Definition check – higher vs. lower calorific value of a fuel Fill in the blank: The heat obtained by the complete combustion of 1 kg of a fuel when the products are cooled to the temperature of the supplied air (so that the steam formed is condensed and its latent heat recovered) is called the ______ calorific value of the fuel.

Introduction / Context:
Calorific values come in two standard forms: higher (gross) and lower (net). The distinction lies in whether the latent heat of water formed during combustion is recovered.

Given Data / Assumptions:

• Complete combustion of 1 kg of fuel.
• Products cooled to intake-air temperature, below the dew point so water condenses.
• Latent heat of vaporisation is included in the measured heat.

Concept / Approach:
When products are cooled enough to condense water, the latent heat released is captured. This condition defines the higher calorific value (HCV), also called the gross heating value. The lower calorific value (LCV) excludes this latent heat by keeping water as vapour in the products.

Step-by-Step Solution:
Recognize condition: products cooled to initial air temperature → steam condensed.Recovered latent heat is counted.Therefore the appropriate term is higher calorific value.

Verification / Alternative check:
Fuel datasheets may list both HCV and LCV; HCV ≥ LCV, with the difference approximately proportional to the fuel hydrogen content.

Why Other Options Are Wrong:

• Lower: excludes latent heat, contrary to the stated cooling to condense steam.
• Other labels (net/apparent/gross for gases only) misuse terminology.

Common Pitfalls:
Forgetting that “gross” = “higher” and “net” = “lower.” Always check whether product water is condensed.

Final Answer:
higher