Numerical fire codes are being widely used for understanding normal gravity fires. The goal of the present project was to modify one such code, the National Institute of Standards and Technology Fire Dynamics Simulator, so that it can be used to accurately describe fires in the variable-gravity environments of space vehicles and habitats. We have used the code to understand limitations to oxygen transport for large fires in a typical module on the International Space Station, and to investigate the characteristics of the combustion products likely released during the Mir oxygen generator fire. We have shown that while zero-gravity environments (0 gn) environments can produce severe oxygen transport limitations for large fires, the levels of gravity typical of moon or Mars bases create buoyant mixing environments which allow oxygen transport much closer to conditions at 1 gn. We have contributed to flammability maps for 0 gn flames through experiments and modeling of co-flow diffusion flame extinction in 1 gn and 0 gn. In the course of the project it became clear that the ability of any fire model to describe fire growth depends upon its ability to describe the fuel generation rate from burning material. Unfortunately, the validation of the numerical fire codes for such applications was severely limited, and early work indicated that improvements were necessary. Hence, we sought to investigate and validate the performance of the code for predicting materials mass loss, and understand which material parameters have the largest influence on the predicted burning rate, so that efforts in the future could focus on those parameters. Finally, in order to ultimately validate numerical burning rate predictions for flame experiments at 0 gn, a method was devised to correlate the measured heat release rate with the flame area (which can be readily obtained in space-based experiments, unlike the load-cell based mass loss measurements which are not possible in 0 gn.
Final report to sponsor
spacecraft fire safety, microgravity combustion, fire modeling, materials flammability