Infrared radiation spectra produced by vibration–rotation transitions in multicomponent gases within the vacuum plume of attitude and orbital control engines constitute crucial radiation sources for optical target identification and space maneuver recognition, and rapid prediction of these signatures is essential for real-time forecasting. This study introduces an axisymmetric vacuum plume flow field model based on a simplified point-source approach that accommodates multicomponent combustion gases. Using the Maxwellian velocity distribution and a velocity–position angle algorithm, normalized number density, velocity, and temperature distributions are derived. A plume–freestream interaction model founded on noncentral fully elastic collision theory is incorporated, and overall plume properties are obtained via density-weighted averaging. Neglecting non-equilibrium radiation effects, the high-temperature gas absorption coefficient is calculated using a statistical narrowband model and radiative transfer is solved via the line-of-sight method. The model is validated against direct simulation Monte Carlo results for single-gas and MBB bipropellant plumes and confirmed using infrared spectral data in the 2.0–4.5 μm band. The proposed framework achieves 10²–10³-fold higher computational efficiency than conventional DSMC approaches. Freestream effects on plume diffusion and momentum exchange diminish with increasing altitude, as does the freestream velocity’s enhancement of radiation intensity, whereas greater plume expansion at higher altitudes increases overall radiation intensity.

Thermochemical non-equilibrium effects directly influence temperature and species distributions in rocket exhaust plumes. However, studies focusing on the thermochemical non-equilibrium effects in rocket plumes are limited. This study develops a two-temperature flow field model incorporating translational–rotational and vibrational–electronic temperatures through an additional internal energy equation coupled with the Navier–Stokes (NS) equations. Energy relaxation is computed using the Landau–Teller formula with Park's high-temperature correction. Transport properties are derived from Wilke's mixing rule combined with Blottner's viscosity curves and Lennard-Jones collision integrals. A nine-species, ten-reaction finite-rate chemistry model describes the chemical kinetics. Simulations of an aluminum-free double-base propellant rocket plume are conducted across altitudes of 20–80 km and free-stream velocities of 1500–2500 m/s. At 20 km, the translational and vibrational temperatures differ by less than 13% locally, indicating near-equilibrium conditions. At 80 km, the temperature separation reaches 300 K in shock regions, and species concentration predictions deviate by over 50% from equilibrium model results. The thermochemical non-equilibrium factor increases by three orders of magnitude from 20 km (10−4) to 80 km (0.3–0.4). The free-stream velocity effect exhibits altitude-dependent reversal: at altitudes below 50 km, higher velocities increase species factors by suppressing dilution, whereas above 60 km, enhanced shear-layer mixing causes species factors to decrease with velocity. For the investigated aluminum-free double-base propellant rocket plume configuration, these findings establish 60 km as the critical altitude above which two-temperature non-equilibrium models become necessary for accurate plume characterization.