Abstract
The superadiabatic combustion for non-stationary filtration combustion is analytically studied. The non-dimensional excess enthalpy function (H) equation is theoretically derived based on a one-dimensional, two-temperature model. In contrast to the H equation for the stationary filtration combustion, a new term, which takes into account the effect of non-dimensional combustion wave speed, is included in the H equation for transient filtration combustion. The governing equations with boundary conditions are solved by commercial software Fluent. The predictions show that the maximum non-dimensional gas and solid temperatures in the flame zone are greater than 3 for equivalence ratio of 0.15. An examination of the four source terms in the H equation indicates that the thermal conductivity ratio between the solid and gas phases is the dominant one among the four terms and basically determines H distribution. For lean premixed combustion in porous media, the superadiabatic combustion effect is more pronounced for the lower .
Highlights
Excess enthalpy combustion in porous media [1,2], known as energy concentration, draws constant interest from researchers due to its wide range of applications and outstanding features of heat recovery and pollutant control
The above equation shows that the enthalpy function is controlled by the combined effect of the modified Lewis number, the thermal conductivity ratio between the solid and gas phases, the porosity of packed bed and the non-dimensional combustion wave speed
It is shown that the non-dimensional enthalpy equation is controlled by the combined effect of the modified Lewis number, the thermal conductivity ratio between the solid and gas phases, the porosity of the packed bed and the nondimensional combustion wave speed
Summary
Excess enthalpy combustion in porous media [1,2], known as energy concentration, draws constant interest from researchers due to its wide range of applications and outstanding features of heat recovery and pollutant control. In contrast to the pronounced superadiabatic combustion effect for the transient combustion in porous media, where the flammability limit can be extended to an extremely low equivalence ratio, only a slight superadiabatic combustion effect was observed for stable combustion in porous media, a lean flammability limit of about 0.4 was reported for natural gas [22] Both solid conduction and radiation were the dominant models of heat recirculation. The extended model allowed the construction of an analytical solution valid over a large range of equivalence ratios In their experimental and analytical studies on excess enthalpy in a twolayer burner [22], it was shown that the H is a function of modified Lewis number, the ratio of the solid and the gas-phase effective conductivities and the porosity of the porous media. The source terms in the non-dimensional H function is examined and the effects of Gs and porosities on the superadiabatic combustion effect are discussed
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