科研之友
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摘要
The phenomenon of superadiabatic flame temperature (SAFT) was discovered and investigated in a low-pressure HN3/N-2 flame using numerical modelling. A previously developed mechanism of chemical reactions in the HN3/N-2 flame at the pressure 50 Torr and the initial temperature T-0 = 296 K was revised. Rate constants of several important reactions involving HN3 (HN3 (+N-2) = N-2 + NH (+N-2), R1; HN3 (+HN3) = N-2 + NH (+HN3), R2; HN3 + H = N-2 + NH2, R4; HN3 + N = N-2 + NNH, R5; and HN3 + NH2 = NH3 + N-3, R7) were calculated using quantum chemistry and reaction rate theories. Modified Arrhenius expressions for these reactions are provided for the 300-3500 K temperature range. Modelling of the flame structure and flame propagation velocity of the HN3/N-2 flame at p = 50 Torr and T-0 = 296 K was performed using the revised mechanism. The results demonstrate the presence of the SAFT phenomenon in the HN3/N-2 flame. Analysis of the flame structure and the kinetic mechanism indicates that the cause of SAFT is in the kinetic mechanism: exothermic reactions of radicals with hydrogen atoms occur in the post flame zone, which results in the formation of super equilibrium H-2 concentrations. The flame propagation velocity is largely determined by the second-order HN3 decomposition reaction and not by the reaction of HN3 with H, as was previously assumed. Calculation of the flame propagation velocity according to the Zeldovich-Frank-Kamenetsky theory with the decomposition reaction as a limiting stage yielded a value that agrees with that obtained in numerical modelling using the complete reaction mechanism.
- 出版日期2012
