Analysis of Saffire II two-sided concurrent flame spread over a thick PMMA slab

This paper reports the results of the microgravity flame spread over a 10 mm flat slab sample and a 4-10 mm structured sample. The samples were 50 mm wide and 290 mm long. They were ignited for 30 seconds in a constant air flow rate of 200 mm/s at one atmosphere pressure. The flame over the structured sample grew faster and was much more luminous than the flat sample. Interestingly, it was also quite non-symmetric on the two sides of the fuel card based on the radiometer readings. This non-symmetry affected the flow in the duct, implying the flame significantly affected the local flow field even in microgravity. The total radiometric output increased for the entire test time, indicating that the overall flame strength was increasing. Both flames over the samples grew to be 80-100 mm long, with soot streaming out the tip of the flames. Compared to normal gravity tests, the microgravity pyrolysis front spread rates were 18 to 24 times slower, but the fuel burnout rates were only 1.6 to 3 times slower. This resulted in a significant difference in overall flame size, with the microgravity flames being much smaller. Vapor jetting of bubbles of MMA monomer rupturing at the surface caused violent perturbations in the flame that got progressively worse as the test progressed. Both tests set off the vehicle smoke detector at levels well above the background reading of the sensor. The highest smoke detector reading occurred after the flow was turned on at the start of the flat sample test, as the residual smoke in the flow duct was flushed out. This may be due to soot agglomeration and/or the generation of a cloud of condensed fuel vapor.