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.