A study on the dynamic behavior of premixed propane-air flames propagating in a curved combustion chamber

Abstract

Experiments and numerical simulations were performed to study the flame dynamics and pressure build-up in a curved combustion chamber filled with propane-air mixture. The configuration of the system allows a direct comparison of flame propagation in a bend to that in a straight duct. The comparison helps reveal the role of the bend in the flame dynamics. In the experiments, a high-speed schlieren system and a pressure transducer were used to record the flame evolution and pressure dynamics, respectively. In the simulations, a dynamically thickened flame (TF) model with a single-step chemistry was adopted to represent the premixed combustion. One important finding is that the bend of the chamber has a significant influence on the flame dynamics by promoting the growth of instabilities. The flame behavior in the bend is different than that in the straight section of the chamber. A salient tulip flame is formed in the bend while a much less pronounced tulip shape in the horizontal straight section. The lower part of flame dominates the burning process in the bend while the opposite is true in the horizontal straight section. Furthermore, the influence of heat transfer and gravity were examined using numerical simulations. It was found that heat transfer has an important effect on the combustion dynamics when the flame interacts with the sidewalls of the chamber. The flame propagation speed and pressure rise are overestimated in the absence of heat losses at the chamber walls. Although the gravity plays a role in the flame evolution in the straight configuration, its effect on flame dynamics is damped by the bend. The gravity effect on pressure build-up in the entire process is minor. In addition, the good agreement between the numerical simulations and the experiments supports the validity and reliability of the TF model with the one-step chemical kinetics for calculating propane-air flame propagation.