This is avery commom problem in the combustion process whatsoever system is used(engines, turbines, boilers, etc...).
In the real field test the follwoing items are known:
1.-fuel composition(main components)
2.-exhaust gas composition(main components) by one standard analysing equipment relative low price and good quality in the market.
3.-Stechiometry relationships
With the values mentioned above one iterative process can be prepared with the follwing steps:
(a)fuel composition
m(excess air): (suppossed to be iterated)
consider 100 units of cble
vCH4:known by fuel analysis
vC2H6:" "
vC3H8:" "
vH2: " "
vN2: " "
vCO: " "
(b)stechiometry relations
CO2->CO2
CO+1/2O2->CO2
CH4+2O2->CO2+2H2O
CH4+3/2O2->CO+2H2O
N2->N2
N2+O2->2NO
C2H6+7/2O2->2CO2+3H2O
C3H8+5O2->3CO2+4H2O
H2+1/2O2->H2O
(c)exhaust gas analysis
vO2hs: with analysis equipment
vCOhs:" "
vNOxhs:" "
(d)calculations
Exhaust flow --> vhs:vCO2hs+vN2hs+VO2hs+vCOhs+vNOxhs
vCO2h:by stechiometrical relations (from above)
vN2hs:" "
vO2hs:" "
vH2Oh:" "
(e)iterative process( 2 to 4 iterations ok if air excess(o) aqurate
vO2hs(d) = vO2hs(c)-->yes(m ok)
No (m')--->(e)
(f)exhaust flow
Units cble/h cble

intro real data from cble flow measurement device)
Nm3 exhaust/h:vhs x Units cble/h
kg/h exhaust:vhs x density(tabulated)
Nm3/h air:m x A(stechiometric air required)