Experimental And Numerical Investigation Of Filtration Combustion In The Porous Medium

The filtration combustion in the porous media combustor has become a hot research topic in the field of combustion for the past few years, because of the advantage of increasing the combustion intensity, broadening the combustion zone, reducing the pollutant emission and broadening the flammable limit and so on. For further application of filtration combustion technology, a intense research on the filtration combustion of propane/air mixture in the porous media is investigated numerically and experimentally, and a exploratory research on the evaporation and combustion processes of diesel sprays in the packed bed is also studied in this paper.The combustion characteristic of filtration combustion of the propane/air mixture is investigated in a packed bed combustor consisting of alumina pellets. In the experiment, the phenomenon of the propagation of the combustion wave is observed, and the influence of equivalence ratio and inlet velocity on the combustion wave velocity, temperature distribution and the exhaust gas emissions is analyzed. The result shows that the combustion phenomenon belongs to low-velocity filtration combustion, because the order of magnitudes of the combustion wave speed is10-lmm/s. Among the pecked bed combustor, the combustion wave velocity reduces at the beginning of the combustion, then it becomes lowest in the middle of the combustor and increases during the late stage of combustion. In the experiment, as the equivalent ratio increases, the peak temperature and the emission load of CO and CO2rises, however, the combustion wave velocity decreases. When the inlet velocity increases, the peak temperature and the combustion wave velocity increases, however, the emission load of both CO andCO2reduces.The pre-evaporation filtration combustion of diesel in porous medium is experimental studied in this paper. The temperature distribution along the axis is analyzed, and the temperature contrast has been done between the center and side of the combustor, and the change laws of both gas and solid spheres are investigated in the experiment. It shows that the propagation of combustion wave has not occurred in the pecked bed combustor for the combustion of liquid fuel. At the earlier stage, the temperature in the center of sphere is lower than that of gas. however, they are approximately same at the later stage. The highest gas temperature in the middle of the combustor can reach1160℃. while the highest gas temperature in the side of the same section is approximately200℃lower, and the temperature in the evaporative section can keep85℃Based on the experiment, a two dimensional model of the filtration combustion of methane/air mixture in the packed bed is built using software Fluent13.0, which includes a double temperature model, the discrete ordinates method, the simplified reaction mechanism and the k-ε turbulence model, etc. The simulation results agree well with the experimental values on the temperature distribution. The temperature distribution of gas and solid spheres is investigated by temperature tracking. The result shows that the temperature of solid spheres exceeds the gas temperature in front of the flame, while the gas temperature is higher than the temperature of solid spheres at the downstream of the flame. That means the solid spheres can preheat the mixture effectively at the upstream of the flame, and absorb the heat in the gas at the downstream of the flame. The influence of equivalent ratio and inlet velocity on the combustion characteristic is in accord with that in the experiment. And the peak temperature reduces and the combustion wave velocity rises when the diameter of the alumina pellet increases.Considering the complexity of the combustion for liquid fuel in porous medium, the evaporation process of diesel droplets in the pecked bed is investigated numerically without considering the combustion. The influence of different injection parameters on the diesel oil evaporation and mixing is discussed in this paper. The simulation results indicate that the preheating temperature has a great influence on the fuel evaporation rate. The diesel vapor distributes more homogeneously at a bigger spray angle and a faster injection speed.