Numerical study of Ultraviolet and Infrared radiation characteristics of pulsed detonation engine exhaust

Abstract

The radiation characteristics of pulsed detonation engine (PDE) exhaust have significant applications in engine performance monitoring, parameter inversion, and target detection. In this work, an effective model for predict the radiation characteristics of PDE exhaust is developed, both the Ultraviolet (UV) radiation from excited OH molecule (OH${}^{\ast }$, $A^2{\Sigma }^{+}\to X^2{\Pi }_r$) and Infrared (IR) radiation from multiple species are considered. Specifically, the OH${}^{\ast }$ total number density is calculate by a combined chemical mechanism and the OH${}^{\ast }$ population is predicted based on an assumption of a local Boltzmann distribution within excited states. Furthermore, an enhanced Reverse Monte Carlo (RMC) method is proposed to address the radiation transfer. A three-dimensional transient PDE exhaust flow is simulated by Computational Fluid Dynamics (CFD), and the radiation characteristics of the exhaust are presented in detail. The results indicate that the developed model can calculate the exhaust radiation characteristics accurately. The PDE exhaust is similar to the supersonic free jet, with exhaust boundaries being more distinct in UV images, while IR images are more sensitive to shock structures. The $0.31\mu m$ and $2.7\mu m$ bands are identified as the two most distinctive spectral peaks, accompanied by several weaker peaks. Whether in the UV or IR band, the image radiance always decreases as the exhaust develops, while the spectral and integral intensities show different trends. The equivalence ratio has a significant impact, particularly on UV radiation. As the equivalence ratio increases, the UV radiation exhibits an enhancement by 1–3 orders of magnitude, while the variation in the IR radiation is relatively modest. The afterburning phenomenon influences UV radiation primarily by chemiluminescence reaction and IR radiation through heat release.