Experimental and numerical study of the effect of water injection into the reaction zone of a flameless combustion furnace

The effect of water injection on the stability and emissions of a flameless combustion regime was evaluated. Flameless combustion operation was studied without self-regeneration, with self- regeneration, and with combustion air oxygen enrichment. For each case, increasing water flows were injected until the combustion regime was unstable. The evaluation criteria were temperature uniformity and pollutant emissions of species such as carbon monoxide and nitrogen oxide. Ansys Fluent 2020 software was used to perform the different simulations, while the experimental evaluations were carried out in a laboratory-scale furnace operating with Natural Gas at a thermal power of 30 kW, based on high heating value.  Flameless combustion without self-regeneration was found to become unstable when the injected water mass to fuel mass ratio (m factor) was >2.5, while selfregeneration and combustion air oxygen enrichment increased the maximum operable m factor to 4.3 and 5, respectively.