Two-Dimensional Experimental Study of Superadiabatic Combustion in a Packed Bed Burner

Abstract

ABSTRACT：High-efficiency use of low-concentration coal mine methane is favorable for energy saving and reduction of greenhouse gas emissions. During the porous media combustion, abundant methane at extremely low concentrations will be used not through stable combustion, but through superadiabatic combustion, which transmits flames to the downstream. To directly study the superadiabatic combustion of low-concentration methane, we set two-dimensional (2D) temperature measuring points in the burners, extended the temperature measurements via a radial basis function (RBF) to the whole burner, and plotted a 2D temperature distribution. Then the effects of working conditions, pellet diameter, and burner length on the superadiabatic combustion of lowconcentration methane were investigated. The results show that unstable phenomena such as flame rupture and inclining occurred during the combustion wave propagation in the porous medium. The effects of the heat dissipation through burner walls and the heat dissipation from the outlet on the 2D temperature distribution provide a basis for validation of heat dissipation coefficient in numerical modeling. When the equivalence ratio was 0.35, the increase of flow velocity (from 25 to 45 cm/s) accelerated the propagation velocity of the combustion wave from 0.10 to 0.25 mm/s, but the peak temperature of the flames was almost unchanged (about 1425 K). When the flow velocity of methane was 30 cm/s, the increase of equivalence ratio (from 0.25 to 0.35) reduced the propagation velocity of combustion wave from 0.22 to 0.14 mm/s, and significantly raised the peak temperature of flames from 1125 to 1375 K. With a smaller pellet diameter, the increase of pellet diameter is less favorable for acceleration of combustion wave propagation. When the burner length was prolonged from 20.8 cm and 25.6 cm at 4.8-cm interval, the propagation velocity of combustion waves declined by 11.4% and 7.3%, which shows that the prolonging of length was less favorable for deceleration of combustion wave propagation with a larger burner length.

Low-Calorific Gas Combustion in a Two-Layer Porous Burner

“…Therefore, the upstream section conductivity is overestimated in the simulation. In comparison to the model adopted in previous studies, 22,23 the estimation for thermal conductivity of packed spheres in the present model is about 1 order of magnitude larger. This leads to an overpredicted heat recirculation effect of the porous media.…”