Liquid n-butane at T0, is sprayed into a gas turbine with primary air flowing at 1.0 MPa,

Question:

Liquid n-butane at T0, is sprayed into a gas turbine with primary air flowing at 1.0 MPa, 400 K in a stoichiometric ratio. After complete combustion, the products are at the adiabatic flame temperature, which is too high, so secondary air at 1.0 MPa, 400 K is added, with the resulting mixture being at 1400 K. Show that Tad 1400 K and find the ratio of secondary to primary air flow.