A comparative study of the effect of cavity and obstacle on premixed methane-air flame evolution

To compare the effect of the cavity and obstacle on the flame evolution, a series of experimental studies are carried out to investigate the premixed methane-air flame propagation in the combustion chamber featured by cavity or obstacle. The flame behavior is obtained by analyzing the flame-front dynamics and pressure variation. The flame stretches into an inclined shape due to the flow contraction with the presence of an obstacle. In contrast, the flame forms a vortex by following the unburned gas vortex owing to the flow expansion in a cavity. Furthermore, the flame downstream of the obstacle is more turbulent than in cavity cases. Moreover, the flow contraction caused by obstacles also contributes to a higher flame-tip velocity than cavity cases. When the change in cross-section caused by obstacle and cavity is equivalent, the maximum pressure in the combustion chamber with an obstacle is generally larger than that in cavity cases ascribed to the combined effect of the changes in fuel amount and heat loss. In addition, the maximum rate of pressure rise in the combustion chamber featured by the obstacle is larger than that in the combustion chamber featured by a cavity, corresponding to the highly turbulent flame downstream of the obstacle.