Study on stretch extinction characteristics of methane/carbon dioxide versus oxygen/carbon dioxide counterflow non-premixed combustion under elevated pressures

Abstract As a clean gaseous fuel, methane (the main constituent of natural gas) has been widely used in the lives of residents and industrial processes. The oxy-fuel combustion technology for methane/carbon dioxide is an effective way to reduce the pollutant emissions of NOx, which is also beneficial to the capture of carbon dioxide. Herein, the stretch extinction characteristics of non-premixed flames induced by methane/carbon dioxide mixtures versus oxygen/carbon dioxide mixtures counterflow combustion with various fuel concentrations were studied in high-pressure environments. The computed flame extinction strain rates of oxygen-enriched and air combustions in low fuel concentration range at pressures of 0.1, 0.5 and 0.7 MPa have a good consistency with the experiment results obtained from previous literature. The results show that the increase of flame extinction limit represented by the stretch rate for the oxygen-enriched combustion with increasing pressure is more significant than that for the air combustion. The analyses of reaction pathways, integral of reaction rates and sensitivity coefficients suggest that the OH formation rates of near extinction flames limits can be used to estimate the ratio of the flame extinction strain rate for oxygen-enriched combustion to that for air combustion under high pressures. The reasons for the enhancement of the OH formation rate aroused by increasing pressures were clarified.