Combustion studies of MMA/[formula omitted] for a hybrid rocket motor

Abstract

Poly(methyl methacrylate) (PMMA) is the synthetic polymer of methyl methacrylate (MMA), which is used in a multitude of everyday applications, can also be used as a solid fuel in hybrid rockets. When used as a fuel in a combustion chamber, PMMA undergoes thermal decomposition and phase-change (solid-to-gas), where gaseous MMA (C5H8O2) is the primary product. The gaseous MMA then undergoes combustion with an oxidizer. Experimental studies of this combustion chamber have been performed in literature, and this study helps produce high-fidelity simulations, which can match experimental observations while giving access to more data in the combustion chamber. Simulations of turbulent diffusion flames are performed with gaseous MMA introduced through the combustion chamber walls. Two different diffusion models are used alongside a finite-rate chemistry model to observe the effects of differential diffusion. The rate of inflow of MMA is controlled by the temperature field in the combustion chamber, and the results from the 3D simulation are comparable to 1D counterflow diffusion flame simulations. Simulations are also performed with a tabulated chemistry model developed to improve the computational efficiency and with two different internal diameters to analyze the geometric effects. If one wishes to capture the flow field profiles and fuel regression rate, chemistry effects need to be included. If one wishes to capture the internal chemistry profiles of the combustion products, differential diffusion effects are important. The fuel regression rate and the radial chemistry profiles from the simulations are compared with the experimental results and show good agreement.