Reciprocating Flow Simulation, Pre-mixed Gas Super-adiabatic Combustion In Porous Media

Reciprocating superadiabatic combustion in porous media(RSCP) is a advanced technique with great potential by which flammability limits of fuels can be significantly extended and premixed gases with extremely low heat content can combust steadily while the emission of NOX and CO can be reduced greatly. This thesis presents a numerical study on RSCP.To simplify simulations, assumptions are put up as follows: the porous media and the working gas are in local thermodynamic equilibrium; the combustion chemistry is simulated by a global reaction; the working gas is optically transparent and nonradiative; porous media are absorbing and emitting gray media. Numerical simulation is carried out with both 1-D and 2-D models. Effects of various operating parameters on combustion are detailedly studied. The Rosseland method is chosen to simulate radiation transfer in the 1-D analysis, while the discrete ordinate method in the 2-D simulation. Based on 1-D model, transient profiles of temperature, species mass fraction and reaction rate during one half cycle are calculated, and influences of half cycle, equivalence ratio, inlet velocity, heat loss, as well as porous media's properties such as extinction coefficient, specific heat capacity and porosity, and the length of combustor on the combustion are studied. The results are qualitatively consistent with experimental results. The configuration of temperature profile is trapeziform-shaped; the half cycle has little influence on the peak of temperature, but when the half cycle become longer, the outlet temperature will become higher; both larger equivalence ratio and faster inlet velocity of gases can cause higher temperature peak and outlet temperature and wider high temperature zone; influence of heat loss on the peak of temperature is little, but with the heat loss becoming greater and greater, the zone of high temperature will be shorter and shorter; the peak of temperature is higher with the greater specific heat capacity of porous media while outlet temperature is lower; with the less porosity, the zone of high temperature is extended and the peak of temperature almost keeps changeless; the length of combustor has little effects on combustion. Profiles of temperature at each time step during one half cycle of the 2-D model are similar with those of 1-D model. With 2-D model, combustion in combustors with and without air gap and the influence of the thickness of insulation and radius of combustor are analyzed. It is found that when combustion happen in porous media, the air gap has little effect on combustion, but higher temperature will come out in air gap with combustion happening in the gap. The radius has insignificant effect on combustion. The numerical simulation indicate that combustion in slender combustors can be predicted satisfactorily with 1-D model; but to accurately predict heat exchange between working gas and porous media, separate energy equations for the solid and the gas are needed.