Comparison of Theoretical and Experimental Burning Rates for a Laminar Wall Fire

Abstract

Laminar methyl methacrylate (MMA) wall fires were studied. The principal objective of the investigation was to obtain and compare theoretical and ex perimental burning rates. The wall fires were produced by burning MMA on a ceramic wick in an oxygen/nitrogen environment. Burning rate measurements were made for several values of ambient oxygen mass fraction, and it was found that a unique burning rate did not exist for a given ambient condition. For supply rates that were great enough to cause fuel to drip from the wick surface, the burning rate was found to increase slightly with supply rate. The burning rates in the limit of zero fuel dripping were chosen as characteristic values for comparison with theoretical results. Diffusion flame theory for laminar burning of a vertical fuel surface was used to predict burning rates. The effects of incomplete combustion were examined (using recently measured values of the effective heat of combustion), and are found to decrease the calculated burning rates by about 5 percent. The variation in the calculated burning rates due to our lack of knowledge of the effective Lewis number and flame emissivity were considered, and found to give an uncer tainty band of ± 12 percent. Comparison of the theoretical calculations with the measured results show a similar, small increase with increasing ambient oxygen concentration. The band of theoretical results, however, predicts burning rates which are at least 10 percent greater than the measured values.