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Structure and Extinction of Low Strain Rate Non-Premixed Flames by an Agent in Microgravity.


pdf icon Structure and Extinction of Low Strain Rate Non-Premixed Flames by an Agent in Microgravity. (8058 K)
Hamins, A.; Bundy, M.; Oh, C. B.; Fuss, S. P.; Logue, J.

NISTIR 7445; 181 p. September 2007.

Keywords:

nonpremixed flames; microgravity; flame structure; flame extinction; extinction; diffusion flames; fire suppression; experiments; nitrogen; carbon dioxide; propane; high temperature; FT-IR

Abstract:

This final report describes the study that has been supported through the National Aeronautics and Space Administration (NASA) microgravity grants program from February 2004 through March 2007. This work was a continuation of a NASA microgravity grant that was active from February 1999 through September 2003. The work has used computations and measurements to investigate the structure and suppression of low strain rate non-premixed flames. This final report, on the latest grant, includes a summary of the work done on the contract and a list of publications. The work during this grant period focused on both measurements and calculations and included the following: (*) Continued development of the two-dimensional simulation with finite rate chemistry. These publications are provided in Appendices 1 and 2. These calculations considered extinction of methane-air diffusion flames with N2 added to the fuel stream. The work compares calculations with our earlier measurements made in normal gravity and in microgravity using the NASA 2.2 s drop tower, (*) Two-dimensional calculations were completed .that considered the extinction of methane-air diffusion flames with CO2 added to the fuel stream in normal and microgravity. This study is provided in Appendix 3. The computations were compared to the N2 addition results, (*) Flame extinction studies on the normal gravity extinction of propane were conducted. The results of this study are provided in Appendix 4, (*) Finally, spectroscopic measurements were conducted on key flame intermediates to support detailed modeling of radiative exchange in near-extinction flames. Wakasuki et al. developed a method to estimate the temperature dependence of absorption coefficients through an extrapolation algorithm. This publication is provided in Appendix 5. Spectroscopic measurements are important to understand the mechanisms of extinction associated with flames being suppressed by agents. CF3Br (Halon 1301) is one of the most important suppressants and has been used on space platforms for many years. Suppression studies often use CF3BR as a reference or baseline in considering the effectiveness of alternative agents. As part of this study, Fourier Transform Infrared Spectroscopy (FTIR) measurements were made on CF3Br at elevated temperatures. Those measurements are reported in Appendix 6. Appendix 7 presents similar spectral measurements and analysis for propane, heptane and propylene. The seven manuscripts mentioned above are included as appendices in this final report. The remainder of the report presents an overview of the work and the main findings of the project. Detailed information on each of the topics can be found in the appendices.