The combustion is an exothermic chemical reaction of a fuel with an oxidant. The release of heat can result of flame or glowing light.
Stoichiometry (complete combustion)
CH4 + 2O2 → CO2 + 2H2O + energy
C8H18 + 12.5O2 → 8CO2 + 9H2O + energy
C8H18 + 12.5(3.76N2+O2 )→ 8CO2 + 9H2O + 47 N2 + energy
Incomplete combustion
CxHy + A(3.76N2+O2 ) → aCO2 + bH2O + cN2+dCO+eNOx