Correlation between burning surface temperature and regression rate for polymethylmethacrylate

Prediction of the regression rate of polymeric fuels is important, especially for the optimal design of solid fuel ramjets or hybrid rocket motors. The burning surface temperature and the surface activation energy in the Arrhenius pyrolysis equation are required for prediction of the regression rate. As a typical polymeric fuel, polymethylmethacrylate (PMMA) was chosen for the present study. The burning surface temperature of PMMA was measured for both end-burning and sandwich-burning experimental devices. In the end-burning experiment, the oxygen flow impinged on the top of the specimen to burn the PMMA. In the sandwich-burning experiment, PMMA sheets were sandwiched between AP pellets. Temperature profiles near the burning surface were measured with a thermocouple embedded in the specimen. Simultaneously, the emergence of the thermocouple from the burning surface was determined with a video camera. The burning surface temperature obtained in the present study was found to be almost independent of the regression rate. The surface activation energy of PMMA was more than 1000 kJ/mol. Our measured surface temperature or the activation energy differs from the values measured with a thermocouple in previous studies. This difference probably is a result of mistaken identification of the burning surface temperature in the previous studies, because it was found that the sudden change or tiny plateau of the slope, in the temperature profile of PMMA, did not signal the burning surface.