Experimental and numerical study on the lean premixed filtration combustion of propane/air in porous medium

•Extra-lean filtration flame is introduced by a pilot flame in the porous medium burner.•A variational local speed of the flame ranging from 0.126 to 0.175 mm/s is discussed.•A polynomial function fitted to the experimental data is developed for initial condition.•Heat transfer process between the gas and a solid pellet is analyzed in the pore scale. This work presents an experimental and numerical study on the lean premixed filtration combustion of propane/air mixtures in a packed bed. A pilot flame of premixed propane/air is employed to introduce an extra-lean sustainable filtration flame with shape of an ellipsoid. The flammability limit of the extra-lean propane/air in the porous medium burner is considered as 0.289 in present experiment. Local velocity of the combustion flame in different positions ranges from 0.126 mm/s to 0.175 mm/s, and the lowest local velocity occurs in the centre of the burner with best preheating and lowest heat lose. The velocity of flame kernel turns slower as the equivalence ratio increases. A critical inlet air velocity for a sustainable flame is suggested as 0.65 m/s no matter what equivalence ratio it is. As a necessary supplement to the experiment, a two-dimensional numerical model is developed to analyze the temperature development of the gas and solid pellets especially in pore scale. A polynomial function is developed to fit the experiments data to form an accurate initial temperature fields. Numerical results are in qualitative agreement with the flame structure trends and the axial temperature distribution, although the predicted velocity of the filtration flame is lower than that in experiment. As the diameter increases from 6 mm to 10 mm, the porosity of the packed bed gets larger, the average velocity of the flame increases, and the temperature difference between the solid and gas becomes smaller. As the flame is transmitted around a solid pellet, the temperature distribution between the gas and solid shows a converse trend upstream and downstream the flame.