Wobbe Index WI = HHV / √SG - measure of thermal energy delivered through a fixed orifice. Combustors are rated by Wobbe, not calorific value.
Formula
$$ WI = \frac{HHV}{\sqrt{SG}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $HHV$ | Gross calorific value | MJ/m³ | ISO 6976 from composition |
| $SG$ | Specific gravity vs dry air | - | MW_gas / MW_air |
Sources
- ISO 6976 - Natural gas calorific value.
- EN 437 - Wobbe family bands.