Investigation on the combustion mechanism for NF3/H2 in DF/HF chemical lasers: a new perspective based on deep potential molecular dynamics simulations

Abstract

Combustion-driven deuterium fluoride/hydrogen fluoride (DF/HF) lasers are a crucial type of chemical lasers. Their chemical efficiency mainly depends on the production efficiency of atomic fluorine in the combustion chamber, where NF₃ serves as the fluorine resource, and H₂ acts as the reducing agent. However, due to the complex combustion process, high reaction temperatures, and potent corrosiveness of the products, the combustion mechanism of NF₃/H₂ in the combustion chamber is still not fully revealed, including the chemical details of F atom generation. In this work, we firstly employed the molecular dynamics (MD) method to simulate the combustion reaction for combustion-driven DF/HF chemical lasers. Additionally, for the first time, a high-accuracy neural network potential (NNP) for the NF₃/H₂ system was constructed using machine learning methodologies. The simulation results reveal that the combustion process of the NF₃/H₂ system comprises three stages: the initiation of combustion, the generation of HF, and the formation of N₂. The fluorine atoms in the system primarily originate from the cleavage of the N–F bond in N₂F₄, which is formed via the dimerization of NF₂. Temperature and molar ratios of reactants are two important factors influencing the F atom formation. Higher temperatures and an excess number of NF₃ favor the generation of F atoms. Besides, we found that the initial HF production stems from H-abstraction reaction between the F radical and H₂, rather than the previously proposed reaction between NF₃ and H₂. The NNP-based MD simulations unveil the atomic-scale reaction mechanisms for NF₃/H₂ combustion in combustion-driven DF/HF chemical lasers, indicating its potential as an effective tool for the studies in the field of chemical lasers. The results also offer theoretical insights for enhancing the performance of the combustion-driven DF/HF chemical lasers.