when you want to calculate this ratio, just change the flow rates to mass rates (by multiplying with the density)

Equivalence Ratio (ER) for Fuel Mixtures { % mole or % volume or mass % known for species}

a) In terms of O2 , ER= Stoich O2 of mix mole / Supplied O2 in mole for the mix or Stoich O2 of mix in kg / Supplied O2 in kg for the mix or Stoich O2 of mix m3/ Supplied O2 in m3 for the mix

If mole % known, Stoich O2 of mix per mole mix= {Mole % of Fuel 1* stoich O2 in mole for Fuel 1/mole Fuel1+ Mole % of Fuel 2* stoich O2 in mole for Fuel 12 /mole Fuel2+….}/100.

If vol % known, Stoich O2 of mix per m3 mix= {vol % of Fuel 1* stoich O2 of Fuel 1 in m3 /m3 Fuel1+ vol % of Fuel 2* stoich O2 in m3 for Fuel 2 /m3 Fuel2+….}/100.

If mass % known, Stoich O2 of mix in kg per kg mix= {mass % of Fuel 1* stoich O2 of Fuel 1 in kg /kg Fuel1+ mass % of Fuel 2* stoich O2 in kg for Fuel 2 /kg Fuel2+….}/100.

b) In terms of air, ER: Stoich air of mix mole / Supplied air in mole for the mix or Stoich air of mix in kg / Supplied air in kg for the mix or Stoich air of mix m3/ Supplied air in m3 for the mix

For air replace “O2” in (a) by “air” .

For e.g. , Stoich air of mix per mole mix= {Mole % of Fuel 1* stoich Air in mole for Fuel 1/mole Fuel1+ Mole % of Fuel 2* stoich air in mole for Fuel 12 /mole Fuel2+….}/100.

c) Examples: For e.g if fuel mix is 60 % CH4 (weight) and 40 % H2, and supplied O2 is 9.33 kg, then stoich O2 of CH4= 4 kg per kg CH4, and 8 kg O2 per kg H2, then stoich O2 in kg per mix is 0.6*4+0.4*8= 5.6 kg O2 per kg mix, ER= 5.6/9.33=0.6

d) If fuel mix is 15.88 % CH4 (mole) and 84.12 % H2, then estimate ER if supplied O2 is 1.24 per mole mix, Stoich O2 per mole fuel = {0.1588 mole CH4 per mole mix} *2 mole of O2 /mole CH4+0.8412*0.5=0.738 mole O2 per mole fuel, ER= 0.738/1.24=0.6

NOTE O2 supplied in moles = Air Supplied in moles *0.21

O2 supplied in kg = Air Supplied in kg *0.23

See Texts by Kalyan Annamalai and Ishwar Puri:

Combustion Book: http://www.crcpress.com/product/isbn/9780849320712

Advanced Thermo book: http://www.crcpress.com/product/isbn/9781439805725

Mass rate is better for calculation.