Studies On The Flame Instabilities Of Combustion For Premixed Gas In Porous Media

Combustion of premixed gases in porous media has received considerable attentions during the last decade due to its advantages such as high combustion efficiency, low lean combustible limits and low emissions, etc., in comparison with the combustion in free space. So the combustion of premixed gases in porous media is a promising and advanced combustion technology. The investigation of the flame characteristics in porous media will benefit the development of the combustion theory. The thesis introduces the studies on the flame instabilities of combustion for premixed gas in porous media by experimental measurements, theoretical analysis and numerical simulation. The main research contents are as follows:(1) The experimental studies. Set up the experimental facility, which consists of a combustor (quartz glass tube), a gas flow system, a measurement system and so on, for the combustion of premixed gases in porous media. The flame instabilities of CH4/air combustion and H2/air combustion in porous media are studied. The flame shapes and evolutions are observed and recorded by giving different experimental conditions, such as different equivalence ratios (fuel concentration) and different inlet velocities. The results show that the equivalence ratio (fuel concentration) and the inlet velocity have great influences on the flame characteristics.(2) The theoretical analysis. The evolutions of flame inclination during the propagation in porous media are studied using two-temperature two-dimensional numerical model. The evolutions of flame inclination and the reasons causing this evolutions are analyzed from three aspects of temperature field, gas velocity field and pressure field, respectively. The results show that, if an initial inclination is set, the flame inclination will progress and become more serious. The temperature field, gas velocity field and pressure field can affect the chemical reaction rate, the direction of gas flow and heat loss at the walls, etc., and further affect the evolution of the flame inclination. These factors can advance the continuously development of the inclination.(3) The numerical simulation.Ini order to simulate the experimental conditions of CH4/air combustion in porous media, a two-dimensional, two-temperature model with initial flame inclinational angles is carried out. The software Fluent is used to simulate the combustion, fluid flow and heat transfer of the combustion. The flame shapes and evolutions are observed and recorded by giving different initial conditions, such as different equivalence ratios, different inlet velocities, different diameters of the pellets and different heat losses of the combustor wall. The results show that the equivalence ratios, the inlet velocities, the diameters of the pellets and the heat losses of the combustor wall have great influences on the flame characteristics. Otherwise, in order to check the possible motivity of the inclination, we assumed profiles (not uniform) of inlet velocity of premixed gas and equivalence ratio at inlet, different porosities in the tube, half the same on the right, half on the left, in the simulations. The results show that the inhomogeneous inlet velocity gives slight influence on the inclination, but the different distribution of porosity and the inhomogeneous equivalence ratio at inlet give great influences on the inclination.