Enter exactly 6 of the 7 variables (fuel mass, air-to-fuel ratio, temperature, pressure, gas constant, compressibility factor, and combustion air volume) into the calculator to solve for the missing value. Use absolute pressure and an absolute temperature (the calculator converts °C/°F to K).

Combustion Air Calculator

Enter any 6 values to calculate the missing variable









Related Calculators

Combustion Air Formula

The following formula is used to calculate the required combustion air volume (or volumetric flow) once the air-to-fuel ratio (mass basis) and air conditions are known:

CA = \frac{m_{fuel}\,\mathrm{AFR}\,Z\,R\,T}{P}

Variables:

  • CA is the required combustion air volume (or volumetric flow) at the stated air conditions
  • mfuel is the fuel mass (or mass flow rate)
  • AFR is the air-to-fuel ratio on a mass basis (mass of air / mass of fuel)
  • T is the absolute temperature of the combustion air
  • P is the absolute pressure of the combustion air
  • R is the specific gas constant of air (about 287.05 J/(kg·K) for dry air)
  • Z is the compressibility factor of air (dimensionless; often close to 1 near atmospheric conditions)

To calculate the required combustion air volume, first compute the required air mass as mair = AFR × mfuel, then convert that air mass to volume using the real-gas form of the ideal gas equation: V = m Z R T / P.

What is Combustion Air?

Combustion air refers to the air that is necessary for the process of combustion to occur. Combustion is a chemical reaction that involves the combination of a substance (usually a fuel) with oxygen, resulting in the release of heat and light energy, often in the form of a flame. The combustion air provides the oxygen needed for this reaction. In a heating system, such as a furnace or boiler, combustion air is typically drawn from the surrounding environment and directed into the combustion chamber where it mixes with the fuel. The quality, temperature, and humidity of the combustion air can significantly affect the efficiency and performance of the combustion process. For instance, if the combustion air contains impurities or if it is not supplied in sufficient quantity, it can lead to incomplete combustion, resulting in lower heat output and higher emissions of pollutants.

How to Calculate Combustion Air?

The following steps outline how to calculate the Combustion Air volume.

  1. First, determine the fuel mass (or fuel mass flow rate), mfuel.
  2. Next, determine the air-to-fuel ratio (AFR) on a mass basis (mass of air per mass of fuel).
  3. Next, determine the combustion air conditions (absolute pressure P, absolute temperature T), choose an appropriate compressibility factor Z (often ~1), and use the specific gas constant of air R.
  4. Finally, calculate the combustion air volume (or volumetric flow) using: CA = (mfuel × AFR × Z × R × T) / P.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

fuel mass flow rate (mfuel) = 10 kg/hr

AFR = 17.2 kg air/kg fuel, T = 25°C, P = 1 atm, Z = 1.00, R = 287.05 J/(kg·K) ⇒ CA ≈ 145.3 m³/hr