Objective Afterburning of rocket exhaust plumes releases a large amount of heat, which significantly raise the temperature level and infrared radiation intensity of the plume and reduce the stealth capability of the vehicle. Therefore, it is very important to accurately predict the afterburning process of the rocket exhaust plume for finely describing the multi-component reaction flows and to improve the calculation accuracy of the infrared radiation of the exhaust plume. The high-fidelity chemical reaction kinetic model is often used to describe the chemical non-equilibrium afterburning reaction of high-speed flow field. Due to the uncertainty of the parameters of the afterburning chemical model, the reliability of the simulation results of the infrared radiation signature of the plume will be affected. This article will quantitatively study the uncertainty of the reburning reaction rate to evaluate its impact on the exhaust plume flow field parameters and infrared radiation characteristics. Based on this, the key reactions that affect the uncertainty of infrared radiation are extracted and reconstructed. This study can provide theoretical support for accurately predicting the infrared radiation characteristics of the exhaust plume.

Methods The finite rate chemical reaction model expressed by Arrhenius equation was adopted, and it was a H₂/CO/HCl system with the 12-species 17-reaction chemical reaction kinetic model. The Latin hypercube sampling (LHS) method was employed to design the sampling of uncertain input parameters. The physical property parameters of the exhaust plume radiation were calculated using the statistical narrow-band (SNB) model. The radiative transport equation was solved employing the light-of-sight (LOS) method. Additionally, uncertainty analysis of the reacting flows and infrared radiation of rocket exhaust plumes were conducted using the No-polynomial Chaos Expansions (NIPC) method and the Sobol index algorithm.

Results and Discussions The maximum uncertainty of the chemical reaction rates on the temperature of the flow field is about 7.63% (Fig.5(a)) and the temperature difference along the plume centerline between the reference value and the mean value calculated by NIPC is up to 6.45% (Fig.6(a)). The maximum standard deviation of the molar fraction of CO₂ is 0.001 2 and the uncertainty is about 2.5% (Fig.5(b)). The maximum standard deviation of the molar fraction of H₂O is 0.012 3 and the uncertainty is about 10.7% (Fig.5(c)). The uncertainty of infrared radiation intensity within the 2.7 μm band is about 20.4%, which is 7.8% higher than that in the 4.3 μm band (Fig.7-Fig.8). The sensitivity of chemical reaction rate to infrared radiation intensity shows that three chain reactions of H+O₂↔OH+O, H₂+O↔OH+H and H+OH+M↔H₂O+M are the main contributors (Fig.9).

Conclusions The uncertainty of the afterburning chemical reaction rate on the flow field structure, temperature and gas mole fraction is small and the uncertainty is negatively correlated with the standard deviation. The uncertainty of chemical reaction rate to infrared radiation is higher than that of flows, the uncertainty of 2.7 μm is the highest and the uncertainty of different bands is different. All the 17 reactions have different effects for the infrared radiation, and the sensitivity of the three chain reactions to infrared radiation is the largest. Based on the reaction rate experimental data, the chemical kinetic rates of the three chain reactions are reconstructed and the relevant parameters are given.