Numerical investigation of premixed methane-ammonia combustion in a mesoscale porous combustor

Abstract

The present study focuses on the numerical modeling of the premixed methane-ammonia combustion in a mesoscale porous combustor. The primary objective is to reduce carbon dioxide emissions by using ammonia as a carbon-free fuel while maintaining constant the combustor wall temperature compared to pure methane. Ammonia addition in the mixture increases nitrogen oxide compared to pure methane-oxygen combustion, which is undesirable. On the other hand, porous material improves fuel and air mixing and leads to more appropriate fuel distribution which could lower the combustion temperature and as well NOx emission. So, simultaneous using ammonia and porous media in the combustion is the effective combination to reduce the consumption of hydrocarbon fuels. In the current study, porosity of porous media is changed within the range of 50 %–90 %, molar fraction of ammonia is varied from 0.1 to 0.9, and equivalence ratios ranging from 0.8 to 1. Also, to find the optimal combustion parameters, the response surface methodology has been employed. The results indicated that to achieve satisfactory conditions for methane-ammonia-oxygen combustion in contrast to the combustion of pure methane-oxygen, it is the best condition to employ a porosity of 63 %, an ammonia mole fraction of 0.9, and a stoichiometric equivalence ratio. Because of the utilization of porous media, the mean wall temperature reached to 1543 K, indicating a 3.5 % reduction compared to pure methane combustion. Simultaneously, nitrogen oxide emission drops to 2270 ppm, showcasing a 10 % reduction compared to the non-porous media ammonia-methane combustion. Additionally, the use of the 0.9 M fraction of ammonia leads to a noteworthy 75 % decrease in the mass fraction of carbon dioxide emissions compared to pure methane combustion. These findings accelerate the optimal use of carbon-free fuels such as ammonia as alternatives to hydrocarbon fuels.