A turbojet is travelling at high Mach number and the ambient pressure, \(p_{\mathrm{a}}\), and temperature, \(T_{\mathrm{a}}\), are 0.5 bar and \(220 \mathrm{~K}\) respectively. It is also known that the stagnation temperature at the inlet of the compressor is \(T_{01}=400 \mathrm{~K}\). If the intake nozzle isentropic efficiency, \(\eta_{\mathrm{i}}=0.8\), find the pressure ratio, \(p_{01} / p_{\mathrm{a}}\).

[5.8]