Numerical investigation of the effect of combustion and turbulence models in estimating the combustion characteristics of a fuel-rich propellant -case study: ramjet

The variety of multiple physical phenomena in the combustion chamber like chemical kinetics, heat transfer (convection and radiation), multiple phases, and thermal decomposition in the absence of oxygen (pyrolysis) related to solid fuel with the accumulation of particles and the liquid film are combustion challenges in the air-breathing combustion systems (ramjet). Understanding the physical and chemical processes involved in combustion is required to predict the physical procedures governing fluid flow, combustion initiation, regression rate, heat release rate, flame, and concentration of species generated during combustion. According to simultaneously solving the combustion and turbulence models, applying the numerical methods in analyzing the governing equations leads to some results, including the effect of variables, performance characteristics, combustion properties, and finally, access to fuel-rich propulsion combustion efficiency in solid fuel ramjet systems. The chemical reactions in the combustor, pyrolysis of Hydroxyl-terminated polybutadiene (HTPB), and the combustion of the pyrolysis products are investigated based on the reduced kinetic mechanisms. Then, by eddy dissipation and finite-rate chemistry models accompanied by K-ε standard and K-ω-SST models in the modeling of solid fuel ramjet combustor, the simulation results are compared with CEA data to identify the best models for accurate combustion prediction. The results showed that the finite-rate model predicts the combustion characteristics of the solid fuel ramjet with much error compared to the eddy dissipation model due to ignoring the effects of flow turbulence and the amount of fuel and air mixing in the combustion chamber. According to the thermodynamic and combustion results, the K-ω/eddy dissipation case was in good agreement with CEA results.
.