Stoichiometric Combustion

Stoichiometric or Theoretical Combustion is the ideal combustion process where fuel is burned completely.

A complete combustion is a process burning all the carbon (C) to (CO2), all the hydrogen (H) to (H2O) and all the sulphur (S) to (SO2).

The combustion process can be expressed:

(C + H (fuel)) + (O2 + N2 (Air)) → (Combustion Process) → (CO2 + H2O + N2 (Heat))

Key Concepts:

• Stoichiometric Ratio: The perfect ideal fuel ratio where chemical mixing proportion is correct and all fuel and air is consumed without excess.
• Excess Air: Additional air supplied beyond the stoichiometric requirement (typically 10-20% in practice).
• Fuel-Lean Mixture: Air content higher than stoichiometric ratio.
• Fuel-Rich Mixture: Air content less than stoichiometric ratio.

Example - Methane Combustion (CH4):

Stoichiometric (0% excess air): CH4 + 2(O2 + 3.76 N2) → CO2 + 2 H2O + 7.52 N2

With 25% excess air: CH4 + 1.25 × 2(O2 + 3.76 N2) → CO2 + 2 H2O + 0.5 O2 + 9.4 N2