Three-dimensional image reconstruction of a thermoplastic rod burning with and without melting

Observation of the deformation process of a thermoplastic rod is important because the burning behavior depends on the instantaneous shape. However, the observation is often difficult because the rod, particularly its top, is hidden by the flame. This study proposes a novel imaging technique that visualizes the deformation process of the burning rod by filtered backprojection of backlight images. An imaging system consisting of two sets of a backlight source and a camera was developed. Tests using cylinder and square rods of cast and extruded polymethyl methacrylate (PMMA) were conducted. The instantaneous three-dimensional shape of the burning rod was successfully visualized for all the samples, which proves the applicability of the proposed technique in the presence of molten material and corner edge. The mass loss was thereafter estimated from the images and compared with reference data obtained in another series of tests using an electric balance. For the cast PMMA rod, the mass loss agreed well with the reference data upon correction of the shrinkage of the cross-section. On the other hand, the result for the extruded PMMA rod showed a significant deviation from the reference data because the decrease in volume by the surface regression was canceled by the increase in the amount of molten material. It was also demonstrated that the vertical regression rate can be measured regardless of material types. The results showed that the vertical regression rate was less sensitive to initial shape for the cast PMMA rod during the steady-state, while it linearly increased with time and never reached the steady-state value within the test time for the extruded PMMA rod. The proposed technique can evaluate various characteristics of a burning thermoplastic that should vary in accordance with the deformation; therefore, it is particularly useful when the steady-state is not achieved. (C) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study proposes a novel imaging technique that visualizes the deformation process of a burning thermoplastic rod. Tests were conducted using different samples, and the instantaneous three-dimensional shape of the burning rod was successfully visualized. The proposed technique can evaluate various characteristics of the burning material and is particularly useful when the steady-state is not achieved.