Dry gaseous fuels: The presence of which component in a dry gaseous fuel does not contribute to its calorific value, and may even dilute it?

Introduction / Context:
Calorific value reflects the heat released upon complete combustion of a fuel. For gaseous fuels, the composition—fractions of combustible species versus inerts or oxidants—determines usable heating value and flame characteristics. Understanding which components contribute and which do not is essential for burner tuning and energy balance calculations.

Given Data / Assumptions:

• “Dry” gaseous fuel excludes water vapor for the analysis.
• Combustibles include H2, CO, CH4 and higher hydrocarbons.
• Oxygen present within the fuel acts as a built-in oxidizer/diluent rather than a fuel.

Concept / Approach:

Only combustible constituents generate heat by oxidizing to final products (CO2 and H2O). Noncombustible or already-oxidized components either do not release heat or can lower the adiabatic flame temperature by dilution. Oxygen in the fuel stream is not a fuel; it reduces the required external air but does not add to calorific value itself.

Step-by-Step Solution:

Verification / Alternative check:

Bomb-calorimetry or calculated heating values confirm that including oxygen in the mixture lowers the net heating value per unit volume compared to an equivalent inert-free, oxygen-free stream with the same combustibles.

Why Other Options Are Wrong:

Hydrogen, CO, and hydrocarbons (carbon) are the main energy contributors in gas fuels. Sulphur compounds (e.g., H2S) are combustible, though undesirable for corrosion and emissions; they do contribute heat upon oxidation to SO2.

Common Pitfalls:

Confusing net heating value effects with stoichiometric air requirements; overlooking safety impacts of oxygen-enriched fuel streams.

Final Answer:

Oxygen