Structure of turbulent non-premixed jet flames in a diluted hot coflow

Moderate and intense low oxygen dilution combustion is a newly implemented and developed concept to achieve high thermal efficiency and fuel savings while maintaining emission of pollutants at very low levels. It utilizes the concept of heat and exhaust gas recirculation to achieve combustion at a reduced temperature, a flat thermal field, and low turbulence fluctuations. An experimental burner is used in this study to simulate the heat and exhaust gas recirculation applied to a simple jet in a hot coflow. Temporally and spatially resolved measurements of reactive scalars are conducted on three different turbulent non-premixed flames of a H-2/CH4 fuel mixture at a fixed-jet Reynolds number and different oxygen levels in the hot oxidant stream. The data were collected using the single-point Raman-Rayleigh-laser-induced fluorescence technique. The results show substantial variation in the flame structure and appearance with the decrease of the oxygen level. By reducing the oxygen level in the hot coflow, the flame becomes less luminous, the temperature increase in the reaction zone can get as low as 100 K, and the levels of CO and OH are substantially lowered. The levels of NO also decrease with decreasing the oxygen levels, and at 3% by mass, it is less that 5 ppm. For this case, a widely distributed NO profile is found which is not consistent with profiles for other oxygen levels.