Experimental Study of Oxygen Enrichment Effects on Turbulent Nonpremixed Swirling Flames

The current paper describes the effects of oxygen enrichment on flame stability and pollutant emissions for turbulent non-premixed swirling flames. The study is motivated by CO2 capture applications further to the increase of the CO2 concentration by the O-2 addition. The burner configuration consists of two concentric tubes with a swirl placed in the annular part for air or oxygen air. The exhaust gas compositions are measured using gas analyzers. OH chemiluminescence experiments are conducted to investigate the stability of flames. The measurements were performed for oxygen concentrations ranging from 21 to 30% by volume, with swirl numbers of 0.8 and 1.4 and global equivalence ratios of 0.8, 0.9 and 1. Results show that oxygen enrichment enhances combustion efficiency and flame stability. The increase of the oxygen concentration in air leads to a decrease of lift-off heights and fluctuations of the flame base. Increasing the swirl number significantly improves the flame stability. Experiments demonstrated that the CO2 emissions linearly increase with an increasing O-2 content in the oxidant. The CO emissions are shown to decay exponentially, whereas the NOx emissions, mainly produced through the thermal pathway, increased exponentially with oxygen addition.