To ensure that the magnetohydrodynamic (MHD) inlet works in starting state

the concept of critical enthalpy extraction ratio was proposed for the MHD inlet.The quasi-one-dimensional model for the critical enthalpy extraction ratio state of MHD inlet was analyzed using the turbojet engine model

the variable cross-section pipe flow theory and the expressions of modified polytropic efficiencies.By comparison of this model with the computational fluid dynamics (CFD) method

the results show that this model fits good

and the error is less than 5.7%

thus providing a reference for design of the MHD inlet.