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    Combustion Properties

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    Wobbe Index 

    Also known as Wobbe Number, it is a critical measure used in the fuel gas and natural gas industries to assess the interchangeability of different fuel gases (such as natural gas, biomethane, LPG, and town gas). It offers information about the heating effect a burner is exposed to during combustion of a fuel. The greater the Wobbe index, the greater the heating effect and thereby the greater the load on the burner. The load on a burner is thus directly proportional to the Wobbe index. Different gases with the same Wobbe index will impose the same load on the burner.

    It relates the heating value (calorific value) of a gas composition to the square root of its specific gravity (relative density compared to air):

    $$\text{Wobbe Index (WI)} = \frac{\text{Higher Heating Value (HHV)}}{\sqrt{\text{Specific Gravity}}}$$

    Why It Matters

    • Burner Compatibility: If two different gas mixtures share the same Wobbe Index, they will deliver approximately the same heat output through the same burner nozzle at the same supply pressure
    • Preventing Equipment Damage: If a gas has a Wobbe Index that falls too far outside the expected range for a burner or appliance, it can lead to incomplete combustion, dangerous carbon monoxide (CO) production, flashback, yellow tipping, or thermal damage
    • Grid Blending & SNG: It is heavily used when injecting alternative or greener fuels—like hydrogen, biogas, or propane-air mixes (Synthetic Natural Gas)—into existing pipelines. Utility standards generally allow variations of up to about 5% in the Wobbe Index without requiring customer appliance adjustment