place in the presence of a sufficient amount of oxygen while an incomplete combustion reaction takes place when there is an insufficient amount of oxygen supply.
The equation for incomplete combustion of propane is: 2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + Heat. If not enough oxygen is present for complete combustion, incomplete combustion occurs. The result of incomplete combustion is, once again, water vapour, carbon dioxide and heat.