采用直接模拟蒙特卡洛方法描述有限个仿真分子的运动、碰撞以及传能效应，计算得到高空羽流非平衡流场特性，利用统计平均方法获取羽流场的宏观参数，并采用佛奥特线型函数描述稀薄气体的展宽，逐线积分得到气体超窄谱红外辐射特性参数，结合反向蒙特卡洛方法计算高空羽流辐射传输方程，利用理论和实验数据验证流动与辐射计算模型的适用性，在此基础上，以某小推力发动机为对象，研究了其流动与超窄谱的红外辐射特性。研究结果表明：高空羽流场由于急剧膨胀，导致密度快速下降，进而产生明显非平衡效应；燃气组分受速度惯性影响，不同分子量的组分会有扩散分离效应；燃气组分谱线细而窄，以多普勒展宽为主，辐射峰值往中波平移，且4.7 μm 的CO及6.5 μm 的H2O发射带辐射能量占有更大份额；辐射亮度轴向分布集中在二倍喷管直径距离内，辐射亮度径向分布集中于分离波线以内的激波区内及内流区，其他区域成指数衰减。

The Direct Simulation Monte Carlo method was used to describe the motion, collision and energy transfer effects of a finite number of simulated molecules. The non-equilibrium flow field characteristics of the high-altitude plume were calculated, and the macroscopic parameters of the plume were obtained by statistical average method. On this basis, the Voigt line function was used to describe the broadening of the thin gas, and line-by-line integration was used to obtain the narrow-spectrum gas radiation. The physical transform equation, combined with the backward Monte Carlo method, were used to calculate the radiation transfer equations of the high-altitude plume. The applicability of the flow and radiation calculation models was verified using theoretical and experimental data. The flow and narrow spectrum infrared radiation characteristics of a small thrust engine were calculated and analyzed by using the above model. The results show that: due to the rapid expansion of the high-altitude plume, the density decreases rapidly, which leads to a significant non-equilibrium effect; the gas is affected by the velocity inertia, and the gas of different molecular weights will have a diffusion separation effect; the gas spectrum is thin and narrow, with Doppler broadening, and the peak of radiation moves to the middle wave, 4.7 μm CO and 6.5 μm H2O emission band radiation energy account for a larger share. The radiance in the axis direction is concentrated within the distance of twice the diameter of the nozzle, while the radiance distributed in the radial direction is concentrated in the shock region and the inner flow region within the separation wave line, and the radiance in other regions decreases exponentially.