Air to Fuel Ratio of Hydrocarbons

Air to Fuel Ratio is the mass ratio of air to fuel present in an internal combustion engine. So how do you find the air to fuel ratio of an hydrocarbon ( one that contains carbon and hydrogen)?

1. We need to set up the equation of combustion.

Hydrocarbon + Oxygen = Carbon Dioxide + Water

CnH(n*2)+2 + O2 = CO2 + H2O

2. Balance the equation

X[CnH(n*2)+2] + Y[O2] = CO2 + H2O

3. Get the mass of the hydrocarbon (CnH(n*2)+2) by:

  3.1. Get the mass of carbon (12 is its atomic mass)
         X*12*n

  3.2. Get the mass of hydrogen (1 is its atomic mass)
         X*1*n
  3.3. Add the mass of carbon and hydrogen = total mass (M hydrocarbon)

4. Get the mass of the oxygen (O2):

 4.1. Get the mass of oxygen (16 is its atomic mass)
         Y*16*2

 4.2. Divide 4.1 by 0.232 (23.2% Oxygen in air) = total mass (M oxygen)

5. Air to Fuel Ratio = (M oxygen)/(M hydrocarbon)