Soot formation and combustion characteristics in confined mesoscale combustors under conventional and oxy-combustion conditions (O2/N2 and O2/CO2)

Abstract

This work investigated soot formation and combustion characteristics in confined mesoscale combustors of two diameters 4 and 6 mm between conventional and oxy-combustion conditions using high resolution transmissions electron microscopy, thermogravimetric analysis and exhaust gases analysis. Results demonstrated that by increasing O2 concentration, the combustion performance can be improved significantly. In 4 mm combustor, both ethylene conversion and mean wall temperature for N2 diluted flame were larger for higher O2 concentration because the reduction of inert diluted gas decreased the heat loss and more O2 content contributed to reactions of more fuel. For N2 diluted flames in 6 mm combustor, soot nanostructure under 21% O2 exhibited amorphous structures but typical fullerene-like structures with more organized fringes could be observed under 30% and 40% O2. The soot carbonization degree increased notably with higher O2 concentration. For the same O2 concentration and combustor, ethylene conversions and temperatures for CO2 diluted flames were always less than those from N2 diluted flames due the larger specific capacity of CO2 than N2. Higher CO concentrations were also detected in exhaust gas from the flame with CO2 dilution than with N2 because CO2 directly participated in the reaction CO2+H⇄CO+OH.