Effect of Obstacle Type on Methane–Air Flame Propagation in a Closed Duct: An Experimental Study

Abstract

The combustion in a closed environment was the subject of many works in the past century due to its importance and complex nature compared with the combustion in an open environment. Most research works in this field have investigated different types of gas mixtures, the governing boundary conditions and their effect on the flame propagation structure. Additionally, several investigations have been performed on creating disturbance through obstacles in the flow path as well as the process of deflagration to detonation transition. This paper, for the first time, investigates the effect of porous and solid obstacles on the propagation and the structure of premixed methane–air flame in a closed duct with dimensions of 50 × 11 × 8 cm. The blockage created in the duct by obstacles is in such a way that the detonation process does not occur. The results for the unconstrained duct correctly represent the process of forming the classical tulip flame inside the closed duct. The location of the obstacles is changed in four different distance of 5, 10, 15, and 20 cm from the spark plug, and its effect on combustion characteristics has been evaluated. The results show that the obstacles create fundamental changes in the structure and flame propagation. A significant difference between solid and porous obstacles is that the porous obstacle, in proportion to the solid obstacle, creates less disturbance in the flow field and also does not cause excessive acceleration in the flame propagation. Porous obstacles also reduce the maximum pressure in the chamber during the process, more than the solid obstacles.