Question

Consider the combustion products of decane (C_10H_22) with air in a steady state, steady flow process at an equivalence ratio of 1.25 and pressure of 1 atm. Estimate the mixture composition assuming no dissociation except for water gas shift equilibrium if the exit temperature is fixed at 2200 K. Estimate the mixture composition and constant pressure adiabatic flame temperature of the process assuming no dissociation except for water gas shift equilibrium.

Answer 1

a)
Equivalence ratio = 1.25 = Mass of 1 mole Air / Mass of 1 mole Decane
So, Mass of 1 mole air = 1.25 * 142 = 177.5 gm/mol
Number of moles of air = 177.5 / 29 = 6.12 moles
Number of moles of Oxysgen = 21% = 21% of 6.12 = 1.224 moles

Reaction is :
C10H22 + 31/2 O2 --> 10CO2 + 11H2O
1 - x 1.224 - 31/2 * x 10*x 11*x
If complete combustion happens then some Decane will be left,
x = 1.224 / 31 = 0.079 moles
Decane left = 1 - 0.079 =  0.921 moles
CO2 formed = 0.79 moles
H2O formed = 0.869 moles