| sWith highly developed inner solid surface and excellent property of heat transfer and heat accumulation, porous media can play an important role in combustion. Premixed combustion in inert porous media has so far proven to be an advanced combustion technology in which premixed fuel and air burn within a porous bed. The technology has many obvious advantages over conventional premixed combustion in which the premixed fuel and air burn as a free flame that is stabilized at the burner exit with respect to reduced emissions of combustion-related pollutants, wider domain of flammability, much higher thermal efficiency and radiant heat outputs, saving energy, uniform heat distribution and so on. Reciprocating Superadiabatic Combustion of Premixed gases in porous media (hereafter, referred to as RSCP) is a completely new porous burner technology. With embedded devices for periodically switching the direction of the premixed gases, RSCP burner not only has the advantages of porous media burner with one-way flow, but also some more attractive combustion characteristics. The thesis presents intensive investigation on RSCP by theoretical analysis, numerical simulation and experiment measure. The main works are as following:1. Applying the principle of fluid dynamics, a set of governing transport equations are derived to describe the reacting flow through an inert and isotropic porous media based on volume averaged hypothesis and previous researchers' investigation. Considering local thermal non-equilibrium between the solid and the gas phases, the equations can be used directly and easily to describe the process of flowing and reacting of mixed gases in inert porous media in different conditions, especially to simulate premixed combustion in porous media.2. The working mechanism of RSCP combustor is analyzed and the functions of the porous media and the devices for periodically switching the direction of the flow in RSCP system are described in detail. By mathematical reasoning, a theoretical description how the superadiabatic flame comes into being is given. The effect of preheat enhancing on the flammability limit of premixed gases is investigated. Thermodynamics efficiency of RSCP is discussed and some important conclusions are drawn out on the basis of previous researchers' investigation.3. Appling the general transport equations of the reacting flow in porous media in the present researching conditions, a two-dimensional mathematical model describing RSCP system is developed. Finite volume method for radiation heat transfer is used to solve the radiative transfer equation. The thermal of radiation the solid in porous burner is intensively investigated. The results indicate that coupling calculating of flow field, combustion reaction and volume radiation of the optically thick media is successively achieved.4. The influence of the porous media on pressure drop of the reacting flow is investigated by numerical method in cold and in hot environment. The results showthat the pressure drop is much bigger in hot environment than that in cold environment, but it is not obvious if the porosity is big enough.5. Numerical analysis has been performed on premixed combustion of lean gas mixture of methane and air in porous media. The thermal structure, in terms of axial temperature distribution, of the combustion systems with one-way flow and with periodically reciprocating flow of the gas mixture, is compared so as to elucidate the performance of the two systems. The influences of geometric parameters, the thermal-physical parameters of the porous media, wall heat loss coefficient and working parameters (half cycle, flow velocity, equivalence ratio) on temperature distribution, heat release rate, combustion efficiency and combustible limit and etc in RSCP system are examined. By comparison, it is shown that all indexes of combustion behavior in RSCP system are better than those in conventional premixed combustion system in porous media with the same working parameters.6. An experimental study of...
|
PDF Full Text Request