Wobbeindeksi

The Wobbe index is a gas-quality parameter used in the energy sector to compare the interchangeability of different fuel gases in pipelines and appliances. It is aimed at ensuring that a replacement or supplementary gas delivers a similar amount of energy per unit of flow at a given pressure, so that burners and equipment operate with stable flame characteristics and efficiency.

The Wobbe index is defined as the higher heating value (HHV) of the gas per unit volume divided by the square root of the gas’s relative density to air. In formula terms, WI = HHV / sqrt(G), where G is the relative density to air, typically calculated as the gas’s molecular weight divided by the molecular weight of air (approximately 28.97 g/mol). Some references use the lower heating value (LHV) in place of HHV; however, HHV is the standard form in many international specifications. Values are usually stated at standard conditions, such as 25°C and 1 atm.

Purpose and use: The WI is used by gas networks, regulators, and appliance manufacturers to assess whether a new or blended gas can be safely and effectively used in existing infrastructure. If two gases have similar Wobbe indices, they tend to produce comparable energy delivery and flame behavior when injected at the same pressure and flow rate. This concept is especially important for natural gas, biogas, upgraded landfill gas, and other mixed or alternative fuels.

Limitations: The Wobbe index is one of several quality criteria; it does not capture all aspects of combustion, such as flame stability under all operating conditions, emissions behavior, or impurities beyond their effect on HHV and density. Changes in WI may require appliance adjustment or certification, even if the index remains within a nominal range.