Prediction performance of chemical mechanisms for numerical simulation of methane jet MILD combustion

Abstract

The prediction performance of five chemical mechanisms (3-STEP, WD4, SKELETAL, DRM-19, and GRI-2.11) was investigated to confirm their suitability for use in numerical simulations of methane combustion in moderate or intense low-oxygen dilution (MILD). A wall-confined jet geometry was introduced to simulate MILD combustion. The oxygen level in the coflowing air was adjusted by mixing the air with combustion products. Each chemical mechanism was analyzed with respect to the flame structure and main product, including CO and NO; the emission indices for CO were also discussed. The temperature distributions and heat-release rates predicted by the chemical mechanisms were similar when the flames were stably attached to the fuel jet exit. The temperature distributions and heat-release rates were dependent on the flame liftoff characteristics, as were the CO and NO emissions. The NO concentration predicted by GRI-2.11 was lower than those predicted using other chemical mechanisms, although DRM-19 predicted a relatively similar value. The emission indices for NO (EINO) and CO (EICO) predicted by each chemical mechanism decreased with increasing dilution rate. The predicted EICO had a negative value even at a small dilution rate, which implies that some of the CO supplied to the air stream is consumed during MILD combustion. © 2013 Yu Jeong Kim et al.