Results of a theoretical description of collisionless kinetics of radial expansion of two-component (electron–ion) plasma in the one-dimensional cylindrical formulation of the problem are presented. The electric-field mechanism of supersonic expansion of the plasma flame due to the motion of the electron–ion ensemble and self-consistent electric field in the diode with the potential difference applied to it is demonstrated. The spatiotemporal evolution of the ion energy distribution function, electric potential, and rate of expansion of the emission boundary of the plasma flame is shown. The calculated rates of flame expansion at the copper cathode (~1.5 × 10 6 cm/s) well agree with the experimental data.