COMBUSTION (AFR, FLAME TEMP, LHV)

Stoichiometric air-fuel ratio (AFR) is the minimum air mass per fuel mass for complete combustion. For C_xH_y: AFR_stoich = (x + y/4)·4.76·28.84 / (12x + y). Excess air λ > 1 ensures complete combustion at the cost of dilution; λ < 1 produces CO. Adiabatic flame temperature is the temperature reached when all heat release goes into raising product enthalpy; real flames sit below this due to dissociation and heat loss. LHV (lower heating value) excludes water vapor latent heat; HHV (higher) includes it.

• CxHy + (x + y/4)(O₂ + 3.76 N₂) → xCO₂ + (y/2)H₂O + 3.76(x+y/4)N₂
• AFR_stoich = mass_air / mass_fuel at λ=1
• λ = AFR_actual / AFR_stoich
• LHV = HHV - n_H2O·h_fg / m_fuel

References & StandardsNFPA 86, API 560, AGA-3, Turns "Combustion" Ch. 2

Use for burner sizing, furnace energy balance, IC engine analysis, gas-turbine combustor design. Compute AFR for the fuel composition, set excess air per code (boilers typically 5-15%, gas turbines 200-400% lean), then estimate flame temperature for material selection in the combustion chamber. Check NOx production sensitivity to peak temperature.