| Resently, gas explosion accidents still happen frequently in Chinese coal mines, which cause considerable losses in lives and property in process industries. By experimental measurements, numerical simulations and theoretical analyses, the thesis presents an intensive investigation on flame characteristics and porous media quenching suppression process of gas turbulent deflagration. The main aim of this work underling the thesis is to reveal the dynamic propagation mechanism of gas turbulent deflagration and porous media quenching suppression, which can contribute to understanding of gas turbulent deflagration propagating laws under complex conditions, and to further development of new explosion suppression technology.Firstly, an experimental facility is set up to study the dynamic characteristics of gas deflagration, such as flame structure, flame front position, and flame propagating velocity. The results confirm that turbulent excitation is the essential reason of the flame acceleration phenomenon. Gas deflagrating flame characteristics under various turbulent excitations are quantitatively analyzed. It is found that the continuous, central, and staggered obstacles are likely to induce higher level of turbulence intensity and to generate greater flame propagating velocity and overpressure. The interaction of flame structure transient evolution and overpressure under various turbulent excitations is described. The flame-turbulence interaction and the relationship between flame structure and pressure in gas deflagration are theoretically explained.Secondly, numerical calculations are performed using Large Eddy Simulation (LES) of gas deflagration under complex turbulent conditions. It is found that the Charlette combustion model is able to better predict the generated pressure and other flame features, such as flame structure, position, and speed. The correlation of flame area and overpressure is theoretically deduced. It is shown that the increasing flame area will increase turbulent flame speed, in turn, overpressure. The numerical results indicate that when the flame continuously crosses over the obstacles, the Mach number is increasing with ever-greater velocities, causing gradually increasing large-scale turbulent vortexes. In this process, the flame is wrinkled and distorted gradually, resulting in higher turbulent vorticity, and even greater turbulence intensity, in turn, increases the turbulent flame speed. In addition, the interaction between gas deflagration and turbulence is described by the Karlovitz number, and the transient flame regimes of the case with central continuous obstacles are identified and analyzed. The results indicate that the gas turbulent flame remains within the two zones of corrugated flamelets and thin reaction, while mainly in the thin reaction zone where the flame is affected by the flame-turbulence-overpressure multi-field couplings.Thirdly, an experimental study has been conducted to analyze the gas deflagrating flame propagation, quenching behaviors, and overpressure characteristics as the flame propagates through a porous media plate. The more obstacles, the more obvious the multi-field interactions, and then the flames are less likely to be quenched in the porous media. The quenching mechanism is relative to the flame propagating velocity and overpressure. In addition, the upstream obstacle number, pore density and thickness of porous media have also great influence on the quenching suppression performance. The higher the pore density or the thicker the porous media plate, the better the flame quenching performance, but the larger the drop of the overpressure for flow-through the porous media. Furthermore, gas-phase temperature and ion currents, upstream, within, and downstream of the porous media, under different conditions, are measured using micro-thermalcouples and ion microprobes. Compared with the case without obstacle, the dereases of gas-phase termperature and ion current of the case with continuous obstacles on both left and right walls are less, resulting in that the temperature of burned gases is higher than the autogenous ignition temperature, and then the unbuned gases downstream the porous media may be reignited.Finally, a numerical simulation to understand the mechanism for porous media quenching suppression is carried out based on a RANS/LES combined turbulence model. The quenching criterion of gas deflagration based on the thermal equilibrium theory is developed, and the combustion model and turbulence model in both non-porous-media zone and porous media zone are revised, respectively. The results show that the gas-phase temperature has been decreased rapidly, and the high gradient zones of the reaction progress variable and gas-phase temperature have been separated. So the unbuned gases in the higher gradient zone of reaction progress variable can not contact with the high-temperature burned gases, eventually causing a significant drop in chemical reaction rate. The results indicate that the flame propagating velosity in porous media is faster, meaning that the residence time of the flame in porous media is shorter, and then the drops of gas-phase temperature and reaction rate are smaller due to the upstream multi-field coupling, and it also means that the gas deflagration flame would be more difficult to be quenched. A further study shows that the higher the pore density, the rapider the decreasing rate of gas-phase temperature and reaction rate in porou media, in which the flame would be easier to be quenched. Correspondingly, the thicker the porous media plate, the longer the time of flame propagation in the porou media, and the more the convective heat transfer between gas and solid two phases, resulting in a lower gas-phase temperature and reaction rate at the outlet section of porous media, and the flame is likely to be quenched. Furthermore, the higher the pore density or thickness, the greater the overpressure drop through the porous media, meaning that the more significant suppression effect on downstream overpressure. |
PDF Full Text Request