Design Calculators - Mechanical

This calculator determines the theoretical minimum amount of air (stoichiometric air) required for complete combustion of a given fuel, based on its elemental composition by mass. It then calculates the Actual Air Requirement by incorporating an engineer-defined excess air percentage, which is crucial for practical industrial combustion system design, optimization, and emission control.

Key Inputs:

• Fuel Composition (% by mass): Enter the mass percentages of Carbon (C), Hydrogen (H), Sulfur (S), Oxygen (O), and Nitrogen (N) in your fuel. The sum of these percentages should ideally be 100%.
• Excess Air (%): The percentage of air supplied in excess of the stoichiometric requirement. This accounts for incomplete mixing and ensures full combustion in industrial burners. Typical values range from 10% to 50% depending on fuel and burner design.
• Unit System: Select whether to display the air requirement in kg of air per kg of fuel or lb of air per lb of fuel.

Calculated Outputs:

• Stoichiometric Air-Fuel Ratio (AFR): The mass of air theoretically required for the complete combustion of one unit mass of fuel.
• Actual Air-Fuel Ratio (AFR_Actual): The practical mass of air required per unit mass of fuel, considering the specified excess air.

Note on Ash & Moisture: This calculator focuses on the combustible elements. While ash and moisture content in real fuels dilute the combustible mass and affect overall fuel-air ratios on a 'wet' or 'as-fired' basis, they do not directly consume oxygen for combustion. Their impact on air requirement is implicitly handled when determining the mass fractions of C, H, S, O, N in the *combustible* portion of the fuel or by adjusting the total fuel mass if calculating for as-fired conditions.

Note on Complex Combustion Products: This calculation assumes ideal complete combustion products (CO₂, H₂O, SO₂). Real-world combustion can produce minor amounts of incomplete combustion products (CO, unburnt hydrocarbons) and NOx (due to high temperatures and nitrogen in air/fuel). These are combustion phenomena influenced by operating conditions and burner design, and not directly by the stoichiometric air calculation.