Question: Combustion model

hi,

I am trying to make a simple model of a combustion. To start i am just calculating the composition of the products for a complete combustion and flame´s adiabatic temperature. The equations used to solve the model are:

equations:

    nch4 = nco2;
    2 * nar = 2 * nco2 + nh2o + 2 * no2;
    7.52 * nar = 2 * nn2;
    4 * nch4 = 2 * nh2o;
    nch4 * hfch4 + nar(hfo2 + 3.76 * hfn2) = nco2(hfco2 + cpco2(Tad - 25)) + nh2o(hfh2o + cph2o(Tad - 25)) + nn2(hfn2 + cpn2(Tad - 25)) + no2(hfo2 + cpo2(Tad - 25));

where the params are: 

hfch4 = -74873, hfo2 = 0, hfn2 = 0, hfh2o = -241826, hfco2 = -393522, cph2o = 42.53, cpn2 = 32.53, cpo2 = 33.55, cpco2 = 48.82.

The variables are: 

eq, inputvariable = [nch4(t), nar(t)], outputvariable = [nco2(t), nh2o(t), no2(t), nn2(t), Tad(t)]

Si i have 5 equations, 5 unknown variables. but when i execute the entire worksheet appear a message bellow "sys" saying:

Error, (in DynamicSystems:-AlgEquation) algebraic equations cannot depend on past/future values of the input/output.

Does anybody knowswhat is the problem with the worksheet?

The worksheet is below:

ReacaoCompletaEqQuiT.mwReacaoCompletaEqQuiT.mwReacaoCompletaEqQuiT.mw

Thanks for the helps,

João Rodrigues