Flow field and emission characterization of a novel enclosed jet-in-hot-coflow canonical burner

The jet-in-hot-coflow is a canonical combustion setup, which has been used in several studies to study Flameless/MILD combustion and auto-ignition of fuels. However, the NO${}_x$ and CO emission measurements from these combustion setups were not possible due to the entrainment of laboratory air and a lack of a well-defined physical system limit. These limitations have been overcome by a new enclosed jet-in-hot-coflow setup. The combustor was operated by injecting a mixture of CH${}_4$-Air in the central jet, and the coflow comprised of hot products from CH${}_4$-Air combustion in burners upstream. The coflow composition was further controlled by adding diluents such as N${}_2$ and CO${}_2$. Measurements were done using stereoscopic particle image velocimetry, suction probe gas analysis, thermocouples, and chemiluminescence imaging. Increasing central jet velocity and equivalence ratio led to lower NO${}_x$ and a reaction zone that enlarged and shifted downstream. The reduction in NO${}_x$ emission was attributed to the returning mechanism. Adding CO${}_2$ and N${}_2$ as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased NO${}_x$ production and increased reburning. These experiments provide relevant flowfield and emissions data for modelers and help characterize combustion regimes such as Flameless/MILD.