Reflected-shock ignition of SiH4/H2/O2/Ar and SiH4/CH4/O2/Ar mixtures

High-temperature experiments were performed behind reflected shock waves with H-2/O-2, SiH4/H-2/O-2, CH4/O-2, and SiH4/CH4/O-2 mixtures highly diluted in argon. Reflected-shock temperatures ranged from 1000-2250 K at a pressure near 1 atm. Reaction progress was monitored by observation of the time histories of several species by the use of emission techniques, including OH*, SiH4, and CH*. The oxidation and ignition data are reported in the form of species concentration profiles and plots of characteristic times as a function of temperature. The presence of silane in the fuel/O-2 mixtures markedly reduced the ignition delay time of all H-2/O-2 and CH4/O-2 mixtures, usually by a factor of two or more, even at molar SiH4 concentrations as low as 1% of the fuel concentration. Although the decrease in ignition delay time was, in some cases, quite significant, the activation energy of ignition when plotted on an Arrhenius diagram remained virtually unchanged; this result indicates that the chain-branching behavior that takes place when silane is present, although faster and through different elementary reactions, is similar to the behavior when silane is not present. The addition of silane to H-2/O-2 mixtures also appears to extend the chain-branching kinetics to lower temperatures, eliminating the classic chain termination seen near the second explosion limit of H-2/O-2 ignition.