Multiscale investigation of oxy-fuel combustion behavior, kinetics, and molecular reaction mechanisms of corn straw

To elucidate the coupled macroscopic and molecular responses of corn straw to O 2 /CO 2 oxy-fuel atmospheres, thermogravimetry/differential thermogravimetry coupled with mass spectrometry (TG/DTG/MS), four isoconversional methods (FWO, KAS, Starink, and Friedman), and ReaxFF reactive molecular dynamics were integrated. Combustion was examined in 21%O 2 /79%N 2 , 30%O 2 /70%CO 2 , 50%O 2 /50%CO 2 , and 70%O 2 /30%CO 2 atmospheres at heating rates of 10-30 °C min −1 . Oxygen enrichment shifted the principal mass-loss interval to lower temperatures, sharpened the DTG peak, and accelerated burnout. At 10 °C min −1 , increasing the oxygen concentration from 21% to 70% decreased the peak and burnout temperatures from 301.8 to 276.2 °C and from 460.33 to 358.67 °C, respectively, while increasing the maximum mass-loss rate from 12.24 to 149.33% min −1 . The normalized TG-MS signals further showed lower total relative release intensities of NO 2 and SO 2 in all O 2 /CO 2 atmospheres than in air, with the lowest values obtained under 70%O 2 /30%CO 2 . The apparent activation energy varied strongly with conversion, confirming the overlap of volatile oxidation, organic-matrix decomposition, char oxidation, and final burnout. FWO, KAS, and Starink produced closely matched activation-energy profiles, while Friedman independently reproduced the atmosphere-dependent peak positions and overall trends. Under 70%O 2 /30%CO 2 , all four methods gave R 2 > 0.96 and located the apparent-activation-energy maximum at α = 0.3 (247.32–285.95 kJ mol −1 ), reflecting a pronounced conversion-dependent redistribution of the overlapping reaction contributions in the early-to-medium conversion region. ReaxFF-MD simulations captured progressive C-C and C-H bond cleavage, O 2 consumption, and the formation of CO, CO 2 , and H 2 O; the strongest cracking-oxidation coupling was observed under 50%O 2 /50%CO 2 . Overall, 70%O 2 /30%CO 2 delivered the highest macroscopic combustion intensity and the most rapid burnout, whereas the strong reaction coupling observed at 50%O 2 /50%CO 2 with a lower oxygen fraction suggests a more balanced operating window. These findings provide a multiscale basis for atmosphere selection in corn-straw oxy-fuel conversion.