Question

Arrange the following based on their calorific value per kg of fuel.
A. Wood Char Coal
B. Dry Cow Dung
C. Kerosene
D. Natural gas
Choose the correct answer from the options given below:

• A. D, C, B, A
• B. A, D, C, B
• C. D, A, B, C
• D. D, C, A, B

Hint:

In general, the state of the fuel often hints at its energy density: Gaseous fuels $>$ Liquid fuels $>$ Solid fuels. Biomass and waste products (like cow dung) almost always sit at the very bottom of the energy scale due to high oxygen and moisture content.

Answer 1

The Correct Option is D

Concept: The Calorific Value (CV) is the amount of heat energy released by the complete combustion of a unit mass of fuel. It generally increases with higher hydrogen content and lower moisture or ash content.

Step 1: Identify the calorific values for each fuel type.

• D. Natural gas: Primarily methane ($CH_4$), it has a very high hydrogen-to-carbon ratio. Its CV is typically around $50,000~kJ/kg$.
• C. Kerosene: A liquid hydrocarbon fuel with a CV of approximately $45,000~kJ/kg$.
• A. Wood Charcoal: A solid fuel created by carbonizing wood. It has a high carbon content and a CV ranging from $25,000$ to $33,000~kJ/kg$.
• B. Dry Cow Dung: A biomass fuel with high moisture and ash content, leading to a much lower CV, typically around $6,000$ to $8,000~kJ/kg$.

Step 2: Arrange in descending order.
Based on these standard values, the descending order is: Natural gas ($50k$) $>$ Kerosene ($45k$) $>$ Wood Charcoal ($\approx 30k$) $>$ Dry Cow Dung ($\approx 7k$). This matches the sequence D, C, A, B.