An investigation of premixed flame propagation in a closed combustion duct with a 90° bend

In this work, the premixed flame propagation and pressure dynamics in a closed combustion tube with a 90° bend are investigated using experiment and numerical simulations to provide further knowledge of premixed combustion process in a curved chamber. In the experiment, high-speed schlieren photography is employed to record the changes in flame shape and position as a function of time. And a pressure transducer is used to measure the pressure rise in the chamber. In the numerical simulations, a dynamically thickened model is applied to allow a detailed insight into the flame dynamics under both isothermal and adiabatic wall conditions. It is revealed that the flame evolves into a notable tulip shape in the straight horizontal section which takes on a four-tongue appearance in the numerical calculations. The lower tongues dominate the flame propagation in the bend. The flame remains concaved after the tulip disappearance and rounds along the inner wall in the bend. It is found that the heat losses to the walls have a great impact on the combustion dynamics, including the flame front evolution and pressure build-up. The numerical combustion dynamics with isothermal walls agrees well with the experimental results. Furthermore, the analytical analysis demonstrates that the flame mechanism in the horizontal section is consistent with that in a straight duct in spite of the presence of the bend.