1. Theoretical oxygen demand from elemental analysis (mass basis)
   Let elemental mass fractions (kg/kg fuel) be $C,H,O,S$, theoretical oxygen demand:

• $O_{2,0} = 2.667C + 8H + 1S - O$ (kg $O_2$/kg fuel)

Oxygen mass fraction in air is about $0.232$, theoretical air demand (mass):

• $L_0 = \dfrac{O_{2,0}}{0.232}$ (kg air/kg fuel)

Actual air:

• $L = \alpha L_0$

2. Volumetric method (standard state)
   First compute theoretical oxygen demand (kmol/kg fuel):

• $n_{O_2,0} = \dfrac{C}{12} + \dfrac{H}{4} + \dfrac{S}{32} - \dfrac{O}{32}$

Theoretical air (kmol):

• $n_{air,0} = \dfrac{n_{O_2,0}}{0.21}$

Standard-state volume:

• $V_{air,0} = 22.414\ n_{air,0}$ (m^3/kg, $0^\circ C$, 101.325 kPa)