The Wobbe Index (WI) or Wobbe number is an indicator of the interchangeability of fuel gases such as natural gas, liquified petroleum gas (LPG), and town gas and is frequently defined in the specifications of gas supply and transport utilities.
If is the higher heating value, or higher calorific value, and is the specific gravity, the Wobbe Index, is defined as:
The Wobbe Index is used to compare the combustion energy output of different composition fuel gases in an appliance (fire, cooker etc.). If two fuels have identical Wobbe Indices then for given pressure and valve settings the energy output will also be identical. Typically variations of up to 5% are allowed as these would not be noticeable to the consumer.
The Wobbe Index is a critical factor to minimise the impact of the changeover when analyzing the use of substitute natural gas (SNG) fuels such as propane-air mixtures.. The Wobbe Index also requires the addition of propane to some upgraded biomethane products, particularly in regions where natural gas has a high calorific value such as Sweden
Read more about Wobbe Index: Wobbe Index of Common Fuel Gases, Usage, Limitations
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