Chemical effects of carbon dioxide in ethylene, ethanol and DME counter-flow diffusion flames: An experimental reference for the fictitious CO2 flame

Abstract

The chemical effects of carbon dioxide on flame chemistry were investigated numerically and experimentally in ethylene, ethanol, and dimethyl-ether (DME) counter-flow diffusion flames. In this work, a method that could add an experimental reference flame for the fictitious CO2 flame (FCO2) was proposed. The fuel/oxidant carrier gas (FCO2+argon+helium) in the FCO2 flames was replaced by an inert gas mixture (nitrogen+argon+helium) whose composition was optimized to maintain approximately the same thermal and dilution effects as FCO2 addition. The differences in the flame temperatures and the measured species concentration between CO2 flame and the inert gas mixture flame could then be attributed to the pure chemical effects. The new experimental strategy was applied to ethylene, ethanol, and dimethyl-ether (DME) counter-flow diffusion flames. Good agreement was found between the experimental and the computational results. The chemical effects of CO2 addition, indicated by both the numerical FCO2 flame and the experimental inert gas mixture flame, both decreased the peak flame temperatures and the concentration of CH4, H2, and C2H2 except CO. The effects of CO2 addition on the production pathways of CO and C2H2 were very similar in ethylene, ethanol, and DME flames. Decreased CO oxidation rate through CO+OH = CO2+H was a significant feature of the chemical effects identified by both the FCO2 flame and the inert gas mixture flame. Thermal effects of CO2 addition decreased the formation rate of C2H2 through C2H3(+M) = H+C2H2(+M) while the chemical effects on this pathway were weaker.