Lean-rich combustion characteristics of methane and ammonia in the combined porous structures for carbon reduction and alternative fuel development

Ammonia as a carbon-free alternative fuel has received much attention with the consumption of fossil fuels. In order to explore the mixed combustion of methane and ammonia, a combined porous media burner was designed with pellets embedded in annular ceramic foam. And the effects of operating parameters on combustion characteristics were investigated. The results showed that the ammonia addition increased the combustion temperature and reduced carbon dioxide emissions at the equivalence ratio of <1. And the ammonia promoted the conversion of CO2 to CO for an equivalence ratio of >1. With the increasing of the ammonia ratio, the CO selectivity increased but the CO2 selectivity decreased. In addition, the mixed combustion of ammonia and methane improved the hydrogen production. The fuel ratio of methane to ammonia (0.80: 0.20) resulted in higher syngas production and lower CO2 mole fraction. The flame propagated faster in ceramic foam with lower pore densities (20 PPI) so the preheating time was greatly reduced. Moreover, the 40 PPI ceramic foam was conducive to the stability of the flame position in the upstream zone, and the H-2 mole fraction achieved 10.60 % at the inlet velocity of 14 cm/s.