Gaoping Feng

Propellants play a crucial role in the propulsion systems of aerospace vehicles, and their combustion characteristics are susceptible to external environmental conditions. This study systematically investigated the impact of various initial conditions on the combustion process of ADN-based propellant, including combustion products, equilibrium pressure, adiabatic temperature, and ignition delay time. The results indicate that the primary combustion products of ADN-based propellant include N₂O, N₂, CO₂, OH, and others. ADN-based propellant exhibits a distinct two-stage combustion process under low pressure and temperature conditions (P₀ = 2 atm, T₀ = 586 K). Conversely, under high pressure and temperature conditions (P₀ = 10 atm, T₀ = 2930 K), the two stages of combustion occur almost simultaneously, making them difficult to distinguish. Furthermore, as the initial temperature increases, the ignition delay time decreases significantly, and the combustion rate accelerates. When the initial temperature rises from 400 K to 2800 K at a pressure of P₀ =10 atm, the ignition delay time decreases from 3.5 ms to 0.6 μs. Interestingly, changes in initial pressure have a relatively minor impact on the ignition delay time compared to changes in temperature. Therefore, temperature has a more crucial influence on the combustion characteristics of ADN-based propellant than pressure. This study holds promise for providing new combustion optimization strategies for the aerospace industry and promoting the development of aircraft designs towards higher performance and sustainability.

The present study explores the influence of diverse nozzle geometries on the combustion characteristics of ADN-based energetic propellants. The pressure contour maps reveal a rapid initial increase in the average pressure of ADN-based propellants across the three different nozzles. Subsequently, the pressure tapers off gradually as time elapses. Notably, during the crucial initial period of 0–5 μs, the straight nozzle exhibited the most significant pressure surge at 30.2%, substantially outperforming the divergent (6.67%) and combined nozzles (15.5%). The combustion product variation curves indicate that the contents of reactants ADN and CH₃OH underwent a steep decline, whereas the product N₂O displayed a biphasic behavior, initially rising and subsequently declining. In contrast, the CO₂ concentration remained on a steady ascent throughout the entire combustion process, which concluded within 10 μs. Our findings suggest that the straight nozzle facilitated the more expeditious generation of high-temperature and high-pressure combustion gases for ADN-based propellants, expediting reaction kinetics and enhancing combustion efficiency. This is attributed to the reduced intermittent interactions between the nozzle wall and shock waves, which are encountered in the divergent and combined nozzles. In conclusion, the superior combustion characteristics of ADN-based propellants in the straight nozzle, compared to the divergent and combined nozzles, underscore its potential in informing the design of advanced propulsion systems and guiding the development of innovative energetic propellants.

MXenes, renowned for their remarkable photothermal properties, have demonstrated significant potential in applications such as solar desalination, photothermal therapy, and flexible photothermal devices. The physical and chemical properties of MXenes are profoundly influenced by their lateral dimensions. However, a comprehensive understanding of how the lateral size affects the photogenerated carrier dynamics in MXenes remains elusive. In this study, Ti₃C₂Tₓ samples with varying lateral sizes were successfully prepared via a centrifugation-based method. Using femtosecond pump-probe spectroscopy, we systematically investigated the ultrafast carrier relaxation processes in MXenes dispersions of different lateral sizes. Our findings reveal that smaller lateral size leads to relatively lower density of photogenerated carriers, strengthened electron-phonon coupling, and increased thermal diffusion rates. Moreover, we observed a redshift of the ground-state bleaching negative peak due to the cooling of hot electrons, with a higher rate in samples with smaller lateral size, further supporting the presence of enhanced electron-phonon coupling. These results provide critical insights into the underlying relationship between lateral dimensions and ultrafast carrier dynamics in MXenes, which shed light on design of MXene-based optoelectronic devices with specific thermal management and photothermal applications.