Near-infrared (IR) and ultraviolet (UV) emission profiles of flame balls at microgravity conditions in H2-O2-diluent mixtures were measured in the JAMIC 10 s drop-tower and compared to numerical simulations and supplemental KC135 aircraft μg 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 H2-air mixtures but closer for IR radii in H2-O2-CO2 mixtures. The large experimental IR radii in H2-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 + O2 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 H2O2* could be identified.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)