mass balance of single species

antonietta

hi, I have a problem with mass balance . I hope that you can help me.. I've simulated a combustion reaction but even if the solution converge, when I have check the mass balance of each species it gives me starnge results. The total mass balance is ok, but the mass fraction of each element is wrong. For example, I've set as boundary condition mass flow inlet for a fule composed of 80% ch4 and 20% hydrogen, when i do a report---area weighted average---mass fraction ---on inlet conditions it gives different composition...why? i should have 3% of o2 in flue gas while i found 0.01% how is it possible???? where is the error?