- Author
- Olson, S. L. | Kashiwagi, T. | Fujita, O. | Kikuchi, M. | Ito, K.
- Title
- Three Dimensional Radiative Ignition and Flame Spread Over Thin Cellulose Fuels. [Slide Presentation]
- Coporate
- NASA John H. Glenn Research Center at Lewis Field, Cleveland, OH National Institute of Standards and Technology, Gaithersburg, MD Hokkaido, Univ.
- Book or Conf
- Microgravity Combustion International Seminar. Presentation No. 7. Proceedings. Host Organizations: Institute of Fluid Science/Tokoku Univ. (IFS), New Energy and Industrial Technology Development Organization (NEDO), Japan Space Utilization Promotion Center (JSUP), Japan Microgravity Center (JAMIC), Ministry of International Trade and Industry (MITI), National Aeronautics and Space Admin. (NASA). August 19-20, 1999, Japan, 58-67 p., 1999
- Keywords
- cellulose fuels | flame spread | microgravity | flame spread rate | ignition
- Abstract
- Radiative ignition and transition to flame spread over thin cellulose fuel samples was studied aboard the USMP-3, STS-75 Space Shuttle mission, and in four campaigns to the 10 second Japan Microgravity Center (JAMIC). A focused beam from a tungsten/halogen lamp was used to ignite the center of the fuel sample while an external air flow was varied from 0 to 20 cm/s. Non-piloted radiative ignition of the paper was found to occur more easily in microgravity than in normal gravity. Ignition of the sample was achieved under all conditions studied (21-50% O2) with transition to flame spread occurring for all but the lowest oxygen concentration (21%) and very slow flow conditions (<0.5 cm/s). While radiative ignition in a quiescent atmosphere was achieved, the flame quickly extinguished in air. Ignition delay time is proportional to the gas-phase mixing time, estimated using the inverse flow. Ignition delay is a much stronger function of flow at lower oxygen concentrations. After ignition, the flame spread initially only upstream, in a fan-shaped pattern. The fan angle for flames spreading in air increased with increasing external flow and oxygen concentration from zero angle (tunneling flame spread) at the limiting 0.5 cm/s external air flow, to 90 degrees (semicircular flame spread) for external flows at and above 5 cm/s, and higher oxygen concentrations. The fan angle is shown to be directly related to the limiting air flow velocity. The downstream flame is inhibited due to the 'oxygen shadow' of the upstream flame for the air flow conditions studied, despite the convective heating from the upstream flame. Downstream flame spread rates in air, measured after upstream flame spread was complete, were slower than upstream flame spread rates at the same flow. The quench regime is skewed toward the downstream, due to the augmenting role of diffusion for opposed flow flame spread, versus the canceling effect of diffusion at very low concurrent flows. For higher oxygen concentrations, there was insufficient time in the 10 second JAMIC tests to observe downstream flame spread.