Experimental and numerical study of flame ball IR and UV emissions

Near-infrared (IR) and ultraviolet (UV) emission profiles of flame balls at microgravity conditions in H-2-O-2-diluent mixtures were measured in the JAMIC 10 s drop-tower and compared to numerical simulations and supplemental KC135 aircraft mu g experiments. Measured flame ball radii based on images obtained in the JAMIC, KC135, and recent space experiments (IR only) were quite consistent, indicating that radius is a rather robust property of flame balls. The predicted IR radii were always 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 experimental IR radii in H-2-air tests is particularly difficult to interpret even when uncertainties in chemical and radiation models are considered. Experimental radii would be consistent with a chemiluminescence reaction 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 its exothermicity is sufficient to create excited states that could emit at the observed wavelengths, however, no appropriate transition of H-2-H-2* could be identified. (C) 1998 by The Combustion Institute.