Analytical and numerical evaluation of flammability limit of magnesium-fueled thermophotovoltaic combustor considering inter-regional radiation, heat loss and O2-N2,Ar,He oxidizers

Flame stability and fuel energy density are among the main parameters in the design of a thermophotovoltaic (TPV) combustion system. In this research, the flammability limit of the TPV combustor is investigated considering magnesium as the energy carrier. By proposing an asymptotic flame structure and considering the inter-regional radiation and heat loss, the premixed combustion of magnesium in O-2/N-2,Ar,He media is modeled. The governing equations and boundary conditions are derived and analytically-numerically solved to determine the lean flammability limit (LFL) as well as the flame features. Subsequently, by modifying flame structure and with the aid of analytical method, the closed-form expressions for flame velocity and temperature are obtained. The results indicate that in N-2-O-2 medium, the increase in the ambient temperature from 300 to 800 K declines the equivalence ratio (ER) of the LFL from 0.16 to 0.03; at 900 K, the flame get stable and has no extinction. Such a rise in the temperature of He-and Ar-containing media decrements the ERs of instability onset by 6.8 and 5.6 times, respectively. For oxygen mass fractions below 0.25, the LFL of Ar-O-2 is higher than He-O-2. The trend, however, exhibits a reverse pattern at oxygen mass fractions greater than 0.35.

Automated summary

This research investigates the flammability limit of a thermophotovoltaic (TPV) combustion system using magnesium as the energy carrier. The study models the premixed combustion of magnesium in different gas media and analyzes the flame features and behavior. The results show that the ambient temperature and the composition of the gas media significantly affect the flammability limit and flame stability.