Analytical investigation of magnesium aerosol combustion based on the asymptotic model of flame structure

摘要

Due to shortage and environmental pollution of fossil fuels and environment-dependent production of renewable energies, the metal fuels are promising candidates for alternative energy sources. In this study, the micron-sized magnesium particles are considered as energy carrier and the flame propagation of lean premixed magnesium-air combustion is investigated under zero gravity condition. To analyze dust cloud combustion, an asymptotic model of flame structure is proposed. According to the combustion behavior of single particle, the flame structure consists of four different zones including preheat, liquid magnesium, vaporized magnesium and post-flame zones in which the melting, vaporization and flame occur instantaneously. Afterwards, the non-dimensional forms of governing equations including mass, energy and gaseous fuel mass fraction conservations and the appropriate boundary conditions are derived and analytically solved. Subsequently, as the important achievements of the present study, the explicit formulas are obtained for flame velocity, location and temperature. Eventually, the effects of involved parameters on combustion characteristics are examined. The results indicate that as the particle diameter enhances from 15 to 60 mu m, the flame front moves to a place 2.5 times farther away. The flame temperature increases linearly with concentration, while it decreases with the inverse of square of the diameter.