| The present study expands the experimental database of boron combustion by studying small crystalline boron particles (<15 μm) ignited in a shock tube in atmospheres consisting of Ar and O2 mixed with varying amounts of F, N2, NO, or CO2. Pressures of 4.25 to 17 atm and temperatures of 1700–3200 K are obtained in quiescent gas mixtures near the shock tube endwall. Visible wavelength emission and absorption spectra are recorded using a spectrometer coupled to a streak camera, and two photodetectors record intensity versus time at a wavelength of 546.1 nm. The streak camera allows recording of multiple time-resolved spectra at rates of approximately 100 μs per spectrum.; Boron particles ignited in Ar/F/O2 mixtures show a rapid decrease by a factor of four in ignition and burning times as the mole fraction ratio is increased from 0 to 0.25. For values of greater than 0.5 there is little change of ignition burning time with . Spectroscopic data taken in pure oxygen environments show residual BO2 emission after particle combustion, while that taken in fluorine-containing environments show little or no emission from BO2, consistent with predictions from theoretical modeling efforts. When boron particles are burned in Ar/N2/O2 atmospheres, there is a decrease of over 60% in ignition delay times as XN2 is increased from 0 to 0. 8 with XO2 held constant at 0.20. Ignition delay times also decrease from 335 μs to 160 μs as XNO is increased from 0.005 to 0.075 ± 0.015 in N2/NO/O2 environments. Addition of CO2 to Ar/O2 mixtures increases ignition delay times. Theoretical predictions of ignition times for boron particles from a boron particle combustion model developed in the course of the present study as well as predictions of ignition and combustion times from a chemical kinetics based boron particle combustion model compare well with experimental times measured in N2/O2 and in O2/F atmospheres. |
