Fuel interchangeability metric: The “Wobbe index” is primarily a characteristic used for which class of fuels?

Introduction:
The Wobbe index is a key parameter for assessing whether one fuel gas can substitute for another without changing burner settings. Utilities and industrial users rely on it to maintain safe, efficient combustion across varying gas compositions.

Given Data / Assumptions:

• Wobbe index W = Higher (or lower) heating value divided by the square root of the specific gravity (relative density) of the gas.
• Burners are orifice-and-pressure based devices sensitive to volumetric energy flow.

Concept / Approach:
For gas-fired equipment operating at a given pressure drop, volumetric flow changes with gas density. The Wobbe index normalizes heating value by density effect, so fuels with similar W values deliver comparable heat input. Therefore, it is specifically a characteristic of gaseous fuels, not liquids or solids.

Step-by-Step Solution:
Identify definition of W.Recognize applicability to gas burners and pipelines.Conclude the relevant class is gaseous fuels.

Verification / Alternative check:
Gas-grid specifications and appliance standards state acceptable Wobbe index ranges to ensure interchangeability.

Why Other Options Are Wrong:

• Solids/liquids/fat coals/biomass slurries: Not used with Wobbe index; other metrics apply.

Common Pitfalls:
Confusing heating value alone with Wobbe index; W accounts for density effects in gas delivery.

Final Answer:
gaseous fuels