Fuel testing — Under what condition will the gross calorific value (GCV) and net calorific value (NCV) of a fuel be numerically the same?

Introduction:
GCV (higher heating value) includes the latent heat released when the water formed during combustion condenses; NCV (lower heating value) excludes it. Knowing when they are equal aids in comparing fuels fairly.

Given Data / Assumptions:

• Definitions: GCV counts condensation heat of water; NCV does not.
• Water arises from fuel moisture and from hydrogen combustion.

Concept / Approach:
When a fuel contains hydrogen (or moisture), combustion generates water. If that water remains vapor, NCV is lower than GCV by the latent heat of vaporisation. If no water is produced (no hydrogen and zero inherent moisture), there is no latent heat term, and GCV equals NCV.

Step-by-Step Solution:
Recognise the difference GCV − NCV ≈ mass of water produced * latent heat.Set water production to zero by eliminating hydrogen and moisture.Conclude: with zero hydrogen/hydrogen compounds (and negligible moisture), GCV = NCV.

Verification / Alternative check:
Pure carbon (dry) is a classic example: C + O₂ → CO₂ yields no water, thus GCV ≈ NCV.

Why Other Options Are Wrong:

• Zero ash or low carbon does not remove the water term.
• “Under no circumstances” is false; dry hydrogen-free fuels are counterexamples.
• Oxygen content does not directly set the latent heat difference.

Common Pitfalls:
Attributing the GCV–NCV gap to ash or nitrogen; forgetting the role of fuel moisture alongside chemically bound hydrogen.

Final Answer:
If the fuel contains no hydrogen or hydrogen-bearing compounds