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Description
Historic fire disasters aboard spacecraft highlight the need for continuing research into spacecraft and microgravity flame spread. Forward heat conduction during simulated microgravity combustion testing in the Narrow Channel Apparatus (NCA) remains an under explored subject in both laboratory testing and computer modeling. An infrared (IR) camera provides a nondestructive way of examining the temperature trends associated with forward heat conduction, namely the surface temperature of solid poly methyl methacrylate (PMMA) fuel ahead of the flame spread. The NCA is a combustion wind tunnel that simulates a microgravity flame spread environment by employing a narrow gap between the fuel and ceiling of the device, limiting the effects of buoyancy. Test conditions of a 5 mm gap height, mean opposed flow velocity of 15 cm/s, and fuel thicknesses of 3, 5, and 10 mm are used. Continuing previous work in simulated microgravity combustion by the Combustion and Solar Energy Laboratory (CSEL), PMMA was selected as the fuel. PMMA remains the fuel of choice due to repeatability of test results, ease of computational modeling, and known combustion mechanics. Using specific lens and bandpass filter combinations the PMMA can be imaged as effectively opaque by the IR camera allowing for surface temperature measurements. The spectral emissivity for PMMA was calculated using a numerical method developed for this thesis and incorporated into the calibration of the camera. A novel calibration process and blocking the direct line of sight from the flame to the camera with a flame shroud ensures that the camera provides accurate data regardless of ambient test conditions and internal heating of camera optics. Surface temperatures from the IR camera are compared to results from thermocouples embedded in the surface of the fuel. Results from the IR camera compared favorably within a few degrees C to the embedded thermocouples with properly selected optics and calibration process. The IR camera and thermocouple results show that nontrivial forward conduction occurs approximately 4 mm ahead of the flame front during tests of all material thicknesses tested, and therefore must be included in future computational models of the process.).
