Investigation on the effects of steam/CO2/N2 on the flame suppression and flame stability of the methane-oxygen mixtures at elevated thermodynamic conditions

This work aimed to study the dilution effect of steam, carbon dioxide, and nitrogen on the unstretched laminar burning velocity and burned gas Markstein length of premixed (100-Z) % (CH4 + (2O(2))/phi) + Z%(H2O/N-2/CO2) mixtures at 300-453 K, 1-4 bar, equivalence ratio (phi)-0.6-1.4, and Z was varied from 40 to 60% for steam and kept constant at 50% for CO2/N-2. Expanding spherical flames method was used. Nonlinear stretch extrapolation schemes were used to extract the burning velocity and Markstein length. All conditions were simulated using the 1D planar flame model in CHEMKIN with GRIMech3.0 and FFCM-1 reaction mechanisms. Present mixture formulation led to the comparison of the absolute dilution effect of each diluent at an identical mixture and thermodynamic conditions. Addition of 50% diluents significantly suppressed the flame propagation. It was the highest for CO2 (87% as compared to no dilution) due to the simultaneous reduction in flame temperature and its kinetic effect, and it was followed by steam (69%) and N2 (61%), and their suppression effect was primarily due to the reduction in the flame temperature. All the studied mixtures were stable to preferential diffusional instability as their: (a) Markstein length was positive and (b) the effective Lewis number of the mixtures were well higher than the critical Lewis number. Predicted LBV with GRIMech3.0 compared well with the experiments than FFCM-1. As the LBV increased beyond 150 cm/s, predicted LBV of both GRIMech3.0 and FFCM-1 showed significant deviation with the measurements.

Automated summary

This study investigates the dilution effects of steam, carbon dioxide, and nitrogen on the unstretched laminar burning velocity and burned gas Markstein length of premixed mixtures. The addition of 50% diluents significantly suppressed flame propagation, with CO2 showing the highest impact due to the simultaneous reduction in flame temperature and kinetic effect. Experimental and simulated results provide valuable insights into the behavior of different diluents in combustion processes.