Evaluation of combustion models and reaction mechanisms to predict NOx and CO emissions from densely distributed lean-premixed multinozzle CH4/H2/air flames

Abstract

This work explores the importance of reaction mechanisms and combustion models on the flame length and emission characteristic prediction by computational fluid dynamics (CFD) simulations of a complex multinozzle combustor configuration, operating under CH4/H2 blend variations. For the study, both RANS and LES turbulence models are explored. Test data used for the analysis is taken from work published by KAIST University, on the investigation of combustion dynamics and NOx/CO emissions from lean-premixed multinozzle CH4/H2 blended flames. The combustion domain consists of densely distributed small-scale multitube injectors called Micromixer nozzles. This setup provides insights into the collective behavior of small-scale multinozzle flames and resultant emission rates. Test data for different inlet compositions, keeping a thermal power condition of 78 kW, are considered for evaluation. Results from simulations for OH*chemiluminescence, OH concentrations, NOx, and CO emissions are compared against the test data. Reduce model fuel library (MFL) mechanism with relevant NOx pathways along with flamelet generated manifold (FGM) model found to predict the trend of flame length and emissions concentration with change in fuel composition reasonably well, compared to detailed chemistry combustion model, as well as test data. However, for capturing the impact of local nonunity Lewis number effects, the detailed chemistry model is found to be better for the low turbulent flow conditions, as considered in the referred experimental data.