Addition of steam to combustors in gas turbines and to internal combustion engines reduces the peak temperatures and lowers emission of NOx. Consider a
modification to a gas turbine, as shown in the figure, where the modified cycle is called the Cheng cycle. In this example it is used for a cogenerating power
plant. Assume 15 kg/s air with state 2 at 1.25 MPa, unknown temperature, is mixed with 2.5 kg/s water at 450°C at constant pressure before the inlet to the
turbine. The turbine exit temperature is T4 = 500°C, and the pressure is 120 kPa. For a reasonable turbine efficiency, estimate the required air temperature at
state 2. Compare the result to the case where no steam is added to the mixing chamber and only air runs through the turbine.