EXPERIMENTAL AND NUMERICAL STUDY OF FLAME BALL IR AND UV EMISSIONS

Near-infrared (IR) and ultraviolet (UV) emission profiles of flame bal ls at microgravity conditions in H-2-O-2-diluent mixtures were measure d in the JAMIC 10 s drop-tower and compared to numerical simulations a nd supplemental KC135 aircraft mu g experiments. Measured flame ball r adii based on images obtained in the JAMIC, KC135, and recent space ex periments (IR only) were quite consistent, indicating that radius is a rather robust property of flame balls. The predicted IR radii were al ways smaller than UV radii, whereas the experiments always showed the opposite behavior. Agreement between measured and predicted flame ball properties was closer for UV radii than IR radii in H-2-air mixtures but closer for IR radii in H-2-O-2-CO2 mixtures. The large experimenta l IR radii in H-2-air tests is particularly difficult to interpret eve n when uncertainties in chemical and radiation models are considered. Experimental radii would be consistent with a chemiluminescence reacti on of the form HO2 + HO2 --> H2O2 + O-2 producing an excited state of H2O2, since HO2 is consumed at large radii through this reaction and i ts exothermicity is sufficient to create excited states that could emi t at the observed wavelengths, however, no appropriate transition of H -2-H-2 could be identified. (C) 1998 by The Combustion Institute.