An experimental and modeling study on combustion characteristics of dimethyl ether/ nitrous oxide/ chlorine

Abstract

PEG and AP are widely used in strategic and tactical missile engines as key components of composite propellants. It remains a challenge to investigate the detailed combustion mechanism of PEG/AP due to the complex structure and complicated chemical reactions. DME, N₂O and Cl₂ are the main intermediates of PEG and AP pyrolysis, respectively, which play a crucial role in PEG/AP combustion. DME/N₂O is also a promising combination propellant because of its high energy content and good combustion and environmental properties. This study systematically investigates the combustion characteristics of DME, N₂O and Cl₂ mixtures based on experimental measurements. The Ignition Delay Times (IDT) of DME/N₂O mixtures at equivalence ratios of 0.5, 1.0, and 2.0 (N₂O as the oxidant) were measured using a high-pressure shock tube at pressures of 10.0 and 20.0 bar and in the temperature range of 1250–1600 K. Besides, half of the N₂O was replaced by Cl₂ to investigate its impact on the ignition characteristics of DME/N₂O. The result shows that although the addition of Cl₂ reduces the activity of the fuel mixture system, the ignition activation energy required for ignition has not changed. The laminar flame speeds of DME/N₂O mixtures were measured by a constant-volume reactor. The equivalence ratios ranged from 0.8 to 1.4, with N₂ content controlled at 60 %, pressure at 1.0 bar, and initial temperature at 298/333 K. The experimental results were simulated using the NUIGMech1.3 model and a constructed model adding Cl₂ related reactions to NUIGMech1.3 in this study. Sensitive and flux analyses were conducted to determine the crucial reactions for the IDT of DME/N₂O and DME/N₂O/Cl₂. The results indicate that the decomposition of DME generates ĊH₃ and ĊH₃O, which is the most reactivity promoting reaction at all temperatures, and it doesn't be influenced by Cl₂ presence. Meanwhile H-atom abstraction from DME by Ḣ is the most reactivity inhibiting reaction, while it shows promoting effect with the Cl₂ addition, and the H-atom abstraction reaction by O₂, which did not show significant sensitivity before the addition of Cl₂, shows the strongest inhibitory effect at this time. H-atom abstraction reactions and C–O bond dissociation are two major pathways of DME primary consumption. Although the presence of Cl₂ did not alter this macroscopic phenomenon, it had a significant impact on the flux of each pathway. Meanwhile, the addition of Cl₂ directly changed the reaction after the third stage in the DME reaction pathways, making the reaction involving Cl₂ dominant at this time. The results in the current study should be a positive contribution to the development and optimization of detailed gas-phase chemical kinetic mechanisms for PEG/AP multicomponent solid propellant.