Heat of Combustion (HHV & LHV) Calculator

How this Heat of Combustion Calculator Works

This tool estimates the energy released when a fuel is burned completely in oxygen. It supports three practical workflows that mirror real laboratory and field practice: (1) computing from an ultimate analysis using well‑accepted correlations, (2) deriving gross heat from bomb‑calorimetry test data, and (3) selecting a preset fuel with editable properties for quick checks. Results are reported as Higher Heating Value (HHV, also called gross calorific value) and Lower Heating Value (LHV, net calorific value). HHV assumes the water produced by hydrogen combustion condenses to liquid at the reference temperature, so the latent heat of vaporization is counted. LHV assumes the water leaves as vapor, subtracting that latent heat. For many engineering comparisons, LHV is preferred because water usually exits the system as steam; for condensing systems or solid fuel standards, HHV is common.

For elemental calculations, we implement the Channiwala–Parikh correlation, which performs well across a wide range of solids and liquids because it explicitly includes ash and moisture. We also show the classic Dulong estimate for reference. The ultimate analysis inputs are mass percentages of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), ash, and moisture. If the numbers do not sum to one hundred percent, the interface warns you so you can normalize your dataset. After HHV is computed, the LHV is corrected by subtracting the latent heat associated with water formed from hydrogen and any initial moisture: LHV ≈ HHV − 2.442·(9·H + M), where H and M are in mass percent and 2.442 MJ/kg is the latent heat of vaporization of water at 25 °C.

Stoichiometry is calculated from the same ultimate analysis. Theoretical oxygen demand in moles per kilogram is n_O2 ≈ n_C + n_H/4 − n_O/2 + n_S, where n denotes moles of the element per kilogram of fuel. Converting to mass, the oxygen required (kg O₂ per kg fuel) is multiplied by 1/0.232 to obtain the theoretical air requirement (kg air per kg fuel), assuming dry air contains twenty‑three point two percent oxygen by mass. Products for complete combustion are reported as carbon dioxide and water on a produced‑per‑kilogram‑of‑fuel basis, which helps when preparing emission and mass‑balance checks.

Key Equations and Notes

Worked Example (as‑received biomass)

Suppose you analyze a chipped wood sample with C=50%, H=6%, O=44%, N=0%, S=0%, Ash=0.5%, Moisture=0%. Channiwala–Parikh gives HHV ≈ 19.5 MJ/kg. The LHV correction subtracts about 2.442·(9·6 + 0) / 100 ≈ 1.318 MJ/kg, so LHV ≈ 18.2 MJ/kg. The carbon moles per kilogram are 0.50/0.012 ≈ 41.67 mol; hydrogen moles are 0.06/0.001 ≈ 60.0 mol; oxygen moles are 0.44/0.016 = 27.5 mol. Therefore, n_O2 ≈ 41.67 + 60/4 − 27.5/2 = 41.67 + 15 − 13.75 = 42.92 mol, or 1.373 kg O₂/kg fuel. Dividing by 0.232 suggests 5.92 kg of dry air per kilogram of fuel. CO₂ formed is 41.67·0.044 ≈ 1.833 kg/kg, and H₂O from hydrogen is 9·0.06 = 0.54 kg/kg.

Tips and Assumptions

• Use as‑received values when comparing to field performance; use dry or dry‑ash‑free bases for intrinsic fuel ranking.
• Preset values are editable; adjust density to obtain volumetric energy (MJ/L) for liquid fuels.
• Calorimetry mode reports gross heat. To estimate LHV from a bomb test, provide hydrogen and moisture from a parallel ultimate analysis.
• Air requirement is stoichiometric; real burners operate with excess air (equivalence ratio less than one).