Fuel chemistry – principal elemental constituents For common fossil fuels used in engines and furnaces, which elements are the principal constituents determining heating value and combustion products?

Introduction / Context:
Combustion analysis and emission predictions begin with understanding elemental composition. Most conventional liquid and gaseous fuels are hydrocarbons, so identifying the dominant elements is essential for stoichiometry and calorific value calculations.

Given Data / Assumptions:

• Fuels include coal-derived gases, petroleum liquids, and natural gas.
• Trace elements (sulphur, nitrogen, oxygen) may be present but in smaller amounts.
• Heating value correlates strongly with carbon–hydrogen content.

Concept / Approach:

Hydrocarbons consist of hydrogen and carbon. On combustion, they yield CO2 and H2O as primary products, with heating value driven by the formation of strong bonds (CO2, H2O). Minor sulphur leads to SO2/SO3; fuel-bound oxygen slightly reduces net heating value but does not dominate composition for most fossil fuels.

Step-by-Step Solution:

Verification / Alternative check:

Fuel standards (ASTM/EN) report ultimate analyses with carbon and hydrogen as the largest mass fractions for petroleum fuels and natural gas, confirming the choice.

Why Other Options Are Wrong:

Pairs including oxygen, sulphur, nitrogen, or inert gases do not represent the dominant elemental makeup in typical fossil fuels.

Common Pitfalls:

Overemphasizing trace sulphur or oxygenated additives; these affect emissions or octane/cetane but are not the principal constituents.

Final Answer:

carbon and hydrogen