Stabilized combustion of circular fuel duct with liquid oxygen

This research is an investigation of the flame spread opposed to a liquid oxidizer flow in a solid fuel duct. Several firing tests were conducted using liquid oxygen as the oxidizer and solid poly methyl methacrylate (PMMA) as the fuel. The results indicate that the flame spread rate decreased with increasing oxidizer port velocity and decreasing port diameter. This study reveals through visual confirmations and empirical correlations of the flame spread rate that the flame spread opposed to liquid oxygen in a solid fuel duct can be classified as stabilized combustion. Extinction and abnormal regression were observed when oxidizer port velocity was high and port diameter was small. Furthermore, the cooling of the solid fuel by the liquid oxygen flow had a strong effect on the transition between normal regression and extinction, or abnormal regression. A model of the flame spread rate which considers the heat balance at the fuel surface assuming a fully developed thermal boundary layer is introduced and shown to agree well with the experimental results. Lastly, it is revealed that the difference in kinematic viscosity between liquid oxygen and gaseous oxygen is the main reason dependency of port diameter on flame spread rates differs between the liquid oxygen tests in this study and gaseous oxygen tests in previous studies. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.