Wobbe Index (WI) is used to compare the combustion energy output of different composition fuel gases. Wobbe index is used to define interchangeability of fuel.
Two fuels with identical Wobbe Index at given pressure and valve setting (orifice size), the energy output will be identical. The variation in WI is typically upto 5% (but maximum could be 10% for some manufacturer).
Wobbe Index (WI) is define as
WI = HHV / Sqrt (SG)
where
Sqrt = Square root of
HHV = High Heating Value (Btu/Scf)*
SG = Specific Gravity (MWgas / 28.96)
- Some may use Lower Heating Value to define WI